060070 Meridian Gyro Compass Issue 3.7 Mar 2004

A Division of VT TSS (UK) Limited

The information in this Manual is subject to

change without notice and does not represent

a commitment on the part of SG Brown

VT TSS (SG Brown Division) Ltd

1 Garnett Close

Greycaine Industrial Estate

Watford

Hertfordshire WD24 7JZ UK

Telephone +44 (0)1923 470800

Facsimile +44 (0)1923 470838

Meridian Gyrocompass

System Manual

Document P/N 060070

Issue 3.7

© SG Brown March 2004

Contents

DPN 060070 Issue 3.7 © SGBrown Page 1 of 6

CAUTIONARY NOTICESYour attention is drawn to the following cautionary notices that apply throughout this Manual.

WARNINGThe Meridian Gyrocompass weighs 15.5kg. To avoid personal injury, take proper pre-cautions if you lift or move the equipment.

CAUTIONThe Meridian Gyrocompass includes precision components and bearings. To avoid causing damage to any part of the System, handle all items with care.

Retain the original transit cases so that you can use them to transport the system when necessary. You will void the warranty if you use improper packing during transporta-tion.

CAUTIONSevere damage to the Meridian Gyrocompass can occur if you move the gyrocompass while the rotor is still spinning without the servo system in operation.

Note that the gyro rotor continues to spin for approximately five minutes after you power-off the system.

To avoid potential damage to the Meridian Gyrocompass, always allow a period of five minutes after power-off for the gyro rotor to come to rest before you attempt to move the gyrocompass.

CAUTIONDuring operation, the gyrocompass must remain level to within ±45°. If it experiences tilt greater than 45° in any direction, it will ‘topple’. Safety routines in the gyro software will then power-off the gyro rotor and show alarm conditions on the RCU. To restore normal operation, establish a level operating attitude and then power-on the gyrocom-pass normally.

Never apply a tilt of more than 45° with the gyro rotor spinning or during the gyrocom-pass initialisation procedure. Note that the gyro rotor continues to spin for approxi-mately five minutes after you power-off the System.

CAUTIONIf you install the gyrocompass in an enclosed space, make certain there is sufficient ventilation and circulation of free air to allow effective cooling.

CAUTIONDo not make any connections to the gyrocompass with power on the supply cable.


Page 2 of 6 © SGBrown Issue 3.7 DPN 060070

CAUTIONYou will void the warranty if you make any modifications to this equipment without prior permission from SG Brown.

DO NOT modify this equipment in any way without obtaining permission from SG Brown.

CAUTIONYou will void the warranty if you operate the gyrocompass outside the environmental conditions detailed in Chapter 4 and in BS EN 60945.

Contents


CONTENTS

1 INTRODUCTION 1–11.1 System Description 1–31.1.1 Gyrocompass 1–31.1.2 Remote Control Unit 1–41.1.3 Auxiliary Inputs 1–41.1.4 Heading Outputs 1–5

1.2 Principle of Operation 1–5

2 INSTALLATION 2–12.1 Unpacking and Inspection 2–22.2 Physical and Electrical Installation 2–32.2.1 Selecting a location 2–32.2.2 Gyrocompass installation 2–42.2.3 External Remote Control Unit 2–92.2.4 Set the Gyrocompass DIP Switches 2–10

2.3 Alignment 2–122.4 Final Gyrocompass Installation Tests 2–122.5 Installation Drawings 2–13

3 OPERATING INSTRUCTIONS 3–13.1 Control Features 3–23.2 Initial Power-on 3–33.3 Operating Procedure 3–43.3.1 Latitude correction 3–43.3.2 Speed correction 3–43.3.3 DG operating mode 3–5

3.4 Error Modes 3–53.4.1 Loss of GPS 3–53.4.2 Loss of speed log 3–63.4.3 Gyrocompass system warnings and failures 3–6

3.5 Operating Considerations 3–83.5.1 General Operating Considerations 3–83.5.2 Corrections for Speed and Latitude 3–83.5.3 Operating at Extremes of Latitudes 3–83.5.4 Operating Considerations for High Speed Craft 3–9

4 TECHNICAL DATA 4–14.1 Specifications 4–14.1.1 Power Requirements 4–14.1.2 Performance (definitions as in ISO 8728) 4–14.1.3 Compensation 4–14.1.4 Environment 4–14.1.5 Signal Inputs 4–24.1.6 Signal outputs 4–24.1.7 Dimensions and Weight 4–24.1.8 Listener load requirement 4–34.1.9 Talker drive capability 4–3



4.1.10 Standards 4–34.2 Data Formats 4–44.2.1 IEC 61162 Serial Data Formats – General information 4–54.2.2 Inputs 4–64.2.2.1 IEC 61162 input signals 4–64.2.2.2 Pulsed input 4–10

4.2.3 Outputs 4–114.2.3.1 IEC 61162 output signals 4–11

4.2.4 IEC 61162 sentence with Checksum 4–154.2.5 Other Output Formats 4–154.2.5.1 Course Recorder Output 4–154.2.5.2 Synchro Output 4–164.2.5.3 Resolver Output 4–164.2.5.4 Stepper S-Code 4–164.2.5.5 Rate of Turn 4–16

5 MAINTENANCE 5–15.1 Built-in Test Equipment 5–25.1.1 Azimuth Drift Adjustment 5–35.1.2 Azimuth Bias Adjustment 5–3

5.2 Test Connector 5–45.3 Diagnostic Output Sentence 5–6

A OPERATING THEORY A–1A.1 North-seeking Gyroscope A–2A.2 Gyrocompass Corrections A–5A.2.1 Latitude Correction A–5A.2.2 Gyro Damping A–5A.2.3 Speed Error A–6

A.3 Summary A–7

B CERTIFICATION A–1

Contents


TABLE OF AMENDMENTS

Old Issue New Issue Date Details

- 2.0 11 May 2000 New release.

2.0 2.0A 12 Dec 2000 Corrected identification of Azimuth Bias potentiometer and other details. Include DIP switch default settings.

2.0A 2.0B 1 Mar 2001 Modify power connection details.

2.0B 2.0C 23 Apr 2001 Add notification to avoid product modifications.

2.0C 3.0 Aug 2002 Substantial amendments to reflect product enhancements

3.0 3.1 Sept 2002 completion of enhancement features including compliance with IEC 61162

3.1 3.2 Jan 2003 Minor amendments and description of Diagnostic Output Sen-tence.

3.2 3.3 Feb 2003 Modification to specifications and addition of Appendix B to demonstrate Certificate of Type Approval.

3.3 3.4 Mar 2003 Minor amendments to a display warning and a note referring to confirming software release.

3.4 3.5 July 2003 Note added regarding modification kit available for alternative orientations when attempting correct speed compensation.

3.5 3.6 August 2003 Minor amendments to specifications throughout

3.6 3.7 March 2004 Amendments to alarm warning / failure designation



1 – Introduction

DPN 060070 Issue 3.7 © SG Brown Chapter 1 Page 1 of 6

1 INTRODUCTIONThe Meridian Gyrocompass is a master heading reference instrument that applies the charac-teristics of a dynamically tuned gyroscope and the effects of gravity and earth rotation to pro-vide a true north reference.

The Meridian Gyrocompass specification makes the System ideal for installation and opera-tion on board vessels of almost any size and in a wide range of applications.

Among the standard features of the Meridian Gyrocompass are:

A short settling time

Operation from a 24V DC electrical supply

This Manual is an important part of the Meridian Gyrocompass. It describes the System and contains full installation and operating instructions. You should retain the Manual with the System for use by personnel who will install and operate it.

Installation and operation of the Meridian Gyrocompass are not complex tasks. However, you should spend time to familiarise yourself with the contents of this Manual before you start to install or use the System. Time spent in identifying the task sequence now will ensure your System is operational in the minimum of time.

WARNINGSWhere appropriate, this Manual includes important safety information highlighted as WARNING and CAUTION instructions. You must obey these instructions:

WARNING instructions alert you to a potential risk of death or injury to users of the System.

CAUTION instructions alert you to the potential risk of damage to the System.

For your convenience, the Table of Contents section includes copies of all the WARNING and CAUTION instructions included in this Manual.

Throughout this Manual all measurements conform to the SI standard of units unless other-wise indicated.

For your convenience, this Manual includes several sections, each of which describes specific features of the Meridian Gyrocompass:

You should read sections 1 and 2 before you attempt to install the System:

Section 1 contains introductory notes and describes those items supplied as standard.

Section 2 describes how to select a suitable location for the gyrocompass. This section includes full instructions to install the System and connect it to external equipment.


Chapter 1 Page 2 of 6 © SG Brown Issue 3.7 DPN 060070

You should read sections 3 and 4 before you use the System:

Section 3 describes how to operate the Meridian Gyrocompass.

Section 4 includes the System specifications and descriptions of the data formats.

You should read sections 5 if you suspect a fault on the System:

Section 5 describes how to use the internal 60-way test connector and explains how to con-duct simple adjustments with the gyrocompass housing removed.

This Manual also contains the following appendices:

Appendix A explains how a gyroscope can be made north seeking for use in a gyrocompass.

CAUTIONYou will void the warranty if you make any modifications to this equipment without prior permission from SG Brown.

DO NOT modify this equipment in any way without obtaining permission from SG Brown.

1 – Introduction


1.1 SYSTEM DESCRIPTIONThe Meridian Gyrocompass comprises two sub-assemblies:

The gyrocompass housing

The Remote Control Unit (RCU)

Figure 1–1 shows the combined gyrocompass housing with the RCU included as an integral unit.

The Meridian Gyrocompass applies dynamic tuning to settle automatically to the meridian. Due to the physical principles of a north-seeking gyrocompass, achievable accuracy depends on the operating latitude and the vessel dynamics. To optimise its performance, the Meridian Gyrocompass uses information supplied by external equipment, for example a GPS receiver and a speed log, to apply latitude and speed corrections.

Refer to Appendix A for a simplified explanation of the gyrocompass theory of operation.

1.1.1 GyrocompassFigure 1–1: Gyrocompass housing with integral RCU

Figure 1–1 shows the gyrocompass housing, which contains the following items:

True north seeking dynamically tuned precision gyroscope and gimbal suspension assembly.

Power supply board.

Digital and analogue control boards.

RFI filter and distribution board.

It is a relatively simple operation to install the gyrocompass and you should be able to accomplish this quickly without the need for special-ised personnel or equipment. How-ever, note that the gyrocompass weighs 15.5kg and you must take due care when you lift and move it.

The care that you take when you align the gyrocompass housing with the surveyed fore-aft axis of the vessel will have a direct impact on the accuracy of heading measurements delivered by the System. Since the Meridian Gyrocompass is an ideal source of heading information for use by other systems on board, such as radars and satellite communication antennas, the accu-racy of its heading measurements will have a wide impact throughout the vessel. You should



therefore take care when you install and align the gyrocompass. Refer to Section 2 for full instructions to install, connect and align the Meridian Gyrocompass.

The only component available for user servicing is a 3.15A line fuse inside the gyrocompass housing. In case of failure, refer to Section 5 for instructions to renew this fuse and check the PSU board supplies.

1.1.2 Remote Control UnitFigure 1–2: Remote Control Unit

The Remote Control Unit (RCU) provides all the functions and indicators necessary to control and operate the Meridian Gyrocompass.

The four-character LED can show a range of information:

Heading in Degrees. 000.0 to 359.9

Latitude. 80S to 80N

Latitude Source

Speed in Knots. 00 to 90

Speed Source

Alarms and Status information

Seperate LED indicators show Power On and Compass Ready conditions

Refer to Section 3 for instructions to operate the Meridian Gyrocompass.

1.1.3 Auxiliary InputsAuxiliary inputs may be used for the Meridian Gyrocompass to apply latitude and speed cor-rections.

1 – Introduction


Ideally, the Meridian Gyrocompass should accept latitude and speed information from exter-nal sources such as a GPS receiver or a speed log. However, you may supply this information manually if external sources are not available. The advantage of using GPS or a speed log to provide correction signals is that they allow automatic corrections to be applied without oper-ator intervention.

Section 2 includes instructions to connect and configure the external sources of latitude and speed information.

Section 3 includes instructions to set the latitude and speed manually.

1.1.4 Heading OutputsThe Meridian Gyrocompass is a self-contained precision navigation instrument that is capable of supplying heading reference information simultaneously to a wide range of equipment on board the vessel. Throughout a typical vessel, applications that can use information supplied by the Meridian Gyrocompass include:

Autopilot

Radars

GPS

Radio direction finder

Course plotter and recorder

Satellite communication systems

Satellite television

To support this wide range of equipment types, the Meridian Gyrocompass can supply heading information simultaneously through multiple channels using any of the common transmission formats.

Refer to Section 3 for a description of the available output channels and their data formats.

1.2 PRINCIPLE OF OPERATIONIn the absence of external influences, a free-spinning gyroscope will try to maintain a fixed orientation in space. The Meridian Gyrocompass exploits this property and uses gravity con-trol and earth rotation to align the gyroscope spin axis with the meridian, i.e. the true north direction.

Refer to Appendix A for the general theory of gyrocompass operation.



2 – Installation


2 INSTALLATIONTo obtain the best performance from the Meridian Gyrocompass you must take care when you install and connect it. This section includes all the information and instructions you will need to complete these tasks.

You should read this section carefully and understand the important instructions that it con-tains before you begin to install or connect the equipment.

2.1 Unpacking and Inspection Page 2

Explains the inspection checks that you should perform as you unpack the Meridian Gyrocom-pass.

2.2 Physical and Electrical Installation Page 3

Choose a suitable location to install the Meridian Gyrocompass. Connect the system to an electrical supply and to external equipment.

2.3 Alignment Page 12

The care that you take as you align the Meridian Gyrocompass with the fore-aft datum on the vessel will have a direct influence upon its accuracy.



2.1 UNPACKING AND INSPECTIONWARNING

The Meridian Gyrocompass weighs 15.5kg. To avoid personal injury, take proper pre-cautions if you lift or move the equipment.

CAUTIONThe Meridian Gyrocompass includes precision components and bearings. To avoid causing damage to any part of the System, handle all items with care.

Retain the original transit cases so that you can use them to transport the system when necessary. You will void the warranty if you use improper packing during transporta-tion.

CAUTIONSevere damage to the Meridian Gyrocompass can occur if you move the gyrocompass while the rotor is still spinning without the servo system in operation.

Note that the gyro rotor continues to spin for approximately five minutes after you power-off the system.

To avoid potential damage to the Meridian Gyrocompass, always allow a period of five minutes after power-off for the gyro rotor to come to rest before you attempt to move the gyrocompass.

The Meridian Gyrocompass undergoes a full series of electrical and mechanical tests during manufacture and before dispatch. The packing case has a special design to protect the contents against shock during transit so that the equipment should arrive without damage or defect.

As soon as possible after you have received the system, check all items against the shipping documents. Inspect all sub-assemblies carefully to check for any damage that may have occurred during transportation. If you see any damage file a claim with the carrier and imme-diately notify SG Brown.

To avoid loss or damage to any components of the system, store all sub-assemblies safely in the transit case until you need to install them. Obey the storage temperature limits listed in Section 4.

Notify SG Brown immediately if there are any components missing from the shipment.

The title page of this Manual lists the contact details for SG Brown.

2 – Installation


2.2 PHYSICAL AND ELECTRICAL INSTALLATION2.2.1 Selecting a locationThere are certain guidelines that you should follow to install the Meridian Gyrocompass suc-cessfully:

CAUTIONDuring operation, the gyrocompass must remain level to within ±45°. If it experiences tilt greater than 45° in any direction, it will ‘topple’. Safety routines in the gyro software will then power-off the gyro rotor and show alarm conditions on the RCU. To restore normal operation, establish a level operating attitude and then power-on the gyrocom-pass normally.

Never apply a tilt of more than 45° with the gyro rotor spinning or during the gyrocom-pass initialisation procedure. Note that the gyro rotor continues to spin for approxi-mately five minutes after you power-off the System.

The gyrocompass weighs 15.5kg. Choose a mounting location that is level, flat and suffi-ciently strong to support the unit without flexing or experiencing extreme vibration. The mounting location can be open, as on a chart table, or enclosed within a cabinet.

CAUTIONIf you install the gyrocompass in an enclosed space, make certain there is sufficient ventilation and circulation of free air to allow effective cooling.

Choose a location that protects the Meridian Gyrocompass from damage.

Do not install or operate the Meridian Gyrocompass where the ambient temperature could fall below 0°C or rise above +45°C, or where rapid changes of temperature can occur.

Do not install the Meridian Gyrocompass close to strong mechanical or electrical noise sources, or in a location susceptible to vibration or shock.

Allow a minimum distance of 0.4m between the gyrocompass housing and any standard magnetic compasses.

Choose a location that allows convenient access to install, connect and service the Merid-ian Gyrocompass. Refer to Figure 2–6 for clearance dimensions.



2.2.2 Gyrocompass installationYou must align the Meridian Gyrocompass so that its fore-aft axis is parallel to the fore-aft datum on the vessel. Any misalignment between the gyrocompass housing and the vessel will have a direct effect on the accuracy of heading measurements delivered by the system.

To install the Meridian Gyrocompass you will need the following tools:

Screwdriver 5.5mm × 150mm

Screwdriver 3mm × 75mm

Nut spinner 5.5mm

Combination spanner 10mm

Hexagon key 2mm

Adjustable spanner opening to at least 33mm

Suitable cables for the installation as indicated in Table 2–1.

There should be no need to remove the gyrocompass cover during installation. You may gain access to make power and signal connections by removing the gland plate assembly, compris-ing the Gland Plate and the Distribution Board. There is a removable panel on the top of the gyrocompass that allows access to the internal DIP switches and a 60-way test connector.

1. During installation you must align the Meridian Gyrocompass so that its fore-aft axis is parallel with the fore-aft datum on the vessel. It is not necessary for the gyrocompass to be on the vessel centre line. There are alignment marks on the base of the Meridian Gyrocom-pass to help you achieve the correct alignment.

2. Three elongated securing holes machined into the gyrocompass base allow you to make fine adjustments to alignment after installation. With the gyrocompass positioned accu-rately, mark the supporting surface with the centre positions for the three securing holes. Refer to Figures 2–5 and 2–6 for dimensions.

Table 2–1: Suitable cable types

Purpose Suitable cable

Power supply 7/0.5mm (1.5mm2) HOFR sheathed to BS6883

Synchro heading outputResolver heading outputStepper S-code output

7/0.4mm (1.0mm2) butyl or EP rubber insulated, CSP sheathed, wire braided and CSP oversheathed.

Serial data heading outputSerial data speed inputSerial data latitude input

1/0.85mm (0.6mm2) twisted pair, butyl or EP rubber insulated, CSP sheathed, wire braided and CSP oversheathed.

2 – Installation


3. Remove the gyrocompass and drill three 8.5mm diameter holes, using the marks you have just made on the supporting surface as hole centres. Deburr the holes and remove any swarf.

4. Reposition the gyrocompass and align it to the fore-aft datum. Use three M8 bolts with washers and nuts to secure the gyrocompass in position.

5. Connect a 24V electrical supply (acceptable range 18V to 36V DC) to the Meridian Gyro-compass at J1, the three-pin power inlet on the Gland Plate. Figure 2–1 shows the Gland Plate.

Figure 2–1: Gyrocompass gland plate

CAUTIONDo not make any connections to the gyrocompass with power on the supply cable.

6. Connect the ship’s safety ground to the earthing stud adjacent to the power connector.

7. Make all necessary signal connections to the Meridian Gyrocompass at the Distribution Board. The Distribution Board accepts open tails for all connections. Pass cables through available glands in the Gland Plate. Glands A, D, E, F and J (identified in Figure 2–5)

Fuse

3.15AF

Compass Min. Safe Dist.

Build Standard No.

Serial No.

Mfg. Date

m

Watford, England.

CAUTION

Before removing the cover or the RCU

unit, remove the gland plate and

disconnect the RCU cable (TB1/17-22)

from the distribution board.

Gland plate release screws

Cover plate release screws



accept cables up to 18mm diameter, while all other glands accept cables up to 14mm diam-eter. Refer to Figure 2–3, and Tables 2–3 and 2–4 for cable connection details.

8. To maintain EMC compliance, connect all the wire braiding on the cables to the grounding posts on the inside surface of the Gland Plate as shown in Figure 2–2.

Figure 2–2: Termination of wire braided cables

9. Refit the Gland Plate, making certain there are no trapped wires or cables.

Figure 2–3: Gyrocompass distribution board

2 – Installation


Table 2–2: J1 – Power supply input pin details

Pin Description

1 Protective ground

2 +24V DC

3 0V

Table 2–3: Input signals

Signal description Signal type Distribution Board connector

DG TB1/1 TB1/2 (0V)

GPS input IEC 61162 RS232 TB1/3 TB1/4 (0V)

GPS input IEC 61162 RS422 TB1/5 (A) TB1/6 (B)

Log input IEC 61162 RS232 TB1/7 TB1/8 (0V)

Log input IEC 61162 RS422 TB1/9 (A) TB1/10 (B)

Log OK TB1/11 TB1/12 (0V)

Log TTL pulses TB1/13 (+) TB1/14 (0V)

Log relay Voltage free contact close TB1/15 (+) TB1/16 (0V)

RCU 24V in TB1/17 (+) TB1/18 (–)

RCU On/Off TB1/19 (N/C) TB1/20 (ON)

RCU Communications RS422 TB1/21 (S+) TB1/22 (S-)

Spare – TB1/23 TB1/24



Table 2–4: Output signals

Signal description Signal type Distribution Board connector

Channel 2 IEC 61162 RS232 (all data) TB2/1 TB2/2 (0V)

Channel 1 IEC 61162 RS232 (all data) TB2/3 TB2/4 (0V

Channel 2 IEC 61162 RS422 (all data) TB2/5 (B) TB2/6 (A)

Channel 1 IEC 61162 RS422 (all data) TB2/7 (B) TB2/8 (A)

Heading TTL S-type TB2/9 (5V) TB2/10 (L1)TB2/11 (L2) TB2/12 (L3)TB2/13 (0V)

Heading Synchro/resolver TB2/14 (36V) resTB2/15 (26V) synTB2/16 (0V) syn/resTB2/17 (S1) synTB2/18 (S1) resTB2/19 (S2) syn/resTB2/20 (S3) syn/resTB2/21 (S4) res

Gyro fail Voltage free contact closure TB2/22 (CC)TB2/23 (normally closed, opens on failure)TB2/24 (normally open, closes on failure)

System Fail TTL TB2/25 TB2/26 (0V)

Gyro ready Voltage free contact closure TB2/27 (CC)TB2/28 (open when not ready, closes when ready)TB2/29 (closed when not ready, opens when ready)

Gyro ready TTL TB2/30 TB2/31 (0V)

Channel 2 IEC 61162 RS232 TB3/1 TB3/2 (0V)



Channel 2 IEC 61162 RS422 TB3/7 (B) TB3/8 (A)









Rate of turn Analogue ±10V TB3/25 TB3/26 (0V)

Course recorder IEC 61162 RS232 TB3/27 TB3/28 (0V)

2 – Installation


2.2.3 External Remote Control UnitThe standard Meridian Gyrocompass has the Remote Control Unit (RCU) mounted integrally and available for immediate operation.

There may be applications where you prefer to install the RCU at some distance from the gyrocompass unit. A mounting kit, part number 929190, is available to use in these circum-stances. The kit includes the following items:

RCU housing

Mounting bracket

Blanking plate for the gyrocompass housing

There is no need to remove the gyrocompass cover to install the RCU externally:

1. Release and remove the four M3 screws at the corners of the RCU that secure it to the gyrocompass housing.

2. Remove the seven Gland Plate release screws marked in Figure 2–1. Remove the Gland Plate. Note the connection sequence of the RCU cable at TB1/17–22 so that you can restore the same connections through the extension cable.

3. Disconnect the RCU cable at TB1/17–22 .

4. Lift the RCU away from the gyrocompass and install it at the remote location.

The cable run between the RCU and the remote location must not exceed 100 metres.

5. Use the bracket with the mounting kit to fix the RCU to a desk or to a bulkhead. You may also flush mount the RCU in a panel. Choose a suitable location to mount the RCU:

The mounting surface can be vertical or horizontal according to requirements.

Avoid installing the RCU where it might experience severe shock or vibration.

Choose a location for the RCU that allows a clear view of the display in all conditions.

6. Use the two star knobs supplied to fit the RCU into the mounting bracket. Tilt the unit to a convenient viewing and operating angle and then lock it in place by tightening both star knobs.

7. Supply and fit a cable to connect the RCU to TB1/17–22 on the Distribution Board . The cable must have three screened twisted pairs and should not exceed 100 metres in length.Route the cable through a vacant cable gland on the Gland Plate and make the cor-rect connections to the TB1 terminals.

8. Refit the Gland Plate and secure it in place using the seven release screws.

9. Fit the blanking plate to fill the gap left in the cover by the RCU.



2.2.4 Set the Gyrocompass DIP Switches1 There is a removable panel on top of the gyrocompass that allows access to the two inter-

nal DIP switches (shown in Figure 2–4) without the need to remove the main gyrocompass cover. Release and remove the three securing screws to lift off the panel.

2. Refer to Tables 2–5 and set the DIP switches carefully for the specific requirements of your installation. Do not adjust the settings of other preset controls inside the gyrocom-pass.

3. Refit the access panel to the top of the gyrocompass cover

Figure 2–4: Location of DIP switches.

2 – Installation


Table 2–5: SW1 and SW2 DIP switch settingsFactory default settings appear in bold and are marked with an asterisk in this table.

The DIP switch settings described in this table are only applicable to gyrocompasses fitted with software versions BPR 0113 (Main) and BPR 0114 (RCU) or later. If neces-sary, you can view the software versions of the main and the control panel processors by pressing both the Up and the Down selection buttons simultaneously. The display will toggle between indications of the main processor software version (with prefix 'M') and the control panel software (with prefix 'R'). The display will continue to toggle for several seconds after you release the buttons and will then return to the heading indi-cation.

SW1 DIP Switches SW2 DIP Switches

Switch number

and settingFunction

Switch number

and settingFunction

1OnOffOnOff

2OnOnOffOff

Speed Log Input Type100 pulses per nautical mile200 pulses per nautical mile400 pulses per nautical mileLOG Serial Data*

1On

Off

Output Sentences typesAnalogue ROT Scaling +/- 60deg/minute = +/- 10VAnalogue ROT Scaling +/- 20deg/s = +/- 10V*

3OnOff

Channel 1 Baud rate96004800*

2OnOff

Channel 2 Heading decimal placesTwo decimal placesOne decimal place*

4OnOff

Channel 2 Baud rate96004800*

3OnOff

Channel 1 Checksum fieldChecksum transmittedNo Checksum transmitted*

5On

Off

Channel 1 update rate10 Hz (defaults to 1Hz if CH1 All Data is selected)1 Hz*

4OnOff

Channel 2 Checksum fieldChecksum transmittedNo Checksum transmitted*

6On

Off

Channel 2 update rate10 Hz (defaults to 1Hz if CH2 All Data is selected)1 Hz*

5 OnOffOnOff

6OnOnOffOff

Channel 1 Output SentencesAll Data (1Hz only)HDT + ROTROT onlyHDT only*

7OnOff

Channel 1 Heading Decimal placesTwo decimal placesOne decimal place*

7 OnOffOnOff

8OnOnOffOff

Channel 2 Output SentencesAll Data (1Hz only)HDT + ROTROT onlyHDT only*

8OnOff

Gyro controlFor special applications onlyFactory default setting*

Notes: 1. If you set All Data Output Sentence, the update rate will default to 1Hz.2. For full IEC 61162 compliance, a checksum must be transmitted.



2.3 ALIGNMENTIt is important to align the gyrocompass to the vessel accurately. Any misalignment between the housing and the vessel will appear directly as a fixed error in heading measurements. Because measurements from the Meridian Gyrocompass are available for use by diverse sys-tems around the vessel, any misalignment between the gyrocompass and the fore-aft datum might have a significant impact in many other areas of application.

There are several methods you may use to align the gyrocompass to the vessel fore-aft datum:

Align the gyrocompass to the fore-aft datum using a known reference line, such as a sur-veyed bulkhead or frame member. The marks on the gyrocompass base plate are precision indicators of the gyrocompass alignment orientation.

To achieve correct speed compensation, the gyrocompass must be orientated so that the gland plate faces the forward end of the vessel. Note that modification kits are available for alternative gyrocompass orientations.

Use the services of a marine surveyor to align the gyrocompass precisely with the fore-aft datum.

Remove any residual misalignment by making minuscule adjustments to the gyrocompass mounting plate. When you have achieved perfect alignment, tighten the securing bolts fully to lock the gyrocompass in position.

2.4 FINAL GYROCOMPASS INSTALLATION TESTSAfter you have installed the gyrocompass and power supplies are available to it, perform the following installation tests:

1. Power-on the gyrocompass by following the instructions in sub-section 3.2. Wait for three hours before you perform the following tests.

2. Check the vessel heading against a known reference mark on a chart. Typically this could be the alongside position of the fitting-out dock. Alternatively, accurately survey an object at least five kilometres ahead of the vessel using the fore-aft line as a datum.

3. Check the displayed gyrocompass heading at intervals to make certain it is consistent with the surveyed vessel heading.

4. If there is an error larger than ±0.5°, re-check the vessel fore-aft datum to confirm that it is correct.

5. Check that all the repeaters are accurately aligned with the gyrocompass heading and make certain they maintain their alignment at all times while the gyrocompass is powered-on.

2 – Installation


2.5 INSTALLATION DRAWINGSFigure 2–5: Gyrocompass installation – Sheet 1

30330 340

170

110

160

SE 130

140

120

150

7090

80100

E

NE 60

40

50

250

230

190 180200

S210

220

SW240

N

NW

320

270

260

W

280

300

290

310

20100350

Fuse

3.15AF

CompassMin.SafeDist.

BuildStandardNo.

SerialNo.

Mfg.Date

m

Watford,England.

CAUTION

BeforeremovingthecoverortheRCU

unit,removetheglandplateand

disconnecttheRCUcable(TB1/17-22)

fromthedistributionboard.

24VDC



Figure 2–6: Gyrocompass installation – Sheet 2

S210

220

SW240

N

NW

320

270

260

W

280

300

290

310

20100350

Fuse

3.15AF

CompassMin.SafeDist.

BuildStandardNo.

SerialNo.

Mfg.Date

m

Watford,England.

CAUTION

BeforeremovingthecoverortheRCU

unit,removetheglandplateand

disconnecttheRCUcable(TB1/17-22)

fromthedistributionboard.

24VDC

30330 340

170

110

160

SE 130

140

120

150

7090

80100

E

NE 60

40

50

250

230

190 180200

2 – Installation


Figure 2–7: RCU installation – Table mount



Figure 2–8: RCU installation – Flush mount

3 – Operating Instructions


3 OPERATING INSTRUCTIONSThis section explains how to power-on and configure the Meridian Gyrocompass after installa-tion. Refer to Section 4 for an explanation of the data formats relevant to the System.

3.1 Control Features Page 2

The RCU provides all the controls you will need to operate the Meridian Gyrocompass. It also includes a four-character display panel that shows the heading indication and any alarm mes-sages and error codes.

3.2 Initial Power-on Page 3

Explains how to power-on the Meridian Gyrocompass after installation and describes the ini-tialisation sequence.

3.3 Operating Procedure Page 4

Explains how to select the latitude and speed correction sources, and how to set the latitude and speed manually if necessary.

3.4 Error Modes Page 5

Identifies the system error modes. Use these indicators to identify a possible fault condition.

3.5 Operating Considerations Page 8

Includes general advice for operating the Meridian Gyrocompass on a vessel and on high speed craft.



3.1 CONTROL FEATURESFigure 3–1: RCU front panel features

The RCU front panel includes all the operator controls for the Meridian Gyrocompass:

Table 3–1: RCU Control and Indicator functions

Control Function

Power switch. Recessed to prevent accidental operation.

Selection Up. Press to increase display brightness.

Selection Down. Press to decrease display brightness

Latitude selection button. Press to display current Latitude source and correction value. Use in conjunction with the Selection Up and Selection Down buttons to pre-set Latitude source and correction value.

Speed Selection. Press to display current Speed source and correction value. Use in conjunction with the Selection Up and Down buttons to pre-set Speed source and correction value.

Alarm. Press to silence the audible alarm.

012.3 Four digit alphanumeric display.Note: The display can show additional information by alternating the display contents at 0.5Hz. This is indicated throughtout the manual as, for example, L52N + SGPS

Power lamp (red) Indicates that the Meridian Gyrocompass is switched on when 24V DC nominal power is connected.

Ready lamp (green)

Indicates that the Meridian Gyrocompass has settled and a True Heading is available.



3.2 INITIAL POWER-ONThe Meridian Gyrocompass starting cycle is fully automatic after power is applied. For correct operation Latitude and Speed correction must be applied.

1. Check that there is a nominal 24V DC electrical supply available to the gyrocompass. The acceptable supply range is 18V to 36V DC.

To ensure continuous operation, the power supply for this unit should have a 200W power rating.

2. To start the Meridian Gyrocompass press the power switch on the RCU.

3. Check that the red ‘Power’ lamp on the RCU illuminates. This lamp indicates only that the Meridian Gyrocompass is receiving power and does NOT indicate a settled condition. Check that the instrument illumination is at maximum during the initialisation sequence. Even at its maximum setting, the instrument illumination may be difficult to see in bright ambient lighting.

4. The RCU will activate the audible alarm for about 1 second. The display will indicate T.E.S.T. and the ‘Ready’ lamp will be lit for about 10 seconds while the system performs a series of self-tests. After successful completion of the self-tests, the display will show the current Gyrocompass dial heading and the ‘Ready’ lamp will go off until the Gyrocompass has settled.

5. Set the source of latitude information by following the instructions in sub-section 3.3.1.

6. Set the source of speed information by following the instructions in sub-section 3.3.2.

Table 3–2: RCU display formats

Format Function

Heading0123.40123.4 + DG0123.4 + DG_L0123.4 + DG_X

Heading OnlyHeading with DG mode set at the RCUHeading with DG mode set by latitude greater than 80 degHeading with DG mode set by Distribution PCB connection

Speed (by pressing the Speed button)S_01 + S.MANS_01 + S.GPSS_01 + S.LOGS_01 + P.LOG

Speed value with Manual selected speed sourceSpeed value with GPS selected speed sourceSpeed value with LOG selected speed source (serial data input)Speed value with LOG selected speed source and Pulse Log DIP switch set (pulse input)

Latitude (by pressing the Latitude button)L.52N + S.MAN

L.52S + S.MAN

L.52N + S.GPS

Latitude value in the Northern Hemisphere with Manual selected Latitude sourceLatitude value in the Southern Hemisphere with Manual selected Latitude sourceLatitude value with GPS selected Latitude source



7. Use the increase and decrease selection buttons to adjust the RCU illumination level to a comfortable setting.

8. Wait for the gyrocompass to settle. This will occur automatically and will take upwards of 24 minutes depending on initial heading offset and sea conditions. The Meridian Gyro-compass signifies its settled condition by illuminating the green ‘Ready’ lamp.

9. If necessary, you can view the software versions of the main and the control panel proces-sors by pressing both the Up and the Down selection buttons simultaneously. The display will toggle between indications of the main processor software version (with prefix ‘M’) and the control panel software (with prefix ‘R’). The display will continue to toggle for several seconds after you release the buttons and will then return to the heading indication.

3.3 OPERATING PROCEDUREThe Meridian Gyrocompass will settle automatically after power-on, to provide a true north reference. The system requires only latitude and speed correction, applied manually or from external sources, to perform to the specified accuracy.

Ideally, the Meridian Gyrocompass should accept latitude and speed information from exter-nal sources such as a GPS receiver or a speed log, which allow the System to apply corrections automatically.

3.3.1 Latitude correction1. Press and hold the Latitude selection button.

2. Use the up and down selection buttons to set the local latitude manually. The display will show the latitude in one-degree increments in the range 80°N to 80°S, for example L70N

To select automatic latitude compensation from a GPS receiver, use the up or down selec-tion buttons to scroll beyond 80°N or 80°S until the display shows LGPS.

If there is no valid input available from a GPS receiver, the display will indicate a LGPS alarm after 30 seconds.

3. Release both buttons to set the latitude to the displayed value or to set the gyrocompass to use GPS as the source of automatic latitude correction. The display will indicate the lati-tude setting and latitude source for several seconds and will then return to the normal head-ing display.

If you input the operating latitude manually, remember to change the setting when nec-essary. Note that, in medium latitudes, a 10° error in setting the operating latitude will result in a compass error of approximately 0.5°.

3.3.2 Speed correction1. Press and hold the Speed selection button.

2. Use the up and down selection buttons to set the speed manually in the range zero to 90 knots.



To select automatic speed compensation from a GPS receiver or a speed log, use the up selection button to scroll beyond 90 knots until the display shows SGPS or SLOG.

If there is no valid input available from a speed log or GPS receiver, the display will indicate a SLOG or SGPS alarm after 30 seconds.

3. Release both buttons to set the speed to the displayed value or to set the gyrocompass to use GPS or a speed log as the source of automatic speed correction. The display will indi-cate the speed setting and speed source for several seconds and will then return to the nor-mal heading display.

If you input the vessel speed manually, remember to set the average vessel speed and to change the setting when necessary. Return the setting to zero on completion of the voyage. For a vessel steaming in a northerly direction, a 5-knot error in speed setting will generate an error of approximately 0.5°.

3.3.3 DG operating modeFollow the instructions in sub-section 3.3.1 to set the latitude correction to the Directional Gyro (DG) mode. In this mode you can use the Meridian Gyrocompass as a direction indicat-ing instrument all the way up to the poles. If the gyrocompass has settled on north immediately prior to entering the DG mode, it will continue to provide a useful indication of the northerly direction for a period, but will not continue to seek north. The length of time that the direction indication remains valid depends entirely on the gyro drift characteristics.

Note: DG mode will be automatically enabled for latitudes set greater than 80 deg.

Note: that the gyrocompass will not north seek while operating in the DG mode.

3.4 ERROR MODESThe Meridian Gyrocompass has three possible Error modes:

1. Loss or corruption of GPS signal

2. Loss or corruption of speed log signal

3. Gyrocompass system warnings and failures

3.4.1 Loss of GPSThis failure mode can occur when you have selected GPS as the source of speed or latitude information and the signal corrupts or becomes lost for a period of 30 seconds. You can recog-nise this condition by the following indications:

The display shows S.GPS + FAIL for the loss of speed correction information.

The display shows L.GPS + FAIL for the loss of latitude correction information.

The audible alarm will sound.

Press the Alarm button to cancel the audible alarm.

1. The Gyrocompass will use the last valid speed and latitude values.



2. The RCU will continue to show the alarm message until a valid input signal is re-estab-lished or a different input source is selected.

3. If the valid input signal has not been established within a period of 30 minutes the audible alarm will be enabled.

3.4.2 Loss of speed logThis failure mode can occur when you have selected speed log as the source of speed informa-tion and the signal corrupts or becomes lost for a period of 30 seconds. You can recognise this condition by the following indications:

The display flashes SLOG + FAIL for the loss of selected serial data source information.

The display flashes pLOG + FAIL for the loss of pulsed selected source information.


Press the Alarm button to cancel the alarm.

1. The Gyrocompass will use the last valid speed value.

2. The RCU will continue to show the alarm message until a valid input signal is restablished or a different input source is selected.

If a valid input signal has not been established within a period of 30 minutes the audible alarm will be enabled.

3.4.3 Gyrocompass system warnings and failuresThe Meridian Gyrocompass has a built-in system that monitors operation of the gyrocompass. The functions that this system checks are split into two categories.

Warning conditions

Failure conditions

A failure condition warning will result in the Gyroscope power supply being disabled. Refer to the maintenance section before activating the Power Supply.

Warning Conditions

If the gyrocompass detects a warning condition, it will use two methods to alert you:

The display shows <Message> + FAIL





Table 3–3: Gyrocompass warning codes

The RCU will continue to show the alarm message until the fault condition has been removed. If the fault condition has not been removed within a period of 30 minutes the audible alarm will be enabled. Refer to sub-section 5.1 which outlines some simple checks that you can make to rectify these fault conditions. If necessary contact SG Brown or an approved local service agent for assistance.

Failure Conditions

If the Meridian Gyrocompass detects a failure condition, it will use six methods to alert you:

The display shows <Message> + FAIL


The ‘Ready’ lamp will extinguish.

The Gyro Fail relay will activate.

Serial output will transmit empty sentences.

Stepper output will transmit an illegal code.


Table 3–4: Gyrocompass failure codes

These failures are considered to render, or be due to an unrecoverable fault condition, possibly due to a component failure.

To prevent damage to the Gyroscope the power supplies to it will be disabled.

The Gyrocompass will be disabled until it has been reset by the operator. Refer to the mainte-nance section before activating the Power Switch.

<Message>RCU Screen Definition of warning code

dc + fail Internal DC power supply is outside operating limits

ac + fail Internal AC power supply is outside operating limits

rdc + fail Loss of internal timing signals

Temp + fail Over or under operating temperature range

rMT + fail Loss of serial communication link with the RMT

<Message>RCU Screen Definition of failure code

rot + Fail Rate of Turn exceeds 300o/s



3.5 OPERATING CONSIDERATIONS3.5.1 General Operating Considerations You should leave the Meridian Gyrocompass running continuously. Power-off the system

only during long periods of lay-up, for example during vessel dry-docking. To power-off the Meridian Gyrocompass, press the ‘Power’ button. The heading display will go blank and the front panel lamps will switch off. The gyro rotor will take approximately five min-utes to come to rest.

If you intend to leave the system powered-off for an extended period, you should arrange to run the gyrocompass for a period of at least thirty minutes at intervals of six months or less.

The Meridian Gyrocompass has full protection against interruption of its electrical supply. It will re-start and align itself automatically on restoration of electrical power. The heading indication will be accurate when the RCU ‘Ready’ lamp is on.

Monitor the Meridian Gyrocompass performance regularly. When functioning correctly, and provided the correct Speed and Latitude compensations are applied, the heading error in latitudes up to 60° and for speeds up to 25 knots will normally be less than 0.75° regard-less of the vessel manoeuvres.

Never move the gyrocompass with the gyro rotor spinning unless you leave the servos operational. Note that the gyro rotor continues to spin for a period of approximately five minutes after you power-off the gyrocompass.

3.5.2 Corrections for Speed and Latitude Gyrocompass operational accuracy depends, to a large extent, upon accurate corrections

for speed and latitude being applied.

Most users find that the facilities for the automatic application of speed and latitude cor-rections, via signal inputs from GPS and/or ships log, are a convenient method of applying corrections.

However, users should be aware that if the input signal contains the wrong information, then the wrong corrections will be applied. For instance, it has been noted that some GPS installations, under certain circumstances, will output a “valid” signal with the speed and latitude fields set to all zeros indicating that the vessel is stationary on the equator.

An incorrect input of speed and/or latitude will cause the gyrocompass to indicate an incorrect heading and in the case of extreme errors could cause, in certain circumstances, the gyrocompass to come out of the “Ready mode”.

3.5.3 Operating at Extremes of Latitudes As latitude increases (north or south) the magnitude of the horizontal component of the

Earth’s rotation rate reduces in proportion to the cosine of latitude. Consequently, the effectiveness of the gyrocompasses north seeking action reduces with increasing latitude.

At latitudes greater than 80o it is recommended that the gyrocompass be operated in the directional gyro mode.



If correction for the effect of latitude on the vertical component of Earth’s rotation is made manually via the RCU, then correction is available to 80o. Thereafter, the directional gyro mode should be manually selected. Errors in the indicated heading will increase with time and increasing latitude above 80o to a maximum of approximately 0.25o /hour. To re-align the gyrocompass, operating latitude must be reduced below 80o and the gyrocompass mode of operation re-selected.

If correction for the effect of latitude on the vertical component of Earth’s rotation is made automatically via a serial data input, then correction is available above 80o and directional gyro mode is automatically selected above this latitude. The compass will still be subject to small inherent drifts while operating in this mode. Reversion to the gyrocompass mode will be made automatically when the serial data latitude input falls below 80o.

3.5.4 Operating Considerations for High Speed Craft The gyrocompass gravity control gives rise to errors whenever the gyrocompass acceler-

ates or decelerates along the north-south line, that is whenever the northerly speed or course changes. These errors are caused by the inertia of the pendulous element of the gyro, which produces a torque about the horizontal axis and therefore a precession in azi-muth. This effect, called ballistic deflection, causes an increase in error during accelera-tion.

The precession in tilt that arises from the damping component of gravity control is called ballistic tilt. The combined effects of ballistic tilt and ballistic deflection cause the gyro-compass to tilt downwards. Because of the factors that guide the behaviour of a damped gyroscope, the gyro spin axis will return to the settled position by the normal anticlock-wise spiral after the acceleration has ceased.

In the Meridian Gyrocompass, gravity control comes from an accelerometer (pendulum), which generates an electrical signal related to the tilt of the gyro spin axis. This devices has two important design features; it is heavily damped and the range of output is restricted to a small angle.

The use of accelerometer damping by the Meridian Gyrocompass is of prime importance in the reduction of a particularly serious form of ballistic error called inter cardinal rolling error. This type of error occurs most noticeably when the vessel steams on an inter cardinal heading while rolling simultaneously through a significant angle.

If the gyrocompass is installed at some distance above the vessel centre of roll rotation, as is usually the case on commercial vessels, the resulting lateral acceleration components along the east-west and north-south axes of the gyrocompass combine to build an error in the northerly settle point.

If the effect persists for long enough, this error might become as large as several degrees. However, by damping the accelerometer using a time constant several times larger than the vessel rolling period, inter cardinal rolling errors are significantly reduced.

Another form of ballistic error arises from north-south accelerations generated by vessel manoeuvres. Such accelerations can arise from changes in speed and/or course. By limit-ing the angular output of the accelerometer, the Meridian Gyrocompass reduces the error potential typically to less than one degree.



It is also possible to eliminate acceleration effects by temporarily operating the compass in the DG (Directional Gyro) mode. In this mode gravity control is used for tilt corrections only, so that ballistic effects would cause negligible heading error during short-term accel-eration periods. The DG mode can be selected manually from the control panel.

The Meridian Gyrocompass complies with all requirements of IMO Resolution A.821(19), Performance Standards for Gyrocompasses for High-Speed Craft.

4 – Technical Data


4 TECHNICAL DATA4.1 SPECIFICATIONS4.1.1 Power RequirementsVoltage 24V DC (acceptable range 18V to 36V DC)

Power consumption 3A at power on, 1.2A continuous (The power sup-ply capacity should exceed 200W)

CAUTIONThe Meridian Gyrocompass should be supplied with power from an SELV source as defined in IEC/EN 60950. The power supply source should be switched and protected by a suitable circuit breaker.

To comply with the requirements of IMO Resolution A.821(19), Performance Standards for Gyrocompasses for High Speed Craft, power to the gyrocompass should be delivered by an uninterruptable power supply.

4.1.2 Performance (definitions as in ISO 8728)Settle point error 0.35° sec latitude

Static error 0.1° sec latitude RMS

Dynamic accuracy 0.3° sec latitude (Scorsby andIntercardinal motion tests)

Settle point repeatability 0.25° sec latitude

Follow up speed 200°/s

Time to settle within 0.7° Less than 45 minutes with a ±30° initial heading offset

4.1.3 CompensationLatitude compensation range 80°N to 80°S

Speed compensation range 0 to 90 knots

4.1.4 EnvironmentOperating environment EN 6095:1997 designated category ‘weather pro-

tected’

Operating temperature 0°C to +45°C (to ISO 8728)–15°C to +55°C (with reduced accuracy)

Storage temperature –25°C to +80°C



4.1.5 Signal InputsLatitude IEC 61162 message string via RS232 or RS422

from GPS

Speed Pulse or contact closure at 100, 200 or 400 per nautical mile from speed log.

IEC 61162 message string at 4800 baud via RS232 or RS422 from GPS or speed log

4.1.6 Signal outputsS-type heading 1 × step-by-step, 6 steps per degree (TTL level)

update limited to 20o/s to prevent repeater mis-alignment

Synchro heading 1 × 26V 400Hz (11.8V maximum line-to-line),sector value 360°

Resolver heading 1 × 36V 400Hz (8V maximum per phase),sector value 360°

Analogue rate of turn 1 × rate of turn ±60°/min (±10V) or ±20°/s (±10V)

Serial data outputs 6 × RS23211 × RS422

Serial data formats IEC 61162 at 1Hz or 10Hz. Course recorder output (heading, date, time)

Status/alarm 5V TTL power/gyro failureVoltage free power/gyro failure contacts5V TTL system readyVoltage free system ready contacts

4.1.7 Dimensions and WeightDimensions 344mm (H) × 267mm (W) × 440mm (D)

Weight 15.5kg

RCU size (when mounted externally) 96mm (H) × 192mm (W) × 108mm (D)0

RCU weight 0.75 kg



4.1.8 Listener load requirementThe gyrocompass presents a listener load of 1.6mA typical at 2V or 3.5mA typical at 5V to all serial data input signals.

Figure 4–1: Listener input circuit

4.1.9 Talker drive capabilityThe gyrocompass has a talker drive capability of 150mA to ground.

Derived from 26C31 line drivers.

4.1.10 StandardsThe Meridian Gyrocompass is designed to meet the requirements of the following:

IMO Resolution A.424 (XI), Performance Standards for Gyrocompasses

IMO Resolution A.821 (19), Performance Standards for Gyrocompasses for High Speed Craft

BS EN 60945 (January 1997), General Requirements - Methods of testing and required test results

BS EN ISO 8728:1999, Shipbuilding – Marine Gyrocompasses

BS 6217:1981, Graphical Symbols for use on Electrical Equipment

CE marking

Electromagnetic Compatibility (EMC) Directive

The Marine Equipment Directive 96/98/EC

IEC 61162-1:2000(E) Maritime navigation and radio communication equipment and sys-tems - Digital interfaces. Note that IEC 61162-1:2000(E) is closely aligned with NMEA 0183 version 2.30.



4.2 DATA FORMATSSet the DIP switches according to your specific input and output requirements. You will find the instructions to do this in sub-section 2.2.4.

Inputs – Refer to sub-section 4.2.2

Acceptable input formats: Latitude information using serial IEC 61162 GNS, RMC, GLL or GGA sentences. If more

than one of these formats is available, the Meridian Gyrocompass makes its selection in the stated preference order. Refer to Figures 4-3, 4-4, 4-5 and 4-6 respectively for a description of these formats.

Datum reference using IEC 61162 DTM sentence. The latitude offset is not used to correct the gyroscope latitude information, however the DTM sentence is re-transmitted.

Speed information using serial IEC 61162 VBW, RMC, VTG or VHW sentences. The sen-tences can contain speed information using knots and/or km/h. The Meridian Gyrocom-pass will use the speed in knots if available, in preference to speed in km/h. If more than one of these formats is available, the Meridian Gyrocompass makes its selection in the stated preference order. Refer to Figures 4-8, 4-4, 4-9 and 4-10 respectively for a descrip-tion of these formats.

If an RMC sentence is used it must contain both speed and latitude information.

TTL-compatible pulsed speed input with a TTL-level signal or contact closure.

Outputs – Refer to sub-section 4.2.3

Serial output formats:The Meridian Gyrocompass transmits selected information through RS232 and RS422 serial lines using the IEC 61162 format. The serial transmission rate can be either 4800 or 9600 baud, with updates occurring at 1Hz or 10Hz as defined by the setting of the DIP switches.

Other output formats:

Synchro Heading Output

Resolver Heading Output

Stepper S-code Heading Output

Rate of turn using a bipolar analogue voltage in the range ±10V

The following sub-sections describe each of the formats supported by the Meridian Gyrocom-pass .



4.2.1 IEC 61162 Serial Data Formats – General informationThe Meridian Gyrocompass accepts and transmits asynchronous serial data using 8 data bits, one stop bit and no parity through RS232 and RS422 transmit-only lines. The data bits occur in each packet with the least significant bit first. The most significant bit of the 8-bit character will always be zero.

Figure 4–2: Serial data format

All data is interpreted as ASCII characters that form IEC 61162 sentences split into individual fields. All fields, including null fields, are separated by commas.

The IEC 61162 format requires a checksum – if included, the checksum occurs as an addi-tional field immediately before the carriage return line-feed characters. It consists of an aster-isk (*) followed by a checksum derived by exclusive OR-ing the eight data bits of each valid character preceding the asterisk, but excluding the $ symbol, in the sentence. The absolute value of the checksum is transmitted in ASCII characters representing the value in HEX. For circumstances where the Meridian Gyrocompass retransmits serial data using the same IEC 61162 sentence format supplied by an external source, it will recalculate any checksum and insert the new value into the output sentence.

IEC 61162 sentences are usually transmitted once per second, however you can set a DIP switch to select a transmission rate of 10 per second. The outputs are grouped into two chan-nels that can be set independently to either 1Hz or 10Hz updates. The output option of head-ing, latitude, speed, datum, rate of turn and time sentences will always be transmitted at 1Hz.



4.2.2 Inputs4.2.2.1 IEC 61162 input signalsThe Meridian Gyrocompass will accept sentences in both the IEC 61162-1:2000(E) and NMEA 0183 version 2.1 data formats.

In the following descriptions of input sentences, the Meridian Gyrocompass uses the data fields marked ‘XXX’ in the IEC 61162 sentence. The system does not use the fields marked ‘???’ and their descriptions are included here for completeness only. The gyrocompass will recognise the arriving sentence format and will extract the required data from it automatically.

GPS Interface (see Table 2-3 for connection details)

The Meridian Gyrocompass can accept speed, latitude, date and time inputs at the GPS inter-face in IEC 61162 format using GNS, RMC, GLL, GGA, VTG, VHW and ZDA sentences.

Figure 4–3: IEC 61162 GNS input sentence structure

Figure 4–4: IEC 61162 RMC input sentence structure

$??GNS,??????.??,XXXX.XX,X,?????.??,?,X--X,??,?.?,?.?, [CRLF]?.?,?.?,?.?*??

Talk

erid

entif

ier

(any

char

acte

rs)

Mne

mon

icfo

rG

NS

Sfix

data

UT

Cof

posi

tion

Nor

th/S

outh

Latit

ude

(ddm

m.m

m)

Long

titud

e

Car

riage

retu

rnLi

ne-f

eed

char

acte

rs

Sta

rtch

arac

ter

Eas

t/Wes

t

Diff

eren

tial r

efer

ence

stat

ion

ID

Che

cksu

mfie

ld

Age

ofdi

ffere

ntia

l dat

a

Geo

idal

sepe

ratio

n,m

Ant

enna

altit

ude,

m, r

e:m

ean-

sea-

leve

l (ge

oid)

HD

OP

Tota

l num

ber

ofsa

telli

tes

inus

e,0-

99

Mod

eIn

dica

tor

$??RMC,??????.??,X,XXXX.XX,X,?????.??,?,X.X,?.?,??????,?.?,?,X[CRLF]

Talk

erid

entif

ier

(any

char

acte

rs)

Mne

mon

icfo

rR

ecom

men

ded

Min

GP

Sda

ta

UT

Cof

posi

tion

(hhm

mss

.ss)

Latit

ude

(ddm

m.m

m

Mne

mon

icfo

rN

orth

orS

outh

Sta

tus,

A=

valid

, V=

Nav

. Rec

eive

rw

arni

ng

Long

itude

(ddd

mm

.mm

)

Mne

mon

icfo

rE

ast o

rW

est

Mag

netic

varia

tion

indi

cato

rea

stor

Wes

t

Gro

und

spee

din

knot

s

Mag

netic

varia

tion

inde

gree

s

Cou

rse

over

grou

ndin

degr

ees

Dat

eof

fix

Car

riage

retu

rnLi

ne-f

eed

char

acte

rs

Sta

rtch

arac

ter

Mod

eIn

dica

tor



Figure 4–5: IEC 61162 GLL input sentence structure

Figure 4–6: IEC 61162 GGA input sentence structure

Figure 4–7: IEC 61162 DTM input sentence structure

$??GLL,XXXX.XX,X,?????.??,?,??????.??,X,X[CRLF]

Talk

erid

entif

ier

(any

char

acte

rs)

Mne

mon

icfo

rge

ogra

phic

alLa

t and

Lon

Latit

ude

(ddm

m.m

m)

Long

itude

(ddd

mm

.mm

)

Mne

mon

icfo

rN

orth

orS

outh

Mne

mon

icfo

rE

ast o

rW

est

Car

riage

retu

rnLi

ne-f

eed

char

acte

rs

Sta

rtch

arac

ter

UT

Cof

posi

tion

(hhm

mss

.ss)

Sta

tus

Mod

eIn

dica

tor

$??GGA,??????.??,XXXX.XX,X,?????.??,?,X,??,?.?,?.?,?,?.?,?,?.?,????[CRLF]

Talk

erid

entif

ier

(any

char

acte

rs)

Mne

mon

icfo

rG

PS

fixda

ta

UT

Cof

posi

tion

(hhm

mss

.ss)

Latit

ude

(ddm

m.m

m

Mne

mon

icfo

rN

orth

orS

outh

Long

itude

(ddd

mm

.mm

)

Mne

mon

icfo

rE

ast o

rW

est

GP

Squ

ality

indi

cato

r

Num

ber

ofsa

telli

tes

inus

e(0

0-

12)

Hor

izon

tal d

ilutio

nof

prec

isio

n

Ant

enna

altit

ude

rela

tive

tom

ean

sea

leve

l

Mne

mon

icfo

rm

etre

s

Mne

mon

icfo

rm

etre

s

Geo

idal

sepa

ratio

n

Age

ofdi

ffere

ntia

l GP

Sda

ta

Diff

eren

tial r

efer

ence

stat

ion

(000

0-

1023

)

Car

riage

retu

rnLi

ne-f

eed

char

acte

rs

Sta

rtch

arac

ter

$??DTM,???,?,?.?,?,?.?,?,?.?,???*hh[CRLF]

Talk

erid

entif

ier

Mne

mon

icfo

rD

atum

refe

renc

e

Loca

l dat

umsu

bdiv

isio

nco

de

Latit

ude

offs

et

Loca

l dat

um

Ref

eren

ceda

tum

Nor

th/S

outh

Che

cksu

mfie

ld

Car

riage

retu

rnLi

ne-f

eed

char

acte

rs

Sta

rtch

arac

ter

Long

itude

offs

et

Eas

t/Wes

t

Alti

tude

offs

et, m



Figure 4–8: IEC 61162 VBW input sentence structure

Figure 4–9: IEC 61162 VTG input sentence structure

Figure 4–10: IEC 61162 VHW input sentence structure

$??VBW,?.?,?.?,?,X.X,?.?,X,?.?,?,?.?,?*hh[CRLF]Ta

lker

iden

tifie

r(a

nych

arac

ters

)

Mne

mon

icfo

rD

ual g

roun

d/w

ater

spee

d

Long

itudi

nal w

ater

spee

d,kn

ots

Sta

tus:

wat

ersp

eed,

A=

valid

, V=

not v

alid

Tra

nsve

rse

wat

ersp

eed,

knot

s

Long

itudi

nal g

roun

dsp

eed,

knot

s

Car

riage

retu

rnLi

ne-f

eed

char

acte

rs

Sta

rtch

arac

ter

Tra

nsve

rse

grou

ndsp

eed,

knot

s

Sta

tus:

ster

ngr

ound

spee

d,A

=va

lid, V

=no

t val

id

Che

cksu

mfie

ld

Sta

tus:

grou

ndsp

eed,

A=

valid

, V=

not v

alid

Ste

rntr

ansv

erse

wat

ersp

eed,

knot

s

Sta

tus:

ster

nw

ater

spee

d,A

=va

lid, V

=no

t val

id

Ste

rntr

ansv

erse

grou

ndsp

eed,

knot

s

$??VTG,?.?,?,?.?,?,X.X,X,XX.X,X,X[CRLF]

Talk

erid

entif

ier

(any

char

acte

rs)

Mne

mon

icfo

rgr

ound

cour

sean

dsp

eed

Mne

mon

icfo

rT

rue

head

ing

Mne

mon

icfo

rM

agne

tiche

adin

g

Cou

rse

inde

gree

san

dte

nths

Mne

mon

icfo

rkn

ots

Spe

edin

knot

s

Spe

edin

km/h

Mne

mon

icfo

rkm

/h

Car

riage

retu

rnLi

ne-f

eed

char

acte

rs

Sta

rtch

arac

ter

Cou

rse

inde

gree

san

dte

nths

Mod

ein

dica

tor



Figure 4–11: IEC 61162 ZDA input sentence structure

Log Interface (see Table 2-3 for connection details)

The Meridian Gyrocompass can accept speed inputs at the Log interface in IEC 61162 format using VBW, VTG and VHW sentences only.

Figure 4–12: IEC 61162 VBW input sentence structure

Figure 4–13: IEC 61162 VTG input sentence structure

$??ZDA,XXXXXX.XX,XX,XX,XXXX,??,??[CRLF]Ta

lker

iden

tifie

r(a

nych

arac

ters

)

Mne

mon

icfo

rT

ime

and

Dat

e

Day

ofm

onth

(01

to31

)

Mon

thof

year

(01

to12

)

UT

C(h

hmm

ss.s

s)

Loca

l zon

eho

urs

(00

to±

13)

Yea

r

Loca

l zon

em

inut

es(0

0to

+59

)

Car

riage

retu

rnLi

ne-f

eed

char

acte

rs

Sta

rtch

arac

ter

$??VBW,?.?,?.?,?,X.X,?.?,X,?.?,?,?.?,?*hh[CRLF]

Talk

erid

entif

ier

(any

char

acte

rs)

Mne

mon

icfo

rD

ual g

roun

d/w

ater

spee

d

Long

itudi

nal w

ater

spee

d,kn

ots

Sta

tus:

wat

ersp

eed,

A=

valid

, V=

not v

alid

Tra

nsve

rse

wat

ersp

eed,

knot

s

Long

itudi

nal g

roun

dsp

eed,

knot

s

Car

riage

retu

rnLi

ne-f

eed

char

acte

rs

Sta

rtch

arac

ter

Tra

nsve

rse

grou

ndsp

eed,

knot

s

Sta

tus:

ster

ngr

ound

spee

d,A

=va

lid, V

=no

t val

id

Che

cksu

mfie

ld

Sta

tus:

grou

ndsp

eed,

A=

valid

, V=

not v

alid

Ste

rntr

ansv

erse

wat

ersp

eed,

knot

s

Sta

tus:

ster

nw

ater

spee

d,A

=va

lid, V

=no

t val

id

Ste

rntr

ansv

erse

grou

ndsp

eed,

knot

s

$??VTG,?.?,?,?.?,?,X.X,X,XX.X,X,X[CRLF]

Talk

erid

entif

ier

(any

char

acte

rs)

Mne

mon

icfo

rgr

ound

cour

sean

dsp

eed

Mne

mon

icfo

rT

rue

head

ing

Mne

mon

icfo

rM

agne

tiche

adin

g

Cou

rse

inde

gree

san

dte

nths

Mne

mon

icfo

rkn

ots

Spe

edin

knot

s

Spe

edin

km/h

Mne

mon

icfo

rkm

/h

Car

riage

retu

rnLi

ne-f

eed

char

acte

rs

Sta

rtch

arac

ter

Cou

rse

inde

gree

san

dte

nths

Mod

ein

dica

tor



Figure 4–14: IEC 61162 VHW input sentence structure

4.2.2.2 Pulsed inputThe Meridian Gyrocompass can accept a speed input as a series of pulses or contact closures occurring at a frequency of 100, 200 or 400 per nautical mile as selected by a DIP switch. The gyrocompass determines the vessel speed by reference against the microprocessor timing cir-cuits. The speed pulses do not need to have a particular mark/space ratio, although they should be TTL-level. Contact closures should be of good quality and electrically floating.



4.2.3 Outputs4.2.3.1 IEC 61162 output signalsThe Meridian Gyrocompass can output serial data through RS232 and RS422 transmit-only serial lines using the IEC 61162-1:2000(E) format. The output of each channel can be set inde-pendently, using DIP switches, to contain either:

1. Heading - as described below, OR

2. Heading and Rate of turn - as described below, OR

3. Rate of turn only - as described below, OR

4. All data - all information described below, transmitted in the order stated

Heading information is transmitted using an HDT format sentence. The resolution of the heading information can be set to one or two decimal places at the DIP switches. Refer to Figures 4-15 for a description of this output format.

Rate of turn information is transmitted using a ROT format sentence. Refer to Figure 4–16 for a description of this output format.

Speed information is transmitted using a VTG format sentence if the gyrocompass is con-figured for manual or a pulsed speed log input. The VTG sentence also has provision for Heading and this is inserted at a resolution as set by the DIP switches. Refer to Figure 4-18 for a description of this output format. If the gyrocompass is configured for a GPS speed input and the speed information arrives at the gyrocompass in either VBW, RMC, VTG or VHW format, then the gyrocompass will retransmit the received format modifying the sen-tence to include the HE talker identifier. Refer to Figures 4-17, 4-20, and 4-18 for a description of these output formats.

Datum reference is retransmitted if the DTM sentence is received on the GPS input. The gyrocompass will re-transmit the received sentence modifying it to include the HE talker identifier. Refer to Figure 4-23 for a description of this output format.

Latitude information is transmitted using a GLL format sentence if the gyrocompass is configured for manual latitude input. Refer to Figure 4-14 for a description of this output format. If the gyrocompass is configured for a GPS latitude input and the latitude informa-tion arrives at the gyrocompass in either GNS, RMC, GLL, or GGA format, then the gyro-compass will retransmit the received sentence modifying the sentence to include the HE talker identifier. Refer to Figures 4-19, 4-20, 4-21 and 4-22 for a description of these out-put formats.

Date and time information is transmitted using a ZDA format sentence. The gyrocompass will transmit the ZDA sentence including the HE talker identifier. If this information is received from a GPS source, all fields will be retransmitted. If there is no valid date and time from an external source, the gyrocompass will transmit the ZDA sentence with empty data fields. Refer to Figure 4-24 for a description of this output format.

If “All Data” output format is selected at the DIP switches, the transmission update rate for that channel will be at 1Hz regardless of the setting of the channel update rate.



In the following descriptions of output sentences, the gyrocompass sets the contents of fields marked XXX and leaves unchanged the fields marked ???

Figure 4–15: IEC 61162 HDT output sentence structure

Figure 4–16: IEC 61162 ROT output sentence structure

Figure 4–17: IEC 61162 VBW output sentence structure$HEVBW,?.?,?.?,?,?.?,?.?,?,?.?,?,?.?,?*hh[CRLF]

Talk

erid

entif

ier

(any

char

acte

rs)

Mne

mon

icfo

rD

ual g

roun

d/w

ater

spee

d

Long

itudi

nal w

ater

spee

d,kn

ots

Sta

tus:

wat

ersp

eed,

A=

valid

, V=

not v

alid

Tra

nsve

rse

wat

ersp

eed,

knot

s

Long

itudi

nal g

roun

dsp

eed,

knot

s

Car

riage

retu

rnLi

ne-f

eed

char

acte

rs

Sta

rtch

arac

ter

Tra

nsve

rse

grou

ndsp

eed,

knot

s

Sta

tus:

ster

ngr

ound

spee

d,A

=va

lid, V

=no

t val

id

Che

cksu

mfie

ld

Sta

tus:

grou

ndsp

eed,

A=

valid

, V=

not v

alid

Ste

rntr

ansv

erse

wat

ersp

eed,

knot

s

Sta

tus:

ster

nw

ater

spee

d,A

=va

lid, V

=no

t val

id

Ste

rntr

ansv

erse

grou

ndsp

eed,

knot

s



Figure 4–18: IEC 61162 VTG output sentence structure

Note In GPS mode only the talker identifier is changedIn manual mode, the magnetic course fields are empty.

Figure 4–19: IEC 61162 GNS output sentence structure

Figure 4–20: IEC 61162 RMC output sentence structure

$HEGNS,??????.??,????.??,?,?????.??,?,????,??,?.?,?.?, [CRLF]?.?,?.?,?.?*??

Talk

erid

entif

ier

(any

char

acte

rs)

Mne

mon

icfo

rG

NS

Sfix

data

UT

Cof

posi

tion

Nor

th/S

outh

Latit

ude

(ddm

m.m

m)

Long

titud

e

Car

riage

retu

rnLi

ne-f

eed

char

acte

rs

Sta

rtch

arac

ter

Eas

t/Wes

t

Diff

eren

tial r

efer

ence

stat

ion

ID

Che

cksu

mfie

ld

Age

ofdi

ffere

ntia

l dat

a

Geo

idal

sepe

ratio

n,m

Ant

enna

altit

ude,

m, r

e:m

ean-

sea-

leve

l (ge

oid)

HD

OP

Tota

l num

ber

ofsa

telli

tes

inus

e,0-

99

Mod

eIn

dica

tor



Figure 4–21: IEC 61162 GLL output sentence structure

Note In GPS mode, only the talker identifier is changedIn manual mode, the longtitude and UTC fields are empty

Figure 4–22: IEC 61162 GGA output sentence structure

Figure 4–23: IEC 61162 DTM output sentence structure$HEDTM,???,?,?.?,?,?.?,?,?.?,???*hh[CRLF]

Talk

erid

entif

ier

Mne

mon

icfo

rD

atum

refe

renc

e

Loca

l dat

umsu

bdiv

isio

nco

de

Latit

ude

offs

et

Loca

l dat

um

Ref

eren

ceda

tum

Nor

th/S

outh

Che

cksu

mfie

ld

Car

riage

retu

rnLi

ne-f

eed

char

acte

rs

Sta

rtch

arac

ter

Long

itude

offs

et

Eas

t/Wes

t

Alti

tude

offs

et, m



Figure 4–24: IEC 61162 ZDA output sentence structure

4.2.4 IEC 61162 sentence with ChecksumWhen the checksum is to be sent with any of the above IEC 61162 sentences, it appears as an extra field inserted before the carriage return character as shown by example in Figure 4-24.

Figure 4–25: IEC 61162 sentence with optional checksum

The checksum consists of an asterisk followed by the checksum calculated by exclusive OR-ing the eight data bits of each valid character preceding the asterisk, but excluding the ‘$’ sym-bol, in the sentence. The Meridian Gyrocompass transmits the absolute value of the checksum in ASCII characters representing the value in HEX.

4.2.5 Other Output Formats4.2.5.1 Course Recorder OutputThe following ASCII data shall be transmitted on the Course Recorder Output every minute, in a suitable format to be output on an 80 column line printer.

359.99 True Lat 52 N Spd 10 Kts UTC 13:34:01 01/01/2001

Table 4–1: Course Recorder Output Sentences

Heading 999.99

Latitude 99

Hemisphere N or S

Speed Kts 99

Time hh:mm:ss

Date dd/mm/yy

$HEZDA,??????.??,??,??,????,??,??[CRLF]Ta

lker

iden

tifie

r

Mne

mon

icfo

rT

ime

and

Dat

e

Day

ofm

onth

(01

to31

)

Mon

thof

year

(01

to12

)

UT

C(h

hmm

ss.s

s)

Loca

l zon

eho

urs

(00

to±

13)

Yea

r

Loca

l zon

em

inut

es(0

0to

+59

)

Car

riage

retu

rnLi

ne-f

eed

char

acte

rs

Sta

rtch

arac

ter



Date and time will only be output if a valid ZDA sentence is available on the GPS input.

4.2.5.2 Synchro OutputThe synchro heading output is available continuously at TB2 on the Distribution Board while the gyrocompass is powered-on – refer to Table 2-4 for connector details. The output is at 11.8V maximum line-to-line voltage derived electrically from a 1:1 resolver driven directly by the gyrocompass azimuth gimbal. The synchro reference voltage is a nominal 26V 400Hz sup-ply generated internally.

Electrical loading specification:

Not less than 5k between any two S lines.

Not less than 1k between the two R lines.

4.2.5.3 Resolver OutputThe resolver heading output is available continuously at TB2 on the Distribution Board while the gyrocompass is powered-on – refer to Table 2-4 for connection details. The output is at 8V maximum voltage per phase signal from a 1:1 resolver driven directly by the gyrocompass azi-muth gimbal. The resolver reference voltage can be set nominal 36V 400Hz or 10V 400Hz supply generated internally by jumper JP30 on PCB929066. The factory default setting is 10V 400Hz.

The resolver sine and cosine outputs must be electrically isolated from each other. Contact the SG Brown Service Department for technical advice if necessary.

Electrical loading specification:

Not less than 5k between any two S lines.

Not less than 1k between the two R lines.

4.2.5.4 Stepper S-CodeThe stepper S-code output is available continuously at TB2 on the Distribution Board while the gyrocompass is powered-on – refer to Table 2-4 for connection details.

The stepper output is a TTL compatible S-encoded signal with a 10mA sink capacity.

4.2.5.5 Rate of TurnThe ROT output is calculated by the internal processor updated at 10Hz and made available continuously at TB3 on the Distribution Board while the gyrocompass is powered-on – refer to Table 2-4 for connection details.

The ROT output is a bipolar analogue voltage in the range ±10V to represent rates of turn from –60° to +60° per minute or –20° to +20° per second. Positive rates of turn are to star-board.

5 – Maintenance


5 MAINTENANCEWARNING

There is a danger of serious injury from voltages inside the Meridian Gyrocompass . Do not remove the gyrocompass cover unless you have the necessary skills and experi-ence to perform maintenance work on a system of this nature. Always power-off the system before you remove the cover for maintenance work.

Observe all local safety regulations as you work on the equipment. Reconnect the safety grounding straps and refit all safety covers to the equipment before you power-on the system.

CAUTIONPerform these simple maintenance instructions only if you have the skills and experi-ence required, and only when necessary. Inappropriate tampering with the internal controls and components of the gyrocompass can lead to damage or serious perform-ance degradation.

NEVER open the gyrocompass cover or make any adjustments inside the gyrocom-pass unless you are entirely confident in your actions.

There is very little need for user maintenance on the Meridian Gyrocompass and you should never need to remove the covers.

The following sub-sections explain some very basic procedures that you may attempt if you suspect the system has developed a fault. If you are in any doubt, contact SG Brown for advice and technical assistance before you begin any maintenance work on the system.

5.1 Built-in Test Equipment Page 2

The Meridian Gyrocompass performs a self-test routine during the initialisation sequence and monitors its status continually during normal operation. Any deviation from normal operation appears as an error message, with the cause declared as a message on the four-character dis-play panel. This sub-section explains some very basic tests and adjustments that you may per-form on the system.

5.2 Test Connector Page 4

There is a 60-way test connector that allows you to measure critical voltages and signals.

Perform the tests described in this section of the manual and have the results available when you contact SG Brown for technical assistance.



5.1 BUILT-IN TEST EQUIPMENTIn Subsection 3.4.3 there are a list of two warning codes and five failure codes delivered by the built-in test equipment if it detects a fault in the gyrocompass. In these conditions, the four-character display will show <Message> + FAIL

If the built in test equipment detects a fault, use the following table to investigate the cause. You can measure the voltages and signals on the pins of the 60-way test connector (refer to Table 5–2 for details of the test connector).

Table 5–1: Test measurements

Failure Code Measure Expected value Signal source

dc+failFailure of DC power supply

DC supply42 (+ve) to 4344 (+ve) to 4317 (+ve) to 1850 (+ve) to 5152 (+ve) to 5145 (+ve) to 18

18V DC to 36V DC+24V DC ±0.5V DC–24V DC ±0.5V DC+5V DC ±0.1V DC+15V DC ±0.2V DC–15V DC ±0.2V DC+5V DC (+0.2V/–0.7V DC)

Ship’s mains/PSUDC/DC PSUDC/DC PSUDC/DC PSUControl Board analogueControl Board analogueControl Board analogue

ac+failFailure of AC power supply

19 to 4320 to 4321 to 4358 to 4357 (+ve) to 18

2.5V AC ±0.125V AC @ 19.2kHz14V AC ±1V @ 480Hz (18V AC ±1.5V at start (1-min))14V AC ±1V @ 480Hz (18V AC ±1.5V at start (1-min))12V AC ±0.2V @ 400Hz+5V DC ±0.2V DC

Control Board analogueControl Board analogueControl Board analogueControl Board analogueControl Board analogue

rdc+FailFailure of synchro-to-digital converter

58 to 4353 (+ve) to 5154 (+ve) to 51

12V AC ±0.2V @ 400Hz(5.4V DC ±0.5V DC) × sin heading(5.4V DC ±0.5V DC) × cos heading

Control Board analogueControl Board analogueControl Board analogue

rMT+failLoss of RMT communication

50 way IDC Cable (Part Number B929157)+ 5V DC Power Supply50 way Cable Loom (Part Number B929161)

ROT+failRate of turn exceed limit

>300o/s Check Gyro connection to the analogue PCB

Temp+failTemperature exceeds operat-ing range

<-20oC>+60oC

Check operating environment and ventilation

5 – Maintenance


5.1.1 Azimuth Drift AdjustmentYou may use the following procedure to measure and, if necessary, adjust the azimuth drift:

1. Ensure that the gyrocompass is static and is operating in DG mode with the Speed input set manually to zero and the Latitude set to local latitude. Use the DIP switches to set DG mode – refer to Table 2–5. Refer to sub-sections 3.3.1 and 3.3.2 to set the latitude and speed.

2. Note the initial heading (H1) shown on the RCU display.

3. Wait for one hour and then note the heading (H2) shown on the RCU display.

4. Calculate the azimuth drift rate (H2 – H1) degrees per hour.

5. Use a digital meter set to measure DC volts and monitor the Tilt Bias between pins 30 and 51 of the 60-way test connector (with the positive test lead on pin 30).

6. Adjust the Tilt Bias potentiometer RV7 by 400mV × drift rate (°/hr). You must turn the potentiometer anticlockwise to compensate for azimuth drift towards higher readings. Fig-ure 2–4 shows the location of the Tilt Bias potentiometer.

7. Repeat steps 1 and 2 above to ensure that the calculated drift rate is less than 0.2°/hr.

5.1.2 Azimuth Bias AdjustmentYou may use the following procedure to eliminate small angles of heading error from the Meridian Gyrocompass . Measure and, if necessary, adjust for azimuth drift as described in sub-section 5.1.1 above before you adjust the azimuth bias.

Take care when you adjust azimuth bias – make only small adjustments each time and then allow the gyrocompass to settle for three hours before you make any further adjustments. Note the original position of the azimuth bias control before you start so that you can restore the starting condition if necessary.

1. Use a digital meter set to measure DC volts and monitor the Azimuth Bias between pins 29 and 51 of the 60-way test connector (with the positive test lead on pin 29).

2. Adjust the Azimuth Bias potentiometer RV9 to cause a change in the azimuth bias voltage that will produce the necessary change in compass heading. Figure 2–4 shows the location of the Azimuth Bias potentiometer.

3. Turn the Azimuth Bias potentiometer anticlockwise to cause the heading to change towards a lower reading. A 60mV DC change in Azimuth Bias will produce a 1-degree change in heading



5.2 TEST CONNECTORThere is a sixty-way test connector accessible behind the removable panel on the top of the gyrocompass cover. Release and remove the securing screws and lift off the panel to see the two DIP switches and the test connector. A test box (SG Brown part number 929220) is avail-able to facilitate connection to the 60-way test connector.

Table 5–2: Sixty-way test connector

Pin Name Function

1 S1_SYNCHRO 11.8V RMS 400Hz synchro S1 phase

2 S2_SYNCHRO_RES 11.8V RMS 400Hz synchro S2 phase

3 S3_SYNCHRO_RES 11.8V RMS 400Hz synchro S3 phase

4 26V_SYNCHRO_R1 26V RMS 400Hz synchro R1 reference

5 0V_SYNCHRO_RES 26V RMS 400Hz synchro R1 reference

6 GA_MODE Directional gyro mode control (+5V logic)

7 GC_MODE Gyrocompass mode control (+5V logic)

8 AA_MODE Auto alignment mode control (+5V logic)

9 LAT_NS Latitude north selection control (+5V logic)

10 SERVO_EN Tilt and azimuth servo enable control (+5V logic)

11 WHEEL_BOOST Gyro wheel supply boost control (+5V logic)

12 LOG_OK Speed log OK flag (+5V logic)

13 GPS_OK GPS OK flag (+5V logic)

14 SYS_FAIL System fail flag (+5V logic)

15 GYRO_RDY Gyrocompass ready flag (+5V logic)

16 PREPARE Prepare mode (servo nulling) (+5V logic)

17 VCC 5V DC supply

18 GND 5V DC supply return

19 PICK_OFF_SUPPLY_1 Gyro pick off supply 2.5V RMS 19.2kHz sine wave

20 WHEEL_SUPPLY_1 Gyro wheel supply 0 phase 10V (18V) RMS 480Hz square wave

21 WHEEL_SUPPLY_2 Gyro wheel supply 90 phase 10V (18V) RMS 480Hz square wave

22 PWMO Compass card illumination PWM control 5V 85Hz square wave

23 ACC Gravity control signal ±150mV DC/min T=60s

24 10V 10V DC positive voltage reference

25 _10V 10V DC negative voltage reference

26 LAT_TORQ Latitude torquing input signal (–10 sin[latitude])V DC

27 SPEED_N_TORQ Speed N torque i/p signal (7.3e–3 × speed(kts) × cos[heading])

28 SPEED_E_TORQ Speed E torque i/p signal (–8.5e–3 × speed(kts) × sin[heading] × tan[latitude]V DC

5 – Maintenance


29 AZ_BIAS Bias adj. to azimuth torquer ±2.2V DC (60mV/deg heading)

30 TILT_BIAS Bias adj. to tilt torquer ±2.2V DC (400mV/deg/hour heading)

31 TILT_TEMP Bias adj. to tilt torquer proportional to temperature (400mV/deg/hr heading)

32 AZ_TEMP Bias adj. to azimuth torquer proportional to temperature (60mV/deg/hr heading)

33 T Temperature ref (non-inverted) from gimbal thermistor (DC V proportional to temp)

34 T_ Temperature ref (inverted) from gimbal thermistor (DC V proportional to temp)

35 TILT_TORQUER_LO Tilt torquer signal 0.013V DC/mA (torquer scale factor 10°/hr/mA)

36 AZ_TORQUER_LO Azimuth torquer signal 0.006V DC/mA (torquer scale factor 10°/hr/mA)

37 TILT_PICK_OFF_DC Demodulated gyroscope tilt pick-off signal

38 AZ_PICK_OFF_DC Demodulated gyroscope azimuth pick-off signal

39 18V10V Gyro wheel positive supply

40 -18V10V Gyro wheel negative supply

41 UP_DOWN Accelerometer - Slave comparator

42 24V 24V DC positive supply

43 0V Supply return for ±24V DC

44 –24V 24V DC negative supply

45 PSU_LO PSU (+5V DC and ±15V DC) under voltage flag (+5V DC logic)

46 NOT USED

47 ACC_COS_LAT Latitude weighted gravity control signal (150/cos latitude)mV DC/min

48 SLAVE Slave accelerometer gravity control signal (10mV/bit)

49 ROT Analogue rate of turn output (0.5V DC/deg/s (10V DC max) CW +ve; ACW –ve

50 15V 15V DC positive supply

51 0Va Supply return for ±15V DC

52 –15V 15V DC negative supply

53 SIN_DC Analogue voltage proportional to sin(heading) (±0.1V DC/deg heading)

54 COS_DC Analogue voltage proportional to cos(heading) (±0.1V DC/deg heading)

55 RS232_RX_TEST RS232 receive port reserved for product testing

56 RS232_TX_TEST RS232 transmit port diagnostic output sentence

57 AC_OK AC supply (19kHz, 480Hz and 400Hz) OK flag (+5V DC logic)

58 400_REF_HI Reference supply 12V RMS 400Hz

59 AZ_MOTOR_HI Drive to azimuth follow-up DC servo motor

60 TILT_MOTOR_HI Drive to tilt follow-up DC servo motor

Table 5–2: Sixty-way test connector (Continued)

Pin Name Function



5.3 DIAGNOSTIC OUTPUT SENTENCEAn ASCII character diagnostic sentence, delivered via RS232 line standard at 4800 baud, is available at test connector PL6/56-18(GND).

Note that this sentence information is only valid for gyrocompasses fitted with soft-ware of the following version or newer: BPR 113 (main) and BPR 114 (RCU).

This sentence may usefully be monitored when communicating with SG Brown for technical assist-ance. The sentence string may be read using "Microsoft Terminal" or similar ASCII reader.

Sentence Structure

Gyro Control 1 = slave accelerometer (new hardware)S = special applications only (new hardware)R = real accelerometer (original hardware)A = special applications only (original hardware)

Mode L = levelA = alignmentC = compassD = DG

Status F = failR = readyS = settle

Latitude (degrees) xx

Hemisphere N or S

Speed (knots) xx

Average Accelerometer (bits) Paxxx

ADC 1 (bits) rxxxADC 2 (bits) hxxxADC 3 (bits) txxxADC 4 (bits) axxxADC 5 (bits) Txxx

DAC 1a (bits) xxxDAC 1b (bits) xxxDAC 2a (bits) xxxDAC 2b (bits) xxxDAC 3a (bits) xxxDAC 3b (bits) xxx

Heading (degrees) $HEHDT,xxx.xx,T

Sentence Example

R CR 51N 06 Pa128r128h128 t128a128 T096 160 198 000 000 128 128 $HEHDT,000.00,T

During start-up, the Mode and Status characters will change in the following sequence:

1. LS for about 4 minutes2. AS for 25 - 60 minutes (dependent upon initial heading misalignment)3. CR in READY mode and functioning

Ensure that the Latitude and Speed values in the sentence correspond with the automatic or manually set values applied to the gyrocompass. Ensure that the Heading value in the sentence is correct.

SG Brown may use the remaining (bits) characters when diagnosing fault conditions.

5 – Maintenance


Figure 5–1: System Block Diagram

GIM

BA

LA

SS

Y

DIS

PLA

YB

OA

RD

CO

NT

RO

LB

OA

RD

RE

MO

TE

DIS

TR

IBU

TIO

N

BO

AR

D

CO

NT

RO

LB

OA

RD

DIG

ITA

LA

NA

LO

GU

E

CO

NT

RO

LB

OA

RD

TE

ST

CO

NN

EC

TO

R

DC

/DC

PS

U

FIL

TE

RS

#1

&#2

24V

d.c

.

Tilt

Moto

r

Azim

uth

Moto

r

Tilt

Pic

koff

Azim

uth

Pic

koff

Tilt

Torq

uer

Azim

uth

Torq

uer

(vert

icalsensor)

(tem

psensor)

Resolv

er

Illu

min

atio

n24-0

-24V

d.c

.

5V

d.c

.

An

alo

gu

eC

on

tro

lS

ign

als

Azim

uth

To

rqu

er

Co

ntr

olS

ign

al

Tilt

Torq

uer

Contr

olS

ignal

Tem

pS

ensor

Sig

nal

Acce

lero

me

ter

Sig

na

l

Re

so

lve

rH

ea

din

gS

ign

al(s

in/c

os)

Tilt

Pic

koff

Sig

nal(a

.c.)

Azim

uth

Pic

koff

Sig

nal(a

.c.)

Tilt

Moto

rD

rive

Sig

nal

Azim

uth

Mo

tor

Drive

Sig

na

l

Illu

min

atio

nC

on

tro

l

Acce

lero

me

ter

Sig

na

l(h

igh

ga

in)

Tem

pS

ensor

Sig

nal

Re

so

lve

rH

ea

din

gS

ign

al(d

.c.)

Tilt

P.O

.S

ignal(d

.c.)

Azim

uth

P.O

.S

ignal(d

.c.)

Analo

gue

Headin

gS

ignals

SerialO

utp

ut

Sig

nals

Serial&

Dig

italIn

putS

ignals

Rem

ote

ON

/OF

FC

ontr

ol

Gyro

Sp

inM

oto

rS

up

ply

Gyro

Sp

inM

oto

r

Rem

ote

ON

/OF

F

Com

munic

ations

Display Driver Signals

Input

Sig

nals

Outp

ut

Sig

nals

5V

d.c

.

Com

munic

ations

929083

929074

929066

929033

929078

929049

929045

Pow

er

Pow

er

Switch I/Ps

Acce

lero

me

ter

Therm

isto

r



Figure 5–2: Gimbal Assembly Functional DiagramZ

H

X

Y

N-S

H

Resolv

er

40

0H

zS

inH

Co

sH

Azim

uth

Torq

uer

Co

ntr

olS

ign

al

Sig

na

l(A

cc)

Acce

lero

me

ter

Co

ntr

olS

ign

al

Tilt

Torq

uer

Moto

r

Azim

uth

Dri

ve

Sig

na

l

Tilt

Moto

r

Dri

ve

Sig

na

l

Te

mp

era

ture

Se

nso

rS

ign

al

Azim

uth

Pic

koff

Sig

na

l

Tilt

Pic

ko

ff

Sig

na

l

1

2

8

5

9

67

3

4

10

1.D

am

pe

r

2.G

yro

sp

inm

oto

r

3.

Tilt

torq

uer

4.

Azim

uth

torq

ue

r

5.

Acce

lero

me

ter

6.

Azim

uth

pic

ko

ff

7.

Tilt

pic

koff

8.T

he

rmis

tor

9.

Tilt

moto

r

10

.A

zim

uth

mo

tor

5 – Maintenance


Figure 5–3: Analogue Control Board Block Diagram

M

TILTTORQUERCOIL

PICKOFFCOILS

TILT

TILTMOTOR

Run

Align

TILT TEMPT+ T-

TILT BIAS+V Ref -V Ref

+/-

Hemisphere

+/-

Servo Enable

SCALING&

SHAPING

AMPLIFIER

FILTER&

AMPLIFIER

SCALING

SHAPING&

FILTER& PICKOFF

AZIMUTH

AZIMUTHMOTOR

COILS

M

COMPARATOR

COILTORQUERAZIMUTH

Align

DG

AZIMUTH TEMPT+ T-

AZIMUTH BIAS+V Ref -V Ref

Run

X10

AlignRun

Hemisphere (+/-)Servo Enable

DG

19.2 Khz Ref

Acc/Cosλ

ACCELEROMETER

THERMISTORAMPLIFIER

THERMISTORT+

T-

To Tilt & Azimuthtemperature pots

PRECISIONREFERENCE

Temperature

+V Ref

-V Ref

DIGITAL CONTROL BOARD ANALOGUE CONTROL BOARD GIMBAL ASSEMBLY

Hemisphere

36V26V

0V

R4R1

R2

ReferencePhase26V Synchro36V Resolver

400HzRESOLVERROTOR

STATORRESOLVER

S1

S311.8V Synchro8V Resolver

Heading Outputs

S2

S4

+/-

+/-

400Hz Ref

400Hz Ref

Wheel Boost

2.5V 19.2KhzPickoff Supply

Gyro Spin MotorSupply

MONO -STABLE

10V/18V 480Hz

V.Sin H.Tan λ R

Acc (High Gain)

Acc (Low Gain) τ = 60s

V.Cos HR

Rate of Turn RoT +/- 10V

10V/18V

10V/18V

∅1

2∅

PLD3.6Mhz

+24V

-24V

400Hz

19.2Khz

BANDPASSFILTER

400Hz Ref

400Hz Ref

BANDPASSFILTER

19.2Khz Ref

Sin H

Cos H

8V.Sin H

8V.Cos H

V = speed (knots x 6080 ft/hr)

λ = local latitude (deg) H = gyro heading (deg) τ = time constant Acc = accelerometer signal

Servo Enable

ω Sin λ

AC OK

+/-

+/-Azimuth Pickoff (d.c.)

Tilt Pickoff (d.c.)

REG+

REG-

480Hz ∅ 0

180∅ 480Hz 90∅ 480Hz

270∅ 480Hz

North seaking

Latitude correction

Easterly speed correction

Northerly speed correction

Damping

ω = earth rotation (15°/hr)

R = earth radius (20.9 x 106 ft)

(temp sensor)

(vertical sensor)


Chapter 5 Page 10 of 12© SG Brown Issue 3.7 DPN 060070

Figure 5–4: Digital Control Board/Remote Control Board Block Diagram

AlignRun

Hemisphere (+/-)Servo EnableDG

Acc/Cosλ

Temperature

ANALOGUE

Wheel Boost

V.Sin H.Tan

λ

R

Acc (High Gain)Acc (Low Gain)

V.Cos HR

Rate of Turn

400Hz Ref

Sin HCos H

V = speed (knots x 6080 ft/hr)

λ = local latitude (deg) H = gyro heading (deg) τ = time constant Acc = accelerometer signal

ω Sin λ

AC OK

Azimuth Pickoff (d.c.)Tilt Pickoff (d.c.)

ω = earth rotation (15°/hr)

R = earth radius (20.9 x 106 ft)

ANALOGUEMUX &10 BITADC

Tem

pera

ture

Azim

uth

Pick

off (

d.c.

)Ti

lt Pi

ckof

f (d.

c.)

Acc

(Low

Gai

n)Ac

c (H

igh

Gai

n)

RX TX

MAX487DRIVERRS422

P4

OPTO-COUPLER

PWMO

P2

P0

uCONTROLLER80C552

X1P4

XTAL

27C512EPROM

ADDR. BUS

DUARTSCN2681

CS

RS232/RS422 I/F

RS422DRIVERS

RS232DRIVERS

ADDR.DECODER CS

RAMHM62256

28C16AEPROM

AC OK

RESOLVERTO DIGITAL

CONVERTER

CS

LS373LATCH

AD7528DAC

CSAcc (Low Gain)

AD7528DAC

Cos H10V Ref

Sin H

AD7528DAC

10V Ref

CS

CS

CS

SCN2681DUART

CONTROL BOARDDISTRIBUTION BOARD

LS373LATCH

CS

SUPERVISORYPSU

MAX8213

DC PSU

System FailSystem Ready

Stepper O/P3 x RS232 IEC 611629 x RS422 IEC 61162RS422 Heading/ROT

GPS SerialNMEA 0183 All Data

Speed Log Serial

Speed Log Pulses

Remote Control

Course Recorder

Spare

DG Mode

RS422 I/FRS232/

CS

DAT

A BU

S

DIGITAL CONTROL BOARD

400Hz RefCos H

Sin H

REMOTE CONTROL BOARD

ADDR. BUS

Remote Control

P4

uCONTROLLER

RX

MAX487DRIVERRS422

MAX813LWATCHDOG

80C32X1 XTAL

PWMO

P2

P0

TX

CS

EPROM28C16A

HM62256RAM

ADDR.DECODER

EPROM27C512

DAT

A BU

S

WD1 PFO

RESET RESETCS

CS

CS

DISPLAYDRIVER

CS

LATCHLS373

CS

LS373LATCH

DISPLAY

READYSYSTEM

SOUNDERFAIL

KEYBOARD

5 – Maintenance


Table 5–3: Spares list for Meridian Gyrocompass 929060

SG Brown P/N Description

929033 Gimbal assembly

929066 Control Board Analogue

929083 Control Board Digital

929049 Control Board Remote

929045 Display Board

929074 DC/DC Power Supply

856000 Filter #1

929160 Filter #2

346808 Fuse link 3.15A 250V

929164 Gland Plate assembly

929190 RCU Mounting Kit

929194 Transit case

929220 Test box


Chapter 5 Page 12 of 12© SG Brown Issue 3.7 DPN 060070

A – Operating Theory

DPN 060070 Issue 3.7 © SG Brown Appendix A Page 1 of 8

A OPERATING THEORYA gyrocompass is a navigational instrument that provides a true north indication without refer-ence to the earth’s magnetic field. For its operation, the gyrocompass depends upon the fol-lowing:

The inertial properties of a freely spinning gyroscope.

The rotation of the earth about its own axis.

Gravity.

Figure A–1 shows a free-spinning gyroscope mounted in a balanced gimbal suspension. The suspension allows unrestricted movement about the vertical and horizontal axes so that the gyro rotor can adopt any orientation.

Figure A–1: Free-spinning gyroscope

With the gyro rotor stationary, it is easy to turn the gimbal suspension about either axis and allow it to remain there in a balanced condition.

However, when it is spinning, the gyro rotor exhibits a property called gyroscopic inertia. This property causes the spin axis of the rotor to remain pointing in the same arbitrary direction in space and to resist any influence that tries to redirect that axis.

For simplicity, this explanation assumes the gyro rotor continues to spin perpetually at a con-stant speed. In a practical gyrocompass, the gyro rotor is the specially designed spindle of a motor that rotates at a constant speed.

To an observer on the surface of the earth, the free spinning gyroscope would appear to ‘tum-ble’ in its gimbal suspension once in every 24-hour period. This apparent deviation occurs because, although the spin axis actually remains fixed in space, the earth rotates relative to it.


Appendix A Page 2 of 8 © SG Brown Issue 3.7 DPN 060070

The apparent movement seen by the observer would depend on the location of the gyroscope and the initial direction of the spin axis.

To an observer at the equator:

With an initial spin axis alignment level and parallel to a meridian (so that it points in a true north-south direction), there would be no observable effect on the gyroscope during the 24-hour period.

With an initial spin axis alignment level and perpendicular to a meridian (so that it points in the east-west direction), the spin axis would appear to tumble about its horizontal axis with the eastern end of the spin axis rising. After 24 hours, the gyroscope would complete a single revolution in its gimbal suspension so that the spin axis would again point in the original direction relative to the observer.

With an initial spin axis alignment somewhere between these two extremes, the gyroscope would appear to tumble about its horizontal and its vertical axes to complete one single revolution in 24 hours.

To an observer at one of the geographic poles:

With an initial spin axis alignment vertical (so that it aligns with the axis of earth rotation), there would be no observable effect on the gyroscope during the 24-hour period.

With the initial spin axis level, the gyroscope would appear to turn clockwise (at the north pole) or anticlockwise (at the south pole) about its vertical axis once in 24 hours.

To an observer at some intermediate latitude with the gyroscope oriented in some arbi-trary initial direction:

The gyroscope would tumble about the north-south direction at and about the

east-west direction at , where Ω is the earth rotation rate (15° per hour) and λ is the latitude of the gyroscope.

A.1 NORTH-SEEKING GYROSCOPEGiven a constant spin rate and frictionless gimbals, the gyroscope described above will always maintain its initial alignment relative to free space. To an observer on the surface of the earth, the revolutions that such a gyroscope performs every 24 hours would make it difficult to use as an instrument of navigation.

The ideal situation is for the gyroscope to align perfectly with the spin axis of the earth so that it maintains a north-south orientation with no apparent tumbling during each 24-hour period.

To make the gyroscope north seeking, the gyrocompass uses gravity control and an effect called precession.

Ω λcos–

Ω λsin



Consider the example shown below where the gyroscope rotates about its spin axis in the direction shown.

When an externally applied torque acts on the gyroscope suspension in the direction shown, a point on the circumference of the rotor at 'O' will attempt to move in two directions simultane-ously:

It will accelerate in the direction OA under the influence of the applied torque.

It will continue to move in the direction OB as the rotor spins.

The net result of these two movements actually starts to move the point on the circumference of the rotor in the direction OC, which is the resultant of the two perpendicular influences.

Since every point on the circumference of the rotor experiences the same effect as it passes through point O, it follows that the rotor will rotate about an axis that lies at right angles to the axis of applied torque. This is the axis of precession. In this example, precession will act in the direction shown.

Eventually, the spin axis of the gyroscope will turn sufficiently so that its spin axis coincides with the axis of applied torque, at which point there will no further tendency for the gyroscope to rotate about the precession axis.

Summary:If a free spinning gyroscope comes under the influence of a torque whose axis is perpendicu-lar to the spin of the gyro rotor, a precession results that tends to align the spin axis with the axis of applied torque. The direction of this precession is such that, should alignment occur, the gyroscope spin direction will be the same as the direction of applied torque.

Precession



Consider the example shown in Figure A–2(a), which shows a free spinning gyroscope aligned so that its spin axis is level with the horizon. In this example, the spin axis of the gyroscope aligns with the local meridian so that its north end points north. In the balanced condition shown, the weight suspended from the gyroscope bearings has no effect on operation and the gyroscope will maintain its alignment with the meridian.

Figure A–2: Gravity control of a gyroscope

It is more common for the initial alignment of the gyroscope to be at some angle away from true north. Two conditions are therefore possible:

1. Gyroscope initially level and aligned to the west of north.

With the spin axis of the gyroscope initially level but with the north end pointing to the west of true north, the arrangement would briefly be balanced as shown in Figure A–2(a).

However, over time the north end of the spin axis would begin to tilt downwards. This is because the earth rotates while the gyroscope maintains a fixed orientation in space. In this off-balanced condition, shown in Figure A–2(b), the weight would try to return to its central location and, in doing so, would apply an anticlockwise torque to the gyro suspension.

With the gyroscope spinning in the direction shown, precession arising from the anticlockwise torque would move the north end of the rotor eastwards. Therefore, because this condition arises from a westerly misalignment between the gyroscope and the meridian, the effect of the bottom weight is to drive the gyro rotor towards closer alignment with the meridian.

2. Gyroscope initially level and aligned to the east of north.

With the spin axis of the gyroscope initially level but with the north end pointing to the east of true north, the arrangement would briefly be balanced as shown in Figure A–2(a).

However, over time the north end of the spin axis would begin to tilt upwards with rotation of the earth. In this off-balanced condition, shown in A–2(c), the weight would apply a clockwise torque to the gyro suspension.



Precession arising from the clockwise torque would move the north end of the rotor further west and therefore into closer alignment with the meridian.

In practice, modern gyrocompasses, such as the Meridian Gyrocompass, exercise gravity con-trol by an indirect method. Tilt is detected by an electronic pendulum or accelerometer and the resultant electrical signals are used to produce torques that have the same effect as a suspended weight.

A.2 GYROCOMPASS CORRECTIONSA.2.1 Latitude CorrectionSub-section A.1 explains how the addition of gravity control to the gyroscope gives it the north-seeking characteristic necessary for use in a gyrocompass.

When operating at the equator, such a simple gravity control would be sufficient to maintain alignment with the meridian with no further need for corrections.

However, as the operating latitude increases towards either of the poles, there is a greater ten-dency for the gyroscope to experience azimuth drift with time.

The rate of change of azimuth due to the earth’s rotation is constant for a given latitude. There-fore, the gyrocompass must apply a controlling correction torque, perpendicular to the spin axis, to cancel the drift caused by the earth’s rotation. To generate this correction torque the gyrocompass needs to know the operating latitude.

A.2.2 Gyro DampingWhenever the gyroscope does not align perfectly with the meridian, precession caused by gravity control and the horizontal component of the earth’s rotation will cause the north end of the gyro rotor to trace out an anticlockwise elliptical path.

The application of latitude correction causes this elliptical path to be symmetrical about a point projected from the north end of the gyro rotor when horizontal and aligned with the meridian. For a given gyroscope, the ratio between the major and minor axes of this error ellipse is constant. The size of the ellipse depends on the initial displacement of the gyro axis away from the meridian and the horizontal plane.

By reducing the amplitude of ellipsoidal excursion in one plane, it follows that the amplitude of excursion in the other plane reduces proportionately to settle the gyro horizontally and in the meridian.

In the gravity controlled gyroscope, a tilt of the rotor spin axis produced a torque about the horizontal axis to drive the spin axis towards alignment with the meridian. However, to pro-duce a workable gyrocompass, there must be some form of damping.

One practical method for doing this is to include electrical feedback so that a tilt in the rotor spin axis also produces a torque about the vertical axis. The sense of this torque would be to cause a precession that would drive the spin axis towards the horizontal.

This would cause the vertical axis of the error ellipse to reduce progressively towards zero, reducing the horizontal axis simultaneously. This process results in the north end of the gyro



rotor tracing a decreasing spiral path, eventually settling with the gyroscope horizontal and aligned with the meridian.

A.2.3 Speed ErrorFigure A–3 shows that the north end of a meridian-aligned free spinning gyro will appear to rise as it moves northwards from the equator. This upward tilt is independent of the earth’s rotation. If left uncorrected, this effect would interfere with the north-seeking properties of the gyrocompass because the compass would be unable to determine whether the tilt came from a misalignment or from the northward motion.

If left uncorrected therefore, the northward travel would cause an upward tilt that would cause the gyroscope to precess towards the west and then to go into a settling spiral. Eventually, given a constant speed of northward movement, the gyro would settle slightly to the west of true north.

Figure A–3: Gyrocompass speed error

Speed-related error is directly proportional to the north-south component of speed, and inversely proportional to the cosine latitude. This means that any error when the compass is on the equator would become twice as large at latitude 60°, three times as large at latitude 70°, and nearly six times as large at latitude 80°. At latitudes above 80° the gyrocompass becomes virtually unusable as a north seeking instrument.

The north-south component of speed is the product of actual speed and the cosine of the course made good. Speed related errors are therefore greatest when travelling in a northerly or a southerly direction.

To correct for these effects, the compass must know the direction and speed of travel. While it uses its own self-generated heading information to determine the direction of travel, speed information must come from an external source such as a speed log or a GPS receiver, or be applied manually.



A.3 SUMMARY A gyrocompass will indicate the true north direction after an appropriate settling period.

To maintain correct true north alignment, the gyrocompass must receive additional infor-mation concerning its operating latitude.

Also to maintain accuracy the gyrocompass needs to know its direction of travel, which it generates itself, and the speed of travel. Speed information must arrive from an external source, or be applied manually.

A gyrocompass becomes progressively less effective as a north seeking instrument at higher latitudes. Note that the Meridian Gyrocompass can be used successfully in high lat-itudes with the DG mode selected. In this mode, the gyrocompass acts as a directional gyro. A directional gyro does not north seek, but can maintain a reference heading for a short period. Follow the instructions in sub-section 3.3.3 to set the DG operating mode.



B – Certification

DPN 060070 Issue 3.7 © SG Brown Appendix B Page 1 of 4

B CERTIFICATIONOn the following pages are the Certificates of Type Approval documentation obtained for the Meridian Gyrocompass.


Appendix B Page 2 of 4 © SG Brown Issue 3.7 DPN 060070

Figure B–1: Certificate of Type Approval

B – Certification

DPN 060070 Issue 3.7 © SG Brown Appendix B Page 3 of 4

Figure B–2: Certificate of Type Approval - Schedule 1


Appendix B Page 4 of 4 © SG Brown Issue 3.7 DPN 060070

Figure B–3: Conditions of Issue

Index

DPN 060070 © SG Brown Issue 3.7 Index Page 1 of 2

AAdjustments

Azimuth bias 5–3Azimuth drift 5–3Test connector 5–4

Alignment 2–4, 2–12Auxiliary inputs 1–4Azimuth bias adjustment 5–3Azimuth drift A–5Azimuth drift adjustment 5–3

CCable types 2–4Connections 2–7Continuous operation 3–8Control unit. See RCUControls 3–2Correction

Speed A–6Corrections 3–4

Latitude 3–4, A–5

DDIP switches 2–10Distribution Board connections 2–7

EError modes 3–5

GPS 3–5Gyro failure 3–6, 3–7Speed log 3–6

GGPS 1–4GPS failure 3–5Gravity control A–2Gyro damping A–5Gyro failure 3–6, 3–7Gyrocompass configuration 2–10Gyroscopic inertia A–1

IInstallation

Alignment 2–4, 2–12Cable types 2–4Choosing a location 2–3Connections to Distribution Board 2–7

LLatitude correction 1–4, A–5Latitude correction. See CorrectionsLoss of GPS 3–5Loss of speed signal 3–6

MMaintenance

Error modes 3–5Test connector 5–4

NNorth-seeking gyroscope A–2

OOperation

Continuous operation 3–8Lay-up 3–8Power failure 3–8Power-off 3–8Power-on 3–3

Operation during lay-up 3–8

PPower failure 3–8Power-off 3–8Power-on 3–3Precession A–2

RRCU

Controls and indicators 3–2External location 2–9

Remote Control Unit. See RCU

SSpeed correction 1–4, A–6Speed correction. See CorrectionsSpeed log failure 3–6

TTest connector 5–4Toppling 2–3


Index Page 2 of 2 Issue 3.7 © SG Brown DPN 060070

Documents

060070 Meridian Gyro Compass Issue 3.7 Mar 2004