Pakscan IIEhigh integritymaster station

Publication S110E issue 09/04

Established Leadersin Actuation Technology

R O T O R K P A K S C A N I I E2

PakscanTwo wire control system

Pakscan is the most successful system for theremote control of valve actuators using atwo wire bus network in use today. It hasbeen developed by Rotork to exactly matchthe market requirement for both long andshort distance remote control of actuatorsand valves. The Pakscan system uses proventechnology to meet the increasing demandsof modern control systems and ensures highavailability and reliability of the controlsystem package

Pakscan sets the standard for two wire control and thePakscan IIE master station provides the high integrity linkfrom the DCS to the valves in the field.

The system combines three key elements – field units, thetwo wire loop cable and the master station itself. Togetherthey provide unparalleled control, high availability andefficiency combined with extremely low maintenance costs.

By adding a completely independent standby Pakscan IIEmaster unit, the availability of the system in the event of acomponent failure is guaranteed. Multiple host ports allowfor connection to two host systems at the same time, ordual redundant comms links where necessary. The fieldcabling is fault tolerant allowing the system to ride throughany type of cable fault without losing actuator control.Further, if subsequent faults occur before the initial failureis repaired, the system will continue to operate as much ofthe plant as possible.

The field network can incorporate other devices into thePakscan loop by using the General Purpose field units inone of their available enclosures.

I I E P U T S Y O U I N C O N T R O L3

Installed Cost Savings• Direct reduction in cable costs by

using a single twisted pair instead of expensive multicore cable.

• Direct reduction in engineering costs due to network’s simple design.

• Lower commissioning costs due to faster and easier installation.

• Increased plant productivity by reducing down time losses.

Low Cost of Ownership• Increased information flow allows

for optimised and correctly planned maintenance of the actuators and valves

• System fault tolerance ensures continuous operation even when a fault exists on the system

• In the unlikely event of a failure Pakscan is simple and quick to repair ensuring the shortest possible downtime

• Large number of inbuilt diagnostic features including communication performance data and fault location indication

High Performance• Priority given to commands to

the plant.

• Full monitoring and control of every field unit and actuator connected.

• Fully compatible with allRotork actuators.

• Master station monitors the full network at all times, relieving the host system.

• Field unit parameterisation from the master station.

Simple Integration• Industry standard Modbus

protocol to PLC, DCS or In-Vision.

• Dual host communications capability.

• Multiple data base organisation for maximum efficiency.

• Proven communications to all major DCS and PLC suppliers.

• Master station suppliedpre-configured.

Large Plant Capacity• Each network has the capacity for

up to 240 actuators distributed over a single 20 km 2 wire loop.

• No restrictions on inter-node distances.

• Capable of controlling various field devices including actuators, pumps, heaters and mixers.

High Reliability• Field units integral with and double

sealed inside Rotork actuators.

• High levels of surge protection for poor field environments.

• Non-intrusive setting of all parameters.

• Full isolation between the network cable and the field unit or master station.

• Secure communication protocol.

• Complete cable fault protection with redundant field communication path.

• Optional fully redundant master station.

• No repeaters necessary.

• Oil and Gas Storage

• Tank Farms

• Refinery plant

• Water Filtration plant

• Potable Water Treatment and Storage

• Waste Water Treatment plant

• Flood control

• Off shore platforms

• Gas production wells

• Power station boilers and turbines

• Metering skids

• Tunnels and Pipelines

4

T H E S Y S T E M A N D A P P L I C A T I O N S

Continuous Monitoring Pakscan continuously monitors the plant status and makes the status availableto the DCS.

Two wire loop Up to 240 field units distributed over a 20 km twisted pair loop.

Compatibility Fully compatible with all current Rotork electric actuators and In-VisionHMI products.

High Integrity Hot standby master station. Second unit takes control in the event of a faulton the main unit.

High Reliability Dual power supplies and fully redundant hardware for maximum reliability.

Dual Host Comms RS485 and RS232 host communications options using Modbus protocol.

Loop Fault Tolerant Short, open or ground faults on the loop do not prevent continuing operation.

Comprehensive Indication All faults are announced to the host system. Display panel shows conditions.

The SystemPakscan includes the experience gained by Rotork in network control systems and their application. The master station takescare of all the network communications. The systems engineer simply has to specify which slave address to use for eachactuator and determine the cable route and length.

ApplicationsSince its inception Pakscan has found acceptance in all industry sectors and many diverse applications. Wherever Rotorkactuators are to be found there will be a Pakscan system to operate them.

5

Hot Standby Master Station

Cable FaultProtection

PC runningInVision s/ware

PLC / DCS

Field UnitFailureProtection

Control and Data Available froma Pakscan IIE master station

Reset system (Reconfigure loop)

Change station to standby mode

Alarm accept

Loop condition register

Loop status

Main station status

Standby station status

Map of field unit locations

Cable fault type (open or short circuit)

Loop data rate

Configuration progress

Actuator alarm present

Field Control Unit alarm present

Data and Control forField Control Unit Actuators

Open/Stop/Close/ESD digital control

Set Position 0-100% analogue control

Actuator current torque value 0-120% *

Valve position digital status (open/closed)

Valve position analogue status (0-100% position feedback)

Actuator Alarm status

Local/Remote selector position

Local Stop selected

Valve opening and closing digital status

Actuator torque tripped at end of travel

Actuator torque tripped in mid stroke

Battery condition low

Motor thermostat status

Valve manual movement

Contactor failure to energise

Excessive valve travel time *

Motor still energised at end of travel

Communication failure

Field Control Unit failure

Torque profile in opening direction *

Torque profile in closing direction *

* = Rotork IQ Range actuators only

P A K S C A N I I E M A S T E R S T A T I O N6

Each Pakscan IIE masterstation is self contained inits 19” rack housing. Itcomes complete withkeypad and display screento allow operators andengineers to see exactlywhat is happening withthe system and the valveactuators at any time.

Simple InstallationThe master station requires a powerconnection and the field cables tobe attached and it is ready to go.Installation could not be simpler. Inthe case of a hot standby unit thereis only a second power supplyrequired. Host communications areadded by simple plug in connectorsand all connections are on the backof the rack.

SimpleConfigurationEach system is supplied pre-configured, already having a fulldata base and Modbus protocolconfiguration installed when it isdelivered. To complete the plantspecific settings the number of fieldunits, loop speed and hostcommunication parameters arequickly entered using the integralkeypad.

Simple DiagnosticsIn-built diagnostics show theperformance of the hostcommunications, the individual fieldunits and network cable. The screenand LED’s show any alarms presenton the system. The loop map showsthe position of every field unitrelative to the master station.

Field UnitConfigurationThe master station also includes theability to alter parameters in thefield units from the master stationitself. All the settings associated

with the Pakscan system such asanalogue value reporting interval,motion inhibit time and so on canbe amended from the field unitscreens of the Pakscan IIE.

High Integrity CommsCable failure protection isautomatically catered for byconnecting the field units in a ring.Any field unit can be accessed eitherway round and when there is a faultin the cabling the unique loopbackfeature ensures that commscontinues to be available.

Additionally all messages passedover the network are totally underthe control of the master station asit contains the only current source.Each field unit is a slave and onlysends information following arequest and all messages areprotected by framing and CRCchecks.

Non-catastrophic failures due tonoise on the system are handled ona repeat as necessary basis. A totalof 3 failures to respond has to occurbefore the master station indicatescomms failure to a field unit.

Where high reliability for the hostcommunication is needed, the twoModbus communication ports maybe set to operate in a high integritymode. Simply connecting thecomms ports on the main andstandby master stations on a singleRS485 highway allows the masterstation to seamlessly transfer controlfrom one unit to the other withoutany loss of host communications.

The addition of PS410 converters tothe master station RS232 ports alsoallows a dual RS485 highway to beset up to give high integrity hostcomms link.

Highway 1 - RS485 2 wire

Port 4 Port 4Port 1 Port 1

Port 4 Port 4Port 1 Port 1

Highway 2 - RS485 2 wire

AB

DCS Gateway

Workstation

Pakscan IIE Master Stations fitted with PS410 RS232/RS485 converters

AB

Workstation

Diagram 3: High integrity communications from the master station to the DCS.

H O T S T A N D B Y M A S T E R S T A T I O N7

AutomaticChange OverThe high integrity, hot standbyversion of the Pakscan IIE includestwo identical modules in one rack.Either may be the main unit andautomatic and transparent transferbetween the main and standby unitoccurs if there is a componentfailure in the main unit. In additionchange-over can be initiated by thehost system or from the keypad ofthe main unit. Should a fault occurwithin the standby unit this too isreported over the communicationlink to the host system.

Operator PasswordProtectionSome systems require protectionagainst operation by unauthorisedpersonnel. The Pakscan IIE masterstation includes a PersonalIdentification Number (PIN)protection method where, ifrequired, the movement of valves orchanges to the system settings canonly be carried out from the keypadif the operator has first entered thecorrect PIN. Several levels ofprotection are available includingone where control is permitted onlyif the host comms link is notoperating.

Fault AnnunciationThe LED’s and screen are used toindicate any alarm condition thatmay arise from a field unit or withinthe master station. In addition thecommunication with the hostsystem includes alarm indicationdata. If an actuator is switched offthe master station will notice itsabsence and report the devicefailure to the host system. The alarmindication differentiates betweensystem, master station, cable,actuator and field unit faults.

Multiple Host Communication PortsEach Pakscan IIE master station module includes two communication ports, one RS232 and one RS485. In addition there isspace for a Pakscan PS412 converter to change either the RS232 port to RS485 or the RS485 port to RS232. The twocommunication ports can each communicate with a different host system or be used as a redundant communication highway.In a hot standby pair the most common configuration is to use two RS485 ports from the primary and the standby units in amultidrop configuration.

Display

Keypad

Loop Processor

Opto-isolation

Power pack

RS232

RS485 Comms

Comms

Master Station A

uP

Main Processor

uP

EEPR

OM Port A

Port B

EEPROM

Selector and

Keyswitch Display

Keypad

Loop Processor

Opto-isolation

Power pack

RS232

RS485Comms

Comms

Master Station B

uP

Main Processor

uPEE

PRO

MPort A

Port B

EEPROMInter-unit comms

Port APort B

uP

EEPROM

Opto-isolation

Detector

Field Control Unit

Actuator Circuit Board

Diagram 4: Hot standby master station showing internal connections and isolation between system components.

E T H E R N E T C O N N E C T I V I T Y8

The optional Pakscan Ethernetbridge enables the IIE masterstation to link with the hostsystem using a Local AreaNetwork and Ethernetcommunications.

The bridge forms an integral part ofthe IIE master station fitting withinthe 19 inch rack assembly. It replacesone of the master station serialcomms ports with an Ethernet portcommunicating using Modbus TCP.

The bridge makes the plantinformation available to the hostsystem with minimal delay by holdingcurrent system data in its memory.

LAN ConnectionThe Pakscan Ethernet bridgeoperates an asynchronouscommunication link to the masterstation, polling it continuously forthe latest data. The Ethernetconnection is provided with thisdata ensuring no delay in respondingto messages from the LAN.

Up to 10 simultaneous connectionsare allowed to the bridge andeffectively several host systems canaccess data at the same time atspeeds of 10Base-T or 100Base-TX.

The LAN can be extended to a widearea network or even to include arouter onto the World Wide Web.Enabling the correct router port forModbus TCP comms only increasesthe security of the system whenused over the Internet. The userconnection is a standard RJ45Ethernet connector.

Modbus TCPThe Ethernet protocol used for dataexchange and control is ModbusTCP. This widely used protocolallows for the data to be brokeninto packets for Ethernettransmission over the LAN.

Most host DCS and PLC systems,including In-Vision, support ModbusTCP and the embedded data followseither the standard Pakscan Generic,Honeywell or Yokogawa formats.

Modbus TCP is very similar toModbus RTU with the samefunction codes used forcommunication control.

Embedded WebServerThe embedded web server allowsthe system performance, diagnosticsand set up to be viewed at any timeby connecting a PC to the EthernetLAN and browsing to the bridgeusing standard Internet Browsersoftware such as Internet Explorer. Ifthe bridge is connected to theWorld Wide Web then the PC canbe anywhere in the world, providedit has a web connection.

In addition to viewing the status ofthe plant, and when the correctpasswords are entered, parameterscan be altered and outputs changedallowing rapid corrective maintenancein the event of a field fault.

The server can even be configuredto send e-mail messages to specifiedrecipients should a system faultdevelop.

• System Configuration

• Alarm Monitoring

• Network Diagnostics

• E-mail notification

SecurityThe Modbus TCP communicationprotocol and the inherent protectionof a router provide a high degree ofsecurity for the system. In additionthe ability to alter the system orissue commands to the actuators isunder password protection.

RS485 RS485

Port 4 Port 4Port 1 Port 1

2 wire loop

Bridge Bridge

PLC or DCS

LAN 1

LAN 2

T H E 2 W I R E L O O P9

Diagram 2: System Fault Tolerance - 2 wire loop integrity.

Master Station

Port B Port A

Add 2

Add 4

Add 3

Add 1

In OutOutIn

Port B Port A

Add 2

Add 4

Add 3

Add 1

In OutOutIn

Master StationNormal operation Broken loop operation

LB on LB on

CableFault

Cable Faults:

Open Circuit

Ground Fault

Short Circuit

Loop WiringThe Pakscan network carries a 15V20 mA current loop signal. Thissignal is modulated by the masterstation to send and receive datafrom the attached field units.

The cable is a single twisted pairwith an overall screen for protectionwhich is easy to install, easy tomaintain, low cost and highlyeffective in all operating conditions.

ComprehensiveData Reporting2 wires carry the data previouslyrequiring 22 conductors. Noadditional actuator hardware isneeded for position or torque datareporting from IQ and IQT actuators.

Noise ProtectionThe Pakscan system protects againstelectrical interference by using acurrent loop and surge arresters.The use of a 20mA current loopautomatically ensures that thesystem offers a low impedance toany noise currents and prevents

these currents from generatingsignificant voltage spikes. Anyvoltage spikes that do result areswiftly clamped to acceptable levelsby the high speed surge arrestersfitted at each field unit and themaster station.

System Fault RecoveryThe two wires are connected to,and taken from, each field unit inturn. They originate from and returnto the master station to create asingle twisted pair two wire loop. Aseach device may now be accessedfrom either direction a redundantcommunication path is available.Pakscan fully utilises this arrangementin the event of a cable fault.

The integrity of the 2 wire cable iscontinuously checked whilst thesystem is running. In normaloperation port A is acting as atransceiver and port B as a receiveronly. The current passes from masterstation port A ‘out’ to port B ‘in’ viaall the actuator field units. Port B isable to monitor all the communicationfrom port A through the cable.

If the communications should failfor any reason, the master stationstops transmission and after a quietperiod all the field units assert theirloopback circuits. A short periodlater the master station beginscommunicating to each field unit inturn from port A. It identifies eachunit’s address and instructs the fieldunit to remove its loopback.Progressively the current loop isextended until the location of thefault is revealed. Port B thenreconfigures as a transceiver and theprocedure is repeated from theother direction. Once the process iscomplete the system will havelocated the position and precisenature of the fault and maintainedcommunication with all the fieldunits on each side of the fault.

The loopback feature is unique tothe Pakscan system and allows thesystem to have two communicationroutes without the need for twocable runs. It also allows the systemto cope with cable breaks, shortcircuits and ground faults.

H I G H P E R F O R M A N C E10

Pakscan networks use aunique proprietaryprotocol that achieves veryfast update times whilstusing relatively low datatransmission rates.Compressing the data fieldto a minimum lengthallows more data to passover the network in agiven time at each datarate. The result is a systemthat can handle longtransmission distances anda large number of unitswhilst still maintaining aquick and efficientcommunication.

Field units are scanned in turn bythe master station and report theircurrent status back in compressedcode messages, shortening thetransaction period to a minimum.

The field cable used for the Pakscannetwork is typical instrumentationcable. A simple twisted pair withoverall screen using polyethyleneinsulation will suffice.

The use of low transmission speedsallows the current loop to achievelong distance communication withfield devices without the need forrepeaters. Where the loop distanceis shorter then higher speeds can beused.

The communication protocol givespriority to instructions sent from the

master station to the field units.Commands are considered moreimportant than reports so theroutine polling of the field units ismomentarily suspended when acommand needs to be issued.Because command instructionsoccur infrequently there is anegligible effect on the the scantime for the system.

Scan Time (seconds)

Baud Number of field unitsRate 60 120 180 240

110 8.4 19.3 31.1 42.9

300 3.1 7.1 11.4 15.8

600 1.6 3.6 5.7 7.9

1200 0.8 1.8 2.9 3.9

2400 0.4 0.9 N/A N/A

Loop Distance (km) with 1.5mm2 cable

Baud Number of FCURate 60 120 240

110 20.3 20.3 20.3

300 17.1 15.9 13.7

600 12.2 11.1 8.8

1200 4.1 2.9 0.6

2400 1.5 0.3 N/A

Time to issue a command (msec)

BaudRate Time

110 614

300 230

600 110

1200 60

2400 30

O P T I O N S A N D A C C E S S O R I E S11

Options

Pakscan IIEControl room or equipment room mounting, the IIE masterstation is capable of controlling up to 240 field units. Eitherone or two fully independent systems can be mounted inthe 133 mm high 19" rack.

The Pakscan IIE is complete with two communication ports,a screen and keypad and the ability to include PS410RS232/RS485 converters.

Pakscan IIE Hot StandbyThe hot standby version of the IIE features two identicalmodules in one rack. Either may be the primary unit andtransfer between the two is transparent and automatic oncomponent failure.

Control room or equipment room mounting, this masterstation is capable of controlling up to 240 field units.

TSI - Touch Screen interfaceRotork's Touch Screen Interface is designed to be usedwith the Pakscan system. The HMI package installed can bea fully configured InVision or InVision MD, themaintenance and diagnostic version of the package.

Accessories PaktesterAllows for setting thefield unit parametersby connecting to theactuator directly.

PakreaderEnables master stationModbus communicationsto be verified.

Converter PS410/PS412Available as the PS412free standing unit(supplied with a universalpower pack) or as aPS410 card for insertionin the master station rack.The unit converts RS232to RS485 and vice versa.

MastertoolsA software utility to allow full system diagnosis, configurationand report generation.

In-VisionA complete HMI package for PC based control of the actuatorson the loop.

As part of a process of on-going productdevelopment, Rotork reserves the rightto amend and change specificationswithout prior notice.

Published data may be subject to change.

For the very latest version release, visitour website at www.rotork.com

The name Rotork is a registered trademark.Rotork recognizes all registered trademarks.Published and produced in the UK byRotork Controls Limited.

A full listing of our worldwidesales and service networkis available on our website atwww.rotork.com

UK head officeRotork Controls Limitedtelephone Bath 01225 733200telefax 01225 333467email mail@rotork.co.uk

USA head officeRotork Controls Inctelephone Rochester (585) 328 1550telefax (585) 328 5848email info@rotork.com Rotork Controls Ltd, Bath, UK

Rotork Controls Inc, Rochester, USA

Enclosure Standard 19” rack mountingto DIN 41494 with rear terminals and connectors.

Supply Voltage a.c. 90 to 264v, 43-440 HzFuse 1 amp.

Power consumption 30 VA for each master station module. 60 VA for the Hot Standby master station.

Current loop 20 mA 15V max, Pakscan protocol.

Cable Single twisted pair,500 ohms max resistance, 3.9 uF max capacitance.

Field Units 240 maximum. Supports all Rotork actuator types IQ, IQM, IQT, Q, A, and AQ plus General Purpose field units.

Host Communications Each module has 2 Modbus RTU half duplex comms ports, 1 off RS232, 1 off RS485 (2 wire)and space to add a PS410 RS232/RS485 converter. Each module optional Single EthernetModbus TCP instead of RS232 or RS485 connection, or dual Ethernet Modbus TCP replacing both RS232 and RS485.

I/O Connections Screw clamp terminals and D-type connectors. Loop connection terminals and 25 way male connector. RS485/RS232 9 way male/female and female.Ethernet RJ45 connector.Supply connector IEC.

Environmental Operating temp 0 to 50ºC.Storage temp –10 to +70ºC.Humidity 5% to 95% R.H. non-condensing.

Display 4 line by 20 character LCD2 loop activity LED’s7 system status LED’sThe LCD contrast may diminishat extremes of working temperature range.

Controls Numeric keypad, 16 keys.

Protection Operations controlled by password protection.

T E C H N I C A L D A T A