PCT51 Issue 1 Instruction Manual

Essentials of Process Control

Flow Control Process

Instruction Manual

PCT51

ISSUE 1

June 2012

Table of Contents Copyright and Trademarks ...................................................................................... 1

General Overview ....................................................................................................... 2

Equipment Diagrams................................................................................................... 3

Important Safety Information....................................................................................... 5

Introduction.............................................................................................................. 5

Electrical Safety....................................................................................................... 5

Water Borne Hazards .............................................................................................. 5

Description .................................................................................................................. 7

Overview.................................................................................................................. 7

PCT51 Flow Control Process .................................................................................. 7

Software .................................................................................................................. 9

Installation................................................................................................................. 11

Advisory................................................................................................................. 11

Electrical Supply .................................................................................................... 11

Connecting the PCT51 to a PC ............................................................................ 11

Filling the Sump Tank............................................................................................ 11

Installing the Software ........................................................................................... 11

Installing the Equipment ........................................................................................ 16

Operation .................................................................................................................. 20

Operating the Software.......................................................................................... 20

Operating the Equipment....................................................................................... 32

Equipment Specifications.......................................................................................... 36

Overall Dimensions ............................................................................................... 36

IFD Connections.................................................................................................... 36

Other Specifications .............................................................................................. 38

Environmental Conditions...................................................................................... 38

Routine Maintenance ................................................................................................ 40

Responsibility ........................................................................................................ 40

General.................................................................................................................. 40

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Table of Contents

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Cleaning the Equipment ........................................................................................ 40

Accessing the electrical circuits inside the electrical enclosure............................. 40

Laboratory Teaching Exercises................................................................................. 41

Index to Exercises ................................................................................................. 41

Exercise A - Manual control of flow (Open loop)....................................................... 42

Exercise B - On/off control of flow (Closed loop) ...................................................... 45

Exercise C - Proportional control flow (Closed loop, P only and P + I) ..................... 48

Exercise D - Optimising proportional control of flow (Closed loop, P+I+D)............... 54

Exercise E - Using a PID controller (PCT54) ............................................................ 58

Exercise F - Using a PLC controller (PCT55) ........................................................... 59

Contact Details for Further Information ..................................................................... 60

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Disclaimer This document and all the information contained within it is proprietary to Armfield Limited. This document must not be used for any purpose other than that for which it is supplied and its contents must not be reproduced, modified, adapted, published, translated or disclosed to any third party, in whole or in part, without the prior written permission of Armfield Limited.

Should you have any queries or comments, please contact the Armfield Customer Support helpdesk (Monday to Thursday: 0830 – 1730 and Friday: 0830 - 1300 UK time). Contact details are as follows:

United Kingdom International

(0) 1425 478781 (calls charged at local rate)

+44 (0) 1425 478781 (international rates apply)

Email: [email protected]

Fax: +44 (0) 1425 470916

Copyright and Trademarks Copyright © 2012 Armfield Limited. All rights reserved.

Any technical documentation made available by Armfield Limited is the copyright work of Armfield Limited and wholly owned by Armfield Limited.

Brands and product names mentioned in this manual may be trademarks or registered trademarks of their respective companies and are hereby acknowledged.

General Overview Four independent but complementary process units provide a compact, hands-on introduction to the fundamental principles of process control engineering. Each fluid-based process provides a clear demonstration of a different single PID loop using Level, Flow, Temperature or Pressure as the measured variable.

Each process is supplied complete with software that allows it to be controlled using a suitable PC via a USB connection. The effect of making changes to the system or to the controller configuration can be quickly investigated by applying repeatable disturbances to the process, clearly demonstrating the need for correct matching of system characteristics and controller settings. The software allows all appropriate measurements and controller settings to be displayed continuously and recorded for later analysis, if required by the user. Alternatively the process can be operated using an external controller such as the optional Industrial PID controller (PCT54) or Programmable Logic Controller (PCT55). If required, a PC can be used to record the responses of the process when using an external controller.

A Sensor Conditioning and Calibration Trainer (PCT56) completes this range of process control products.

The range of products comprises the following small-scale processes, optional controllers and sensor calibration trainer:

PCT50 Level Control Process

PCT51 Flow Control Process

PCT52 Temperature Control Process

PCT53 Pressure Control Process

PCT54 Industrial PID Controller

PCT55 Programmable Logic Controller

PCT56 Sensor Conditioning and Calibration Trainer

This instruction manual describes the operation of the PCT51 Flow Control Process when used with a PC to control and record the process.

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Equipment Diagrams

Figure 1: Front View of the PCT51 Flow Control Process

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Armfield Instruction Manual

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Figure 2: Schematic diagram of the PCT51 Flow Control Process

Important Safety Information

Introduction All practical work areas and laboratories should be covered by local safety regulations which must be followed at all times.

It is the responsibility of the owner to ensure that all users are made aware of relevant local regulations, and that the apparatus is operated in accordance with those regulations. If requested then Armfield can supply a typical set of standard laboratory safety rules, but these are guidelines only and should be modified as required. Supervision of users should be provided whenever appropriate.

Your PCT51 Flow Control Process has been designed to be safe in use when installed, operated and maintained in accordance with the instructions in this manual. As with any piece of sophisticated equipment, dangers exist if the equipment is misused, mishandled or badly maintained.

Electrical Safety The equipment described in this Instruction Manual operates from a mains voltage electrical supply via a 24Vdc adapter. It must be connected to a supply of the same frequency and voltage as marked on the equipment or the mains lead. If in doubt, consult a qualified electrician or contact Armfield.

The equipment must not be operated with any of the panels removed.

Water Borne Hazards The equipment described in this instruction manual involves the use of water, which under certain conditions can create a health hazard due to infection by harmful micro-organisms.

For example, the microscopic bacterium called Legionella pneumophila will feed on any scale, rust, algae or sludge in water and will breed rapidly if the temperature of water is between 20 and 45°C. Any water containing this bacterium which is sprayed or splashed creating air-borne droplets can produce a form of pneumonia called Legionnaires Disease which is potentially fatal.

Legionella is not the only harmful micro-organism which can infect water, but it serves as a useful example of the need for cleanliness.

Under the COSHH regulations, the following precautions must be observed:

Any water contained within the product must not be allowed to stagnate, ie. the water must be changed regularly.

Any rust, sludge, scale or algae on which micro-organisms can feed must be removed regularly, i.e. the equipment must be cleaned regularly.

Where practicable the water should be maintained at a temperature below 20°C. If this is not practicable then the water should be disinfected if it is safe and appropriate to do so. Note that other hazards may exist in the handling of biocides used to disinfect the water.

A scheme should be prepared for preventing or controlling the risk incorporating all of the actions listed above.

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Further details on preventing infection are contained in the publication “The Control of Legionellosis including Legionnaires Disease” - Health and Safety Series booklet HS (G) 70.

Description Where necessary, refer to the drawings in the Equipment Diagrams section.

Overview The PCT51 Flow Control Process consists of a combined sump tank and process loop assembly together with an electrical connection box, mounted on a common base plate. It belongs to a family of four processes having common features, as follows:

All four processes are free standing, without the need for a permanent water supply or drain connection, and suitable for locating on a work bench alongside a PC.

Each process incorporates an electronic interface with sensor conditioning, drive circuits and integrated USB connection. This means that the user only needs to fill the process with water (where appropriate), connect the mains adaptor and connect the supplied USB cable to a suitable PC for the equipment to be operational.

The use of transparent materials gives clear visibility of the process in operation and the location of control components such as sensors and control elements.

The facility to vary the operating characteristics to allow optimization of the PID settings to suit the characteristics and to demonstrate the differing responses of both optimum and non-optimum controller configuration.

Supplied with software and USB lead allowing control and data acquisition using a PC.

Disturbances (step changes) can be applied to the process, remotely from the PC, to test the stability of the system with the controller settings under investigation. The magnitude of the disturbance can be changed in fixed steps for repeatability or varied continuously to achieve a specific response in the system.

Manual operation via the PC will allow open loop testing of each process to determine the system response prior to assigning appropriate values for the P, I and D terms, cycle time etc in a closed loop configuration.

In addition to control of the process and initiation of step changes, the software supplied will also allow recording of the responses, graphing etc. when testing any of the control loops.

The electrical interface, mounted alongside the process, incorporates additional front panel connectors that allow the input and output signals to be connected to an alternative PID controller, Programmable Logic Controller or similar control equipment if required by the end user.

The electrical supply is provided by a universal 24 Volt DC in-line adaptor with interchangeable leads to suit the local electrical supply.

PCT51 Flow Control Process Refer to the equipment diagrams for details about the PCT51 Flow Process. The front view shows the layout of the PCT51 and the circuit diagram shows the process in operation with the flow through the process loop controlled by varying the pump speed and the bypass operated by opening a solenoid valve SOL to disturb the flow.

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PCT51 is a flow control process using water as the working fluid for safety and convenience in use.

Water stored in the sump tank is transferred to the process loop above via a submerged, variable speed centrifugal pump (6). A quick release connector (5) allows the flexible pump outlet tube to be disconnected to aid priming of the pump after filling the sump tank with water. An inline ball valve (CV1) above the quick release connector allows the flow of water through the process loop to be varied to suit a particular demonstration.

The process loop consists of a parallel pipe arrangement mounted on the lid of the sump tank with two outlets that return water to the sump tank. The flow of water through the main outlet is continuous and measured using an electronic flowmeter F (1) mounted upstream. The second outlet, upstream of the flowmeter, incorporates a solenoid valve (SOL) that allows the flow to be started and stopped under remote control. When the solenoid valve opens and closes, the flow through the solenoid valve changes the flow to the main outlet causing a step change in the measured flow. Both outlets incorporate a hand operated valve (CV2 and CV3) that allows the flow of water to be varied continuously to suit a particular demonstration. The solenoid valve outlet also incorporates an interchangeable orifice (4) that allows the flow to be fixed at a predetermined value, varying only with the pump head upstream, so that system characteristics, step changes etc can be repeated precisely allowing direct comparison of different controller settings. The orifice size is changed by unscrewing the plastic fitting containing the orifice and replacing it with the required alternative. The fitting incorporates an ‘O’ ring seal and only requires hand tightening. The alternative sizes of orifice (8) are stored in threaded holes at the front of the base plate when not in use.

Flow through the main outlet is delivered to a flow indicator (2) located inside the sump tank. This consists of a vertical transparent tube with a series of holes and a vertical level scale that allows visualisation of the flow through the process. The holes are arranged to give an approximately linear change in height with change in flow. The holes are arranged in a spiral so that the hydrostatic characteristics can be observed. Water exiting the flow indicator is returned to the sump tank for reuse.

The electronic flowmeter, the centrifugal pump and the solenoid valve are connected to an electrical interface (3) that incorporates the necessary signal conditioning, allowing the process to be operated directly from a PC using a single USB port. Alternatively the process can be operated using a controller such as PCT54 (PID Controller) or PCT55 (Programmable Logic Controller) connected to the electrical interface.

The computer software supplied with PCT51 allows control of the flow process and data logging of the responses using a PC. Alternatively the software allows data logging only while operating the process remotely using a PID controller or PLC.

A single process control loop is available for demonstration, namely:

Flow control by proportionally varying the pump speed (Inflow control)

A process loop with on/off control using a solenoid valve is not included with PCT51 because it is not appropriate to a flow process. The flow cannot be varied proportionally using an on/off solenoid valve as in level control or temperature control because the flow is simply on or off. This can be demonstrated in the single loop by configuring on/off control of the water pump.

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Description

When filled with water, the PCT51 is self contained requiring only a mains electrical supply to the in-line DC converter and connection to either a PC via the USB port or to a process controller such as PCT54 (PID Controller) or PCT55 (PLC with PID controller).

The unit is drained using the ball valve (7) located at the rear.

Software The PCT51 is supplied with an educational software package with a wide range of facilities and functions. The computer is the primary interface between the user and the equipment. The software displays a real time process mimic diagram with readings of the relevant sensor outputs and controls for the system inputs. Manual, On/off, time proportioned and PID control loops can be configured using a predetermined student exercise:

Ex 1 Flow control (PC)

Exercises demonstrating Inflow Control by varying pump speed:

Exercise A - Manual control of flow (Open loop)

Exercise B - On/off control of flow (Closed loop)

Exercise C - Proportional control of flow (Closed loop, P only and P + I)

Exercise D - Optimising proportional control of flow (Closed loop, P + I + D)

Two alternative exercises are included that allow the process to be monitored and recorded on the PC while using an external controller such as PCT54 or PCT55:

Ex 2 Flow control (External Control)

Exercise E - Using a PID controller (PCT54)

Exercise F - Using a PLC controller (PCT55)

When controlling using a PC all control and sensor signals including the setpoint, and controller configuration can be logged continuously using the PC. Disturbances of fixed magnitude can be introduced remotely using the PC to evaluate the stability of a particular process / controller configuration.

When using the PC to monitor the process the input and output signals can be monitored and logged. Disturbances are introduced remotely from the external controller.

This eliminates the need for a separate process recorder or chart recorder for analysis of the process control responses. This software is compatible with PCs using Microsoft WindowsTM 98, 2000 and XP. The computer communicates to the PCT51 using a standard universal serial bus (USB) interface. Installation instructions are included in the section Installing the Software. The software includes a comprehensive online Help Text.

The use of a Virtual Serial Port to allow the USB port to communicate with the software allows users to write their own software if they have the necessary skills and appropriate software such as Labview. Information about the USB channel configuration is included in the section IFD connections.

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Note: Armfield cannot provide assistance in writing alternative software to operate the PCT52.

Installation

Advisory Before operating the equipment, it must be unpacked, assembled and installed as described in the steps that follow. Safe use of the equipment depends on following the correct installation procedure.

Electrical Supply The universal adaptor supplied with PCT51 requires connection to a single phase electrical supply. Leads are included with PCT51 allowing connection to:

220 V / 50 Hz via European style 2 pin plug

220 V / 50 Hz via UK style 3-pin plug

120 V / 60 Hz via USA style 125 V 3-pin plug

220 V / 60 Hz via USA style 250 V 3-pin plug

The 24 V output from the adaptor is connected to the socket marked 24 V DC IN at the rear of the electrical console on PCT51.

Connecting the PCT51 to a PC After installing the PCT51 software and the driver on the PC the PCT51 is connected to the PC using the USB lead supplied with the PCT51. The USB socket is located on the rear panel of the electrical enclosure.

Filling the Sump Tank No permanent supply of water is required when operating the PCT51.

Ensure that the drain valve at the rear if the sump tank is closed before filling the sump tank.

The sump tank can be filled using a hose or by pouring water through the cut out at the front. When filled, the water should be approximately level with the 0 datum on the flow indicator tube.

Note: To ensure reliable priming of the water pump after filling for the first time or after draining and refilling the equipment, the flexible tube from the pump outlet should be temporarily disconnected from the system by pressing the latch on the quick release connector. After running the pump briefly at approximately 50% speed, with the tube disconnected to expel any trapped air, the tube can be reconnected for normal operation. This procedure is described below in the section Installing the Equipment.

Installing the Software The -306 version of the software supplied with this product is designed to operate on PC’s with either 32 or 64 bit operating systems provided that the equipment carries a label stating 32/64 bit os compatible alongside the USB port on the equipment.

If -306 software is to be used with equipment not displaying this label then the software can be operated using a PC with 32 bit operating system. If it is required to

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use a PC with 64 bit OS then it will be necessary to contact Armfield Ltd to upgrade the hardware.

To enable the -306 version of the software to communicate with the equipment the USB port on the PC utilizes a virtual serial driver that must be enabled each time the software is operated. Correct installation and operation of the -306 software is achieved as described below.

Install the -306 software supplied with the product

To successfully install the driver associated with the Armfield software it will be necessary for the user to be logged on to the computer as administrator or as a user that has been granted equivalent administrator rights. If any problems are experienced when installing the driver as described below then refer to the leaflet supplied with the CD-ROM that describes the detailed procedure for installing the driver.

Insert the CD-ROM in the CD/DVD drive. If autorun is disabled or installation does not start automatically choose the file Setup.exe on the CD-ROM.

The Welcome screen will be displayed showing the available options:

Choose Install Software from the options, wait for the welcome screen to clear then follow the onscreen instructions to install the software on the PC. All of the default options can be accepted unless installation in a particular location is required.

When the Welcome screen is displayed again choose Exit the CD but leave the CD-ROM in the CD/DVD drive of the PC to enable the USB driver to be installed later.

Note: It is not appropriate to choose Install Driver unless it is intended to operate the equipment using software other than that supplied by Armfield.

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Installation

Connect the USB port on the equipment to the USB port on the PC using the lead supplied. A message will be displayed showing that new hardware has been found and the appropriate driver must be installed:

When the location of the driver is requested, browse to find the CD/DVD drive containing the -306 Armfield CD-ROM then follow the onscreen instructions to install the driver.

Correct installation of the driver will be confirmed by the illumination of the green ‘Active’ LED alongside the USB connector on the equipment.

If there are any problems locating or installing the driver then refer to the leaflet supplied with the CD-ROM that describes the detailed procedure for installing the driver.

The CD-ROM can be removed from the CD/DVD drive.

Load the software

Locate the appropriate Armfield Folder using Start \ Programs then choose the required Armfield product, and accessory (if appropriate).

The opening screen will display the range of experiments available. Choose the appropriate experiment to undertake (choose any experiment if not sure which).

A Welcome screen will be displayed with a toolbar across the top.

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Enable the USB virtual serial COM Port

At the right hand end of the top menu bar click the Start COM Session icon as shown to enable the port:

The Select Port window will open. Display the available COM ports by pulling down the menu:

Highlight the last COM port in the list (highest number) then click OK to enable the port:

Confirm that the Serial Port has been enabled

If the Serial Port has been correctly enabled then the virtual COM Port number followed by SE or Diff will be displayed in the bottom right hand corner of the screen:

If the wrong Serial Port has been selected then the number of the port will be displayed but SE or Diff will not be displayed:

Repeat the above procedure and select the last COM port in the list.

If the serial port has not been enabled or if the device driver has not been installed correctly then IFD: Device Error will be displayed:

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Installation

If the USB connection between the PC and the equipment has been broken then a warning message will be displayed:

Clearing this message will result in a message in the bottom right hand corner indicating an error, typically:

Check that the USB lead is connected between the USB ports on the Armfield equipment and the PC. Reload the software then enable the virtual serial COM port as described above.

If the problem persists check that the device driver has been correctly installed as described above.

Note: Where the equipment has two USB ports the messages for both ports will be displayed in the bottom right hand corner of the screen. Each connection will use a different virtual COM port and the two ports must be configured separately as described above. The master port will include m in the message and the slave connection will include s to differentiate between the two. When installed correctly, typical messages will be:

Similarly, a connection or driver error with either or both ports will be indicated:

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Operate the -306 software supplied with the product

From the Welcome to Armsoft screen either chose the View icon in the top menu bar or choose View then Diagram to display a diagram showing the equipment and any relevant measured variables.

For details about operating the software refer to the Help facility in the software (accessible using the Help icon in the top menu bar then choosing Operating the Software). Alternatively refer to the section Operating the Software in the product instruction manual.

Installing the Equipment To install the equipment:

1. Carefully remove the PCT51 from its packing and remove any loose protective materials. Retain the power supply, connecting leads and CD-ROM in a safe place until required for use.

2. Place the PCT51 on a firm, level bench top or table where the equipment is to be operated with access to a mains electrical supply.

Note: No permanent connection is required to a water supply but it will be necessary to fill the sump tank before use with approximately 7 litres of clean cold water. The equipment should be drained before moving the PCT51 to a different location.

3. Wipe the equipment, especially the inside surfaces of the sump tank with a soft damp cloth to remove any dust etc. before proceeding.

4. Before operating the equipment ensure that a 3 mm diameter orifice is fitted below the solenoid valve SOL. The orifice size is changed by unscrewing the plastic fitting containing the orifice and replacing it with the required alternative. The fitting incorporates an ‘O’ ring seal and only requires hand tightening.

Alternative sizes of orifice are stored at the front of the support plinth.

5. Ensure that the drain valve at the rear of the sump tank is fully closed then fill the sump tank with clean water. When filled the water should be level with the zero graduation on the scale attached to the flow indicator tube. If the local water is hard or contains impurities then demineralised or deionise water is recommended to minimise any scaling in the system or on the wall or floor of the sump tank.

6. Ensure that the flow control valve CV1 is fully open at the inlet to the process loop so that water can flow through the loop when the pump is running.

7. Ensure that outlet valve CV2 is fully open to allow water to return to the sump tank when the process loop has filled with water.

8. Ensure that valve CV3 is fully open above the solenoid valve SOL to allow water to return to the sump tank when the solenoid valve is open. With CV3 fully open the outflow is determined by the size of the orifice allowing repeatable disturbances to be applied to the process.

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Installation

9. Switch on the PC and connect the USB lead from the rear of the PCT51 console to the PC.

10. Load the PCT51 software then choose experiment ‘Ex1: Flow control (PC control)’ from the menu.

For detailed information about operating the software refer to ‘Operating the Software’.

11. Enable the Virtual COM port using the red telephone icon in the top toolbar. Refer to the section Operating the Software if necessary.

12. Display the mimic diagram by choosing View then Diagram or via the mimic

diagram icon .

13. The mimic diagram will be displayed as follows:

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14. Connect the lead from the 24V dc power adapter to the socket marked 24V DC IN at the rear of the electrical enclosure. Connect the mains lead with appropriate plug to the mains inlet socket on the power adapter.

15. Click Power On (in Controls) to allow the PCT51 to be operated via the PC

16. Each time the software starts the PID controller is reset to Off, with the pump off and the solenoid valve closed. Default values for the Set point and control parameters are restored unless a previous set-up has been saved. The flow measured by the flowmeter is indicated directly in engineering units i.e. L/min of flow.

Correct operation of the PCT51 can be checked using the manual controls in the software before using the equipment for automatic control exercises.

17. Ensure that flow control valves CV1 and CV2 are fully open. Disconnect the flexible tube from the pump outlet by pressing the latch on the quick release connector (this allows the pump to prime by expelling any trapped air). On the mimic diagram (in Controls), gradually increase the pump speed to 50 % by clicking on the up arrow until 50 % is displayed.

When water is flowing steadily from the flexible tube return the pump speed to 0 % by clicking the down arrow then reconnect the quick release connector. Gradually increase the pump speed again, briefly to 100 % then back to 50 % to ensure that the pump is fully primed. Check that the pump operates smoothly and the water level inside the flow indicator starts to rise. Check that the water flowrate (F1) through the process loop is displayed on the mimic diagram.

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Installation

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18. Check that the ball valve CV3 above the solenoid is fully open then open the solenoid valve SOL from the mimic diagram (in Controls).

The switch is represented as a button on the screen, and is operated by clicking on it. The switch will display a ‘0’ when the valve is off (closed) and a ‘1’ when the valve is on (open). Check that water returns to the sump tank via the solenoid valve when the switch indicates ‘1’ and stops when the switch indicates ‘0’.

When the solenoid valve is open check that the flow reduces slightly, indicated by the value of F and the level in the flow indicator. Close the solenoid valve then check that the flow returns to the original value on the mimic diagram and the level is restored in the flow indicator.

19. Set the pump speed to 0 %, and allow the contents of the process loop to drain into the sump tank.

20. The operation of the PCT51 has been confirmed and the equipment is ready for use.

The sump tank should be drained to prevent fouling or scaling if the PCT51 is not to be used immediately. The flow indicator tube is drained by lifting the tube vertically upwards up off the sealing O-ring.

Operation Where necessary, refer to the drawings in the Equipment Diagrams section.

Operating the Software NOTE: The diagrams in this section are included as typical examples and may not relate specifically to the individual product described in this instruction manual.

The Armfield Software is a powerful Educational and Data Logging tool with a wide range of features. Some of the major features are highlighted below, to assist users, but full details on the software and how to use it are provided in the presentations and Help text incorporated in the Software. Help on Using the Software or Using the Equipment is available by clicking the appropriate topic in the Help drop-down menu from the upper toolbar when operating the software as shown:

Before operating the software ensure that the equipment has been connected to a USB port on the PC (not supplied) using the USB lead supplied with the equipment. Where a separate USB interface (E.g. IFD5) has been supplied ensure that the equipment is connected to the interface and the interface is connected to a USB port on the PC. For further information about these actions refer to the sections Installing the Software and Installing the Equipment.

Load the software. If multiple experiments are available then a menu will be displayed listing the options. Wait for the presentation screen to open fully as shown:

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Operation

Check that the green Active LED (alongside the USB port on the equipment or IFD interface as appropriate) is illuminated to confirm that the USB port is connected and the USB driver is correctly installed. If the green LED is not illuminated refer to the section Installing the Software.

Before operating the software it will be necessary to enable the USB virtual serial COM port. At the right hand end of the top menu bar click the Start COM Session icon as shown to enable the port:

The Select Port window will open. Display the available COM ports by pulling down the menu:

Highlight the last COM port in the list (highest number) then click OK to enable the port:

Confirm that the Serial Port has been enabled

If the Serial Port has been correctly enabled then the virtual COM Port number followed by SE or Diff will be displayed in the bottom right hand corner:

If the wrong Serial Port has been selected then the number of the port will be displayed but SE or Diff will not be displayed. Refer to the section Installing the Software if there are any problems.

Presentation Screen - Basics and Navigation

As stated above, the software starts with the Presentation Screen displayed. The user is met by a simple presentation which gives them an overview of the capabilities

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of the equipment and software and explains in simple terms how to navigate around the software and summarizes the major facilities complete with direct links to detailed context sensitive ‘help’ texts.

To view the presentations click Next or click the required topic in the left hand pane as appropriate. Click More while displaying any of the topics to display a Help index related to that topic.

To return to the Presentation screen at any time click the View Presentation icon

from the main tool bar or click Presentation from the dropdown menu as shown:

For more detailed information about the presentations refer to the Help available via the upper toolbar when operating the software.

Toolbar

A toolbar is displayed at the top of the screen at all times, so users can jump immediately to the facility they require, as shown:

The upper menu expands as a dropdown menu when the cursor is placed over a name.

The lower row of icons (standard for all Armfield Software) allows a particular function to be selected. To aid recognition, pop-up text names appear when the cursor is placed over the icon.

Mimic Diagram

The Mimic Diagram is the most commonly used screen and gives a pictorial representation of the equipment, with continuously updated display boxes for all the various sensor readings, calculated variables etc. directly in engineering units.

To view the Mimic Diagram click the View Diagram icon from the main tool bar or click Diagram from the View drop-down menu as shown:

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Operation

A Mimic diagram is displayed, similar to the diagram as shown:

The details in the diagram will vary depending on the equipment chosen if multiple experiments are available.

In addition to measured variables such as Temperature, Pressure and Flowrate (from a direct reading flowmeter), calculated data such as Motor Torque, Motor Speed and Discharge / Volume flowrate (from pressure drop across an orifice plate) are continuously displayed in data boxes with a white background. These are automatically updated and cannot be changed by the user.

Manual data input boxes with a coloured background allow constants such as Orifice Cd and Atmospheric Pressure to be changed by over-typing the default value, if required.

The data boxes associated with some pressure sensors include a Zero button alongside. This button is used to compensate for any drift in the zero value, which is an inherent characteristic of pressure sensors. Pressing the Zero button just before starting a set of readings resets the zero measurement and allows accurate pressure

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measurements to be taken referenced to atmospheric pressure. This action must be carried out before the motor is switched on otherwise the pressure readings will be offset.

The mimic diagram associated with some products includes the facility to select different experiments or different accessories, usually on the left hand side of the screen, as shown:

Clicking on the appropriate accessory or exercise will change the associated mimic diagram, table, graphs etc to suit the exercise being performed.

Typical Control Facilities in the Mimic Diagram

A Power On button allows the motor to be switched off or on as required. The button always defaults to off at startup. Clicking this button switches the power on (1) and off (0) alternately.

A box marked Pump Speed allows the speed of the motor to be varied from 0 to 100% either stepwise, by typing in values, or using the up / down arrows as appropriate. It is usual to increase the motor speed gradually until the required operating speed is reached. On some products it is usual to operate the equipment with the motor set at 100% while gathering performance data, and then reduce the setting as required to investigate the effect of reduced speed on performance of the equipment.

When the software and hardware are functioning correctly together, the green LED marked Watchdog Enabled will alternate On and Off. If the Watchdog stops alternating then this indicates a loss of communication between the hardware and software that must be investigated.

Details on the operation of any automatic PID Control loops in the software are included later in this section.

Data Logging Facilities in the Mimic Diagram

There are two types of sampling available in the software, namely Automatic or Manual. In Automatic logging, samples are taken regularly at a preset but variable interval. In Manual logging, a single set of samples is taken only when requested by the operator (useful when conditions have to be changed and the equipment allowed to stabilize at a new condition before taking a set of readings).

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Operation

The type of logging will default to manual or automatic logging as appropriate to the type of product being operated.

Manual logging is selected when obtaining performance data from a machine where conditions need to stabilize after changing appropriate settings. To record a set of

data values from each of the measurement sensors click the icon from the main

toolbar. One set of data will be recorded each time the icon is clicked.

Automatic logging is selected when transients need to be recorded so that they can

be plotted against time. Click the icon from the toolbar to start recording, click

the icon from the toolbar to stop recording.

The type of logging can be configured by clicking Configure in the Sample drop-down menu from the upper toolbar as shown:

In addition to the choice of Manual or Automatic sampling, the parameters for Automatic sampling can also be set. Namely, the time interval between samples can be set to the required number of minutes or seconds. Continuous sampling can be selected, with no time limit or sampling for a fixed duration can be set to the required number of hours, minutes or seconds as shown:

Tabular Display

To view the Table screen click the View Table icon from the main tool bar or click Table from the View dropdown menu as shown:

25


The data is displayed in a tabular format, similar to the screen as shown:

As the data is sampled, it is stored in spreadsheet format, updated each time the data is sampled. The table also contains columns for the calculated values.

New sheets can be added to the spreadsheet for different data runs by clicking the

icon from the main toolbar. Sheets can be renamed by double clicking on the sheet name at the bottom left corner of the screen (initially Run 1, Run 2 etc) then entering the required name.

For more detailed information about Data Logging and changing the settings within the software refer to the Help available via the upper toolbar when operating the software.

Graphical Display

When several samples have been recorded, they can be viewed in graphical format.

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Operation

To view the data in Graphical format click the View graph icon from the main tool bar or click Graph from the View drop-down menu as shown:

The results are displayed in a graphical format as shown:

(The actual graph displayed will depend on the product selected and the exercise that is being conducted, the data that has been logged and the parameter(s) that has been selected).

Powerful and flexible graph plotting tools are available in the software, allowing the user full choice over what is displayed, including dual y axes, points or lines, displaying data from different runs, etc. Formatting and scaling is done automatically by default, but can be changed manually if required.

To change the data displayed on the Graph click Graph Data from the Format dropdown menu as shown:

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The available parameters (Series of data) are displayed in the left hand pane as shown:

Two axes are available for plotting, allowing series with different scaling to be presented on the same x axis.

To select a series for plotting, click the appropriate series in the left pane so that it is highlighted then click the appropriate right-facing arrow to move the series into one of the windows in the right hand pane. Multiple series with the same scaling can be plotted simultaneously by moving them all into the same window in the right pane.

To remove a series from the graph, click the appropriate series in the right pane so that it is highlighted then click the appropriate left-facing arrow to move the series into the left pane.

The X-Axis Content is chosen by default to suit the exercise. The content can be changed if appropriate by opening the drop down menu at the top of the window.

The format of the graphs, scaling of the axes etc. can be changed if required by clicking Graph in the Format drop-down menu as shown:

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Operation

For more detailed information about changing these settings refer to the Help available via the upper toolbar when operating the software.

PID Control

Where appropriate, the software associated with some products will include a single or multiple PID control loops whereby a function on the product can be manually or automatically controlled using the PC by measuring an appropriate variable and varying a function such as a heater power or pump speed.

The PID loop can be accessed by clicking the box labelled either PID, Control, Flow or Heater depending on the particular product software:

A PID controller window is then displayed as shown:

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The Mode of operation always defaults to Manual control and 0% output when the software is loaded to ensure safe operation of the equipment. If appropriate, the operator can retain manual operation and simply vary the value from 0 to 100% in the Manual Output box, then clicking Apply.

Alternatively, the PID loop can be changed to Automatic operation by clicking the Automatic button. If any of the PID settings need to be changed from the default values then these should be adjusted individually before clicking the Apply button.

The controller can be restored to manual operation at any time by clicking the Manual button. The value in the Manual Output box can be changed as required before clicking the Apply button.

Settings associated with Automatic Operation such as the Setpoint, Proportional Band, Integral Time, Derivative Time and Cycle Time (if appropriate) can be changed by the operator as required before clicking the Apply button.

Clicking Calculations displays the calculations associated with the PID loop to aid understanding and optimization of the loop when changing settings as shown:

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Operation

Clicking Settings returns the screen to the PID settings.

Clicking OK closes the PID screen but leaves the loop running in the background.

In some instances the Process Variable, Control variable and Control Action can be varied to suit different exercises, however, in most instances these boxes are locked to suit a particular exercise. Where the variables can be changed the options available can be selected via a drop-down menu.

Exporting Data

All logged data can be saved as a Formula 1 .vts data file that can be for read back into the software at a later date using the Open tab. Alternatively the data can be exported in Microsoft Excel format that can be loaded into a spreadsheet. To save data choose File / Save, enter the required location and filename then choose the required data format from the drop down menu as shown.

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Advanced Features

The software incorporates advanced features such as the facility to recalibrate the sensor inputs from within the software. Other features for use with specific products include an integral Oscilloscope for fast date capture and a Scheduler to vary parameters with time.

For more detailed information about these advanced functions within the software refer to the Help available via the upper toolbar when operating the software.

Operating the Equipment Note: Before operating the equipment ensure that it has been correctly installed in accordance with the section Installing the Equipment, and that you have read the section Important Safety Information.

Connecting the electrical supply to the PCT51

Connect the lead from the 24V dc power supply to the socket marked 24V DC IN at the rear of the electrical enclosure. Connect the mains lead with appropriate plug to the mains inlet socket on the power supply.

Connecting the PCT51 to a PC

After installing the PCT51 software and driver on the PC the PCT51 is connected to the PC using the USB lead supplied with the PCT51. The USB socket is located on the rear panel of the electrical enclosure.

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Operation

After loading the software and displaying the mimic diagram click Power On (in Controls) to allow the PCT51 to be operated via the PC.

Filling the Sump Tank

No permanent supply of water is required when operating the PCT51.

Ensure that the drain valve at the rear of the sump tank is fully closed before filling the sump tank.

The sump tank can be filled using a hose or by pouring water through the cut out at the front. The water level should be approximately level with the zero graduation on the scale attached to the flow indicator for normal use. For safe handling the sump tank should be drained before moving the equipment to a different location.

Note: To ensure reliable priming of the water pump after filling for the first time or after draining and refilling the equipment, the flexible tube from the pump outlet should be temporarily disconnected from the system by pressing the latch on the quick release connector. After running the pump briefly at approximately 50% speed, with the tube disconnected to expel any trapped air, the tube can be reconnected for normal operation.

Operating the Water Pump (Manual operation)

The speed of the pump can be varied by the operator to change the flow through the process pipework.

On the mimic diagram (n Controls) set the pump speed to the required percentage of maximum speed by typing in the value or clicking on the up arrow until the required percentage is displayed. For example, to achieve half speed type 50 or click the appropriate arrow until 50 % is displayed.

Operating the Water Pump (PID Control)

The speed of the pump is varied via the PID window on the mimic diagram.

When set to Manual Mode the PID controller gives a fixed pump speed that is set by the operator. The fixed pump setting is also indicated on the mimic diagram. In Manual mode the pump speed can also be varied from the mimic diagram.

When set to Automatic Mode the PID controller varies the pump speed in an attempt to maintain the required flow in the process loop. The output from the controller will depend on the current measured flowrate, the setpoint in the PID controller and the P, I and D settings of the controller.

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In Automatic mode the pump speed is indicated on the mimic diagram but cannot be changed on the mimic diagram.

Operating the On/Off Solenoid Valve (Flow Control)

The solenoid valve is used to inject a small step change to the outflow from the process loop to test the stability of the control loop.

The solenoid valve SOL is opened and closed as and when required by the operator from the mimic diagram (in Controls).

The switch is represented as a button on the screen, and is operated by clicking on it. The switch will display a ‘0’ when the valve is off (closed) and a ‘1’ when the valve is on (open).

The magnitude of the step change can be varied in steps by changing the size of the orifice fitted below the solenoid valve. The orifice size is changed by unscrewing the plastic fitting containing the orifice and replacing it with the required alternative. The fitting incorporates an ‘O’ ring seal and only requires hand tightening. The alternative sizes of orifice are stored in threaded holes at the front of the base plate when not in use.

Alternatively, the magnitude of the disturbance can be varied continuously to any intermediate value using the hand operated valve CV3 above the solenoid valve. However, the magnitude of the step cannot be replicated accurately on different runs when adjusting the flow in this manner.

Changing the characteristics of the flow loop

The flow of water through the process loop and through the solenoid valve can be varied by adjusting inlet valve CV1 and outlet valve CV2 in combination.

34

Operation

35

Closing inlet valve CV1 with outlet valve CV2 open will reduce the flow through the process loop but reduce the head in the process loop, reducing the flow through the solenoid valve when it is open.

Closing outlet valve CV3 with inlet valve CV1 open will reduce the flow through the process loop but increase the head in the process loop, increasing the flow through the solenoid valve when it is open.

Connecting the PCT51 to an external controller

The water pump, solenoid valve and flowmeter on PCT51 are permanently connected to the electrical enclosure.

The 0-5 Volt output from the flowmeter, the 0-5Volt input to control the pump speed and the digital input to open the solenoid valve are available via connectors on the front of the electrical enclosure. This allows a PID controller such as PCT54 or a PLC such as PCT55 to operate the process. The connections between PCT51 and the external controller should be made using the leads supplied with PCT54 or PCT55.

Using Guest (Push) Fittings

Tubes that may be connected to a Guest push fitting require a corresponding rigid tube coupling on the end of the tube. Align the parallel section of the rigid tube with the loose collet on the Guest push fitting and push firmly until the tube stops.

To remove the tube, push the loose circular collet against the body of the Guest push fitting while pulling the tube firmly. The tube will slide out from the fitting. The tube/fitting can be assembled and disassembled repeatedly without damage.

Calibration of the flowmeter

The software includes the facility to recalibrate the flowmeter should this become necessary. Choose Options, Calibrate IFD channels then choose the flowmeter sensor F1 measuring the flow of water. The procedure for calibrating the sensor is described in Operating the Software.

Equipment Specifications

Overall Dimensions Height - 450 mm

Width - 425 mm

Depth - 350 mm

IFD Connections The electrical interface on PCT51 incorporates a PCB that provides the USB connection to a PC. The pin-outs of the 50 way connector on this PCB are as follows:

Pin No

Channel No PCT51 Function Signal Eng Unit

1 Channel 0 Analog Input Not used






7

Channel 6 Analog Input

Drive 1 monitor

(Pump speed)

0-5 V




11

Channel 10 Analog Input

Water Flowrate

(Flowmeter)

0-5 V

0 – 4 l/min




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17 Ground 0V

18 Ground 0V

19 Analog Output 2 Not used

20 Analog Output 3 Not used

21 Ground 0V

22 Channel 0 Analog Output Water pump speed 0-5 V 0-100%

23 Channel 0 Analog Ground 0V

24 Channel 1 Analog Output Not used

25 Channel 1 Analog Ground 0V

26 Ground 0V

27 Ground 0V

28 Channel 0 Digital Input Not used

29 Channel 1 Digital Input Solenoid valve monitor 0/5V



32 Ground 0V





37 Ground 0V

38 Digital Output Line 0 Power enable 0/5V

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39 Digital Output Line 1 Watchdog 0/5V

40 Digital Output Line 2 Remote / Local operation 0/5V

41 Digital Output Line 3 Output 1 (Pump On/Off) 0/5V

42 Digital Ground 0V

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Digital Output Line 4

Output 1 Solenoid Valve

(On/Off)

0/5V

44 Digital Output Line 5 Not used



47 Ground 0V

48 Ground 0V

49 Not used

50 Not used

Other Specifications

Environmental Conditions This equipment has been designed for operation in the following environmental conditions. Operation outside of these conditions may result reduced performance, damage to the equipment or hazard to the operator.

a. Indoor use;

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39

b. Altitude up to 2000 m;

c. Temperature 5 °C to 40 °C;

d. Maximum relative humidity 80 % for temperatures up to 31 °C, decreasing linearly to 50 % relative humidity at 40 °C;

e. Mains supply voltage fluctuations up to ±10 % of the nominal voltage;

f. Transient over-voltages typically present on the MAINS supply;

NOTE: The normal level of transient over-voltages is impulse withstand (over-voltage) category II of IEC 60364-4-443;

g. Pollution degree 2.

Normally only nonconductive pollution occurs.

Temporary conductivity caused by condensation is to be expected.

Typical of an office or laboratory environment

Routine Maintenance

Responsibility To preserve the life and efficient operation of the equipment it is important that the equipment is properly maintained. Regular maintenance of the equipment is the responsibility of the end user and must be performed by qualified personnel who understand the operation of the equipment.

General The equipment should be disconnected from the electrical supply when not in use.

The process loop and sump tank should be drained after use if the equipment is not to be used in the near future. The water should be changed at regular intervals to prevent the growth of algae that may present a hazard to health.

In areas of hard water, the amount of scale in the sump tank and pipework can be reduced by using de-ionised water when filling the sump tank.

Cleaning the Equipment Build-up of scale on the inside of the sump tank can be minimised by drying the vessel when it is to be left unused for some time. Scale that does develop within the sump tank may be cleaned by hand, using a suitable descaler to remove stubborn deposits if required.

Any build up of scale in the pipe work can be removed by passing a mild descaler through the system then flushing thoroughly with clean water. Always follow the instructions provided with the descaler regarding suitable dilution of the chemical.

Accessing the electrical circuits inside the electrical enclosure Maintenance of the PCT51 does not require access to the electrical circuits or components located inside the electrical enclosure. However, in the event of an electrical problem it may be necessary for a competent electrician to gain access to the inside of the enclosure as follows:

Ensure that the equipment is disconnected from the electrical supply (not just switched off).

The electrical circuits inside the enclosure are accessible after unscrewing the front panel then carefully sliding the loose side panel forwards, but only as far as the flexible ribbon cable will allow.

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Laboratory Teaching Exercises

Index to Exercises

Index to Exercises demonstrating Inflow Control by varying pump speed



Exercise C - Proportional control flow (Closed loop, P only and P + I)

Exercise D - Optimising proportional control of flow (Closed loop, P+I+D)

Index to Exercises demonstrating Inflow Control or Outflow Control using an external controller



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Objective

To control the flow of water exiting the process loop by manually varying the speed of a pump supplying water to the loop.

To determine the characteristics of the flow process with different ranges of flow rate through the flowmeter.

To disturb the process by opening and closing a solenoid valve upstream of the flowmeter that diverts water away from the flowmeter.

Method

Using a PC to operate the process, the pump speed (water flow through the flowmeter) will be varied by the operator in an attempt to maintain a steady water flow.

An electronic flowmeter measures the flowrate of the water flowing through the process loop. A flow indicator in the sump tank gives a visual indication of the changes in flowrate and can be used to measure the flow by creating a calibration chart.

With valves CV1 & CV2 fully open, water will be pumped from the sump vessel continuously, the rate determined by the speed of the pump.

Disturbances will be applied to the process by opening and closing the solenoid valve. This changes the flow through the flowmeter resulting in a change in the water level into the flow indicator tube. The magnitude of the disturbance is determined by the size of the orifice fitted below the solenoid valve.

Equipment Required

PCT51 Flow Control Assembly

PC with PCT51 software loaded

Theory

For the flow to remain constant through the process loop, pump speed must match the required flowrate taking into account the solenoid valve, if open. Since the flow of water is proportional to pump speed, the speed must be increased to raise the flow and decreased to lower the flow.

Equipment set up

Ensure that the apparatus has been set up according to the Installation section, the sump filled with clean water and the power supply connected to the socket marked 24V DC IN at the rear of the electrical enclosure.

Before starting this exercise open valves CV1, CV2 and CV3 fully. Fit a 3 mm orifice below the solenoid valve.

Connect the USB socket at the rear of the electrical enclosure to a suitable PC, on which the PCT51 software has been installed, using the USB cable supplied. Check that the PC is switched on then run the PCT51 software and select Experiment Ex1: Flow Control (PC Control).

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Exercise A

Ensure that the Virtual COM port has been enabled using the red telephone icon in the top toolbar.

Choose the icon (or View \ Diagram) to display a mimic diagram of the process.

Click Power On (in Controls).

Set the pump speed to 50 % by typing in the value or by clicking the up arrow (in Controls), so that water is pumped through the flowmeter and into the flow indicator tube. Check that the flow rate indicated is typically 1.5 L/min which equates to approximately 73 mm on the flow indicator tube (the actual values may vary due to manufacturing tolerances).

Click the solenoid valve on the mimic diagram (in Controls) and confirm that water flows from the solenoid and the indicated flow reduces.

Close the solenoid valve and reset the pump speed to 0 %. The equipment is ready for operation.

Procedure

Gradually vary the speed of the pump until the flow rate indicated is 1.5 L/min.

With the flow at a steady value choose the icon to begin data logging and note the flow reading F1 in L/min.

Open the solenoid valve by clicking the button on the mimic diagram (1 indicates that the valve is open). Observe that the indicated flow and the level in the flow indicator tube decrease slightly because the additional outflow via the solenoid valve reduces the flow to the flowmeter. Now increase the pump speed to restore original flow reading of 1.5 l/min.

Close the solenoid valve by clicking the button on the mimic diagram (0 indicates that the valve is closed).

Observe that the indicated flow and the level in the flow indicator tube rises slightly because the water flow from the pump is now passing solely through the flowmeter. When the flow has stabilized note the current pump speed indicated on the mimic diagram then reduce the pump speed to restore original flow reading of 1.5 l/min.

Choose the icon to finish data logging.

Return to the mimic diagram and reduce the pump speed to 0 %.

Choose the icon (or View \ Graph) to display a graph of the response obtained. Observe the rising and falling flowrate as the solenoid is opened and closed and action is taken to restore the flowrate.

Create a new results sheet by selecting the icon in the tool bar of the software

then choose the icon to begin data logging.

Adjust the pump speed until the flowmeter reads 0.05 L/min then note the pump speed and the level in the flow indicator tube. Now increase the pump speed until the flowmeter reads 2 L/min and note the pump speed and the level in the flow indicator

43


44

tube. Increase the pump speed until the flowmeter reads 3 L/min and note the pump speed and the level in the flow indicator tube.

Partially close valve CV1 then try to restore the flowrate to 3 l/min. Observe that the available flow from the pump reduces as the valve is closed.


Return to the mimic diagram and reduce the pump speed to 0 %.

View the graph and observe the different flowrates at different pump speeds. These characteristics will affect the control of the process.

If time permits repeat the exercise with different sizes of orifice fitted to the solenoid valve, E.g. 2 mm to give a smaller disturbance or 4 mm to increase the disturbance. The flow characteristics with different settings of CV1 or CV2 could also be investigated.

Create a new results sheet for each run by selecting the icon in the tool bar of the software.

Results

Save a copy of the results obtained so that the data can be viewed in graphical or tabular format at a later date.

Conclusion

The flow from the pump will only remain steady if the pump speed is constant or there are no disturbances made to the flow.

Water leaving the process loop upstream of the flowmeter, caused by opening of the solenoid valve, will result in reduced flow through the flowmeter. An increase in pump speed is required to restore the required flowrate through the flowmeter.

Closing of the solenoid will result in increased flow through the flowmeter requiring a reduction in pump speed to restore the original flowrate.

It is important that the range of flowrates available from the pump, over the available range of pump speeds, matches the required flow through the process.


Objective

To demonstrate the operation of an On/Off Controller using flowrate as the measured variable to control the operation of a water pump.

To show that On/Off control is not suitable for controlling a variable such as flowrate because a steady flowrate cannot be maintained.

Method

Using a PC to operate the process, the pump speed will be started and stopped by the controller in an attempt to maintain the flowrate at the required setpoint.

An electronic flowmeter measures the flowrate of the water flowing through the process loop. A flow indicator in the sump tank gives a visual indication of the changes in flowrate.

Equipment Required

PCT51 Flow Control Assembly.


Theory

An On/Off controller is a simple and effective way of controlling many processes but does have disadvantages because its output can only be on or off. In the case of the flow process in this exercise the pump is started and stopped.

An on/off controller incorporates a dead band to avoid rapid switching of the controlled variable when at the setpoint i.e. in this case the flow must rise above the setpoint by a fixed amount before the pump switches off and the flow must fall below the setpoint by a fixed amount before the pump starts again.

Note: On PCT51 an On/Off controller with fixed dead band is created by setting the Proportional Band to 0 % in the PID controller. In a commercial On/Off controller the dead band can be varied to suit the process. This allows the choice of less frequent switching but larger variations in the process variable or closer control of the process variable but more frequent switching with attendant wear etc. of the components.

When the measured flow is below the setpoint the pump will be switched on and when the flow exceeds the setpoint the pump will be switched off by the on/off controller. This results in alternate starting and stopping of the pump with corresponding oscillation of the flowrate showing that on/off control is unsuitable for such a process.

Equipment set up



Connect the USB socket at the rear of the electrical enclosure to a suitable PC, on which the PCT51 software has been installed, using the USB cable supplied. Check

45


that the PC is switched on then run the PCT51 software and select Experiment Ex1: Flow Control (PC Control).







Procedure

Choose the PID box on the mimic diagram, set the Proportional Band to 0 %, Integral Time to 0 and Derivation time to 0 then set the Set Point to 1.5 L/min (default at start up). Click ‘Apply’ to enter the changes to the settings.

Choose the Automatic Mode of Operation.

Select the icon to begin data logging.

46

Exercise B

47

The pump will switch on, the flowrate will quickly increase and water will flow into to the flow indicator tube. The flow will instantaneously increase until it reaches the flow set on the controller i.e. the setpoint of 1.5 L/min. When the flow rises above the setpoint by a fixed amount (the dead band) the pump will switch off and the water flow will rapidly drop-off as the pump has stopped. When the flow falls below the setpoint by a fixed amount (the dead band) the pump will switch on again and the cycle will continue resulting in widely fluctuating flowrate that is completely unacceptable. Observe that the level rises and falls in the flow indicator but at reduced amplitude because of the time constant of the indicator (the tube does not indicate instantaneous flowrate because it must fill or drain to indicate a new level).

In the PID controller adjust the set point to 1.0 L/min, click ‘Apply’ then observe the same behaviour at the reduced setpoint.

Adjust the set point to 2.5 L/min and observe the same behaviour the increased setpoint.


Select Manual Mode of Operation and reset pump speed to 0 % on the mimic diagram.

Results

Choose the icon (or View \ Graph) to display a graph of the responses obtained. Observe that the flowrate varies dramatically as the pump starts and stops, indicating that On/Off control is unsuitable for a process with a fast response such as this flow loop.

Conclusion

Where a low cost solution is required, small variations in process variable are acceptable and the response of the process is slow enough then an on\off controller can be used to control a process. The flow process is a fast process and therefore not suitable for on\off control.

The device controlled by an on\off controller (in this case a water pump) is simply on or off as required to maintain the process variable.

The flowmeter and the flow indicator have different response times so the indication from the two devices is different. The flowmeter with a fast response indicates the instantaneous flowrate but the indicator tube with a slow response indicates more of an average.

Exercise C - Proportional control flow (Closed loop, P only and P + I)

Objective

To control the flow of water through the process loop using a proportional controller to automatically vary the speed of the feed pump (flow control).

To determine the response of a process loop when using a P only controller to vary the pump speed.

To determine the response of a process loop when using a P+I controller to vary the pump speed.

To change the flow of water through the process loop by changing the set point on the P or P+I controller.

To test the stability of the flow control loop by applying disturbances using the solenoid valve.

To investigate the effect of different ranges of flow.

Method

Using a PC to operate the process, the pump speed (water flow from the sump tank) will be varied automatically by a proportional controller in an attempt to maintain a steady water flow through the flowmeter into the flow indicator tube.

An electronic flowmeter measures the flowrate of the water flowing through the process loop. A flow indicator in the sump tank gives a visual indication of the changes in flowrate.

The effect of the Proportional Band setting (P) can be demonstrated by configuring a P only controller and observing the response of the process to different settings of P.

The contribution of the of the Integral Time setting (I) can be demonstrated by configuring a P+I controller and observing the response of the process to different settings of I with P fixed then different combinations of P+I.

Disturbances can be applied to the process by opening and closing the solenoid valve. This changes the outflow before the flowmeter resulting in a change to the flow to the flow indicator tube. The magnitude of the disturbance is determined by the size of the orifice fitted below the solenoid valve.

Equipment Required

PCT51 Flow Process.


Theory

Proportional Band (P)

The Proportional Band, P, setting on a process controller makes a change to the output (pump speed on PCT51) that is proportional to the current error value (the difference between the measured flowrate and the set point on the controller). The proportional response can be adjusted by multiplying the error by a constant Kp,

48

Exercise C

called the Proportional Gain. This is related to the Proportional Band setting on the controller as follows:

Proportional Gain (Kp) = 100 % / Proportional Band %

i.e. 100 % P term means unity gain (change in controller output = error at input)

and 50 % P term means a gain of 2 (change in controller output = 2x error at input)

A low setting of the P term (large gain) results in a large change in the output for a given change in the error. If the P term is too low, the system can become unstable. In contrast, a large setting of the P term (low gain) results in a small output response to a large input error, and a less responsive or less sensitive controller. If the P term is too high, the control action may be too small when responding to system disturbances resulting in slow response and offsets of the resulting process variable from the set point.

A Proportional-only controller will not always settle at the set point, but may retain a steady-state offset. Offset can be reduced in Proportional-only control by reducing the P term setting. However, if the P-term is set too small then hunting or oscillating will occur. The offset can be minimised by adding a bias to the set point (setting the set point above or below the required value to compensate for the offset) but this technique is only appropriate if the system characteristics are known and fixed. A better solution is to remove the offset by adding Integral action to the controller (P+I) as described below.

Integral term (I)

The contribution from the integral term is proportional to magnitude and duration of the error. The Integral term in a PID controller is the sum of the instantaneous error over time and gives the accumulated offset that should have been corrected previously. The resulting controller output is the sum of the contribution from the Integral term and the contribution from the P term.

When the I term is correctly adjusted any residual offset in the process variable due to the P term will be gradually reduced by the Integral term until the offset is eliminated. If the time setting of the I term is too long then correction to any offset will be very slow.

However, since the integral term responds to accumulated errors from the past, it can cause the present value to overshoot the setpoint value or to make the process completely unstable if the time setting of the I term is too short. If this occurs the I term makes adjustments to the controller output faster than the process can respond, i.e. the I term winds up the controller output so that the process overshoots considerably, hence the term Integral Wind-up or Integral saturation.

Careful selection of the I term in combination with the P term will give efficient response to changes in the system.

Derivative term (D)

The derivative term slows the rate of change of the controller output. Derivative control is used to reduce the magnitude of the overshoot produced by the I term and improve the combined controller-process stability. However, the derivative term slows the response of the controller. Also, differentiation of a signal amplifies noise and thus this term in the controller is highly sensitive to noise in the error term, and can

49


cause a process to become unstable if the noise and the derivative gain are sufficiently large.

The effect of Derivative action is demonstrated in a later exercise.

Equipment set up



Connect the USB socket at the rear of the electrical enclosure to a suitable PC, on which the PCT51 software has been installed, using the USB cable supplied. Check that the PC is switched on then run the PCT51 software and select Experiment Ex1: Flow Control (PC Control).







Procedure - P only controller

Choose the PID box on the mimic diagram, set the Proportional Band, P, to 200 %, the Integral Time I to 0 and the Derivation time D to 0 then set the Set Point to 1.5 L/min (default at start up). Click ‘Apply’ to enter the changes to the settings.

50

Exercise C


Choose the Automatic Mode of Operation.

The pump will start, the flowrate will gradually increase and water will pass into the flow indicator tube. The water flow will very slowly rise until it reaches a steady state but this will not correspond with the setpoint of 1.5 L/min on the controller because of the offset inherent in a P only controller.

Adjust the set point to 2.0 L/min then click apply and observe the response to a requested increase in water flow. When the flow has settled, return the set point to 1.5 L/min and observe the response.

Open the solenoid valve on the mimic diagram to divert water from the flowmeter. Observe the drop in flowrate and the response of the controller. Close the solenoid valve and observe the response.

Adjust the P term to 150 %, note the response regarding the stability of the pump speed / flowrate and any reduction in offset. Change the setpoint then open and close the solenoid valve as before and observe the responses.

Adjust the P term to 100 % and repeat the above steps.

Gradually reduce the P term and repeat the above steps until the pump speed and flowrate become unstable.


Results – P only controller

Choose the icon (or View \ Graph) to display a graph of the responses obtained.

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Choose Format \ Graph Data and Plot Flow F1 and Set point on 1 axis and Controller Output on the second axis.

Observe the changes in flow and the stability of the responses for each change in P setting with a disturbance or change in set point.

Choose a setting for P that will reduce the offset as much as possible without the pump becoming unstable; this setting will be used in the next part of the exercise introducing Integral action.

Procedure - P+I Controller

Create a new results sheet for this run by selecting the icon in the tool bar of the software.

Choose the PID box on the mimic diagram, set the Proportional Band, P, to the value selected above, the Integral Time, I, to 0 seconds and the Derivation time, D, to 0 then set the Set Point to 1.5 L/min. Click ‘Apply’.


Choose the Automatic mode of operation and allow the flowrate to stabilise.

Set the I term to 100 seconds in the PID controller then click ‘Apply’. Observe that the pump speed changes very slowly until the flowrate matches the set point. When the flowrate has settled, open the solenoid valve to disturb the process, observe that the flow initially reduces slightly, the pump speed increases and the flowrate gradually returns to the set point. When the flowrate has settled close the solenoid valve and allow the flow to settle again.

Adjust the set point to 2 L/min then click ‘Apply’ and observe the response to a requested increase in flowrate. When the water flow has settled, return the set point to 1.5 L/min and observe the response.

Set the I term to 50 seconds in the PID controller then click ‘Apply’. Observe that the flowrate gets closer to the set point faster than before. When the flow has settled as much as possible open then close the solenoid valve as before to disturb the process.

Adjust the set point to 2 L/min then click ‘Apply’ and observe the response to a requested increase in flowrate. When the water flow has settled, return the set point to 1.5 L/min and observe the response.

Continue reducing the Integral time and repeating the disturbance and set point changes until the pump speed and flowrate become unstable.

Results – P+I controller

Choose the icon (or View \ Graph) to display a graph of the responses obtained.

Choose Format \ Graph Data and Plot Flow F1 and Set point on 1 axis and Controller Output on the second axis.

Observe the changes in flowrate and the stability of the responses for each change in I setting with a disturbance or change in set point.

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Exercise C

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Choose a setting for I that gives stable control and reduces any offset swiftly without causing the system to be unstable.

Since the effect of Integral Action is related to the Proportional Band setting (reduced PB gives greater effect for any setting of I) the above exercise should be repeated at a completely different value of PB to determine the necessary change in I for effective control of the flow and to demonstrate the relationship between P and I.

If time permits repeat the exercise with different sizes of orifice fitted to the solenoid valve, e.g. 2 mm to reduce the disturbance or 4 mm to increase the disturbance. The flow characteristics with different settings of CV1 and CV2 could also be investigated e.g. partly closing valve CV1 to reduce the flow or increasing the flow by opening the valve.

Conclusion

A large Proportional Band setting will result in stable control but will result in slow changes and large offsets in the process variable.

Reducing the Proportional Band will improve the speed of response and give smaller offsets but the process may become unstable if the proportional band in reduced too far.

Optimum results are obtained with a suitable combination of Proportional and Integral action to eliminate any offset from the setpoint.

Reducing the Integral time setting increases the speed at which any offset is reduced but settings that are too short will result in instability because the process is unable to respond quickly enough to the changes from the controller. The effect is called integral saturation or integral wind up and must be avoided.

Increasing the Proportional Band reduces the effect of Integral Action so shorter setting of I is required to eliminate offset quickly.

Exercise D - Optimising proportional control of flow (Closed loop, P+I+D)

Objective

To control the flow of water in the process loop using a proportional PID controller to automatically vary the speed of a pump.

To determine the optimum settings for the P, I and D terms appropriate to the Temperature process and to test the stability of the system by applying disturbances and changing the set point.

Method

Using a PC to operate the process, the pump speed (water flow through the process loop) will be varied automatically by a proportional controller in an attempt to maintain a steady flowrate (F).

Appropriate settings for the Proportional Band setting (P), the Integral Time (I) and the Derivative Time (D) will be determined by applying a step change to the process and observing the response of the system (the Reaction Curve Method).

The parameters determined using the Reaction Curve Method can be refined by testing the response of the system with these parameters set.

Disturbances can be applied to the process by opening and closing the solenoid valve. Opening the valve diverts flow away from the flowmeter resulting in a change in the flow through the flowmeter and floe indicator tube. The magnitude of the disturbance is determined by the size of the orifice fitted below the solenoid valve.

Note: This exercise assumes a basic knowledge of the equipment and the software from experience gained performing previous exercises. Refer to previous exercises if further information is required.

Equipment Required

PCT52 Temperature Process.


Theory

REACTION CURVE METHOD

The controller output is operated manually so that a step change is applied to the process without corrections being applied by the controller.

The start of the step change is determined from the graph of controller output, the size of the step change is recorded as M % (change in controller output) and the shape of the Flow curve is recorded.

A typical response curve is shown below:

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Exercise D

Typical response with the Reaction Curve method

Draw a straight line through the point of maximum slope so that the line intersects the time axis.

Measure the dead time L in minutes. (Time at which step change is applied to time where straight line intersects time axis.)

Calculate the maximum slope R.

Determine R1 using the equation

The optimum settings for the controller may be calculated as follows:

ULTIMATE PERIOD METHOD (Ziegler-Nichols)

This alternative technique utilises the response of the system with the controller configured for Proportional control only. It cannot be applied to relatively stable processes because the system must have the ability to oscillate continuously.

The Proportional Band is gradually reduced in steps and at each step a step change is applied to test the stability of the system. This is repeated until the process variable continually oscillates. The correct point is achieved when the amplitude of the oscillations remains constant. If the oscillations gradually die away then the P term should be decreased slightly. Conversely if the oscillations gradually increase then the P term should be increased until the amplitude remains constant.

Note the setting of the Proportional Band, PBc, at which continual cycling occurs. From the graph obtained, measure the period of the oscillation, Pc, in minutes.

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Typical response with the Ultimate Period method

The optimum settings for the controller may be calculated as follows:

Equipment set up

Ensure that the apparatus has been set up as in previous exercises. Ensure that the Virtual COM port has been enabled using the red telephone icon in the top toolbar allowing the pump and solenoid valve to be operated from the PC and the Flowmeter to read correctly.

Procedure

REACTION CURVE METHOD

Set the PID controller for Manual Mode of operation.

Adjust the output from the controller to give a steady flowrate (F) with the pump speed set to 50%.


Leave the controller in manual operation and apply a step disturbance to the process by increasing the output slightly (motor speed). Note the magnitude of the step change applied (delta = M %).

The step change will result in an increase in flowrate. The open loop response may be analysed from the graph to determine the optimum settings for P, I and D using the equations listed in the theory above.

Having calculated the starting values set the controller for Automatic operation and enter these values for P, I and D then click Apply.

Test the stability of the process by applying disturbances by changing the set point or opening and closing the solenoid valve. (Refer to previous exercises if necessary for information about this).

ULTIMATE PERIOD METHOD (Ziegler-Nichols)

Set the controller for Proportional control only, initially with a P term of 200 %. Set the controller for Automatic Mode of operation.

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Exercise D

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Allow the process variable to settle then apply a step change to the process by opening the solenoid valve.

If the process variable settles to a steady new value, decrease the P term and re-apply a step change.

Continue adjusting the P term and applying a step change until the process variable continually oscillates.

Note the setting of the P term, PBc, at which continual cycling occurs.

From the graph obtained measure the period of the oscillation, Pc, in minutes.

The closed loop response may be analysed from the graph to determine the optimum settings for P, I and D using the equations listed in the theory above.

Having calculated the starting values set the controller for Automatic operation and enter these values for P, I and D then click Apply.

Test the stability of the process by applying disturbances by changing the set point or opening and closing the solenoid valve. (Refer to previous exercises if necessary for information about this).

Results

Retain graphs for each test showing the response of the system using Open Loop and close Loop tuning techniques.

Conclusion

Starting values for P,I and D terms on a process controller can be determined by testing the response of the system using Open Loop or Closed Loop tuning techniques.

The values obtained using these techniques are only a starting point and minor adjustments may be necessary to obtain optimum control of a process.


Objective

To control the flow of water in the process loop using a Commercial PID controller to automatically vary the speed the pump to vary the flow into the process loop (inflow control).

To demonstrate the operation of a commercial controller and the use of menus to configure the instrument.

To configure the controller to indicate process variables in engineering units (default setting 0 – 100% input).


Method

The PCT54 PID Controller, or equivalent PID controller, can be used to control the process by connecting the signals from the controller to the electrical sockets on the front of the electrical console.

Equipment Required

PCT51 Flow Process

PCT54 PID Controller or alternative PID controller with appropriate input and output signals:

For Inflow control: 0 – 5 Volt input and 0 – 5 volt output

For Outflow control 0 – 5 Volt input and relay output

PC with PCT51 software loaded (only required for logging the response of the process).

Theory

Any of the previous exercises performed using a PC to control the process can be repeated using a commercial PID controller, typically PCT54. A PC can be used to log the response of the process by selecting the appropriate exercise when loading the software:

Choose Ex 2 - Inflow Control (External Control) when controlling the water pump in a PID loop

Step changes can be applied to the process using the front panel controls on PCT54.

Equipment set up / Procedure

Refer to the instruction manual supplied with PCT54 for details about connections to the electrical console on the process and operating the PID controller itself.

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Objective

To control the flow of water in the process loop using a Commercial Programmable Logic controller to automatically vary the pump speed to vary the flow into the process loop (inflow control).

To demonstrate the operation of a commercial Programmable Logic Controller with touch panel interface.


To demonstrate how the configuration of a PLC can be changed using downloadable software.

Method

The PCT55 Programmable Logic Controller, or equivalent PLC, can be used to control the process by connecting the signals from the controller to the electrical sockets on the front of the electrical console.

Equipment Required

PCT51 Flow Process

PCT55 Programmable Logic Controller or alternative PLC with appropriate input and output signals:

For Inflow control: 0 – 5 Volt input and 0 – 5 volt output

For Outflow control 0 – 5 Volt input and relay output

PC with PCT51 software loaded (only required for logging the response of the process).

Theory

Any of the previous exercises performed using a PC to control the process can be repeated using a commercial Programmable Logic Controller, typically PCT55. A PC can be used to log the response of the process by selecting the appropriate exercise when loading the software:

Choose Ex 2 - Inflow Control (External Control) when controlling the water pump in a PID loop

Step changes can be applied to the process using the front panel controls on PCT55.

Equipment set up / Procedure

Refer to the instruction manual supplied with PCT55 for details about connections to the electrical console on the process and operating the Programmable Logic Controller itself.

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Contact Details for Further Information

Main Office: Armfield Limited

Bridge House West Street Ringwood Hampshire England BH24 1DY

Tel: +44 (0)1425 478781 Fax: +44 (0)1425 470916 Email: [email protected] [email protected] Web: http://www.armfield.co.uk

US Office: Armfield Inc.

436 West Commodore Blvd (#2) Jackson, NJ 08527

Tel: (732) 928 3332 Fax: (732) 928 3542 Email: [email protected]

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Documents

PCT51 Issue 1 Instruction Manual