38-004 Pron Pressure Process Manual v2p0 CD

7/24/2019 38-004 Pron Pressure Process Manual v2p0 CD

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Electricity & Electronics

Control & Instrumentation

Process Control

Mechatronics

Telecommunications

Electrical Power & Machines

PressureProcessCon

trol

R

eferenceM

anual

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Procon Pressure Process

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Feedback Instruments Ltd, Park Road, Crowborough, E. Sussex, TN6 2QR, UK.Telephone: +44 (0) 1892 653322, Fax: +44 (0) 1892 663719.

email: [email protected] website: http://www.feedback-group.com

Manual produced from software version: v2.0

Date: 19/10/2010

Feedback Part No. 116038004


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Procon Pressure Process Preface

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THE HEALTH AND SAFETY AT WORK ACT 1974

We are required under the Health and Safety at Work Act 1974, to make available to users of this equipment certain informationregarding its safe use.+

The equipment, when used in normal or prescribed applications within the parameters set for its mechanical and electricalperformance, should not cause any danger or hazard to health or safety if normal engineering practices are observed and they are usedin accordance with the instructions supplied.

If, in specific cases, circumstances exist in which a potential hazard may be brought about by careless or improper use, these will bepointed out and the necessary precautions emphasised.

While we provide the fullest possible user information relating to the proper use of this equipment, if there is any doubt whatsoeverabout any aspect, the user should contact the Product Safety Officer at Feedback Instruments Limited, Crowborough.

This equipment should not be used by inexperienced users unless they are under supervision.

We are required by European Directives to indicate on our equipment panels certain areas and warnings that require attention by theuser. These have been indicated in the specified way by yellow labels with black printing, the meaning of any labels that may be fixed tothe instrument are shown below:

CAUTION -RISK OFDANGER

CAUTION -RISK OF

ELECTRIC SHOCK

CAUTION -ELECTROSTATIC

SENSITIVE DEVICE

Refer to accompanying documents

PRODUCT IMPROVEMENTS

We maintain a policy of continuous product improvement by incorporating the latest developments and components into our equipment,even up to the time of dispatch.

All major changes are incorporated into up-dated editions of our manuals and this manual was believed to be correct at the t ime ofprinting. However, some product changes which do not affect the instructional capability of the equipment, may not be included until it isnecessary to incorporate other significant changes.

COMPONENT REPLACEMENT

Where components are of a Safety Critical nature, i.e. all components involved with the supply or carrying of voltages at supply

potential or higher, these must be replaced with components of equal international safety approval in order to maintain full equipmentsafety.

In order to maintain compliance with international directives, all replacement components should be identical to those originallysupplied.

Any component may be ordered direct from Feedback or its agents by quoting the following information:

1. Equipment type

3. Component reference

2. Component value

4. Equipment serial number

Components can often be replaced by alternatives available locally, however we cannot therefore guarantee continued performanceeither to published specification or compliance with international standards.


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OPERATING CONDITIONS

This equipment is designed to operate under the following conditions:

Operating Temperature 10C to 40C (50F to 104F)

Humidity 10% to 90% (non-condensing)

DECLARATION CONCERNING ELECTROMAGNETIC COMPATIBILITY

Should this equipment be used outside the classroom, laboratory study area or similar such place for which it is designed and sold thenFeedback Instruments Ltd hereby states that conformity with the protection requirements of the European Community ElectromagneticCompatibility Directive (89/336/EEC) may be invalidated and could lead to prosecution.

This equipment, when operated in accordance with the supplied documentation, does not cause electromagnetic disturbance outsideits immediate electromagnetic environment.

COPYRIGHT NOTICE

Feedback Instruments Limited

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by anymeans, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of Feedback Instruments Limited.

ACKNOWLEDGEMENTS

Feedback Instruments Ltd acknowledge all trademarks.

IBM, IBM - PC are registered trademarks of International Business Machines.

MICROSOFT, WINDOWS 7, WINDOWS VISTA, WINDOWS XP, WINDOWS 2000, WINDOWS NT, WINDOWS ME, WINDOWS 98,

WINDOWS 95, WINDOWS 3.1 and Internet Explorer are registered trademarks of Microsoft Corporation.

WARNING:

This equipment must not be used in conditions of condensing humidity.


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Chapter 1Procon Pressure Process Pressure Rig Introduction

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Pressure Rig Introduction

Objectives

To learn how to navigate the Discovery software

To familiarise the student with the Pressure rig and how to pressurise the system.


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Chapter 1Procon Pressure Process Pressure RigIntroduction

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Practical 1: Navigating the Discovery Software

Objectives and Background

Although the Discovery Laboratory environment is very easy to operate, these notes willhelp you use all its facilities more quickly.

If there is a demonstration assignment, slider controls in the software perform functionsthat would normally be performed on the hardware. In normal assignments, if the any ofthe hardware systems fail to initialise the system reverts to demonstration mode. Thismeans that none of the test equipment is available.


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Practical 1: Navigating the Discovery Software

Perform Practical

This Practical requires no patching connections and there are no measurements to betaken.

The assignment window opens when an assignment is launched. The assignment windowconsists of a title bar across the top, an assignment side bar at the right-hand edge, andthe main working area. By default, the overall assignment objectives are initially shown inthe main working area whenever an assignment is opened. The assignment windowoccupies the entire screen space and it cannot be resized (but it can be moved bydragging the title bar, and it can be minimised to the task bar). The title bar includes thename of the selected assignment. The side bar contains the Practicals and any additionalresources that are relevant for the selected assignment. The side bar cannot berepositioned from the right-hand edge of the assignment window. An example of anassignment window is shown below.

The precise appearance of the assignment window will depend on the skin that has beenselected by your tutor. However, the behaviour of each of the buttons and icons willremain the same, irrespective of this.

The clock (if you have one active) at the top of the side bar retrieves its time from thecomputer system clock. By double clicking on the clock turns it into a stop watch. To startthe stop watch single click on the clock, click again to stop the stop watch. Double clickingagain will return it to the clock function.


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There are a number of resource buttons available in the assignment side bar. These arerelevant to the selected assignment. In general, the resources available will vary with theassignment. For example, some assignments have video clips and some do not. However,the Technical Terms, Help and Auto Position buttons have identical functionality in everyassignment. You can click on any resource in any order, close them again, or minimisethem to suit the way you work.

Practicals are listed in numerical order in the side bar. When you hover the mouse over aPractical button, its proper title will briefly be shown in a pop-up tool-tip. There can be upto four Practicals in any assignment. You can have only one Practical window open at anytime.

To perform a Practical, left-click on its button in the assignment side bar. The assignmentobjectives, if shown in the main working area, will close, and the selected Practical willappear in its own window initially on the right-hand side of the main working area, asshown below. You can move and resize the Practical window as desired (even beyond theassignment window) but its default size and position allows the test equipment to bedisplayed down the left-hand side of the main working area without overlapping theinstructions for the Practical.

Again, the precise appearance of the Practical window can be determined by your tutorbut the behaviour of each of the buttons and icons will remain the same, irrespective ofthis. Whatever it looks like, the Practical window should have icons for the test equipment,together with buttons for Objectives & Background, Make Connections, Circuit Simulatorand Test Equipment Manuals. These resources are found in side bar, located on the right-hand edge of the Practical window. The resources will depend on which Practical youhave selected. Therefore not all the resources are available in every Practical. If aresource is unavailable, it will be shown greyed out. To open any resource, left-click on its


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icon or button. Note that when you close a Practical window, any resources that you have

opened will close. You may open any resource at any time, provided it is available duringthe Practical. The Circuit Simulator will only be available if you have one loaded.

Note that if the hardware is switched off, unavailable, or its software driver is not installed,all the test equipment is disabled. However, you can open any other window. If you switchon the hardware it will be necessary to close the assignment window and open it again toenable the test equipment.

Resource Windows

These are standard, browser-like windows that may be moved, resized and scrolled. Youmay minimise or maximise them. The system defaults to Auto Position, which means thatas you open each resource window it places it in a convenient position. Most resourcewindows place themselves where the main lab window opens out. Each one lays over theprevious one. You can select which one is on top by clicking the tab at the top of eachwindow. You can see how many windows you have open from the number of tabs. If youwant to see several at once then drag them to where you wish on the screen. If you closea window it disappears from the resources tab bar.

If you want to return all the windows to their default position simply click the Auto Positionbutton in the assignment side bar.

Make Connections Window

This movable and resizable window shows the wire connections (4mm patch leads) youneed to make on the hardware to make a practical work. The window opens with noconnections shown. You can show the connections one by one by clicking the Show Nextbutton or simply pressing the space bar on the keyboard. If you want to remove theconnections and start again click the Start Again button. The Show Function buttontoggles the appearance of the block circuit diagram associated with the Practical.

Test Equipment

The test equipment will auto-place itself on the left of the screen at a default size. Youmay move it or resize it at any time. Note that below a useable size only the screen of theinstrument will be shown, without the adjustment buttons. Each piece of test equipmentwill launch with default settings. You may change these settings at any time. There is an


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auto anti-alias feature that prevents you setting time-base or frequency settings that maygive misleading displays.

You may return to the default settings by pressing the Default button on each piece of testequipment. If you wish to return all the equipment to their original positions on the left ofthe screen click Auto Position on the side bar of the assignment window.

Note that if you close a piece of test equipment and open it again it returns to its defaultposition and settings.

If you want more information on how a piece of test equipment works and how to interpretthe displays, see the Test Equipment Manuals resource in the Practical side bar.

On slower computers it may be noticeable that the refresh rate of each instrument isreduced if all the instruments are open at once. If this is an issue then only have open theinstrument(s) you actually need to use.

Test Equipment Cursors

If you left click on the display of a piece of test equipment that has a screen, a greencursor marker will appear where you have clicked. Click to move the cursor to the part ofthe trace that you wish to measure. If you then move the mouse into the cursor a tool-tipwill appear displaying the values representing that position. Note if you resize or changesettings any current cursor will be removed.

Perform Practical Window

This window contains the instructions for performing the practical, as well as a block, orcircuit, diagram showing the circuit parts of the hardware board involved in the Practical.On the diagram are the monitoring points that you use to explore how the system worksand to make measurements. The horizontal divider bar between the instructions and thediagram can be moved up and down if you want the relative size of the practicalinstruction window to diagram to be different. Note that the aspect ratio of the diagram isfixed.

Information Buttons on Practical Diagrams


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On many of the symbols on the diagram you will find a button that gives access to new

windows that provide more information on the circuit that the symbol represents. Note thatthese windows are modal, which means that you can have only one open at a time andyou must close it before continuing with anything else.

A Further Information point looks like this

Probes

The practical diagram has probes on it, which start in default positions. These determinewhere on the hardware the signals are being monitored.

Selecting and Moving the Probes

Probes are indicated by the coloured icons like this .

If this probe is the selected probeit then looks like this (notice the black top to theprobe). You select a probe by left clicking on it.

Monitor points look like this

If you place the mouse over a monitor point a tool-tip will show a description of what signalit is.

You can move the selected probe by simply clicking on the required monitor point. If youwant to move the probe again you do not have to re-select it. To change which probe isselected click on the probe you want to select.

You can also move a probe by the normal drag-and-drop method, common to Windowsprograms.

Probes and Test Equipment Traces

The association between probes and traces displayed on the test equipment is by colour.Data from the blue probe is displayed as a blue trace. Yellow, orange and green probes

and traces operate in a similar way. Which piece of test equipment is allocated to whichprobe is defined by the practical.


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Note that the phasescope shows the relative phase and magnitude of the signal on itsinput probe using another probe as the reference. The reference probe colour is indicatedby the coloured square to the top left corner of the phasescope display.

Practical Buttons

On some Practicals there are buttons at the bottom of the diagram that select someparameter in the practical. These can be single buttons or in groups. Only one of each

button in a group may be selected at one time.

Slider Controls

Where slider controls are used you may find you can get finer control by clicking on it andthen using the up and down arrow keys on your keyboard.


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Practical 1 Introduction


The successful designand operationof industrial plant requires the optimum choices ofinstrumentation and control equipment together with the ability to commission, monitorand maintain such equipment.

Technicians and engineers need to be trained in these skills, particularly in view of therapid advances in the use of electronics and microcomputers in process control.

This range of specially designed equipment allows practical appreciation andunderstanding of the whole spectrum of process control technology from thecharacteristics of individual components to complex control loops operating on realprocesses.

This assignment describes the 38-714 Pressure Process Rig, which is part of the Proconrange of equipment designed to introduce and demonstrate the principles of processmeasurement and control.

The system includes those pneumatic control components of interest to the processindustries. The design allows study of component operation and connection to electrical

control devices through the use of pressure/current transducers.

A photograph of the Pressure Process Rig38-714 is shown below:


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The front panel of the rig incorporates a schematic diagram of the equipment whichidentifies the major components and relevant connections in standard pneumatic notation.

The unit consists of a pipeline on which are mounted a Pneumatic Control Valve, OrificeBlockand pressure tappings.

The flow discharges directly to atmosphere or via an Air Receiverto vary the process lag.The valve is operated from a Current to Pressure Converter, and sensors for direct anddifferential pressure facilitates measurement of pressure and flow respectively.


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Practical 1 Introduction to the Pressure Rig

Perform Practical

This Practical requires no patching connections and there are no measurements to betaken.

Process Rig Controller

The square root extraction facilityof the 38-300 Process Controller is used with theCurrent to Pressure Converter (I/P) to provide a linear signal. Both sensors are providedwith conditioners. The pipework and fittings are mounted on a support frame which isdesigned to stand on a bench top.

The unit is designed to operate with the 38-200 and 38-300 Process InterfaceandProcess Controllerto configure open or closed loop control circuits. These are exploredin greater detail within a later assignment.

Compressed air for the pneumatic instrumentation and process is connected to a commoninlet. Air for the instrumentation is regulated by a Regulator R1and the operating pressureis indicated on a Gauge G1. Air for the process is regulated by a Regulator R2and the

operating pressure is indicated on Gauge G3.

The pneumatic instrumentation comprises an I/P Converterand Pneumatic ControlValve. The I/P Converter accepts a 4-20mA control signal from the 38-200 ProcessInterface and converts this to a 3-15psi pneumatic signal which operates the control valve.

Rig Control Valves

The control valvecomprises a diaphragm actuator which positions the stem of a plugtype valve. An indicator on the valve stem shows the actual position of the valve.

A gaugeG2indicates the pneumatic signal applied to the control valve by the I/PConverter. The 4-20mA input to the I/P Converter can be connected to the 38-200Process Connections or the Servo Valve connection.

The air flowing through the process pipe passes through the Pneumatic Control Valve andan Orifice Block assembly before discharging to atmosphere via a Diffuser.

A set of manual valvesV1, V2and V3allow a rear-mounted air receiverto be connectedin series or parallel with the process pipe to change the response of the system (to varythe process lag). The Air Receiver incorporates a pressure relief valve.

Step changes may be applied to the process by bleeding air through an additional Diffuserby opening and closing the Valve V4, V5 and V7.


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This rig incorporates pneumatic control components of great interest to the processindustries. The design allows study of component operation and connection of controldevices through the use of current to pressure converters.

Process Controller and Interface

This Discoverysoftware contains an integral data loggerand configuration program.

This software automatically configures the 38-300 Process Controller, through a serial portallowing it to be immediately used with each practical.

Before attempting any of the practicals:

Ensure that the Process Controller is connected to the serial port of your computer.Communication Port 3 (Com3) is used by default. If you connect your Process Controllerto a different Com port, the Com port the software uses can be changed to the appropriateCom port using the supplied Discovery 3 Com Port Changer software.

Ensure that the controller is given the identity '1'. If you are unsure about how to check thisvalue, please refer to the ABB manual that is supplied with your controller.

Ensure that the switches on the rear of the controller are correctly set up. If they areswitched incorrectly, the computer will not be able to communicate to the controller.

When you start certain practicals, a small delay will occur while the computer sets theprocess controller parameters.

You will be presented with different controls depending upon the assignment and practicalthat is being studied.


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Practical 2 System Pressurisation


This practical instructs how to set-up the 38-714 Pressure Process Rig and its associatedcomponents.


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Practical 2 System Pressurisation

Perform Practical

The Pressure Rig is made up of the following components:

Pneumatic Control Valve, this contains a 'diaphragm actuator'.Gauge G2. This shows the pneumatic signal applied to the Control Valve by the I/PConverter.

I/P Converter. This component accepts a 4-20mA signal from the Process Interface andconverts this to a 3-15psi signal.Gauge G1. Displays the operating pressure which is controlled by a regulator.Regulator R1. This control is used to control the pressure going into the I/P converter.Air Filter. Source of Compressed air for the whole process rig. Arrow indicates directionof flow.Regulator R2. Used to control the pressure to parts of the process rig.Gauge G3. Used to display the operating pressure.Flowmeter. An instrument used to determine the rate of flow.Gauge G4.Orifice Block.

Gauge G5.Valve V1. When connected to a rear-mounted air receiver, allows you to vary theresponse of the system (by changing the process lag).Gauge G6. Measures the pressure in air receiver.Valve V2. Allows air to be transferred into the air receiver.Valve V3. Allows air to be transferred into the air receiver.Valve V4. Changes in the behaviour of the process can be performed by bleeding airthrough a diffuser.Valve V5. Changes in the behaviour of the process can be performed by bleeding airthrough a diffuser.Valve V6 + V7. Changes in the behaviour of the process can be performed by bleedingair through the valve and adjustable diffuser.Pressure Sensors. The Differential Pressure Sensor and the Pressure Sensor are used totake measurements across the orifice block. This information can then be used by theprocess controller.Representation of Process Rig. On the bottom lies a schematic representation of all thecomponents of the Pressure Process Rig. Identify all the parts that have been displayed.

Practical

Connect a supply of clean compressed air to the inlet using a reinforced air hose. The

supply must be capable of providing the required volume of compressed air at theoperating pressure, otherwise flow and pressure in the system will be inadequate forsatisfactory demonstrations.


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Warning !!

The maximum supply pressure should not exceed 40psi. Supply pressure should beadequately and reliably regulated prior to presentation to the Pressure Process Rig.

Identify all the relevant gauges and valves on the Pressure Rig. Open valve V1and V3adjacent to the air tank connection, close valves V2, V4, V5and V6.

Adjust instrumentation pressure regulator R1to give 25psiat G1. Pull the collar out toadjust the regulator. Turn the collar clockwise to increase the downstream pressure andanticlockwise to reduce the pressure. Push the collar back into place after adjustment.

Adjust process pressure regulator R2to give 10psiat G3. Air will flow through the system,pressurising the pipes and Air Receiver to 10 psi.


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Chapter 2Procon Pressure Process Pressure Rig Familiarisation

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Pressure Rig Familiarisation

Objectives

To familiarise the student with the Pressure Rig and demonstrate how to calibrate thevarious components.


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Chapter 2Procon Pressure Process Pressure RigFamiliarisation

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Practical 1 Current Source Calibration


This practical demonstrates the procedure that should be employed when calibrating theProcess Interface 38-200 Current Source


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Block Diagram

Make Connections Diagram


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Practical 1 Current Source Calibration

Perform Practical

Use the "Make Connections" diagram to make the required connections on the hardware.

Calibrate the Process Interface 38-200 Current Source as follows.

Connect the Current Source to the Digital Display Module 38-490 as shown in the "MakeConnections" diagram

Turn on the 38-200 Process Interface.

Turn the Current Source control fully anticlockwise to reduce the output to the minimum.The display should read 4mA or 0%. If it does not, adjust the zero control using a smallscrewdriver or trim tool until the display shows 4mA or 0%.

Turn the Current Source control fully clockwise to increase the output to the maximum.The display should read 20mA or 100%. If it does not, adjust the span control.

The Current Source is now calibrated.


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Practical 2 I/P Converter and Pneumatic Control Valve Operation


The aim of this practical is to understand the operation of the I/P converter, and how itcontrols the pneumatic control valve.


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Block Diagram



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Practical 2 I/P Converter and Pneumatic Control Valve Operation

Perform Practical


Check operation of I/P Converter and Pneumatic Control Valve.

The Pressure Sensors are very delicate instruments. They may be damaged if presentedwith differential pressures in excess of 30psi.

Connect the I/P Converter to the 38-200 4-20mA supply by making the connections shownin the "Make Connections" diagram.

Turn on the 38-200 and pressurise the system as per the pressurisation practical

Set the Current Source Output to minimum (4mA) by turning the adjusting knob fullyanticlockwise. Gauge G2should indicate 3 psiwith control valve fully open. The indicatoron the valve stem should be in the raised position.

Set the Current Source Output to maximum (20mA) by turning the adjusting knob fullyclockwise. Gauge G2should indicate 15 psiwith control valve fully closed. The indicatoron the valve stem should be in the lowered position.

Note that the indicator on the valve stem provides only an approximate indication of valve

position.

Note:If the pressures indicated on G2differ from the values stated above it will benecessary to recalibrate the I/P Converter. This procedure is detailed in the I/P ConverterAssignment.


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Practical 3 Pressure Sensor and Transmitter


In this practical you will learn the method of checking the operation of the Pressure Sensorand Transmitter.


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Block Diagram



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Practical 3 Pressure Sensor and Transmitter

Perform Practical


Checking the operation of the Pressure Sensor and Transmitter.

Pressurise the System as in the pressurisation practical

Drain all pressure from the system by fully closing R2and fully opening V2, V4and V5.After a minute or two the system will be at atmospheric pressure throughout. The DigitalDisplay Module should show 4mA or 0%. If it does not, adjust the zero control until thedesired reading is obtained.

Pressurise the Air Receiver by opening V1and closing V2,V4and V5 then adjusting R2toproduce a reading 0.7 baror 10psion G3. After a few moments the Air Receiver pressuregauge G6 will read 10psi.

The Digital Display Module should read 20mAor 100%. If it does not, adjust the spancontrol until the desired reading is obtained. Repeat the above process checking readings

of 0% at atmospheric pressure and 100% at 10psi.


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Practical 4 Differential Pressure Sensor and Transmitter


In this practical you will learn the method of checking the operation of the DifferentialPressure Sensorand Transmitter.


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Block Diagram



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Practical 4 Differential Pressure Sensor and Transmitter

Perform Practical


Checking operation of Differential Pressure Sensor and Transmitter.

Pressurise the System as in the pressurisation practical

Open valves V2, V4, V5, V6and V7. Close valves V1and V3(ensure V7is fully open).

Drain all pressure from the system by fully closing R2and fully opening V2. After a fewmoments the system will be at atmospheric pressure throughout. The Digital DisplayModule should show 4mA or 0% to indicate the zero flow condition. If it does not, adjustthe zero control until the desired reading is obtained.

Create a full flow condition by adjusting R2until a 10psidifference is shown between thereading on G4and the reading on G5. This should easily be achieved. The Digital DisplayModule should show 20mA or 100%. If it does not, adjust the span control until the desired

reading is obtained. When G4indicates 10psi and G5indicates zero the flow meter willshow a flow of approx 24 litres/min.


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Chapter 3Procon Pressure Process Controller Familiarisation

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Controller Familiarisation

Objectives

To familiarise the student with the process controller and demonstrate how to setupvarious parameters including the serial communications with a PC..

To learn about control systems and automatic control systems.


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Chapter 3Procon Pressure Process ControllerFamiliarisation

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38-300 Process Controller

The Process Controller (38-300)unit is powered by the Process Interface(PI) andincludes the ABB Kent-Taylor Commander 350process controller and labelled inputsand outputs, to and from the Process Interface (PI).

The ABB Commander 350is a universal digital microprocessor-based single loopprogrammable controller, that measures, displays and controls temperature, pressure,liquid level, flow and other process parameters.

For this reason, the controller accepts a large variety of input signal types:

Thermocouple (THC)Resistance thermometer (RTD)Linear voltage or currentResistanceNon-linear voltage or current from temperature transmittersand other variables transduced to a suitable voltage or current.

In your case, since the 38-300 will control the Process Interface (PI), its process inputsand control outputs are of the 4-20mA loop current type. The 38-300 features local,

remote or dual set-point, and retransmission of set-point or process variable. In addition,according to the user requirements, there are four logic inputs (one on the rear) and fourtime proportioned, voltage activated relays, labelled n.o(normally open) and n.c(normallyclosed).

The industry standard serial communication RS485 and RS232 interfaces are included asstandard on the rear panel of the 38-300, so that a personal computer (PC) cancommunicate with it and control of the process carried out using the Discovery softwarepackage.

The 38-300 is equipped with control algorithms for various types of control, including;

On/OffPIDRamp/Soak (profile sequencing with up to 9 programs)Dual Output (Heat/Cool)Current ProportioningTime ProportioningPosition ProportioningAutomatic bumpless transfer from manual to auto mode and vice versa

An autotunefacility is provided, which can analyse the requirements of a process undercontrol, and select suitable control parameters for optimum performance.


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Anti-reset windup is a technique included to prevent a large control effort building up when

attempting to eliminate a deviation caused by a physical problem.

Each of these features will be explained fully as it arises through the increasing use of the38-300 in this and further assignments. Instrument set up is restricted to authorised usersthrough multiple levels of security.

Users can select the instrument functionality required, from menus, using the eight tactilemembrane keys and the three high intensity seven-segment displays plus the deviationbar graph. Configuration data is stored in non-volatile memory.

The controller is equipped with control algorithms for various types of control that werementioned earlier. These will be illustrated in later assignments, so that you becomefamiliar with the full capabilities of the 38-300.

The 38-300 contains analogue-to-digital and digital-to-analogue converters. The sampletime of these devices must be faster than the dynamics of the process for the controller tooperate the system reliably.

The sample time of the 38-300 for both converters is 125 ms, which is much faster thanany dynamics that exist in this process; fluids, pipes, tanks, pumps and servo valves arerelatively slow elements in terms of time response and disturbance introduction.


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The Pneumatic Control Valve

The plug-type valve provides a fine adjustment of flow through the valve and is ideal forthe purpose of pressure control.

A 4-20mA control signal may be used to open or close a valve to any intermediateposition. This facility to operate a valve remotely allows a process to be controlledautomatically when the valve is connected to an appropriate sensor and controller.

Although the Pneumatic Control Valvesupplied does not have a truly linear

characteristic, it is satisfactory for control purposes at the operating pressure suggested.As the pressure is increased, the relationship becomes less linear.

The control valve must be carefully selected to give the correct characteristics over thenormal range of operation.


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Automatic Control Systems

The control of an industrial process by automatic rather than human means is calledautomation.

In its modern usage, automation can be defined as a technology that uses programmedcommands to operate a given process, combined with feedback of information todetermine that the commands have been properly executed. This kind of automation isprovided by the digital PIDprocess controller Commander 350.

Modern control systems are self-organising, adaptive, robust, able to learn about a

process, and can optimise control.

Automation is often used for processes that were previously operated by humans.

When automated, the process can operate without human assistance or interference. Infact, most automated systems are cabable of performing their functions with greateraccuracy and precision, and in less time, than humans are able to do.

However, semi-automated(hybrid, or human-robot) processes that incorporate humanworkers and robots (computer controlled machines) and manually controlled systems, stillexist, since some tasks are best carried out by humans.

Automatic Control Systems - Classes

Control systems are sometimes divided into two classes.

If the object of the control system is to maintain the physical variable at some constantvalue in the presence of disturbances, the system is called a regulator.

One example of a regulator control system is the speed-control system on the acgenerators of power utility companies. The purpose of this control system is to maintainthe speed of the generators at the constant value that results in the generated voltage

having a frequency of 50 Hz in the presence of varying electrical power loads.

Another example of a regulating process control system is the biological system thatmaintains the temperature of the human body at approximately 36

oC in an environment

that usually has a different temperature.

The second class of control systems is the servomechanism(sometimes called a Kineticcontrol system). Although this term was originally applied to a system that controlled amechanical position or motion, it is now often used to describe a control system in which aphysical variable is required to follow, or track, some desired time function.

An example of this type of system is an automatic landing system, in which the aircraftfollows a 'ramp' trajectory to the desired touchdown point.


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A second example is the control systems of a robot, in which the robot 'hand' is made tofollow some desired path in space.

Different types of control can be carried out by the Process Controller (38-300), dependingon the requirements of the process and the desired output.

All types are covered thoroughly in their own assignments, but an introduction to each isgiven in this theory. Each type is shown by applying it to a simple level control problem,and by doing this you will gain an insight into the types of control that are available.

A tank is holding liquid to feed a process. The process being supplied requires a constanthead of liquid and so a control system is required to keep the tank level constant. A valveis located in the tank inlet to vary the flow rate.

The diagram below illustrates the situation.

Open-loop Operation

The simplest strategy is to calibrate the inlet valve. By experimentation, a relationshipbetween tank level and position of the handwheel can be obtained.

If the outflow is constant, a position of the handwheel can be found that keeps the levelconstant. If the valve is opened a little more, so that more water is coming into the tankthan is going out, then the level will rise. Conversely if the valve is closed a little, so thatmore water is going out than is coming in, then the level will fall.

Now, if a different level is required, the handwheel can be changed to increase ordecrease the flow until the new level is reached.

This method is Open-Loop Operation. It is simple and will work well, provided there is nochange in the outflow of the liquid, and all other parameters affecting the level in the tankremain constant.


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There is no electrical or mechanical feedback path, so the system is open loop, butfeedbackis being provided through the user. He/she is deciding if the actual level isabove or below the desired level, and adjusting the actuator accordingly.

Feedforward Control

The major cause of disturbances affecting the tank level is likely to be changes in the tankoutflow rate. An increased outflow will cause the tank level to drop. Therefore, a morereasonable approach is to produce calibration curves for a number of outflow rates.

By monitoring the outflow rate, the correct position of the handwheel can be determinedby examining the calibration curve for the new flow.

The handwheel is then adjusted to keep the tank at the required level.

This technique is Feedforward Control, and requires a measurement of the outflow ratein order to calculate the change in the position of the inlet valve.

Feedforward Control - Disadvantages

Although feedforward control is an improvement over open-loop operation, it does have

disadvantages that restrict its usefulness.

One of these disadvantages is the calibration curvesbetween the handwheel position,outflow and level.

These must be accurate for the process to function correctly. Another is that the processmay vary with time, or disturbances occur that are not included in the calibration curves orare not monitored. Under these circumstances, feedforward control will not be successful.

Feedback Control

We could carry out more measurements to compensate for the errors that can occur infeedforward control.

However, the obvious solution to keep the level in the tank constant, is to monitor the levelitself. If it deviates from the desired value, the inlet valve is adjusted by an amountdependent on the difference between the actual level and the desired level. This controlstrategy is called Feedback Control.

Feedback control is error driven in that the control effort is a function of the differencebetween the desired and the actual levels. The relationship between the error and thecontrol effort is called the control law.


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Feedback level control does require a more elaborate level measurement technique, andan accurate valve actuator. It also requires a signal related to the actual level (i.e a leveltransmitter). In addition, the valve actuator must be able to hold the valve in any position,and to also change its position gradually and smoothly.

The diagram below illustrates how this may be implemented for the situation describedearlier.

The important characteristic of feedback control is that it is capable of providing a range ofcontrol effort, that is, it can produce small as well as large corrections.

An appropriate control law must be designed or selected to produce a satisfactoryperformance.

Control Law

The control law represents the action of the controller. Common control law types are theP-type(proportional), I-type(integral) and D-type(derivative), or a combination of these,i.e PI, PID.

Examples of feedback control systems can be found in nature, one of which is thetemperature-control of the human body.

This control system attempts to maintain the body temperature at a constant value.Generally, the environment tends to vary the body temperature.

The body responds to a difference in temperature by perspiring, by increasing ordecreasing blood flow, by shivering, and so on.

This control system has one characteristic that control systems designed by humans do

not often have : it normally operates in a satisfactory manner for seventy years or more.


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Another characteristic of this system, and one that is usually present in control systems

that we design, is that if the magnitude of the error becomes too large, the system fails.

On/Off Feedback Control

A simplification of the general feedback control type is On/Off Feedback Control.

The level in our example would now only have two states; either above the desired level orbelow it. Monitoring can now be carried out by a float switch, mounted at the desired level.

The switch produces a binary (on/off) signal that indicates whether the level is above orbelow the desired value. The signal can then be used to operate the inlet valve directly.

When the level is above the reference value, the inlet valve is closed, and when below, itis opened. The control law in on/off control is kept simple, it switches the control effortbetween two extremes, depending on the sign of the error.

The diagram below illustrates the control method in the context of the equipment set-up.

Whatever the cause of the change in level, provided the deviation is large enough to

activate the switch, then control action will be applied to correct the situation.

On/Off Feedback Control - Disadvantages

By using on/off control our equipment requirements have been simplified. However, thereare several problems associated with on/off control.

One problem concerns the abrupt fluctuations in flow as the valve switches between fullyopen and fully closed.

Another problem is that the precision of on/off control depends heavily on delays

associated with the switch, the inlet valve and the rate of change of flow. With lengthy


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delays, overflow could occur if the valve is not shut as soon as the desired level isreached.

The answer is not just to make the switch quick and sensitive as this can lead tounnecessary switching caused by waves or ripples.

The type of control chosen for a particular situation will depend on the accuracy required,cost of equipment, maintenance (the simpler the system, the easier it will be to maintain),disturbances expected and the degree of disturbance rejection expected, degree ofhuman intervention required, health and safety (how dangerous is an overflow of theprocess in question?), and so on.


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Practical 1 Serial Communication


Practical 1will take you through the steps that must be carried out before you canattempt any practical that uses the Process Controller (38-300) and a personal computertogether. It is vital that these steps are completed successfully to allow the 38-300 tocommunicate with your personal computer.

Steps 1and 2concern the physical link between the 38-300 and your personal computer.

They ensure that the cable supplied to link the two devices is connected to the correctports, and that the 38-300 is terminated correctly. It is possible to use more than one 38-300 if a practical demands it, and in such a case the controllers form a chain from thecomputer. This is when the termination of the serial lines is important.

Step 3deals with the parameters that must be set up in the 38-300 to allow it tocommunicate with your personal computer. The parameters are the speed ofcommunication (or Baud rate), the identity of the 38-300 (to allow more than one to beused), the type of parity checking and the block check character enable (the last two areboth error checking facilities). These four amount to the 'language' that is being spoken, ifthey are set up incorrectly the 38-300 will not understand the messages being sent by

your personal computer.

Questions

1 Why is it vital that this practical is completed before any othersthat involve the Process Controller (38-300) and a personalcomputer?

2 The first two steps deal with the physical link between the 38-300and a computer, what does the third deal with? What would bethe effect of incorrectly completing this step?


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Practical 1 Serial Communication

Perform Practical

This practical has no patching diagram as its aim is to get you familiar with the procedurethat must be followed before any other practical that uses the 38-300 Controller.

Essentially the completed practical is the patching diagram for serial communication,although it includes steps that are not only hardware links (wires and plugs and the like)but parameter assignments in the 38-300.

Step 1: Link

There is a serial lead supplied with your equipment to connect the Process Controller (38-

300) to your computer. This is plugged into the port marked RS-232on the rear of the 38-300 and to a COM Port on the rear of your computer. An adapter is commonly used tochange the 25-way connector to a 9-way connector that many modern computers use. Ifthere are no available serial ports on the PC then a USB to serial adaptor can be used.The Discovery 3 software is setup to use COM port 3.

Step 2: TerminationThere are two switches on the rear of the 38-300, marked Terminationand Connection,that deal with the communication lines to the 38-300. You will be using it as a singlecontroller linked to your computer, so both of these switches must be ON.

Step 3: Serial ParametersPlug the 38-300 power lead into one of the ac supply sockets on the rear of the ProcessInterface (not the switched ac supply), turn both on and observe the LED Displays.

Practical Setting the Serial ParametersPress and hold the Page Advanceand the Increasebuttons together for three seconds.It is helpful to press the Page Advancebutton first, then with another finger, press the Upbutton.

Parameter Advance Button


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Up Button

until the RED 38-300 LED display shows LEV.6.

User interface of the controller is divided into a number of levels. Each level contains anumber of related parameters that can be adjusted. Pressing those two buttons togethersets the controller on the first of the configurationlevels, the Basic Configuration level.

Press the Raisebutton to increase to higher levels. Press the Raise button seven times

until LEV.d, the Serial Configuration Level is displayed. If a higher level is selected, pressthe Lowerbutton.

Raise Button

Lower Button

Use the Page Advanceto move between individual parameter settings. Use the UpandDownbuttons to adjust each parameter.

Up Button

Down Button

Ensure that the controller is configured with the values shown in the below table.

Parameter Value Description

S.CFG 4 Whether 2 or 4 wire serial connectionand baud rate. Value 4 indicates a 4wire connection, running at 9600baud.

PrtY none Parity error checking. Default is none.

Addr 1 Unique address of this controller. Thisis defined as a part of the MODBUSprotocol that the controller uses tocommunicate to the PC. This must beset to 2 if you are configuring asecond controller.


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When all parameters have been set, press the Alarmbutton:

Alarm Button

Pressing this button will return you to the Operating Display where you can observe theProcess Variable, Set Pointand Controller Output.


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Practical 2 Navigating the 38-300


Practical 2considers the 38-300 in much greater detail, and explains the control paneland how it functions, but this practical must be completed first. Although you may not fullyunderstand all of the steps yet they will become clear in the next practical. It is sufficientjust to follow them for now.

The reason for keeping this in a separate practical is that it can now be referenced at any

time very easily. Linking the 38-300 to a computer is accomplished by completing thispractical.

The following diagram shows the configuration of the front control panel of the ABBCommander 350 controller.

The buttons used on the controller are described in more detail on the following pages.

Controller ControlsRaise

Lower

Raise is used to increase a parameter value, or step up through a selection of parameters.

Lower is used to decrease a parameter value or step down through a selection ofparameters.


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Continued pressure on these buttons causes the rate of change of the displayed variable

to increase. To make small adjustments, press the keys momentarily.

Parameter Advance

The various configuration options are held in a number of different 'levels', each levelcontaining a set of related parameters.

When a level has been selected, as shown within the Process Variable Display, pressingthe Parameter Advance moves between different controller Frameswithin a level.

If a parameter has changed within a level, pressing the Parameter Advance button willstore the value within the controllers memory.

Auto/Manual

This button is used to change the controller operation mode between automatic andmanual.

In manual mode, the displays automatically revert to control output (bottom display) andthe process variable values (top display), and the Raiseand Lowerbuttons can be used toalter the control output. When in automatic mode this facility is disabled, since the outputis calculated by the controller.

When the controller is in manualoperation, a small Mcan be seen in the output display.

Up

Down

When the controller is in manualoperation, these buttons allow the changing of thecontroller output.

When the controller is being configured, these allow specific controller parameters to bechanged.

Alarm


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During normal controller operation, this button allows the controller user to acknowledgean alarm, a state that a process may have entered into, requiring user intervention. Whenan alarm occurs, an alarm symbol will be seen within the bottom output panel.

When the controller is being configured, this button is used to return to the OperatingDisplay.

Controller Levels

The controller contains two types of Level, operation levels and configuration levels.Operation levels allow the operator to change simple operational characteristics of thecontroller during normal functioning, while the configuration levels allow moresophisticated settings to be adjusted.

This section describes the controllers Operational Levels, whereas the next describes thecontrollers Configuration Levels.

Level 1 : Operator LevelNormal day to day operation of the controller, depending upon which Control Templatehas been selected.

Level 2 : TuningAllows the setting of important control parameters used to control a process. Keyparameters include Proportional Band, Integral Action timeand Derivative ActionTime. These concepts are explored and studied in future assignments and practicals.

This level should be accessed to manually adjust operating parameters.

Level 3 : Set PointsThe Commander 350 has the ability to support a number of different Set Points, giving thecontroller flexability. This allows Set Point variables to be configured. This Level is notexplored within the software.

Level 4 : Alarm Trip PointsAllows the configuration of conditions under which Alarms can occur.

Level 5 : Valve SetupThis level is not applicable to the Procon training software. It is used in conjunction withspecial types of motorised valve.

Levels labelled 6though Eallow the controller to be configured.

For safety reasons, there are many controller settings that have to be configured throughthese level using the front panel of the controller, rather than the controllers RS485communications port.


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Warning!Only change the configuration parameters if you are sure they need to be

changed. Changing the configuration parameters without fully understanding what theyare may cause your controller to enter a state which is not compatible with the Proconassignments and practicals! If you are in doubt, do not change!

Level 6 : Basic ConfigurationThe basic configuration level allows the operator to select a required Template, choosethe type of Control Output and set the Control Action.

For some Procon Practicals, the Control Action setting is required to be changed. ControlAction can be set to two different modes, Direct Actionor Reverse Action.

The type of mode depends entirely upon the type of actuators that are used in the Proconrig. The Basic Process Rig servo valve requires Direct Action, whereas other actuatorswithin the Pressure Rig requires the setting of Reverse Action.

Level 7 : Analogue InputsThe controller is designed to be flexible, lending itself to a number of different controlsituations and needs. Subsequently, the controller can be configured to use different typesof signalling.

Analogue Inputs also allows the operator to configure the number of Decimal Places,

operational Engineering Range, amongst other settings.

Level 8 : AlarmsLevel 8 is dedicated to the setting up of Alarms. This level contains setting for alam type,alarm trip level and hysteresis settings. It also allows alarms to be associated to relays,allowing audible warnings to alert operators.The concept of an alarm is explored within a number of Procon assignments.

Level 9 : Set PointsThe Commander 350 supports 4 different set points. This level allows the selection of setpoints and the choosing of local or remote set points in process control. It also allows Set

Point Tracking, a useful control facility to start and stop processes, to be configured.

Level A : Control ConfigurationLevel A contains general controller configuration settings, such as what should occurfollowing a power failure and the defining of controller Output limits.

Level B : Operator ConfigurationIn an industrial environment, it is useful to prevent access to the controller to those who donot require it. Within safety critical systems and processes, this is particularly important.

The Operator Configuration level allows the enabling or disabling of certain keys, such asthe Auto/Manual key, Local/Remote Set Point key and the Alarm Acknowledge Key.


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Level C : Output AssignmentsThe Commander 350 provides both Analogue (Proportional) and Digital (On/Off) Outputs.This level allows the output facilities of the controller to be configured. Since the ProconProcess Rigs only use a small fraction of the controllers overall abilities, this level shouldrarely be accessed.

Level D : Serial CommunicationSetting of the type of serial cable used, and the baud rate. This level is described in theprevious practical. One of the most important parameters in this level is the Modbusaddress.

Level E : CalibrationThe controller is calibrated before it is used in the Procon system. Provision is made toadjust the controller settings. This level is described for completeness and should nothave be to accessed.

The following documentation is supplied with the controller:

User GuideModbus Communication Guide

It is useful to reference these manuals when carrying out practicals involving thecontroller. The user guide is especially useful, since it describes each level in detail.

Questions

1 When controlling the PI, of what type are the process inputs andoutputs of the Process Controller (38-300)? What input signalsdoes the 38-300 accept?

2 What is the major restriction when using the 38-300 controller interms of monitoring process variables? What is the majorrestriction when using the 38-300 controller in terms ofmonitoring process variables?

What sort of control can be implemented using this controller,

and so how many variables can be controlled?


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3 Considering the operations carried out before the parameters onthe Control and Set Point pages were recorded, and theinformation given in the background to this practical (2) oncomputer initialisation, what do you suggest is the reason for thedifferences in the two sets of parameter values recorded?

4 As well as saving time and effort, what is another advantage ofusing a computer to initialise the 38-300 before attempting apractical?


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Block Diagram


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Practical 2 Navigating the 38-300

Perform Practical

In a similar way to the previous practical, this practical has no patching diagram.

Its aim is for you to become familiar with the Commander 350 controller, its keys anddisplays, its parameters and pages, and the use of a personal computer and the controllertogether.

Set up the Process Controller (38-300) in exactly the same way as you did in the firstpractical, so that the 38-300 and your computer are able to communicate. Please gothrough that practical again if you are unsure.

When the 38-300 is switched on it will perform a self-test, show the version of the

controller operating system that is installed and the date, followed by the main operatingdisplay.

If a practical is selected and the controller is switched off an error message will beproduced on screen as shown below. Close the practical and switch on the controller thenrestart the practical.

To begin, ensure that the controller is set in Manualoperation mode. When the controlleris running in manual operation mode, parameters can be set using the front panel or bythe computer. To change the controller operation mode, press the:

Automatic/Manual Button


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If the Process Controller is not set to manual mode, the controller will not accept newsettings from the computer. An error message will be produced on screen as shown belowif the controller is in Automatic mode when a practical is selected.

Alwaysensure that the controller has been set to Manualmode before a practical isstarted.

Step 1 : Configuration Setting 1

Pressing the configuration 1 button below begins to transmit commands from thecontroller from the computer, changing a number of key parameters. The transmissiontakes approximately 2 seconds.

Press and hold the Parameter Advancekeys on the control panel until CodEisdisplayed. Press Parameter Advancetwice more to move to the first level of theconfiguration displays. Press the Raisebutton so LEV.2is displayed. This is the tuninglevel.

Use the Upand Downto move between individual parameters. Record all the settingswithin this level. When you have done, return to the top of the level (LEV.2), and change

to level 1, the operating level. Press the Parameter Advanceto return to the mainoperating display.

Step 2 : Configuration Setting 2Press the configuration 2 button to transmit a different configuration to the controller.Using the previous instructions, record the same parameters as you did earlier andcompare the two sets of values.

Press Page Advanceand then Enterto return to the operating page, and pressParameter Advanceonce to display output, shown by OP 100.0. The output can be

decreased and increased with Lowerand Raise. Check this. Pressing Auto/Manualwilldisable this facility, the output is set automatically. The L.E.D. is off, showing Autooperation.


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Practical 3 Using the 38-300


In this practical you shall make use of some of the facilities of the Process Controller (38-300) that are available for different modes of control.

This practical is kept simple. It introduces a number of basic features of the controller,including manual control of controller output and the use and purpose of alarms.

As the assignments develop, so too will the use of the 38-300 and more of its full capacityshall be seen.

Manual Control

Initially you will control the output of the 38-300 using the Up and Down keys on thecontrol panel.

The 38-300 will take the place of the current source on the Process Interface (PI), and theUp/Down keys will carry out the same function as the current source control knob on thePI.

You will be the operator of the process, manually controlling its operation, and it is a verysimple matter to set the level of the tank.

Here the manual control effort, Um, is you, changing the output at will. The actuator is theservo valve, and the measurement section is also you watching the level in the tank.Disturbance is normally included in this sort of situation to account for any fluctuations thatare out of your control (environmental changes can affect the flow for example).

Transfer between Automatic and Manual Control

When switching control modes (manual-auto or auto-manual) a problem can arise whenthe automatic set-point and the measured operating point are not equal. Normally acontroller will start in manual mode, where the automatic set-point is adjusted until it is

equal to the required operating point.


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The controller output will then be adjusted until the deviation between set-point and actual

operating point is zero, and the controller switched to auto mode. This ensures that theplant is operating steadily at the desired operating point at the instant of switching.

If the actual operating point is changed (using the manual controls) but the set-point is not,when the plant has reached steady state and is switched to auto there will be a deviation(because the measured operating point is not equal to the set-point), and the automaticcontroller will attempt to correct this.

This will cause a bump and will drive the plant away from the operating point set manuallyby the operator. The same effect can occur when switching from auto to manual, if themanual output control is not equal to the actual automatic controller output.

The way to avoid this is to employ automatic bumpless transfer, which is a facility mostmodern controllers include.

When using the 38-300, if there is a deviation between the desired operating point (as setby the manual controls) and the automatic set-point at the time of switching from manualto auto, the plant will continue at its desired operating point (with no bump).

This is slightly anomalous as there will be a (possibly large) deviation and an incorrect set-point, but it has prevented bumps.

Although bumpless transfer is available on modern controllers, it is good engineeringpractice to ensure no deviation in operating points (automatic set-point and actualmeasured operating point) before switching modes, rather than rely on this facility.

Alarms

The ABB Commander 350 like other industry process controllers, is capable of triggeringalarmsshould certain predefined conditions be met.

Up to 8 different alarms can be used, numbered 1 through to 8. Each alarm can be

programmed separately.

On the control panel of the Commander 350, an alarm LED will appear in green at thebottom of the middle LED display. The LED will flash to show that an alarm has beentriggered but not acknowledged.

Each alarm can be assigned a Type, a Trip Level and a Hysteresis setting.

Alarm Types

The alarm Type describes the situation that the alarm is watching for and it can be one of

the following;


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High or Low Process ValueHigh or Low OutputHigh or Low DeviationHigh or Low calculated mathematical value

The trip level is the level of the selected type that should trigger the alarm. For example,alarm A can be set to 'high output' with a trip level of 80%. If the output of the Controller isincreased to 80% or above, an alarm will be triggered.

The hysteresis settingis another way of checking process parameters.

The hysteresis setting is operational when an alarm is active, and it is specified as apercentage or in engineering units.

It is best shown with the above example; alarm A has been triggered by the output of thecontroller increasing above 80%, and the hysteresis setting is 5%. The output is lowered,but it must decrease below 75% (80% trip level - 5% hysteresis setting) before the alarm isturned off.

The output must move into the safe region by an amount equal to the hysteresis setting.

Viewing Alarm Settings

When you are carrying out this practical, after the alarms have been set, the alarmsettings can be seen on the Alarms Trip Pointpage.

Press and hold the Parameter Advancekey to change to the configuration mode, thenpress the button again twice to move to LEV.1, the operational level.

Finally, press the Raisekeys to move to LEV.4, the alarms level. Use the Upand Downkeys to observe the parameters

Configuring Alarms

The practical requires the operator to configure two of the controllers alarms.When the display shows LEV.4, press and hold the Raisekey to move to the higherconfiguration levels. The alarm level is situated at level 8, as shown by the display AL_S.

Use the controls on the controller to view the parameters that can be set at this level. Noteparticularly the tyP.nsetting, where nrefers to the alarm number.

With the tyP.1 parameter displayed, change the setting by pressing the Raiseand Lowerkeys. This manual control practical uses alarms to indicate control output that is too high,indicated by the letters HO, and the control output is too low, indicated by LO.


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All available parameters are described in the following table for completeness. Do not

worry about understanding them all. Only a small fraction of the available alarm types areused.

Alarm Settings

Display DescriptionNONE No alarm currently assigned.HPU andLPU

High and Low Process Variable values

HLP and LLP High and Low Latch Process Variable

Hd and Ld High and Low DeviationHPnand LPn High and Low Input values, where nrefers todifferent inputs

HO and LO High and Low Process Output settings, potentiallyused to prevent actuators going beyond preset limits.

Lbnand Hbn Programmable mathematical calculations, high andlow settings.

Alarms are set either by using the front panel or by the ABB configurator software, ratherthan using the main serial communications link for security purposes. This prevents thelikelihood of software accidentally changing the alarm operation that could be used to

indicate potentially hazardous process states.

Since the alarms are used in a number of different ways, they will be have to bereconfigured during a number of practicals. Always remember that the alarm settings canbe found at Level 8.

When all alarms have been configured, the trip levels for all alarms that have beenenabled, can be set using the Alarms Trip Pointpage. Press and hold the ParameterAdvancekey to change to the configuration mode, then press the button again twice tomove to LEV.1, the operational level. Finally, press the Raisekeys to move to LEV.4, thealarms level. Use the Upand Downkeys to observe the parameters.

If no alarms have been enabled, no parameters can be changed.

Now that alarms are familiar, select the practical page to begin to use and configure thecontroller.

Questions

1 Hysteresis, with regard to the 38-300 alarms, is the differencebetween the switch-on level and the switch-off level of the

variable assigned to the alarm. Did you find your experimentalresults were the same as the values set up in the controller?


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When is hysteresis operational, and when using it, what can besaid about the variable as it moves inside the trip level?

2 When transferring between modes of the 38-300, what is a'bump' and what are the conditions that would cause a bump?

What steps should be carried out to prevent bumps, and whatfacility is available on modern controllers to prevent bumps?What is the anomalous situation that can occur if care is nottaken when transfering modes in a modern controller?

3 Considering what you have learnt in this and previousassignments about automatic and manual control systems, splitthe following into Automatic Controland Manual Control: (a) Aheater with a thermostat. (b) A refrigerator. (c) Filling a bath tub,(d) A burglar alarm which has been set, (e) Traffic lights at aroad junction, (f) A pedestrian crossing with traffic lights, (g) Awashing machine once it is turned on, (h) A petrol-drivenlawnmower once it has been turned on.


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Block Diagram



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Use LEV.4, the Alarm Trip Pointslevel to adjust the trip leveland observe the alarmbehavior. Try changing the hysteresisvalue using LEV.8.

Change the operation of the controller between automatic and manual mode by pressingthe Automatic/Manual button.

Return to LEV.8 and set all alarm types to NONE so you are ready for the next practical.


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Chapter 4Procon Pressure Process Controller Calibration

38-004

Controller Calibration

Objectives

To further explore the 38-300 process controller, its settings and how to read data fromthe controller using the Discovery software.


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Each of these features will be explained fully as it arises through the increasing use of the38-300 in this and further assignments. Instrument set up is restricted to authorised usersthrough multiple levels of security.

Users can select the instrument functionality required, from menus, using the eight tactilemembrane keys and the three high intensity seven-segment displays plus the deviationbar graph. Configuration data is stored in non-volatile memory.

The controller is equipped with control algorithms for various types of control that werementioned earlier. These will be illustrated in later assignments, so that you becomefamiliar with the full capabilities of the 38-300.

The 38-300 contains analogue-to-digital and digital-to-analogue converters. The sampletime of these devices must be faster than the dynamics of the process for the controller tooperate the system reliably.

The sample time of the 38-300 for both converters is 125 ms, which is much faster thanany dynamics that exist in this process; fluids, pipes, tanks, pumps and servo valves arerelatively slow elements in terms of time response and disturbance introduction.


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General Process Controllers

The task of a controller is to maintain the desired system performance despite anydisturbances in the system.

Controllers are usually implemented electronically, either using analogue circuits, or adigital computer (microprocessor). However pneumatic and hydraulic controllers are still inuse.

In process control, it is unusual to design a specific controller for a particular plant,because the dynamics of the plant are uncertain and often very dependent on operating

conditions.

Therefore, a general purpose controller is normally implemented, which has a number ofvariable parameters that can be set to meet the static and dynamic requirements of thecontrol system.

The static characteristics of a system are independent of time and the response of thesystem depends only on the inputs. The dynamic characteristics of a system depend onboth time and inputs.

Various types of general purpose controllers exist, and each can be characterised by its

actions and methods of controlling a system.

A block diagram of a General Process Control Systemis shown below:

This shows the plant, and some means of measuring a process variable. This measuredvariable is fed back to the controller to determine how well the system is operating.

With the addition of the feedback loop it has now become a closed loopsystem.

The controller will compare the measured output and the desired output (the Set Point) todetermine the control effort. Umis the manual input, and the manual/auto switch can alsobe seen.

With the switch in the manual position the control law has been disconnected from theprocess plant and the system is controlled by the operator only (a manual control system,the type of control we have been implementing so far).


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With the switch in the automatic position the control law is added to the manual input andthis will determine the behaviour of the process. The process can now be controlledautomatically, provided it is given desired operating levels.

An automatic controller cannot determine how to control a process, it can only carry outdesired control, determined by a third party, you.

We shall be carrying out various types of feedback control in later assignments.


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The controller you are provided with is a single loop, digital controller. The DAC and ADC

are integral parts of the controller, and as such they will not concern you through yourpracticals.


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As mentioned in the Interface Calibration Assignment this calibration should now be

carried out before every practical that uses the 38-300. The more often it is carried out themore familiar you will become with the importance of calibration and the need to carry itout before every practical.

Before beginning this practical, make sure that your process interface is switched on sothat the 38-300 controller is powered up.

Questions

1 What are the steps that make up the 38-300 pre-practical setup

procedure?

2 Why is it unnecessary to calibrate the 38-300 in the same waythat the current source on the Process Interface was calibrated?

3 What devices would be needed to calibrate the 38-300 to anaccuracy level greater than the one it has already been calibratedto?


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Practical 1 38-300 Calibration

Perform Practical

This practical has no patching diagram as it only deals with parameters of the 38-300. Itsaim is to show you where and how to reset the 38-300 analogue input configurationparameters.

You will use the controllers keys to locate the specific parameters and reset them. This issomething that should be done before every practical using the 38-300, to ensure that allmeasurements made with it are within a predefined level of accuracy.

Now you have had experience of starting the initialisation process by clicking on an on

screen button in the previous practical, this shall be carried out automatically from now on,when a practical is started.

Remember: Set the controller in Manual mode before selecting a practical for theinitialisation process to take place.

As mentioned in the background pages and the patching diagram associated with thispractical, you will check the analogue input settings of the 38-300 controller.

The Commander 350 provides three analogue inputs. Two analogue inputs are universallyconfigurable, allowing the controller to accept Thermocouple, Resistance Thermometer,

mV, Volts, mA and resistance signals. The third analogue input signal can only accept mAand mV signals.

Level 7 (LEV.7), the Analogue Input Level allows the input type (tyP.1), decimal point(dP.1) settings, engineering ranges (EN1.H), (EN1.L), Broken sensor drive (bSd.1) andInput Filter Time Constant (FLt.1) to be configured for all three inputs. To go to theAnalogue Input Level, press and hold the Parameter Advanceand press twice more tojump to the first lev

38-004 Pron Pressure Process Manual v2p0 CD

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Transcript of 38-004 Pron Pressure Process Manual v2p0 CD