JABATAN KEJURUTERAAN MEKANIKALPOLITEKNIK SULTAN AZLAN SHAH

J5800 INSTRUMENTATION AND

CONTROL

Synopsis

INSTRUMENTATION & CONTROL emphasizes to the students on the importance of

instrumentations and the basic principles of control system and its application in the

industrial sector.

This module shall provide knowledge and understanding to students on measurement

components in control systems normally used in the industry.

Assessment

Course work (50%) Quiz – 4 – 20% Assignment – 3 – 20% Practical – 4 – 20% Test – 2 – 40%

Final Examination (50%)Attendance >80%

Chapter

1. INTRODUCTION TO INSTRUMENTATION

2. TYPES OF MEASUREMENT IN INDUSTRIAL APPLICATION

3. INTRODUCTION TO CONTROL SYSTEM

4. TYPES OF CONTROL SYSTEM

5. APPLICTION OF COMPUTER IN PROCESS CONTROL

Course Objective

At the end of this module, the student shall be able to:

1. Explain The Instrumentation Concept And Measurement System.

2. Elaborate On The Basic Elements In Instrumentation System.

3. Identify Four (4) Types Of Measurements In Industrial Application Such As Electrical, Pneumatic And Hydraulic Control.

4. Elaborate On The Four (4) Types Of Control Action.

5. Application Of Computer Usage In Process Control.

References

1. Franklyn, W.K., Thomas, A.W., Philip, K. Instrumentation 4th Edition. 2005. ATP.

2. W. Bolton. Instrumentation and control system. 2004. Newnes.3. Eckman, D.P. Industrial Instrumentation. 2004. CBS.4. Ruzairi A.R. Pengukuran dan Transduser. 1999. UTM.5. Peter, E. Sensors for Measurement and Control. 1998. Prentice

Hall.6. W. Bolton. Engineering Instrumentation & Control. 1996. BH.7. Ruzairi, A.R., Herlina, A.R., Nasarudin, A. and Anita, A.

Pengukuran & Insrtumentasi Elektrik. 2003. UTM.8. Mohd Fua’ad, R. and Sallehuddin, I. Instrumentasi. 2003. UTM.9. http://instrumentationandcontrollers.blogspot.com/2010/10/de

ad-weight-tester.html.

THIS IS AN INTRODUCTORY TOPIC TO THE BASIC ELEMENTS IN INSTRUMENTATION

AND THE TERMINOLOGIES USED IN MEASUREMENT SYSTEM.

INTRODUCTION TO INSTRUMENTATION

Content:

1. Requirement and importance of Instrumentation in industry

2. Basic elements of Instrumentation system

3. Calibration of instrument and measuring instrument

4. Error in instrument calibration

5. Accuracy and precision

Requirement and importance of Instrumentation in industry

Definition of Instrumentation

Process control instrumentation is the technology of using instruments to measure and control manufacturing, conversion, or treating processes to create the desired physical, electrical and chemical properties of materials.

Measures, controls, and interacts with computer, electrical, hydraulic, and mechanical systems.

Instrumentation and industry

Technicians often read instruments as part of the job of managing complex industrial processes.

Pneumatic controllers have mechanical internal components that make it easy to see how they work. Modern digital controllers operate electronically, but the internals are not as easy to see and understand.

Application: stack gas analysis

A boiler operator is responsible for using instruments that indicate boiler operation efficiency.

Applications: air flow measurement

An HVAC technician measures airflow to troubleshoot an air handing system.

Application: electrical troubleshooting

An electrician is often required to troubleshoot electrical systems related to instrument system.

Boiler use primary elements to measure the steam pressure and temperature, feedwater flow and conductivity, boiler water level, fuel flow and pressure, and composition of the stack gas.

Question?

Now you know why the instrumentation is very importance in industrial processes? Why?

Answer:

To calibrate machine or systemTo monitor system operationTo collect data for research and development

Purpose/function of instrumentation

To give the user a numerical value corresponding to the variable being measured.

Thus, a thermometer may be used to give a numerical value for the temperature of the liquid.

Measurement system

Input:pressure

Output:Value forThe pressure

Measurement system

Input:speed

Output:Value forThe speed

Measurement system

Input:Flow rate

Output:Value forThe flow rate

Examples of sensors to be used in the measurement process

Three (3) basic elements in a instrumentation system

Transducer / sensor contact with the process for which a variable is

being measuredSignal conditioner

Which converts the output of a sensor into a suitable form for further processing.

Display This presents the measured value in a form which

enables an observer to recognize it.

Transducer/sensor

Signalconditioner

Record

Transmit

Display

Input:

TrueValue of variable

Output:measuredValue of variable

Measurement system elements:

Transducer/sensor

Signalconditioner

DisplayTemperaturesignal

Movement ofPointer acrossA scale

Measurement system elements for temperature:

Resistance change

Current change

Advantages / Disadvantages

Electrical/electronic instrument

Easy to installNeed the electric

signal to operate Space less Easy to damagePrice less

Mechanical instrument

Difficult to installNo need the electric

signal to operateLarge spaceDifficult to damageMore expansive

Basic elements of Instrumentation system

Transducer

Application of transducer in the industry: Fluid pressure – hydraulic, piping Fluid level – Tank, reservoir Fluid flow – drinking water inlet Temperature – furnace

Signal conditioning methods

Mechanical methods Lever system Gear system

Electrical methods Signal amplifier

Display methods

Analogue Indicator – the moving coil meter involving a pointer

moving across a fixed scale.Digital

Illuminative displays – light-emitting diodes (LEDs), liquid crystal displays (LCD), visual display units (VDUs)

Analogue Digital

Overall accuracy: ± 0.1 to ± 0.5

The time taken for moving coil meter to reach a steady deflection is typically in the region of a few seconds.

Low resistance of the meter can present loading problems.

LED require low voltages and low current to emit light and are cheap.

LED can give red, yellow and green colors.

Alphanumeric display LCD do not produce any light

of their own but use reflected light and can be arranged in segment like LEDs.

VDUs used to display alphanumeric, graphic and pictorial data.

Calibration Of Instrument And Measuring Instrument

Definition of calibration

Process of comparing the output of measurement system against standards of known accuracy.

The standards may be other measurement systems which are kept specially for calibration duties or some means of defining standard values.

In many companies some instruments and items such as standard resistors and cells are kept in a company standards department and used solely for calibration purposes.

Calibration should be carried out using equipment which can be traceable back to national standards with a separate calibration record kept for each measurement instrument.

This record is likely to contain a description of the instrument and its reference number, the calibration date, the result, how frequently the instrument is to be calibrated and probably details of the calibration procedure to be used, details of any repairs or modifications made to the instrument, and any limitations on its use.

Traceability chain

International standards International agreement and are maintained by

national establishments e.g. the National Physical Laboratory in Great Britain and the National Bureau of Standards in the United States.

Calibration centre standard SIRIM

In-company standardsProcess instruments

1. National standards are used to calibrate standards for calibration centre.

2. Calibration centre standards are used to calibrate standards for instrument manufacturers.

3. Standardized instruments from instrument manufacturers are used to provide in-company standards.

4. In-company standards are used to calibrate process instruments.

Example for simple traceability chain

Let say a glass bulb thermometer, the traceability might be: National standard of fixed thermodynamic temperature

points. Calibration centre standard of a platinum resistance

thermometer with an accuracy of ±0.0o5°C. An in-company standard of a platinum resistance

thermometer with an accuracy of ±0.01°C The process instrument of a glass bulb thermometer

with an accuracy of ±0.1°C

Dead Weight Tester.

Applications It is used to calibrated all kinds of pressure gauges such as

industrial pressure gauges, engine indicators and piezoelectric transducers.

Advantages It is simple in construction and easy to use. It can be used to calibrated a wide range of pressure measuring

devices. Fluid pressure can be easily varied by adding weights or by

changing the piston cylinder combination.Limitations

the accuracy of the dead weight tester is affected due to the friction between the piston and cylinder, and due to the uncertainty of the value of gravitational constant 'g'.

Operation The dead weight tester is basically a pressure

producing and pressure measuring device. It is used to calibrate pressure gauges. The following procedure is adopted for calibrating pressure gauges. Calibration of pressure gauge means introducing an accurately known sample of pressure to the gauge under test and then observing the response of the gauge. In order to create this accurately known pressure, the following steps are followed.

Calibrating a pressure gauge

A known weight is placed on the platform.Now by operating the plunger, fluid pressure is applied to the other side of the piston until enough force is developed to lift the piston-weight combination.

When this happens, the piston weight combination floats freely within the cylinder between limit stops.

In this condition of equilibrium, the pressure force of fluid is balanced against the gravitational force of the weights pulls the friction drag.

1.4 Error In Instrument Calibration

The difference between the result of the measurement and the true value of the quantity being measured, i.e. Error = measured value – true value

Thus, if the measured value is 10.1 when the true value is 10.0, the error is +0.1. if the measured value is 9.9 when the true value is 10.0, the error is -0.1.

Errors can arise in a number of ways and the following describes some of the errors that are encountered in specifications of instrumentation systems.

Hysteresis error The different in outputs given from the same value of

quantity being measured according to whether that value has been reached by a continuously increasing change or a continuously decreasing change.

Thus, you might obtain a different value from a thermometer used to measure the same temperature of a liquid if it is reached by the liquid warning up to the measured temperature or it is reached by the liquid cooling down to the measured temperature.

Non-linearity error The error that occurs as a result of assuming a linear

relationship between the input and output over the working range, i.e. a graph of output plotted against input is assumed to give a straight line.

Insertion error When a cold thermometer is put in to a hot liquid to measure

its temperature, the presence of the cold thermometer in the hot liquid changes the temperature of the liquid. The liquid cools and so the thermometer ends up measuring a lower temperature than that which existed before the thermometer was introduced.

The act of attempting to make the measurement has modified the temperature being measured.

This effect called loading and the consequences as an insertion error.

If we want this modification to be small, then the thermometer should have a small heat capacity compared with that of the liquid. A small heat capacity means that very little heat is needed to change its temperature.

1.5 Accuracy And Precision

Accuracy

The extent to which the value indicated by a measurement system or element might be wrong.

For example, a thermometer may have accuracy of ±0.1°C.

Accuracy is often expressed as a percentage of the full range output or full-scale deflection (f.s.d).

For example, a system might have an accuracy of ±1% of f.s.d. If the f.s.d is, say 10 A, then the accuracy is ±0.1 A.

The accuracy is a summation of all the possible errors that are likely to occur, as well as the accuracy to which the system or element has been calibrated.

Precision

The degree of freedom of a measurement system from random errors.

Thus, a high precision measurement instrument will give only small spread of readings if repeated readings are taken of the same quantity.

A low precision measurement system will give large spread of readings.

For example, consider the following two sets of readings obtained for repeated measurements of the same quantity by two different instruments:

Set 1 - 20.1mm, 20.2mm, 20.1mm, 20.0mm, 20.1mm

Set 2 - 19.9mm, 20.3mm, 20.0mm, 20.5mm, 19.8mm

The result of the measurement give values scattered about some value. The first set of results shows a smaller spread of readings than the second and indicates a higher degree of precision for the instrument used for the first set.

Terms used to specify A measurement system

Reproducibility The ability of a system to give the same output when used with a

constant input with the system of elements of the system being disconnected from its input and then reinstalled.

Drift The change in output that occurs over time.

Response time This is the time which elapsed after the input to a system or element is

abruptly increased from zero to a constant value up to the point at which the system or element give an output corresponding to some specified percentage, e.g. 95% of the value of the input.

Range / span The limits between which the input can vary. For example, a resistance

thermometer sensor might be quoted as having a range of -200 to +800°C.

ASSIGNMENT 1

Please explain the measuring sensor that had been given to you. Please include on your presentation the description, applications, operation, advantages & disadvantages of that measuring sensor.

Presentation Duration = 15 minutes Q&A = 5 minutesThe marks will be given depend on your

contain, presentation skill, & the ability to answer the question.

Temperature RTDs Thermistors Thermocouples

Fluid flow Differential pressure method – orifice plate & rota meter electromagnetic flow meter Ultrasonic flow meter

Fluid level Floats Capacitive level indicator Nucleonic level indicator

Fluid pressure Diaphragm sensor Piezoelectric sensor Bourdon tube