Pen Gen Alan Kepada Sistem Instrumentasi Latest (Sem 2 2011.2012)

8/2/2019 Pen Gen Alan Kepada Sistem Instrumentasi Latest (Sem 2 2011.2012)

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Pengenalan kepada Sistem

Instrumentasi dan Pengukuran

EMM 3242


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Rangka Kursus

Ujian 30% -Ujian 1 (15%) & Ujian 2 (15%) Kuiz /Assignment/Tugasan (20%)

Peperiksaan Akhir-50%

Passing Marks = 40%


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Sillibus


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BUKU RUJUKAN

Anthony J.Wheeler & Ahmad R Ghanji, Introduction to EngineeringExperimentation, 3 rd edition,2009.

J.P. Holman, Experimental Methods for Engineers,7 th edition,

McGraw Hill, 2001 D.G. Alciatore & M.B Histand, Introduction to Mechatronics and

Measurements Systems, 2 nd edition . Mc Graw hill 2003 C.D Johnson, Process Control Instrumentation Technology, Pearson A.S Morris, Principle of Measurements and Instrumentation, 2 nd

edition, Prentice Hall, 1993


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Contoh Sistem Pengukuran


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Definasi

Pengukuran -suatu langkah yang diambil untuk

melakukan proses perbandingan antaranilar sebenar dengan nilai yang diuji.

Sistem Pengukuran- Untuk mengukur sesuatu pemboleh ubah

atau measurans dan menukarkankepada suatu bentuk yang mudahdifahami oleh pengukur


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Sistem Unit

Diperlukan untuk memperterjemahsesuatu nilai yang diukur.

Contoh:a) Sistem Unit Antarabangsa (International

System-SI)

b) Sistem Unit CGS (Centimeter-Gram-Second)c) Sistem English (Imperial)


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7 unit asas SI


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Unit Asas CGS


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Perbandingan antara Unit


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EX 1

Ex: Convert the length 56.43ft to itsequivalent units of metres..


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EX 2

According to one internet site the distancefrom Vancouver B.C to Hong Kong is 5550nautical miles as the crow flies. Determinewhat this distance in units of kilometers..


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Definasi Instrumentasi

Sistem peranti (device,equipment) yangdigunakan dalam pengukuran

Kompenen utama :transducer,penyesuaian isyarat & unitpaparan


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WHY NEED MEASUREMENT?

1.? 2.?

3.?


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Why Need Measurement?

1. Monitoring or logging of processes andoperations

2. Experimental analysis of processes3. Control of processes


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1> the measurements simply provide a record whichmay be used as required. Example .. Whether data,aircraft black box recorders

2> the measurements are being taken for specificpurposes.. Example.. To determine the performance of anew engine, or to verify the accuracy of a mathematicalsimulation model

3> measurements are used as part of an automaticfeedback control system.. Example .. Include thethermostat in a central heating system or car engine,robot arm position measurement


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Hubungan antara masukan dan keluaran bongkah atauoutput.

Terdiri daripada 2 bahagian : statik & dinamik

Statik -menghubungkan masukan (input) dan keluaran (output

apabila masukan (input) tidak berubah dengan masa.-diwakili oleh persamaan, jadual atau graf

Dinamik -diwakili oleh persamaan kebezaan. (bab akan datang)

Rangkap Pindah (Transfer Characteristics)


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Ralat (error)

e , Perbezaan diantara nilai sebenar X n dan nilai yang diukur Y n e = Y

n - X

n Boleh diklasifikasi kepada 2 jenis:a) Ralat Sistematik (Systematic Error)

b) Ralat Rawak/Rambang (Random Error)


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Ralat Sistematik-ralat yang berlaku berulangkali dengan nilai

yang tetap.Punca:i) tidak mengunakan alat dengan teknik yang betul

ii) Ketentu ukuran yang silapiii) Kesilapan manusia apabila membacaiv) Kesilapan rekabentuk atau fakbrikasi alatv) Pengukuran yang berubah-ubah

Peratus Ralat= Yn - Xn x 100 e x 100Yn Yn


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Ralat Rawak-ralat yang tidak konsisten dalam sistem

pengukuran.Punca:i) Pemerhati yang tidak dapat menganggarkan dengan

tepat semasa mengambil bacaanii) Kebisingan atau gangguan dari persekitaran atau

sistem lain mempengaruhi pemboleh ubah yangdiukur


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Analog and digital data Variables are analog in nature, and before digital processing evolved, sensor signals were processed using analog circuits and techniques, which still exist in many processing facilities. Most modern systems now use digital techniques for signal processing [5]. Analog Data

Signal amplitudes are represented by voltage or current amplitudes in analogsystems.

Analog processing means that the data, such as signal linearization, from the sensor is conditioned, and corrections that are made for temperature variations are all performed using analog circuits. Analog processing also controls the actuatorsand feedback loops. The most common current transmission range is 4 to 20 mA, where 0 mA is a fault

indication.


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Example The pressure in a system has a range from 0 to 75 kPa. What is the

current equivalent of 27 kPa, if the transducer output range is from 4to 20 mA?

Equivalent range of 75 kPa = 16 mAHence, 27 kPa = (4 + 16 27/75) mA = 9.76 mA


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Digital Data

Digital Data Signal amplitudes are represented by binary numbers in digital systems.

Since variables are analog in nature, and the output from the sensor needsto be in a digital format, an analog to digital converter (ADC) must be used,or the sensor s output must be directly converted into a digital signal usingswitching techniques.

Once digitized, the signal will be processed using digital techniques, whichhave many advantages over analog techniques, and few, if any,disadvantages.

Some of the advantages of digital signals are: data storage, transmission of

signals without loss of integrity, reduced power requirements, storage of setpoints, control of multiple variables, and the flexibility and ease of programchanges.

The output of a digital system may have to be converted back into ananalog format for actuator control, using either a digital to analog converter(DAC) or width modulation techniques.


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FIGURE 1.11 Graph (a) shows how output variable b changes as an analog of variable c . Graph (b) shows how a digitaloutput variable, n , would change with variable c .

Curtis JohnsonProcess Control Instrumentation Technology, 8e]

Copyright 2006 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458

All rights reserved.


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Introduction to process control The technology of controlling a series of events to transform a material into

a desired end product is called process control. For instance, the making of fire could be considered a primitive form of

process control. Industrial process control was originally performedmanually by operators.

Their sensors were their sense of sight, feel, and sound, making theprocess totally operator-dependent.

To maintain a process within broadly set limits, the operator would adjust asimple control device.

Instrumentation and control slowly evolved over the years, as industry found

a need for better, more accurate, and more consistent measurements fortighter process control.


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Process Control

Process control can take two forms:(1) sequential control,

which is an event-based process in which oneevent follows another until a process sequenceis complete; or

(2) continuous control,

which requires continuous monitoring andadjustment of the process variables.


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Sequential Process control Control systems can be sequential in nature, or can use continuous

measurement; both systems normally use a form of feedback for control. Sequential control

is an event-based process, in which the completion of one event follows the

completion of another, until a process is complete, as by the sensing devices. Figure 1.1

shows an example of a process using a sequencer for mixing liquids in a set ratio [2].

The

sequence of events is as follows:


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1. Open valve A to fill tank A. 2. When tank A is full, a feedback signal from the level sensor tells the sequencer to turn valve A Off. 3. Open valve B to fill tank B. 4. When tank B is full, a feedback signal from the level sensor tells the sequencer to turn valve B Off.

5. When valves A and B are closed, valves C and D are opened to let measured quantities of liquids A and B into mixing tank C. 6. When tanks A and B are empty, valves C and D are turned Off. 7. After C and D are closed, start mixing motor, run for set period. 8. Turn Off mixing motor. 9. Open valve F to use mixture.

10. The sequence can then be repeated after tank C is empty and Valve F is turned Off.


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Continuous Process Control

Continuous process control falls into two categories: (1) elementary On/Off action, and (2) continuous control action. On/Off action is used in applications where the system has high inertia,

which prevents the system from rapid cycling. This type of control only hasonly two states, On and Off; hence, its name. This type of control has been

in use for many decades, long before the introduction of the computer.

HVAC is a prime example of this type of application. Such applications donot require accurate instrumentation.

In HVAC, the temperature (measured variable) is continuously monitored,

typically using a bimetallic strip in older systems and semiconductorelements in newer systems, as the sensor turns the power (manipulatedvariable) On and Off at preset temperature levels to the heating/coolingsection.


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EX 1..automated controlprocess

An example of an unsophisticated automated control process is shown inFigure 1.2.

A float in a swimming pool is used to continuously monitor the level of thewater, and to bring the water level up to a set reference point when thewater level is low.

The float senses the level, and feedback to the control valve is via the floatarm and pivot. The valve then controls the flow of water (manipulatedvariable) into the swimming pool, as the float moves up and down.


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Ex 2. continuous control forliquid mixing

A more complex continuous process control system is shown inFigure 1.3,

where a mixture of two liquids is required. The flow rate of liquid A is measured with a differential pressure

(DP) sensor, and the amplitude of the signal from the DP measuringthe flow rate of the liquid is used by the controller as a referencesignal (set point) to control the flow rate of liquid B.

The controller uses a DP to measure the flow rate of liquid B, andcompares its amplitude to the signal from the DP monitoring the flowof liquid A. The difference between the two signals (error signal) isused to control the valve, so that the flow rate of liquid B(manipulated variable) is directly proportional to that of liquid A, andthen the two liquids are combined


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Measurement VS

Sensors VSInstruments ?


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Measurement is the determination of the physical amplitude of aparameter of a material; the measurement value must be consistentand repeatable.

Sensors are typically used for the measurement of physicalparameters. A sensor is a device that can convert the physicalparameter repeatedly and reliably into a form that can be used orunderstood.

Examples include converting temperature, pressure, force, or flowinto an electrical signal, measurable motion, or a gauge reading. InFigure 1.3, the sensor for measuring flow rates is a DP cell.


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The subtle difference between an instrumentand a sensor is that an instrument is a devicethat measures and displays the magnitude of a

physical variable, whereas a sensor is a device that measures the

amplitude of a physical variable, but does notgive a direct indication of the value


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Definition of elements in acontrol loop


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Controller is a microprocessor-based system that candetermine the next step to

be taken in a sequential process, or evaluate the errorsignal in continuous process

control to determine what action is to be taken. Thecontrollers are normally referred to as

programmable logic controllers (PLC). These devicesuse ladder networks for programming

the control functions.


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Control Element is the device that controls theincoming material to the process

(e.g., the valve in Figure 1.3).

The element is typically a flow control element,and can have an On/Off characteristic or canprovide liner control with drive.

The control element is used to adjust the input tothe process, bringing the output variable to thevalue of the set point.


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The measuring element consists of a sensor to measure thephysical property of a variable, a transducer to convert the sensorsignal into an electrical signal, and a transmitter to amplify theelectrical signal, so that it can be transmitted without loss.

The control element has an actuator, which changes the electricalsignal from the controller into a signal to operate the valve, and acontrol valve.


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Pen Gen Alan Kepada Sistem Instrumentasi Latest (Sem 2 2011.2012)

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