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Instrumentation & MeasurementsIntroduction, advantages of electronic instrumentation, instrument classification, types of measurement 1/23/201615th SEMESTER BE (Electrical)1 What is Instrumentation?Instrumentation is a branch of engineering, related to study of various instruments and their control.

An instrument is a device that measures a physical or electrical quantity such as flow, temperature, current, voltage, level, distance, angle, or pressure.

What is measurement?The measurement of a given parameter or quantity is the act of a quantitative comparison between a predefined standard and an unknown quantity to be measured.

1/23/20162Advantages of electronic instrumentsFollowing are the advantages of electrical or electronic instrumentation.Different physical quantities can be converted into electrical signal by transducers.

Electrical signals can be amplified, multiplexed, filtered and measured easily.

Electrical signals can be converted from A/D or D/A signal.

Electrical signals can be transmitted over long distances by wire or radio link etc.1/23/20163Many measurements can be carried simultaneously.

Digital signals are compatible with computers.

7. High Sensitivity, low power consumption, high reliability.

1/23/20164Classification of InstrumentsInstruments can classified into many categories, one classification is given as under.

Active/Passive instruments

Null or deflection type

Monitoring or control type

Analogue or digital

Absolute or secondary

1/23/20165Active/PassivePassive Instruments: (Easy design, cheap)In which the output produced depends entirely on quantity being measured.Example: Analogue ammeter, Pressure gauge

Active Instruments: (Difficult to design, costly)In which the quantity being measured activates the magnitude of some external power input, which in turn produces the measurement.Example: Liquid Level Indicator, LUX meter using LDR.

1/23/20166Null/Deflection

Null type instruments: In which a zero or null indication leads to the determination of magnitude of the quantity being measured.

Example: DC potentiometer

Deflection type instrument:In which the quantity being measured produces some effect due to which pointer deflects.

Example: PMMC instrument.1/23/20167Monitoring /Control

Monitoring type instruments:In which some indication or condition of parameter value under study is obtained.Example: All deflection type or digital instrumentsControl type instruments:These are used in automatic control systems in the feedback path, to send a feedback signal from the output of a process to its input.

Example: Automatic air- conditioning system, AVR.1/23/20168Analogue/digital

Analogue type instruments:In which output varies in continuous fashion as quantity being measured, having infinite values in a given range.

Example: Deflecting Instruments are good examples of analogue instruments.

Digital Instruments:In which output varies in discrete step and thus give finite values in a given range.Example: Digital Multi-meter

1/23/20169Absolute/ Secondary

Absolute Instruments:In which magnitude of quantity is measured in terms of physical constants of the instrument.

Example: tangent galvanometer

Secondary type instruments:In which the reading shown by the instrument gives directly the measurement of the quantity being measured.

Example: Voltmeter, ammeter, wattmeter.

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Absolute instruments are rarely used except in laboratories and for scientific work. The quantity to be measured will be given in terms of deflection and the constant of the instrument. No calibration is needed in these type of instruments. Division on the graduated scale will not have any value marked on it. Example: tangent galvanometer10Secondary instrumentsThere are 3 types of these instruments.Indicating RecordingIntegrating 1/23/201611

Indicating InstrumentIntegrating InstrumentRecording InstrumentMethods of measurementThere are two methods of measurement.Direct measurementIndirect Measurement

Direct Measurement:In direct measurement the quantity being measured produce certain effect which gives the indication on meter.

Example: Measurement of current by ammeter.1/23/201613Direct methods are classified asDeflection methodsComparison methods

Deflection method includes the deflection of pointer on a scale due to the quantity to be measured.

Example: Wattmeter, ammeter voltmeter

Comparison method include the comparison of the quantity under measurement with a pre-defined standard quantity which gives measurement.

Example: potentiometer.1/23/201614Indirect measurement:

In which the quantity to be measured is not measured directly, but other parameters related to the quantity are measured.

Example 1: For measurement of power (P) we measure voltage (V) and current (I) then P = V*I

Example 2: For measurement of resistance (R) we measure (V) and current (I) then R=V/I1/23/201615