Introduction, advantages of electronic instrumentation, instrument classification, types of measurement

Instrumentation And Measurement

1. Instrumentation & Measurements Introduction, advantages of electronic instrumentation, instrument classification, types of measurement 5/27/2015 1 5 th term BE (Electrical)

2. 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. 5/27/2015 2

3. Advantages of electronic instruments Following are the advantages of electrical or electronic instrumentation. Different physical quantities can be converted into electrical signal by transducers. Electrical signal can amplified, multiplexed, filtered and measured easily. Electrical signal can be converted from A/D or D/A signal. Electrical signals can be transmitted over long distances by wire or radio link etc. 5/27/2015 3

4. Many measurements can be carried simultaneously. Digital signal are compatible with computers. 7. High Sensitivity, low power consumption, high reliability. 5/27/2015 4

5. Functional elements of an instrument Any instrument or measuring can be represented by a block diagram, that indicates necessary elements and its functions. The entire operation of a measuring system can be understand from the following block diagram. 5/27/2015 5

6. Primary Sensing Element Variable Conversion Element Variable Manipulation Element Data Transmission Element Data Storage Element (Not necessary) Data presentation element 5/27/2015 6

7. Just take an example of analogue meter used to measure current (Ammeter), all necessary elements are shown in block diagram. 5/27/2015 7

8. Classification of Instruments Instruments 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 5/27/2015 8

9. Active/Passive Passive 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 . 5/27/2015 9

10. Null/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. 5/27/2015 10

11. Monitoring /Control Monitoring type instruments: In which some indication or condition of parameter value under study is obtained. Example: All deflection type or digital instruments Control 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 . 5/27/2015 11

12. Analogue/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 5/27/2015 12

13. Absolute/ 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. 5/27/2015 13

14. Methods of measurement There are two methods of measurement. Direct measurement Indirect 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. 5/27/2015 14

15. Direct methods are classified as Deflection methods Comparison 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. 5/27/2015 15

16. Indirect measurement: In which the quantity to be measured is not measured directly, but other parameter 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/I 5/27/2015 16