Classification of measuring instruments

If you can’t measure, you can’t analyze.

Measurement is very beneficial for understanding the outcome. Any device or instrument that measures an unknown quantity is known as a measuring device.

Classification of measuring instruments

Measuring instruments are classified into the following categories:

  1. Primary and Secondary instruments
  2. Electrical, Electronic, and Mechanical instruments
  3. Analog and Digital instruments
  4. Manual and Automatic instruments
  5. Deflection type and Null type instruments
  6. Self-operated and Power operated instruments

All these different types of measuring instruments are discussed below:

Primary and secondary instruments

  • Primary or absolute instruments: This type of instrument indicates the value of measuring quantity in terms of instrument constant and its deflection. Such instruments do not require comparison with other standards. Eg. galvanometer
  • Secondary instruments: These instruments indicate the magnitude of the measuring electrical quantity. Before using, these instruments require calibration with either an absolute instrument or with an already calibrated secondary instrument. Secondary instruments are further classified:
  1. Indicating instruments: Those instruments are known as indicating instruments which indicate the magnitude of an electrical quantity at the time of measurement. Eg. of these type instruments are ammeter, voltmeter, etc.
  2. Integrating instruments: Those instruments that measure the total amount of energy over a period are known as integrating instruments. Total energy measured by the instrument is the product of time and electrical quantity under measurement. Eg. energy meters, wattmeters.
  3. Recording instruments: The recording instruments are those instruments that continuously measure the variation of the magnitude of an electrical quantity at a particular interval of time. In this instrument, the moving system carries a marker/pen which lightly touches the paper sheet. A curve is traced on the sheet that shows the variations in the magnitude of electrical quantity under measurement.

Electrical, electronic, and mechanical instruments

  • Electrical instruments: Electrical instruments measure electrical quantity current, voltage, etc. When the pointer deflects by the action of some electrical methods, then the instrument is known as electrical instrument. The operating time of electrical instruments is fast than mechanical instruments. Few electrical instruments are ammeter, voltmeter, etc.
  • Electronic instruments: Electronic instruments are fast, accurate, and can detect the smallest signal possible. Mechanical and electrical instruments lag in these circumstances. Electronic instruments have a small response time.
  • Mechanical instruments: Mechanical instruments are the first preference for measuring physical quantities. It is very reliable for static and stable conditions because this instrument lacks behind in response time. It can not follow the rapid change that occurs during the time of measurement of dynamic conditions. This is because most of the mechanical instruments are bulky, rigid, and extremely heavy.  

Analog and digital instruments

  • Analog instruments: The output analog signal of this instrument varies continuously.
  • Digital instruments: Instruments that show the measuring signals in the numeric form are called digital signals. These instruments have a high speed of operation and high accuracy. Eg. Digital multimeter

Manual and automatic instruments

  • Manual instruments: Manual instruments require an operator most of the time.
  • Automatic instruments: No requirement of operator all the time.

Deflection and null type instruments

  • Deflection instruments: Deflection type instrument indicates the measurement of the unknown quantity. In this type of instrument, the measuring quantity produces a deflecting torque. And an opposing torque helps in achieving balance in the instrument. Eg. permanent magnet moving coil, moving iron, etc.

Read more: Working of permanent magnet moving coil instrument

  • Null instruments: Zero or null indication indicates the magnitude of the measured quantity. null instruments show null deflection when the unknown measuring quantity becomes equal to the known quantity. The null instrument Is very sensitive. A DC potentiometer is a null-type instrument.

Read more: How does a DC potentiometer works?

Self-operated and power operated instruments

  • Self-operated instruments: Those instruments that do not require any power from outside for performing operations are known as self-operated instruments.
  • Power-operated instruments: This type of instrument performs its operation when external power is supplied to it.

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