Electrical Measuring Instruments


What is a Measuring Instrument?

The device used for comparing the unknown quantity with the unit of measurement or standard quantity is called a Measuring Instrument.
An instrument may be defined as a machine or system which is designed to maintain functional relationship between prescribed properties of physical variables & could include means of communication to human observer.

Classification of Electrical instruments

Electrical instruments may be divided into two categories, that are;
  • Absolute instruments.
  • Secondary instruments.
- Absolute instruments gives the quantity to be measured in term of instrument constant & its deflection.
- In Secondary instruments the deflection gives the magnitude of electrical quantity to be measured directly. These instruments are required to be calibrated by comparing with another standard instrument before putting into use.

Classification of Secondary instruments

Secondary instruments can be classified into three types;
  • Indicating instruments
  • Recording instruments
  • Integrating instruments
- Indicating Instruments: It indicate the magnitude of an electrical quantity at the time when it is being measured. The indications are given by a pointer moving over a graduated dial.
Indicating Instruments
Fig. 1: Indicating Instrument.
- Recording Instruments: The instruments which keep a continuous record of the variations of the magnitude of an electrical quantity to be observed over a defined period of time.
Recording Instruments
Fig. 2: Recording Instrument.
- Integrating Instruments: The instruments which measure the total amount of either quantity of electricity or electrical energy supplied over a period of time. For example energy meters.
Integrating Instruments
Fig. 3: Integrating Instrument.

Use of electrical instruments

The electrical instrument is used for measuring electrical quantities likes current, voltage, power, etc. The ammeter, voltmeter, wattmeter are the examples of the electrical measuring instrument. The ammeter measures the current in amps; voltmeter measures voltage and Wattmeter are used for measuring the power.

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