Electrical Measuring Instruments
- The instruments which are used to measure electrical quantities are called electrical instruments.
Classification of Electrical Instruments
- Absolute instruments: these instruments give the value of the quantity to be measured in terms of the constants of the instrument. Example: tangent galvanometer.
- Secondary Instruments: these types of instruments determine the electrical quantity to be measured directly in terms of deflection.
|Sr. No.||Type||Effect Produced||Suitable for||Instrument|
|1||Moving-Iron||Magnet effect||DC and AC||Ammeter, Voltmeter|
|2||Permanent Magnet Moving Coil (PMMC)||Electrodynamic effect||DC only||Ammeter, Voltmeter|
|3||Dynamometer Type||Electrodynamic effect||DC and AC||Ammeter, Voltmeter, Wattmeter|
|4||Induction type||Electro-magnetic induction effect||AC only||Ammeter, Voltmeter, Wattmeter, Energy-meter|
|5||Electrothermic type||Thermal effect||DC and AC||Ammeter, Voltmeter|
|6||Electrolytic meter||Chemical effect||DC only||Ampere-hour meter|
|7||Electrostatic Type||Electrostatic effect||DC and AC||Voltmeter only|
Types of secondary instruments
- Indicating instruments: these instruments indicate the magnitude of electrical quantity being measured. Examples Ammeter, voltmeter, wattmeter etc.
- Integrating instruments: measure the total energy (in KWh) in a given period. Example, Energy meter.
- Recording Instruments: the instruments which give a continuous record of the variations of the electrical quantity being measured are called recording instruments. Example, ECG, EEG, etc.
Essentials of Indicating Instruments
- Spring control method
- Gravity Control Method
- Air friction damping
- Fluid Friction Damping
- Eddy Current Damping