Advantages and Disadvantages of Electrodynamometer Instruments

Advantages and Disadvantages of Electrodynamometer Instruments Points : Advantages and Disadvantages of Electrodynamometer Instruments Advantages

1. As the instrument coils are air cared, so these instruments are free from hysteresis and eddy current errors.
2. These instruments can be used on both a.c. and d.c. and since they have a precision grade accuracy, they are very useful as transfer instruments.
3. Electrodynamometer voltmeters are very useful where accurate rms values of voltage, irrespective, of waveforms, are required. This is also true for an ammeter where the two circuits have the same time constant.
4. They have a precision grade accuracy for frequencies up to 40 to 500 Hz. The low range being decided by the oscillations of the pointer. Lower grade instruments can be used for frequencies up to 10KHz.

Disadvantages

1. These instruments have a low torque/weight ratio and hence the low sensitivity.
2. Low torque/weight ratio gives increased frictional losses. These errors must be minimized, if high accuracy is desired. This action makes the instruments costly.
3. These instruments are more expensive than either the PMMC or the moving iron type instrument.
4. These instruments are sensitive to over loads and mechanical impacts, therefore they must be handled with great care.
5. The operating current of these instruments is large due to the cat that they have week magnetic field. The power consumption of meters is high as compared with PMMC instruments.
6. They have a non-uniform scale as the instruments have square law response.
7. Adequate screening of the movements against stray magnetic fields is essential.
8. The measurement of frequencies as low as 5Hz to becomes impractical.