8.1. Essential Characteristics of Energy Meters. The essential characteristics of energy meters are given below:
- They must be simple in design and must not contain any parts which may rapidly deteriorate.
- The readings may be given directly by the dials and must avoid any multiplying factors.
- The casing of the meter should be dust, water and insect proof.
- Permanency of calibration is a prime requisite and to attain it, the friction at the pivots etc., and retarding torque of the magnetic brakes must remain constant. The magnets should be so placed that they are not affected in their strength by the magnetic field of the current coil.
- The friction losses should be minimum (being unavoidable) and must remain practically constant over long periods of time. This requires that the moving parts should be light, and the jewels and pivots should be of best quality and kept in good order.
- There should be minimum possible friction in the counter device. The torque of the meter should be high so that the unavoidable irregularities in friction may not cause inaccuracies.
- The energy meter should maintain its accuracy under reasonably varying conditions of voltage and load.
- The energy loss in the meter itself must be small.