SOLUTION

Problems in Measurement of High Resistance

There are some problems and difficulties that occurred in the measurement of high resistance. Due to very high resistance, a very small current flows through the measuring circuits, which is very difficult to sense. The various problem and difficulties are as follows:

1. Leakage Currents: The leakage current is produced and is of comparable magnitude to the current being measured. Such currents cause errors. These currents depend on humidity and hence are unpredictable. Hence leakage currents must be eliminated from the measurement.

2. The stray charges may appear due to the electrostatic effect such charges and alternating fields can also cause serious measurement errors.

3. One point of the circuit may be connected to the earth for accuracy in measurements.

4. When the voltage is applied to the insulation resistance, it takes some time for charging and absorbing currents. The measurement should be delayed till these current vanish completely. In some cases, this may take a very long time hence the testing conditions include the time between the application of voltage and the observation of the reading.

5. A very high voltage is required in order to raise the current magnitudes. The galvanometer should be very sensitive and proper steps must be taken to prevent the damage of the galvanometer due to high voltages.