Protection of MetersPublished on 24/2/2012 and last updated on Monday 18th of June 2018 at 07:39:01 PM
- The meter may be connected wrongly to the circuit.
- The rating of the meter is selected wrongly for the measurement.
- Occurrences of over current in the circuit itself during measurement.
Whenever a meter is connected in the circuit to measure an electrical signal, there must be a voltage drop across it. If the current through the meter is increased beyond safety limit, the voltage drop also crosses the rated limit. Suppose the rated voltage drop limit of the meter is 0.6 volt. Now, let us connect a diode across the meter, whose forward barrier voltage is 0.6 volt. Now, if due to excess current through the meter, if the voltage drop across the meter becomes more than 0.6 volt, the diode becomes short-circuited, since this excess voltage also appears across the diode.
As soon as the diode is short-circuited, the meter current is diverted through the diode. As result, the meter is being protected from excess heating. If only one diode is used it is called Single Diode Protection.
If two diodes are connected across the meter in opposite direction, it is called double diode protection. This arrangement protects the meter for both directions of current.