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What is the difference between instrument earthing and normal earthing? and why is it necessary to do so?
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Answer Posted / jigaranadkat
Dear Shashank,
There are mainly three types of earthing used in instrumentation.
1) Power earth
2) Signal / Instrument Earth
3) IS Earth
Power earth :
Provides ground reference to all power cables. Usual practice to have MAX . Earthing resistance ~ 100 Ohms (There is no harm if it is lower)
Signal / Instrument Earth :
Provides ground reference to all Signal cables (including ICS systems).
Usual practice to have MAX . Earthing resistance ~ 10 Ohms (There is no harm if it is lower)
3) IS Earth (Intrinsically Safe Earth) :
Provide ground reference for all IS signals. MUST NOT EXCEED 1 OHM.
You can have multiple earthing pits of same kind of earth and can be connected in parallel in order to reduce the over all resistance.
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