Why Instrument grounding required?

Instrument signal loop

1V-to-5V signal for an Instrument. At 4mA, the voltage measured by the instrument is 1V (250 ohms2.004A). At 20mA, the measured voltage is 5V. Normally, the instrument scale is calibrated so the voltage reads directly in DegrF, psi, etc.

Instrument ground

For LV (Instrument) system it should be less than 1 ohm and

For MV (electrical) system it should be in rage of 1 to 5 ohm

Ideal is 0 resistance but practically it is not possible

The major consideration is for:–

· Ground system maintains reference potential for instrument/Equipment safety

· Protect against static Charge

· Limit the system to casing voltage to enhance operator safety

· Grounding provides a discharge path for short duration current during lightening and prevent damage from surges on power lines

Credits - Amit Upadhyay

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