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Why field instruments operating voltage is 24 Vdc?

Why field instruments operating voltage is 24 Vdc?

Why field instruments operating voltage is 24 Vdc?

(OP)
Why field instruments operating voltage is 24 Vdc?

please explain

Regards
Rajesh.M

RE: Why field instruments operating voltage is 24 Vdc?

High enough voltage so that sufficient power can be delivered at modest current.

Low enough voltage that there is no electric shock risk during live maintenance- much safer than 120 VAC.

But not low enough to make circuits intrinsically safe without resorting to a device such as a Zener barrier.

RE: Why field instruments operating voltage is 24 Vdc?

When an earthquake scrams your nuclear reactor and then the Tsunami floods your back-up generators, you can scavenge 12V auto batteries from the cars in the employee parking lot, hook up a couple batteries in series and get your instruments back on-line.

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