Why we not use 2-20Ma or 1-20Ma

Answer Posted / larry thompson

As with all analog loop standards the range must be divisible by 4 so the technician can determine which quartile the signal is (25%, 50%, 75%, 100%) in. 4 mA was deemed the minimum current necessary to power most analog signal transmitters (it had previously been 10 to 50 mA)

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