Why transmitter signal range is from 4-20 mA only

Thursday, June 18, 2009

Interview Question: Why transmitter signal range is from 4-20 mA only? Why can’t it be from 0-100 or 0-20mA?

Answer:

Because if use 0-100% instead of 0 -20 mA ,and if there is any signal cable damage or open cable then it will show only 0%.So we will not be able to know any error in the reading.But in the case of 4-20mA, a zero mA value means error.

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