NCCER Control Systems And Fundamental Concepts (26211-23) Practice Test

What is the standard range of a 4-20 mA signal?

0-10 V 1-5 V 4-20 mA 0-20 mA

Correct Answer:

4-20 mA

Explanation:

In process control, signals are often sent as current in a loop because current is less affected by resistance in long cables and can also power the transmitter. The standard range for a 4-20 mA signal is from 4 mA to 20 mA. Here’s why that range is used: 4 mA corresponds to the minimum measured value (0%), and 20 mA corresponds to the maximum value (100%). Having a lower limit above zero helps the receiver distinguish a valid minimum signal from a fault, since an open or broken loop would typically read near zero current. The other options describe voltage ranges or a 0-20 mA range, which aren’t the standard signaling convention for a 4-20 mA loop.

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