In a 4-20 mA control loop, what does a current of 4 mA represent?

In a 4-20 mA control loop, what does a current of 4 mA represent?

• A. The maximum process variable.
• B. The minimum process variable.
• C. The normal operating point.
• D. An alarm condition.

Answer: (B)

In a 4-20 mA loop, the current is the signal that represents the process variable. The range from 4 mA up to 20 mA maps to the full span of that variable—from minimum to maximum. Therefore, a current of 4 mA corresponds to the minimum process variable in the configured range. The normal operating point is usually somewhere between 4 and 20 mA, often near mid-scale, depending on the process. An alarm condition would typically involve currents outside the 4-20 mA range or other diagnostic signals, not just the 4 mA value itself.

In a 4-20 mA loop, the current is the signal that represents the process variable. The range from 4 mA up to 20 mA maps to the full span of that variable—from minimum to maximum. Therefore, a current of 4 mA corresponds to the minimum process variable in the configured range. The normal operating point is usually somewhere between 4 and 20 mA, often near mid-scale, depending on the process. An alarm condition would typically involve currents outside the 4-20 mA range or other diagnostic signals, not just the 4 mA value itself.