How should a digital multimeter (DMM) be connected to measure 4-20 mA?

To accurately measure a 4-20 mA signal with a digital multimeter (DMM), it is essential to connect the meter in series with the circuit. This is because a current measurement requires the meter to become part of the circuit so that all the current flowing through the loop also flows through the multimeter.

When connected in series, the DMM will display the current flowing in the circuit, which in the case of a 4-20 mA signal indicates the variable measurement of the process being monitored. Disconnecting one wire in the circuit creates a point where the meter can be inserted, allowing it to measure the current accurately without interrupting the circuit's functionality.

Connecting the DMM in parallel with the circuit would not yield a correct current measurement, as it would instead measure the voltage across the circuit components, which is not the desired measurement for current analysis. Similarly, connecting the multimeter directly across the power supply or using a voltage clamp meter would also fail to provide an accurate representation of the current flowing in the specific loop of the 4-20 mA signal.