Which instrument is typically used to measure 4-20 mA signals?

The correct instrument for measuring 4-20 mA signals is a DC clamp meter. The 4-20 mA signal is a common standard used in industrial instrumentation for transmitting analog signals over long distances while minimizing the effects of electrical noise.

A DC clamp meter is specifically designed to measure direct current, making it the ideal choice for measuring this type of signal. The clamp feature allows the user to take measurements without interrupting the circuit, which is especially useful when working in live environments or on panels where access may be limited.

Additionally, while a digital multimeter can also measure 4-20 mA signals if set correctly, a DC clamp meter provides the added benefit of being able to quickly and safely clamp onto the wire without making contact with the circuit. Other options, such as an AC voltmeter, are not suitable for measuring DC signals, and a resistor box is not an instrument for measurement but rather a tool for simulating resistance in a circuit. Hence, the DC clamp meter stands out as the most effective instrument for this specific task.