Comparing clamp meters to digital multimeters

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The Fluke 376 clamp meter, left, and the Fluke 87V digital multimeter.

Comparing clamp meters to digital multimeters

A digital multimeter is essentially a voltage-measuring tool with some current abilities. A clamp meter is basically a current-measuring tool with some voltage abilities. They are distinctly different instruments, each with its own advantages.

A digital multimeter (DMM) allows you to do electronic work because it offers high resolution, measuring in milliunits—millivolts, milliamps and milliohms. It also allows you to do electrical measurements, though current is usually limited to less than 20 amps. A digital multimeter, however, can measure higher currents if a plug-in clamp accessory is attached.

A clamp meter usually measures to the nearest tenth or hundredth of a unit, rather than in the milliunits available with a DMM. This is sufficient for electrical tasks.

Measuring situations

In years past, electricians used test probes rather than a clamp to measure current. A clamp allows you to measure current without breaking the circuit and get a current reading. 

In addition, a new generation of clamp meters utilizes flexible current probes, which Fluke calls iFlex®. These Rogowski coil probes can squeeze between tightly packed wires or around large conductors. They can be handy in a number of situations:

Simultaneous voltage and current measurements are part of troubleshooting. Yet you cannot do simultaneous measurements with one meter unless you step up several price ranges into equipment used for power quality work.

Effective troubleshooting often requires two meters, one to measure electrical current and one to measure voltage. For electricians, a clamp meter is the most versatile diagnostic tool available. Persons doing industrial troubleshooting, meanwhile, benefit from a separate clamp and DMM.

A cost-effective approach for many technicians is to buy one quality instrument designed primarily for voltage (a DMM) and another tool primarily used for current (a clamp meter).

The right combination of test equipment depends on the equipment you work on and the measurements you make. With a clamp meter, for example, you might need a low-pass filter to eliminate electronic interference that could distort readings.

Here are some general guidelines for deciding which tool might be right for you:

Advanced clamp meter: If you need to accurately measure motor inrush current. Also, if you need a clamp meter with advanced signal processing to measure the output of a variable frequency drive.

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