# using clamp on meter with dc

Discussion in 'General Electronics Chat' started by lokeycmos, Nov 13, 2010.

1. ### lokeycmos Thread Starter Active Member

Apr 3, 2009
432
7
hello, i have a question about using an ac clampon meter with pulsed dc. i have a tenma 72-7222 clamp meter. i am using it to measure high frequency (21khz) pulsed dc. i do get a reading, but wondering how accurate it is(ac vs pulsed dc)? TY

Last edited: Nov 13, 2010
2. ### Wendy Moderator

Mar 24, 2008
20,735
2,499
Good question. I get the feeling not, but I really don't know. Look up the meter specs for frequency response and RMS response.

3. ### timrobbins Active Member

Aug 29, 2009
318
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For starters it has to be specified for DC operation (given that you say it is an ac clampon.

Jul 7, 2009
1,585
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It's a \$35 meter, but I couldn't find a spec sheet on the first few items from a search (I'll let you do the work).

From the experience I have with the 3 clamp-on DC meters I have, I would be surprised if your meter was able to respond at the frequencies you're trying to measure. Most meters I've used are good up to around 1 kHz. In other words, the meter you're using is worthless for what you're trying to do.

What you're trying to do is a whole different kettle of fish than what these clamp-on meters are intended to do -- which is measure AC and possibly approximately-line-frequency-at-best DC currents. Here are three possible tools to consider. First, use a non-inductive resistor in series with the load and use a scope to view the voltage across the resistor (i.e., the resistor converts the current into a voltage). Don't attempt this unless the voltages in the circuit are low, as you need knowledge and e.g. a good differential amplifier to do it safely.

Next, you can find a clamp on current probe. These are instrumentation quality and not cheap (new ones can be thousands of dollars depending on the bandwidth).

Or, you can look for a suitable current transformer. This will also involve some cost and need some knowledge to use.

I'm a home hobbyist, so fancy equipment is out of the question. I use the shunt resistor approach myself.