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
    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


    Mar 24, 2008
    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

    Senior Member

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

    Senior Member

    Jul 7, 2009
    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.