Measuring chokes with a DMM

Discussion in 'General Electronics Chat' started by Art, Feb 6, 2014.

  1. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
    Moderator Edit: This thread was split from here:

    Sorry to butt in, but it seemed like an appropriate thread,
    and it appears to be done with.

    Can a modern cheapish DMM be trusted to accurately measure inductance of say
    an RF choke or power choke?
    I've never used the feature, as normally you'd have markings on the parts themselves for replacement,
    but I need to know the value of a power supply choke in case it fails and needs to be replaced.

    Cheers, Art.
    Last edited by a moderator: Feb 8, 2014
  2. WBahn


    Mar 31, 2012
    Why butt in and hijack someone else's thread at all? :confused:

    Just start your own thread with a title that is appropriate to what you are trying to find out.

    Doesn't that seem a much more reasonable (not to mention courteous) way to get a response then hoping that someone that is interested in a thread titled, "Find LC by frequency" but who really wants to answer questions about DMM inductance meters will happen along?

    I'll ask a moderator to split out your post into a thread of it's own, perhaps titled "Are cheap handheld inductance meters accurate?" You can ask them to rename it if you have something better in mind.
  3. takao21203

    Distinguished Member

    Apr 28, 2012
    The case where a power suply choke fails and you are still able to measure the inductance is not occuring very often.
  4. crutschow


    Mar 14, 2008
    You'd have to look at the specs for the DMM to determine how accurately it measures inductance. Since we don't know which DMM you are referring to, it's rather difficult to make an informed answer to your question.
  5. vk6zgo

    Active Member

    Jul 21, 2012
    One case would be shorted turns.

    The dc resistance will not be affected much,but the inductance will change between a good & bad choke.

    A proper LCR meter with a "Q" function will show the change in "L",but will show the fault up most clearly in the "Q"position.

    I am a bit more dubious about the Inductance range of a DMM.
    Last edited: Feb 9, 2014
  6. Art

    Thread Starter Distinguished Member

    Sep 10, 2007
    No, I mean the choke is fine now, but has no identifying markings,
    so that if or when it does fail, I want to know what to replace it with.
    I want to test it before it does fail.

    I don't actually know the specs of my meter, but it is the cheapest junk that will measure
    both capacitance and inductance (or at least says it does).

    The power choke might be something like 15H, and the radio will still work with a
    14H choke, so ideally it would only need to be a whole Henry unit accurate,
    but I believe small RF chokes can be much smaller values.

    So I guess the question is whether it's fair to expect at least a Henry unit of inductance
    accuracy out of the cheapest multimeter that will measure inductance at all?
  7. Wendy


    Mar 24, 2008
    You can buy an LC meter from BG Micro.

    I tried to come up with either a gyrator circuit to convert Henrys into Farads, or build a RL oscillator to do the same thing , but finally gave up. Their are some interesting schematics using the ocsillator approach people pointed out. I have a hard head, and wanted to design it for myself.

    Gyrator for inductance measurement
    Last edited: Feb 10, 2014