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What is Digital Multimeter Impedance?

Discussion in 'Electronic Design' started by Kevin Doyle, Jul 14, 2005.

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  1. Kevin Doyle

    Kevin Doyle Guest

    Hi all
    I have a Fluke 12 DMM and was wondering what is a impedance of such a
    I know that the older analogue Multimeters would be in the range of 10 to
    11M ohms.

  2. John  Larkin

    John Larkin Guest

    Measure it with a DVM!


    yes, you can also measure a supply through an xx meg resistor and do
    the math.

  3. Kevin Doyle

    Kevin Doyle Guest

    Oh thanks.
    I should have known that!!

  4. Joel Kolstad

    Joel Kolstad Guest

    Unless your older analog meters had a FET input, the impedance wouldn't have
    been anywhere near that high -- more in the ballpark of 1k-100k, actually!

    That Fluke Multimeter probably is about 10M, although it's likely to be spec'd
    as something like 10M in parallel with, say, 20pF, so by the time you hit
    10kHz you'd be down to under 1M.

  5. Jim Yanik

    Jim Yanik Guest

    doesn't it say in the manual?
    Some DMMs are 22 Mohms.
  6. John Fields

    John Fields Guest

  7. Pooh Bear

    Pooh Bear Guest

    Quite high. Have you checked the manufacturer's data ?
    Analogue ? You mean moving coil ? Those were usually 50uA movements giving a
    20kOhms/V input impedance e.g. 200k when on the 10V range.

  8. Kevin Doyle

    Kevin Doyle Guest

    I got it 10M using measurement and a little maths!
    Thanks I couldn't find the manual.
    I actually threw it out as there isn't that muc hto know about the flke 12
    there are only 4 buttons on the thing.

  9. Jim Yanik

    Jim Yanik Guest

    You mean like specifications?
    Smarter to put all your manuals in a file,maybe write the serial number and
    date of purchase on them at that time.
    Then if you have anything stolen,you have proof of ownership,and if you
    choose to sell something,the manual can go along with it.(besides being
    able to refer back to the manual if needed.)
  10. Steve Sousa

    Steve Sousa Guest

    You should really rethink that and get the manual, that fluke is one of the
    special cases that had V-check and because of that its input impedance can
    vary a lot, depending on the input voltage. The link to download is
    If that doesn't work, on the fluke site select: support then manuals, on the
    drop down list:digitalmultimeters, model 10.

  11. 10/11 Megohm analog meters were built with a dual triode or a pair of
    FETs to reduce loading the circuit you were working on. AKA VTVM or

    They had 10 Megohm input impedance on AC, plus a 1 Megohm resistor in
    the DC probe to reduce the capacitance of the meter lead to keep it from
    interfering with the D.U.T.

    I can post a schematic to A.B.S.E if you are not familiar with this
    type of meter.

    Link to my "Computers for disabled Veterans" project website deleted
    after threats were telephoned to my church.

    Michael A. Terrell
    Central Florida
  12. Kevin Doyle

    Kevin Doyle Guest

    Thanks for that!
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