Need Help: Digital Multimeter Caliberation

Discussion in 'General Electronics Chat' started by rxyzm, Jun 19, 2016.

  1. rxyzm

    Thread Starter New Member

    Apr 7, 2013
    11
    0
    Hi,

    I am looking for information for calibration of METEX - 3610D or 3650D digital multimeter.
    This meter has a high ohm range of 2000M. When I purchased this meter, with prods open it would show a reading of 10M. Per MFG. manual, this was OK and I would need to subtract that reading from the reading on this range.

    Now the same range shows 88M as reading with prods open.

    I have the circuit diagram for this meter but do not have key voltages/current values. Also, the calibration information. Looking for this information.

    With Regards,

    Ravi
     
  2. dl324

    Distinguished Member

    Mar 30, 2015
    3,250
    626
    Welcome to AAC!
    Do you mean 10M with the probes shorted? With nothing connected (probes open), it should read over range.
     
  3. rxyzm

    Thread Starter New Member

    Apr 7, 2013
    11
    0
    Oops - my over sight. You are right. it's probed shorted
     
  4. EM Fields

    Member

    Jun 8, 2016
    183
    32
    With the meter switched to OHMS, at any range chosen, and with the leads open, the display should read "1." in order to indicate overrange. If it doesn't, the meter's broken.
     
  5. dl324

    Distinguished Member

    Mar 30, 2015
    3,250
    626
    Try using a wire to short the connectors on the meter. If you get a better reading, could be defective probes.

    I don't hold out much hope for calibrating a consumer grade DVM. A real calibration procedure would involve calibrating every range. The best I've seen for inexpensive meters is a pot that affects all ranges for all settings.
     
  6. benta

    Member

    Dec 7, 2015
    101
    24
    The M3610D can measure up to 20 Mohms (pretty standard for most meters).
    Where your 2000M comes from is anyone's guess.

    Benta
     
  7. bertus

    Administrator

    Apr 5, 2008
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  8. rxyzm

    Thread Starter New Member

    Apr 7, 2013
    11
    0
    Thank you everyone and sorry for not replying earlier. Just got time today to sit down an pen few words.

    To EM - This is a Radio shack meter. I think Radio shack took that meter from a company called METEX and re-stamped their name.

    In this meter, when the meter is switched, with open probes, the reading shows OL... Sort of Over-range as you stated.

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    To dl324 - You are right in stating that this being a commercial grade DVM, much calibration may not be possible. However, after posting the message, I was reading a design note on ICL7106 chip and it stated that on the ref+ pin the voltage should be 100 mv. There is a 10 turn pot in circuit with a resister chain biasing this pin. So, I am going to try for that tomorrow.
    Will share the results of my work here.

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    To Benta - this model is close to METEX 3650D. This has 2000 M range.

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    To Bertus - Thank you and appreciate your help. I, too am member of elektrotanya site. Got the schematic from there. That's how I got to know about the 10 turn pot.

    Warm Regards,
     
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