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Fluke 89iv funny reading

Discussion in 'General Electronics Discussion' started by LEDlou, Mar 3, 2016.

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  1. LEDlou

    LEDlou

    15
    0
    Feb 24, 2016
    Hi

    Just got a Fluke 89iv Multimeter from ebay. It is in very good condition but I am wondering if it IS 100% OK. I understand I should not get a reading when I short the cables but I am getting these readings

    AC V 0-1000= 0.0027 . Wires not touching 0.0140
    AC V 0mV- 1500mv= 00.17 Wires not touching does not fully settle wanders around 5.900
    DV V 0-1000 V = 0.0000 Wires not touching 0.0000
    DC 0mV-3000mV = 0.16 Wires not touching does not fully settle wanders around 0.049
    Resistance 0- 3000 OHM = 0.13
    Is this normal and acceptable. Are there any other test I can do.
    Apologies if this is very silly question.
    Thanks for your help.
    Lou
     
  2. dorke

    dorke

    2,342
    665
    Jun 20, 2015
    1. Measuring voltages with wires not touching is mostly meaningless (there is pickup from the air ,worse for AC-line pickup).
    Short the wires, you should get 0.000V in all ranges.

    2. In resistance measurement it is fine,you are measuring the resistance of your probes.

    3. For more tests you need calibrated sources/resistors.
    If you don't have them:
    You can measure a new AA/AAA battery for VDC.
    You can measure line voltage VAC(carefully!)
    You can measure a known resistor.

    4.That is an excellent and expansive professional DMM you got...
     
  3. LEDlou

    LEDlou

    15
    0
    Feb 24, 2016
    Hi
    Thank you very much for your response.
    Here are the reading I have:
    I am not getting 0 on any of the readings, except for DCV. when wires are shorted. Getting approx below

    AC V 0-1000= 0.0027 .
    AC V 0mV- 1500mv= 00.17
    DV V 0-1000 V = 0.0000
    DC 0mV-3000mV

    VDC on new AA battery: 1.6254. Settles in couple of seconds.
    VAC (I live in the UK) Does not settle ( should it?) getting various reading between 243.75 -242.82.


    Am mostly happy with the meter,the continuity tested fine and quick on a pcb. It is just the fact that readings seem to be off. Calibration is going to cost a lot.
     
  4. ModemHead

    ModemHead

    69
    20
    Dec 2, 2010
    From the Fluke 87 & 89 Series IV Users Manual (Rev.3 11/00) on page 7-5:

    2. A residual reading of 8 to 80 digits with leads shorted, will not affect stated accuracy above 5% of range.

    This note is in reference to the AC measurement functions, and arises because the RMS converter inside the meter has a small output offset voltage which is always present even if there is no input. This is why the accuracy is only specified above 5% of the range, because the offset is mathematically negligible there. Generally, all brands and types of "True RMS" handheld DMMs will have these same characteristics.

    Mains voltage is typically always fluctuating and will probably never "settle", especially when you're looking at it with 10mV resolution. In the absence of AC calibration equipment, a function/signal generator, or an audio amp playing a computer-generated tone, can substitute as reasonably stable AC sources.
     
  5. LEDlou

    LEDlou

    15
    0
    Feb 24, 2016
    Thank you again.

    So my main question is whether not getting a 0 reading when wires are shorted is a concern.

    Read somewhere if you dont get 0 on Ohm readings when wires shorted, there is something wrong with meter.

    The DC readings seem to just inside 5% accuracy.( seem to get more accurate read from my cheap MM)

    Thanks

    Lou
     
  6. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    I think you are seeing the effect of too much resolution. The meter has more digits than it can accurately display.

    If you have a meter with 3 digits and it reads 0.00 is that more accurate than a 5 digit meter that read 0.0012?

    Bob
     
  7. ModemHead

    ModemHead

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    20
    Dec 2, 2010
    This is incorrect. As dorke previously pointed out, the meter will measure the test lead and banana jack contact resistance when the probes are shorted in Ohms mode. This can easily add up to 200 milliohms (0.20) even with leads and jacks that are in good condition. This offset is only significant in the lowest ohms ranges, and can be compensated for by using the REL (relative) function.

    I reviewed your posts and the only DCV measurement you mentioned is an AA battery at 1.6254V. That is a believable nominal voltage for a fresh battery, but this is nowhere near accurate enough to assess the calibration status of your DMM. For more confidence, you could compare your meter's readings with a calibrated unit from a friend or school/company lab, etc. You can also buy a cheap "voltage reference module" on eBay. Those are not lab-quality calibration standards, but are perfectly fine for hobby/home use.
     
  8. Minder

    Minder

    3,092
    661
    Apr 24, 2015
    One thing to keep in mind with Fluke meters is when the internal battery is getting low, before the battery symbol comes up you can get very weird readings.
    I have experienced it with mine, so when a maintenance electrician approached me and said he was measuring 240vac instead of the expected 120v I got him to change the battery and it cured the problem.
    M.
     
  9. LEDlou

    LEDlou

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    0
    Feb 24, 2016
    Thank you all.
    I tested some chargers for domestic electronics; multi remote, camera battery charger, and they both seem to be slightly out .
    8vDC output read at 8.54 v by DMM
    3vDc output read at 3.25 v by DMM. Of course there is no way of knowing how accurate these chargers are. Will try and get "voltage reference module".
    Interesting what you said about cables as the readings change if the cables are tangled.
     
  10. LEDlou

    LEDlou

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    Feb 24, 2016
    I am using re chargeable nimh batteries, I understood it is ok to do so.
     
  11. Jyfre

    Jyfre

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    Jul 11, 2015
    You can check the calibration of your DMM by resistance and DCV measurement. Resistance - Just short the test probe and you must get the 0 ohm. DCV - You need have known 12vdc supply and measure it. If the result is not on same way. DMM have potentiometer inside it, and you can adjust it by turning potentiometer until you get the exact reading both resistance and voltage....
     
    Last edited by a moderator: Mar 8, 2016
  12. LEDlou

    LEDlou

    15
    0
    Feb 24, 2016
    Thanks Jyfre
    I am away for a few weeks, but will do once i get back. As mentioned I am getting 0.13 on resistance when shorted.
    How difficult is it to access and locate potentiometer, and is a matter of turning a dial
    Lou
     
  13. dorke

    dorke

    2,342
    665
    Jun 20, 2015
    Your meter is fine!
    Don't even open it or touch anything,
    just use it as it is.

    As mentioned above a few times,
    your are measuring the test leads resistance and a reading of 0.13 ohm is normal.
     
    Last edited by a moderator: Mar 9, 2016
  14. LEDlou

    LEDlou

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    0
    Feb 24, 2016
    Thanks Dorke.
     
  15. ModemHead

    ModemHead

    69
    20
    Dec 2, 2010
    The 89IV uses "closed case calibration", which means it has no trimmer pots to tweak. Instead it has a built-in firmware cal procedure during which it will store calibration constants in memory, as certain proscribed inputs are applied.

    dorke's advice is solid.
     
  16. LEDlou

    LEDlou

    15
    0
    Feb 24, 2016
    Thanks. Calibration is definitely beyond me and as the great Harry Callahan said: A man's gotta know his limitations.
    Lou
     
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