Multimeter Question

Discussion in 'General Electronics Chat' started by sweatyk, Apr 17, 2014.

  1. sweatyk

    Thread Starter Member

    Aug 13, 2013
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    Can you adjust/zero the ohms reading on an autoranging DMM? I opened it up and found 2 trim pots but can't find any schematic or chatter about this. I do not want to adjust them unless I'm sure of what they are for. When I short my leads together they read about 1.2 ohms so I have to recalculate when measuring resistors. It could be the leads them selves but the local radio shack sells crappy stuff. It's a craftsman model 82029. While I'm at it could anyone recommend a decent DMM for a novice that's not overly priced or too complicated to use? I'm looking to spend 60 to 75 dollars if I buy one to replace this one.
     
  2. #12

    Expert

    Nov 30, 2010
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    Don't do it.
    You will throw all the ranges off by trying to adjust for the resistance in your leads and connectors.

    There are meters that will auto-zero on the ohms scale. I have an old Fluke that does that, but I'm not up to date on meters right now. Other people will steer you in a few minutes.
    I just got a $10 DMM at Harbor Freight last week for free. Sometimes they are doing a give away.
     
  3. ian field

    Distinguished Member

    Oct 27, 2012
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    Apparently, a few super expensive professional DMMs have a zeroing button to compensate for the test leads - otherwise just press the test prods together and note the lead resistance to subtract from your low Ohms measurements.

    My first ever DMM (which I still have) was fished out of the bin where I worked at the time, when I got it home I found the resistance and ACV ranges were dead. When I opened it up there was a big chip with lots of pins - and a dual op-amp in 8-pin DIL, as I had nothing to lose, I replaced the op-amp and much to my surprise the dud ranges were working again.

    That was the only time I've ever messed with the presets in the back of a DMM - I had to beg and plead to borrow a meter with an up to date calibration certificate to set mine to.
     
  4. wmodavis

    Well-Known Member

    Oct 23, 2010
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  5. Lundwall_Paul

    Member

    Oct 18, 2011
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    The low ohm reading you are seeing is lead resistance. If you need to measure low resistance I would recommend a 4 wire measurement.
     
  6. #12

    Expert

    Nov 30, 2010
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  7. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    The MM1000 ($65) or MM2000 ($110) from Klein are good meters. Auto ranging, auto shutoff, max/min over test period, ... I don't remember the feature(s) missing from the cheaper one. The best part is that you can get them at your local Home Depot.

    We've had good luck with both. Tracks well with my Fluke 87 - just slightly slower response.
     
  8. crutschow

    Expert

    Mar 14, 2008
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    To check the low ohms zero, connect a large wire directly across the meter terminals with the ohms set to the lowest range. That will tell you what it reads with essentially zero lead resistance.
     
  9. ian field

    Distinguished Member

    Oct 27, 2012
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    I think there might be such thing as *REALLY* expensive meters that have Kelvin connected test leads.
     
  10. crutschow

    Expert

    Mar 14, 2008
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    Here's an example of a high-quality, multimeter with a 4 lead connection. Of course its price is typical of such commercial multimeters.
     
    Last edited: Apr 18, 2014
  11. ian field

    Distinguished Member

    Oct 27, 2012
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    A few months ago Elektor magazine published a project to build a Kelvin lead LCR analyser.
     
  12. Lundwall_Paul

    Member

    Oct 18, 2011
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    Crutschow that is the exact meter that I was thinking about when I posted above. I worked at places that appeared to have unlimited budgets and I always liked this meter.
     
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