Thread: Fluke accuracy

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  1. #1
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    Fluke accuracy

    The specs for the 115 show the accuracy of DC voltage to be +/- 0.5%. That is the same spec as the inexpensive DMM that I currently own.

    Is Fluke being overly conservative with their spec? Anybody really know how much the 115 deviates from true voltage in real life? Since you can buy it with NIST certification is it just a matter of calibration that is baked into the spec?
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  2. Electrical/Wiring/Trolling Motors Moderator CatFan's Avatar
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    #2
    Like I said in the other thread, multimeter accuracy is much more complicated than just a number. The accuracy on a 115 is 0.5% of the reading, plus 2 counts. Without getting too deep, counts are an indicator of meter resolution and are a function of the meter D/A conversion process and the number of digits on the display. An inexpensive may have 6000 counts, while a good one may have 50,000. More counts means they are smaller so accuracy is better.
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    #3
    I guess I didn’t pose my question very well. I wasn’t questioning the actual accuracy of the DMM but the spec itself. It is very possible I don’t really know what NIST Certificates are which is leading to confusion.

    Is it just certifying how far off the DMM is or is it certifying that it falls within a standard?
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  4. Electrical/Wiring/Trolling Motors Moderator CatFan's Avatar
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    #4
    A NIST certificate in this case is a trail to a device that has been tested against a standard. Calibration labs use standards that have been tested against very high accuracy standards. Doesn’t mean anything regarding the actual accuracy of the meter, just that it was tested against something that is very accurate.
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    #5
    Quote Originally Posted by CatFan View Post
    A NIST certificate in this case is a trail to a device that has been tested against a standard. Calibration labs use standards that have been tested against very high accuracy standards. Doesn’t mean anything regarding the actual accuracy of the meter, just that it was tested against something that is very accurate.
    Sorry to be so dense but what is it saying? It was tested against a known entity and?
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    #6
    Zelmo, Unless you are using that meter for some sophisticated job, you are way overthinking this. Besides your batteries and jobs on the car. What are you going to use it for? You don't need certification on the thing. Even if you are concerned with accuracy, it's is a relative thing anyway. Bob

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    #7
    I “overthink” everything. It doesn’t matter if I need it or not. I want to know how things work.
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    #10
    There is a link to(multi meter spreadsheet) a 2017 updated list in that post. Very good info. Thanks Lou
    Last edited by bobcoy; 08-25-2019 at 11:15 AM.

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    #11
    Quote Originally Posted by zelmo View Post
    Sorry to be so dense but what is it saying? It was tested against a known entity and?
    I calibrate these things for a living.

    Basically, it was tested on something like a Fluke 5502 or 5522, and found to be within the published spec. Just a NIST cert won't have uncertainties, but on DCV it's usually exceptionally small, probably around 10-20mV. As someone said, it's 0.5% of reading plus 2 counts. So if you're checking 60v and the meter reads with 0.01 resolution, then your plus/minus is 0.32v.

    Most Flukes will read DCV exactly right, worst I ever see is 2 counts low (59.98v @60v, 898v @900v etc). If you feel yours is off, put a new battery in. Even if it doesn't show dead, it can cause a meter to read much more innacurately.

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    #12
    Quote Originally Posted by ParDeus View Post

    Most Flukes will read DCV exactly right, worst I ever see is 2 counts low (59.98v @60v, 898v @900v etc).
    Thank you. That really changes my thoughts on which model to get.
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    #13
    I have used just about all makes over the years. Get the fluke and you wont have to buy another one.

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