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My LB02A vs my new Brymen BM869s vs Keithley 2000 vs HP 34401

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jorgemef:
Hello,

I bought a BM869s uncalibrated and tried to test its accuracy.
I have a LB02A which I also hadn't tested before against a calibrated source and finally got access to a keithley 2000 and a HP 34401, both calibrated back in may 2019.

I measured LB02A against Brymen and Keyhtly and HP.

Here the chart of deviation against set values on the LB02A of the 3 equipments for Volt and mV settings of LB02A.

What can I conclude? Bryman is accurate within 1 mV in volt range and within 50 uV in mV range, and LB02A has an accurate set value between 2,5 and 3 v and voltage progression given b "V = Set V + 0,0004 x SetV - 0,0013"?

Unfortunately I checked with Brightwin and they informed me the LB02A cannot be calibrated by end user, but even if I would try to calibrate via the internal potentiometer which I will not do without understanding what it does, this seems not a linear error. Maybe some error due to DAC?

BR,
Jorge

bdunham7:
Are you measuring the meters all three at once in parallel or one at a time?  I'd be concerned about the larger than expected discrepancy between the Keithley and the HP. 

jorgemef:
It was measured one at a time, after warm-up of 15 minutes in an environment of 24ÂșC.

bdunham7:
I'd try that again, all 3 in parallel.  One at a time allows your source to drift as you go. Your two 6.5 digit meters should agree to better than 30ppm or so unless you are very unlucky.  Also a 15-minute warmup is very short, in my experience the 34401A would like a 3-hour warmup for highest stability, no idea on the other 3 instruments.

jorgemef:
Thank you for the feedback. Will try again in a few days once I get access to the calibrated multimeters as per your suggestion.

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