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UT61E drift and recalibration
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Rick Law:

--- Quote from: M0BSW on November 27, 2013, 07:40:42 am --- My experience with the 61E is also on resistance, I have  in a box a 5.7 ohm 1% resistor, my two Alpatek's  trusted meters read 5.7 dead on , however my 61e did read 5.7 now its drifted to 6.0 ohms , in a year. I would adjust it but have know ideal which pot to twiddle plus I'm not sure if 1.3 ohms is acceptable with the specs of the 61E.

--- End quote ---


I assume you are using the lowest which is 220ohm range.  Auto-range would have selected this range for you.

Spec spec for this range is 0.5%+-10 digits.
% error: reading is 6.0ohm. 0.5% of that is 0.03ohm
digit error: At this range, each digit is 0.01ohm so digit error is 10*0.01=0.1ohm.

Total error from spec +-(0.03+0.1) = +- 0.13ohm

You are out 6.0-5.7=0.3ohm off.  Spec is 0.13ohm error for 1 year.  Your meter is out of spec.  But, I think it may be dirt building up in a year.  I cleaned my probe plugs and I took down the resistance by 0.5ohm just from the cleaning.

If you are tired of flipping through the manual or don't have the spec handy, I posted this a while back:

--- Quote from: Rick Law on February 17, 2013, 01:07:30 am ---I hate flipping through the manual to look for the %accuracy/specs each time I change the dial on my meter.  So, I cut and pasted the UT61E's spec for all the selections into a single-page layout.  Small prints, but I can see all the %accuracy for all the ranges on this little poster on my wall.

Thought other UT61E may find this useful.  If you like it, feel free to use it.

(Since the original manual is available for the public to download, I am rather sure this consolidating into single page would fall under the "fair-user" clause of the copyright act.  Well, I think so anyway.)

https://www.eevblog.com/forum/testgear/uni-t-ut61e-multimeter-teardown-photos/?action=dlattach;attach=39571

--- End quote ---
Rick Law:
Anyone trying to calibrate UT61E resistance measurement?

Looking at the schematic, it looks like VR3 may do the job.  But VR3 has (CAP) written right next to it, so I am not sure the schematic is out of date since I know there are a few revisions of UT61E out there.  (EDIT: add this:)Further investigation points to VR3 is for capacitor measurement 220nF range.  Looks like the resistance measurement is not adjustable but controlled purely by the reference resistors.  I hope I am wrong with this because I sure would like to be able to recalibrate resistor measurement.

Has anyone tried calibrating the ohms range?  Success? failure?

Thanks
Rick
stephenlm324:
I have been looking at calibration of the resistance range. I can confirm that VR3 is for cap.
The resistance calibration appears to be fixed, set by the voltage divider resistors (the black side on package). The divider pack would need to be removed and trimmed with external resistors, which would require a good meter. That would then mess up the AC and DC volts ranges.
Further reading to shed light on how it works can be found in the KAD7001 data sheet, similar chip with better documentation.
http://images.ihscontent.net/vipimages/VipMasterIC/IC/SAMS/SAMSD027/SAMSD027-63.pdf
Rick Law:

--- Quote from: stephenlm324 on December 18, 2013, 10:18:16 pm ---I have been looking at calibration of the resistance range. I can confirm that VR4 is for cap.
The resistance calibration appears to be fixed, set by the voltage divider resistors (the black side on package). The divider pack would need to be removed and trimmed with external resistors, which would require a good meter. That would then mess up the AC and DC volts ranges.
Further reading to shed light on how it works can be found in the KAD7001 data sheet, similar chip with better documentation.
http://images.ihscontent.net/vipimages/VipMasterIC/IC/SAMS/SAMSD027/SAMSD027-63.pdf

--- End quote ---

I think you mean VR3 there.  VR4 looks like it is for AC adjustments.
stephenlm324:
Yes, thanks, I have corrected it.
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