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LCR meter V300 failed to equalize ADC I/U

Equipment, circuits, projects, procedures

Postby Guest » Tue Feb 04, 2014 12:00 am

My LCR meter was built up from a pre-fitted board. I am full of admiration for this design. My compliments to Jean-Jaques. It worked fine (also the calibrations), apart for the extreme ranges, as he described in the forum, later. So I made the modifications to V3.0.0.
Since then I cannot perform phase adj. calibrations as the ADC U and I values differ (and can not be made equal by P11 or P7). Also the PGA phase adj. did not work (ADC I 0 mV, which it is. I tried several obvious things (shielding, grounding, erasing calibrations and reloading firmware). No effect. Does anyone have an idea as to what else I can try?
One Idea came up, but I cannot decide about this without more information: Could this be caused by an incorrect Input offset adjustment? I started another thread: Inconsistancy in Input offset adjustment I/U.
If anyone has ideas how to fix the ADC I<>U problem (whether or not due to Input offset adjustment failure), I would be grateful to learn.
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Postby snoopy_94 » Mon Feb 10, 2014 12:00 am

Firstly, it is very important that various offset compensation are carried out successfully.

"Gain informations" and "access to adjust. menus" must be marked (in the Preferences window)

Frequency of 10 kHz must be selected and start measurement.

Input phase adjustment:
Put in place the jumper J7. Value is about 156nF (3x47 + 15). Gain information (R) must be 322, , IE range 3 (Rsense = 100 ohm) and level 2 for final amplification U and I. If not, adjust R100.
Select "Calibration/Input Phase Adjustment" Menu, and perform the compensation.
Same procedure with jumper J6 (R=400, 15nF), J8 (R=500, 1.5nF) and J9 (R=600, 150pF)

PGA phase adjustment:
Put in place the jumper J2. Value is about 10 ohms and R= 200. Do compensation.
Same with jumper J3 (R = 100, 0.95 ohm). For this last compensation, R17 must be populated with a 10R resistor. Take care to the contact resistor of jumper used!

Jean-Jacques
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Postby Guest » Tue Feb 11, 2014 12:00 am

Thanks for trying to clarify the procedure. However, the problem is not the procedure; the problem is that I cannot create valid starting conditions for the phase compensations. The ADC U and I levels can not be made equal. I will give some more observations: ADC I is about 40 to 80 mV lower than ADC U. If I change R100 (R 7 in case frequ < 10 kHz), ADC I varies and ADC U keeps its distance, 40 to 80 mV higher than ADC I. Further, ADC I is very instable. Its value changes by every measuring cycle. Finally, the range is 7, which also is out of limits.
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Postby hadihf » Wed Feb 12, 2014 12:00 am

I think it is normal
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Postby snoopy_94 » Wed Feb 12, 2014 12:00 am

1- Phase compensation must be made at a frequency of 10 kHz.
2- You must allow the display of the gain information.
3- Do not try to have the same level of voltage (mV), but the same index for the post-amplifier when U and I measured. It means, in most cases 0 0 (2 and 2 for the range 3, with jumper J7).

On the attached screenshot, you can see that ADC U and ADC I voltages are different, but that levels of gain for post-amplifier on range 4 are 0 and 0.

Jean-Jacques
Attachments
AU2011-main-window.jpg
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Postby Guest » Thu Feb 13, 2014 12:00 am

This did it, J.J.! You pointed me in the direction I had missed. A matter of more accurate reading.
Now that the instrument is calibrated, I hope to enjoy a long life of it.
Many thanks for the work and for helping out.
Arnold
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Re: LCR meter V300 failed to equalize ADC I/U

Postby smithy » Sat Apr 12, 2014 6:55 am

I am going through the same procedure, but with J6 fitted can only get 3 4 4, and with J7 4 1 1, J8 5 1 1 and J9 6 1 1. I can't adjust R100 any further. Any suggestions?
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Re: LCR meter V300 failed to equalize ADC I/U

Postby snoopy_94 » Sun Apr 13, 2014 4:41 pm

smithy wrote:I am going through the same procedure, but with J6 fitted can only get 3 4 4, and with J7 4 1 1, J8 5 1 1 and J9 6 1 1. I can't adjust R100 any further. Any suggestions?

For the phase compensation the important think is to have the same index "U" and "I" for the post-amplifier. 4 0 0 or 4 1 1 is ok.

Jean-Jacques
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Re: LCR meter V300 failed to equalize ADC I/U

Postby smithy » Mon Apr 14, 2014 9:56 am

Thank you Jean-Jacques. I thought that was the case, as everything is working perfectly.
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