Products > Test Equipment
UT61E drift and recalibration
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hgg:

Have you noticed if the UT61E has a drift "preference"?
(Showing a greater than or a smaller than the actual measured voltage)

Thanks.
Nisei:

--- Quote from: stephenlm324 on December 30, 2013, 09:41:05 pm ---Big problem is that 2k multiturn, the data sheet for this type of pot states 1% error with vibration which is 20ohm. I replaced with a 50ohm and a couple of resistors in series (there wasn't one standard value so used two). Vibration susceptibility now 0.5ohm and much easier to adjust.
--- End quote ---
How many counts does that leave you to correct up and down? If it's still a lot then perhaps an even a lower Ohm trimmer would be possible?
DrMag:
Bringing up an old thread--I'm very interested in doing the Vref mod on my UT61E. Unfortunately, I think I have a later version of the meter, and there's no U4 at all, that I can find.  :-//

Does anyone with a newer UT61E know about this? Is this mod still easily done (without jumpering directly to the processor, at least)? There are spots on either side of the board labeled as VREF-, and I'll do some sleuthing to see if these are connected to the right pin, but before I get crazy I wanted to check and see if anyone has made this modification recently.
Fixup:
Hi,

I also was planning to do some modifications to the UT61E. I opened it up and it is a bit different from the pictures found on the forums.
I am planning to at least change the potentiometer and possibly also do the reference modification. In my case I am more interested in long time stability than in temperature stability. Temp stability could be fixed with the thermistor.
Temp stability could possibly be measured with a known voltage in some different temperatures. After that I would use LTspice or some other simulation program to calculate the needed thermistor with some serial resistance to adjust the slope.

Please tell us how you modification went  :)
 

 
MosherIV:
Hi

I am new to the forum here.

Been thinking about getting the UT61e, so have been looking at the tear downs, the schematic, etc.
(I have a Tenma - re-badged UT70b)

With regards to doing the U4 Vref mod on the later revision boards, where the U4 pads have gone.
Try looking at the post (same thread) "My UT61E (~3 years old) came with an "out-of-the-box" modification: An LM385 (TO92) and a series resistor" (2nd page)
The mod looks simple to do : disconnect R15 from the chip (this provides the Vref from the chip).
Copy where the resistor and LM385 goes in the photo.
You can get LM385 with temp co of 20ppm/C which is better than the 75ppm/C of the Cyrustek chip.

I would also definitely replace VR1 which calibrates DC Volts and resistance, 100ppm/C is easily available.
Bournes or other reputable brand from known good source.
Better than 100ppm/C is going to cost serious money (£15 upwards) and have wrong footprint.

I am curious to know what is in the black package - is it a precision laser trimmed resistor pack?
(That is the only way to get 0.1% claimed accuracy. You see them in Flukes. Not sure how they do it for the price.
Maybe because they use cheap ones, that is why we get localised temperature drift)
Personally, I would not do the thermistor mod for temp drift. Need to work out the root cause of the temp drift instead of a work around.
As I said, I wonder if it is the resistor pack they have used.

Also, definitely fit the MOVs (labeled SG1, 2, 3) - if nothing else will protect the meter from ESD.
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