UT61E drift and recalibration

[Rick Law]

UT61E owners – What is your experience with the UT61E's first year drift?

My UT61E is near 1 year old now.  I am curious as to what the typical drift may be.  I am considering getting the DMM Check Plus, but want to compare notes with fellow owners.

I also noted from another post on this forum on “replace dc calibration potentiometer on ut61e” that if/when calibrating the UT61E using VR1, even closing the case back will cause a few digit difference, and that the UT61E is rather temperature sensitive.

That post was about replacing VR1 and not about (re)calibrating the UT61E in general.  What are your thoughts with recalibrating using DMM Check+?  Worth the trouble?

Thanks
Rick

[Wytnucls]

Here is a drift comparison between my UT71B/D and 61E, which was done about 6 months ago. The meters all have the original factory calibration. The 71D was used as a reference. You will notice that the 71s are very close to each other, while the 61E had drifted quite a bit.

[Lightages]

The drift problem is probably why I never replaced my blown UT61E. I liked it at first but I found I had to keep tweaking it and that really isn't the way a good meter should behave.

[Wytnucls]

Just did another drift comparison between meters. The UT61E seems to be getting worse, whereas the UT71s are pretty much together. The 71s have 5ppm/c precision film 0.02% resistors, hence less drift I assume.
The table lists the LSD differences, with the 71D as the standard. All readings were very steady, down to the last digit, with a linear power supply from 2 to 14V DC.

[Rick Law]

Just did another drift comparison between meters. The UT61E seems to be getting worse, whereas the UT71s are pretty much together. The 71s have 5ppm/c precision film 0.02% resistors, hence less drift I assume.
The table lists the LSD differences, with the 71D as the standard. All readings were very steady, down to the last digit, with a linear power supply from 2 to 14V DC.

Thanks for the info!  From your post, it looks like I am looking at about 10 count drift.  My requirement (with accuracy) is not high.  10 count drift doesn't please me, but it is (unhappily) acceptable to me.

The drift problem is probably why I never replaced my blown UT61E. I liked it at first but I found I had to keep tweaking it and that really isn't the way a good meter should behave.

While I am curious about the drift, at the same time, I feel a little silly spending $62 (DMM Check Plus) to check on my $60 DMM.  You "tweak it" and get it back in line.  Are you tweaking VR1 alone?

Thanks, both for the info.  You are very helpful.

Let me rephrase the question this way:
The DMM Check Plus gives me a +5v +- 0.1% to 5 digits.  If I can re-calibrate VR1 (alone) with the 5V reference, I am hoping to bring it back to say reduce the error by 1/2 (say from 10 digit off to 5 digit off).  Am I dreaming or is that realistic?

I still feel a little silly spending $62 to adjust a $60 DMM, but that would be at least more than merely satisfying my curiosity...

Thanks again, both Mr Wytnucls and Mr Lightages.  I appreciate your help.

Rick

[Lightages]

A DMM Check, or DMM Check Plus are good investments. You mad a small mistake. The DMM Check Plus gives you 5VDC at 0.01% accuracy. This is what is needed to provide a calibration reference for something on the order or 0.1% accuracy. So, it is the perfect thing to use for the UT61E.

It is hard, if not impossible, to get a better spec'd meter than the UT61E for the price. If you buy another meter then you might end up having two meters you are not sure of. If you buy another meter in the future the DMM Check will still be useful and can help confirm the accuracy of both.

If you are considering buying a second multimeter, I would suggest you need to spend around $150 to get much better functionality than the UT61E. What you should be looking for is a safer meter for higher energy circuits to compliment UT61E.

[Monkeh]

If you are considering buying a second multimeter, I would suggest you need to spend around $150 to get much better functionality than the UT61E. What you should be looking for is a safer meter for higher energy circuits to compliment UT61E.

Assuming he's working on high energy circuits.

[Lightages]

If you are considering buying a second multimeter, I would suggest you need to spend around $150 to get much better functionality than the UT61E. What you should be looking for is a safer meter for higher energy circuits to compliment UT61E.

Assuming he's working on high energy circuits.

Yes of course. 

[Rick Law]

A DMM Check, or DMM Check Plus are good investments. You mad a small mistake. The DMM Check Plus gives you 5VDC at 0.01% accuracy. This is what is needed to provide a calibration reference for something on the order or 0.1% accuracy. So, it is the perfect thing to use for the UT61E.

It is hard, if not impossible, to get a better spec'd meter than the UT61E for the price. If you buy another meter then you might end up having two meters you are not sure of. If you buy another meter in the future the DMM Check will still be useful and can help confirm the accuracy of both.

If you are considering buying a second multimeter, I would suggest you need to spend around $150 to get much better functionality than the UT61E. What you should be looking for is a safer meter for higher energy circuits to compliment UT61E.

You are right! 0.01% and not 0.1%.  Typo error on my part.

I don't work on anything more than 20v-30v.  I am merely poking around trying to do something fun so it is hard to say I need it.

I am really itching for the darn thing (getting the DMM Check Plus), and I think I am close to talking myself into it.  Your "So, it is the perfect thing to use for the UT61E" is helpful in my decision making...

[BravoV]

What kind of voltage references that is used in this kind of DMM ? External or built-in at the main chip ?

[iloveelectronics]

You can also get one of those Chinese voltage reference devices with 4 voltages (2.5, 5, 7.5 and 10V) that has been discussed here at a lower price. In fact I have some of those too (just never had the time to list them on eBay) but I won't be shipping the lithium battery like other sellers. They are really just taking their chances to be honest, because both HK Post and China Post officially do not allow air shipment of lithium batteries.

A DMM Check, or DMM Check Plus are good investments. You mad a small mistake. The DMM Check Plus gives you 5VDC at 0.01% accuracy. This is what is needed to provide a calibration reference for something on the order or 0.1% accuracy. So, it is the perfect thing to use for the UT61E.

It is hard, if not impossible, to get a better spec'd meter than the UT61E for the price. If you buy another meter then you might end up having two meters you are not sure of. If you buy another meter in the future the DMM Check will still be useful and can help confirm the accuracy of both.

If you are considering buying a second multimeter, I would suggest you need to spend around $150 to get much better functionality than the UT61E. What you should be looking for is a safer meter for higher energy circuits to compliment UT61E.

You are right! 0.01% and not 0.1%.  Typo error on my part.

I don't work on anything more than 20v-30v.  I am merely poking around trying to do something fun so it is hard to say I need it.

I am really itching for the darn thing (getting the DMM Check Plus), and I think I am close to talking myself into it.  Your "So, it is the perfect thing to use for the UT61E" is helpful in my decision making...

[Wytnucls]

What kind of voltage references that is used in this kind of DMM ? External or built-in at the main chip ?

The band-gap voltage reference (-1.2V) is inside of the UT61E Cyrustek ES51922 chip (75 ppm/C).
So has the 71D, fitted with Cyrustek ES51966, with a slightly better 50 ppm/C.
However, the 71 series uses a Maxim external voltage reference with a 2ppm/c specification (max 5ppm/c).

[PedroDaGr8]

The UT61E has a smattering of unpopulated spots which make up the circuit for an external vref (IC, resistors and filter caps). It SHOULD be relatively easy to add if you can figure out the required dividers (mainly I couldn't find a value for the input impedence of the external Vref pin). This is a project that I have had on the back burner for a while now.

[Monkeh]

The UT61E has a smattering of unpopulated spots which make up the circuit for an external vref (IC, resistors and filter caps). It SHOULD be relatively easy to add if you can figure out the required dividers (mainly I couldn't find a value for the input impedence of the external Vref pin). This is a project that I have had on the back burner for a while now.

Would that be U4?

Please elaborate on the details here, I'm rather curious.

[PedroDaGr8]

The UT61E has a smattering of unpopulated spots which make up the circuit for an external vref (IC, resistors and filter caps). It SHOULD be relatively easy to add if you can figure out the required dividers (mainly I couldn't find a value for the input impedence of the external Vref pin). This is a project that I have had on the back burner for a while now.

Would that be U4?

Please elaborate on the details here, I'm rather curious.

Yeah it is U4 and the unpopulated spots near by. I'll try to find the IC that will work with it when I get home this evening.

[Rick Law]

Ahem,  Just to close off my thoughts on UT61E and DMM Check Plus...

Taking advantage of a moment of lax of self discipline, I stumbled into the voltagestandard site quite by accident, (I was controlled by unknown alien presence at the time) and some how I managed to click BUY...

I promised myself that I will not exceed my entertainment budget and I just did - The alien control was so powerful that I even clicked the dual frequency option and enclosure option.  I will punish myself later for such lack of discipline.

Now that is really really silly.  I just spend $90+ to check on my $60 dmm.  You can now begin laughing at me.

I am well prepared with proper excuses:
Excuse 1 - I have 5 dmm's, I need to know which one is more wrong
Excuse 2 - with the dual frequency, I can use my $90 checker to check if my $70 cheap USB scope drawing different square waves
Excuse 3 - My next project is to do a "Tricorder", it should be able to measure anything.  I need something to validate the tricorder readings.
Excuse 4 - I didn't do it.  I was temporarily controlled by aliens taking over my clicking finger.

Now let me go kick myself for exceeding my self-imposed entertainment budget.  But I really like the idea that I can do a sanity check.  That my measurement is by some standard with certain percentage of some standard...

[M0BSW]

 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.

[Rick Law]

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.

I found part of the problem is the probe and the socket doesn't make very good contacts.  I can twist the probe banana plug (as if it is a dial) and get +- 0.3ohm delta easily as I turn the plug like a dial.  Cleaning the contacts helps for a while.

I suspect if you clean the plugs, jiggle it, you may get 6.0 ohms back down to 5.7ohms.

[stephenlm324]

I have recently purchased a UT61E and found that the stability could be better. I found some interesting information on an external Vref which deserves credit but I don't do Chinese. The link "http://forum.eepw.com.cn/thread/239953/1" has the required info to retro fit the UT61E with an external Vref LT1790. The temp co. is typ. 5ppm. as opposed to 75ppm in the ES51922. I can confirm the accuracy of this info as I have just completed the mod along with replacing the pot VR1 with a resistor network and a 50ohm pot. The standard is 2k and drifts 1% (20ohm) with vibration alone.
The mod requires the LT1790ACS6-1.25 two 10k resistors one 10uF cap all SMD. R15 needs to be removed and replaced in position R51.
My meter is already looking much more stable, I suspect the standard Vref warms up after switch on inside the main chip, taking some time to settle.

[george graves]

^That's nice!  I think I'll wait for someone to do a English write up before I would give it a go! 

Since the 61E is a 22,000 count meter, would it be better to calibrate it at something just below 2.2 volts so that you get the full count on the meter?

[Rick Law]

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.

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:

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

[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]

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

I think you mean VR3 there.  VR4 looks like it is for AC adjustments.

[stephenlm324]

Yes, thanks, I have corrected it.