Unit-61E Accuracy

[Bryan]

Picked up a 61E a while back, good meter. However I don't think the accuracy of the meter is as promised. I required a 10v calibration source so picked up 2 Max876A reference samples. these have a accuracy of (0.03%) min 9.997v max 10.003v. So tried both samples and they were identical. let them burn in for a week and hooked up to the 61E. The reading on the 61E was 9.976v. Seems quite a bit off in their specs. Maybe my math is wrong, but if I assume worse case that the 876a is at 9.997v and the 61e with a accuracy of 0.1% +2 counts then it should  have a worse case at the low end of 9.987

http://datasheets.maximintegrated.com/en/ds/MAX873-MAX876.pdf

http://sdrv.ms/15jirmq

[toli]

Does seem off specs (although the minimum should be ~9.985 if you take into account the 2 LSD error).
I did a measurement of my UT-61E a few months ago (March) compared to my Agilent U1253A which was tested and was within spec a couple of weeks before that (in an actual cal lab, not at home ). I've attached the file in case anyone is interested in this data. I did the test a few months before that as well (November 2012), just to see how stable the UT-61E really is (this files attached as well). Obviously the Agilent is a 0.03% reference on all ranges, but its good enough for my needs

I didn't really expect the UT-61E to keep its specs or be within spec from the get go, but since its used as my second meter, even if its X10 worse than what the spec claims I can totally live with that.

Edit: cant upload .xlsx files, so I'll add a link to my public dropbox folder:
https://dl.dropboxusercontent.com/u/37472979/comparison_AgilentU1253A_UniT61E_23March13.xlsx
https://dl.dropboxusercontent.com/u/37472979/comparison_AgilentU1253A_UniT61E.xlsx

[Bryan]

There is a trim pot on the board, but not sure if one should attempt to adjust. It may be specific to a certain voltage. I am thinking of picking up a Penta from Voltage Standards. Will see over a range of multiple voltage how it fares. maybe pick up some 0.1 resistors from Newark as well to test the resistance ranges.

http://www.voltagestandard.com/PentaRef.html

[KARADENIZ]

have you seen this video?   06:22  there he makes a calibration

and a accuracy comparison to othere Multimeters
  25:14

[alm]

Sounds like the UT-61E is out of spec. Either that or Maxim shipped two references that are out of spec. Unlikely if you got them from an authorized distributor. Ideally you'd want someone with a calibrated (or at least more accurate) meter to also measure the references.

Can you go back to the distributor that sold you the meter? I assume these are 1 year accuracy specs, so if it's well outside these limits within a short time span, then either the initial accuracy was off or it's drifting more than it should. I probably would not adjust the DMM without the ability to check the other ranges and functions. Do you also have indications that the resistance or current ranges may be off? What about higher/lower ranges?

There have been a few (first second) complaints about Uni-T shipping meters that don't meet specs, but the problem does not seem very widespread.

[mariush]

Check the temperature in your house while calibrating the meter or comparing with the manual.
Check the temperature near the voltage reference, especially if you may have a potentially hot linear regulator near the reference.

Uni-T UT61E is a bit sensitive to temperature, and if I remember correctly the manual says it's calibrated at around 25-28c. 
The maxim datasheet says  the reference should be 9.997-10.003 at 25c

Martin (the guy who made the videos a couple of posts above this post) has tested how much the meter drifts with temperature drops and rises and it does vary by a few counts. I think that's in part 3 or 5 (if there is one) of that series.

But even so, like the video shows, the meter has a few trimpots that allow you to adjust it.  Get a proper voltage standard if you plan to tweak it.

[Bryan]

The reference samples were direct from Maxim, and they both had the same output, so pretty confident they are accurate. Ambient temp was within the test specs. At the end of the day it is a $60.00 multimeter so can't expect a lot.

The two videos are good, and once I get a quality 5v reference I will trim it up. It seems to be accurate on the resistance ranges on the few 0.1% resistors that I had available to test.

[alm]

I'm not familiar with the circuit design of the UT-61E, but I wouldn't be surprised if the trimmer also adjusted resistance readings, since the trimmer probably adjusts the voltage reference inside the meter. It may also be that the input divider for the DC range you're testing is off. Which is why I'd want to test multiple functions and ranges before and after adjustment.

[Lightages]

Here are the schematics for the UT61E, and the data sheet for the main IC, and a data sheet for the TRMS chip

It appears that VR3 is for adjusting resistance readings, and VR1 is for the DC adjust, VR2 for AC volts and VR4 is to adjust the TRMS chip DC offset. Sorry this might be wrong but it was just a quick skim through the data.

[Ig_sherwood]

I've read a lot about this interesting multimeter .
I wanna sell out my new fluke 87/5 and replace it with Uni-t 61E .
However i wanna ask you only one thing.
Is that true that i can replace the analog trimpod for dc voltage with an digital reference ??
Im asking this ,because month's ago i had read an article about this.

[MosherIV]

However i wana ask you only one thing.
Is that true that i can replace the analog trimpod for dc voltage with an digital reference ??   

Simple answer No.

The pot adusts a voltage divider for a 50ppm voltage reference. The pot is unknown.

Any DC reference you use will also be derived from a voltage reference, thereafter every part you use will add to the inital error/tolerance.

The best mods I have read about is changing the voltage reference and pot to higher spec ones. Voltage reference can be improved to 5ppm parts and the pot can be improved to 100ppm or maybe 50ppm.

[Lightages]

I've read a lot about this interesting multimeter .
I wanna sell out my new fluke 87/5 and replace it with Uni-t 61E .

Really? The UT61E is in no way a good replacement for a 87/5. I would rethink that idea.

[Ig_sherwood]

Simple answer No.

The pot adusts a voltage divider for a 50ppm voltage reference. The pot is unknown.

Any DC reference you use will also be derived from a voltage reference, thereafter every part you use will add to the inital error/tolerance.

The best mods I have read about is changing the voltage reference and pot to higher spec ones. Voltage reference can be improved to 5ppm parts and the pot can be improved to 100ppm or maybe 50ppm.

Can you show me some source ? so i can learn about it.

[Ig_sherwood]

Really? The UT61E is in no way a good replacement for a 87/5. I would rethink that idea.

Yes really , it's overpriced and also overkilled for my hobby .
I think to sell it for 270 euro or trade with an gossen 26s .

[joeqsmith]

However i wana ask you only one thing.
Is that true that i can replace the analog trimpod for dc voltage with an digital reference ??   

Simple answer No.

The pot adusts a voltage divider for a 50ppm voltage reference. The pot is unknown.

Any DC reference you use will also be derived from a voltage reference, thereafter every part you use will add to the inital error/tolerance.

The best mods I have read about is changing the voltage reference and pot to higher spec ones. Voltage reference can be improved to 5ppm parts and the pot can be improved to 100ppm or maybe 50ppm.

Interesting idea.  Why not trim it with some low PPM resistors and get rid of the pot?  By the time you change out the crap fuses, add MOVs, change the PTCs, cut some traces and add a few resistors,  don't forget the dope.  Then we need a backlight.  I like my adaptive one so figure a couple of LEDs, transistors, resistors, sensor.    Now to top it off we need to add a good reference and a couple of low PPM Caddocks..  Not to mention time.  What are we up to now for price?      

I ran a pretty big temperature test with all the meters I had left.  I did not have a working 61E at the time.   

Really? The UT61E is in no way a good replacement for a 87/5. I would rethink that idea.

Yes really , it's overpriced and also overkilled for my hobby .
I think to sell it for 270 euro or trade with an gossen 26s .

I can understand your reasoning that the 61E would be a better fit for you.   Personally, I am not a fan of it.  The front end is just too weak and the lack of a back light, come on, really?   What I don't understand is why you would have bought an 87V in the first place if you didn't have a need for it.   

[Ig_sherwood]

What I don't understand is why you would have bought an 87V in the first place if you didn't have a need for it.   

I get my fluke 87/5 as gift from my father ,for my "happy"birthday.

[joeqsmith]

What I don't understand is why you would have bought an 87V in the first place if you didn't have a need for it.   

I just get my fluke 87/5 for my "happy"birthday.

Ah that makes sense.  Consider this my late Happy Birthday to you! 

[hopski]

I would stick with the fluke. it will still be working many birthdays after the UNI-T has packed up.
The UNI-T is good value for the price, but it won't handle the knocks and the inevitable "mistakes" that a fluke will cope with.

[tszaboo]

The UT61E is a good meter for electronics. I have one myself. But I would keep the Fluke, because it was a gift (and that is a big one), and it has better protection, so overall, you can use it for mains power and such. The fluke for sure will last decades, so you might end up using it for stuff, you never imagined doing.

[Fungus]

I wanna sell out my new fluke 87/5 and replace it with Uni-t 61E .

I have a brand Uni-t 61E I can swap you for the Fluke.

[MosherIV]

Can you show me some source ? so i can learn about it.

Read through this thread :

https://www.eevblog.com/forum/testgear/ut61e-drift-and-recalibration/
Read through the WHOLE post before asking questions !

Skip past the stuff at the start about the poor drift performance, PedroDaGr8 on reply 12 starts to talk about fitting a replacement 'external' Volt Ref.
They are talking about an early revision board that had the component pads on the PCB, the current revision of the meter no longer has the unpopulated pads   

Look at reply 42 on page 2 - look at the picture of how the through hole Vref is attached to the PCB, and the current limiting resistor.
The original pot needs to be replaced with a higher quality one.

[Bryan]

The UT61E is a good meter for electronics. I have one myself. But I would keep the Fluke, because it was a gift (and that is a big one), and it has better protection, so overall, you can use it for mains power and such. The fluke for sure will last decades, so you might end up using it for stuff, you never imagined doing.

True on that, fried my UT61E probing some HV. Fluke probably would have survived.

[Ig_sherwood]

I have a brand Uni-t 61E I can swap you for the Fluke.

  no thx i will kept my fluke ,maybe im just too hurry to buy others stuff that i need .

[joeqsmith]

From a safety standpoint, I would suspect the 87V being certified is safer than a non-GS certified UT61E.  The pictures of the GS version shows it is not the same inside as the non-GS product.   From an input robustness standpoint, there is no contest.  The 61E is crap and I doubt even the GS certified meter would withstand the grill starter test.   The 87V was also a poor performer.  Not very robust at all but much better than the 61E.  However,  I would put my modified 61E, against an 87V any day on my transient tester and the 61E would out perform it by a fair margin.  Oh wait, I have!  Again, not suggesting it's safer (more than likely less safe) but certainly more robust.   

[Fungus]

True on that, fried my UT61E probing some HV. Fluke probably would have survived.

Weirdly enough. the 87V isn't very robust. In the robustness testing thread it failed at just 1.5kV.

Many meters have gone much higher than that, including some really cheap ones.

https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/