UT61E uA measurement problem

[metRo_]

Hi,

When I bought the UT61E 5 or 6 years ago I was able to measure a uC sleep current that is about 600nA (that same value indicated by the datasheet). Today I tried to measure the same uC sleep current but I got a lower value 230nA and sometimes nothing is displayed.

What could be wrong?

[rsjsouza]

Any measuring equipment can suffer drift over time and the UT61E is not an exception.

There are many potentiometers that regulate the calibration in various ranges - depending on the generation of your meter, you may want to look at:
http://gushh.net/blog/ut61e-calibration/

https://www.eevblog.com/forum/testgear/ut61e-drift-and-recalibration/

[metRo_]

Any measuring equipment can suffer drift over time and the UT61E is not an exception.

There are many potentiometers that regulate the calibration in various ranges - depending on the generation of your meter, you may want to look at:
http://gushh.net/blog/ut61e-calibration/

https://www.eevblog.com/forum/testgear/ut61e-drift-and-recalibration/

The voltage calibration is also related to current measurements?

[joeqsmith]

I've heard others post about how their 61E's had drifted.  If you really want to measure down this low, you may want to look into something better.

I have one but it has had several changes made to it that may effect the performance and it would not make for a good comparison.  I've been tracking it for just over two years now.   

[001]

I've heard others post about how their 61E's had drifted.  If you really want to measure down this low, you may want to look into something better.

I have one but it has had several changes made to it that may effect the performance and it would not make for a good comparison.  I've been tracking it for just over two years now.

Your photo looks intersting
Can You say more about mods?

[Nusa]

Hi,

When I bought the UT61E 5 or 6 years ago I was able to measure a uC sleep current that is about 600nA (that same value indicated by the datasheet). Today I tried to measure the same uC sleep current but I got a lower value 230nA and sometimes nothing is displayed.

What could be wrong?

Contact resistance, particularly for the no-read cases?

[joeqsmith]

I've heard others post about how their 61E's had drifted.  If you really want to measure down this low, you may want to look into something better.

I have one but it has had several changes made to it that may effect the performance and it would not make for a good comparison.  I've been tracking it for just over two years now.

Your photo looks intersting
Can You say more about mods?

There are several hours of videos that detail the changes I made to this meter.   

Before going to the link,  you have posted about my tests being a circus and you not being happy about seeing the products damaged.  I also understand that you have no desire to try and educate yourself about the testing.  Again, to be clear  I am fine with that.   However,  keep in mind that these changes came as a direct result of me damaging a few of these meters during my evaluations of them.   These videos will not only show me chopping up a brand new working meter but also stressing it in order to demonstrate the effects the changes had to the meter's overall robustness.  I am just warning you that you will find no happiness in these videos based on your previous posts.   The videos are there for the few people that are interested learning a little more about problem solving and design choices.  They are not intended to be viewed by children trying to make changes to their low cost meters.   As such, many details are left out on purpose. 

With that said, the UT61E playlist.  Normally, I make conclude with enjoy but I think in this special case, you have been warned is more appropriate. 

https://www.youtube.com/playlist?list=PLZSS2ajxhiQDrk4o1Y45auwK7LomjnNBU

[rsjsouza]

... and THAT, ladies and gentleman, is what I call a real trigger warning! 

Great job, joeqsmith! You now unlocked the
Millenial-certified guardian-of-all-triggers badge of honor.

[metRo_]

I measure the shunt resistors following this manual and got these values:
 R32 - 900ohm - 901.7ohm
 R31 - 90ohm - 90.24ohm
 R30 - 9ohm - 9.05ohm
 R29 - 2(2x1)ohm - 1.00 and 1.02 ohm

If I'm correct R32 is the one responsible for uA range. Is it possible that the resistor the resistance changed over time? or does the dmm was calibrated for this value after assembly?

Thanks

[joeqsmith]

They do have a switch in common.  I have never life cycled any of the UNI-T products.  The switch on one of my UT210E clamp meters did start to have problems after about a year of service.   This is the only UNI-T product that I have that actually gets used a modest amount.   

If you have a good meter, you could inject a known current and try reading voltage across the divider network and see if it makes sense.   It's a combination of these resistors depending what range you are in.   For the uA, all of them are in series or roughly 1K ohms.  You should be able to measure this from the high side of the fuse and the common lead.  Maybe one or more of the diodes is now leaking.   Too many blown fuses or the wrong fuse installed causing a failure?    Easy enough to pull them and see. 

[joeqsmith]

See attached.  Maybe rotate the switch when measuring or clean it for starts.   You could also try adjusting the reference.