Author Topic: New uCurrent offset way out of spec (-6mV!)  (Read 6658 times)

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Offline InsatmanTopic starter

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New uCurrent offset way out of spec (-6mV!)
« on: January 12, 2018, 05:57:34 am »
I just received a new uCurrent Gold today and thought I'd give it a little test.  The unit has a fresh battery (CR2032) and has never seen over 50mA input on it's mA range.  I am measuring millivolts of offset without any current input as opposed to the spec of <50uV.   Shorting the input makes no difference.  I tried three different meters and got the same result.  The offset voltage is a bit less on the nA range, but unchanged on the uA range.  See photos.   Note if I use the null feature on the multimeter and apply my precision 50mA source I will get a reading of around 49.5mV.  So the op-amps are working but the accuracy is out of spec as well. 
« Last Edit: January 12, 2018, 06:19:29 am by Insatman »
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Offline keox

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Re: New uCurrent offset way out of spec (-6mV!)
« Reply #1 on: February 04, 2018, 09:29:51 pm »
Hi, I just got my uCurrent Gold v5 serial no: 5153 and also observe an offset of the output voltage. Did you sort out the problem?

There is a dependency between an offset of the output voltage and supplied battery voltage (all measured in 1mV/mA range, all tests were with done without any current input):

Batt voltage: 2.7V (close to batt ok cut off), offset: -5.8mV
3.0V -> -4.9mV
3.5V -> -3.7mV
4.0V -> -2.8mV
4.5V -> -2.4mV
5.0V -> -2.1mV

I did not go beyond 5.0V ;)
« Last Edit: February 04, 2018, 09:47:21 pm by keox »
 

Offline InsatmanTopic starter

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Re: New uCurrent offset way out of spec (-6mV!)
« Reply #2 on: February 05, 2018, 02:20:07 am »
Hi, I just got my uCurrent Gold v5 serial no: 5153 and also observe an offset of the output voltage. Did you sort out the problem?

There is a dependency between an offset of the output voltage and supplied battery voltage (all measured in 1mV/mA range, all tests were with done without any current input):

Batt voltage: 2.7V (close to batt ok cut off), offset: -5.8mV
3.0V -> -4.9mV
3.5V -> -3.7mV
4.0V -> -2.8mV
4.5V -> -2.4mV
5.0V -> -2.1mV

I did not go beyond 5.0V ;)

I have not sorted out the problem.  I did some measurements and determined that the offset is from the last op-amp in the chain.  I have made 4 attempts to email Dave Jones with the data and have had no  response (can you hear crickets?).   I also sent him 3 private messages on this Forum...again no response.   
 
I have not been able to find any link on his webstore to report problems, so I tried emailing.   I am very dissappointed in Dave's customer service at this point.   He (or his workers) were quick to process my order and the unit arrived fairly quickly, but ZERO response to my attempts to get this resolved.

I have purchased a replacement op-amp but have not yet touched the board in the hope that Dave contacts me.

I am not surprised that the offset is battery voltage related. 
Retired Pulsed Power Engineer/Physicist...now I just dabble in electronics
 

Offline keox

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Re: New uCurrent offset way out of spec (-6mV!)
« Reply #3 on: February 05, 2018, 05:43:20 am »
I PMd Dave and hope he will chime in.
Meanwhile, how did you find the culprit? Can you pls help me to find mine? I am a newbie to electronics, but not a newbie in CS, if it will help..
 

Offline EEVblog

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Re: New uCurrent offset way out of spec (-6mV!)
« Reply #4 on: February 05, 2018, 07:25:41 am »
We are investigating this now.
 

Offline EEVblog

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Re: New uCurrent offset way out of spec (-6mV!)
« Reply #5 on: February 09, 2018, 05:58:33 am »
Solved!


 
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Offline imidis

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Re: New uCurrent offset way out of spec (-6mV!)
« Reply #6 on: February 09, 2018, 06:59:51 am »
Why is this not (video) showing under my subscriptions? Is it unlisted?  >:D
Gone for good
 

Offline BU508A

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Re: New uCurrent offset way out of spec (-6mV!)
« Reply #7 on: February 09, 2018, 07:20:18 am »
Solved!

And now for the new batch you have to replace all these OpAmps?

Lot of work, though ...
“Chaos is found in greatest abundance wherever order is being sought. It always defeats order, because it is better organized.”            - Terry Pratchett -
 

Offline imidis

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Re: New uCurrent offset way out of spec (-6mV!)
« Reply #8 on: February 09, 2018, 07:38:30 am »
Ah good point!  :)
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Offline EEVblog

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Re: New uCurrent offset way out of spec (-6mV!)
« Reply #9 on: February 09, 2018, 07:49:59 am »
Why is this not (video) showing under my subscriptions? Is it unlisted?  >:D

Yes. I released it early to Patrons, so unlisted. And it's best to release videos in the morning (my time) to catch the most people at the best time.
 
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Offline EEVblog

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Re: New uCurrent offset way out of spec (-6mV!)
« Reply #10 on: February 09, 2018, 07:50:38 am »
It is unlisted. My bet is Dave doesn't want to post 2 videos on one day, and wants to post this one later so he can ease a little bit on producing the next video.
Many content creators pile videos and release them one by one to create a production buffer.

I should do that but I suck at it.
 

Offline InsatmanTopic starter

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Re: New uCurrent offset way out of spec (-6mV!)
« Reply #11 on: February 09, 2018, 11:24:57 am »
I used a piece of coax and two banana jack adapters between the uCurrent and all three meters I tested when I did my original measurements.  Looks like the coax capacitance and the bad op-amp was the culprit.   Ironically, I used a coax so the measurement would have less noise...lol.   
Retired Pulsed Power Engineer/Physicist...now I just dabble in electronics
 
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Offline Thetatronics

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Re: New uCurrent offset way out of spec (-6mV!)
« Reply #12 on: February 09, 2018, 03:10:30 pm »
When will there be a new batch of the uCurrent Gold available in your shop?  I could really use it for a contract I'm picking up in the next couple of weeks.
 

Offline Simon

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Re: New uCurrent offset way out of spec (-6mV!)
« Reply #13 on: February 09, 2018, 05:07:00 pm »
I have one but the chip that does the battery monitoring is missing. I have ordered some from Texas instruments and am still waiting for them to arrive but assumed I have them it should be as good as new. I'll be setting up my shop again shortly now that I have moved so and decided which particular control panel I want running my new cloud server. If that helps you out.
 
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Offline Thetatronics

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Re: New uCurrent offset way out of spec (-6mV!)
« Reply #14 on: February 09, 2018, 06:54:52 pm »
Yes I would be very interested in purchasing it.  Please let me know when your shop is back up and I'll order it ASAP.  Do you know whether your boards have the same dodgy part that Dave found in his video?
 

Offline Simon

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Re: New uCurrent offset way out of spec (-6mV!)
« Reply #15 on: February 09, 2018, 07:20:21 pm »
it probably does as its out of the last batch , well serial 004706
 

Offline blackdog

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Re: New uCurrent offset way out of spec (-6mV!)
« Reply #16 on: February 09, 2018, 08:41:19 pm »
Hi,

I think the feedback capacitor of the last opamp should be connected to the opamp output en NOT to the output connector...


Kind regarts,
Blackdog
Necessity is not an established fact, but an interpretation.
 
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Offline InsatmanTopic starter

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Re: New uCurrent offset way out of spec (-6mV!)
« Reply #17 on: February 13, 2018, 06:52:50 am »
Yesterday the recommended replacement IC for the split-ground op-amp arrived from Digikey (LMV321IDBVR from TI).  I viewed Dave's two videos on EEV on doing a fix which does not involve replacing the op-amp but both methods have their drawbacks.  So I replaced the IC in question this morning and ran several tests afterward.   My offset voltages are now <100uV using shielded-twisted pair or coaxial hookup.  The offsets are a bit larger with bare leads at times likely due to noise pickup.   I'm not great at surface mount soldering but managed it anyway.   The IC costs less than $1, so I just piggybacked it onto my next Digikey order.   I recommend you go this route if you can get the IC easily. 
« Last Edit: February 13, 2018, 09:53:54 am by Insatman »
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Offline jeremy

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Re: New uCurrent offset way out of spec (-6mV!)
« Reply #18 on: February 13, 2018, 07:12:53 am »
What I learned from this video: if you need to debug a basic op amp design, better have 4 kidneys worth of test equipment  :-DD

Interesting video!
 

Offline InsatmanTopic starter

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Re: New uCurrent offset way out of spec (-6mV!)
« Reply #19 on: February 13, 2018, 08:46:42 am »
What I learned from this video: if you need to debug a basic op amp design, better have 4 kidneys worth of test equipment  :-DD

Interesting video!

Sold off kidneys of all my family and several neighbors...lol...but at least I have test equipment... :-DD
Retired Pulsed Power Engineer/Physicist...now I just dabble in electronics
 

Offline EEVblog

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Re: New uCurrent offset way out of spec (-6mV!)
« Reply #20 on: February 13, 2018, 09:24:49 am »
When will there be a new batch of the uCurrent Gold available in your shop?  I could really use it for a contract I'm picking up in the next couple of weeks.

New opamps are on the Digikey truck now to the assembler
 
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Online tcottle

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Re: New uCurrent offset way out of spec (-6mV!)
« Reply #21 on: February 13, 2018, 06:34:11 pm »
After watching the video last night I checked my brand new uCurrent Gold this morning.  S/N 5199 and U2 is 321T  :o

I am also going down the "piggyback onto my next Digikey order" repair route.  Here is the link for the lazy:
https://www.digikey.com/product-detail/en/texas-instruments/LMV321IDBVR/296-9567-1-ND
 

Offline lapse

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Re: New uCurrent offset way out of spec (-6mV!)
« Reply #22 on: February 20, 2018, 03:57:24 pm »
I have (had) a uCurrent with the 321T.  I received a LMV321IDBVR from Digikey and replaced the 321T.  I'm still reading an offset on my Fluke 15B+ in the mV scale with nothing on the current input.

Without a capacitor across the output:

OFF->nA/uA/mA->0.0mV
ON->nA->0.0mV, ON->uA->-0.2mV, ON->mA->-0.2mV
SHORT->nA->-0.8mV, SHORT->uA->-0.3mV, SHORT->mA->-0.2mV

With a capacitor across the output:

OFF->nA/uA/mA->0.0mV
ON->nA->0.0mV, ON->uA->-0.1mV, ON->mA->-0.2mV
SHORT->nA->-0.5mV, SHORT->uA->-0.1mV, SHORT->mA->-0.1mV
 

Offline Lightages

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Re: New uCurrent offset way out of spec (-6mV!)
« Reply #23 on: February 20, 2018, 05:05:49 pm »
I am confused or missed something. The uCurrent Gold has a manufacturing flaw that some customers have received. Is there no warranty? The customer needs to fix the problem him/herself? I must have missed something.
 

Offline rsjsouza

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Re: New uCurrent offset way out of spec (-6mV!)
« Reply #24 on: February 20, 2018, 05:55:41 pm »
Playing devil's advocate: I don't see warranty terms on the purchase page - buy at your own risk.

On the other hand, perhaps Dave is giving some sort of compensation via other means. I don't know, as I haven't purchased one from this new batch - I have an older generation.

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