Author Topic: CurrentRanger readings [SOLVED]  (Read 749 times)

mik

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CurrentRanger readings [SOLVED]
« on: January 25, 2019, 05:06:16 PM »
I was using the uCurrentGold and getting expected results.   I just received my CurrentRanger and I am getting quite different results.   In all other respects my test environment is identical. 

uCurrent
DUT powered from LiPo.  Driving a Fluke 75, set on the V scale (not mV)
uCurrent measures ~600nA in deep sleep mode (on nA scale), and around 600 - 1291uA (on uA scale) in regular sleep mode.  This is entirely as expected and inline with current measurements taken on my elderly Agilent 34401A.

CurrentRanger
Checked battery, it is now 3.95V.  The following problems occurred at full charge too. 
Always measures 2.892V on the Fluke regardless of sleep mode, or scale set. 
Auto mode is OFF

Above Fluke measurements were obtained while OLED was not inserted.

OLED inserted, and Fluke disconnected:  Powered up on mA scale.  Immediately reports OVERLOAD ~3254 mA.  It then proceeds to slowly count down the mA, dropping about 250mA a minute.  When switching DUT between sleep, and deep sleep the displayed voltage flicks around the bottom digit and then settles down to the old value.

If I set it into AUTO mode the nA and uA LEDs flicker at about 20Hz.  If I switch auto-mode off and set mA mode, then it starts counting up from zero mA to 75mA.  Moving to deep-sleep mode there ought to be a 1000x drop off, but it sticks around 70mA,

I like the potential of this device because I don't need to haul out all my gear to do a simple current check. 
Obviously I have done something dumb, but I can't figure it out. 
Please throw me a line somebody.
Sorry to be a nuisance.
 


« Last Edit: February 16, 2019, 10:08:01 PM by Felix »

Felix

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Re: CurrentRanger readings
« Reply #1 on: January 25, 2019, 07:08:37 PM »
Always measures 2.892V on the Fluke regardless of sleep mode, or scale set. 
Auto mode is OFF

Above Fluke measurements were obtained while OLED was not inserted.

OLED inserted, and Fluke disconnected:  Powered up on mA scale.  Immediately reports OVERLOAD ~3254 mA.  It then proceeds to slowly count down the mA, dropping about 250mA a minute.  When switching DUT between sleep, and deep sleep the displayed voltage flicks around the bottom digit and then settles down to the old value.

If I set it into AUTO mode the nA and uA LEDs flicker at about 20Hz.  If I switch auto-mode off and set mA mode, then it starts counting up from zero mA to 75mA.  Moving to deep-sleep mode there ought to be a 1000x drop off, but it sticks around 70mA,

I like the potential of this device because I don't need to haul out all my gear to do a simple current check. 
Obviously I have done something dumb, but I can't figure it out. 
Please throw me a line somebody.
Sorry to be a nuisance.

Maybe a separate thread for this specific behavior which is different than what @shivams describes, but it really sounds very abnormal, never seen anything like this, especially the slowly counting up/down.
My first question would be: Did it always do this, from the very beginning?

Anyway, let's assume MANUAL mode only, with no OLED (although it should make no difference with OLED), and DMM on output. Upon power up, it should range to MA, and read typically <0.05mV with nothing attached.
If you say that it OVERLOADS in manual MA mode, that is definitely not normal, unless you're truly overloading it (3A+). it should be <0.05mV on the output.

The auto-ranging flicker could be because of temporary burden voltage during lower range overload+switching (that takes several milliseconds, and if your DUT cannot handle it, it will brown out), to avoid this you can add a diode to clamp the inputs and limit the burden voltage to the diode drop, until ranging-up is complete.
Also depending when you bought it, there are firmware updates which I recommend updating to, which can help solve some issues, particularly with auto-ranging, but not with damaged/defective opamps. The OLED readings are coming directly from the opamps output, so if the output is behaving erratically, the OLED readings will also be erratic/invalid.


If it's of any value:
I spend quite a bit of time to test each unit, and ensure they are within claimed limits and:
- auto-ranging and hysteresis works going from nA all the way to mA
- offset is "0" with no DUT in all ranges
- all other functions work
- unit is powered on multiple times to check for various things and do measurements, no way it would work once then act weird later
- this ensures you should have a functional unit that does not do weird stuff when you first turn it on

What I can offer:
- if we can't find a solution here (forum support), you have the option to return for me to inspect, hopefully find what's going on, and depending on what I find I will offer to repair or replace the unit.

mik

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Re: CurrentRanger readings
« Reply #2 on: January 27, 2019, 07:17:08 PM »
Hi Felix,  Thanks for the swift response.

I'm a Noob and I'm quite willing to admit that I have done something dumb; broken it, and should pay the penalty. I don't want a small outfit to take a hit for my stupidity.  I did follow the assembly instructions which seemed pretty simple and non-ambiguous, and I did have experience with the uC Gold, so I had some clues about how to set it up and use it.   

To answer your questions:
I never saw a stable behavior that squared with my uC Gold expectations.
It only arrived a few days ago, so I assume the firmware is current.  But this doesn't look like a firmware issue to me.

After a couple of minutes.

The thing that makes me suspicious is that I can swap the CR with the uC Gold, or with my Agilent 6.5 digit DVM and get and get the expected results.  The CR just seems well... weird.
Do you think this is something I can fix, or should I send it back for forensics? 

Felix

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Re: CurrentRanger readings
« Reply #3 on: January 28, 2019, 12:51:40 PM »
I'm a Noob and I'm quite willing to admit that I have done something dumb; broken it, and should pay the penalty. I don't want a small outfit to take a hit for my stupidity.  I did follow the assembly instructions which seemed pretty simple and non-ambiguous, and I did have experience with the uC Gold, so I had some clues about how to set it up and use it.   

To answer your questions:
I never saw a stable behavior that squared with my uC Gold expectations.
It only arrived a few days ago, so I assume the firmware is current.  But this doesn't look like a firmware issue to me.

The thing that makes me suspicious is that I can swap the CR with the uC Gold, or with my Agilent 6.5 digit DVM and get and get the expected results.  The CR just seems well... weird.
Do you think this is something I can fix, or should I send it back for forensics?

What I see in your videos, I have never seen on my end. It looks like a very broken behavior.
I can guarantee that unit did not do that when it left from here.
What happened I cannot be sure of, and there is no blame to you at all. I appreciate you reporting this, and in the hope that I/we can learn something from this, I would be happy to try to assist and investigate/repair it. I am willing to bet that replacing the opamps will fix the problem. Unfortunately debugging the many parameters that I usually look at, is not a simple task that we can do over email or even over the phone. I would like to first do some checking, then do the opamp replacement.
I would like you to contact me over email and we can arrange a return as soon as possible - felix at this domain dot com.
Thanks

mik

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Re: CurrentRanger readings
« Reply #4 on: January 28, 2019, 02:44:13 PM »
email sent.

Felix

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Re: CurrentRanger readings
« Reply #5 on: January 31, 2019, 09:59:44 AM »
The CR in question has some components removed/damaged during installation of terminals. Those components are essential for the correct biasing and avoiding opamps overloads. This explains the behavior seen.
A return is now pending, and will follow up once an attempt to repair the damage is complete.

Here's a close-up of the damage:
« Last Edit: March 11, 2019, 10:22:12 AM by Felix »

alexsh1

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Re: CurrentRanger readings
« Reply #6 on: February 03, 2019, 04:04:03 AM »
The CR in question has some components removed/damaged during installation of terminals. Those components are essential for the correct biasing and avoiding opamps overloads. This explains the behavior seen.
A return is now pending, and will follow up once an attempt to repair the damage is complete.

Felix,

It would be good if you could video this repair and post it on the blog. I have changed terminals many times - with inserts / without inserts / different terminals etc. until I ended up with a good quality terminals covered by plastic inserts - this helps to measure nA when inserting wires and not touching terminals. Otherwise readings may fluctuate in the beginning and have to settle down. Anyway back to the topic, I knew some components were closed and exercised extra care, but in case such damage occurs I would like to repair it myself.
Also this would be a supurb heads up for other users to VERY CAUSIOSLY install terminals.

Thanks
Alex


Felix

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Re: CurrentRanger readings
« Reply #7 on: February 04, 2019, 10:58:43 AM »
Alex,
I posted a photo with a warning in the guide.
Everyone is warned to read the guide before they install and use the unit, or they can damage it if they're not careful.

https://lowpowerlab.com/guide/currentranger/assembly-terminal-options/

alexsh1

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Re: CurrentRanger readings
« Reply #8 on: February 04, 2019, 02:15:56 PM »
Alex,
I posted a photo with a warning in the guide.
Everyone is warned to read the guide before they install and use the unit, or they can damage it by being careless.
That's the best I can do.

https://lowpowerlab.com/guide/currentranger/assembly-terminal-options/

I have just given you an idea for next youtube review.
Appreciate your time may be limited.


mik

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Re: CurrentRanger readings
« Reply #9 on: February 15, 2019, 08:36:04 PM »
The problem was that in tightening the terminal posts I had dislodged two components.  Anyone with an ounce more sense than me would not have done this. 

Felix, thanks for letting me send it back to you for fixing.  Under the klutzy circumstance that was more than generous.

It's working fine now and is indeed a really convenient way to monitor current on UC projects..

Felix

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Re: CurrentRanger readings [SOLVED]
« Reply #10 on: February 16, 2019, 10:12:01 PM »
Thanks Mik, I appreciate the follow up and your "review" commend in the blog ;)

As always, it's a pleasure to see one of my creations come back to life after a little caring love and attention.
I was actually really glad to see that it worked perfectly once the damaged components were replaced and broken traces were resoldered.

And I did learn from this - next revision will have those larger caps further away from the terminals to help avoid this. I also put more photos and warnings in the guide.

This is how - with your help and cooperation - we can turn a "problem" into a better product going forward :D