Documentation for uCurrent Gold

[JDW]

I tested uCurrent with a 10M 1% resistor at 0.1V to 1V, result shows ~-1mv offset plus -1%.

No question.  It's clear I need to buy a uCurrent Gold.  But again, NO STOCK!  A fellow can't win! 


Wytnucls, after reading your posts it would appear you did not read every post in this thread.  I posted the official word from Fluke regarding nA measurements on the 8845A in my post here:

https://www.eevblog.com/forum/testgear/documentation-for-ucurrent-gold/msg1184028/#msg1184028

My 8845A was purchased in June 2012.  It is only used every now and then, perhaps once every couple weeks for a short period.  It has never been calibrated.  Regardless, see Fluke's reply to my previous post above.  What they wrote would seem to apply to old 8845A and brand spanking new fully just-calibrated 8845A's too.  Besides, even if one wishes to argue my meter is way off and needs to be calibrated, I counter that by presenting this data.  Take note that uA measurements are accurate but only nA measurements are way off in la-la land.  If my meter was messed up calibration wise, I would expect my uA or even mA measurements to be way off too, but they are not.

Anyway...

Anyone know when there will be more stock of the uCurrent? 

[evava]

Flukes and offset:
When I first held Fluke 87V in my hands, I was surprised how much offset it has in DC uA range, I thought that  was faulty instrument. Then I found that thread https://www.eevblog.com/forum/chat/fluke-87v-non-zero-current-reading/ and I finally put up unwillingly with that.
But every time I switch on my second meter UT61e and range to DC uA with 0,00uA dead on, I do not know what to think - maybe it has something with better input protection on Flukes?
How many Flukes is plagued with that feature (large offset on uA range)?

[Wytnucls]

Fluke is only quoting the accuracy figures for the 8845A that you could have known about before post No.8, if you had bothered to read the manual.
25nA accuracy on low DC currents is the worst it should display, within 1 year of calibration. Most will do a lot better than that.
External influence factors are negligible at nA level.

Best of luck with the uCurrent.

[JDW]

Fluke is only quoting the accuracy figures for the 8845A that you could have known about before post No.8, if you had bothered to read the manual.

Why such a smarty-pants reply? I've read the manual as has Fluke.  And I would encourage everyone to read through all the posts in this thread prior to casting  a stone of judgement.  For as I said earlier in this thread, and as the DATA which I posted clearly shows, my Fluke meter is not a "problem unit" insofar as the uA measurements are quite accurate.  If one wishes to argue "it's been 5 years since you bought it and therefore it needs to be recalibrated" or "you have a problem inside your meter," then logic dictates that even my uA readings should also be "way off" but they are not.  Because they are not, it seems reasonable to conclude that, just as Fluke said, this particular meter (model 8845A), is simply inaccurate in the nA range.  I find that terribly unfortunate but not surprising in light of the fact that such is what drove Dave to create the uCurrent in the first place.

As to uCurrent availability, the good news is that 49pcs magically appeared "in stock" as of today.     This must mean that there are in fact many units in stock, just untested.  Dave probably tests them before making them appear "in stock," which is a good sign about the quality of the unit.

I still think there should be "official documentation" for the uCurrent -- hence the name of this thread.  But until then we will just have to be diligent about reading through posts in this forum to ensure we avoid common usage pitfalls.

My thanks to everyone who posted test data and otherwise contributed in a positive way to this thread.

[Jacon]

Anyone know when there will be more stock of the uCurrent? 

Another place, especially for European customers:

http://www.simonselectronics.co.uk/

[luisprata]

Interesting post for ucurrent owners...

https://www.eevblog.com/forum/projects/ucurrent-ma-range-error-using-oscilloscope-and-function-generator/msg1192329/?topicseen#msg1192329

[JDW]

I finally acquired a uCurrent Gold and tested it for the first time today.  uA and mA switch settings tested to be highly accurate, but the nA switch setting is so bad I think it is defective.  Here's a video of my testing of all 3 switch settings.  Please watch the entire video and then let me know what could be wrong with the nA switch setting. 

https://youtu.be/ji0_YW1b57k

Please bear in mind how accurate my uA and mA test results are when formulating your conclusions.  I used a fresh CR2032 too.

I checked the uCurrent Gold SCHEMATIC and then used my Fluke 8845A & 4W probes to test R2, R1 & R9, which measured as follows:

R2 = 9.870k-ohm (nA switch setting)
R9 = 10.00-ohm
R1 = 0.0129-ohm

Thank you.

[FrankBuss]

I finally acquired a uCurrent Gold and tested it for the first time today.  uA and mA switch settings tested to be highly accurate, but the nA switch setting is so bad I think it is defective.  Here's a video of my testing of all 3 switch settings.  Please watch the entire video and then let me know what could be wrong with the nA switch setting. 

Might be the same problem I had, see this thread:

https://www.eevblog.com/forum/testgear/problem-with-ucurrent-gold/

TL;DR: Avoid feedback loops and terrible oscillation created by wires coupling from the output to input, and use a 100 nF capacitor at the input, if you need only DC.

[JDW]

Thanks for your suggestion, Frank.  Specifically, the 0.1uF cap across the uCurrent's INPUTs:



I left the uCurrent Gold at the office, and we are not closed for the next week in honor of Japan's "Golden Week" Spring holiday, but when I get back to the office I'll try the cap and try isolation and then report back here.

[JDW]

The 0.1uF cap is the key to making the uCurrent usable.  Or at least, it transforms your uCurrent into a nano-Current, which is why I wanted one in the first place.  I don't care about AC, so the added capacitor solves my problem. Here are my test results with a ceramic radial lead capacitor installed externally atop the board:

TEST#1
Voltage: 1.003V
Resistance: 99.00M-ohm
Measured Current: 10.06nA (using Fluke 8845A set to 1V range since I get OVERLOAD in the mA range for some reason)
Calculated Current: 1.003/99E6 = 10.13nA
Percent Error: 0.69%  (very accurate!)

TEST#2
Voltage: 1.002V
Resistance: 98.142M-ohm (SMD resistors, 10pcs)
Measured Current: 10.18nA (using Fluke 8845A set to 1V range since I get OVERLOAD in the mA range for some reason)
Calculated Current: 1.002/98.142E6 = 10.21nA
Percent Error: 0.29%  (extremely accurate!)

TEST#3
Voltage: 1.002V
Resistance: 197.142M-ohm (all my resistors in series, 20pcs)
Measured Current: 5.06nA (using Fluke 8845A set to 1V range since I get OVERLOAD in the mA range for some reason)
Calculated Current: 1.002/197.142E6 = 5.08nA
Percent Error: 0.39%  (extremely accurate!)

After these tests I removed the radial lead 0.1uF capacitor and put a ceramic SMD version on the bottom of the PCB as shown in the photo below.  I repeated TEST#3 and measured 5.07nA -- spot on!



I also added hot glue to the 4 corners of the button cell battery holder because that thing will break off over time if the battery is swapped in and out too often.  That's because it appears to be held down to the PCB by only 2 solder points!

This photo shows my SMD resistor block in series with my axial lead resistors.  And as you can see, despite my having used a breadboard and despite my having used a DC power supply instead of a battery, I still got very accurate results.  But again, ONLY because I modded the uCurrent with a 0.1uF capacitor.  BLESS YOU, FRANKBUSS!




I also swapped out the 270-ohm resistor at R4 for a 1k-ohm.  Previously, there was 2.2mA flowing through the LED, but now there is only 0.9mA, and the LED is still quite bright:



Suffice it to say, I am very pleased at this outcome!

[Lbud4]

@Dave why not add a switch for AC coupling to future versions of the u Current?