Author Topic: Question about Firmware Version and Current Resolution  (Read 213 times)

MotoDan

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Question about Firmware Version and Current Resolution
« on: February 06, 2020, 01:21:53 PM »
Hi Felix,

I've had my Current Ranger for a few months now and just have a few questions:

1) Is there a way to determine which firmware version is loaded? I would like to update my firmware if a newer version exists.

2) What is the resolution on the uA range? My unit toggles between 0.0uA and 1.6uA as I slowly increase the current from 0uA. Is 1.6uA the lowest resolution on the uA range?

3) I'm injecting a 3.0uA current source (3.0V and 1.0 MOhm) into the CR and am measuring 11.5mV on the output with my Fluke 187. I was expecting closer to 3.0mV (3V/1M). I have never changed the firmware or messed with any calibrations. I set my 3V supply and my 1M resistance with a 5-1/2 digit DMM. The error is less than 1%.

Thanks and keep up the great work!

Felix

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Re: Question about Firmware Version and Current Resolution
« Reply #1 on: February 06, 2020, 07:22:47 PM »
Hi MotoDan!
I'll try to answer below in order:

1) Unfortunately no. It could be a #define in the sketch but it should be changed every time an update happens. I find that a little difficult given that unless you pair documentation and releases and notes and a lot of keeping track of changes, a version is not more useful that just an out-of-date indicator. Which reminds me I should find some time to update the github sketch. I will think about adding a version string.

2) The resolution is the same across all ranges - the ADC reference is the 3.3v AVDD, so at 12bits that yields "0.8". So 1.6uA would indicate a reading of "2" from the ADC.
There is a "OLED" threshold of 2 I believe in most of the units sold at LPL and WELECTRON. That's to avoid noise (especially in nA and uA) to be picked up and toggle between [0..0.8] when there is nothing attached. So that's why it will jump to 1.6.

3) Should definitely give you around 3uA. But ensure you're measuring on the HIGH side as with anything else.
What happens if you go to nA range? That should give you a much more accurate number in nA. Since that's below 3.3uA (overload in nA range) you should see around 3000nA.

MotoDan

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Re: Question about Firmware Version and Current Resolution
« Reply #2 on: February 07, 2020, 12:31:56 PM »
Thanks for your reply Felix. I think I may have something else going on with my CR.

My UUT is connected on the high-side of the CR, my scope is powered through an isolation transformer and my USB programmer is also connected, but as soon as I connect the ground of my scope to the (-) side of the CR's voltage output I get an over-current at my DC supply. I tried disconnecting the CR from the USB-powered supply, but it didn't remove the short. The short also goes away when I disconnect the programmer (with scope connected). This short only happens with the CR in the circuit.

Are you aware of a failure mode with the CR that might cause this short condition?

The only CR schematic I could find was in PNG format and is difficult to read. Do you have either a PDF or Eagle version of the schematic available?

MotoDan
« Last Edit: February 07, 2020, 12:34:30 PM by MotoDan »

Felix

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Re: Question about Firmware Version and Current Resolution
« Reply #3 on: February 07, 2020, 01:02:32 PM »
The key is to have at most 1 earth ground device connected.
It sounds like in your case you have an isolation transformer which powers your scope. Does it also power your USB programmer? That would be a problem.
Have you checked with continuity that there is no connection between the transformer and earth ground?

I just sat on the phone for 30 minutes explaining to someone else the rules of how to/not to connect things to CR. Although ... I have spent a lot of time putting it all together in the guide.
An overload probably means a lot of current is pushed through the CR because 2 things that can source and sink current (and have a common ground) are connected to it.

MotoDan

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Re: Question about Firmware Version and Current Resolution
« Reply #4 on: February 07, 2020, 01:15:11 PM »
Thanks Felix. Looks like the shorting condition was due to a wiring error on my part. Doh!

MotoDan