When to calibrate?

Support
1

Dear all,

I know that this is kind of a newbie question and I do apologize in advance, but I wonder when I should calibrate.
This image shows the following process (with the same program running on device):

  • Before calibration, average 2.94mA
  • Calibration (current goes down to 0, of course)
  • After calibration, average 69.02 uA

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I mean, that’s a huge difference and it looks like after each flashing of the device I have to calibrate again - maybe because the flashing goes to the > 10mA?
Device: PCB powered with 5V with SMD device running at 3.3V
Project settings: Supply Power Box (9V), main voltage 5V, current: main current only (no autoranging)

Versions: Firmware 1.0.7, otii GUI 1.5.4

2

Hi,

No need to appologize.
You need to calibrate Otii Arc when you want to have the measurements with uA precision.
The calibration is needed due to small offset drifts within Otii Arc due to temperature variations.
You also need to calibrate Otii Arc if you have changed supply voltage, both if you have changed DC adapter or if you use another computer or USB hub (different USB VBUS voltage).

So, if you need high precision, always do a calibrate before.

However it seems like you have a larger difference.
Could you reply with your project saved as attachment.
If it is large, you can send the project cropped where the screen shot is from.

Best regards,
Björn

1 Like
3

Hi Björn,

thanks for the quick reply.
Here’s the really simple “baseline” project:
calibration.otii (996.4 KB)

4

Along those lines -
We have a 7.5 digit bench DMM, and this is our reference instrument, so is calibrated regularly.
Do you have a “full” calibration process for the various source/sink/measurements?

This came up recently once our second Otii arrived and one of the other guys was doing some measurements - my Otii (running my special FW and app builds and calibration scripts) shows our products quiescent current is ~800nA. Whereas Otii#2 shows for the same board 1.7uA (which is about what our bench DMM gives also).

5

Hi Jared,

Yes, we calibrate the Otii Arcs in factory with a calibrated DMM.
If you create a case and includes the two Otii Arc IDs, then I can have a look at the calibration files.

Best regards,
Björn

6

Did you ever get this sorted? It sounds like your device might leave it’s debugger interface active after you have flashed it. I know for example that Nordic NRF51 does that. There’s a section about how to turn it of in the Nordic manual, but I know one of the ways is to cut the power, which is done during calibration as we change the voltage. (Sorry for the (very) late reply)