Device calibration fails silently, causing 2x measurement errors

[igoraltvidal2]

I have a few units of the Power Profiler Kit 2, and I was doing some measurements when I noticed that sometimes the readings are way higher than expected (like 2x higher).

Checking the log file for those measurements that failed, I can see the following messages:

  17:47:36.616    Failed to start PPK
  17:47:36.617    PPK opened

This is different from successful sessions:

  17:42:29.444    PPK started
  17:42:29.445    PPK opened

I investigated and found that the Failed to start PPK message indicates that the device-specific calibration modifiers couldn't be loaded. The critical issue is that the app continues anyway, using default (uncalibrated) modifiers, with no warning to the user.

This results in measurement errors because:

• Each PPK2 has unique calibration values (resistor tolerances, ADC characteristics)
• Default modifiers ignore this factory calibration

I believe this is a critical issue, because after the message Failed to start PPK, the nRF Connect should take some actions here, as:

1. Show a clear and visual warning dialog: "Device calibration failed. Measurements will be inaccurate (±15% error or worse). Please reconnect device."
2. Block sampling: Don't allow measurements until calibration succeeds
3. Auto-retry: Attempt to reload calibration 2-3 times before showing error
4. Fix root cause: Add boot delay + buffer flush
5. Add validator: Check if modifiers match defaults and warn user

[datenreisender]

@igoraltvidal2 Thanks for finding and reporting this. We do not yet have a timeline on it but we will investigate it. Maybe we can reproduce or find a solution without that.

It sounds as if the code at https://github.com/NordicSemiconductor/pc-nrfconnect-ppk/blob/main/src/actions/deviceActions.ts#L480 isn't executed in your case. The app should then already disconnect from the device, but your description sounds like that currently does not happen.