Power Profiler Kit II measurement error

[MartinZ]

I made some tests with PPK-II in source meter mode by connecting a load resistor in series with a Fluke 8846A ampere meter to the PPK output. A also hooked a GW Instek GDM-8351 voltmeter in parallel to the PPK output.

Here are the results:

The PPK is out of spec around 500uA. From time to time, while changing the output voltage up and down, those red values suddenly got much better, in accordance with the +/-10% specified max. error. But I couldn't figure out what exactly makes the PPK suddenly jump in/out of spec. However, most of the time I observed the large errors from the table above.

Given the described behavior, I suspect a FW error in range changing logic. Are you aware of this? Can this be fixed in a future FW upgrade?

[Audun]

Hi,

thanks for the detailed results and setup!

As you mention, it could indeed be an issue with the measurement ranges. We will investigate internally with the same setup as you have used and see if we can make adjustments to improve this behavior.

As a side note, the updated PPK2 firmware has a secondary COM port used for command line access. To determine if it is actually an issue with the ranges, you can open this COM port and execute the "sampling metrics" shell command after sampling has stopped. The command line interface is non-responsive while sampling, to avoid interfering with the primary function of PPK2.

See this screenshot as a reference:

If the "samples dropped" metric is high, it indicates that there is an issue with the measurement ranges.

Finally, you can use the shell command "sampling discard_switch_samples 0" to never discard any samples. I would be very interested to know if this improves the behavior or not.

Best regards,

Audun

[MartinZ]

EDIT: This of course replies to Audun's 1st post but even if I click Reply, it gets placed at the bottom of the thread.

Hi,

I tried what you propose. Here is the setup:

- 6k8 load resistor

- start at U_set=2500mV, sample for a few seconds, current is correct

- switch to U_set=2600mV, sample for a few seconds, current is correct

- switch to U_set=2700mV, sample for a few seconds, current is >20% too high

- stop the sampling

- execute "sampling metrics":

shell:~$ > sampling metrics
sampling metrics
Metrics:
  Samples in session=2741521
  Samples dropped=3 (+1)
  Blocks dropped=114 (+39)

Immediately after that, I typed in the command "sampling discard_switch_samples 0" and repeated everything from above. The results were practically the same. Sampling metrics output:

shell:~$ > sampling metrics
sampling metrics
Metrics:
  Samples in session=3622159
  Samples dropped=3 (+0)
  Blocks dropped=135 (+21)

Please let me know if this gives you any insight into what might be happening.