Power Profiler Kit Lowest Range Doesn't Work

RE: Power Profiler Kit Lowest Range Doesn't Work

wlgrd — Fri, 06 Jul 2018 06:29:14 GMT

That's great to hear! This has confused me for some time now ;D

RE: Power Profiler Kit Lowest Range Doesn't Work

FUEN — Fri, 06 Jul 2018 02:16:21 GMT

Sorry for the extremely slow reply. For anyone who comes across this in future it turned out to be an issue with the hardware I was measuring. This would have been apparent much sooner had I just tested the PPK using a resistor value that would be on the low range of the PPK.

RE: Power Profiler Kit Lowest Range Doesn't Work

wlgrd — Mon, 26 Mar 2018 09:46:34 GMT

I agree. Yes, your keen eye has spotted a current mirror quite correctly ;) Unfortunately, this is not in use at the moment, but we are planning on using it in the near future for calibration. Right now, the hardware does an offset calibration on every startup (for the 2.0 firmware), and resistor calibration only in production.

Since this problem intrigues me, I really am looking forward to your reply. Please do not hesitate to ask further questions if there is anything I can help you with.

RE: Power Profiler Kit Lowest Range Doesn't Work

FUEN — Mon, 26 Mar 2018 04:33:30 GMT

Hi wlgrd, thanks for taking the time to give an in-depth reply. Unfortunately I am out of the office for awhile but when I am next in I will look at replacing R2 as it would be an easy fix. Am I correctly understanding that the PPK re-calibrates itself on start-up or with the press of a button in the PC software? It looks as if Q1A/B and Q2A form a current mirror that allows recalibration in software?

I have had a bit more of a look over the schematic and think I am able to follow most of it. If replacing R2 yields no results I will check that the other switches are working correctly. Unless something has gone wrong with one of the amplifiers or references there is not really much else to fail, and given that the other ranges give sensible values it is extremely unlikely.

RE: Power Profiler Kit Lowest Range Doesn't Work

wlgrd — Fri, 23 Mar 2018 14:05:13 GMT

Hi FUEN, this does indeed sound strange. We have had some issues the other way around (higher currents are too high), which has been due to ESD breaking the switching circuitry.

The measured values for the resistors are unfortunately not straight forward to measure, this is why it is calibrated during production. The path of the power line passes a some switches and other analog components that themselves introduces some series resistance, so only using a multimeter across the resistors will not give a proper result. Your understanding of the switching circuitry is correct.

When in highest range, all switches are latched in, causing a parallell connection between the three resistors. When middle range, only R3 and R2 is active, and lowest range, the R2 is the only on in. What you are explaining, seems to be an overflow value of what the ADC is able to handle, hence I thought that a switch was broken. We see this overflow when the system thinks it has latched in all resistors, but for some reason hasn't, and the calculations are wrong because the voltage drop is way to high.

So it seems like yes, R2 is not "active" when the system thinks it is (all analog switches are open), which makes me wonder if R2 is not properly attached to the board, or we have a connection break there. It is not activated by any switch, it is always used, so it is hard to believe that any components are broken since the rest of the measurement system is working properly.

If you have the schematic, and you seem to know how to find your way through it, I would suggest you to measure continuity in and out from R2 to the appropriate connections, and maybe also swap it out with another 510R in the rare case it is broken somehow.

Sorry for the long post, but I'm trying to make sure you have enough info to be able to fix this yourself :)

RE: Power Profiler Kit Lowest Range Doesn't Work

ketil — Fri, 23 Mar 2018 09:56:51 GMT

Hi,

Just wanted to let you know that we have not forgotten about your questions. Due to upcoming holidays there will likely be some days before we are able to provide an answer. Apologies for any inconvenience.

Ketil

RE: Power Profiler Kit Lowest Range Doesn't Work

ketil — Mon, 19 Mar 2018 12:50:12 GMT

Hi,

We are looking into your issue and will get back to you as soon as possible.

Ketil