Frequency measurement accuracy

RE: Frequency measurement accuracy

ovrebekk — Thu, 27 Sep 2018 06:23:33 GMT

And you are sure that the external HF clock is running all the time?

I just tested this myself and I typically see the result vary between two values (198 and 199 in my case), which is to be expected. Since the external signal will not be synchronized to the clock of the nRF52, you can get slightly different results depending on what the phase of the nRF52 clock is when the external signal triggers.

This doesn't fully explain why you see variation between 175, 176 and 177.

In either case I would suggest averaging the result over multiple pulses for more accurate results.

Best regards
Torbjørn

RE: Frequency measurement accuracy

Sylvain — Tue, 25 Sep 2018 19:21:13 GMT

Hello,

No, the MCU never enters into sleep mode. My program is as simple as possible ...

Sylvain.

RE: Frequency measurement accuracy

ovrebekk — Tue, 25 Sep 2018 10:30:29 GMT

Hi Sylvain

Do you put the MCU to sleep at any time?

If so the PPI latency can increase and you might see less accurate results.

Best regards
Torbjørn

RE: Frequency measurement accuracy

Sylvain — Mon, 24 Sep 2018 13:33:06 GMT

I know that my signal is stable because I use a professional signal generator.

Not precise enough for what I want to do. I perform the same measurement on a STM32 and the value is stable.

I would like to understand and fix the variation of the nRF52.

RE: Frequency measurement accuracy

awneil — Mon, 24 Sep 2018 13:10:19 GMT

[quote userid="68596" url="~/f/nordic-q-a/38819/frequency-measurement-accuracy"][/quote]

The frequency of my signal is stable

How do you know that?

Exactly how stable is it?

[quote userid="68596" url="~/f/nordic-q-a/38819/frequency-measurement-accuracy"]the return captured value varies a bit[/quote]

only by +/- 1 in 176; which is about 0.5% - which is pretty for any measurement!