[time-nuts] Looking for off-the-shelf device to timestamp multiple PPS inputs
Hal Murray
hmurray at megapathdsl.net
Wed Sep 28 18:19:33 UTC 2011
kevin at rosenberg.net said:
> I'm looking for device with an external clock input as well as inputs for
> multiple PPS signals that outputs timestamped messages for each input pulse
> via RS232. ...
What sort of accuracy and/or resolution do you want/need?
> 5) Using a FreeBSD or Linux box with multiple RS-232 inputs and using their
> PPS API. However, outside of some ARM boards, I haven't found any boxes
> that can be clocked by a external reference. And, I haven't enough
> experience running FreeBSD or Linux on ARM to know how well this will work
> for me.
> 7) Use a box like in #5, and capture the PPS from the PRS-10 as well and
> using that to scale the other PPS inputs that arrive around the same time.
If you have a Linux box handy, that one is easy to try.
After the 60Hz grab-every-cycle experiment, I started collecting every-cycle
data for PPS signals. I have a box with 3 PPS signals: one from a Z3801A
and 2 from low cost GPS units.
I can send you some files if you want to investigate. (5-6 megabytes per day)
I'll have to make some graphs. The ballpark is several microseconds of
noise, but that's on top of your system clock offset. I think it would be
easy to see 10 microseconds of offset. You would have to work harder to see
smaller numbers.
Reminder: Your system may have troubles catching 10 microsecond PPS signals.
TAPR says "no longer available" for the FatPPS. I poked John. He was going
to see if they could build another batch.
--
These are my opinions, not necessarily my employer's. I hate spam.
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