Measuring single pulse with an HP 53131a - Page 1
Forum section: electronics / projects

author: 99wombats
author_rank: Contributor
timestamp: September 03, 2022, 02:11:47 am
content: I am trying to measuring the width of a single 5V pulse, duration around 50ms. Is this something that is possible with an HP 53131a? I have tried the “pos pulse width” option in the period / timing menu but I just get “—————“ on the display, regardless of what settings I try for other things, triggering etc. I read a note on the Agilent website that both channel 1 and 2 needed to be set up properly to do this kind of measurement, and I followed their advice on channel settings but still no reading. If anyone has any info on a) if this is possible and b) what setting I could try to get it to work that would be great!

author: 99wombats
author_rank: Contributor
timestamp: September 04, 2022, 02:25:21 pm
content: If anyone has any thoughts I’d be interested to hear them. Wondering if there is actually an issue with the counter, although it seems to do frequency measurement fine.

author: gamalot
author_rank: Super Contributor
timestamp: September 04, 2022, 03:19:10 pm
content: I set up my 53132A following the instructions on the Keysight website and it does measure 50ms pulses.I think the only thing you might want to pay attention to is that if your signal level is 0-5V, you might want to set a higher trigger level instead of 0V, for both channels.https://edadocs.software.keysight.com/kkbopen/why-cant-53131a-measure-pulse-width-of-signal-below-30hz-580260961.html

author: HighVoltage
author_rank: Super Contributor
timestamp: September 04, 2022, 03:28:55 pm
content: I have just tried this.My 53131A does not work to measure a single 50ms pulse, but my 53132A works well, but I have to turn the low pass filter on and set the trigger level manually to 1V on a 5V pulse.

author: gamalot
author_rank: Super Contributor
timestamp: September 04, 2022, 04:03:15 pm
content: Quote from: HighVoltage on September 04, 2022, 03:28:55 pmHmmm, I found my 53131A and it works just fine.

author: HighVoltage
author_rank: Super Contributor
timestamp: September 04, 2022, 04:29:03 pm
content: OK, after a little tweaking of the settings, both are working to show the 50ms pulse.50ms seems to be too slow for these counters.

author: 99wombats
author_rank: Contributor
timestamp: September 04, 2022, 10:52:12 pm
content: Thanks everyone for the useful reports, I’ll have another go tomorrow and let you know how I get on.

author: 99wombats
author_rank: Contributor
timestamp: September 05, 2022, 08:57:17 am
content: Hm still no joy. I have it set as 1V manual trigger for both channels, DC coupled, low pass on, 1M Ohm, no attenuation, and running. The indicator above the channel input flashes once on the rising edge. I don’t get a second flash for the falling edge though with a longer pulse. Can anyone confirm if that is expected or not? Eg if you apply a 500 ms pulse does the channel indicator led flash on both the rising and falling edge?

author: gamalot
author_rank: Super Contributor
timestamp: September 05, 2022, 09:27:53 am
content: Quote from: 99wombats on September 05, 2022, 08:57:17 amDid you mean you pressed the 'Run' button when you said "and running"?When you have everything set up, you have to press the "Stop/Single" button until the "Gate" symbol appears on the right side of the screen, which means it is waiting for a pulse input.When the rising edge comes, the "Trigger" indicator will light up, and it will turn off when the falling edge comes.

author: 99wombats
author_rank: Contributor
timestamp: September 05, 2022, 10:28:23 am
content: Oh right, sorry yes should be in “Stop/Single”. When I do that (so “gate” annunciator is lit) the indicators remain lit for both channels while the signal is high, but the display still just reads “——————“. Not really sure what else to try! Can anyone think of a hardware issue that might cause this? I can verify the pulse is 0-5V and see it on the scope.

author: 99wombats
author_rank: Contributor
timestamp: September 21, 2022, 11:28:06 am
content: I've still not been able to get this to work, with everything set as explained up-thread.I have also run self-tests on CPU, ROM, RAM, EEPROM, QSPI, FPGA, FR END, MEAS and INTERP and all pass.The counter has a relatively old firmware version (3335), so it only has a "TI 1 -> 2" calibration option, however when I try to run this with the specified input wave (10 MHz, 1 Vpp, 0V DV offset) the instrument appears to hang with "CALIBRATING" on screen. None of the buttons except the soft power button are responsive. I've left it for 15+ minutes and no change. Any ideas how long this calibration would normally take? Would this behaviour be expected if e.g. my square wave didn't have a fast enough rising edge (rise-time is about 12 ns according to oscilloscope)? The "gate" annunciator is illuminated while the calibration is running and the trigger indicators over both inputs 1 and 2 are flashing rapidly.Again if anyone had any ideas what might be wrong I'd be interested to hear!

author: HighVoltage
author_rank: Super Contributor
timestamp: September 21, 2022, 11:42:58 am
content: Usually the calibration procedure goes fast on these instruments.Unless the input signal is missing.Are you sure you have the correct reference signal on the input?

author: 99wombats
author_rank: Contributor
timestamp: September 21, 2022, 12:06:11 pm
content: The signal is definitely there, the counter gives 10 MHz as frequency reading and +/-0.5 V amplitude, plus I have checked it on a scope with BNC t piece..

author: 99wombats
author_rank: Contributor
timestamp: September 21, 2022, 12:07:36 pm
content: Could it have anything to do with the third-party TCXO I have installed? I can try disconnecting it but it seems unlikely that’s the problem given the frequency measurements are ok?

author: 99wombats
author_rank: Contributor
timestamp: November 04, 2022, 01:19:04 pm
content: I have established this is in fact an issue with all timing type measurements on my instrument. I believe it is the same problem Tony G reported herehttps://www.eevblog.com/forum/repair/53131a-counts-frequency-but-not-time/.I have posted the following to the HP boards but with no response yet so thought I'd try here too.QuoteThe component level manual ishttps://www.bitsammler.de/downloads/Manuals/HP_Agilent/53181A%20Frequency%20Counter/5989-6307EN_Agilent%2053131A%20Component%20Level%20Information.pdf, I think the relevant bit is page 8

author: 99wombats
author_rank: Contributor
timestamp: November 07, 2022, 04:22:33 pm
content: If anyone was able to probe the state of some of the lines on their machine I would be very grateful. In particular what state are CH1 (pin 82 on U58 / the FPGA), TIMEINT (pin 15 on U58), and CNTDISABLE (pin 18 on U58) in when doing frequency and time measurements. You can access the FPGA quite easily just by taking the cover off the instrument.