SWH Posted March 27, 2020 Share Posted March 27, 2020 Hi, I'm logging some data on the Digital Discovery using the high speed inputs, and I was wondering about the accuracy of the time stamps. According to my scope, my digital signal is high for 100ms, but when I use the time stamp data in waveforms (sampled at 10kHz) I get around 97ms. Cheers, Stephen Link to comment Share on other sites More sharing options...
JColvin Posted March 30, 2020 Share Posted March 30, 2020 Hi @SWH, I have moved your question to a more appropriate section of the Forum where the engineer much more familiar with the Digital Discovery and WaveForms software will be able to see and respond to your question. Thanks, JColvin Link to comment Share on other sites More sharing options...
attila Posted March 30, 2020 Share Posted March 30, 2020 Hi @SWH You can increase the number of samples to capture at higher rate, to have higher resolution, but a more precise measurement would be using the trigger position. Like here the trigger is set on rising edge, position is set to 100ms, the sample rate is set to 800MHz (time base to low value). The falling edge is at 100ms + 11.25ns, so we measured the pulse length of 100.00001125 ms with a resolution of 1.25ns Note: the cursors are no intended to display such high precision time values, that is why I added 2 cursors Link to comment Share on other sites More sharing options...
SWH Posted April 1, 2020 Author Share Posted April 1, 2020 Thanks for your response. I tried this and I still get values that differ by 1ms or more from my scope. What did you use to generate the 100ms pulse? Was it something external to the Digital Discovery? Cheers, Stephen Link to comment Share on other sites More sharing options...
attila Posted April 2, 2020 Share Posted April 2, 2020 Hi @SWH The oscillator in the device is DSC1033CC1-12.000MHz. Based on this stable 100/800MHz internal sampling clocks are generated. In case you are reading unexpected values: - make sure to have common ground between the devices - make sure the logic threshold is good in the Supplies window Earlier I have shown you internally generated pulse with 'high zoom' / low time base. You can use higher time, depending on your signal. Like here an externally generated 101ms pulse end is captured with 5ms window. Link to comment Share on other sites More sharing options...
SWH Posted April 2, 2020 Author Share Posted April 2, 2020 Hi @attila, When I measure a 100ms internally generated pulse on the Digilent I measure 100ms. When I measure the internally generated 100ms pulse with my scope, I see roughly 103ms. Please could you measure an externally driven 100ms pulse using the Digilent, and see what you get? Cheers, Stephen Link to comment Share on other sites More sharing options...
attila Posted April 2, 2020 Share Posted April 2, 2020 Hi @SWH Here the 100ms pulse is generated with NI Virtual Bench FGen, 0/3V With DD I measure about 99.9995ms (+/-10ns), which is 5ppm. It should be even better with digital signals source and proper wiring, but this VB is the only non Digitent product I have at hands. The 2us difference is due to sampling resolution: Link to comment Share on other sites More sharing options...
attila Posted April 2, 2020 Share Posted April 2, 2020 Hi @SWH Could you post a screenshot with you oscilloscope capture/measurement? Link to comment Share on other sites More sharing options...
SWH Posted April 2, 2020 Author Share Posted April 2, 2020 Hi @attila Which measurement would you like to see? The 100ms pulse from the DD on my scope?? Cheers, Stephen Link to comment Share on other sites More sharing options...
SWH Posted April 2, 2020 Author Share Posted April 2, 2020 Hi @attila I seem to be making some progress..... I have been using a Macbook to take all of these measurements, but when I tried on a windows machine I got the expected results. I'll do some more experiments and let you know what I find. Cheers, Stephen Link to comment Share on other sites More sharing options...
attila Posted April 3, 2020 Share Posted April 3, 2020 Hi @SWH The captures and measurements from your oscilloscope and also from the WF/DD might help. The more info, screenshots and photos we have the better the understanding on the problem... Link to comment Share on other sites More sharing options...
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SWH
Hi,
I'm logging some data on the Digital Discovery using the high speed inputs, and I was wondering about the accuracy of the time stamps.
According to my scope, my digital signal is high for 100ms, but when I use the time stamp data in waveforms (sampled at 10kHz) I get around 97ms.
Cheers,
Stephen
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