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fairly high speed DIO


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I have an application where i need to send a variable DC voltage output (from 50-250mV) then time when an event happens after the voltage is applied. I envision a switch tied to a DO then measure the time to the DI event. Some of these events will occur within 1ms of the output event. Can anyone suggest hardware that is capable of this kind of timing?

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Why not just using your DO signal as trigger for starting the DI acquisition? Subsequent analysis of the acquired waveform would measure the time of what you define as event, isn't it? 1ms and the desired DI time resolution alone dictate the required sampling rate, but nowadays even the entry DAQs are capable of ksps.

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It occurs to me that maybe only NI-SCOPE cards have real trigger inputs. But for normal DAQ cards, you could use some scheme in which, even with software start, you first start the acquisition on the event channel and on a fiducial channel, then you output the control signal which is also routed to the fiduciary input. Since relative timing of the sampled data is deterministic (channels are either simultaneously sampled in high end cards, round-robin in lower), analysis of the two sampled signals should give you the answer.

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Is it possible to do a pulse width measurement or a two edge separation measurement? Counter resolution is very high, compared to most analog acquisition. You might need to look at how you would generate the signals in your hardware, but it might work. Another option is to start a high-speed analog acquisition when you send your output signal and then set an analog reference trigger to stop the acquisition. You could count the samples to get an event length, but you could also refine the waveform first to give a more accurate result.

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