time transition between two waveforms

[*LJ]

Hello everyone,

I have a project which need to measure the time transition at the rising edge of two digital waveforms. I have try myself to find how to do this but in vain, please help on this matter. Thank you.

Warmest Regards,

Lee Joon

[ShotSimon]

Do you know the approximate speed of the two wave forms?  Also what hardware are you planing to use to measure the rising edges, i.e., a DAQ, oscilloscope?  SS

[*LJ]

Hi,
I create an analogue signal of 2.15V by using the PXI power supply card, then convert this analogue signal into digital signal through a npn Bipolar transistor. After that I should expect two digital waveforms from two points, and I use the DAQ card to read the waveform. DAQ assistant VI seems to be able to accquires the analogue signal only but not the digital. Hope to hear from all of you again.

[BrowningG]

Hello *LJ,

Which NI device are you using to acquire the digital signal?  Most National Instruments boards require TTL signals for digital input (DI) and counter input.  If the signal does not match TTL specifications, then connecting it to the DI or counter input lines could result in unexpected measurements.  Make sure that your signal matches TTL specifications for level and rise time to ensure that it will work with the DI.

If both signals match the counter input specifications for your device and are on separate lines, you can use the edge separation functionality of a counter input.  The example Meas Two Edge Separation.vi in the NI Example Finder (Help -> Find Examples) following the path Hardware Input and Output -> DAQmx ->Counter Measurements -> Two-Signal Edge-Separation shows how to configure this with the DAQmx VIs.  The function Two Edge Separation in the DAQ Assistant indicates which two PFI lines are used for this task. 

If your signals do not match the digital specifications for your device, then it will be necessary to use the analog inputs for your device and determine the edge separation in LabVIEW.