Pulse width measurement

[Jeff1962]

I am trying to measure a  single 25ms pulse w/ a PXI-6225 DAQ Card. I am wired to the AI input. I can capture the pulse and can see the waveform ona waveform chart, but am having trouble determining the pulse width from the data that I have, which is a Wavform.  i have also used the 1D Dbl. I have used the 'Pulse Measurement.vi" and the "Timing and transitions.vi". The measurement always returns a zero.

I have seen examples based on using the counter, but I am currently not wired into the counter for the 6225 card.

Any suggestions would be greatly appreciated.

Thanks,

Jeff C.

[Kevin_Price]

If the pulse is TTL-compatible (very roughly: low state between 0 and 0.5 V, high state between maybe 3.5 and 5 V, sub-microsec rise and fall times) then my suggestion is:

Change your wiring to one of the counter inputs.  You'll get far better resolution on your measurement because it'll be based on a 80 MHz timebase resolution rather than a 250 kHz sampling rate resolution.

-Kevin P.

[Jeff1962]

Kevin,

Thanks for the response. My level ranges from about 5Vdc to 10Vdc and I would like to avoid the rewiring option, if possible.

I have this data captured in an array. Is there a way to parse out the data that I need (which would be the pulse and time data) and determine the pulse width from that?

Jeff C.

[Dennis_Knutson]

Your data should be in a waveform data type and not an array. An array has no timing information. Also, you might want to check if the Pulse Measurement function is returning an error. Some of the other measurements it takes (i.e. period, duty cycle), requires that there be multiple pulses in the waveform. If you only need pulse width, you can modify the VI to only do that.

[Jeff1962]

Dennis,

Sorry for the late response. That did it. Modified the pulse width VI and that took care of it. Thanks for the help.

Jeff C.

[Grant_C]

Dennis, i want to remove the duty cycle and the period from Pulse Measurements.vi  I can see that i need to edit the call library function node inside the vi but cant figure out how to rename and save as.

Can you help?

[Dennis_Knutson]

I see that this is a duplicate post. What I don't understand is why you would want to do this. They are just outputs from the VI and if you wire them to anything, it's the same thing as if they weren't there.

[Grant_C]

Hi Dennis, yes i have indeed posted to all forum members.  What i am trying to do is use this vi for the second time on a second pulse. As you said previously, you cannot do this because the vi will look for a third pulse in order to satisfy the requirements for measurements; duty cycle and period.  I only want the pulse width measurement for the second pulse so ideally i would like to edit the node to only output this value.

I am taking the raw information from a power meter.

Thanks for your help.

Grant

[Dennis_Knutson]

That was an old post and refered to an old version of LabIEW. The current version is much, much different and there is nothing that can be removed. What version of LabVIEW are you using?

[Grant_C]

Hi Dennis i am using 8.5 Professional.