Acquiring voltage with external clock

[Eyal_S.]

Hello all,

I'm trying to measure the voltage from  a input analog signal each time a digital signal "arrives".
I'm using the digital signal as an external clock while I'm doing continuous voltage measurements (1 channel & 1 sample). The digital signal has an average frequency of 500Hz.
When I start acquiring the data I get an error that the ADC wasn't able to convert the samples fast enough. There is always the probability of a quick burst in the digital signal but for a 500Hz signal I would not expect it to happen very often. When I use a constant external clock I do not have this problem.
I also tried to use the digital signal as a trigger but it seemed like the number of measured points did not correspond to the frequency of the triggering signal.
Can anyone suggest a better  way of measuring the voltage or at least explain why I have these problems?

I'm using Labview 8 &  pci- 6251

Thank you,
Eyal

[Chris_K_]

Hi Eyal

Thank you for using our discussion forums.

Can you let me know exactly which error you are getting during your acquisition?  A screen shot of this error would be very helpful but just the number would be ok as well.  Also are you working with one of our shipping examples?  If so, which one, if not I would suggest using one as a starting point.  I was able to modify and successfully run the Acq&Graph Voltage-Ext Clk.vi with a 500hz external digital signal.  The shipping examples can be found at Help>>Find Examples.

Without knowing exactly which error you are seeing, I can’t be sure how to resolve the issue, however here is a link that may be helpful.

What Causes Error -200019 When Increasing the Sampling Rate of an Analog Input Task with an External...

Let me know about the exact error and I can be of more assistance.

Chris_K