Timing problem using multiple modules in Compact DAQ with high sample rate.

[phil.zakielarz]

I'm attempting to measure single phase AC power using a cDAQ-9188 and  9225 and 9205 modules.  I have the AC line voltage going into channel one of the 9225, and I'm using a 9205 to measure a +/- 100 mV signal from a current probe.  (There is one additional channel active on the 9205 - unrelated to ac power).  I've set up a project in LabView using a single DAQmx assistant object for all channels connected to a waveform graph output object.

When I set the sample rate to 1kHz, everything works fine.  The ac voltage and current waveforms are displayed as expected.  However, when I set the sample rate to anything above 1.5kHz, it appears that timing errors begin to creep into the measurements.  The timing error shows up as a phase shift between the two waveforms.

If I can provide any more information please let me know.

[phil.zakielarz]

UPDATE:  It looks like my previous post about the phase angle being OK at low sampling rates was wrong.  The phase may actually improve as sample rate increases, but the waveforms are still >25 degrees out of phase at 50 ksamples/channel/second

[MarkGrot]

Hi Phil,

It looks like you're seeing the input delay from the 9225.  See this KB for more details:  Why Is My Data Delayed When Using DSA Devices?