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Issues observing waveform on a DSO3152A

Question asked by dest2ko on Jul 8, 2013
Latest reply on Jul 8, 2013 by dest2ko
I am in the process of converting some of our control systems (National Instruments cRIO PAC (PLC)) to use high-speed digital output modules instead of 0-10V analog output modules. This is primarily to eliminate the requirement of having a standalone converter module outside the NI system that is given a 0-10V signal and outputs a pulse-width modulation waveform to our existing equipment. Right now I am having trouble seeing that waveform on my DSO3152A oscilloscope. The module, an NI 9478 16-channel 0-50V sinking digital output module (documentation), seems like it would be fairly straight forward to probe, but I can't figure out what I am missing. I have the digital out (DO) terminal probed with reference lead grounded to common on the module. I have also tried Vsup on the reference lead similar to page 8 on the documentation, but to no avail. Interestingly, I have been able to observe a waveform that directly responds and correlates to my switching in the program I use to control the pulsing, but it is on the mV scale instead of the 24VDC I am expecting to see. I am still under the assumption I am probing this incorrectly as the documentation schematic seems to be more centered around powering a device when DO switches and sinks to ground, though am not sure how this approach would differ if I probed the potential across the two lines. I have set the oscope to DC coupling and 1X probe to match my own probe, though I have attempted other settings as well.