pci-6251 for square wave voltage measurement

[detech]

HI, NI experts,

We just bought PCI-6251 card for square wave voltage measurement from x-ray tube. The voltage is a negative square wveform.  I want to use software trigger to trigger the falling edge of the voltage at certain level (can be adjusted based on the noise level in the site of measurement). It is going to be a function of single trigger of digital scope. Once the trigger level is settled down, it will wait for the voltage signal to trigger. Once it triggered, the voltage waveform will be recorded.

I found a lot exsample under ../hardware input and output/daqmx/analog mesurement/...

But I am not sure which one is close to my application. There are some opitions like internal clock, external clock, and all kinds of digital triggering.

Please give some advice which example is close to my application and how to modify it for my application.

Thank you very much for help.

Liming

[Nathan_R]

Hi detech,

It sounds like you need an analog start trigger to start your acquisition. An example of this can be found in the NI Example Finder under Hardware Input and Output >> DAQmx >> Analog Measurements >> Voltage >> Cont Acq&Graph Voltage-Int Clk-Analog Start.vi. The physical channel should be set to the channel you are measuring. The rate is the speed at which you want to sample the data. A good value for sample to read is 1/10th the rate. The trigger source can be the same as the physical channel. This means that it will analog trigger off the same signal that it is acquiring. Set the slope to falling and the level where you want to trigger at. This will set everything up so that when the measured signal falls below the trigger level the acquisition starts.

For more information of different types of triggering check out this great Developer Zone article, Tips and Techniques in Data Acquisition Triggering - NI-DAQmx

Let me know if you have any questions and take care.

Thanks,