Multifunction DAQ

cancel
Showing results for 
Search instead for 
Did you mean: 

Compaq DAQ Square wave analysis

Hi 


I am using a CDAQ-9178 with NI9229 4 channel 50 kS/s analogue card. I have fed in two independt square wave signals that are 90° out of phase. The two signals are below 20hz. The sample rate is set to 25khz and i am sampling for a finite period of 50khz so two seconds. The two seconds should show 40 pulses on both indpenedent channels.

 

I want to do the following measurements.

 

-Measure minimum and maximum phase shift between between the two channels for the two seconds

-Measure minimum and maximum pulse width of both channels for two seconds. 

 

Is there VI created that can do this. I am using the DAQ assistant with data output. Both set of data for the two channels are save in this data signal. 

 

Thanks 

0 Kudos
Message 1 of 4
(3,729 Views)

Hi ,


As I understand the problem, you want to know if there is a VI to measure the max/min phase shift and pulse width between two channels.

 

There are some VIs that can help you with this: if you open the Functions Palette>>Signal Processing >>Waveform Measurements

Tone Measurements  can help you measure the phase of your signal and Timing and transition measurements can help you with the pulse width.

 

Kind Regards,

 

Mark 

 

Applications Engineer Intern
National Instruments UK and Ireland
0 Kudos
Message 2 of 4
(3,706 Views)

Hi Mark

 

If i use DAQ assistant to take two signals from two of the channels from the 9229 this outputs a dyanmic data line, If i use the split signal vi i can then get the two channels independently. When i feed these two signals into the two channel spectral measurement VI to measure phase of the signals does this take the average phase for the entire collected data or just one waveform from the selected data.

 

I want to be able to measure maximum and minimum phase between all rising edges of the two signals. If i measure maximum and minimum for the entire trace and they are within tolerance then i dont need to know the actual phase shift between each pulse for the two channels. 

 

I seem to get a random phase error everytime i run the VI, i assume this is because its taking phase at a random point and not looking for the phase difference of the seperate rising edges. 

 

 

The same question applies for timing and transition measurements vi and amplitude and level measurement VI,  When i feeed a dynamic signal into the VI (Signal is 50K bits @ 25Ks/s, so two seconds of data. 30 pulses) does the VI measure just one waveform or look at the entire data and take an average. 

 

I would like to get more of an understanding how the VIs actually acquire the values from the data feed in. 

 

Thanks 

 

 

0 Kudos
Message 3 of 4
(3,697 Views)

Hi JWinstanley,

 

 

The VI does look at the entire data and measures the average phase.

 

There are two different ways for you to understand more about the express and SubVIs you are using:

-The first would be to right click the express VI and select Open Front Panel then examine the VI from there.

-The second would be to use Context Help , shortcut CTRL+H, to view information of the VIs , and even access more detailed help if needed.

 

 

I hope this helps, feel free to let me know if there are any other issues I can help you with.

 

Kind Regards,

 

Mark 

 

Applications Engineer Intern
National Instruments UK and Ireland
0 Kudos
Message 4 of 4
(3,677 Views)