Phase between two daqmx signals

[jool]

Hi,

I have recorded a few signals in two different groups. For this I have created two steps (DAQmx Acquire analog input) in one I have two full bridge strain gages with 50 KHz sampling rate and in the second step I have 3 signals of 0-10V with 80 KHz sampling rate. I use labview 2010 signal express with cDAQ-9174 with NI 9237 module for strain gages and NI9205 for the voltage channel

when I plotted the results it seems I have a 0.03 s of phase between the two group of signals.

Is it possible? can I correct it easily with DIAdem?

[majoris]

What does it mean to have a phase delay between two signals that aren't of the same frequency?

[jool]

when i plot the signals one group of signals has an advance of about 0.03 s respect to the other group of signals. in the attachment you can see that the signal in red has an advance on the signal in blue.

red is sample in 50 KHz with module 9237

blue is sample with 80 KHz with module 9205

i hope i explained myself better

[majoris]

Yeah I guess I kinda read that wrong and I apologize.

How do you synchronize the acquisitions across the two modules?

[jool]

i suppose i didnt synchronize them...... i had just started the acquisition from  labview for all daq steps together. then i plotted them in diadem and the results are in the jpg i attached

the group of 80 KHz has three signal that were picked up from different instruments; they are synchronized between themselves. that should eliminate the suspicion of physical delay. ofcourse a delay of 0.03 s for cables shorter then 2 meter should as well eliminate this

the group of 50KHz are also synchcornized between them selves

thnk you very much for the quick response

[majoris]

Since I dunno what you're doing, one of the issues could be simply that you've plopped two DAQmx Assitant VIs on a VI and they aren't being forced to start at the same time. If you can combine them into one Assistant VI that's good.To be super accurate, you need to provide them with a common start trigger.

Labview has some examples on this...

Look in NI Example Finder > Hardware I/O > DAQmx... maybe Synchronization or Analog Measurement under that.

Acq&Graph Voltage -Int Clk-Dig Start under Analog Measurement is very close to what you want to do with a digital starting edge.

Anyways, since I don't know exactly how your VI looks I can only guess.

[ben64]

I'm not that much familiar with Signal Express but you can try this:

For each of your step go to the step setup -> execution control tab. In the sequence setting area uncheck Start this step after (check by default). Probably your sequence step 2 start after the first one.

You can also try to add a software trigger in the recordings options.

Also, if you've added digital filtering (doesn't seems to be the case) it will delay the signal a bit depending on the filter lenght.

Ben64

[jool]

thank you for quick reply..

i am not sure what is "Acq&Graph Voltage -Int Clk-Dig" mean but i have already did my data acquisition and now i try to sychronize them in diadem. any idea how to do so? 

gal

[ben64]

You could try posting your question to the Diadem forum.

Ben64

[Danny_Funk]

jool,

You can do some synchronization in SignalExpress, but it requires a Digital I/O module such as a 9402. Here's an article on how to do it if you have a module.

How Do I Synchronize Multiple AI Tasks with cDAQ 2 in SignalExpress?

In general I recommend using LabVIEW which is much more capable of performing synchronization. You would not need extra hardware if you used LabVIEW. majoris's post was right that there are good examples on how to do this.

Regards,

Danny F