How to synchronize the acquisition start of two different daq boards

[MichaGue_01]

Hello,

I am running a continuous acquisition with a PCI-6133 (@2,5 MS/s per channel, 8 channel) and a PCI-6259 (@250 kS/s per channel, 3 channel). Both run in the same while loop. The raw data of both DAQ boards will be written in a seperate tdms file. Because the sample rate of the 6133 is 10 times higher than 6259, each loop the number of values to read of the 6133 is 10 times higher than 6259. If I look in the tdms file I see, that both acquisitions do not start at the same time.

timestamp of the acquisition

PCI-6259: 02.06.2016  13:09:14,866

PCI-6133: 02.06.2016  13:09:14,941

Also the number of samples of the 6133 is not 10 times higher.

number of samples

PCI-6259:   4949658

PCI-6133: 49309378

questions

- How can I synchronize the start of the acquisition? Are there any tutorials?

- What could be the reason of the wrong ratio of samples (should be 10 between the both daq boards)?

Thanks a lot.

Michael

[AlexanderBeckmann · Accepted solution]

Hello Michael,

the acquisition start does not happen at the same time since you are not using a shared trigger. If you are adjusting for the different starting time, the difference in in the number of samples is only around 300 samples (0,075s difference in start of acquisition, this amounts to 187500 samples).

This difference of 300 samples occurs because the timings of the 2 cards are not synchronized.

If you want to synchronize the start and the acquisition between the 2 cards you need to connect them with an RTSI cable. This way you can route the sample clock from 1 device to the other. The routing of the sample clock through the RTSI cable is done automatically by the DAQmx driver.

You can get more information in this documentation article: http://www.ni.com/product-documentation/4322/en/#toc9