Starting point for sample clk signal

[rYan7]

I am currently trying to synchronize my PXI-7344 Motion Controller with my PXI-6221 DAQ device. The devices are connected via PXI/SCXI Chassis 1050.

I wrote an onboard program waiting for an RTSI signal and then doing a high-speed capture. The data is buffered and then transferred to the PC in bigger chunks.

To synchronize this data with my DAQ data, I want to export the Sample Clock to the RTSI bus. My question is: Does the sample clock start sending RTSI signals after I prepared and reserved the task (the sample frequency is known) or do these signals not occur before I actually start the task?

In the latter situation it would be much easier to merge the data beacuse both devices produced the same amount of samples.

Regards

Andre

[Dan_K · Accepted solution]

Hello Andre,

Clock signals are not exported across the RTSI bus until the task is started unless triggering is configured. In that case clock signals will not be sent until the start trigger is received.

[Jochen]

Andre,

I just want to add a little comment. Please be aware of the fact, that with a 7344 the high-speed capture rate is limited to a value in the region of 200 Hz because you have to reenable it after each occurrence of a trigger signal (sample clock). Onboard programming doesn't increase the rate significantly compared to host programming.

If you need higher rates, you could either route the encoder signals to RTSI and do a buffered position measurement with a counter of your DAQ board or you could use a 7350, which supports buffered HSC rates up to  2kHz.

Kind regards,

Jochen Klier

National Instruments

[rYan7]

Thanks for the hint Jochen, but I have already considered those solutions.

Unfortunately I have 4 encoders to read out and the PXI-6221 only has two counters. Buying more hardware is also not an option at the moment. So single HSC is the only possible way right now.

Maybe we need some more DAQ hardware in the future.

What would be the maximum sample frequency with the DAQ method?

[Jochen]

Andre,

so for your application an X-Series device would be a perfect solution as it provides 4 counters with DMA transfer and big input buffers for high speed buffered counter operations (> 1 MHz capture rate). Still with your 6221 you can reach up to 150 kHz capture rates.

Jochen