Log synchronized analog inputs and position

[pelleK]

I want to read eight analog inputs (just three AI in the code capture) with a PCI-6221 at a rate of 100 samples/sec, reading 10 samples/iteration. At the same time I want to read position synchronized with the analog inputs. Is this possible? If I just merge the position signal with the analog inputs I will only get 10 position readings for every 100 analog input readings (see graph - the red one is position). For motion control I'm using the pci-7342 with the UMI-7764. Could anyone help me out here please?

[Jochen]

To synchronize motion and DAQ you can use an RTSI cable and High Speed Capturing (HSC) to acquire the position exactly when an analog value is sampled. Please refer also to the examples that ship with NI-Motion.

Please note, that the maximum HSC rate is system dependant but typically it's around 200 Hz. With a PCI-7350 HSC works with onboard memory up to a rate of 2 kHz.

Kind regards,

Jochen Klier

National Instruments

[pelleK]

Thank you Jochen. I was hoping that it would exist a good way to to this with my pci-7342. But it seems like I might have to buy me a new controller then..

[Jochen · Accepted solution]

Not necessarily. As said, rates up to 200 Hz should work fine with a 7342. If this is not enough, of course a 7350 could be used, but there is also a completely different approach that should work with your current hardware:

From the 7342 you could also route the encoder phases to RTSI pins. You can use a counter on the 6221 to measure the position of your axis based on the singlas that you have routed to the RTSI pins. Now you can use "Buffered Position Measurement" (see DAQ examples) to measure the position with the same timing source as your analog signals.

I hope that helps,

Jochen

Message Edited by Jochen on 01-08-2009 10:58 AM

[pelleK]

The routing of the encoder phases to RTSI worked perfectly. Thanks again!

[AndySchütte]

Hello,

i have got the same Problem, but I have to use three encoder-signals. To route the phases from PCI-7340 to RTSI is interesting. But my PCI-6221  only have 2 counters. Is it possible or should I use HSC.

Thanks.

Andy

[Jochen]

Hi Andy,

with two counters you only can acquire data from two encoders, so one option is to exchange the PCI-6221 with a board with more counters. E. g. the PCI Express board PCIe-6321 with 4 counters or the PCI-6602 with 8 counters. The PCI-6601 is not a good option for your application, as it can run only one buffered counter operation via DMA.

The other option is using HSC with the restrictions, that I have mentioned before.

Jochen

[AndySchütte]

Thank you for the fast answer.

Andy

[christophe.A]

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@Jochen wrote:

To synchronize motion and DAQ you can use an RTSI cable and High Speed Capturing (HSC) to acquire the position exactly when an analog value is sampled. Please refer also to the examples that ship with NI-Motion.

Please note, that the maximum HSC rate is system dependant but typically it's around 200 Hz. With a PCI-7350 HSC works with onboard memory up to a rate of 2 kHz.

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Using the tutorial and its last example, rtsi_comp_cap_multi_point and acquiring continuously AI, I managed to work with the PXI 7350 at a rate of 300Hz.

Christophe