Position acquiring method used by MAX

[ggenc]

Hello everyone dedicated to LabVIEW,

I'm working on a PCI-7358 and  I have a problem about reading position data of the system.

The thing is that MAX can capture the position data much faster than the available .vi's offered in NI-MOTION library. So I thought that MAX has an access to a method that makes the capturing position data with speeds upto 5kHz or faster sampling rate. This bit of information is also confirmed by Jochen Klier in one of my older threads using the same words

" I got the information from R&D. In fact MAX is using another method to acquire position data much faster. Unfortunately this method can't be used for longer moves, so it's not available in the public NI-Motion API. So my former statements are still valid. The best option is an additional counter/timer board."

I know that triggering the register of PCI-7358 using an external clock would be a better solution but in my system I just can't afford to use another card. So I want to learn more about the aformentioned method that MAX is using and that is not available in public API because it's turned out that the short moves such as used in the STEP RESPONSE function of MAX would be sufficient enough as my commanded position.

Thanks for your help....

Gencer Genc

[ggenc]

Hello everyone,

Is there anyone who can help me about this problem?

ggenc

[Jochen]

ggenc,

sorry for the late response. I'll forward this request to R&D.

Regards,

Jochen Klier
National Instruments

[Jochen]

Here is what I have found:

"Something that you can do to retrieve data faster is use the Acquire Trajectory Data.flx.  This vi sets the update rate with a maximum update rate of 3ms.  Then use Read Trajectory Data.flx to read the position."

This will increase the reading rate by 40%. If this is not enough, you could use buffered High-Speed-Capturing (HSC)which allows you to read a limited amount of hardware timed position data. The maximum acquisition speed is 2 kHz but it requires an external clock signal. Please reger to the shipping HSC examples.

The other option is to use the counters of an additional DAQ board. This option allows you to read position data continuously at much higher rates. You even could route the counter signals from the motion control board internally to the DAQ board using a RTSI connector.

I know that you are aware of these options, but I have posted them to this thread to make it more valuable for other users, too.

Jochen

[serkanb]

Hello Jochen,
Could we use PXI based system instead of PCI  to read data faster?
What is the PXI-7358's data update rate?

[Jochen]

serkanb,

the data update rate of the 73xx boards is not limited by the bus bandwidth of the host PC, so a PXI board is not faster than a PCI board. In fact PXI means PCI Extension for Instrumentation. That means, that it is based on the standard PCI specs, so even if the bus bandwidth mattered, there wouldn't be any difference between PCI and PXI in this context.

Just as general information: Meanwhile the PXI specification was extended to the PCI Express standard, which means a significant bandwidth growth while maintaining compatibility to standard PXI. But this is just a sidenote.

Jochen