The maximum position reading rate with a 7344 is limited by many factors like the CPU speed and of course also the internal speed of the board itself.
Internally the positions are sampled at every PID cycle. To be able to monitor three position feedbacks you need to enable three axes. This results in a minimum PID cycle time of 180 microseconds or a maximum theoretical position capturing rate of 5.56 kHz but this is only the internal processing rate of the DSP and by far not the position capturing rate that can be reached by either a host program or an onboard program.
Even if the overall position capturing rate was high enough it's not advisable to run this task in a host program by polling the position in software because the time between each captured posit
ion is not deterministic on a Windows system.
The conclusion is that there is no possible way to reach the position capturing rate you need with the 7344 alone.
So what's the way out of here?
A good solution would be the use of an additional counter/timer board like the PCI-6602 (http://sine.ni.com/apps/we/nioc.vp?cid=1123〈=US)
The PCI-6602 provides direct connectivity to quadrature encoders and is capable of capturing positions with a rate of several 100 kHz (hardware triggered = deterministic). For transferring data to the PC it provides three DMA channels which would perfectly meet your needs.
Best regards,
Jochen Klier
Applications Engineering Group Leader
National Instruments Germany GmbH
