RTOS speed

[MikeGo]

I'm working on a PC-based application that involves counting pulses from 50-60 different sensors (pulses may be coming from sensors as quickly as every 700 microseconds, and the minimum pulse width is 350 microseconds).  Based on the sensor counts, the PC computes a vehicle's position every 500 microseconds.  I've never used LabView before, but I was considering running LabView on the PC, and using an NI encoder card to capture input pulses from the sensors.  Does this kind of an architecture sound feasible (i.e. would a PC running LabView be able to read sensor counts from the encoder card and compute position every 500 microseconds)? 

Any direction would be greatly appreciated!

[Laura F.]

Hello MikeGo,

Using an encoder product such as the NI 6602 or 6608 would work fine with your timing specifications.  Were you thinking of using LabVIEW RT for your application?  If you are going to use a PC running Windows, you need to be aware that Windows is non-deterministic and therefore you cannot be sure that your code will run in the same amount of time from one iteration to the next.  Generally, with Windows you cannot get better timing resolution than 1 - 2 ms.  LabVIEW RT is deterministic and different controllers have different guaranteed loop rates to meet your needs.  A loop time of 500 microseconds is feasible to perform calculations on your encoder measurements with LabVIEW RT. 

Let us know if you have additional questions,

Laura

[MikeGo]

Hi Laura,

Thanks for the reply.  Yes, I was thinking about using LabView RT for the application.  It's important that vehicle position be computed every 500 us, so I'm planning on using a RTOS.  I've had trouble finding a RTOS with drivers available for encoder cards though.  LabView RT seems like a good choice, since it presumably supports NI encoder cards.

It looks like the encoder cards provide 8 up/down counters.  Considering the number of sensors I need to analyze, multiple encoder cards would probably be necessary for my application (the application needs to count pulses from each sensor separately).  Do you think that would be a problem?  Again, my primary concern is speed.  The processor needs to get current counts from each counter and then compute position within 500 us. 

Message Edited by MikeGo on 12-02-2005 12:55 PM

[Laura F.]

Hi Mike,

Yes, LabVIEW RT does support our encoder cards - you would use our data acquisition driver, NI-DAQmx.

I do not foresee any problems with performing calculations on multiple encoder positions - that loop rate should be easily attainable.  You can see the loop rate specifications on the specific controllers, such as the one I linked to in my first post.

Good luck with your application!

Laura