watchdog blocks and the 6514

[rmschal]

We have an NI systems with a 6514 Daq board as part of a real time PXIe-1075 chassis.  Our system design requires a safety feature implemented with a watchdog timer that will send a digital signal output in the event of the software locking up.  The dynamics of our system is on the order of milliseconds response time which is well within the capability of the hardware.  I've seen a watchdog example for the 6514, but looking at it more closely has raised more questions in my mind that I'd like to ask.  The example was found by filtering to the 6514 hardware platform.

(1) The example uses non-real time watchdog blocks, should I be using the real time version of these watchdog blocks? Are the non real time versions specific to the 6514 which does support watchdog functionality?

(2) Should I consider using a real-time loop structure in this code?  I believe I should and this loop should get the highest priority in the task scheduling of the real time process as it is safety feature of the system.

Thanks for any feedback

Rob

[Process_Systems]

From the content of your question, I suspect that you may be mistaken on the watchdog function built into the 6514. You will require an externl digital signal from an external watch dog module to operate in conjunction with the NI card.

WDT205 Watchdog Timer Module

The above link is such a module. I have personally never used this particular module, but its specs look good, and the price is YAYYYY!  The ones I have used are 3 to 4 times the price.

As a general rule, you should not ever consider doing watchdog funtionality in software, simply because if your software crashes, and you want the watchdog to catch it; well what can your software do if it has already crashed??

Anyhow, my two bits for what it may be worth.

Good luck,

Dave