Shutdown on loss of communications

[wg1000]

I have an application where I am programming a machine to run test on a product. Using Labiew and a cDaq with a 9472 digital output card. I have found if I turn an output on in software and then close the software the output stays on. This is a problem for our applicaiton which could lead to someone getting hurt. Say we turn a valve on with the digital output and the program or computer stops, the output would remain on. Does anyone know a way around this?

[johnsold]

You need to add a hardware watchdog timer circuit.  A few DAQ devices may have these. PLCs usually have them.  Or you could design your own.  Basically what the watchdog does is to monitor some signal coming from your software which changes periodically and predictable as long as the software is running.  When it fails to change for more than some time interval you specify, it activates a circuit which forces your external machine to a  safe state (such as truning off the power).

Lynn

[wg1000]

I have dont that before on a RIO but thought there was way to do this with a cDaq

Thanks for the reply

[johnsold]

I am not familiar with that device.  Look at the documentation for the device or ask your NI rep.

Lynn