Letting PXI monitor certain channels, for the purpose of emergency shutown

[Peeker]

We are developing a system, which is using the same multifunction PXI DAQ board for generating power signals to the UUT (via power modules) as for monitoring the current of the resulting power signals. What we would like to do is to have a process that monitors these current signals (translated into voltage) and that sets all output signals to zero if the current would exceed a certain value, while ideally generating an error message. This should be done while different operations take place on other channels of the DAQ board. We also need it to be pretty quick.
Does anyone know how to do this?

[rgharrison]

Hi Peeker,

This will be difficult to implement if it is needed quicker than software resolution times. Your only option is to read in each channel to monitor the current into a voltage analog input and in software, monitor each using software to make sure that the threshold hasn't been exceeded. Once it has, the software would automatically reset the analog outputs controlling the UUT. This would be ok if you can accept a delay on the order of 10s of ms. This is the quickest a software loop can perform processing on data.

The reason we have to read in the values is because there is no "stop" trigger for analog output. There is no way to change your analog output values depending on the input of a signal.

Hope that clears things up. Have a good day.


Ron

[Peeker]

Thanks Ron.

Well, I'll stop looking for faster SW solutions then. One or two more questions though: Would a reset of the DAQ board "immediately" set all signals to 0? And do you know how a reset of a PXI switch card would work (all signals low?)?

//Martin

[rgharrison]

Hi Martin,

Reseting the DAQ board will reset all signals. However, there is a small capacitor that needs to release its charge. If your source impedance is high, it might not "reset" as instantaneous as you would like. It will morelikely "float" to ground. This might do the trick for you though. As for the PXI switch card, IVI supports a "disconnect all" function which will disconnect all inputs. Reseting a switch card will usually put it in a default state (Normally Open is the usual state) but this depends on your switch card. This switch reset/disconnect might be your best option for your application.

Have a good day.

Ron