FPGA Chassis Temperature Scan Mode

[Gary@B]

I plan to use a Compact RIO (9023 Controller on a 9114 Chassis) in scan mode but want to monitor the chassis temperature to control a cooling fan.  I don't see a way to directly access the chassis temperature from the RT controller.  My plan right now is to create a single VI that runs on the FPGA to monitor the chassis temperature and then use an FPGA read/write control in the Real Time code. 

Is there a better way?  I really don't want to create a FIFO just for chassis temperature. 

On a related note, what is the maximum chassis temperature before additional cooling is needed?  The 9023/9114 combo is rated for 70 C ambient.

[speleato · Accepted solution]

Hello Gary,

You are correct, chassis temperature is not available when using pure Scan Mode. You will have to use a hybrid project, as described in this KB

http://digital.ni.com/public.nsf/allkb/0DB7FEF37C26AF85862575C400531690

For transfering the data I'd suggest an indicator read or a User Defined Variable. The indicator read is faster, but possibly less convenient to use. The user defined variable will only update once per scan, but you can use the variable API and perhaps that is fast enough for your application.

You could also consider either controlling the fan directly from the FPGA, or implementing some logic in the FPGA that raises an interrupt when the temperature threshold is reached.

Let me know if you have any other questions,

Sebastian

[Gary@B]

I plan to read the temperature only once per second as temperature doesn't change all that fast so a variable would work but I will probably use the indicator read.  I would monitor temperature and control the fan purely within the FPGA as you suggest but I am controlling the other channels of my relay module with the RT controller (scan mode) so that won't be an option for me.