Programmatic Front Panel Communication

[vakost]

Hello.

My set up is the cRIO 9082 with embedded Windows 7. In the cRIO I have the module the Analog Input module 9220.

I want to transfer one measurement at a time from a NI 9220 to the host application that is running in LabVIEW, also in the cRIO.

I create front panel controls for all the AI of the 9220 in the LabVIEW FPGA front panel and I update them constantly with a delay of some (let's say 600 usec) time between each measurement.

From the host application, I grab one measurement every time the program needs it, once every about 5 ms.

What I notice is that the measurements I am having are not right, it looks like LabVIEW FPGA introduces a delay when I zero the input in the AI.

For example, I give 5 Volts, the front panel gets to 5 Volts almost immediately and when I give 0 Volts, it takes about a minute to get there.

I hope I wrote this question clear.

Can anyone help?

Thanks,

Vasileios.

[Sam_Sharp]

How have you implemented your host & FPGA software? Reading from the front panel of FPGA VIs is normally very quick (ms...) using the FPGA I/O node. There is certainly no reason for such a large delay - the only cause for that would be if you were using a Queue / FIFOs and your buffer was filling up with about ~1min of data.

Do you have any code/screenshots you can post?

[vakost]

Thanks for the answer.

The problem was that my Ground was only connected to the COM and not to the individual negative signal.

I am embarassed :(.

Vasileios.

[smithd]

If you want to eliminate any risk that its something in your FPGA code you can always switch over to scan mode and monitor the values using distributed system manager. The latency should just be a few scan cycles (100s of ms usually) and so you'll know for sure that its not the fpga code.

Still, it sounds like you're not doing anything too crazy so my guess would be you need to check the signals, grounds, etc. Since this is a slow-moving signal have you tried just multimetering the inputs of the module to compare values?

[vakost]

I tried that.

As I wrote in the previous post, it works now and it works good :).

This forum is a blessing! Without it I was going to be a couple of months behind schedule.

Thanks again.