NI 9205 always returns rail to rail noise.

[AlexAAuck]

HI all,

I'm completely stumped on this one. I've gone through the procedure of setting up the NI 9205 in my project. Setting the channel to the correct type. Placed the IO node in my FPGA code, read from it, and all I'm getting is rail to rail noise, i.e. whatever the measurement range is, I'm getting full range noise. I've run it as an RSE measurement, as a differential measurement, differential with COM grounded wrt my power supply, differential with COM and the chassis ground connected to my powersupply ground.

Does rail to rail noise ring any bells for anyone?

I've verified using an oscilloscope that the correct signal is seen at the pins in all of the above configurations. I've even disconnected everything and connected a 3V battery across the pins and still get rail to rail noise.

Help!

[GregFreeman]

What type of signal are you putting in, sine wave square wave? How fast are you sampling? How fast is your input signal? What is the expected magnitude of your signal in volts? Are you sure you're on the right channel (sounds dumb but I have definitely done this). How are you determining the signal is noise; are you plotting it? Are you using a FIFO to transfer the data or are you just reading an indicator that is on the FPGA? As you can tell, there are a lot of things which may either cause the problem, or cause you to think there's a problem. Can you post your code? If not, can you at least post a few screenshots? Have you tried multiple channels? I know it's a pain to recompile, but you may want to set up some test code that is only loop that reads all available AI channels and plots them, that way if you're on a wrong channel, you'll see it. The constant voltage idea is a good one, because you can have a slow sample rate, you can even use scan engine. That would be one recommnedation I have, now that I think about it. Write a program that uses scan engine and drop a bunch of nodes, one for each AI channel. Put a constant voltage into your 9205 and see if you can read that on any of the AI channels. That takes your FPGA code out of the picture and you also won't have to recompile as you test.

[AlexAAuck]

I'm running wires from an AO module direct into the AI0 channel (reading a motor drive signal). The signal is a square wave impulse, usually having duration between 1ms and 5ms. Amplitude is max 5V. The channel is being sampled in FPGA at a rate of 100kHz, this is slower than the minimum conversion time for the channel (8usec, giving rate of 125kHz), so I don't think I'm hitting a wall at the ADC level. The indicator associated with this read is then polled at a rate of 100kHz in short bursts (record times last for 30 to 100ms).

I've attached pictures of my FPGA code and Host code (which is running on a real-time machine).

There is no nod to initialising the module via the host code, as I assumed this was done when I right click the module in the project window and set its properties, this may be my mistake?

[AlexAAuck]

So, I just read the calibration voltage out of it and it gave me back: 439846963

???

I guess I need to calibrate it because that looks ridiculous to me.

[GregFreeman · Accepted solution]

Hm, I have used the 9205 before, but have never seen anything like this. I'm more of a fan of buffering the data in a FIFO rather than reading a control value, but still, you shouldn't be seeing those kind of values for any reason I can think of. I have had issues with modules where something is messed up and randomly the signal will drop out then come back (in fact, I'm about to send one to NI because it's still under warranty, but it was in a portable box so I think it may have had issues with shock or something along those lines). I wish I had a good answer for you, but you seem like you know what you're doing, so it could be one of those cases where there is a hardware problem.  Do you have any other AI modules you can swap out and see if those work in that slot? Can you try it in another slot to maybe see if it's a bad backplane connection? You may also want to check if your local NI rep has a loaner they can let you try for a day, just to see if a different 9205 works. Those are usually the steps I take when I think there may be a hardware issue. Unfortunately, other than that I don't have a lot of input for you.

[AlexAAuck]

Thanks anyway, I have dropped a second 9205 in, this time with spring clips instead of DSUB, didn't think to try a different slot in case of back plane error. Will try that now.

[AlexAAuck]

That fixed it! Thank you you beautiful genius! You wouldn't believe how frustrating the last day or so has been!

[GregFreeman]

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@AlexAAuck wrote:

That fixed it! Thank you you beautiful genius! You wouldn't believe how frustrating the last day or so has been!

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HAHA, I'm glad it worked. I'm assuming it was switching the slot that fixed it? If your hardware is under warranty, I suggest getting it looked at by NI to see if there is anything they can do. Also, you may want to mark the solution here, in case anyone runs into a similar issue and comes across this thread.