Starting analog read corrupts analog write waveform

I have come across an odd condition that can occur if I am running a diagnostic routine on my system. My diagnostic routine is basically four while loops, each containing code to control specific items in the system hardware. Two of the items are DIO's and always work no problem.
(Am running LV 2013 on Win 7 with a PCI-6014 daq)
Another contains an analog read using AI8 and the last contains an analog write on AO0.
When I run the analog write task, I am feeding in a waveform that essentially pwm's the output. By itself it works fine. The only parameter I edit for the waveform generation is the total duration in seconds. I set at two seconds and I get the modulated output for 2 seconds.
The problem occurs when I try to do this and read the analog input (a simple voltage in from a pressure transducer) at the same time.
If I start the read task while the write task is running, the modulation goes away and the signal goes high and stays there, not shutting off until I force it. If I have the read task already running (in a loop remember so I can monitor pressure) the write task acts even more wiggy. When I start the task it runs for maybe 100-200 ms with the modulated signal and stops. On about the fourth start, the signal goes straight to high again and stays there until forced off.
So, is there some kind of limitation on this older hardware on reading and writing (at least a waveform) at the same time?
The write task was orginally created in front of the loop and I tried creating it in daqmx and using that but it made no diffference. I use a daqmx timing vi to set the sample clock rate based on the same waveform with a setting of finite samples.
Any thoughts are appreciated. This isn't stopping me from going forward but I would like to know why it's acting the way it is.
Thanks....
Doug
"My only wish is that I am capable of learning each and every day until my last breath."
Solved!
Go to Solution.

As I have not got this figured out yet, I am posting the guilty code in hopes someone might shed some light on what is causing the issue. Code is pretty generic in nature with only one sub vi (also attached) and a couple simple tasks for reading the analog-in.
This is on LV 2013 on a win-7 32 bit system using a PCI-6014 daq. Analog read tasks are both on AI8. One task is configured to read the straight voltage from the transducer (0-10vdc) and the other uses a custom scale to convert to pressure. Either one causes the conflict.
Pressing the button to start the motor run works as intended by itself. Default values for waveform are correct for my application though total pulse time (4 seconds) can be adjusted without consequence. (Note, waveform output controls an isolated SSR that contrls the higher level voltage)
Running either option on the read pressure routine causes the analog out for the motor to wig out. Stops pulsing and goes to a straight high condition. If it is on first, starting the motor causes just a little blip of output for 4 - 5 clicks then eventually just sets the AO to high as well. Continued clicking of the start eventually returns it to blip mode but not to the regular waveform that it is configured for.
I have removed all un-related code from the routine that exhibits this behavior. I returned the analog out to creating a task in the vi as was the original approach used. I had tried a preconfigured task in MAX but it made no difference.
Small loop inside of motor state is to allow minor adjustments in power supply voltage while motor is running. This has not even come into play at this point.
If anyone can point out the error in my ways, I would much appreciate it. I know the power supply vi is not the most robust and I will end up changing that to something better that uses the dll supplied by the mfg. Current code is legacy material that I inherited. Everything else though looks on the up and up from my persepctive.
Thanks for any insight........
(just had a thought, if the ground between the two drive voltages is made common, could that impact things ? will have to see what the internal grounding connection on the daq is)
Doug
"My only wish is that I am capable of learning each and every day until my last breath."
Attachments:
Analog_Conflict_.vi ‏43 KB
Serial Pwr Sply Driver.vi ‏68 KB

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