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Oscillation of NI9403 Outputs

Hi,

we are using a cRIO9022 System equipped with 2 NI9403 and 3 NI9205 cards to control a selfbuilt instrument for atmospheric research.

Now the following problem occur:

All I/Os oft the 9403 cards are set to output. One 9403 card is used to control one module of our experiment.  Sometimes all output lines of this card are going in an oscillating state. All 32 lines are pulled down by 47k each. During this test mode a Stirling cooler is running, which generates a lot of noise on the 9403 control lines. But this alone doesn't make this problem. We must swich on in addition a heater with PWM control. Then sometimes this problem occurs, not always!

Have anybody an idea what the reason for this problem could be?

 

Thanks in advance!

 

Peter Knieling

University of Wuppertal

Germany

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Hi Peter,

 

can you please post your project plus the FPGA or (if Scan Engine) the RT-VI. I would like to rule out a programmatic error.

Can you describe the oscilating a bit more detailed? Is there a certain frequency to it? Do all output oscillate with the same pattern or more randomly?

 

If you switch both 9403 modules does the behaviour stay with the slot or the module?

 

Can you reproduce the issue in another environment without the attached equipment to rule out some kind of EMC?

 

Regards,

Christoph

Staff Applications Engineer
National Instruments
Certified LabVIEW Developer (CLD), Certified LabVIEW Embedded Systems Developer (CLED)


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Hi Peter,

 

you sent me a private message, that you could not answer to that post. I guess there has been a update to the forum server so the forum was read-only. For me it works again, so I assume the same applies to you.

 

Regards,

Christoph

Staff Applications Engineer
National Instruments
Certified LabVIEW Developer (CLD), Certified LabVIEW Embedded Systems Developer (CLED)


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Hi Christoph,

 

thanks a lot for your reply. Yes I can now post a reply.

 

Now to your questions:

 

The oscillations frequency is in the order of some 10kHz. I was not able to monitor all the output channels of the 9403. But all channels I have monitored show the same pattern. The second 9403 don't show this. I have changed also a little bit the grounding concept of our experiment. After this the problem disappeared!

But a bad feeling is still there.

I have attached the corresponding LabView programs. They were written by a colleague of me.

 

Thanks in advance

 

Peter

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Hi Peter,

 

even though your FPGA has potential for some improvements, I dont see how the error could be introduced due to some weired I/O behaviour.

Do I understand that correctly that only the lines of one DIO module is pulled down by the 47k resistors? The other uneffected module is not pulled down?

Could it be that the PWM signal and the pulsed power consumption of the heater could be affecting the ground the 47k resistors? What is the PWM frequency of the heater?

 

Regards,

Christoph

Staff Applications Engineer
National Instruments
Certified LabVIEW Developer (CLD), Certified LabVIEW Embedded Systems Developer (CLED)


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