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Judson_At_PSL
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PCI-6733 has gain fluctuation ~200mV when wiggling card or external cable?

We have a PC-6733 analog output setup that has been working pretty well now for a couple years.  However, we recently noticed very large errors, on the order of 200mV at +/- 9V.  It appears to be a gain error (reversing polarity of output produces a gain error, not an offset or noise error).  It also seems to drift in time, but the physical strain of the cable definately plays a large role.

 

This is very disturbing when a $2000 piece of equipment can't handle a little bit mechanical strain.

 

I am pretty sure it is not the PCI connector, as those signals are digital - unless it is some kind of grounding issue - but the card is now securely connected at the screw that holds the metal slot filler to the rear of the computer case.

 

The cable connector was loose at the metal case slot filler, so I tightened the cable screw socket screws down to secure it.  This did seem to help a little, but the errors are still relatively big.  Also wiggling the front corner of the board (farthest from the cable and PCI connector) a little bit produces similiar effects.

 

Also, reversing the cable did not change anything, and whatever end is plugged to the breakout box is not affected by mechanical strain - it is definately something at the PCI card.

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Paul-D
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Re: PCI-6733 has gain fluctuation ~200mV when wiggling card or external cable?

Hi, this is Paul with Applications Engineering at National Instruments.

 

First off, I would like to clarify when this problem developed.  Have you always experienced this problem or has it developed recently?  What has changed in your system since you began experiencing this?

 

What is causing stress on this card, and what can you do to eliminate this stress?  Could you develop a way to reduce the cable's stress on the PCI card?  Do you possibly need a longer cable so that you have more cable to work with?

 

Our PCI cards our designed to remain stationary, and not designed to endure significant amounts of stress on them.  Over time, this stress may have caused damage to your card in the form of loose connections or connections or components becoming stretched.  Additionally, this flexing of the actual board may cause a change in resistance in some of the components of the board, which could cause these fluctuations.

 

Regards,

Paul Davidson
Multimedia Test Product Support Engineer
Sound and Vibration Software Product Support Engineer
National Instruments
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Judson_At_PSL
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Re: PCI-6733 has gain fluctuation ~200mV when wiggling card or external cable?



Paul-D wrote:

Hi, this is Paul with Applications Engineering at National Instruments.

 

First off, I would like to clarify when this problem developed.  Have you always experienced this problem or has it developed recently?  What has changed in your system since you began experiencing this?

 

What is causing stress on this card, and what can you do to eliminate this stress?  Could you develop a way to reduce the cable's stress on the PCI card?  Do you possibly need a longer cable so that you have more cable to work with?

 

Our PCI cards our designed to remain stationary, and not designed to endure significant amounts of stress on them.  Over time, this stress may have caused damage to your card in the form of loose connections or connections or components becoming stretched.  Additionally, this flexing of the actual board may cause a change in resistance in some of the components of the board, which could cause these fluctuations.

 

Regards,



It was first noticed a couple weeks ago.  It's drastically worse than it would "normally" be.
The stress is induced by the cable on the back.  I have attached a picture of what we have done to attempt to remedy the situation, but it still drifts in time, even when secured like this and left alone, so I can't just find the magic angle to tilt the cable and hold it at that angle. Also I can't devote a whole lot more real estate to the cable behind the computer, as the combined depth of the computer and the cable assembly will be impractical.

 

I should also note that it appears to happen on every channel synchronously. In other words, every channel seems to exhibit the same magnitude of error at the same time.
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Paul-D
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Re: PCI-6733 has gain fluctuation ~200mV when wiggling card or external cable?

I just wanted to let you know that I am still reviewing this issue with our R&D department, and should have a response for you soon.

 

Thanks,

Paul Davidson
Multimedia Test Product Support Engineer
Sound and Vibration Software Product Support Engineer
National Instruments
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Judson_At_PSL
Posts: 4
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Re: PCI-6733 has gain fluctuation ~200mV when wiggling card or external cable?

Thank you, I appriciate it.

- Judson

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Paul-D
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Re: PCI-6733 has gain fluctuation ~200mV when wiggling card or external cable?

[ Edited ]

Judson,

 

This sounds like a grounding issue given that all of the channels change at the same time.  Try pulling out the board and take a look at the screws on either side of where the I/O connector connects with the PCI board (they make the CHSGND connection).  If they are loose then tighten them.

 

Let us know how that works out for you.  If these are secure as well as all of your other connections and your problem wasn't resolved, its possible you may have damaged a trace or connection on your board with all of the flexing.  This would be consistent with the problem only occuring when the cable is moved around, in that it may possibly be opening the ground connection, which would explain the floating values.  We do offer repair options for our products.

 

Thanks,

Paul Davidson
Multimedia Test Product Support Engineer
Sound and Vibration Software Product Support Engineer
National Instruments
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Judson_At_PSL
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Re: PCI-6733 has gain fluctuation ~200mV when wiggling card or external cable?

Before I made the initial post we did notice that the connection between the cable connector housing and the case slot filler was loose as you describe.  We tightened it down (which caused another issue I will explain below), and we thought we had cured the problem, but it did not completely solve it.  There is definately more to this, and I would like to send it in for repair.  I am not sure if you should give me a case number that I can take to your repairs department for reference? I will wait for a response from you on how to appropriately proceed.

 

With regard to tightening the socket screws that secure the pci card -> cable connector  to the slot filler metal:  When we did this, the female screws are of the design such that you can tighten them with a flat head screw driver. The type on this card has a round outer jacket, and a slot across the female end.  When we tightened the screw down into the connector receptical, the metal deformed.  Because this metal intersects the female part of the screw, it caused the inner threads of this female screw to deform.  Now I cannot screw the cable screws into it properly.  See the attached picture.  I'm not pleased with this design, because it is inevitable that the female screws will come loose sooner or later, and tightening them can cause this problem.  I would prefer the screws to be spaced out further so you could use a female screw with a hexagonal outer profile so that the female threads will not be affected by tightening them into the receptical body.

 

Anyways, thank you for any assistance. I am hoping to resolve this affordably with some confidence this won't be a recurring problem.

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Paul-D
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Re: PCI-6733 has gain fluctuation ~200mV when wiggling card or external cable?

Judson,

 

I have private messaged you about your repair options.

 

In regards to your concerns, our R&D department browses these boards, and I will also bring this to their attention.  I don't have any direct solution for you on this at this time.

 

Thanks,

Paul Davidson
Multimedia Test Product Support Engineer
Sound and Vibration Software Product Support Engineer
National Instruments
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Samuel_S
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Re: PCI-6733 has gain fluctuation ~200mV when wiggling card or external cable?

Paul,

 

I approved him for an RMA and we talked with the coordinator and he is going over the options 

Sam S
Applications Engineer
National Instruments