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PCI-6251 Inter chennal effect is modifying signal.

Hi all,

Do anyone knows why we have inter chennal influence fo signal in PCI cards.

I am using PCI-6251 with BNC-2111, now if i connect cable in chennal 2 and read both the chennals then i am having signal in chennal 2 as well as in chennal one but not of same amplitude. the same thing i found with many other chennals..  I recently bought this setup (in January 2007). and i am new at labview. I am using this BNC connector with NRSE, and if i switch to RSE still no change in signal.

Can anyone help me in this regards..

Thank you very much in advance .. 🙂
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Message 1 of 6
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Hello,

One of the most common issues with Cross-Talk is a high source impedance. So check your system if the signal you are connecting has a high (approx. above 10Kohm) input impedance. This can cause settling time issues in your ADC. Some more issues and possible solutions can be found in the following KB:

http://digital.ni.com/public.nsf/allkb/73CB0FB296814E2286256FFD00028DDF?OpenDocument

I hope this helps,

Regards,

RikP - National Instruments Applications Engineering
 

 

Rik Prins, CLA, CLED
Software Development Engineer
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Message 2 of 6
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In addition to Rik's comments I would add a reminder to connect all unused analog input terminals to AI Ground or a suitable low impedance source within the input range.

Lynn
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Message 3 of 6
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hi there,

Thanks for replying.

well, can u tell me how to know abt impedance. i have to measure voltage and impedance is Volt/current , i know what voltage i have to measure ..

but how to know current or impedance..

I am measuring voltage from hot wire anemometer which varies between 1 to 2 volts .. and pr transduce around .1 V and a photo multiplier tube ~3V.

and i haven't connected my A2D card to ground. but by default that has to be ground with computer, (I am using BNC 2111), so how do i connect them to ground??

is it okey to short those empty chennal.

can u help me more ??

thank you..
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Message 4 of 6
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Are the transducers connected directly to the BNC-2111 or are there some signal conditioning device between the transducers and the BNC-2111? The signal conditioners will likely have low impedance outputs and be acceptable. Pressure transducers are often strain gauge bridges and have around 300 ohms impedance. A photomultiplier tube is a current output device which will have very high output impedance. The anemometers may have moderate or low impedance depending on the circuitry included. For all these sensors a signal conditioner or amplifier would probably give the best performance.

With the BNC connections the shield should be connected to the appropriate return point on the A/D board. You should be able to short the center conductor to the shield on the BNC cables connected to the unused input channels. (Do not short an analog or digial output channels).

Lynn
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Message 5 of 6
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Sorry for not to mentioning that.. there are charged amplifire connected between the pr transducer and BNC2111

and we do not have any signal conditionar here niether we are planning to buy one.

Thanx for the advice specially the analog or digital output shorting i might have done that 😉

thank you
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Message 6 of 6
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