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9207 Analog Input always reading 10.4V disconnected

Hello,

 

I'm running a cDAQ-9174 which is populated with 4 cards (2x 9207 in slots 1 & 2, 9265 slot 3, 9485 slot 4). I was attempting to configure the system to measure analog inputs across the two 9207 cards using MAX. With nothing connected, I found that all of the Analog Ins on card 1 were reading close to 0V while all of the Analog Ins on card 2 were clipped at 10.4V. I swapped the cards between slots 1 & 2 and the 10.4V signal follows the board from slot 2 in the slot 1 position. Do I have a bad board? The system has never been connected to an input and passes all of the "self tests". The trend is the same regardless of if I try to make a voltage task or use the test panel. Interestingly, even if I switch the max input range for the card in the test panel to 0-5V it still clips at 10.4V.

 

Thanks,

Justin

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In altenbachs link I miss the basic explanation of bias currents.

Your DAQ input will output a tiny current. If no current path (bias resistor) is provided, this current  flow into the (usually small) input capacity resulting in an increasing voltage over that cap. 

 

If you want to measure that current, make a short cut and measure the voltage and replace the shortcut with a 1M (or other higher value) resistor and measure the voltage. The voltage difference and the resistor value used together with Ohms law give a good estination of the bias current. 

Greetings from Germany
Henrik

LV since v3.1

“ground” is a convenient fantasy

'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'


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