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ni 9207 - Voltage channel

Dear,

 

I’m using the NI 9207 with 16 analog input channels: 8 voltage and 8 current. I’m trying to use all the channels at the same time. The results for the current channels are exactly what we expected (we are testing with a pressure transducer and a dead weight machine). However, when I tried to use the voltage channel the results were different of what I expected. To see what was the problem runned two tests.

 

Test 1: First I tried to connect only voltage channel (I didn’t connect the COM channel). In this case, the result obtained using the NI Max was exactly what I expected (1.838v). To check if the result was correct, I used a multimeter, and the result in the multimeter was the same of the NI Max.

 

Test 2: The problem happened when I tried to connect the COM channel (it is necessary to use the current channels). In this case, the result obtained using the NI Max was different of the expected result (1.44). However, when I used the multimeter the result was the same of the previous test (1.838). With that, I concluded that the connection of the COM channel changed the voltage result. I don’t know why it happens. Could you help me to solve this problem? Probably I’m making some mistake in the wire connections. It is important to note that this is the first time that I’m using a DAQ.

 

Thanks!

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Nice documentation, however some important informations are missing:

 

How does the ground scheme of the your voltage and current sources look like?

 

Multiple current sensors , all driven by the same power supply?

Powersupply ground referenced or floating?

What are your Voltage sources and how are they related to grnd?

 

 

 

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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