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# Multifunction DAQ

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## Differential mode operation

Hi:

Could you tell me how the current through AI+ and AI-.There is also one biase resistor from AI- to AIGND.

Attached is the digram that I cut from ni site. The AI- input is also connected to my test fixture ground at the end. I could not see how to current flow. Could you please tell me?

I am in a very urgent. I really a quick reponse.

Regards.
John
Message 1 of 29
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## Re: Differential mode operation

In the 2nd image, current flows through the lump sum parameter RIN nodes (1) and (2) regardless if VS- terminal 0 is connected to ground or not.
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"It’s the questions that drive us.”
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Message 2 of 29
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## Re: Differential mode operation

Hi AnalogKid:

Thanks for your replying. You said current flows through the lump sum parameter RIN nodes (1) and (2) regardless if VS- terminal 0 is connected to ground or not.

Then what is Rin? Rin is the resistor inside the 6250 board or the bias resistors from AI- to ground? Could you please tell me?

Attached is my graph. I take VS as the voltage across 100ohm resistor. Is that correct? I would like to verify with you.

Message 3 of 29
(3,093 Views)

## Re: Differential mode operation

Rin is the simplification of the all the circuitry of the amplifier input. I do not think it would represent bias resistors since those are typically added by a user when using differential mode of operation. Rin is typically a high value, in the range of 100's of kilohms up to 10's of megohms.

Yes, VS could represent the voltage that is generated by the current flowing through a 100 ohm resistor that is placed across the input of the amplifier. If 0.010A was flowing through 100 ohms, Ohm's law calculates that (0.010A)*(100ohms)= 1volt
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"It’s the questions that drive us.”
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Message 4 of 29
(3,077 Views)

## Re: Differential mode operation

Hi AnalogKid:

Attached is my graph. How does current flow at the point where bias resistor started? Could you please tell me?

Message 5 of 29
(3,057 Views)

## Re: Differential mode operation

Graph attached it is not
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"It’s the questions that drive us.”
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Message 6 of 29
(3,052 Views)

## Re: Differential mode operation

Graph attached it is not
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"It’s the questions that drive us.”
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Message 7 of 29
(3,054 Views)

## Re: Differential mode operation

Sorry, here is the attached graph.
Message 8 of 29
(3,039 Views)

## Re: Differential mode operation

Hi:

I would also like to ask the AI+ and AI-. input. I might ask before, but I forgot. The AI+ and AI- input can only measure AC and DC voltage, am I correct? no current.

Message 9 of 29
(3,025 Views)

## Re: Differential mode operation

Your schematic is incomplete, you do not show a connection to anything on the bottom side of the bias resistor.

Correct, inputs will only measure voltage directly.

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"It’s the questions that drive us.”
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Message 10 of 29
(3,007 Views)