Differential mode operation

[nyborn]

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

[AnalogKid2DigitalMan]

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.

[nyborn]

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.

[AnalogKid2DigitalMan]

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

[nyborn]

Hi AnalogKid:

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

[AnalogKid2DigitalMan]

Graph attached it is not

[AnalogKid2DigitalMan]

Graph attached it is not

[nyborn]

Sorry, here is the attached graph.

[nyborn]

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.

[AnalogKid2DigitalMan]

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.