Omega Engineering PCI-DAS1200 manual Differential Input

			CH IN	+
~
	V s	Vs + V g2 - V g1		Inp ut	To A /D
				A m p
			LL GN D	-

g1

g 2

An y volta ge differential betw een grounds g1 and g2 show s up as an error signal at the input am plifier

S in gle -ended input w ith C om m on M ode Voltage

Differential Inputs

Differential inputs measure the voltage between two distinct input signals. Within a certain range (referred to as the common mode range), the measurement is almost independent of signal source to PCI-DAS1200 ground variations. A differential input is also much more immune to EMI than a single-ended one. Most EMI noise induced in one lead is also induced in the other, the input measures only the difference between the two leads, and the EMI common to both is ignored. This effect is a major reason for twisted pair wire because the twisting ensures that both wires are subject to virtually identical external influence. The diagram below shows a typical differential input configuration.

CH High

CH Low

LL GN D

I/O

Connector

+

Inp ut	To A /D
A m p

-

Differential Input

~	CH High
	Vs

+

Inp ut

Vs

CH Low

Vcm

LL GND

A m p

-

To A/D

g1	Vcm = Vg2 - Vg1
	g 2

Common Mode Voltage (Vcm) is ignored by differential input configuration. However, note that Vcm + Vs must remain within

the am plifier’s comm on mode range of ±10V

Diffe rential Inp ut

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