Measurement Computing PCIM-DAS1602/16, User Manual

Page: 14 / 50

Figure 5-1b. Single-Ended Voltage Input Theory
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
PCIM-DAS1602/16 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 only
measures the difference between the two leads, and the EMI common to both is ignored. This effect is a
major reason there is twisted pair wire as the twisting assures that both wires are subject to virtually
identical external influence. Figure 5-2a and 5-2b below show a typical differential input configuration.
Figure 5-2a . Differential Input Theory
10
+
-
Inp ut
A m p
To A /D
LL G ND
C H IN
~
1
2
V s
V s + V g2 - V g 1
A n y v olta ge differe ntial be tw een ground s
g1 an d g2 sho w s up a s a n error sig nal
at the inp ut am plifier
S in g le -e n de d in p ut w ith C o m m o n M od e Volta g e
g
g
+
-
Inp ut
A m p
To A /D
D ifferen tial In pu t
I/O
C o nn ector
LL G N D
C H H igh
C H L ow