Measurement Computing CIO-DAS08-PGH - Manual (Page 15)

3.2.5 Common Mode Voltage > +/-10V
The CIO-DAS08-PGx will not directly monitor signals with common mode voltages greater than +/-10V. You will either need to
alter the system ground configuration to reduce the overall common mode voltage, or add isolated signal conditioning between the
source and your board. See Figures 3-7 and 3-8.
Figure 3-7. Common Mode Voltage - >+/- 10V Single-Ended Input
Figure 3-8. Common Mode Voltage - >+/- 10V Differential Input
11
S ys tem w ith a Large C om m on M ode Voltage ,
C onne cte d to a S ingle-E nded Input
I/O
C o n n e c to r
+
-
In p u t
A m p
To A /D
LL G N D
C H IN
A /D B o a rd
L arge com
m on
m
od e v
oltag
e
bet
w ee n
signal
sou rce
& A
/D boar
d
G N D
Is o la tio n
B a rrie r
W h en the voltage difference
betw e en sign al source a nd
A /D boa rd gro un d is large
eno ugh so the A /D bo ard ’s
com m o n m od e ra n ge is
excee de d, isolate d sig nal
cond ition ing m ust be add ed.
System w ith a La rge C o m m on M ode Vo ltag e,
C o nne cte d to a D iffe rential Inp ut
L arge co
m m on
m
ode vo
ltage
be tween
signa
l
sour ce &
A/D b
oard
G N D
Iso la tio n
B a rrie r
W hen the voltage difference
between sig nal source and
A/D board g round is large
enough so the A/D boa rd’s
com m on m ode range is
exceeded, isolated sig nal
conditioning m ust be added.
+
-
Inp ut
A m p
To A /D
A /D B o a rd I/O
C o nn ecto r
LL GN D
CH H igh
CH Low
1 0 K
1 0K is a reco m m e nd ed va lu e. You m ay sh ort LL G N D to C H L ow
in s te ad , b u t this w ill re du c e yo ur s ystem ’s n o ise im m u nity.