RedLab 1208FS User's Guide
Functional Details
19
If you decrease the common-mode voltage to -7 V, the differential stays at ±8 V. However, the solution now
violates the input range condition of -10 V to +20 V. The voltage on each analog input now swings from -3 V to
-11 V. Voltages between -10 V and -3 V are resolved, but those below -10 V are clipped (see Figure 8).
-3V
-11V
-7V
+/-7V
8V Differential
-11V
-7V
-3V
3V
CHLO
CHHI
Measured Signal
Figure 8. Differential voltage example: common mode voltage of -7 V
Since the analog inputs are restricted to a
−
10 V to +20 V signal swing with respect to ground, all ranges
except
±20V can realize a linear output for any differential signal with zero common mode voltage and full scale signal
inputs. The ±20 V range is the exception. You cannot put
−
20 V on CHHI and 0 V on CHLO since this violates
the input range criteria.
The table below shows some possible inputs and the expected results.
Sample inputs and differential results
CHHI CHLO Result
-20 V
0 V
In Valid
-15 V
+5 V
In Valid
-10 V
0 V
-10 V
-10 V
+10 V
-20 V
0 V
+10 V
-10 V
0 V
+20 V
-20 V
+10 V
-10 V
+20 V
+10 V
0 V
+10 V
+15 V
-5 V
+20 V
+20 V
0
+20 V
For more information on analog signal connections
For more information on single-ended and differential inputs, refer to the
Guide to Signal Connections
(this
document is available on our RedLab CD (root directory))
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