Omega OM-USB-1208FS - page 15

OM-USB-1208FS User's Guide Functional Details
15
Figure 6. Differential voltage example: common mode voltage of 11 V
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 7).
Figure 7. 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