Measurement-computing USB-1208FS Manuel d'utilisateur télécharger pdf (Page 13)

USB-1208FS User's Guide Functional Details

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 Invalid

–15 V +5 V Invalid

–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 DAQ Signal Connections

(this document is available on our web site at www.mccdaq.com/signals)

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Measurement-computing USB-1208FS Manuel d'utilisateur Page 13