Figure 4.25. Extending voltage range of auxiliary inputs by using external attenuator.
A further limitation of these function is that their common mode voltage is limited to ±3V relative to the
V- terminal. This means that to preserve accuracy and proper operation, neither terminals should have a
voltage higher than this value as it is measured between the respective terminal and the V- terminal. For
instance, while measuring a differential output voltage of 10mV of a load cell, which is stimulated by the
DMM internal DCV source, both terminals as at a common mode voltage of about 2.5V, which is within
the 3V limit. Actually the I+ terminal’s common mode is 2.505V. Provided the stimulus applied to the
cell would have been 10V, a common mode voltage of 5V would have resulted, exceeding the 3V limit.
In Figure 4.26 the stimulus voltage to the load cell is measured using the
DMMRead
function and the
output of the cell is measured using
DMMReadHiLoSense
function.
61
Signametrics