Differential Inputs - Intab PC-Logger 2100 User Manual

3.3.1 Differential Inputs

OBSERVE !!!
When connecting signals from sensors and/or transducers some simple rules
about referencing them to logger signal ground must be followed.
All analogue channels are differential with a very high impedance to signal
ground. Their inputs have no internal connection to signal ground.
Differential channels measure (as the name implies) the difference in voltage
between the + and the - in relation to signal ground.
Another way of saying this is that each channel really measures two voltages:
- the minus input measures the voltage between signal ground and "-";
- the plus input measures the voltage between signal ground and "+";
- the difference between these two voltages is then calculated internally and
finally presented as the channel value.
A third way is to say that signals must never be allowed to float electrically with
respect to signal ground of the "2100". They must in some way be connected!
The figure above shows one input channel. Note that the ground sign point is
common to all circuitry and channels.
3 CONNECTIONS
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