© 2018 imc Test & Measurement GmbH
imc C-SERIES - Manual, Version 4 R 3 - 2018-10-19
110 Device description
5.8.1.1 Voltage source with ground reference
The voltage source itself already has a connection to the device's
ground. The potential difference between the voltage source
and the device ground must be fixed.
The device is grounded. Thus, the input -VB is also at ground
potential. If the voltage source itself is also grounded, it's
referenced to the device ground. It doesn't matter if the
ground potential at the voltage source is slightly different from
that of the device itself. But the maximum allowed common
mode voltage must not be exceeded.
In this case, the negative signal input -IN may not be connected
with the device ground -VB. Connecting them would cause a
ground loop through which interference could be coupled in.
In this case, a genuine differential (but not isolated!)
measurement is carried out.
5.8.1.2 Voltage source without ground reference
The voltage source itself is not referenced to the amplifier
ground but is instead isolated from it. In this case, a ground
reference must be established. One way to do this is to ground
the voltage source itself. Then it is possible to proceed as for
Voltage source with ground reference . Here, too, the
measurement is differential. It is also possible to make a
connection between the negative signal input and the device
ground, in other words to connect -IN and -VB.
An ungrounded voltage source is measured, for instance a
battery whose contacts have no connection to ground. The
device module is grounded.
110
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