Appendix; Connecting Signal Sources To Analog Modules - Wieland ricos Manual

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Appendix

4.1

Connecting signal sources to analog modules

Voltage inputs
The 4 analog inputs are differential inputs which are linked electrically with each
other. The voltage potentials of the positive and negative signal poles should not
exceed the permitted common-mode range (-12.1 ... + 12.8 V based on AGND), as
signals outside this range are capped in the series-connected amplifiers and thus
invalidate the measured value.
The analog input potentials are electrically isolated from the power supply (+24 V,
0 V) and the PE.
The following should therefore be noted when connecting signal sources to the
analog inputs:
a) Potential-free signal sources:
If a fully potential-free signal source is only connected to AIx+ and AIx-, high-
resistance resistors in the module ensure that the potentials are drawn from the
middle of the range. However, since the equipotential coupling has an extremely
high resistance (to avoid corruption of the measured value) and is therefore very
weak, the high level of ripple voltage that is typically present can lead to
considerable fluctuations in the potentials so that they even exceed the common-
mode range. This can be detected by measured values that fluctuate considerably
or are completely invalidated. To avoid this, it must be ensured that the potentials
operate as open-circuit potentials via an external potential interface to AGND.
b) Non-isolated signal sources:
If several non-isolated signal sources are connected to different analog inputs of
the module, a potential interface to AGND must likewise be carried out to avoid
free floating signal potentials. In general, a single connection of a signal source
potential to AGND is sufficient. With non-isolated signal sources, particular care
should be taken to ensure that the respective potentials lie within the common-
mode range. If the potentials of two signal sources are widely different (example:
first signal source supplies voltage based on external 0 V while the second signal
source supplies voltage based on external +24 V), they must not be connected to
the same analog input module under any circumstances!
In the case of open voltage inputs (differential input), the digital value 07FF hex is
transferred.
© 2002 Wieland Electric GmbH Version 2.4* (December 2002)
Part no. 05.591.3389.0 © 2002 Wieland Electric GmbH
IMPORTANT
Appendix
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