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S5-95F
4.2.2
Short-Circuit Test for Sensor Lines
If signal cores run in mechanically stressed light plastic-sheathed cables, conductor-to-conductor
short circuits can occur between the cores. Lines subject to this danger can be monitored by means
of the check DQs.
A conductor-to-conductor short circuit between two signal cores results in:
•
Common-mode corruption of the input signals in the case of single-channel sensors
•
Loss of sensor redundancy in the case of two-channel sensors.
The test is optional and is used for checking the sensor lines. You should use it, if
•
diagnostics for the connected sensor lines is required,
•
a conductor-to-conductor short circuit must be excluded, e.g. in the case of light plastic-
sheathed cables or coiled cables.
With one check DQ you can monitor up to 8 sensor lines simultaneously, no matter whether the
sensor lines lead to onboard inputs or to external inputs. If you connect several sensor lines to one
check DQ, a conductor-to-conductor short circuit between these lines must be physically excluded
(e.g. lines laid separately and/or with double insulation).
Note
A separate check DQ is required for the inputs of IB 59; mixing of IB 59 inputs with other
IB inputs is not permissible.
Method of Operation
The operating system can monitor sensor lines endangered by conductor-to-conductor short circuit,
if these are supplied by different check DQs.
By calling FB252, you can initiate the test for checking the sensor lines (see Chapter 9). To test the
sensor lines, the operating system temporarily resets the check DQs and thus the sensors supplied
by them.
The tested inputs must now have "0" signal. If the input remains on "1" signal, the S5-95F
responds with a fault signal and the programmed system reaction.
Sensor Supply for the DIs with Short-Circuit Test
If a short circuit to reference potential occurs at a check DQ, the S5-95F automatically disables the
output without a fault signal (however, the LED on the module remains set).
The output remains set until
•
the short circuit is removed and
•
the output has been reset (e.g. by calling the short circuit test via FB252).
EWA 4NEB 812 6210-02
Installing and Connecting the Basic System
4-11
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