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2TLC172001M0211_A
6.4
Monitoring of external short circuit
The system offers three main methods for avoiding that short circuit in input cabling leads to
loss of the safety function. The drawing below illustrates the different methods by which
emergency stop buttons can be connected.
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The first button has two NC contacts supplied by one dynamic signal and +24V. The inputs
are configured just to accept the expected signal and will therefore detect a short circuit
between the channels as well as to other foreign voltage.
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The button in the middle has one NC and one NO contact supplied by +24V. The software
requires that the inputs operate in opposition to each other. A short circuit in the connecting
cable will have the effect that both inputs will at sometime during the cycle be ON, which
the system does not accept.
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The last emergency stop button uses a short circuit proof single channel technique. A
dynamic signal is converted by an inverter mounted close to the contact. The input is
configured just to accept the inverted result of the supplied dynamic signal. A short circuit in
the connecting cable will result in an incorrect signal being presented to the input which will
not be accepted by the system.
