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Siemens 3TK2845 Manual page 15

Safety relays, multifunction device
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mats establish a cross-circuit between the two input channels of the evaluation
system when stepped on. This means that
1. in the case of a sensor which interrupts the sensor circuit, a cross-circuit
leads to a fault.
2. in the case of safety mats an interruption of the sensor circuit leads to a
fault.
All safety mats and switching strips with 4-conductor-technology functioning
according to the cross-circuit tripping principle can be connected to the 3TK2845
safety relays.
The tripping of the 3TK2845 is initiated by a cross-circuit in the sensor cables.
A safe evaluation according to DIN EN 1760-1 and DIN EN 1760-2 is possible
with a safety mat resistance of < 1000 Ω for the safety mat + connecting cables.
The 3TK2845 automatically recognizes the mode of operation of the connected
sensor.
If, during first activation of the sensor after a device restart,
1. an opening of the sensor circuits is detected, the 3TK2845 only accepts
sensors which open the sensor circuits (floating NC contacts such as
EMERGENCY-STOP control switches or position switches). A cross-circuit
between the sensor circuits leads to a fault.
2. a cross-circuit is detected between the sensor circuits, the 3TK2845 only
accepts sensors causing a sensor circuit short-circuit (safety mats). An
opening of the sensor circuits leads to a fault.
3TK2845 Multifunction Device Manual
GWA 4NEB 926 2087-22 DS 01
Functional Information
2-3

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