Siemens CU240B-2 - Page 337

Advanced commissioning
6.8 Safe Torque Off (STO) safety function
Converter with the CU240B-2 and CU240E-2 Control Units
Operating Instructions, 01/2016, FW V4.7 SP6, A5E34259001B AC
337
Tolerance time for the simultaneity monitoring
The inverter checks whether the signals at both inputs always have the same signal status
(high or low).
With electromechanical sensors (e.g. emergency stop buttons or door switches), the two
sensor contacts never switch at exactly the same time and are therefore temporarily
inconsistent (discrepancy). A long-term discrepancy indicates a fault in the wiring of a safety-
related input, e.g. a wire break.
When appropriately set, the inverter tolerates brief discrepancies.
The tolerance time does not extend the inverter response time. The inverter selects its safety
function as soon as one of the two F-DI signals changes its state from high to low.
Image 6-66 Tolerance regarding discrepancy
Filter to suppress short signals
The inverter normally responds immediately to signal changes at its safety-related inputs.
This is not required in the following cases:
● When you interconnect a safety-related input of the inverter with an electromechanical
sensor, contact bounce may result in signal changes occurring, to which the inverter
responds.
● Several control modules test their safety-related outputs using bit pattern tests
(light/darkness tests) to identify faults due to either short-circuiting or cross circuiting.
When you interconnect a safety-related input of the inverter with a safety-related output of
a control module, the inverter responds to these test signals.
A signal change during a bit pattern test usually lasts:
– On test: 1 ms
– Off test: 4 ms