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7.5
TwinSAFE reaction times
The TwinSAFE terminals form a modular safety system that exchanges safety-oriented data via the Safety-
over-EtherCAT protocol. This chapter is intended to help you determine the system's reaction time from the
change of signal at the sensor to the reaction at the actuator.
7.5.1
Typical reaction time
The typical reaction time is the time that is required to transmit information from the sensor to the actuator, if
the overall system is working without error in normal operation.
Definition Description
RTSensor
Reaction time of the sensor until the signal is provided at the interface.
Typically supplied by the sensor manufacturer.
RTInput
Reaction time of the safe input, such as EL1904 or EP1908. This time can
be found in the technical data. In the case of the EL1904 it is 4 ms.
RTComm
Reaction time of the communication This is typically 3x the EtherCAT cycle
time, because new data can only be sent in a new Safety-over-EtherCAT
telegram. These times depend directly on the higher-level standard
controller (cycle time of the PLC/NC).
RTLogic
Reaction time of the logic terminal. This is the cycle time of the logic
terminal and typically ranges from 500 µs to 10 ms for the EL6900,
depending on the size of the safety project. The actual cycle time can be
read from the terminal.
RTOutput
Reaction time of the output terminal. This typically lies within the range of 2
to 3 ms.
RTActor
Reaction time of the actuator. This information is typically supplied by the
actuator manufacturer
WDComm Watchdog time of the communication
The following formula results for the typical reaction time:
=
+
ReactionTime
RT
RT
typ
Sensor
Example for reaction time calculation:
ReactionTime
=
typ
EK1914
+ *
+
+ *
3
RT
RT
3
RT
Input
Comm
Logic
5
ms
+
4
ms
+ *
3 1
ms
+
10
ms
+ *
3 1
Version: 2.0.0
+
+
RT
RT
Comm
Output
Actuator
ms
+
3
ms
+
20
ms
=
48
ms
Installation
39
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