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Definition Description
RT
Response time of the sensor, until the signal is made available at the interface. Typically
Sensor
provided by the sensor manufacturer.
RT
Response time of the safe input, e.g. EL1904 or EP1908. This time can be found in the
Input
technical data. In the case of the EL1904 it is 4 ms.
RT
Response time of the communication. This is typically 3 times the EtherCAT cycle time, since a
Comm
new Safety-over-EtherCAT telegram has to be generated before new data can be sent. These
times depend directly on the higher-level standard controller (cycle time of the PLC/NC).
RT
Response time of the logic terminal. This is the cycle time of the logic terminal and typically
Logic
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.
RT
Response time of the output terminal. This is typically between 2 and 3 ms.
Output
RT
Response time of the actuator. This information is typically provided by the actuator
Actuator
manufacturer
WD
Watchdog time of the communication
Comm
The typical response time is based on the following formula:
ReactionTime
=
RT
+
RT
typ
Sensor
with
ReactionTime
=
5
ms
+
4
ms
typ
Worst case response time
The worst-case response time is the maximum time required for switching off the actuator in the event of an
error.
Fig. 27: Worst case response time
It is assumed that a signal change takes place at the sensor, and that this is passed to the input. A
communication error occurs just at the moment when the signal is to be passed to the communication
interface. This is detected by the logic once the watchdog time of the communication link has elapsed. This
information should then be passed on to the output, resulting in a further communication error. This fault is
detected at the output once the watchdog time has elapsed, resulting in shutdown.
This results in the following formula for the worst-case response time:
ReactionTime
=
WD
+
max
Comm
with
ReactionTime
=
2 *15
ms
+
max
EL2912 and EL2912-2200
+
3*
RT
+
RT
+
3*
Input
Comm
Logic
+
3*1
ms
+
10
ms
+
3*1
ms
+
3
ms
WD
+
RT
Comm
Actuator
20
ms
=
50
ms
Version: 2.0.0
RT
+
RT
+
RT
Comm
Output
Actuator
+
20
ms
=
48
ms
Operation
45
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