Beckhoff TwinSAFE EL2912, Operating Instructions Manual

Page: 38 / 54

Operation
EL2912 38 Version: 1.0.0
Definition Description
RT
Sensor
Response time of the sensor, until the signal is made available at the interface. Typically
provided by the sensor manufacturer.
RT
Input
Response time of the safe input, e.g. EL1904 or EP1908. This time can be found in the
technical data. In the case of the EL1904 it is 4 ms.
RT
Comm
Response time of the communication. This is typically 3 times the EtherCAT cycle time, since a
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
Logic
Response 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.
RT
Output
Response time of the output terminal. This is typically between 2 and 3 ms.
RT
Actuator
Response time of the actuator. This information is typically provided by the actuator
manufacturer
WD
Comm
Watchdog time of the communication
The typical response time is based on the following formula:
3 * 3 *
typ Sensor Input Comm Logic Comm Output Actuator
ReactionTime RT RT RT RT RT RT RT = + + + + + +
with
5 4 3 *1 10 3 *1 3 20 48
typ
ReactionTime ms ms ms ms ms ms ms ms = + + + + + + =
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:
max Comm Comm Actuator
ReactionTime WD WD RT = + +
with
max
2 *15 20 50 ReactionTime ms ms ms = + =