Siemens SIMATIC ET 200AL, System Manual

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Response times
B.3 Response time parameters for the F-DI 4/F-DQ 2 digital outputs
Digital I/O module F-DI 4+F-DQ 2x24VDC/2A, 4xM12 (6ES7146-5FF00-0BA0)
Equipment Manual, V1.0, 05/2021, A5E51082342-AA
85
B.3 Response time parameters for the F-DI 4/F-DQ 2 digital outputs
Maximum response time of the F-DI 4/F-DQ 2 Fail-Safe module digital outputs
T
WCDT_q
= T
rb
+ MAX (T
rb
, T
rb_swon
) + 2 x T
cycle
T
OFDT_q
= T
WCDT_q
When dark testing is disabled, a channel fault might not be detected until a process value
change "1" to "0" takes place on the corresponding output. When dark testing is disabled and
the process value is "1" for a given channel, the respective output switches are not
manipulated by the various safety measures.
Where:
T
cycle
Internal cycle time of the fail-safe module
T
OFDT_q
One Fault Delay Time: Maximum response time for the module's digital outputs to turn an output OFF
upon detection of a channel or module fault
T
rb
Configured "Maximum readback time" for the channel
T
rb_swon
Configured "Maximum readback time switch on test" for the channel
T
WCDT_q
Worst Case Delay Time: Maximum response time of the fail-safe module's digital output DC from the
receipt of a safety message frame from the safety program in the fail-safe CPU to the signal transition at
the digital output
The term "2 x T
cycle
" allows for a new process value to be delivered from the fail-safe CPU just
after the beginning of a cycle. The fail-safe module's digital outputs process the changed
output request and apply new data to the output switches on the next cycle.
After the fail-safe module's digital outputs command the output switch to change, the actual
voltage on the load might not be realized until the configured readback time completes. If a
bit pattern test is in progress, the new process value cannot be applied to the switches until
the applicable readback time completes.
Minimum permissible OFF time for F-DI 4/F-DQ 2 Fail-Safe module digital outputs
The fail-safe module's digital outputs expect to complete and confirm each ON to OFF
transition before receiving a new command to go from OFF to ON. A process value of "0"
presented for less than T
WCDT_q
can cause the channel to passivate.