Monitoring and Response Times of F-Systems
A.5 Response Times of Safety Functions
Safety Engineering in SIMATIC S7
System Manual, 04/2006, A5E00109529-05
A-15
A.5
A.5
Response Times of Safety Functions
Definition of Response Time
The response time starts with the detection of an input signal and ends with the modification
of a gated output signal.
Fluctuation Range
The actual response time lies between a minimum and maximum response time. You must
always take the maximum response time into account in your system configuration.
Rules for Maximum Response Time of a Safety Function
The maximum response time of a safety function must be less than the process safety time
of the process.
Definition of Process Safety Time
The process safety time is the time interval during which the process can be left on its own
without causing injury to operating personnel or damage to the environment.
Within the process safety time, any type of F-system process control is tolerated. That is,
during this time, the F-system can control its process incorrectly or it can even exercise no
control at all. The process safety time of a process depends on the process type and must
be determined on a case-by-case basis.
Procedure for Response Time Calculation
A formula is available for calculating the maximum response time of a safety function:
•
For S7 Distributed Safety on the Internet at
http://support.automation.siemens.com/WW/view/en/11669702/133100.
•
For S7 F/FH Systems: in
...\Siemens\STEP7\S7BIN\S7ftimeb.xls directory
Use one of these MS Excel files to calculate the maximum response time of the safety
function and ensure that the process safety time is not exceeded.
If necessary, reduce the specific F-system monitoring times (see
"F-Related Monitoring
Times for S7 Distributed Safety" and "F-Related Monitoring Times for S7 F/FH Systems").
