Response Times - Siemens S7-300 Installation And Operating Manual

Response times

D.1 Response Times
Introduction
The next section shows the response times of fail-safe signal modules. The response times
of fail-safe modules are included in the calculated response time of the F-system.
For information on the calculated response time of the F-system, refer to the Safety
Engineering in SIMATIC S7 (http://support.automation.siemens.com/WW/view/en/12490443)
system description.
The elements used in the formulae below are available in the technical data of the relevant
module.
Response time definition
For fail-safe digital inputs: The response time represents the interval between a signal
change at the digital input and reliable availability of the safety message frame on the
backplane bus.
For fail-safe digital outputs: The response time represents the interval between an incoming
safety message frame from the backplane bus and the signal change at the digital output.
For fail-safe analog inputs: The response time results from the number of channels/channel
pairs, the response time per channel/channel pair, the basic response time and, in the case
of SM 336; F-AI 6 x 0/4 ... 20 mA HART, also the configured smoothing.
Response time of SM 326; DI 8 x NAMUR
Calculation of the response time of SM 326; DI 8 x NAMUR (without active error and with
active error):
Response time = internal signal preparation time + input delay
Example SM 326; DI 8 x NAMUR
Response time = 55 ms + 3 ms = 58 ms
An active error extends the response time by the amount of the assigned discrepancy time, if
the "1oo2 evaluation" of the sensors was assigned.
Note
Calculate the maximum response time by inserting the maximum values derived from
technical data of the fail-safe signal modules in the formula shown earlier.
Fail-safe signal modules
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