11.03
3 Safety-Related Functions
3.12 SI I/Os using fail-safe modules connected to PROFIBUS DP (840D from SW 6.3.30)
© Siemens AG 2003 All Rights Reserved
SINUMERIK 840D/SIMODRIVE 611 digital SINUMERIK Safety Integrated (FBSI) - Edition 11.03
3-189
The PROFIsafe clock cycle defines the time frame in which new F telegrams
are generated by the F master for transfer to the F modules. The PROFIsafe
clock cycle is derived as standard from the interpolation cycle in the ratio 1:1.
As part of the PROFIsafe communications, a cyclic interrupt of the PLC user
program (OB1) in the PROFIsafe cycle is made via OB40.
Note
The OB40 run time increases by 0.5 ms per F module.
To reduce the resulting computational load, use the NCK machine data:
•
MD 10098: $MN_PROFISAFE_IPO_TIME_RATIO,
(factor, PROFIsafe communications cycle)
to change the PROFIsafe clock cycle/interpolation clock cycle ratio.
In order to achieve sufficiently fast response times regarding the PROFIsafe-
communications, the PROFIsafe clock cycle may not be parameterized longer
than 25 ms. The selected PROFIsafe clock cycle is displayed in the NCK
machine data:
•
MD 10099: $MN_INFO_PROFISAFE_CYCLE_TIME,
(PROFIsafe communications clock cycle)
If a PROFIsafe cycle is longer than 25 ms, an alarm is issued the next time the
NCK is started:
•
Alarm: 27200 "PROFIsafe cycle time
time
[ms] is too long"
The PROFIsafe clock cycle should be parameterized longer than the DP clock
cycle time displayed by the STEP7: HW Config (refer to Chapter: Configuring
and parameterizing the ET 200S F I/Os). Otherwise, the load on the PLC user
program is increased as a result of unnecessary OB40 interrupts.
Note
The PROFIsafe clock cycle should be parameterized so that the following
applies:
12 ms < PROFIsafe clock cycle < 25 ms
Even if the parameterized software operates error-free in normal operation,
runtime fluctuations in the PLC operating system (e.g. processing diagnostic
alarms) can mean that the processing of the OB40 interrupt was not able to be
completed before the start of the next PROFIsafe clock cycle.
In this particular case, the NCK attempts, up to a limit of 50 ms after the last
correctly processed PROFIsafe clock cycle, to initiate an OB40 interrupt. The
repeated attempts to initiate the OB40 interrupt are no longer executed in the
PROFIsafe clock cycle but in the IPO clock cycle. Alarm 27253: PROFIsafe:
Communications error is not issued within this time.
An alarm is displayed after the 50 ms limit is exceeded:
•
Alarm: 27253 "PROFIsafe communications error F master components
Components
, Error
Error code
"
and the configured Stop response (Stop D or E) is output at the Safety axes.
PROFIsafe clock cycle
PROFIsafe clock cycle
and DP clock cycle
time
PROFIsafe clock cycle
overruns
