Rockwell Automation T8094 8000 Series TMR System Safety Manual - Manual (Page 53)

SAFETY MANUAL
D oc N umber T8094
I ssue 27 – June 2013
Page 32 of 103
3.6 PROCESSOR CONFIGURATION
3.6.1 Timing
The TMR Processor supports a limited set of configuration options; the system will
verify many of the configuration options, for example module locations against actual
module types. The configuration options include the maximum application program
scan time and sleep period between application program scans.
It is important to
ensure that the overall application program scan period (scan and sleep
periods) be set according to the PST
E
.
3.6.1.1 ISAGRAF_CONFIG Section
Sleep Period (ISA_SLEEP_PERIOD)
This parameter defines the period that the application program should “sleep” between
program scans. This parameter works in conjunction with the allowed scan time
defined within the
IEC1131 TOOLSET. The default value for this parameter is zero.
This value may be increased to allow higher levels of processing resource to be
allocated to other tasks, e.g. external communications. Increasing this parameter will
increase the overall scan time.
If this parameter is increased, it is important to
ensure that this overall scan time does not result in a response time exceeding
that dictated by PST
E
.
The sleep period or the allowed scan time, set in the IEC1131 TOOLSET, should be
adjusted to free up processing resource for other activities. If the sleep period is set to
zero and the application execution to “fast as possible” the system will switch between
the necessary activities as required. Allowing a “free” amount of resource reduces the
switching, improves overall efficiency for the specific application and results in greater
scan period consistency under a range of conditions, rather than a faster scan period,
but variable depending on load.
Maximum Scan Period (MAX_SCAN_TIME)
This parameter defines the maximum application scan time. The default setting is
1000ms. If the defined time is exceeded the system will automatically and immediately
initiate its overall fail-safe response.
This value should be set to ensure that the
overall scan time does not exceed the period dictated by PST
E
.
3.6.1.2 Composite Scan Time Estimation for the Trusted TMR System
The composite scan time for a Trusted system represents the time required to read
the input data, solve the application logic, and write the output data. This sequence is
repeated cyclically for as long as the Trusted system is executing an application. For
details of the scan time see the scan time calculation section of the TMR Processor
PD for the 8110 & 8110B module.