Rockwell Automation T8082 Trusted Toolset Suite - Manual (Page 45)

Trusted
TM
Toolset Suite T8082
Issue 14 Feb 10 PD-T8082 45
2.8.1. Scanning Controls: Pre Release 3.5
The Scanning area allows the minimum scan rate for the module to be defined. An interval of zero is
the default and instructs the system to scan the module as frequently as possible. Where the signals
associated with the module may have a slower rate of change, higher priority is required for other
signals, or greater time is required to be allocated to the application program execution the scan
interval may be set to a slower rate.
Before release 3.5, the only mode selection available for use is time and the scan interval is entered in
milliseconds.
The rate at which the input module information is passed to the application program may be defined
within the Check For Change Rates area. If no update rates are defined, all the input information will
be passed to the application program at the rate defined by the scan interval except Housekeeping
information which is updated once per second. Setting slower rates for individual rack information
allows the system performance to be optimised to meet the application specific needs, e.g. voltage
information may be used for reporting only and require only relatively slow updates, whereas the
Boolean Input status information may be required at the maximum possible rate.
For most applications, it is not necessary to adjust these parameters. If adjustment becomes
necessary, the user must enable the function by clicking the mouse in the adjacent box then entering
the required data.
Note: All input information that is used for safety-critical functions must have an update rate less than
one-half the Process Safety Time.
2.8.2. Scanning Controls: From Release 3.5
From release 3.5, the module may be configured to be polled only when required. Check ‘Enable
Scheduled Polling’ to set the module as polled.
'Poll Interval' is how often the module will be scanned, for example 5 means that the module will only
be scanned once every 5 application scans.
'Poll Offset' sets which actual application scan will scan the module. This enables module scans to be
evenly distributed. For example, if two modules had the Poll interval set to 5, and one have the poll
offset set to 3 and the other to 4, the first module would be polled in the third scan and the other would
be polled in the fourth scan, so that they do not get polled in the same application scan.
Note: All input information that is used for safety-critical functions must have an update rate less than
one-half the Process Safety Time.
The User Description area may be used to enter any descriptive information about the input module if
required. This information is saved in the System.INI file for documentation commentary only and is
not used for any operational function of the input module.
Output modules are configured in the same manner as described above.