FUNCTION_BLOCK SCDModeBA

An instance of this Function Block type provides an implementation of the Block Alarm Mode state machine defined in Annex F.3.3 of the NORSOK I-005 Standard for System Control Diagrams. This mode is used to determine blocking of actions following alarms. Annunciation of the alarm is still made. The mode is controlled both from the logic (FB) and from the operator station (OS). In order to provide an event-driven implementation, the following changes are made with respect to Figure F.6 of the NORSOK Standard:
  1. The "OS Blocking Off" input is replaced with a REQ (Request) event input, and the OSB (Operator Station Blocking) input is used for the OS blocking signal.
  2. A single BB (Blocked) output is used, and a CNF (Confirm) event output is used to provide an indication that the REQ event has been processed.
  3. The "OS Status Blocked" and "OS Status Coincidence" outputs shown in Figure F.6 are not shown on the mode control block. As described in NORSOK I-005-F.2.2.4, reporting of mode states to the OS is to be handled separately.
  4. The state machine is implemented with a simple Ladder Diagram (LD) OR operation.
This implementation has the following advantages:

Enter data for the input variables.
Exercise the FB by clicking on the REQ event input.
Last updated: 2013-03-27.
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