The following sequence diagrams indicate the intended SPCS and DCS interface operational steps. The sequence diagrams are used only to visualise different choke operations and to provide helpful information for implementation of the MDISChokeObjectType in OPC UA.
Figure 33 – Choke Move to Position
Sequence description; the above sequence details a successful execution of a Move to Position command [open or close] from the DCS to SPCS in addition to intermediate acknowledgements and states.
Sequence description; the above sequence details a Fault during the execution of a Move to Position command [open or close] from the DCS to SPCS in addition to intermediate states.
Figure 35 – Choke Move Interlocked
Sequence description; the above sequence details a failed execution of a Move to Position command [open or close] from the DCS to SPCS due to an Interlock being active.
Sequence description; the above sequence details abort of a Move to Position command [open or close] from the DCS to SPCS.
Figure 37 – Choke Move Interlock Override
Figure 39 – Choke Step Success
Sequence description; the above sequence details a successful execution of a Step Open / Close command from the DCS to SPCS in addition to intermediate acknowledgements and states. The sequence diagram also includes information from instruments such as the Linear Variable Displacement (Differential) Transmitter (LVDT) to help illustrate what the actual information flow is.
Sequence description; the above sequence details a failed execution of a Step Open / Close command from the DCS to SPCS due to a choke fault.
Sequence description; the above sequence details a successful execution of a Choke Abort command from the DCS to SPCS in addition to intermediate acknowledgements and states.
Figure 42 – Choke Set Position
Sequence description; the above sequence details a successful execution of a Set Calculated Position command from the DCS to SPCS.
Figure 43 – Choke Enable / Disable
Sequence description; the above sequence details a successful execution of an Enable / Disable Choke from the DCS to SPCS in addition to intermediate acknowledgements and states.
Figure 44 – Choke Step Interlock Override
Sequence description; the above sequence details a successful execution of a Defeat / Override Interlock Choke command from the DCS to SPCS in addition to intermediate acknowledgements and states