B.5 MDIS Choke Object Sequence Diagrams
B.5.1 Overview

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.

B.5.2 Move to Position – Success

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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.

B.5.3 Move to Position – Fault

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Figure 34 – Choke Move Fault

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.

B.5.4 Move to Position – Failure, Interlock active

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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.

B.5.5 Abort Choke (Position)

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Figure 36 – Choke Move Abort

Sequence description; the above sequence details abort of a Move to Position command [open or close] from the DCS to SPCS.

B.5.6 Defeat / Override Interlock (Move)

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Figure 37 – Choke Move Interlock Override

B.5.7 Fault – No Move Operation

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Figure 38 – Choke Fault

B.5.8 Step Open / Close – Success

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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.

B.5.9 Step Open / Close – Failure, choke fault

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Figure 40 – Choke Step Fault

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.

B.5.10 Abort Choke (Step)

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Figure 41 – Choke Step Abort

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.

B.5.11 Set Calculated Position

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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.

B.5.12 Enable Disable Choke

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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.

B.5.13 Defeat / Override Interlock (Step)

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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