Annex B Sequence Diagrams (Informative)

B.1 Introduction

The following section provides sample sequence diagrams for each of the MDIS ObjectTypes. These sample sequences are not mandated or the only valid variant.

B.2 MDIS Discrete Instrument Object Sequence Diagrams

B.2.1 Enable Disable

Figure 27 – Discrete Instrument

B.3 MDIS Digital Instrument Object Sequence Diagrams

B.3.1 Enable Disable

Figure 28 – Digital Instrument

B.4 MDIS Instrument Object Sequence Diagrams

B.4.1 Enable Disable

Figure 29 – Instrument Enable / Disable

B.4.2 Write to Setpoint

Figure 30 – Instrument Setpoint changes

B.4.3 Display Limits

Figure 31 – Instrument Limits

B.4.4 Display Engineering units

Figure 32 – Instrument Engineering Units

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

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

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

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)

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)

Figure 37 – Choke Move Interlock Override

B.5.7 Fault – No Move Operation

Figure 38 – Choke Fault

B.5.8 Step Open / Close – Success

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

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)

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

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

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)

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

B.6 MDIS Valve Object Sequence Diagrams

B.6.1 Overview

The general functionality of the valve is to control the flow, in that it is either open and flowing or closed and not flowing. The MDISValveObjectType provides the information available for valves and provides access to control and management functionality in the valve. The following sequence diagrams indicate the intended subsea and DCS interface operational requirements and should be used in conjunction with the MDISValveObjectType generic properties. The final result described in the sequence diagram will be held until the next command is issued to the Valve, or until the state of the Valve changes (Fault or Interlock clears).

[Note: in most of the failure cases described below, the Method call should not have been made. But the error case is still described, since the Server still needs to be able to correctly handle the case where a Client sends an inappropriate command. Warning states do not affect commands.]

B.6.2 Valve command – Success

Figure 45 – Valve command - success

Sequence description; the above sequence details a successful execution of a command [Open or Close] from the DCS to SPCS in addition to intermediate state changes.

B.6.3 Valve command – Overridden Interlock

Figure 46 – Valve command – overridden Interlock

Sequence description; the above sequence details a successful execution of a command [Open or Close] with an interlock override active from the DCS to SPCS in addition to intermediate states changes. The Interlocks listed in the interlocks folder that are overridden are updated to reflect not interlocked.

B.6.4 Valve command –- Interlocked not overridden

Figure 47 – Valve command – Failed - Interlocked

Sequence description; the above sequence details the rejection to execute a command [open or close] owing to a non-defeatable interlock active status in the subsea system. The interlock is one reason a command may be rejected but there are others.

B.6.5 Valve command – Disabled

Figure 48 – Valve command – Failed- Disabled

Sequence description; the above sequence details the rejection to execute a command [Open or Close] owing to the valve being disabled. The move Method may return successful or a failure depending on whether it knows if the valve is disabled.

B.6.6 Valve command – Failed – Fault case 1

Figure 49 – Valve command – Failed - Fault

Sequence description; the above sequence is a failure of a command. The value fault maybe the result of the lack of action from the valve for a period of time greater that the OpenTimeDuration, it could also be some other fault that is reported from the subsea system.

B.6.7 Valve command – Failed – Fault case 2

Figure 50 – Valve command – Failed - Faulted

Sequence description; the above sequence details what the possible outcomes for moving a valve that has a fault set. The valve may immediately fault, may fault again after some time or the move may succeed. All outcomes are possible from a Client point of view. On some Servers only the last two may be possible.

B.6.8 Valve Signature Request – Completed

Figure 51 – Valve Profile Request – Completed

Sequence description; the above sequence details the valve signature request of a valve during operation [open or close] from the subsea system level. The valve may also report Failed or Not Available.

B.6.9 Valve command – Shutdown

Figure 52 – Valve command – Shutdown

Sequence description; the above sequence details the execution of a Shutdown command [Open or Close]. The intermediate acknowledgements and states as applicable are indicated. The Shutdown command will attempt to override all interlocks, including any non-defeatable interlock if possible