The following section provides sample sequence diagrams for each of the MDIS ObjectTypes. These sample sequences are not mandated or the only valid variant.
Figure 27 – Discrete Instrument
Figure 28 – Digital Instrument
Figure 29 – Instrument Enable / Disable
Figure 30 – Instrument Setpoint changes
Figure 32 – Instrument Engineering Units
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
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.]
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.
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.
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.
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.
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.
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.
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.
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