Branches can be configured in two ways:
- Directly with the Hazard
- Pre-configured using the Branch Manager
Branches can be configured directly on a Hazard by clicking on the required Hazard -> SIL Verification -> RBD Analysis.
Branches can be preconfigured using the Branch Manager by clicking on Tools -> Branch Manager.
Note: Subsystems that do not have Elements configured within those subsystems will be disabled, and will appear greyed out (i.e. “Add Sensor Branch” option is disabled if there are no Sensor Elements configured).
The new SIL Verification module within ProSET allows complex voting arrangements such as nested voting configurations using Sub-Branches, such as a 1oo2 in a 1oo2.
A table of the Branches will be presented showing the contribution of each Branch towards the overall PFD / PFH.
The overview shows the Results of the SIL Verification, including
- Selected PFD Target – The PFD Target from the SIL Determination
- PFD Achieved – The total PFD calculated by adding the PFD of each subsystem
- Selected SIL Target – The SIL Target from the SIL Determination
- SIL Achieved (Architecture) – The SIL Achieved based on the architectural requirements of the subsystems. This is calculated to be the minimum Architectural SIL of the subsystems
- Result – Presents the results of the analysis. A green tick denotes the SIF meets both PFD and Architectural targets. A red cross denotes that either the PFD Target, SIL Target or both are not met
- Status – The status of the of the SIF from the SIL Determination
Note: If the SIL Determination has been carried out in Continuous Demand mode, then PFH Target and PFH Achieved are used with the units of per hour.
Adding a new Branch
When adding a new Branch you must select New Branch from the drop down box and provide the following information:
- Voting (MooN) – The voting configuration of the devices. The voting configuration is unrestricted, however only voting configurations with up to 4 channels (N <= 4 – i.e. 1oo2, 1oo3, 2oo3, 1oo4, 2oo4 and 3oo4) can be configured with independent channels (i.e. different Elements in each channel)
- Name – The Branch name used as a reference when searching for a preconfigured Branch
- Description – Allows expansion on the purpose of the Branch
- Non-Redundant Voting – The Non Redundant voting method allows you to include all devices which are configured within a function that in isolation, e.g. 1oo1, can achieve the required action. The devices may be configured within a logic solver with redundant voting, e.g. 1oo2, but in reality this is not correct for the detection / effect with the equipment. See below for full Non redundant Voting details
- Active Standby Voting – Allows for factors to be applied within the calculations. See below for full Active Standby Voting details
- Channel – The number of Channels displayed is dependent on the Voting configuration. Where M is not equal to N you can configure multiple devices in each Channel in series. When configuring a Channel provide:
- Type – Select from either:
- Device – Select a preconfigured Element
- Branch – Select a preconfigured Branch to be used as a Sub-Branch (ie. a 1oo2 in a 1oo2)
- Device Tag – If adding a Device, start typing in the autocomplete box and select the preconfigured Element
- Dangerous Failure Mode – If adding a Device, select the appropriate Dangerous Failure Mode for Devices with multiple DFMs
- Branch – If adding a Sub-Branch, start typing in the autocomplete box and select the preconfigured Branch
- Type – Select from either:
Note: The MooN voting is limited to N <= 15
Adding an existing Branch
When adding an existing Branch you must select Existing Branch from the drop down box. Branches can be preconfigured in the Branch Manager.
A live view of the Reliability Block Diagram (RBD) is shown as it is being created.
Non Redundant Voting
The Non Redundant voting method allows you to include all devices which are configured within a function that in isolation, e.g. 1oo1, can achieve the required action. The devices may be configured within a logic solver with redundant voting, e.g. 1oo2, but in reality this is not correct for the detection / effect with the equipment.
The benefit of using this functionality is that within the system and reports the proof test interval is identified for all device tags.
Two examples of where this may be helpful are:
- Area with multiple ESD buttons, say 2. Either button can be activated to trip the function. This is not a 1oo2 voting arrangement as each button is in a different location and therefore in reality only 1 button will be activated
- Duty / Standby ESD valves – part of the time Valve A will be de-isolated and part of the time Valve B will be de-isolated. Therefore, only a 1oo1 voted system but it could be either valve
In both of the examples above you could model a single device in a 1oo1 arrangement, having to remember to test both devices within you proof test scheduling. This option allows the software to prompt this testing. So using this method you would model as 2oo2 and apply a modifier factor of ½ = 0.5.
Simplified demonstration of the formula:
M/N * NooN (where NooN is Element1 + Element2 + ElementN in series but through our generic formula as NooN)
So in examples above: tick NRV, set M = 1, N = 2, and model both devices as if 2oo2
Active Standby voting
The Active Standby voting method allows for factors to be applied within the calculations. This differs from the Non redundant voting method as in this method you can allocate different factors for different devices. The Non redundant voting method assumes that the devices are equally shared in time e.g. 50% of the time for 2 devices.
A typical example for this method would be for a dual fuel heater, where there may be three operating modes:
- Gas fuel only
- Liquid fuel only
- Gas and Liquid fuel
Each mode would have a percentage of time in which it is operated.
- Gas fuel only – 10% of the time
- Liquid fuel only – 5% of the time
- Gas and Liquid fuel – 85% of the time
In this example the final elements of the system, modelled in this method, will have different devices (gas valves and liquid valves).
So the model would be:
0.1*(Gas Valves) + 0.05*(Liquid Valves) + 0.85*(Gas Valves + Liquid Valves)
A second example would be if there is a stream passed to the heater for a limited amount of time. Therefore, the third stream would only be required to close for a limited amount of time. The example above could be three fuels for part of the time:
- Gas fuel – 100% of the time
- Liquid fuel – 100% of the time
- Waste stream – only passed to the heater when certain conditions are met (e.g. heater above 1000°C, Waste stream unit operating etc) – <100% of the time e.g. 30% of the time
In this example the gas and liquid fuel would be modelled as a 2oo2 plus a 1oo1 of the waste stream valves with a time factor.
(Gas Valves + Liquid Valves) + 0.3*(Waste Stream Valves)