2000 - Draper Laboratory

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SUBSYSTEM CONTROL REQUIREMENTSRedundant SensorsIf A = B = C, Then X = A or B or CIf A = B ≠ C, Then X = A or B,If A ≠ B = C, Then X = B or C,A = C ≠ B, X = A or C,ABCno failureC is failedA is failedB is failedXBefore investigating how I/O networks can be applied to produceaffordable fault- and damage-tolerant subsystem controlsfor ships, it is important to define the types of systemsthat are to be controlled and to establish some basic I/Orequirements for these systems. Table 1 summarizes systemsthat are candidates for control or monitoring using I/O networksand lists a few of the basic control system functionsrequired. Tables 2 and 3 list sensors and actuators needed tosupport these functions. Typically, for control applications, thesensors and actuators are sampled/updated at rates of 1 to 10times per second.Figure 2.TMR systems provide highly dependable operation.Table 1. Subsystem control functions supported by network I/O.PropulsionElectrical Power Generation, Distribution, and ControlMechanical Fluid Systems• Hydraulic power• HVAC• Liquid cooling (chilled water, sea water)• High- and low-pressure compressed air• Steam• Machinery speed control• Pressure and temperature limiting• Torque sensing/limiting• Startup/shutdown sequencing• Performance monitoring (vibration, temperature, oil quality, etc.)• Voltage and frequency regulation• Load management/load shedding• Short circuit detection and recovery• Damage detection/reconfiguration• Performance monitoring (normal current loading, temperatures, vibration, etc.)• Electrical motor control• Pressure control and monitoring• Temperature control and monitoring• Flow control/diversion• Performance monitoring (temperatures, vibration, oil quality, flow rates, etc.)Fire Detection and SuppressionFlooding Detection and ControlWeapons Handling Machinery ControlMiscellaneous Winches, Lifts, Elevators, Cranes• Smoke, heat, flame detection• Suppression agent activation• Readiness testing• Seawater intrusion detection• Pump activation and flow routing• Readiness testing• Conveyor and lift control• Sequencing• Stores inventory measurement• Electric motor control• Sequencing• Performance monitoring (vibration, oil quality, actuation speeds, etc.)Fault-Tolerant Input/Output (I/O) Networks Applied to Ship Control 27
Table 2. Potential sensors requiring network I/O interfaces.• Pressure• Temperature• Shaft speeds• Linear and rotary positions• Limit switches• Flows• Liquid levels• Voltages• Currents• Switch positions• Lever positions• Vibration• Acoustic• Strain• Oil quality (conductivity, other)• Smoke• Heat• Flame (IR)• Seawater intrusion (conductivity)• Joysticks• Keypads• Barcodes, other ID devicesTable 3. Potential actuators requiring network I/O interfaces.Valve Control (modulated and two position)• Hydraulically actuated• Pneumatically actuated• Electromechanically actuated (EMA)Linear Actuator Control (modulated and two position)• Hydraulically actuated• Pneumatically actuated• EMAElectrical Switching and Contactors• Solid-state• ElectromechanicalElectric Motors• ac and dc• Fixed and variable speed, indicators, lamps, displaysNETWORK I/O DESIGN TRADE-OFFSThe design of an effective network I/O system requires theinvestigation and evaluation of a number of alternatives. Afew of these selected for discussion in this paper are:• Network media selection.• Powering the I/O network electronics.• Network topology.• Network data rate requirements.• Centralized or distributed I/O processing.• I/O channel cross-strapping.NETWORK MEDIA SELECTIONThree good choices are available for the network media: opticalfiber, copper wire, and wireless (RF or Infrared (IR)). Eachoffers advantages, and all have drawbacks. It is likely thatfuture ships will make use of all three, matching the strengthsof a particular media to a specific problem. The following arethe trade-offs between these media, with advantages precededby a plus (+) sign and disadvantages preceded by a minus(-) sign.Optical Fiber+ Supports very high data rates.+ Insensitive to Electromagnetic Interference (EMI).+ Does not propagate electrical faults (electrically isolated).- Optical signal is attenuated by connectors and splitters.- Attenuation makes fiber poorly suited to bus topologies(see I/O Network Topology).- Requires complex terminals.- Installation is complicated if wires are needed to power theterminal.Wire+ Small, low-cost terminals are available.+ Wiring can deliver power in addition to data.+ Electrical connections are easy to make.- Limited speed compared to optical fiber.- Requires shielding from EMI.Wireless (RF and IR)+ Very low cost to install (no wiring or fiber).+ Small, low-cost RF electronics are available.- To remain wireless, requires a battery (needs replacement)or power scavenging.- Vulnerable to EMI (RF).- Vulnerable to optical path obstruction by smoke, dust,equipment, or personnel (IR).- Limited bandwidth compared with wire or fiber.28Fault-Tolerant Input/Output (I/O) Networks Applied to Ship Control
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presented.The economic benefits of
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over conventional analyzers. A plan
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Smith, J.; Proulx, R.J.; Cefola, P.
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Donald E. GustafsonDavid J. LuciaAu
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onald E. GustafsonbiographiesDonald
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DOCTOR ROBERT D. MAURERDr. Maurer l
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All Draper employees (excluding Off
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Chauddhry, A.I.; Supervisors: Kang,
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