Product Overview
The TRICONEX 4351Bis a high-integrity,triple modular redundant(TMR)digital input module manufactured by Triconex,a division of Schneider Electric and a global leader in safety instrumented systems.This module forms a critical component within the Tricon Tricon or Trident safety platforms,specifically designed to read binary(on/off)signals from field devices in the most demanding safety-critical processes.Its core function is to reliably acquire discrete status signals—such as emergency stop button presses,pressure switch closures,valve limit switch positions,or flame detector status—and convert them into a digital format that can be processed by the TMR safety controller.The 4351Bis engineered not merely for data acquisition but for achieving and maintaining a specified Safety Integrity Level(SIL),making it an indispensable part of the safety loop in industries where failure could lead to catastrophic consequences.
In the architecture of a Triconex safety system,the TRICONEX 4351Bembodies the principle of fault tolerance through hardware redundancy.Unlike a standard PLC input card,this module internally comprises three independent,isolated input circuits per channel.Each of the three main controllers in the TMR system reads its own version of the field signal through its dedicated circuit within the 4351B.A hardware voter inside the controller chassis then performs a 2-out-of-3 vote on these three signals to determine the definitive state.This design ensures that a single failure within the input module’s circuitry,or a discrepancy caused by noise or a faulty field contact,does not cause an erroneous trip or,more critically,a failure to trip when required.For safety engineers,specifying and maintaining the 4351Bis a foundational step in building a safety instrumented function(SIF)with a verifiable and certified probability of failure on demand(PFD),directly contributing to the protection of human life,the environment,and capital assets in facilities such as oil refineries,chemical plants,and offshore platforms.
Technical Specifications
Parameter Name
Parameter Value
Product Model
TRICONEX 4351B
Manufacturer
Triconex(Schneider Electric)
Product Type
Triple Modular Redundant(TMR)Digital Input Module
Compatible System
Tricon/Trident Safety Systems
Number of Channels
16 channels,in electrically isolated groups
Input Type
24 V DC Sinking(NPN compatible)
On-State Voltage Range
Typically 15 to 30 V DC
Off-State Voltage
0 to 5 V DC
Input Current
Approximately 6 to 9 mA per point at nominal voltage
Isolation
Channel-to-channel and channel-to-system isolation(e.g.,1500V AC)
TMR Architecture
Three independent input circuits per channel for true triple redundancy
Diagnostic Coverage
High,with continuous monitoring of circuit health
Response Time
Fast,suitable for safety-critical shutdown sequences
Connection
Removable terminal block connectors
Power Supply
Powered from the Triconex I/O bus in the chassis
Operating Temperature
0°C to 60°C(standard)
Certifications
TÜV certified for use in safety applications up to SIL 3
Main Features and Advantages
The TRICONEX 4351Bdistinguishes itself through an uncompromising focus on safety,reliability,and diagnostics.Its most defining feature is the genuine Triple Modular Redundant(TMR)per-channel architecture.This isn’t a software-based redundancy;it is a hardware implementation where three separate input paths exist for each of the 16 field points.This physical redundancy,combined with the 2-out-of-3 voting logic,provides an extremely high level of fault tolerance.A latent fault in one of the three input circuits will be masked by the other two,allowing the system to continue operating safely while reporting the diagnosed fault for maintenance.This inherent resilience prevents nuisance trips caused by random hardware failures,a critical factor in maintaining operational availability in continuous processes,while still guaranteeing that a valid demand signal from the field(like a high-pressure switch closing)will be acted upon.
Beyond redundancy,the module incorporates sophisticated continuous diagnostics.It constantly monitors the health of its internal circuits and the state of the field wiring.For example,it can detect conditions like field wire breakage(open circuit)or loss of field power by monitoring the current flow in the input loop.These diagnostics are not just simple alarms;they are integral to calculating the module’s contribution to the overall Safety Integrity Level(SIL)of the loop.The diagnostic information is communicated to the main TMR controllers and can be accessed via the engineering workstation,providing maintenance teams with clear,actionable intelligence to perform predictive and preventative maintenance.Furthermore,the 4351Bis designed for maintainability.It supports hot swap replacement in configured systems,meaning a faulty module can be removed and a new one inserted without taking the safety system or the process offline,a vital capability for maximizing plant uptime.
Certified Safety Integrity:TÜV certified for use in safety loops up to SIL 3 per IEC 61508/61511,providing a verified foundation for safety instrumented functions.
True Hardware TMR Design:Three isolated input paths per channel ensure maximum fault tolerance and protect against common-cause failures,preventing both spurious trips and dangerous failures.
Comprehensive On-line Diagnostics:Continuously monitors module health and field wiring integrity,enabling proactive maintenance and contributing to quantifiable safety metrics.
High Noise Immunity and Isolation:Excellent electrical isolation and filtering ensure reliable operation in electrically noisy industrial environments,preventing false triggering.
Hot Swap Capability:Allows for module replacement without system shutdown in redundant configurations,supporting both safety and high availability objectives.
Application Field
The TRICONEX 4351Bis deployed exclusively in applications where safety is the paramount concern,functioning as the eyes of the safety instrumented system.Its primary role is to connect critical field-initiated shutdown devices to the TMR logic solver.
In an offshore oil and gas platform,multiple 4351Bmodules are used to read signals from Emergency Shutdown Valves(ESDV)limit switches,pressure safety high(PSH)and low(PSL)switches on separators,fire and gas detection system outputs,and manual emergency shutdown(ESD)push buttons.The module’s reliability ensures that a true emergency signal will always be seen by the system,while its diagnostics warn of a switch or wiring failure before it compromises the safety function.Within a petrochemical cracker or refinery,these modules interface with sensors for high reactor temperature,compressor surge detection,flammable gas detection,and burner management system permissives.The TMR voting logic is crucial here to differentiate between a true process hazard and a single sensor failure.
Similarly,in chemical processing plants,the module connects to interlocks for mixer overload,runaway reaction temperature,and spill containment system status.In power generation,particularly in turbine controls,it may be used for overspeed detection and critical lube oil pressure monitoring.Essentially,the TRICONEX 4351Bis specified anywhere a process hazard analysis identifies a need for a highly reliable digital input to trigger a safety action,protecting against fires,explosions,toxic releases,or major equipment damage.
Related Products
Triconex Main TMR Processors(e.g.,3008,3101,3102):The central logic solvers that receive and vote on the input data from the 4351Bmodules.
Triconex Digital Output Modules(e.g.,3625,3626):The complementary TMR output modules that execute the safety actions(e.g.,close valves,stop motors)based on logic that uses 4351Binputs.
Triconex Analog Input Modules(e.g.,3700A,3704E):For safety applications requiring analog measurement(e.g.,pressure,temperature)instead of discrete status.
Triconex Power Supplies(e.g.,8312):The redundant power supplies that provide clean,reliable power to the chassis containing the 4351Band other modules.
Triconex Chassis(e.g.,4300,4400 series):The physical enclosures and backplanes that house and interconnect the I/O modules and processors.
TriStation 1131 Software:The integrated engineering environment used to configure the hardware,program the safety logic,and perform diagnostics on the entire system,including the 4351B.
Competitor safety I/O modules(e.g.,HIMA or ICS Triplex):Alternative safety system components that serve similar functions in other vendor platforms.
Installation and Maintenance
Pre-installation preparation:Installing a TRICONEX 4351Bmodule must be performed in accordance with strict safety and procedural guidelines,often as part of a formal Management of Change(MOC)process.Ensure the specific chassis slot is designated for this module type in the system configuration.Verify that the field wiring is complete,correct,and that the field devices(switches,contacts)are in a safe state.Have the TriStation project file and latest configuration backup readily available.Ground yourself using an ESD strap to prevent damage to sensitive electronics.Identify and document any slot-specific termination boards or cables.
Maintenance recommendations:Routine maintenance is heavily reliant on the module’s diagnostic capabilities.Regularly review diagnostic reports and alarm logs in the TriStation or operator interface for any alerts related to the 4351Bor its channels(e.g.,field wire break,channel disagreement).Do not ignore diagnostic warnings,as they impact the calculated PFD of the safety loop.During planned outages,visually inspect the module and terminal connections for signs of corrosion or looseness.The most critical practice is maintaining and validating configuration backups.When replacing a module due to a diagnosed fault,follow the documented hot-swap procedure if the system is online,ensuring the replacement 4351Bis an identical part number.After insertion,the system will automatically recognize the new module and download the configuration;verify its status is”Healthy”and perform a functional test of the associated safety function if possible.
Product Guarantee
We guarantee that every TRICONEX 4351Bdigital input module supplied is a 100%genuine Triconex component,sourced exclusively through authorized and traceable channels to ensure its integrity,performance specifications,and safety certification remain valid.Each module undergoes a comprehensive validation process in our facility before dispatch.This includes meticulous visual inspection,verification of all connector integrity,and a functional test on specialized safety system test equipment that validates proper power-up,communication with a simulated TMR backplane,and correct response to applied input signals.We understand the critical,life-preserving role this module plays within your safety instrumented system.Therefore,we provide full warranty coverage and support with technical documentation.Our experts are versed in functional safety principles and can assist with compatibility verification.Our commitment is to deliver a fully tested,authentic 4351Bmodule that meets the stringent demands of your safety application,helping you uphold the highest standards of operational safety and compliance.
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