TRICONEX Tricon 3721 Analog Input Module In stock

The TRICONEX 3721 is a Triple‑Modular Redundant (TMR) analog input module that serves as the primary sensing interface for the Tricon safety instrumented system. It accepts 32 differential analog inputs (0‑5 V, ±5 V or 0‑20 mA with external shunt) and converts them to digital values with programmable 12‑ or 14‑bit resolution. The 3721 contains three independent measurement channels per input point, ensuring fault tolerance: if any single channel fails, the remaining two continue to supply valid data via mid‑value selection. The module updates all 32 channels simultaneously in 10 ms and features comprehensive onboard diagnostics with front‑panel status LEDs. Certified to IEC 61508 SIL 3, the TRICONEX 3721 supports hot‑swap replacement and requires a compatible External Termination Panel (ETP) for field wiring. It is the preferred high‑density analog input solution for Emergency Shutdown (ESD), Fire & Gas (F&G) and critical process control applications in oil & gas, petrochemical and power generation environments.

Emergency Shutdown (ESD) Systems – continuous monitoring of pressure, level and temperature transmitters for safety‑critical trip logic in refineries, LNG plants and chemical reactors

Fire & Gas (F&G) Detection – high‑integrity acquisition of analog signals from flame detectors, gas sensors and combustible gas monitors in offshore platforms and petrochemical facilities

Burner Management Systems (BMS) – monitoring furnace draft pressure, fuel flow and combustion parameters for safe boiler and furnace operation

Turbine Control & Protection – sensing vibration, temperature and speed signals for gas and steam turbine overspeed protection and startup sequencing

High‑Integrity Process Control – monitoring flow, pressure and level in chemical reactors, pipelines and compressor stations where SIL‑3 certified analog data is mandatory

Nuclear Safety Systems – providing triple‑redundant analog input acquisition for nuclear reactor protection and monitoring systems

Offshore Oil & Gas Platforms – acquiring pressure, level and flow signals in corrosive and environmentally harsh conditions (3721C conformal‑coated version recommended)

riple‑Modular Redundancy (TMR) – each input channel has three independent signal paths; 2‑out‑of‑3 (2oo3) voting is performed by the Main Processors after data transfer across the TriBus

IEC 61508 SIL 3 certified – TÜV approved for safety instrumented functions up to the highest integrity level; MTBF > 450,000 hours

32 high‑density analog input channels – 32 differential, DC‑coupled inputs per module; each channel can be software‑configured for voltage or current (with external shunt)

Programmable 12‑/14‑bit resolution – allows the user to optimise between measurement granularity and update speed

Simultaneous 10 ms update rate – all 32 channels are refreshed synchronously every 10 ms, providing deterministic input timing for safety logic

High accuracy across temperature – < 0.15 % of FSR from 0 °C to 60 °C; low drift for critical safety loops

Complete galvanic isolation – 1,500 Vdc channel‑to‑field, 800 Vdc field‑to‑system; opto‑isolated inputs prevent ground loops and protect the backplane

Comprehensive onboard diagnostics – continuous self‑tests include reference voltage verification, offset calibration, signal wire break detection and out‑of‑range checks

Differential input design – excellent common‑mode rejection (–85 dB DC‑100 Hz) eliminates noise pickup from long field cable runs

Front‑panel LED indicators – PASS (module passed self‑tests), FAULT (channel or module fault), ACTIVE (module is operational and configured), FIELD (field power or transmitter status)

Hot‑swap support – online module replacement without system shutdown; the module can be removed and reinstalled while the Tricon chassis remains powered

Overrange protection – 150 Vdc / 115 Vac continuous; input circuitry protected against accidental connection of high voltages

Mechanical keying – the 3721 is keyed to prevent insertion into an incorrect chassis slot; field termination cables are similarly keyed

Conformal coating (3721C) – the “C” version includes conformal coating that protects PCB assemblies against moisture, condensation, dust and corrosive atmospheres (e.g. high sulfur or salt content)

Compatible with HART pass‑through – when used with appropriate HART termination boards, the 3721 supports HART digital communication superimposed on the 4‑20 mA loop

Triplicated analog‑to‑digital conversion – each of the three TMR channels (A, B and C) independently measures the field signal using its own multiplexer, PGA and ADC. The measured values are transmitted to the corresponding Main Processor over the triplicated I/O bus.

Mid‑value selection algorithm – after each scan, the three Main Processors exchange their input tables across the TriBus. For each analog input point, the Main Processor discards the highest and lowest values and selects the middle (median) value. This eliminates the effect of a single divergent or faulty channel.

Continuous self‑diagnostics – the module periodically performs internal voltage reference checks, ADC offset and gain calibration, and signal path integrity tests. Failure of any diagnostic on any channel activates the FAULT indicator and sets the corresponding chassis alarm; however the module continues to operate correctly with one or even two faulty channels (the remaining healthy channels continue to provide valid data).

Open‑circuit detection – the module can detect a broken field wire or an open‑circuit transmitter (over‑range condition). When an open circuit is detected, the corresponding channel value is forced to a user‑configurable safe state and the FIELD LED is illuminated.

Out‑of‑range detection – input signals that exceed the calibrated voltage range (e.g. > 5.3 V for the 0‑5 V range) are reported as over‑range or under‑range faults, allowing the application to trip or alarm before the sensor signal goes completely invalid.

Cold start and power‑up calibration – each power‑up cycle, the module performs an automatic self‑calibration using internal precision voltage references. This compensates for long‑term drift and temperature effects, maintaining specified accuracy without manual intervention.

Input filtering – differential inputs with high common‑mode rejection (85 dB) reduce noise pickup from electromagnetic interference (EMI), radio frequency interference (RFI) and common‑mode voltages that may be induced along long field cables.

Hot‑spare support – when a secondary 3721 is installed in the companion slot, the system automatically transfers control to the standby module upon detection of a fault in the primary module, enabling online maintenance without interruption of the safety function.

Field wiring fault reporting – the module detects loss of field loop power and reports it to the Main Processors via dedicated status bits in the I/O data block.

Q1: What is the maximum number of analog input channels supported by one Tricon chassis when using the 3721?
A1: The 3721 provides 32 analog inputs per module. A fully populated Tricon expansion chassis (8 logical slots) can house up to 8 modules, giving a total of 256 analog input channels per chassis. However system power and backplane capacity must be considered – refer to the Tricon Planning and Installation Guide for full loading calculations.

Q2: Can the 3721 accept 4‑20 mA current signals directly?
A2: Yes, but an external 250 Ω precision resistor is required. The 4‑20 mA current loop must be terminated through a compatible External Termination Panel (ETP) that contains the resistor, converting the current to a 1‑5 Vdc signal. The 3721 then reads the resulting voltage. Direct 4‑20 mA connection without a termination panel is not supported.

Q3: What is the difference between the standard 3721 and the 3721C?
A3: The 3721C (where “C” indicates conformal coating) has all PCB assemblies coated with a protective lacquer. This provides enhanced resistance to moisture, condensation, dust, corrosion and “silver whiskering” – making it the preferred choice for offshore platforms, chemical plants and other environments with high salt, sulfur or humidity content. Electrically and functionally the two versions are identical.

Q4: Is the 3721 compatible with HART instrumentation?
A4: Yes. When used with a HART‑compatible External Termination Panel (ETP), the 3721 can pass the HART frequency‑shift keying (FSK) digital signal superimposed on the 4‑20 mA loop. A separate HART multiplexer or HART interface card (e.g. Pepperl+Fuchs termination board) is required to extract the digital data.

Q5: What happens if one channel of the 3721 fails?
A5: Because the 3721 is a Triple‑Modular Redundant (TMR) module, each field input is sampled by three independent measurement circuits (one per slice). If a fault occurs in one channel (e.g. a failed ADC or a broken component), the remaining two channels continue to acquire and report the field signal. The Main Processors vote the data using a mid‑value selection algorithm, so the failure is masked and the output to the control program remains correct. The module FAULT LED will flash (or illuminate steady) to alert maintenance, but the safety function is not interrupted.

Inguiry Now: [email protected]