TRICONEX 3722X Analog Input Module

The TRICONEX 3722X is an advanced analog input module for the Tricon triple modular redundant (TMR) safety system. It provides 32 differential 4-20 mA input channels with enhanced diagnostic coverage and optional HART (Highway Addressable Remote Transducer) pass-through communication. The module is certified for SIL 3 applications per IEC 61508/61511 and is designed for high-availability process safety applications.

Key Enhancements Over 3721

Compared to the earlier 3721 module, the 3722X introduces several improvements: on-board HART modem for each channel (allowing simultaneous analog measurement and digital HART communication), increased diagnostic coverage including line impedance measurement, improved channel-to-channel isolation, and a faster update rate (25 ms for all 32 channels). The X suffix denotes extended diagnostics and HART capability. The module also features a more robust power supply design with redundant voltage regulators.

Input Characteristics

Each channel accepts 4-20 mA signals from field transmitters. Input impedance is 250 Ω ±0.1% for precise measurement. The module provides loop power (24 VDC, 28 mA per channel) for 2-wire transmitters. Overvoltage protection clamps inputs to ±30 V DC. Common mode voltage range: ±5 V between any channel negative and chassis ground. Channel-to-channel isolation: 60 V DC continuous. Differential mode noise rejection: 60 dB at 50/60 Hz. The analog input resolution is 16 bits (0.0015% of full scale), and effective resolution is 1 µA.

HART Communication Capabilities

Each of the 32 channels includes an integrated Bell 202 frequency shift keying (FSK) modem. HART digital signals superimposed on the 4-20 mA loop are demodulated and passed to the Tricon processor or to a dedicated HART master (e.g., TriStation HART interface). The module acts as a HART pass-through device, allowing external configuration tools to communicate with HART transmitters without disconnecting the loop. Up to 8 HART commands per second can be processed per channel. The module also supports HART burst mode for continuous digital data from smart transmitters.

Diagnostic Features

The 3722X performs advanced diagnostics beyond standard overrange/underrange detection:

• Line impedance measurement: detects partial open circuits (e.g., corroded contacts) before complete failure.

• Transmitter loop test: injects a test current (4, 12, 20 mA) and verifies the transmitter response.

• HART health monitoring: verifies that HART communication is established and checks for communication errors.

• Internal temperature monitoring of each ADC.

• Power supply ripple detection.

All diagnostic results are reported via the backplane to the processor and can be viewed through TriStation software. The module also stores a history of the last 100 diagnostic events with time stamps.

Triple Modular Redundancy Implementation

Three independent analog measurement circuits are housed in the 3722X. Each circuit includes its own ADC, reference voltage, and input multiplexer. The three values are voted by the Tricon processor using a median or average algorithm (configurable). A deviation check compares the three channels; if any channel deviates more than a set threshold (e.g., 0.5% of span), it is flagged as faulty. The module also includes a hardware voter that can bypass a faulty channel autonomously. Fault tolerance extends to the HART modems: each channel has three HART demodulators; the module uses a majority vote on the digital data.

Termination and Field Wiring

The 3722X uses a 96-pin DIN connector on the module face. Field wiring connects through a separate termination assembly (part number 7400260-100), which provides screw terminals for each channel’s signal and loop power return. A ribbon cable (supplied) connects the termination assembly to the module. This design allows field wiring to remain in place while the module is replaced. The termination assembly also includes fuses (replaceable, 0.1 A slow-blow) for each channel to protect against overcurrent. For HART applications, a terminating impedance of 250–500 Ω must be present; the module’s internal 250 Ω resistor serves this purpose.

Power and Environmental Specifications

Current draw: 0.8 A from 5 V backplane, 1.5 A from 24 V field supply. Power dissipation: 15 W maximum. Operating temperature: 0°C to 60°C (extended option -20°C to 70°C available by special order). Humidity: 5–95% non-condensing. Vibration: 2 g (5–100 Hz). Shock: 20 g, 11 ms half-sine. The module carries TÜV SIL 3, FM Class I Division 2, and ATEX Category 3 certifications.

Compatibility and System Requirements

The 3722X is compatible with Tricon processors 3006, 3007, 3008, and 3009 (firmware version 9.0 or later). It works in both main and remote expansion chassis. TriStation software version 4.5 or later is required for configuration and HART support. The module can coexist with 3720 and 3721 modules in the same chassis. For HART functionality, an external HART multiplexer is not required; the module directly communicates with HART devices via the analog loop.

Calibration and Maintenance

Factory calibration data is stored in the module’s EEPROM. Recalibration using the TriStation calibration tool is recommended every 24 months. The calibration tool automatically steps through each channel with a precision current source. The module supports in-situ calibration without removing field wiring (using a calibration bypass relay). The replaceable fuses on the termination assembly should be checked annually; a blown fuse is indicated by a missing channel LED and diagnostic fault. No other user-serviceable parts are present.

The TRICONEX 3722X offers the highest level of analog input functionality in the Tricon lineup, combining TMR safety with HART intelligence for modern process safety systems.