Invensys Triconex 3700 / 3700A Analog Input Modules

Overview

The Invensys Triconex 3700 / 3700A, also cataloged as the 3700 Analog Input Module, converts 0 to 5 VDC differential analog signals into digital values within Triconex TMR safety instrumented systems. The module supports 32 DC-coupled input channels and can accept 0 to 20 mA signals through external 250 ohm shunt resistors.

Hardware Specifications

Triconex TMR Signal Processing and Diagnostics

The 3700 / 3700A uses a TMR architecture to process analog input data through independent signal paths. The three processor paths apply mid-value selection to the processed input values, which allows the system to identify and isolate a discrepant signal path without depending on a single processor result.

The module accepts differential DC-coupled signals and provides a 12-bit conversion path. In addition, continuous channel diagnostics monitor the input channels during operation. The Pass, Fault, and Active LEDs provide local module status information.

For current-loop signals, the supplied specification supports 0 to 20 mA operation through external 250 ohm shunt resistors. Therefore, the external resistor and field wiring must match the intended input configuration.

The module also supports hot-spare replacement within the documented Triconex architecture. Mechanical keying restricts incorrect module insertion into the configured slot.

Frequently Asked Questions

Q: Can the 3700 / 3700A directly accept 0 to 20 mA signals?

A: The supplied specification states that 0 to 20 mA signals require external 250 ohm shunt resistors to convert the current input for the module’s 0 to 5 VDC input range.

Q: What input resolution does the 3700 / 3700A provide?

A: The module provides 12-bit analog-to-digital resolution with a specified 55 ms update rate.

Q: Does the module support hot-spare replacement?

A: Yes. The supplied data specifies hot-spare capability. The replacement procedure must follow the installed Triconex system configuration and applicable maintenance documentation.

Field Installation Guidelines

Install the module only in the chassis and slot configuration specified for the Triconex system. Verify the module model, hardware revision, connector arrangement, and mechanical keying before insertion.

Route analog signal wiring separately from high-voltage power conductors and high-current switching circuits. Maintain the applicable installation separation required by the plant wiring standard.

Use shielded analog wiring where required by the site instrumentation design. Terminate cable shields according to the project grounding scheme and avoid creating unintended ground loops.

For 0 to 20 mA inputs, install the specified external 250 ohm shunt resistor at the designated termination point. Confirm resistor placement and field polarity before energizing the circuit.

Before commissioning, verify channel-to-channel wiring, input polarity, signal range, module status LEDs, and diagnostic indications. Then compare measured field signals with the values reported by the Triconex control system.

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