Allen Bradley 1756-IRT8I Analog Input Module

Product Overview

The Allen Bradley 1756-IRT8I is a high-resolution analog input module for the ControlLogix system. This module features eight isolated channels configurable for Resistance Temperature Detector, thermocouple, and millivolt input signals. The 1756-IRT8I is specifically designed for temperature sensing applications requiring high accuracy and channel-to-channel isolation in industrial automation environments.

Technical Specifications

Input Characteristics

The 1756-IRT8I module provides eight isolated channels, with each channel independently configurable for different input types. The module supports multiple input ranges including 1 to 500 Ohms, 2 to 1000 Ohms, 4 to 2000 Ohms, 8 to 4000 Ohms, and -100 to 100 millivolts. The module utilizes 24-bit resolution via Sigma-Delta analog-to-digital conversion, with the converted data stored in IEEE 32-bit floating point format.

Resolution Specifications

The module provides precise resolution across its input ranges: 0 to 510 Ohms with 0.06 milliohms per count, 0 to 1020 Ohms with 0.12 milliohms per count, 0 to 2040 Ohms with 0.25 milliohms per count, 0 to 4080 Ohms with 0.50 milliohms per count, and -101 to 101 millivolts with 0.01 microvolts per count. This high resolution enables accurate temperature measurement for critical process applications.

RTD Support

The 1756-IRT8I supports a comprehensive range of RTD sensor types. Platinum RTDs with alpha values of 385 and 3916 are supported for 100, 200, 500, and 1000 Ohm configurations. Nickel RTDs with alpha 672 are supported for 120 Ohm configurations, and nickel RTDs with alpha 618 are supported for 100, 120, 200, and 500 Ohm configurations. The module also supports 10 Ohm copper RTDs with alpha 427. The module supports 2-wire, 3-wire, and 4-wire RTD connections.

Thermocouple Support

The module supports thermocouple types B, C, D, E, J, K, N, R, S, T, and TXK/XK (L). Thermocouple linearization is performed using the ITS-90 standard. The module includes two Cold Junction Compensation sensors with an accuracy of ±0.3°C for thermocouple temperature referencing.

Module Features

The 1756-IRT8I incorporates extensive features for temperature measurement applications. These include multiple input range selection, notch filter for noise rejection, under-range and over-range detection, digital filter for signal conditioning, process alarms, rate alarm monitoring, sensor offset adjustment, 10-ohm copper offset compensation, wire-off detection, selectable temperature units, sensor type configuration, thermocouple wire length compensation, synchronized sampling, and cold junction compensation.

Noise Rejection

The module provides excellent noise rejection characteristics for reliable measurements in industrial environments. Normal mode noise rejection is 75 dB at 60 Hertz. Common mode noise rejection is 125 dB at 60 Hertz with 1000 Ohms differential, 120 dB at 50 Hertz with 1000 Ohms differential, and 160 dB at 600 Volts with 100 Ohms differential.

Termination and Installation

The 1756-IRT8I requires a 36-pin Removable Terminal Block for field wiring connections. Compatible RTBs include the 1756-TBCH or the 1756-TBS6H. The module is part of the ControlLogix system and mounts in any ControlLogix chassis. Channels configured for thermocouple inputs perform lead resistance self-calibration when module power is cycled.

System Integration

The 1756-IRT8I integrates seamlessly with ControlLogix controllers and Rockwell Automation programming software. Converted analog data is accessible by Human Machine Interface systems, Supervisory Control and Data Acquisition systems, and other industrial automation software. The tight integration between programming software, controller, and I/O modules reduces development time and cost during commissioning and normal operation.