Allen-Bradley 1771-IR PLC-5 RTD Input Module | 3-Wire Resistance Temperature Detector

Functional Capabilities

The 1771-IR (Part Number: 1771-IR) is a high-precision analog input module designed for the Rockwell Automation PLC-5 platform. It provides a specialized interface for Resistance Temperature Detectors (RTDs), converting low-level resistance signals into temperature data that is directly usable by the processor. This module supports up to six 3-wire RTD sensors, utilizing an internal circuit to compensate for lead-wire resistance, which ensures high accuracy even in distributed installations where sensors are located far from the control cabinet.

Detailed Technical Specifications

The 1771-IR is engineered for industrial-grade thermal monitoring with the following hardware parameters:

• Input Configuration: 6 Three-Wire RTD Inputs

• Sensor Compatibility: 100-Ohm Platinum (385/3916), 10-Ohm Copper, 120-Ohm Nickel, and 604-Ohm Nickel-Iron

• Data Resolution: 16 bits plus sign (1.0° Celsius or 1.0° Fahrenheit per bit)

• Sampling Rate: 50 ms for an 8-channel update cycle (effective for all 6 active inputs)

• Backplane Current Load: 800 mA at 5V DC

• Power Requirement: Powered entirely via the 1771 backplane; no external power source required

• Data Formatting Options: Natural Binary, BCD (Actual Temperature), or Ohms (Resistance reading)

• Signal Propagation Delay: 10 ms (DC On); 50 ms (DC Off); 45ms ± 15ms (AC Off)

• Physical Mounting: In-chassis, standard 1771 Universal I/O slot

• Wiring Termination: Requires 1771-WH Wiring Arm for field connections

• Weight: 0.45 kg (1.00 lbs)

Operational and Environmental Limits

Designed for continuous duty in harsh automation environments, the module adheres to the following tolerances:

• Operating Temperature: 0°C to 60°C (32°F to 140°F)

• Storage Temperature: -40°C to 85°C (-40°F to 185°F)

• Humidity Control: 5% to 95% relative humidity (non-condensing)

• Isolation: Opto-electrical isolation between the backplane and field-side circuitry to protect the controller from transients

Integration FAQ

How does the module handle different RTD types?The 1771-IR is versatile. While optimized for 100-Ohm Platinum sensors, it can be configured via the PLC-5 output image table to read 10-Ohm or other supported resistance ranges. Users must select the correct sensor type during configuration to ensure the linear conversion from resistance to temperature is accurate.

What is the benefit of the 3-wire connection supported by this module?Standard 2-wire RTDs often suffer from inaccuracies caused by the resistance of the lead wires. The 1771-IR utilizes a 3-wire configuration to measure and subtract the lead-wire resistance, providing a more stable and accurate temperature reading in industrial environments.

Can I read raw resistance instead of temperature?Yes. By configuring the data format to "Ohm Readings," the module will bypass the temperature linearization and report the actual resistance value in the data table.