Overview
The Allen-Bradley 1771-IR /D is a Resistance Temperature Detector (RTD) input module designed for the PLC-5 series. The module features six three-wire RTD inputs, accommodating multiple temperature sensors, making it ideal for multi-point thermal monitoring in industrial automation. This used-condition module is fully functional and provides reliable temperature acquisition without requiring external power—drawing power directly from the 1771 Series I/O chassis backplane.
Key Features
- Six three-wire RTD input channels compatible with both Copper and Platinum RTD types
- Supports Natural Binary, BCD Actual Temperature, or Ohm Readings data formats
- 16-bit resolution with 1.0°C or 1.0°F per-bit sensitivity
- 50 millisecond channel update time across all six inputs
- Open-wire detection capability for fault diagnostics
- Life expectancy of up to 100 million operations
- Front-panel status indicators for troubleshooting
- No external power supply required—backplane-powered
Technical Specifications
- Input Channels: 6 three-wire RTD inputs
- Sensor Compatibility: 100 Ohm Platinum and 10 Ohm Copper RTD sensors
- Data Formats: Natural Binary, BCD Actual Temperature, Ohm Readings
- Resolution: 16-bit (+sign) with 1.0°C/1.0°F per bit
- Scan Time: 50 milliseconds for all six channels
- Temperature Range: -200 to +870°C (Platinum); -200 to +260°C (Copper)
- DC On-state Signal Delay: 10 milliseconds
- DC Off-state Signal Delay: 50 milliseconds
- AC Off-state Signal Delay: 45 (±15) milliseconds
- Backplane Current: 800 milliamperes at nominal voltage
- Power Dissipation: 4.75 Watts
- Isolation Voltage: Meets UL Standard 508 and CSA Standard C22.2 No. 142
- Module Location: 1771 Series I/O Chassis
- Interface: Uses 1771-WF swing-arm termination connector
Typical Applications
The 1771-IR /D is suitable for use in a variety of industrial automation applications, including motion control, HVAC, and process control. Common uses include furnace and oven monitoring, batch reactor temperature management, refrigeration system supervision, steam generation control, and multi-sensor hot-spot detection in motors and transformers. The module’s open-wire detection and precise resolution make it valuable for safety-critical thermal monitoring where equipment failure cannot be tolerated.
Compatibility & Replacements
The 1771-IR /D is designed for Allen-Bradley PLC-5 and 1771 Series I/O systems. The module is compatible for use with PLC-2, PLC-3, and PLC-5 controller platforms. It installs into 1771-A1B, 1771-A2B, 1771-A3B, and 1771-A4B I/O chassis. This is a legacy module; modern RTD input alternatives include the 1756-IRT6 (CompactLogix-compatible) and 1771-IR7 (higher channel density). However, for existing PLC-5 installations, the 1771-IR /D remains the standard drop-in choice. Block Transfer Write (BTW) and Block Transfer Read (BTR) instructions are used to communicate with the module in firmware-based control strategies.
