Allen-Bradley 1794-IR8 FLEX I/O RTD Input Module

Precision Temperature Acquisition for Distributed Networks

The Allen-Bradley 1794-IR8 functions as a specialized resistance-to-digital converter within the FLEX I/O family. By utilizing an advanced 16-bit analog-to-digital converter, this module translates minute resistance changes from RTD sensors into highly accurate temperature data for a central processor. Because industrial environments often present significant electrical interference, the 1794-IR8 employs sophisticated digital filtering and high-performance noise rejection to ensure signal integrity. Consequently, this module enables plant operators to maintain tight thermal control in applications where even fractional temperature variances can impact product quality or safety.

Technical Capabilities and Sensor Compatibility

• Manufacturer: Allen-Bradley / Rockwell Automation
• Model Designation: 1794-IR8
• Input Architecture: 8 Non-isolated Differential Channels
• Analog Resolution: 16-bit (1 to 433 Ohms)
• Supported RTD Standards: Platinum (385 and 3916), Nickel, and Copper
• Excitation Current: 718.36 µA (Minimizes sensor self-heating)
• Sampling Accuracy: 0.05% in Normal Mode; 0.01% in Enhanced Mode
• Data Format: 16-bit 2’s complement integer
• Isolation Barrier: 850V DC for 1s (User-to-system)
• Power Requirements: 20mA at 5V DC (Backplane); 140mA at 24V DC (External)
• Operating Temperature Range: -20°C to +55°C

Advanced Signal Processing and Integration

The 1794-IR8 maximizes system performance by offering programmable hardware filters that suppress 50Hz and 60Hz line noise. Furthermore, the module facilitates flexible installation through its compatibility with various terminal bases, such as the 1794-TB3 or 1794-TB3S. This modular design allows technicians to wire the system once and “hot-swap” the electronic component without disturbing the field connections. Since the module supports both 2-wire and 3-wire RTD configurations, it effectively compensates for lead-wire resistance, which prevents measurement drift over long distances. Moreover, its integration with FLEX I/O adapters like the 1794-AENTR allows these temperature points to be accessed via EtherNet/IP, effectively bridging the gap between field-level sensors and enterprise-level monitoring systems.

Diverse Industrial Applications

• Chemical Processing: Monitoring reactor vessel temperatures where high-precision Platinum RTDs are required.
• Power Generation: Tracking bearing temperatures in turbines and large motors to prevent mechanical failure.
• Cold Chain Logistics: Providing stable thermal data for industrial refrigeration and climate-controlled storage.
• Food and Beverage: Controlling pasteurization temperatures where repeatable accuracy is critical for regulatory compliance.