Allen-Bradley 1746-NR8 SLC 500 RTD and Resistance Input Module | 8-Channel

Module Functional Capability

The 1746-NR8 (Catalog Number: 1746-NR8) is a high-density analog input module designed for the SLC 500 platform, providing eight independent channels for temperature sensing and precision resistance measurement. By utilizing Sigma-Delta modulation for A/D conversion, the module ensures high noise immunity and exceptional accuracy for critical thermal monitoring. It is engineered to interface directly with a variety of Resistance Temperature Detectors (RTDs) and direct resistance sources, converting low-level signals into digital temperature data accessible by the SLC processor.

Technical Specifications

The 1746-NR8 features extensive sensor compatibility and robust backplane performance for industrial environments.

• Input Capacity: 8 Channels (Differential)

• Conversion Technology: Sigma-Delta Modulation

• Temperature Resolution: 0.01°C

• Backplane Power Consumption: 1.82W maximum (comprising 100 mA @ 5V DC and 55 mA @ 24V DC)

• Update Interval: Variable from 6 milliseconds to 2 seconds depending on channel configuration and filter selection

• Step Response: 60 milliseconds

• Thermal Range: 0°C to 60°C (32°F to 140°F) Operating; -40°C to 85°C Storage

• Chassis Slot Compatibility: Any slot in a 1746 chassis except the CPU slot (Slot 0)

• Module Weight: 0.34 kg (0.75 lbs)

Supported Sensor Types and Ranges

This module is compatible with a wide array of RTD types (Platinum, Nickel, Copper, and Nickel-Iron) and linear resistance inputs:

• Platinum (Alpha = 0.00385/0.003916): 100, 200, 500, and 1000 Ohm

• Nickel (Alpha = 0.00618/0.00672): 120 Ohm

• Copper (Alpha = 0.00426): 10 Ohm

• Nickel-Iron (Alpha = 0.00518): 604 Ohm

• Direct Resistance Ranges: 0–150 Ω, 0–300 Ω, 0–500 Ω, and 0–1000 Ω

Technical Integration FAQ

Does the 1747-NR8 require external power?The module is powered entirely through the SLC 500 backplane. However, the user must ensure the power supply (e.g., 1746-P1, P2, etc.) has sufficient current capacity for the module’s 5V and 24V requirements.

How does the module handle lead wire compensation?The 1746-NR8 supports 2-wire, 3-wire, or 4-wire RTD configurations. For maximum precision in applications with long cable runs, a 3-wire or 4-wire setup is recommended to automatically compensate for lead wire resistance.

Can I mix RTD types and resistance inputs on the same module?Yes, each of the eight channels can be individually configured for a specific sensor type or resistance range via the processor's output image table.