1746-NR8 | Allen-Bradley RTD/Resistance Analog Input Module

Introduction to the 1746-NR8 RTD/Resistance Analog Input Module

When your SLC 500 system demands accurate temperature or resistance readings, the 1746-NR8 from Allen-Bradley provides a reliable solution. This RTD/Resistance Analog Input Module features eight channels, compatible with Platinum (385), Platinum (3816), Copper (426), Nickel (618), Nickel (672), and Nickel Iron (518) sensors. It also accepts direct resistance inputs ranging from 0 to 150 Ohms, 0 to 500 Ohms, 0 to 1000 Ohms, and 0 to 300 Ohms. Part of the SLC 500 series, this module fits fixed and modular hardware styles, powered by the backplane.

Key Features and Technical Specifications

• Inputs: Eight (8) channels for RTD or resistance signals.
• Backplane Current: 100 mA at 5 VDC and 55 mA at 24 VDC.
• Backplane Power Consumption: Maximum 1.82 W (0.5 W at 5 VDC, 1.32 W at 24 VDC).
• Update Time: Ranges from 6 milliseconds to 2 seconds.
• Step Response: 60 milliseconds in, 2.5 milliseconds out.
• Resolution: 0.01 °C.
• Operating Temperature: 0 to 60 °C (32 to 140 °F).
• Storage Temperature: -40 to 85 °C.
• I/O Chassis Location: Any slot except Slot 0.
• A/D Conversion: Sigma-delta modulation.

Unique Insight: The 0.01 °C resolution enables precise temperature monitoring, critical for processes requiring tight thermal control.

Applications and Use Cases

In industrial environments, the 1746-NR8 excels at temperature measurement using RTD sensors. For example, in a chemical processing plant, it monitors reactor temperatures with Platinum (385) sensors, ensuring safe operation. Additionally, its resistance input capability measures displacement in mechanical systems, such as tracking valve position over time. This dual functionality reduces the need for separate modules, simplifying maintenance.

Installation and Setup

Installing the 1746-NR8 is straightforward. Place it in any chassis slot except Slot 0, and it draws power from the backplane—no external supply needed. For wiring, use Belden 9501 shielded cable for 2-wire RTDs, or Belden 9533 or 83503 for 3-wire and 4-wire configurations. Ensure single-wire connections per terminal to maintain accuracy. The module supports 2-wire, 3-wire, and 4-wire RTDs, with auto-calibration at power-up or every 5 minutes.

Maintenance and Reliability

From a maintenance engineer's perspective, the 1746-NR8 offers reliability through its low-pass digital filter and programmable input filters, reducing noise interference. The sigma-delta A/D conversion ensures stable readings. To extend service life, keep the module within its 0 to 60 °C operating range and 5 to 95% non-condensing humidity. Regular inspection of the LED status indicators helps catch issues early, minimizing downtime.

Compatibility and Integration

The 1746-NR8 integrates seamlessly with SLC 500 fixed and modular systems. It works with any compatible chassis and does not require additional communication modules for basic operation. For advanced integration, refer to the official Allen-Bradley documentation.

Frequently Asked Questions about the 1746-NR8

Q: What RTD sensors are compatible with the 1746-NR8?

A: It supports Platinum (385) 100, 200, 500, 1000; Platinum (3816) 100, 200, 500, 1000; Copper (426) 10; Nickel (618) 120; Nickel (672) 120; and Nickel Iron (518) 604.

Q: What is the backplane power consumption of the 1746-NR8?

A: Maximum 1.82 W, with 0.5 W at 5 VDC and 1.32 W at 24 VDC.

Q: Can the 1746-NR8 measure resistance directly?

A: Yes, it accepts resistance inputs from 0 to 150 Ohms, 0 to 500 Ohms, 0 to 1000 Ohms, and 0 to 300 Ohms.

Q: What is the update time of the 1746-NR8?

A: It ranges from 6 milliseconds to 2 seconds, depending on configuration.

Q: How do I wire a 3-wire RTD to the 1746-NR8?

A: Use Belden 9533 or 83503 cable, connecting each wire to a separate terminal. Refer to the manual for exact pin assignments.

Product Support and Availability

The 1746-NR8 is available from Petro Auto Tech, a trusted industrial automation parts supplier. In stock and ready to ship, it supports your maintenance needs with fast delivery. Please verify current lifecycle status and availability with Petro Auto Tech before ordering.