Introduction
Temperature measurement errors can cripple process control, leading to costly downtime and wasted materials. The Allen-Bradley 1746-NR8 RTD/Resistance Analog Input Module delivers reliable, high-accuracy data for SLC 500 systems. With eight channels and support for multiple RTD types, it reduces hardware costs by consolidating temperature and resistance measurements into a single module. This cost-effective solution minimizes wiring complexity and installation time, directly improving your bottom line.
Key Specifications and Cost Implications
The 1746-NR8 offers eight input channels, each compatible with a wide range of RTD sensors: 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. It also accepts direct resistance inputs of 0–150 Ohms, 0–500 Ohms, 0–1000 Ohms, and 0–300 Ohms. This flexibility means you can standardize on one module for diverse sensors, reducing spare parts inventory and training costs.
The module draws 100 mA at 5 VDC and 55 mA at 24 VDC from the backplane, with a maximum power consumption of 1.82 W (0.5 W at 5 VDC, 1.32 W at 24 VDC). This low power draw minimizes the load on your power supply, potentially extending its life and reducing energy costs. The update time ranges from 6 milliseconds to 2 seconds, and the step response is 60 milliseconds in and 2.5 milliseconds out, ensuring responsive control for dynamic processes. The resolution of 0.01 °C enables precise temperature monitoring, which can improve product quality and reduce waste.
Industry Applications
In food and beverage processing, the 1746-NR8 monitors temperatures in pasteurization and fermentation, where accuracy directly impacts product safety and shelf life. By using a single module for multiple RTD sensors, you reduce wiring and installation costs. In HVAC systems, it measures supply and return temperatures to optimize energy usage, lowering utility bills. For test benches, the resistance input mode allows measurement of displacement or movement, providing valuable data for mechanical testing without additional instruments.
Installation and Setup
The 1746-NR8 installs in any SLC 500 chassis slot except Slot 0. It is compatible with both fixed and modular hardware styles. The module supports 2-wire, 3-wire, and 4-wire RTD connections. For 2-wire RTDs, use Belden 9501 shielded cable or equivalent; for 3-wire or 4-wire, use Belden 9533 or Belden 83503. Avoid long cable runs with 2-wire RTDs to maintain accuracy; if unavoidable, use lower gauge wire such as AWG #16 instead of AWG #24 to minimize resistance. The removable terminal block (RTB) accepts single wires only. The module is powered by the backplane, so no external power supply is needed, saving on installation cost and space.
Maintenance and Reliability
The 1746-NR8 features auto-calibration at power-up and can be programmed to calibrate every 5 minutes, reducing manual calibration costs and ensuring long-term accuracy. Channel status and module operation are monitored via LED indicators, enabling quick diagnostics. Operating temperature range is 0 to 60 °C (32 to 140 °F), and storage is -40 to 85 °C (-40 to 185 °F). Non-condensing relative humidity is 5 to 95%. Periodic inspection of connections and environment is recommended to prevent drift and ensure reliable operation. By minimizing downtime and maintenance, this module delivers a low total cost of ownership.
Compatibility and Integration
The 1746-NR8 is designed exclusively for SLC 500 systems, both fixed and modular. It integrates seamlessly with existing SLC 500 processors and I/O, protecting your automation investment. The module uses sigma-delta modulation for analog-to-digital conversion, providing stable and accurate readings. It communicates via the backplane, so no additional communication modules are required. This simplifies integration and reduces overall system cost.
Selection Guide
When selecting the 1746-NR8, verify your RTD type and resistance range match the module’s capabilities. Ensure your SLC 500 chassis has an available slot (not Slot 0). The compatible terminal block is Allen-Bradley 1746-RT-35. For reliable supply and expert support, consider SpareTechPLC as your source. They offer competitive pricing and fast shipping to minimize your downtime costs.
FAQs
What RTD types does the 1746-NR8 support?
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.
Can I use the 1746-NR8 for resistance measurement?
Yes, it accepts direct resistance inputs of 0–150 Ohms, 0–500 Ohms, 0–1000 Ohms, and 0–300 Ohms.
What is the power consumption of the 1746-NR8?
It consumes 100 mA at 5 VDC and 55 mA at 24 VDC, with a maximum power of 1.82 W.
How often does the 1746-NR8 calibrate?
It auto-calibrates at power-up and can be programmed to calibrate every 5 minutes.
What cable is recommended for 2-wire RTDs?
Belden 9501 shielded cable or equivalent is recommended for 2-wire RTDs.
