Purchase now: Allen Bradley 1746-NR4 RTD Input Module
Purchase now: Atlantechdrives provides you the 1746-NR4, a highly specialized, precision temperature measurement module designed by Allen Bradley for the legacy SLC 500 programmable logic controller system. This module provides 4 dedicated input channels specifically engineered to interface directly with Resistance Temperature Detectors (RTDs) and direct resistance signals. The 1746-NR4 is the industry standard for monitoring precise temperatures in critical applications such as food and beverage processing, pharmaceutical autoclaves, and chemical reactors. Unlike standard analog voltage or current modules, the NR4 translates the subtle changes in metallic resistance caused by temperature fluctuations into highly accurate 16-bit digital values for the PLC processor.
Technical Specifications of the 1746-NR4
The 1746-NR4 supports a vast array of standard RTD types, including Platinum (Pt100, Pt200, Pt500, Pt1000), Nickel, and Copper probes across various alpha curves (like the European standard 385 or US standard 3916). It also supports direct resistance measurements up to 3000 ohms.
- Part Number: 1746-NR4
- Module Type: Analog RTD / Resistance Input
- Compatible System: SLC 500 (1746 Chassis)
- Number of Channels: 4 Isolated RTD inputs
- Supported RTDs: Platinum, Nickel, Copper, Nickel-Iron
- Resistance Range: 0 to 3000 Ohms
- Resolution: 16-bit (Ultra-high precision)
- Wiring Configurations: 2-wire, 3-wire, or 4-wire RTDs
- Backplane Current Draw: 50 mA at 5V DC, 50 mA at 24V DC
Expert Installation Advice: 3-Wire RTD Compensation
Achieving accurate temperature readings depends entirely on your wiring strategy. Expert Tip: Always use 3-wire or 4-wire RTDs whenever possible, and avoid 2-wire RTDs for industrial runs. Why? A Pt100 RTD changes only about 0.38 ohms per degree Celsius. If you use a 2-wire setup with 100 feet of copper cable, the inherent resistance of the long cable might add 5 ohms to the circuit. The 1746-NR4 will interpret this extra cable resistance as a significantly higher temperature, ruining your process control. By using a 3-wire configuration, the 1746-NR4 module utilizes the third wire to actively measure and mathematically cancel out the lead wire resistance, ensuring that the PLC only reads the true temperature at the probe tip.
Maintenance and Calibration
The 1746-NR4 features autocalibration at power-up, meaning manual trimpot adjustments are obsolete. However, to ensure maximum reliability during maintenance, periodically inspect the Removable Terminal Block (RTB). Because RTD signals are based on tiny resistance measurements, even a slight layer of oxidation or a loose screw terminal will introduce artificial resistance, causing temperature spikes in your HMI. Clean the terminals and ensure all connections are torqued to factory specifications.
Frequently Asked Questions (FAQs)
Q: Can I use the 1746-NR4 to read a standard 4-20mA temperature transmitter?
A: No. The 1746-NR4 is designed to read bare RTD probes directly. If your temperature probe has a «head-mounted transmitter» that converts the reading to 4-20mA, you must wire it to a 1746-NI4 or 1746-NI16I current input module instead.
Q: Can I mix different RTD types on the same module?
A: Yes. You can configure channel 0 for a Pt100 Platinum RTD and channel 1 for a 120-ohm Nickel RTD. Configuration is done channel-by-channel within the RSLogix 500 software.
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This RTD input module provides accurate temperature feedback when integrated into an SLC system powered by a 1746-P2 power supply.
