Product Overview

The 1746-NR4​ is a four-channel RTD and resistance input module manufactured by Allen-Bradley, a brand of Rockwell Automation, for the long-established SLC 500 family of programmable controllers. Purpose-built for direct temperature and resistance measurement, the 1746-NR4​ eliminates the need for external transmitters, signal conditioners, and analog input cards by accepting RTD sensor elements and variable-resistance devices straight into the controller backplane. Seated in any available I/O slot of a 1746 modular or fixed-style SLC 500 chassis, the module communicates with the processor through an image table of eight input words and eight output words, delivering temperature data in degrees Celsius or Fahrenheit, or resistance values in ohms, already scaled and ready for use in ladder logic.At the heart of the 1746-NR4​ is a sigma-delta analog-to-digital converter that provides 16-bit input resolution and strong inherent noise rejection. Each of the four channels is independently configurable for RTD type, wiring configuration, filter frequency, excitation current, open-circuit response, and data format, meaning a single module can simultaneously read a Pt100 probe on channel 0, a Ni120 sensor on channel 1, a Cu10 element on channel 2, and a potentiometer on channel 3. The module supports platinum sensors with alpha coefficients of 0.00385 and 0.003916, copper RTDs at 10 and 427 ohms, nickel RTDs at 120, 618, and 672 ohms, and nickel-iron sensors at 518 and 604 ohms, covering a temperature span from -200 °C to +850 °C depending on sensor selection.What makes the 1746-NR4​ technically distinctive is its three-wire Kelvin lead-resistance compensation. Because an RTD changes resistance with temperature while the copper extension leads add their own resistance, a long cable run can introduce a significant temperature offset if uncompensated. The 1746-NR4​ excites one pair of leads and senses only through the third, mathematically subtracting the lead drop and reporting the element’s true resistance. The module also performs automatic self-calibration whenever a channel is enabled or a configuration parameter changes, requires no external power supply, and carries UL, CSA, CE, C-Tick, and Class I Division 2 certifications. Rockwell Automation has since classified the 1746-NR4​ as a mature, end-of-life product, but it remains in daily service in thousands of legacy SLC 500 installations and is widely available through aftermarket channels.

Technical Specifications