Description

The Allen-Bradley 1746-NT4 is a four-channel thermocouple and millivolt analog input module from the SLC 500 family, manufactured by Rockwell Automation. It receives and digitally converts thermocouple or millivolt signals from up to four independent sensors, storing the data in its image table for retrieval by any fixed or modular SLC 500 processor.

The 1746-NT4 supports a wide range of thermocouple types including J, K, T, E, S, R, B, and N, as well as direct ±50 mV and ±100 mV analog inputs, making it a versatile solution for temperature monitoring and low-level signal acquisition in legacy SLC installations.

 

Application Scenarios

A heat treatment facility operated a batch furnace with six temperature zones monitored by a legacy SLC 5/04 control system. The original analog input cards required external signal conditioners for each Type K thermocouple, adding cost and failure points to the system. The maintenance team replaced three existing slots with 1746-NT4 modules, connecting thermocouples directly to the modules’ removable terminal blocks. With built-in cold-junction compensation and per-channel configuration through RSLogix 500, the 1746-NT4 eliminated the external conditioners and provided more accurate temperature readings. When a thermocouple wire broke due to mechanical fatigue, the module’s open-circuit detection immediately flagged the affected channel, allowing the operator to identify the exact zone and replace the sensor during a scheduled maintenance window rather than discovering the fault mid-batch.

 

Parameter

Main Parameters	Value/Description
Product Model	1746-NT4
Manufacturer	Allen-Bradley (Rockwell Automation)
Product Category	Thermocouple/mV Analog Input Module
Product Line	SLC 500
Input Channels	4 differential, backplane-isolated
Thermocouple Types	J, K, T, E, S, R, B, N
mV Input Ranges	±50 mV, ±100 mV
Resolution	16-bit input (15 bits + sign); 14-bit output data
A/D Conversion	Sigma-Delta modulation
Cold-Junction Compensation	2 built-in CJC sensors
Backplane Current	60 mA @ 5V DC; 55 mA @ 24V DC
Update Time	26 ms to 1.2 s (configurable)
Open-Circuit Detection	Zero, upscale, or downscale (selectable)
Operating Temperature	0°C to +60°C
Chassis Location	Any slot except Slot 0
Compatible Terminal Block	1746-RT25G (green terminal block)
Lifecycle Status	Discontinued

 

Technical Principles and Innovative Values

• Innovation Point 1: Integrated Cold-Junction Compensation. The 1746-NT4 contains two cold-junction compensation sensors within its removable terminal block, eliminating the need for external reference junction hardware. This design maintains thermocouple accuracy without additional wiring complexity, reducing installation time and potential error sources in temperature-critical applications.
• Innovation Point 2: Per-Channel Software Configuration. Each of the four 1746-NT4 channels is individually configurable via software for a specific thermocouple type or mV range. There are no DIP switches to set. This flexibility allows a single module to simultaneously monitor Type K, Type J, and mV signals, simplifying inventory and panel design.
• Innovation Point 3: Comprehensive Diagnostic Detection. The 1746-NT4 provides open-circuit, over-range, and under-range detection on every channel, with user-selectable fault response behavior. These diagnostics allow the control system to respond intelligently to sensor failures, preventing unmonitored processes from drifting out of specification.