Allen-Bradley 1746-NT8 SLC 500 Thermocouple/mV Analog Input Module

Product Introduction

When your process demands precise temperature measurement from multiple thermocouple types, the Allen-Bradley 1746-NT8 delivers reliable performance. This SLC 500 Thermocouple/mV Analog Input Module accepts eight channels of input from J, K, T, E, S, R, B, and N thermocouples, as well as ±50 mV and ±100 mV signals. It converts analog signals to digital values using sigma-delta modulation, storing results in local memory for the SLC processor to access. The module fits fixed-style chassis like the 1746-A2 or any slot except slot 0 in modular SLC 500 systems.

Technical Specifications Breakdown

Key specifications from the 1746-NT8 include:

Inputs: Eight (8) channels for thermocouple or millivolt signals.

Backplane Current: 120 mA at 5 VDC and 70 mA at 24 VDC, with total power consumption of 2.28 W maximum.

Resolution: 16 bits in, 14 bits out for accurate digital conversion.

Update Time: Ranges from 356 milliseconds to 4.05 seconds, depending on filter settings.

Step Response: 60 milliseconds input, 2.5 milliseconds output for fast signal tracking.

Open Circuit Detection: Selectable options: Zero, Upscale, or Downscale.

Operating Temperature: 0 to 60 degrees Celsius; storage from -40 to 85 degrees Celsius.

A/D Conversion: Sigma-delta modulation with a digital low-pass filter.

The module provides input overvoltage protection up to ±30 VDC and 600 W pulsed for 1 ms. It offers 12.5 VDC circuit isolation tested at 500 VDC for 1 minute between inputs and chassis ground, and between inputs and backplane. Normal mode rejection exceeds 100 dB at 50–60 Hz, and common mode rejection also exceeds 100 dB at 50–60 Hz. The module auto-calibrates every 2 minutes after power-up.

Industry Applications

The 1746-NT8 excels in industrial temperature monitoring and control. Typical applications include:

Process Heating: Monitor furnace or oven temperatures using Type K or Type J thermocouples, with upscale open-circuit detection to alert operators of sensor failure.

Chemical Processing: Use Type T or Type E sensors for precise temperature measurement in reactors, leveraging the module's high common-mode rejection to minimize noise from nearby motors.

Quality Control: In manufacturing lines, the module's 16-bit resolution ensures accurate temperature data for compliance with strict product specifications.

For each application, the 1746-NT8's selectable data formats (engineering units, scaled for PID, or proportional counts) simplify integration with existing control systems.

Installation & Setup Guidance

Install the 1746-NT8 in any SLC 500 chassis slot except slot 0, which is reserved for the processor or communication adapter. Use the included 1746-RT34 removable terminal block for wiring. The terminal block comes with two cold-junction compensation (CJC) sensors for accurate thermocouple readings. Ensure input devices have impedance below 100 ohms to meet accuracy specifications. Select input type and open-circuit detection via software configuration. The module supports fixed-style chassis (1746-A2) and modular controllers (SLC 5/01 through 5/05).

Maintenance & Reliability

To maintain reliable operation, keep the module within its operating temperature range of 0 to 60 degrees Celsius and humidity between 5–95% without condensation. The module's auto-calibration feature reduces drift over time. Periodically verify that CJC sensors are functioning correctly and that terminal block connections remain tight. The 1746-NT8 is UL and CUL-approved, ensuring compliance with safety standards. For extended life, avoid exposing the module to temperatures above 85 degrees Celsius during storage.

Compatibility & Integration

The 1746-NT8 works with all SLC 500 processors, including SLC 5/01, 5/02, 5/03, 5/04, and 5/05. It integrates seamlessly with fixed-style or modular chassis. The module communicates over the backplane, and its digital data is accessible via the processor's data table. It supports monitoring through HMI and SCADA systems by reading error bits for open circuit, under-range, over-range, and channel error conditions. For remote I/O applications, use a communication adapter in slot 0.

For complete technical specifications for the 1746-NT8, please contact BluePLC Industrial.