Allen Bradley 1746-NT4 Analog Input Module

The 1746-NT4 is a 4-channel thermocouple/millivolt (mV) input module belonging to Allen-Bradley’s SLC™ 500 series (Series B), designed for industrial temperature and low-voltage signal measurement in compact PLC systems. It specializes in collecting signals from thermocouples (Types J, K, T, E, R, S, B, N) and linear millivolt devices (±50 mV, ±100 mV), making it suitable for temperature monitoring in processes such as industrial heating, cooling, and material processing.

Each channel is independently configurable for input type, data format, temperature units, and filter frequency via software (no DIP switches), supporting flexible adaptation to different sensor requirements. The module integrates cold-junction compensation (CJC) sensors in the terminal block to eliminate measurement errors caused by ambient temperature changes at the connection junction. It uses a sigma-delta A/D conversion method with programmable digital filters (10 Hz, 50 Hz, 60 Hz, 250 Hz) to suppress high-frequency noise, ensuring stable and accurate signal acquisition.

It is fully compatible with SLC 500 modular and fixed controllers, drawing 5V DC and 24V DC power from the system backplane (no external power required). The module features a removable green terminal block for easy wiring and maintenance, with built-in diagnostics for open-circuit, over-range, under-range, and configuration errors. Status is indicated via 5 green LEDs (4 channel-specific, 1 module-wide). It supports retentive programming and autocalibration (triggered by power-up, channel enable, or configuration changes) and receives continued technical support from Rockwell Automation.

Core Specifications: 4 differential input channels, no output channels. Supports thermocouple types J (-210°C to 760°C), K (-270°C to 1370°C), T (-270°C to 400°C), E (-270°C to 1000°C), R (0°C to 1768°C), S (0°C to 1768°C), B (300°C to 1820°C), N (0°C to 1300°C); and millivolt ranges ±50 mV, ±100 mV.

Performance Metrics: A/D conversion resolution up to 16-bit effective resolution (varies by filter frequency). CJC accuracy ±1.5°C (0°C to 85°C). Overall module accuracy at 25°C (77°F) ranges from ±0.72°C (Type E) to ±3.61°C (Type S); temperature drift ±0.019°C/°C to ±0.053°C/°C. Non-linearity complies with IPTS-68 standard and NBS Monograph 125/161.

Signal Processing: Programmable filter frequencies with corresponding cut-off frequencies (2.62 Hz to 65.5 Hz) and step response times (12 ms to 300 ms). Normal mode rejection (NMR) ≥100 dB at 50/60 Hz; common mode rejection (CMRR) ≥150 dB at 50/60 Hz. Open-circuit detection time ≤500 ms or 1 module update time (whichever is longer).

Electrical Parameters: Input impedance ≥10 MΩ. Channel-to-channel common-mode voltage separation ≤2V (Series B). Field wiring to backplane isolation 500V DC. Maximum loop impedance 25 Ω (for <1 LSB error). Open-circuit detection leakage current ≤12 nA.

Power Consumption: Backplane current draw max 60 mA (5V DC) and 40 mA (24V DC); power consumption max 0.8W (0.3W at 5V DC, 0.5W at 24V DC).

Environmental Adaptability: Operating temperature 0–60°C (32–140°F), storage temperature -40–85°C (-40–185°F). Relative humidity 5–95% (non-condensing). Compliant with EMC directives EN 50081-2 and EN 50082-2 for industrial environments.

Mechanical & Wiring: Recommended cable: shielded twisted-pair thermocouple extension wire (for thermocouples) or Belden #8761 (for mV inputs). Maximum wire size #14 AWG. Terminal block torque 0.565 Nm (5 lb-in). Module dimensions match SLC 500 single-slot design.

Programming & Addressing: Module ID code 3510. Uses 8 input words (4 data words, 4 status words) and 8 output words (4 configuration words, 4 unused) in the I/O image table. Data formats include engineering units (x1, x10), scaled-for-PID (0–16383), and proportional counts (-32768–32767). Temperature units selectable between °C and °F.

Certifications & Compliance: C-UL Listed for Class 1, Div 2 hazardous locations; CSA approved. Suitable for installation in NEMA-rated enclosures.

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