Allen-Bradley 1746-NT8 SLC 500 8-Channel Thermocouple Input Module

Description

Key Technical Specifications

Product Introduction & Supply Chain Strategy

The Allen-Bradley 1746-NT8 is an 8-channel high-density thermocouple input module designed for the SLC 500 PLC platform. It processes microvolt signals from thermocouples or millivolt sensors into 16-bit digital values for precise temperature monitoring in industrial ovens, multi-zone heat treating, and plastics processing.

Since Rockwell Automation has officially retired the SLC 500 family, keeping uncommissioned New Surplus 1746-NT8 units in buffer stock mitigates the risk of catastrophic process shutdowns. Procuring genuine New Surplus guarantees factory-calibrated cold-junction circuits and zero component aging, preventing reading drift and sensor failure errors common in second-hand pull-outs.

1746-NT8

1746-NT8

Installation & Configuration Guide

Stage 1: Pre-Installation (Prep & Safety)

1. Execute Lock-Out/Tag-Out (LOTO) on the main 1746 chassis power supply and connected field sensor loops.
2. Put on an ESD-grounded wrist strap attached to cabinet earth ground.
3. Document terminal wiring assignments, wire colors, and shielding connections using clear reference photos.

Stage 2: Removal

1. Unfasten the top and bottom retaining screws on the removable terminal block (RTB) and carefully pull it off the front header.
2. Depress the upper and lower module release latches on the SLC 500 chassis frame simultaneously.
3. Slide the card straight out of the slot along its guide rails to prevent bending or stressing the backplane connector pins.

Stage 3: Installation (Clone & Seat)

1. Verify DIP switch or jumper settings on the replacement 1746-NT8 board match the configuration of the original card.
2. Align the module circuit board edges with the top and bottom chassis slot guide tracks.
3. Push the module firmly into the chassis slot until both upper and lower release latches snap into place.
4. Align the pre-wired RTB onto the terminal header and tighten the retaining screws to 0.5 N·m (4.4 lb·in). Ensure CJC sensors remain properly mounted.

Stage 4: Power-On & Testing

1. Verify thermocouple polarity (positive/negative leads) and ensure cable shields are grounded at a single point to prevent ground loops.
2. Apply power to the 1746 power supply and observe the front status LEDs:
   • MODULE STATUS: Solid green indicates normal initialization and POST diagnostic pass.
   • CHANNEL STATUS (0–7): Green indicates valid channel conversion; flashing red indicates an open sensor, wrong thermocouple type, or out-of-range signal.
3. Establish communication using RSLogix 500, verify the module’s Class 1 or Class 3 configuration setup (sensor types, filter frequency, ^\circC vs ^\circF scaling), and monitor input registers (I:e.0 through I:e.7) for accurate live readings.

Firmware/Software Versions & Upgrade Notes

• Class Configuration: The 1746-NT8 can operate in Class 1 or Class 3 mode. Class 3 mode enables complete software configuration per channel (e.g., mixing Type K and Type J sensors on different channels) via RSLogix 500 write words.
• Filter Frequency Selection: Ensure the ladder logic program properly transmits configuration words to the module on initial CPU boot to establish filter speed and ambient noise rejection (50/60 Hz).
• Firmware Notes: Temperature input modules contain factory-calibrated EEPROMs and do not support field firmware upgrades. Always replace hardware with identical Series designation (Series A or Series B) to ensure configuration bit mapping remains fully compatible.

Frequently Asked Questions (FAQ)

Q: Is this 1746-NT8 module a Brand New Surplus unit or a refurbished card?

A: This product is a Brand New Surplus unit. It is not used, not pulled from a decommissioned plant, and not refurbished. All modules undergo rigorous quality verification to ensure OEM-level reliability.

Q: Why shouldn’t I buy a cheaper refurbished 1746-NT8 for my facility?

A: Thermocouple modules rely on sensitive microvolt measurement circuitry and calibrated cold-junction thermistors. Refurbished units frequently exhibit signal drift, channel noise, or trace corrosion from previous harsh thermal environments. Purchasing New Surplus ensures factory accuracy, a 10 to 15-year operational lifespan, and zero risk of unexpected thermal trips.

Q: How do you verify the quality and authenticity of legacy Allen-Bradley stock?

A: Every unit passes through our inbound SOP quality checks: inspecting original OEM ESD packaging, checking backplane edge connectors for zero insertion wear, verifying CJC sensor integrity, and conducting live thermocouple signal verification on an SLC 500 test chassis.

Q: What is the main difference between the 1746-INT4 and the 1746-NT8?

A: The 1746-INT4 provides 4 individually channel-to-channel isolated inputs, whereas the 1746-NT8 provides 8 high-density group-isolated channels. If your thermocouples are ungrounded, the 1746-NT8 provides double the channel density in a single slot.

Q: Is it safe to hot-swap the 1746-NT8 while the SLC 500 rack is under power?

A: No. Allen-Bradley SLC 500 chassis backplanes do not support Hot-Swapping (RIUP). Pulling or inserting any 1746 module while backplane power is active causes electrical arcing that can destroy the module, adjacent I/O cards, or the primary CPU. Always disconnect chassis power first.

Q: What warranty coverage applies to this New Surplus 1746-NT8?

A: All 1746-NT8 New Surplus cards carry our comprehensive 1-year functional replacement warranty. If any channel or hardware failure occurs under standard operating parameters, we will immediately supply a replacement card or issue a full refund.