Allen-Bradley 1746-INT4 SLC 500 Isolated Thermocouple/mV Analog Input Module

The Allen-Bradley 1746-INT4, also cataloged as the 1746-INT4 isolated thermocouple/mV analog input module, serves as the primary 4-channel temperature and millivolt acquisition interface utilized to execute thermocouple signal conversion across SLC 500 backplane I/O platforms.

Configured for isolated analog signal acquisition in SLC 500 scan cycles, the module converts thermocouple and ±100 mV DC inputs into 16-bit digital process values through internal linearization and cold junction compensation processing. Input channels are galvanically isolated to reduce channel interaction during high-density temperature measurement.

Suffix Breakdown & Model Matrix

No structured suffix or option coding is defined for 1746-INT4. The part number represents a fixed SLC 500 catalog identifier without configurable hardware variants.

Hardware Specifications

Backplane Communication and Channel Isolation Behavior

The module exchanges digitized temperature and mV values through the SLC 500 backplane during cyclic scan execution. Each channel is independently isolated to reduce cross-channel coupling during simultaneous thermocouple acquisition. Backplane load is distributed across 5 VDC and 24 VDC rails with fixed current draw independent of signal activity.

Cold Junction Compensation and Thermocouple Linearization Processing

Temperature conversion is performed using embedded IPTS-68 and NBS standard linearization tables. Cold junction compensation is applied at the terminal interface with ±1.5 deg C accuracy across 0 to 70 deg C reference conditions. Open-circuit detection logic supports upscale, downscale, or zero configuration with a typical detection time of 5 s.

Frequently Asked Questions (FAQ)

Q: Can the 1746-INT4 be hot-swapped in an energized SLC 500 rack?
A: No. Backplane power must be removed before insertion or removal to prevent analog channel offset corruption.

Q: Does each channel operate independently in isolation mode?
A: Yes. Each of the 4 inputs is galvanically isolated to reduce channel-to-channel electrical interaction during thermocouple measurement.

Q: What happens if a thermocouple wire breaks?
A: Open-circuit detection triggers upscale, downscale, or zero output depending on configuration, with a typical detection delay of 5 s.

Field Installation Guidelines

The module shall be installed in a compatible SLC 500 chassis slot with proper backplane alignment and secure seating of the terminal assembly prior to energization.

Thermocouple extension wires must follow correct polarity and be routed separately from high-voltage conductors to prevent induced thermal EMF distortion. Shielding shall be grounded at a single reference point to avoid ground loop formation. Cold junction reference area must remain within the specified environmental range to maintain compensation accuracy.