Allen-Bradley 1756-CJC/A ControlLogix Cold Junction Compensation Module

Configured for thermocouple reference junction temperature correction in ControlLogix analog input signal conditioning chains, the Allen-Bradley 1756-CJC/A, also cataloged as the 1756-CJC/A cold junction compensation module, provides direct physical temperature reference compensation for thermocouple measurement circuits within ControlLogix I/O architectures. The device interfaces mechanically with the RTB assembly of compatible analog input modules and supplies junction temperature correction data used during thermoelectric voltage linearization.

Hardware Specifications

Backplane Interface and Temperature Compensation Behavior

The 1756-CJC/A operates as a passive thermistor-based reference element integrated into the RTB structure of ControlLogix thermocouple input modules. Temperature sensing is applied at the terminal block interface to compensate for junction voltage drift caused by ambient temperature variation. The resulting compensation value is consumed by the analog input module during A/D conversion and thermocouple linearization. Signal integrity is dependent on stable backplane reference and correct mechanical seating within the RTB assembly.

Frequently Asked Questions

Q: Does the 1756-CJC/A generate its own signal processing output?
A: No. The module provides only cold junction reference sensing. Signal processing is performed by the connected thermocouple input module.

Q: Is the 1756-CJC/A electrically active on the ControlLogix backplane?
A: It operates passively and does not consume defined backplane current as a functional I/O module.

Q: Can the module be installed independently without an analog input module?
A: No. It must be installed into the RTB of a compatible thermocouple input module.

Field Installation Guidelines

Install the 1756-CJC/A directly into the RTB of the corresponding ControlLogix thermocouple input module. Ensure full mechanical seating to maintain stable thermal coupling between terminal block and compensation element. Power shall be removed from the chassis prior to installation. Maintain separation between thermocouple wiring and high-current conductors to reduce thermal and electrical coupling errors. Do not bend or stress the RTB assembly during insertion. Verify correct module pairing before energization.