Allen Bradley 1756-CJC ControlLogix Cold Junction Compensation Thermistor Kit

Product Overview

The Allen Bradley 1756-CJC functions as a precision Cold Junction Compensation (CJC) thermistor kit designed exclusively for the ControlLogix platform. These sensors provide the critical reference temperature data required by thermocouple input modules to perform accurate "cold junction" calculations. By measuring the ambient temperature at the Removable Terminal Block (RTB) connection point, the 1756-CJC allows the PLC to subtract the parasitic voltage generated by the junction of dissimilar metals. This ensures the controller reports only the actual process temperature at the thermocouple tip.

Technical Specifications

Engineering Advantages

• Critical Accuracy Restoration: Thermocouple measurements inherently suffer from errors caused by the temperature at the terminal connection. The 1756-CJC eliminates these offsets by providing a real-time thermal reference, ensuring laboratory-grade accuracy in industrial heat-treatment and process-heating applications.

• Seamless Hardware Integration: These thermistors install directly into the pre-drilled mounting holes of the 1756-TBNH or 1756-TBSH terminal blocks. This integrated design places the sensor in direct thermal contact with the copper screw terminals, minimizing the thermal gradient between the junction and the compensator.

• Optimized Signal Integrity: By utilizing high-sensitivity thermistor technology, the 1756-CJC provides a non-linear resistance change that the 1756-IRT8I and 1756-IT16 modules interpret with high resolution. This ensures the PLC compensates for even minute fluctuations in cabinet temperature caused by cooling fan cycles.

• Standardized Maintenance Kits: We supply the 1756-CJC as a set of two. This packaging allows maintenance teams to fully equip or refresh high-density modules (like the 16-channel 1756-IT16) where multiple compensation points are required for balanced thermal monitoring.

• Rugged Component Lifecycle: Despite their small size, these thermistors withstand the thermal cycling common within sealed control enclosures. The 100% Brand New original units ensure the resistance-temperature (R-T) curve remains within factory tolerances, preventing "drift" over years of continuous operation.

FAQs

• Is the 1756-CJC supplied as Brand New?

  Yes. We supply the 1756-CJC as 100% Brand New original components. Each kit contains two factory-sealed thermistors to ensure the highest accuracy for your ControlLogix temperature loops.

• Which modules require the 1756-CJC?

  This kit specifically supports the 1756-IRT8I (Isolated RTD/Thermocouple) and 1756-IT16 (16-channel Non-isolated Thermocouple) modules. Without these thermistors, the modules will trigger a configuration fault or report highly inaccurate temperature data.

• Where exactly do I install these thermistors?

  You must secure the 1756-CJC thermistors into the specialized mounting cavities located on the top and bottom of the Removable Terminal Block (RTB) attached to the module. Tighten the mounting screws appropriately to ensure constant thermal contact with the terminal mass.

• Do I need to calibrate the 1756-CJC?

  No. The ControlLogix thermocouple modules contain the necessary R-T curve profiles for the 1756-CJC. Once you install the hardware and select the "CJC" option in Studio 5000, the system automatically applies the compensation logic.