Machine Design

Temperature control in a convenient package

Thermal controllers that use feedback traditionally consist of nine or more components that designers match to each other and the application.

Then a technician has to wire them together, often using several different types of connectors and cables.

To simplify the task, and bring down the cost, engineers at Watlow Electric Mfg. Co., St. Louis (, developed the EZ Zone ST control loop. It includes a PID temperature controller connected to a highamperage solid-state relay. Users specify whether or not they want a heat sink, current measurement, over/undertemperature limit, definite-purpose mechanical contactor, or a digital communications package, which could include a remote user interface. This makes the controller modular and scalable. This means users can add single thermal control zones one at a time, rather than buying in increments of four, a practice common with other temperature controllers. And for maintenance, modularity means replacing only defective or worn modules, not the entire controller.

Temperature accuracy is ±0.1%. And the controller is approved by UL, CSA, and CE and meets RoHS, WEEE, NEMA-4X, and IP65 regulations. Units can be stacked and back-panel or DIN-rail mounted. Although the current version handles only single-phase switching, a future version will do three-phase switching.

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