Abstract: A dryer control system for controlling the drying of polymer plastic pellets within a dryer hopper is provided. A series of temperature snap switches and pressure switches are strategically located within the dryer control system to cause a variety of passive fault lights to be activated to signal faults while the system continues to operate or to cause an alarm light to be activated which stops the drying cycle. The passive fault lights indicate a situation within the drying cycle which should be corrected but which is not sufficiently serious to stop the drying cycle. An alarm being activated, on the other hand, indicates a situation which requires shut-down of the drying system until the problems which caused the alarm are corrected. A programmable logic controller and a temperature controller control the operation of the system by receiving signals from the snap switches and pressure switches throughout the system.

Abstract: An apparatus and process for heating and dehumidifying plastic materials in a container, such as a hopper, using a current of warm dry air. The apparatus having a desiccant for removing the moisture picked up from the material, and having a heater and cooler downstream from the desiccant. The dryer control operates in three modes to control the cooler only, to control the heater and cooler, and to control the heater only. Measured temperatures and operating conditions control the selection of specific modes.