Appliance Design - July 2008 - (Page 38)

CONTROLS & SENSORS ing software, and an expansion valve. A power transistor may also be needed, depending on the type of valve used in the application. An optional ZigBee transceiver may also be included to provide a wireless link to another device, such as a utility meter or service technician’s computer. A schematic of the control system is shown in Fig. 2. As the heat load increases from nominal, the evaporator superheat rises. The controller senses this condition and adjusts the expansion valve aperture to allow more refrigerant into the evaporator, thus causing the superheat to fall. Conversely, as the heat load decreases from nominal, the evaporator superheat falls. The controller senses this condition and adjusts the expansion valve aperture to allow less refrigerant into the evaporator, causing the superheat to rise. The result is optimized evaporation within the evaporator coil and maximum heat absorption from the indoor air. A logic flowchart for the control system is shown in Fig. 3. Recall that the above description is specific to home air conditioning. However, the same control methodology can be applied to refrigerators, freezers, heat pumps or any other home, commercial or industrial appliance that uses a compressor-based refrigeration cycle. The Freescale evaporator superheat control system is 100 percent compatible with all commonly used refrigerants, including the environmentally friendly R-410A and R-134A types. < HIGH PERFORMANCE HVAC/R TEMPERATURE SENSORS Temperature Sensors · Wide range of unit housing materials · Wide temperature range (from -40°C to +300°C) · 0.1 to 1M Ohm resistance range · Long term stability · Precise temperature measurement · Custom probe length and thread sizes · Variety of thermistor casings Fig. 3. Control System Logic Flowchart. Applications Include - Heating - Central Air - Water Temperature Control Systems - Appliances For Information log on to www.zettlercontrols.com ZETTLER CONTROLS, INC. Phone: 949-360-5840 · Fax: 949-360-5839 75 Columbia, Aliso Viejo California 92656 www.zettlercontrols.com July 2008 38 applianceDESIGN www.applianceDESIGN.com www.zettlercontrols.com http://www.zettlercontrols.com http://www.zettlercontrols.com www.zettlercontrols.com http://www.zettlercontrols.com www.appliance http://www.appliancedesign.com

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Appliance Design - July 2008 Contents Editorial Shipments/Forecasts News Watch Heating Elements Gas Technology Motors & Pumps Controls & Sensors Design Marts Association Report: AHAM Advertiser's Index

Appliance Design - July 2008

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