Appliance Design - February 2008 - (Page 26) CONTROLS & SENSORS Fig. 2. The IR transmitter emits light, which is reflected back and is captured by photosensors on either side of the transmitter. Fig. 3. Here movement is detected as the IR light is reflected to the photosensor in the direction of movement. ficient,” even if the user is wearing rubber gloves. This also provides immunity against ambient light and permits low resistance sensor circuits. The low resistance sensor circuit features high EMI immunity, no problems with heat or humidity under the glass on the electronics, easy cooktop construction, and low system costs. The optical principle upon which the control system is based means that it is extremely insensitive to electromagnetic interference, says Zapf, which can be a problem with other technologies such as traditional capacitive sensors. This is also true of electrostatic discharge; while traditional capacitive sensors can be suscepSlider technology controls four burners. tible to ESD, the IR technology cannot be affected by electrostatic discharge because the finger that actuates the control is fully isolated from the sensor. The company offers a variety of standard and customized products including the standard comfort modules (SCM I, II, III and Quattro). These standard modules consist of two PCBs. The first board includes the power supply, relays, a buzzer and connectors that are used to connect the various burners, the power supply and an optional main relay to isolate the secondary circuit from the main. In addition, a pot detection module can be connected using edge connectors. The second control board contains the infrared emitters, photosensors, display elements and the microcontroller. The microcontroller processes the data from the photosensors and controls the displays, the buzzer and the relays on the power board. The two PCBs are attached to each other by springs, which press the upper sensor board against the glass ceramic surface. The travel of the springs compensates to a certain degree for mechanical tolerances. The module can be mounted in the cooktop by plastic posts. The display elements used for the burners are 13-mm, seven-segment displays that can be read from a considerable dis- 26 applianceDESIGN February 2008 www.applianceDESIGN.com http://www.appliancedesign.com
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