Reed Sensors Detect Dishwasher Spray Arm Obstruction REED RELAYS REED SENSORS REED SWITCHES Introduction Most modern kitchens today have as an essential component - a dishwasher. Actually dishwashers if designed properly can be very power efficient and represent a healthier approach to washing dishes. One of the essential actions that takes place within the dishwasher is rotation of the spray arm. This generally sprays hot water/steam and/or hot air under high pressure to all the dishes. If a dish is improperly positioned in the washer blocking the rotation of the spray arm trouble will ensue. However, reed sensors have solved this commonly occurring problem. Figure 1. MK17-X-3 Sensor physical layout Features • Magnet and Reed Sensor are isolated and have no physical contact by typically having the magnet mounted to the spray arm and the Reed Sensor is mounted on the inner casing of the body such that it will detect the magnetic field of magnet on the spray arm when it rotates by the reed sensor. • The reed switch used in the Reed Sensor is hermetically sealed and is therefore not sensitive to rough, wet, moist, high temperature environments Figure 2. A magnet is mounted to the underside of the dishwasher spray arm and its rotation is sensed when it passes over the reed switch sensor mounted to the bottom of the dishwasher. • The magnet is not affected by its environment • Tens of millions of reliable operations • Surface mount and through hole packages available • Cylindrical hole and screw fastening mounting • Contacts dynamically tested Applications • Ideal for sensing the rotating dishwasher spray arm • Ideal for applications sensing any kind of rotation in a host of different configurations Figure 3. When there is an obstruction to the spray arm, the magnet and arm do not rotate causing the sensor to send a signal to the electronics sounding an alarm and turning off the dishwasher. Reed Sensors Solve the Spray Arm Blockage Problem People take their dishwashers for granted assuming they will get the job done. In most cases this is a good assumption. However, many people like to run their washer only when it is completely full and sometimes overloaded. In the overloaded case, a dish or utensil may be inadvertently in the way of the rotating spray arm blocking the rotation. In this case two things happen: first, the spray arm is not longer rotating and is therefore only spraying in one area only; and secondly, when the motor is stopped from rotating (called a locked rotor condition), the motor will automatically increase the current, and therefore increasing power trying to start the motor moving. This heavy draw of power dramatically reduces the efficiency and potentially could burn out the motor. Furthermore, the dishes end up not very clean with the spray only penetrating certain dish areas. Dishwasher manufacturers offer models where this problem is solved using reed sensors. MEDER electronic Application MEDER electronic AG | Germany | tel.: +49(0)7731/8399-0 | Email: [email protected] MEDER electronic Inc. | USA | tel.: +1 508.295.0771 | Email: [email protected] Page 1 of 3 www.meder.com Reed Sensors Detect Dishwasher Spray Arm Obstruction REED RELAYS REED SENSORS REED SWITCHES Specifications Defining the MK06 & MK15 Series Operate specs Min Max Units Must close distance 5 25 mm Must open distance 5 25 mm Hysteresis Load Characteristics Switching voltage Switching current Carry current Contact rating Static Contact resistance Dynamic contact resistance Breakdown voltage Operate time Release time Operate Temp (MK6) Storage Temp (MK6) Operate Temp (MK15) Storage Temp (MK15) Typical 50% Min Max Units 200 0.5 1.5 10 150 200 320 -20 -35 -20 -35 0.5 0.1 85 85 130 130 Volts Amps Amps Watts mΩ mΩ Volts msec msec °C °C °C °C A magnet is generally mounted to the spray arm/s and rotates with the spray arm. A reed sensor is conveniently mounted to the internal chassis such that it will be energized with every rotation of the spray arm. When the spray arm is blocked, the reed sensor fails to energize, which sends a signal to the electronics alerting it that the spray arm is no longer operating. In this case, three things generally happen: 1. a signal is sent to turn off the spray arm motor, 2. a light on the outside panel begins to flash; and 3. a beeper begins to alert the user of the jam internally in the dishwasher. Once the blockage is removed the dishwasher is reset and will resume its normal operation. In this application, the reed sensor may be in a direct line with the sprays including the high and low temperatures. Because MEDER’s sensors use hermetically sealed reed switches that are further packaged in strong high strength plastic, they can be subject to rough treatment and environmental concerns such as water sprays, and moisture without any loss of reliability. The reed sensor reed sensor is an excellent choice because it can operate reliably over a wide temperature range, and represents an economical way to carry out the sensing function. MEDER’s sensors are packaged for surface mounting as well as through hole mounting. Also, MEDER has cylinder packages as well as screw fastening packages having lead wires for remote attachment to the electronics. Surface Mount Series Series MK15 MK16 MK17 MK22 MK23MK23-35 MK23MK23-66 MK23MK23-87 Figure 4. MK15 Tape & Reel MK23 MK23-90 Dimensions mm W 2.5 H 2.5 L 19.50 W 2.3 H 2.3 L 15.60 W 2.1 H 2.1 L 9.61 W 2.7 H 2.3 L 15.60 W 2.2 H 1.95 L 15.75 W 2.2 H 2.7 L 19.60 W 2.0 H 2.1 L 15.60 W 2.54 H 3.05 L 24.9 Illustration Illustration inches 0.098 0.098 0.768 0.091 0.091 0.614 0.083 0.083 0.378 1.060 0.091 0.614 0.087 0.077 0.620 0.087 1.060 0.772 0.079 0.083 0.614 0.100 0.120 0.980 MEDER electronic Application MEDER electronic AG | Germany | tel.: +49(0)7731/8399-0 | Email: [email protected] MEDER electronic Inc. | USA | tel.: +1 508.295.0771 | Email: [email protected] Page 2 of 3 www.meder.com Reed Sensors Detect Dishwasher Spray Arm Obstruction REED RELAYS REED SENSORS REED SWITCHES Through Hole Series Series MK06MK06-4 MK06MK06-5 MK06MK06-6 MK06MK06-7 Dimensions mm W 3.3 H 3.3 L 12.06 W 2.8 H 3.2 L 14.30 W 3.3 H 4.2 L 17.24 W 3.3 H 4.2 L 19.78 Illustration inches 0.130 0.130 0.475 0.110 0.126 0.563 0.130 0.165 0.679 0.130 0.165 0.779 Cylindrical Panel Mount Series Series MK03 MK03 Dimensions mm Dia 5.25 L 25.5 Illustration inches 0.207 1.004 MK14 MK14 Dia L 4 25.5 0.157 1.004 MK18 MK18 Dia L 5 17 0.197 0.669 MK20/1 MK20/1 Dia L 2.72 10 0.107 0.394 Rectangular Screw Flange Mount Series Series MK04 MK05 MK05 MK12 MK12 Dimensions mm W 13.9 H 5.9 L 23.0 W 19.6 H 6.1 L 23.2 W H L 14.9 6.9 32.0 Illustration inches 0.547 0.232 0.906 0.772 0.240 0.913 0.587 0.272 1.260 **Consult our factory for your specific design requirements. ** MEDER electronic Application MEDER electronic AG | Germany | tel.: +49(0)7731/8399-0 | Email: [email protected] MEDER electronic Inc. | USA | tel.: +1 508.295.0771 | Email: [email protected] Page 3 of 3 www.meder.com