Detect And Control Appliance Doors Doors Using A Reed Sensor REED RELAYS REED SENSORS REED SWITCHES Introduction Appliances, particularly refrigerators and freezers, must have their doors closed at all times. If the door is left open for any length of time the compartments will warm up and the food contained within will begin to spoil. Reed sensors are a simple choice to solve this 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 appliance door, and the Reed Sensor mounted and positioned usually on a PCB on the appliance chassis to accurately detect the opening of the door Figure 2. Reed Sensor is mounted to appliance chassis PCB. Magnet is mounted to the moving door. When door is closed the magnetic field of the permanent magnet holds the switch contacts in the closed position. • The reed switch used in the Reed Sensor is hermetically sealed and is therefore not sensitive to cold, wet, moist environments • The permanent magnet is not affected by its environment • Tens of millions of reliable operations • Surface mount and through hole packages available • Cylindrical mounting and screw fastening mounting with various connectors available in, made to order lead lengths • Contacts dynamically tested Applications • Ideal for sensing the status of appliance doors whether in the open or closed state Figure 3. When the door is opened the magnetic field moves out of proximity to the sensor causing the contacts to open and activating the system timer. When timer reaches its limit, the alarm with sound. • Ideal for applications sensing any kind of motion in a host of different configurations Reed Sensors Solve the Problem of Leaving an Appliance Door Open We have all at one time or another left the refrigerator door open. Most times its only for a short period of time so no damage is done, but sometimes the time is substantial. In this case, a few things can happen: first, the food in the refrigeration will spoil; and secondly, any ice in the refrigerator will melt and potentially flow onto the floor and perhaps damage it. This same problem can also happen with a freezer. 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 Detect And Control Appliance Doors Doors Using A Reed Sensor REED RELAYS REED SENSORS REED SWITCHES Specifications 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 resistance Dynamic contact resistance Breakdown voltage Operate time Release time Operate Temp Storage Temp Typical 50% Min Max Units 200 0.5 1.5 10 150 V Amps Amps Watts mΩ Appliance designers have chosen the reed sensor to solve the problem. Generally, a magnet is mounted to the door. The reed sensor is usually mounted to a PCB on the chassis of the appliance. When the door is closed the reed sensor is activated. When the door is opened, the contacts open, activating a timer in the electronics. After a specified period of time, an alarm or beeper will be activated alerting the user that the door has been left open. This of course saves them the replacement costs of spoiled food. The reed sensor is a excellent choice because it can operate reliably from -50˚C to 150˚C and represents an economical way to carry out the sensing function. 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 grit, water, and moisture without any loss of reliability. MEDER’s sensors are packaged for surface mounting as well as through hole mounting. Also, MEDER has cylinder packages and well as screw fastening packages having lead wires for remote attachment to the electronics. Surface Mount Series Series 200 320 0.5 0.1 -20 85 -35 85 mΩ V msec msec °C °C MK15 MK16 MK17 MK22 MK23MK23-35 MK23MK23-66 MK23MK23-87 MK23MK23-90 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 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 Figure 3. MK15 Tape & Reel 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 Detect And Control Appliance Doors Doors Using A Reed Sensor REED RELAYS REED SENSORS REED SWITCHES Through Hole Series 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 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 the factory for more options not listed above. ** 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