Detect End Limit Position On Hospital Beds And Mobility Equipment Using Reed Sensors REED RELAYS REED SENSORS REED SWITCHES Introduction Figure 1. MK14 Sensor physical layout There are a large number of applications requiring the detection of end limit position, where electric shock can be a real concern. Hospital beds, for example, need end position limits when adjusting the bed position. Reed Sensors are ideal here because they reliably pass very low level voltages and currents well under any potential power that could cause a shock. Mechanical limit switches have been used successfully in the past, but can fail prematurely because they need a higher level of power to operate properly. Mechanical sensors exposed to the environment will develop films on the contacts. To break through these films higher switching voltages may be necessary. These higher voltages are not ideal in a hospital bed environment. Now designers have turned to the Reed Sensor which uses hermetically sealed reed switches, which are ideal for switching low signal levels reliably. Features • The reed switch used in the Reed Sensor is hermetically sealed and is therefore not sensitive to spillage or wet environments • The hermetically sealed reed switch is ideally suited for switching low signal level voltages and currents • Magnet and Reed Sensor are isolated and have no physical contact by typically having the magnet mounted to the movement and the Reed Sensor mounted and positioned to pick on the end limit position/s • The magnet is not affected by its environment Figure 2. Sensor is mounted to each end position. When the piston reaches its top end limit position, the magnet actuates the sensor and sounds an alarm. • Millions of reliable operations • Cylindrical hole and screw fastening mounting • Contacts dynamically tested • Large sensing distances possible Applications • Ideal for sensing end position(s) • Ideal for applications sensing any kind of end movement even in dirty or wet environments • Medical mobility equipment • Hospital beds • Lift chair position • Mobility scooter • Patient lift • Power wheelchair • Stair lift position • Wheelchair ramp position Figure 3. Sensor is mounted to each end position. When the piston reaches its bottom end limit position, the magnet actuates the sensor and sounds an alarm. Reed Sensors Are Ideal for Sensing End Position On Hospital Beds And Other Mobility Equipment Hospital beds, motorized chairs, special lifts for bath tubs, massage chairs, etc. all require end position detection. Since these are used by the consumer, care needs to be taken to use low power switching devices eliminating the threat of electrical shock to the user. Also, dust, dirt, and moisture may be present with the potential for spillage occurring, all of which, could create faulty operation of switching devices. 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 End Limit Position On Hospital Beds And Mobility Equipment Using Reed Sensors 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 Dynamic contact resistance Breakdown voltage Operate time Release time Operate Temp Storage Temp Mechanical limit switches have been used in the past, but can fail prematurely, because they require higher switching power to operate properly. Designers have tried to operate them with lower power, have found they are not very reliable. Increasing the power level would result in the threat of electrical shock. Designers have not turned the MEDER’s reed sensors solving both of the above issues. The reed sensor uses hermetically sealed reed switches which are ideal for switch low power signals eliminating the potential for electric shock. And since the reed switches are hermetically sealed and packaged in strong high strength plastic, they are virtually fault free in any environment. Typical 50% Min Max Units 200 0.5 1.5 10 150 200 320 0.5 0.1 -20 85 -20 85 V Amps Amps Watts mΩ mΩ V msec msec °C °C In these requirements the magnet is usually mounted to the movement mechanism and the reed sensor is mounted at the end position detection point. When the mechanism and magnet are moved and approach the reed sensor the reed contacts will close sending a signal to the electronics, which in turn halts the motion. In this way reliable operation is achieved. It is also easily accomplished to sense several positions in a given motion and not only the end movement. Reed sensors can be strategically placed at all interested sensing points to carry out this operation. Also multiple magnets can be used to accomplish a similar task. If the motion is very complex, combinations of reed sensors and magnets may be used effectively to accomplish the given detection. MEDER’s reed sensors are available in several packages with various connector or lead options allowing the users to meet exact design details. The magnets can also be packaged in an assortment of ways as well. Because of the multitude of design requirements, MEDER, in a matter of fact manner, has the capability of developing specialized packaging for both the reed sensor and the magnet to meet the user’s specific needs. Consider some of the below options in cylindrical and rectangular versions for end limit sensor or other similar applications. 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 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 End Limit Position On Hospital Beds And Mobility Equipment Using Reed Sensors REED RELAYS REED SENSORS REED SWITCHES 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