The Comus International group of companies consists of: DESCRIPTION Reed Switches consist of two or three ferromagnetic blades (or reeds) hermetically sealed inside a glass envelope.The construction ensures protection from the external environment. Three types are available: Form A (normally open), Form B (normally closed), and Form C (changeover). Form B reed switches are obtained by two methods: By using normally closed blade of a Form C switch, or, by using a Form A switch, and biasing the contacts closed using a small block magnet.The switch is then able to re-open by the use of another stronger external magnet of opposite polarity. Sensitivity of a reed switch is measured in ampere turns (A.T.) and it should be noted that lower switch (A.T.) ratings are more sensitive as they require less magnetic field strength to operate them.Various voltage and current switching levels are available and contact plating materials can be varied to accommodate specific types of load. Lamp Loads Reed Switches are operated by a magnetic field, via a magnet or a current carrying coil. When the field is removed the switch reverts to its previous state. Operation by a magnet can be achieved in a large variety of ways, either moving the magnet toward and away from the reed either perpendicularly, or parallel to the glass. Reed Switches are used in a variety of Comus Group products including Proximity Switches, Float Switches and Reed Relays. They are now available in housed packages affording protection from damage and Surface Mount styles. With lamp load applications it is important to note that cold lamp filaments have a resistance 10 times smaller than already glowing filaments. This means that when being turned on, the lamp filament experiences a current flow 10 times greater than when already glowing. This high inrush current can be reduced to an acceptable level through the use of a series of current-limiting resistors. Another possibility is the parallel switching of a resistor across the switch. This allows just enough current to flow to the filament to keep it warm, yet not enough to make it glow. Actuation of Reed Switches with a Permanent Magnet (Examples of switching with the use of a moving magnet.) Examples of switching through rotational movement. Direct Actuation: Comus International 454 Allwood Road Clifton New Jersey 07012 U.S.A Tel: (1)973 - 777 - 6900 Fax:(1)973 - 777 - 8405 email: [email protected] Website: http://www.comus-intl.com Comus Europe Limited Unit 7, Rice Bridge Industrial Estate Thorpe - Le - Soken Essex England CO16 0HL Tel: +44 (0)1255 862236 Fax: +44 (0)1255 862014 email: [email protected] Website: http://www.comuseurope.co.uk A magnet moved perpendicularly towards and away from a Reed Switch turns it off and on once. Comus Belgium BVBA Overhaamlaan 40 B-3700 Tongeren Belgium Closed Open A magnet swung towards and away from a Reed Switch operates it once. CONTACT PROTECTION Ring Magnet Lamp load with parallel or current limiting resistor across the switch Cutting and Bending: As the Reed Switch blades are part of the magnetic circuit of a Reed Switch shortening the leads results in increased pull-in and drop-out values. Comus Technology BV Jan Campertstraat 11 6416 SG Heerlen The Netherlands Switching Technologies Gunther B-9, B-10, & C-1 Special Economic Zone (MEPZ) Kadapperi Tambaram Chennai 600 045 India Tel: +31(0)45-54.39.345 Fax: +31(0)45-54.27.216 email: [email protected] Website: http://www.dry-reeds.com Capacitive Loads Unlike inductive loads, capacitive and lamp loads are prone to high inrush currents which can lead to faulty operation and even contact welding. When switching charged capacitors (including cable capacitance) a sudden unloading can occur, the intensity of which is determined by the capacity and length of the connecting leads to the switch. This inrush peak can be reduced by a series of resistors. The value is dependent on the particular application but should be as high as possible to ensure that the inrush current is within the allowable limits. Comus Electronics and Technologies India Private Limited 2nd Floor, 31/33, Anjugam Nagar, 2nd Street, Ashok Nagar, Jaferkhanpet, Chennai 600083 Tamil Nadu, India Tel: +(91)-(44)-42023510 Fax: +(91)-(44)-22628198 email: [email protected] Website: http://www.comusindia.com Closed Magnet With the stationary arrangement of a Reed Switch and magnet, the contact Reeds are closed. Should the magnetic field be diverted away from the Reed Switch by a shield of ferromagnetic material placed between the switch and the magnet, the contacts will open. When the shield is removed, the contact Reeds become magnetically actuated and close. Magnet Closed A ring magnet moved parallel to a Reed Switchs’ axis operates it from one to three times. Inductive Loads Indirect Actuation: Shielding Magnet Tel: +32 (0)12 390400 Fax: +32 (0)12 235754 email: [email protected] Website: http://www.comus.be A magnet moved parallel to a Reed Switch operates it from one to three times. A reverse voltage is generated by stored energy in an inductive load when the reed contacts open. This voltage can reach very high levels and is capable of damaging the contacts. An RC network may be used as shown below to give protection. Closed Magnet Magnetic shield Pull-in Sensitivity: The given pull-in sensitivity of the Reed Switch has a test equipment tolerance of ± 2 AT. For all Reed Switches the standard pull-in sensitivity is given in the table. Other pull-in sensitivities are available on request. Life Expectancy: The life expectancy of a reed switch is dependent upon the load being switched. At maximum rated loads life expectancy is approximately 106 switching cycles. Lower load ratings can increase the life expectancy up to 5x108 operations. The mechanical life expectancy can reach at least 109 operations. Through the switching of inductive, capacitive, and lamps loads, the life expectancy is considerably reduced due to exceeding the specified maximum current. Magnet Biasing Contact Contact Form B or C Normally Closed Contact (Form B) RELAYS -UNLIMITED.com COMPUTER COMPONENTS INC. When cutting or bending Reed Switches, it is important that the glass body should not be damaged. Therefore, the cutting or bending point should be no closer than 3mm (.118) to the glass body. Computer Components Inc. 18-B Kripes Rd. East Granby Connecticut 06026 U.S.A Normally Open Contact (Form C) Tel: (1)401 - 228 - 5459 The above diagram illustrates a resistor/capacitor network for protecting a Reed Switch against high inrush currents. R1 and/or R2 are used depending upon circuit conditions. All dimensions are nominal, in millimeters unless otherwise stated. If further information is required, individual datasheets are available on our websites, and on CD. As part of the group’s policy of continued product improvement, specifications may change without notice. Our sales office will be pleased to help you with the latest information on our products. email: [email protected] Website: http://www.relays-unlimited.com We also have a large network of worldwide agents. These can be seen on any of our websites, or on our company profile brochure. Com/1/Oct14/Iss.4 HOUSED & SMD REED SWITCHES From the Comus Group of Companies All dimensions are nominal, in millimeters unless otherwise stated. If further information is required, individual datasheets are available on our websites, and on CD. As part of the group’s policy of continued product improvement, specifications may change without notice. Our sales office will be pleased to help you with the latest information on our products.