LEADING BRANDS Reed Technology

Content Reed Switch Characteristics Reed Switch Operational Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 The Basic Reed Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Basic Electrical Parameters of Reed Switch Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 How Reed Switches are used with a Permanent Magnet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Reed...

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Standex Electronics is a worldwide market leader in the design, development and manufacture of standard and custom electro-magnetic components, including magnetics products and reed switch-based solutions. We offer engineered product solutions for a broad spectrum of product applications in all major markets, including but not limited to: Our magnetic offerings include planar, Rogowski, current, and low- and high-frequency transformers and inductors. Our reed switch-based solutions include KENT, MEDER and KOFU brand reed switches, as well as a complete portfolio of reed relays, and a comprehensive...

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Reed Switch Characteristics Reed Switch Operational Characteristics The Reed Switch was first invented by Bell Labs in the late 1930s. However, it was not until the 1940s when it began to find application widely as a sensor and a Reed Relay. Here it was used in an assortment of stepping/ switching applications, early electronic equipment and test equipment. In the late 1940s Western Electric began using Reed Relays in their central office telephone switching stations, where they are still used in some areas today. The Reed Switch greatly contributed to the development of telecommunications technology....

Reed Switch Characteristics The Basic Reed Switch Fig. #1 The basic hermetically sealed Form 1A (normally open) Reed Switch and its component makeup. Fig. #2 The 1 Form C (single pole double throw) three leaded Reed Switch and its component makeup. A Reed Switch consists of two ferromagnetic blades (generally composed of iron and nickel) hermetically sealpowered in a glass capsule. The blades overlap internally in the glass capsule with a gap between them, and make contact with each other when in the presence of a suitable magnetic field. The contact area on both blades is plated or sputtered...

Reed Switch Characteristics Figure 3 shows the general function of a Reed Switch with the us of a permanent magnet. Fig. #3 The basic operation of a Reed Switch under the influence of the magnetic field of a permanent magnet. The polarization of the reed blades occurs in such a manner to offer an attractive force at the reed contacts. The use of a coil wound with copper insulated wire. See Figure 4. Fig. #4 A Reed Switch sitting in a solenoid where the magnetic field is strongest in its center. Here the reed blades become polarized and an attractive force exists across the contacts. When a permanent...

Reed Switch Characteristics Basic Electrical Parameters of Reed Switch Products Pull-In (PI) is described as that point where the contacts close. Using a magnet, it is usually measured as a distance from the Reed Switch to the magnet in mm (inches) or in field strength AT, mTesla, or Gauss. In a coil, the Pull-In is measured in volts across the coil, mA flowing in the coil, or ampere-turns (AT). Generally, this parameter is specified as a maximum. No matter how well the reed blades are annealed, they will still have a slight amount of retentivity (a slight amount of magnetism left in the blades...

Reed Switch Characteristics Drop-Out (DO) is described as that point where the contacts open and has similar characteristics as the Pull-In above. It is also described as release or reset voltage current or AT. Hysteresis exists between the Pull-In and Drop-Out and is usually described in the ratio DO/PI expressed in %. The hysteresis can vary depending upon the Reed Switch design, (Figure #7), where variations in plating or sputtering thickness, blade stiffness, blade overlap, blade length, gap size, seal length, etc. will all influence this parameter. See Figure 7 for example of hysteresis...

Reed Switch Characteristics Fig. #9 A schematic diagram of a typical circuit used for measuring the dynamic contact resistance across the contacts of a Reed Switch. Fig. #10 A typical dynamic contact resistance portrayal showing the first closure, bouncing, dynamic noise and pattern generated by waver-ing contacts Applying the frequency described above to a coil, the contacts will operate and close in approximately ½ mA. The contacts may then bounce for about 100ms and undergo a period of dynamic noise for as much as ½ ms. This dynamic noise is generated by the contacts continuing to bounce but...