However, because of the small size and magnetic efficiency of the reed switch, the power required to drive the coil is lower than most other types of relays. Like other relays, this provides galvanic isolation between the coil input and the controlled contact(s). That is why Littelfuse works closely with customers to provide custom solutions, including additional components such as resistors, triacs, or circuit board related work.Ī reed relay is made by combining a reed switch with a copper coil.
Although Littelfuse offers a wide variety of standard parts, they cannot fit every application. Electrical termination may be for a circuit board, by an integrated connector, or wires may be terminated with connectors, terminals, fastons, or just tinned leads. Sensors may be placed into a hole and held in place with nuts (threaded barrel sensors) or with setscrews or retaining clips (firecracker sensors). Mounting may be with screws or by soldering to a circuit board. Sensor capsules may be plastic or stainless steel. There are many types and options of reed sensors that are available. The amount of change with temperature depends on the type of magnet and reed switch used. Both magnets and reed sensors become more magnetic at low temperatures and less magnetic at high temperatures. Another influence to be aware of is temperature. Motors, transformers, and other high current electrical devices near the reed sensor may also cause unwanted influence. Since a reed sensor is a magnetic sensor, ferromagnetic materials such as steel in close proximity to the sensor can influence its behavior. There are many considerations that are the same as for both reed sensors and reed switches, such as electrical switching load, activation methods, etc. Fortunately, Littelfuse has much expertise in reed sensors and produces custom as well as standard reed sensors with high levels of quality and reliability. Depending on the type of mechanical shock, the damage can take the form of a loss of the hermetic seal, a change in sensitivity, or no operation due to glass capsule breakage.
There are several considerations in incorporating a reed switch into a sensor capsule, such as damage to the reed switch from mechanical shock and change in sensitivity due to mechanical stress. These packages offer resistance to mechanical stress by protecting the bare glass of the reed switch. However, for an application such as a door security sensor, the reed switch needs a protective shell/housing for handling and mounting. A bare reed switch can easily be mounted on circuit boards. These sensors are typically mounted in mechanical systems. Reed sensors are reed switches that are packaged within an external housing for simplified mounting/connecting and additional protection against environmental influences. Options include standard surface mount reed switches, custom cropping & forming of leads, modifications to existing standard products, and fully custom products. Since Littelfuse manufactures both standard and custom reed sensors and relays, applications can very often benefit from our engineering expertise, production capabilities, and quality systems to provide parts in a cost-effective and timely manner. Reed switches are the major component in reed sensors as well as reed relays. Littelfuse reed switches are sealed with an inert nitrogen atmosphere inside the switch. That is, gas-tight glass-to-metal seals prevent the contacts from being exposed to the environment. The electrical contacts in a reed switch are hermetically sealed. This is a “break-before-make” switch in that the closed contact opens before the open contact closes. This is also known as a changeover switch or a SPDT switch. By adding an additional nonmagnetic contact that is electrically closed with no magnetic field present, a Single-Pole, Double-Throw switch can be made. The basic reed switch is a Single-Pole, Single-Throw – Normally Open switch, also known as a SPST-NO or Form A switch. The contacts open when the external magnetic field is reduced so that the magnetic attractive force between the reeds is less than the restoring spring force of the reeds. Poles of opposite polarity are created at the contact gap and the contacts close when the magnetic force exceeds the spring force of the reeds. The two reeds act as magnetic flux conductors when exposed to an external magnetic field from either a permanent magnet or an electromagnetic coil. The nickel-iron leads are tin plated so that they can be soldered. The overlap or contact area of the reeds is coated with special metals such as ruthenium. The reed ends are carefully aligned with a small overlap and then permanently sealed inside the glass capsule. The two wires are formed into "reeds" by flattening one end.
The basic reed switch consists of two ferromagnetic nickel-iron wires and a glass capsule.