A reed switch like this is normally open (NO) (normally off), unless a magnet is positioned right next to it, when it switches on, allowing a current to flow through it. Take the magnet away and the contacts—made from fairly stiff and springy metal—push apart again and return back to their original positions.
How does a magnetic reed switch work?
How Does a Reed Switch Work? The switching mechanism is comprised of two ferromagnetic blades, separated by only a few microns. When a magnet approaches these blades, the two blades pull toward one another. Once touching, the blades close the normally open (NO) contacts, allowing electricity to flow.
How do you test a magnetic reed switch?
Listen for the operation of the reed switch
When a reed switch is activated there is a low but audible click of the magnet drawing the reed switch’s contacts together. To test the reed switch using this method, you need to open the door or window and then close the door or window.
Where are reed switches used?
Reed switches are used in fluid level sensors for brake fluid reservoirs and to monitor motor oil levels. They are also used in speed sensors for engine control and power steering. Automatic door locks, air bags, parking brakes, seat, door, and hood proximity sensors also utilize reed switches.
How much current can a reed switch handle?
When selecting a reed switch for a specific application, one of several concerns is to determine how much load current the switch will be required to handle. If one is just switching a low-current signal, this is generally not a concern, as almost any reed switch can handle at least 100mA.
Why is it called a reed switch?
The reed switch is an electrical switch operated by an applied magnetic field. It was invented at Bell Telephone Laboratories in 1936 by Walter B. Ellwood. … The contacts are usually normally open, closing when a magnetic field is present, or they may be normally closed and open when a magnetic field is applied.
Is a reed switch a sensor?
A reed switch is a sensor that closes the circuit in the presence of a magnetic field. Reed sensors can be used in many applications where contactless on/off is required. However, reed switches can be fragile to use directly, hence this module can make it easier to handle and mount the sensor in various applications.8 мая 2020 г.
How do you activate a reed switch?
Although a reed switch can be activated by placing it inside an electrical coil, many reed switches and reed sensors are used for proximity sensing and are activated by a magnet. As the magnet is brought into the proximity of the reed sensor/switch, the device activates.
Why do reed switches fail?
Reed switches or relays eventually fail in one of three ways . They do not open when they should (usually called “sticking”), they fail to close when they should (“missing”), or their static contact resistance gradually drifts up to an unacceptable level .
How long do reed switches last?
Because a reed switch only has internal components that bend and the electricity is completely contained in the reeds and lead wires, it does not have a failure mode related to mechanical wear. With some electrical loads, the operating life exceeds 50 years and one billion switching cycles.
Do reed switches have polarity?
Just as your magnet may have two poles, the reed switch’s pair of ferrous contacts are also polarized. … The polarity and position of the magnet plays an important role in how your reed switch activates.
How do you protect a reed switch?
The reed switch contact can be protected with a series resistor calculated to reduce the surge. Alternatively, the filament can be kept warm by means of a bias current, again avoiding the high Inrush current.
What does Reed mean?
(Entry 1 of 6) 1a : any of various tall grasses with slender often prominently jointed stems that grow especially in wet areas. b : a stem of a reed. c : a person or thing too weak to rely on : one easily swayed or overcome.
How sensitive are reed switches?
The high-sensitivity range for a Hall-effect sensor, for example, is about 30 gauss typical. This means a reed switch can sense a magnetic target at two times the distance or more of a high-sensitivity Hall-effect sensor, offering higher design flexibility for those applications that require a large air gap.