Reed switch proximity sensors, also known as reed switch or reed switch, is a magnetic special switch, is the reed relay and proximity switch of the main components. Reed swtich usually has two soft magnetic materials made of non-magnetic break when the metal reed contacts, and some also have a third as a normally closed contact reed. The reed contacts are enclosed in a glass tube filled with an inert gas (such as nitrogen, helium, etc.) or vacuum, and the reeds in parallel in the glass tube overlap and leave a gap or contact with each other to form a normally open Or normally closed contacts. Reed switch than the general mechanical switch structure is simple, small size, high speed, long working life; and compared with the electronic switch, it has anti-load impact capability and other characteristics, high reliability.
Working principle editor
The working principle of the reed pipe is very simple, the two ends of the overlap of the magnetizable reed, sealed in a glass tube, the two reed separated by only about a few microns, the glass tube filled with high purity inert gas , The two reeds are not in contact, and the applied magnetic field causes different polarities near the two reed end points, with the result that two different polar reeds will attract and close each other. This technology can be made into a very small size of the switching components, and the switching speed is very fast, and has a very excellent reliability. The orientation and orientation of the permanent magnets determine when and how many times the switch is turned on and off.
Reed work principle
Reed work principle
So that a changeover switch is formed such that when the permanent magnet is magnetized against the magnetic field formed by energizing the reed tube or the coil wound around the reed tube, the contact portion of the reed is attracted by the magnetic force, and when the attraction force is greater than the reed Of the elastic, the normally open contact will pull; when the magnetic force to a certain extent, the contact is reed to open the elastic.
A good electrical connection is achieved by plating a very thick non-magnetic noble metal with a contact portion of the two reeds. The low resistivity silver is more suitable as a coating material than the corrosion-resistant gold . The use of mercury vents, wet spring contacts must be used in pairs.
Two spring wires are made of ferroalloy.
Affected, the magnetic spring lead through the magnetic field must be ferromagnetic.
Three of the most popular materials of nature, easy to anneal to ferromagnetism: iron, cobalt and nickel.
The tip of the two reed contacts is plated or sputtered with rhodium, ruthenium or iridium.
Reed contact construction
Reed contact construction
For the outer package of a glass tube, the temperature expansion coefficient (TCE) is perfectly matched for the NiFe alloy.
The two ends of the glass tube are heated and the glass is melted to form a hermetic seal covering both ends.
During the glass sealing process, the glass chamber is usually filled with an inert gas (usually nitrogen) or a cavity, which may produce a vacuum and vacuum. The vacuum typically supports high voltage switches (over 1000 volts).
Pull-in (PI, Pull In) reed switch contact point close
Disconnect (DO, Drop Out) is to open the reed switch contact point
Most companies measure ampere-turns (AT) reed switches
“A” type (normally open)
When the magnetic field is present, the switch contact will close
“C” type (single stage, double vote)
The “C” type switch has a transfer type contact. When a magnetic field is applied, the common contact will be moved from the normally closed (N.C.) contact to the normally open (N.O.) contact.
Reed switch structure
Reed switch structure
Rhodium-plated contacts are most commonly used. This contact has a very stable working characteristic and a long working life from low load to heavy load because rhodium has high melting point and high hardness performance.
Mercury contact reed with non-beating operation characteristics, so no additional suppression of the beating circuit. They have high power switching capability, low and stable contact impedance characteristics and long service life characteristics. They can also be used for high inrush current switches.
Ruthenium has a higher hardness than rhodium. Rhodium-plated contacts have good mechanical wear and heat loss characteristics, but only for small load switches. Because of these characteristics of ruthenium, Hua Ren Electronics has successfully developed ruthenium oxide covered with rhodium or platinum above the double plating contacts. These double-plated contacts have very good switching characteristics from low load to heavy load.
Reed switch with the general relay the biggest difference is as follows:
The electrical and magnetic circuits use the same media (reed).
Since the switch and the coil are separated from each other, it can be driven by a permanent magnetic field, and it is extremely easy to carry out only when the contact portion is sealed.
According to the different characteristics of the reed tube according to the following classification:
Type A: It is a normally open reed switch. When the external magnetic field is applied, the contact is closed and, in normal condition, remains open.
Type B: is a normally closed reed switch. When the external magnetic field is applied, the contact is opened, and in the normal state, it remains closed.
Type C: Transfer switch type.
Non-self-retaining type: has the characteristics of the presence or absence of external magnetic field (monostable type).
Self-retaining type: Once active, even if the external magnetic field is removed, the original state (bistable) can be maintained.
Large: glass tube length 30 ~ 60mm, glass pipe diameter 3.5 ~ 6mm.
Medium: glass tube length 20 ~ 30mm, glass diameter 2.5 ~ 3.5mm.
Small: glass tube length 5 ~ 20mm, glass diameter 1.5 ~ 2.5mm.
In addition, for the shape of the reed, the structure of the contact portion, there are often different designs, but as long as the reed is used, it belongs to the range of the reed switch.
Advantages and Disadvantages of Editing
The advantages of the reed pipe is its small size, light weight, which makes them easy to install and inconspicuous. Because the operating switch is very small, and therefore no need for complex cam or crank, so there will be no metal fatigue phenomenon, to ensure almost unlimited life. And can be installed in a limited space, it is suitable for micro-equipment. Reed switches and suitable magnets are cheap and easy to obtain. The main part of the reed switch is a non-contact seal switch.
The switch components of the reed switch are sealed in an inert gas and do not come into contact with the external environment, thus greatly reducing the contact in the opening and closing process due to contact spark caused by contact oxidation and carbonation. And to prevent the external vapor and dust and other impurities on the joints of erosion. Long working life.
The reed is thin and short, has a high natural frequency, improve the contact of the breaking speed, the switching speed than the average electromagnetic relay 5 to 10 times faster.