When the input quantity (such as voltage, current, temperature, etc. ) reaches the specified value, the controlled output circuit is turned on or off. Can be divided into electrical relays (such as current, voltage, frequency, power, etc. ) and non-electrical relays (such as temperature, pressure, speed, etc.). It has the advantages of fast action, stable work, long life and small size. Widely used in power protection, automation, sports, remote control, measurement and communication equipment.
Relay is an electronic control device, which has a control system (also called input loop) and a controlled system (also called output loop). Usually used in automatic control circuits, it is actually an "automatic switch" that controls a larger current with a smaller current. Therefore, it plays the role of automatic adjustment, safety protection and conversion circuit in the circuit.
1, working principle and characteristics of electromagnetic relay
Electromagnetic relay generally consists of iron core, coil, armature and contact reed. As long as a certain voltage is applied to both ends of the coil, a certain current will flow in the coil, thus generating an electromagnetic effect. Under the attraction of electromagnetic force, the armature overcomes the pulling force of the return spring and attracts the iron core, thus driving the moving contact of the armature to attract the stationary contact (normally open contact). When the coil is disconnected, the electromagnetic attraction disappears, and the armature will return to its original position under the reaction of the spring, so that the moving contact and the original static contact (normally closed contact) attract each other. In this way, it is attracted and released, so as to achieve the purpose of making and breaking the circuit. For the normally open contacts and normally closed contacts of relays, we can distinguish them as follows: the static contacts that are disconnected when the relay coil is not energized are called "normally open contacts"; Static contacts in the on state are called "normally closed contacts".
2. Working principle and characteristics of hot reed relay.
Thermal reed relay is a new type of thermal switch which uses thermomagnetic materials to detect and control temperature. It consists of a temperature-sensing magnetic ring, a constant magnetic ring, a reed switch, a heat-conducting mounting piece, a plastic substrate and other accessories. The hot spring relay does not need coil excitation, but the magnetic force generated by the constant magnetic ring drives the switch to act. Whether the permanent magnet ring can provide magnetic force to the reed switch is determined by the temperature control characteristics of the temperature sensing magnetic ring.
3. Working principle and characteristics of solid state relay (SSR)
Solid-state relay is a four-terminal device, two of which are input terminals, the other two are output terminals, and an isolation device is used in the middle to realize the electrical isolation of input and output.
According to the type of load power supply, solid state relays can be divided into AC type and DC type. According to the switch type, it can be divided into normally open type and normally closed type. According to the isolation type, it can be divided into hybrid type, transformer isolation type and photoelectric isolation type, with photoelectric isolation type being the most.
Second, the relay main product technical parameters
1, rated working voltage
Refers to the voltage required by the coil when the relay works normally. Depending on the model of the relay, it can be AC voltage or DC voltage.
2. DC resistance
Refers to the DC resistance of the coil in the relay, which can be measured by multimeter.
3. Pull-in current
Refers to the minimum current that relay can produce pull-in action. In normal use, the given current must be slightly larger than the pull-in current before the relay can work stably. In general, the working voltage applied to the coil should not exceed 1.5 times of the rated working voltage, otherwise a large current will be generated and the coil will be burned.
4. Discharge current
Refers to the maximum current that the relay produces release action. When the current in the pull-in state of the relay decreases to a certain extent, the relay will return to the non-energized release state. At this time, the current is much less than the pull-in current.
5, contact switching voltage and current
Refers to the voltage and current allowed by the relay to the load. It determines that the relay can control the voltage and current, and cannot exceed this value when it is used, otherwise it will easily damage the contacts of the relay.
Third, relay testing.
1, measure contact resistance.
Measure the resistance of normally closed contact and moving point with multimeter resistance file, and its resistance value should be 0; The resistance of normally open contact and moving point is infinite. This can distinguish which contact is normally closed and which contact is normally open.
2. Measure the coil resistance
The resistance value of relay coil can be measured by multimeter R×10Ω, so as to judge whether there is an open circuit in the coil.
3. Measure the pull-in voltage and pull-in current.
Find an adjustable regulated power supply and ammeter, input a set of voltages to the relay, and connect the ammeter in series in the power supply circuit for monitoring. Slowly raise the power supply voltage, and when you hear the pull-in sound of the relay, write down the pull-in voltage and pull-in current. In order to be accurate, you can try several times and take the average.
4. Measure the discharge voltage and current.
It is also a connection test as described above. After the relay is pulled in, the power supply voltage gradually decreases. When the relay is released again, write down the voltage and current at this time. You can also try several times to get the average discharge voltage and current. In general, the release voltage of relay is about 10 ~ 50% of the pull-in voltage. If the discharge voltage is too small (less than the pull-in voltage of110), it will not be used normally, which will threaten the stability of the circuit and make it unreliable.
Four, relay electrical symbols and contact forms
The relay coil is represented by a long square symbol in the circuit. If the relay has two coils, draw two parallel long boxes. At the same time, the literal symbol "J" of the relay is marked in or beside the long box. There are two representations of relay contacts: one is directly drawn on one side of a long box, which is more intuitive. The other is to pull each contact into its own control circuit according to the needs of circuit connection. Usually, the contacts and coils of the same relay are marked with the same characters, and the contact groups are numbered to show the difference. There are three basic forms of relay contacts:
1. When the movable (H-type) coil is not energized, the two contacts are disconnected, and when energized, the two contacts are closed. Represented by the combined pinyin prefix "h".
2. When the dynamically disconnected (D-type) coil is not energized, the two contacts are closed, and when energized, the two contacts are disconnected. It is represented by the phonetic prefix "d" of hyphen.
3. Conversion type (Z type) This is the contact group type. This contact group has three contacts, namely a moving contact in the middle and a static contact up and down. When the coil is not energized, the moving contact and one stationary contact are disconnected and the other is closed. After the coil is energized, the moving contact moves, so that the original disconnected contact is closed, and the original closed contact is in the disconnected state, thus achieving the purpose of conversion. Such a contact group is called a transfer contact. It is represented by the phonetic prefix "z" of the word "Zhuan".
Verb (abbreviation of verb) Selection of relay
1. Understand the necessary conditions first.
(1) The power supply voltage of the control circuit and the maximum current it can provide;
② Voltage and current in the controlled circuit;
(3) How many groups of contacts are needed for the controlled circuit? When selecting relay, the power supply voltage of general control circuit can be used as the basis for selection. The control circuit should be able to provide enough working current for the relay, otherwise the pull-in of the relay will be unstable.
2. After consulting relevant materials to determine the conditions of use, you can find relevant materials to understand the model and specification number of the required relay. If you have a relay at hand, you can check whether it works according to the data. Finally, consider whether the size is appropriate.
3. Pay attention to the volume of electrical appliances. If used in general electrical appliances, the small relay mainly considers the installation layout of the circuit board in addition to the volume of the box. For small electrical appliances, such as toys and remote control devices, subminiature relay products should be selected.
Development of relay technology
The rapid development of microelectronic technology, computer technology, modern communication technology, optoelectronics technology and space technology puts forward new requirements for relay technology, and the development of new technology and new technology will undoubtedly promote the development of relay technology.
The rapid development of microelectronics and VLSI also puts forward new requirements for relays. The first is miniaturization and flaking. For example, the military TO-5 (8.5× 8.5× 7.0 mm) relay encapsulated by IC has high vibration resistance and can make the equipment more reliable. Second, the combination of multi-function, compatible with IC and built-in amplifier, requires the sensitivity to be improved to microwatt level; The third is full curing. Solid-state relay has high sensitivity and can prevent electromagnetic interference and radio frequency interference.
With the popularization of computer technology, the demand for relays by microcomputers has increased significantly, and relays with microprocessors will develop rapidly. In the early 1980s, digital time relays made in America could be controlled by commands. With the development of the combination of relay and microprocessor, a compact and perfect control system can be formed. At present, industrial robots controlled by computers are growing at a rate of 3.5% every year. Now, the computer-controlled production system can produce all kinds of low-cost relays on one production line, and can automatically complete all kinds of operations and tests.
The development of communication technology is of far-reaching significance to the development of relays. On the one hand, the rapid development of communication technology has increased the application of the whole relay. On the other hand, because optical fiber will be the transmission artery of the information society in the future, with the advancement of optical fiber communication, optical sensing, optical computer and optical information processing technology, new relays such as optical fiber relay and reed switch optical fiber switch will appear.
Photoelectric technology will greatly promote the development of relay technology. In order to realize the reliable operation of optical computer, a bistable relay is developed.
In order to improve the reliability of space relay, it is expected to reduce the failure rate of relay from the current 0. 1PPM to 0.01ppm. . Manned space station requires 0.00 1PPM. The temperature resistance is above 200℃, the vibration resistance is above 490m/s, and it can withstand α -ray radiation of 2.32× 10(4)C/Kg. In order to meet the space requirements, it is necessary to strengthen the reliability research and establish a special production line with high reliability.
The development of new special structural materials, new molecular materials, high-performance composite materials, photoelectric materials, oxygen-absorbing magnetic materials, temperature-sensitive magnetic materials and amorphous soft magnetic materials is of great significance to the development of new magnetic latching relay, temperature relays and electromagnetic relays, and relays with new principles and effects will surely appear.
With the development of microelectronics and chip technology. Relays will develop in the direction of miniaturization and surface mounting, with two-dimensional and three-dimensional dimensions of only a few millimeters; At present, the size of relays produced by some international manufacturers is only 1/4 ~ 1/8 years ago. Because when the size of the electronic machine is reduced, a smaller relay is needed, and its height does not exceed the height of other electronic components. Communication equipment manufacturers are more eager for dense relays. A BA series ultra-dense signal relay produced by Fujitsu Komeize Company in Japan, the size of which is only 14.9(W)×7.4(D)×9.7(H)mm, is mainly used in fax machines and modems, and can withstand the fluctuating voltage of 3kV. The volume of AS series surface-mounted relays introduced by this company is only 14 (width) × 9 (depth) × 6.5 (height) mm. ..
The field of power relay especially needs safe and reliable relays, such as high insulation relays. The JV series power relay introduced by Fujitsu KOMIZE in Japan includes five amplifiers, which are designed with high insulation and small cross section, and the size is17.5 (w )×10 (d )×12.5 (h) mm. Due to the reinforced insulation system between the movement and the outer edge, the insulation performance reaches 5kV. The power consumption of MR82 series power relays introduced by NEC in Japan is only 200mW.
The relay is equipped with various circuits such as amplification, delay, contact jitter elimination, arc extinguishing, remote control and combinational logic, which can make it have more functions. With the breakthrough of SOP technology (small outline package), it is possible for manufacturers to integrate more and more functions. The combination of relay and microprocessor will have a wider range of special control functions, thus achieving a high degree of intelligence.
The rise of new technologies will promote the development of relays with different principles, different performances, different structures and different uses. Driven by the progress of science and technology, demand traction and the development of sensitive and functional materials, the performance of special relays such as temperature, radio frequency, high voltage, high insulation, low thermal potential and non-electric quantity control will be improved day by day.
Electromagnetic relay (EMR) has a history of 150 years since telephone relay was first used. With the development of electronic industry, especially the breakthrough of optical coupling technology in the early 1970s, solid-state relays have mushroomed. Compared with the traditional relay, it has the advantages of long life, simple structure, light weight and reliable performance. Solid-state relay has no mechanical switch, and has the important characteristics of high compatibility with microprocessor, high speed, shock resistance, vibration resistance and low leakage. At the same time, because the product has no mechanical contact and does not produce electromagnetic noise, there is no need to add resistors, capacitors and other components to keep silent. Traditional relays need these additional components, so traditional relays are often cumbersome and complicated, and the cost is high.
In the future, the market development of small sealed relays will focus on to-5 relays and 1/2 crystal cover relays compatible with IC. Military relay will accelerate the transfer to industry/commercialization. American military relay accounts for about 20% of the total relay. The general relay market continues to develop in the direction of small, thin and plastic packaging. Relays for small printed boards will still be the mainstream products in the development of general relay market, solid relays will be more widely used, and the price will continue to drop, and they will be closer to high reliability, small size, high surge current impact resistance and anti-interference performance. The reed relay market will continue to expand. The application fields and demands of surface-mounted relays will increase.
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