Definition of relay: A relay is an automatic control device that changes the output when the input quantity (electricity, magnetism, sound, light, heat) reaches a certain value.
The working principle and characteristics of the relay
An appliance that turns the controlled output circuit on or off when the input amount (such as voltage, current, temperature, etc.) reaches a specified value. It can be divided into electrical quantity (such as current, voltage, frequency, power, etc.) relays and non-electrical (such as temperature, pressure, speed, etc.) relays. It has the advantages of fast action, stable operation, long service life and small volume. Widely used in power protection, automation, motion, remote control, measurement and communication devices.
A relay is an electronic control device that has a control system (also called an input loop) and a controlled system (also called an output loop). It is usually used in an automatic control circuit. It actually uses a small current to control the larger. An "automatic switch" of 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 relays are generally composed of a core, a coil, an armature, a contact spring, and the like. As long as a certain voltage is applied to both ends of the coil, a certain current flows through the coil, thereby generating an electromagnetic effect, and the armature absorbs the tension of the return spring against the tension of the return spring under the attraction of the electromagnetic force, thereby driving the armature. The moving contact is in contact with the stationary contact (normally open contact). When the coil is de-energized, the electromagnetic suction force also disappears, and the armature returns to the original position in the reaction force of the spring, so that the movable contact and the original static contact (normally closed contact) are attracted. In this way, the suction and release are achieved, thereby achieving the purpose of turning on and off in the circuit. For the "normally open, normally closed" contacts of the relay, it can be distinguished as follows: a static contact that is in an open state when the relay coil is not energized, called a "normally open contact"; a static contact that is in an on state It is a "normally closed contact".
2. Working principle and characteristics of thermal reed relay
The thermal reed relay is a new type of thermal switch that uses temperature sensitive magnetic materials to detect and control temperature. It consists of a temperature-sensitive magnetic ring, a constant magnetic ring, a reed switch, a thermally conductive mounting piece, a plastic substrate, and other accessories. The thermal reed relay does not use coil excitation, and the magnetic force generated by the constant magnetic ring drives the switching action. Whether the constant magnetic ring can supply the magnetic force to the reed switch is determined by the temperature control characteristics of the temperature sensitive magnetic ring.
3. Working principle and characteristics of solid state relay (SSR)
The solid state relay is a kind of four-terminal device with two terminals as the input terminals and the other two terminals as the output terminals. The isolation device is used to realize the electrical isolation of the input and output.
Solid state relays can be classified into AC type and DC type according to the type of load power supply. 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, and the photoelectric isolation type is the most.
Relay main product technical parameters
1, rated working voltage
Refers to the voltage required by the coil when the relay is working normally. Depending on the type of relay, it can be either an AC voltage or a DC voltage.
2, DC resistance
Refers to the DC resistance of the coil in the relay, which can be measured by a universal meter.
3, pull-in current
It refers to the minimum current that the relay can generate the pull-in action. In normal use, the given current must be slightly larger than the pull-in current so that the relay can operate stably. For the working voltage applied to the coil, generally do not exceed 1.5 times the rated working voltage, otherwise a large current will be generated and the coil will be burnt.
4, release current
It is the maximum current that the relay generates to release. When the current in the state of the relay is reduced to a certain level, the relay will return to the unenergized release state. The current at this time is much smaller than the pull-in current.
5, contact switching voltage and current
Refers to the voltage and current that the relay is allowed to load. It determines the size of the relay to control the voltage and current, and should not exceed this value when used, otherwise it will easily damage the contacts of the relay.
Relay test
1, measuring contact resistance
Use the resistance file of the universal meter to measure the normally closed contact and the dynamic point resistance, the resistance value should be 0, (the contact resistance value can be measured within 100 milliohms in a more precise way); and the normally open contact and movement The resistance of the point is infinite. This makes it possible to distinguish between a normally closed contact and a normally open contact.
2, measuring coil resistance
The resistance value of the relay coil can be measured by the universal meter R×10 Ω file to judge whether the coil has an open circuit.
3. Measure the pull-in voltage and pull-in current
Find adjustable power supply and ammeter, input a set of voltage to the relay, and serially connect the current meter in the power supply circuit for monitoring. Slowly increase the power supply voltage. When you hear the relay's pickup sound, record the pull-in voltage and pull-in current. For accuracy, you can try to average and try several times.
4. Measure the release voltage and release current
It is also connected test as described above. When the relay is pulled in, the power supply voltage is gradually reduced. When the relay is heard again, record the voltage and current at this time. You can also try to get the average release several times. Voltage and release current. Under normal circumstances, the release voltage of the relay is about 10 to 50% of the pull-in voltage. If the release voltage is too small (less than 1/10 of the pull-in voltage), it will not be used normally, which will threaten the stability of the circuit. The work is not reliable.
Electrical symbol and contact form of the relay
The relay coil is indicated by a long square symbol in the circuit. If the relay has two coils, draw two long square boxes. At the same time, the relay's text symbol "J" is marked in the long box or next to the long box. There are two ways to represent the contacts of a relay: one is to draw them directly on the long square side, which is more intuitive. The other is to draw the respective contacts into their respective control circuits according to the needs of the circuit connection. Usually, the same text symbols are marked on the contacts and coils of the same relay, and the contact groups are numbered. To show the difference.
There are three basic forms of relay contacts:
1. When the moving type (H type) coil is not energized, the two contacts are disconnected. After energization, the two contacts are closed. It is represented by the pinyin head "H" of the word.
2. When the breaking type (D type) coil is not energized, the two contacts are closed, and the two contacts are disconnected after power-on. It is represented by the pinyin head "D" of the hyphenation.
3. Conversion type (Z type) This is the contact type. This contact group has three contacts, that is, the middle is a moving contact, and one static contact is provided. When the coil is not energized, the movable contact and one of the static contacts are opened and the other is closed. After the coil is energized, the movable contact moves, so that the original disconnection is closed, and the original closed state is turned off, and the conversion is achieved. purpose. Such a set of contacts is called a changeover contact. It is represented by the pinyin head "z" of the "turn" character.