Definition of relay: relay is a kind of automatic control device whose output will jump when the input quantity (electricity, magnetism, sound, light and heat) reaches a certain value.
1、 Working principle and characteristics of relay
When the input quantity (such as voltage, current, temperature, etc.) reaches the specified value, the controlled output circuit is connected or disconnected. It can be divided into electrical quantity (such as current, voltage, frequency, power, etc.) relay and non electric quantity (such as temperature, pressure, speed, etc.) relay. It has the advantages of fast action, stable operation, long service life and small volume. It is widely used in power protection, automation, movement, remote control, measurement and communication devices.
It is usually used in the control system of electric current, also known as an automatic control circuit with larger current. Therefore, it plays the role of automatic regulation, safety protection and conversion circuit in the circuit.
Working principle and characteristics of electromagnetic relay
Electromagnetic relay is generally composed of iron core, coil, armature, contact spring, etc. As long as a certain voltage is applied to both ends of the coil, a certain current will flow through the coil, which will produce electromagnetic effect. The armature will overcome the pull of return spring and attract to the iron core under the action of electromagnetic force, thus driving the moving contact and static contact (normally open contact) of armature to pull in.
When the coil is cut off, the electromagnetic suction will disappear, and the armature will return to its original position under the reaction force of the spring, so that the moving contact and the original static contact (normally closed contact) are closed. In this way, the circuit can be connected and cut off. For the "normally open and normally closed" contacts of the relay, it can be distinguished as follows: the static contact in the disconnected state when the relay coil is not energized is called "normally open contact"; the static contact in the on state is called "normally closed contact".
Working principle and characteristics of thermal dry spring relay
The use of a new type of thermosensitive material for temperature sensing control of a magnetic relay. It consists of a temperature sensing magnetic ring, a constant magnetic ring, a reed tube, a heat conducting mounting piece, a plastic substrate and other accessories. The thermal dry spring relay does not need coil excitation, but the magnetic force generated by the constant magnetic ring drives the switch action. Whether the constant magnetic ring can provide magnetic force to the reed is determined by the temperature control characteristics of the temperature sensing magnetic ring.
Working principle and characteristics of solid state relay (SSR)
Solid state relay is a kind of four terminal device with two terminals as input terminal and two terminals as output terminal.
According to the type of load power supply, solid state relay 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, and the photoelectric isolation type is the most.
2、 Technical parameters of relay products
1. Rated operating voltage
It refers to the voltage required by the coil when the relay works normally. According to the type of relay, it can be AC voltage or DC voltage.
2. DC resistance
It 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 pull-in action. In normal use, the given current must be slightly greater than the pull-in current, so that the relay can work stably. The working voltage of the coil should not exceed 1.5 times of the rated working voltage, otherwise it will produce larger current and burn the coil.
4. Release current
It 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 UN energized release state. The current is far less than the pull-in current.
5. Voltage and contact switching
It refers to the voltage and current allowed to be loaded by the relay. It determines that the relay can control the size of voltage and current, can not exceed this value in use, otherwise it is easy to damage the relay contact.
3、 Relay test
1. Measuring contact resistance
When the contact point is less than 100, the resistance value can be measured with the resistance meter. It can be distinguished that the contact is normally closed and that contact is normally open.
2. Measuring coil resistance
The resistance value of relay coil can be measured with R10 universal meter to judge whether the coil has open circuit.
3. Measure the pull in voltage and pull in current
Find the adjustable regulated power supply and ammeter, input a group of voltage to the relay, and connect the ammeter in the power supply circuit for monitoring. Slowly increase the power supply voltage. When you hear the relay closing sound, record the pull in voltage and pull in current. For accuracy, you can try several more times to find the average value.
4. Measure the release voltage and current
The connection test is also conducted as above. When the relay is pulled in, the supply voltage is gradually reduced. When the release sound of the relay is heard again, record the voltage and current at this time, or try several times to obtain the average release voltage and current.
In general, the release voltage of the relay is about 10-50% of the pull-in voltage. If the release voltage is too small (less than 1 / 10 of the pull-in voltage), it can not be used normally, which will threaten the stability of the circuit and work unreliable.
4、 Electrical symbol and contact form of relay
The relay coil is represented by a rectangular box symbol in the circuit. If the relay has two coils, draw two parallel rectangular frames. At the same time, the text symbol "J" of relay shall be marked inside or beside the rectangular box.
There are two ways to express relay contacts: one is to draw them directly on one side of the rectangular box, which is more intuitive. The other is to draw each contact into its own control circuit according to the needs of circuit connection. Usually, the same text symbols are marked beside the contact and coil 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 dynamic closing (H-type) coil is not energized, the two contacts are disconnected, and after being electrified, the two contacts are closed. It is represented by the phonetic prefix "H".
2. When the dynamic break type (D type) coil is not electrified, the two contacts are closed, and the two contacts are disconnected after being electrified. It is represented by the phonetic prefix "d" of the hyphenated character.
3. Conversion type (Z type) this is the contact group type. This kind of contact group has three contacts, namely the middle is the moving contact, the upper and lower each static contact. When the coil is not electrified, the moving contact and one of the static contacts are disconnected and the other is closed. After the coil is electrified, the moving contact moves to make the originally opened one closed and the original closed into open state, so as to achieve the purpose of conversion. Such a contact group is called a change-over contact. It is represented by the phonetic prefix "Z" of "Zhuan".
5、 Selection of relay
1. First understand the necessary conditions:
① The power supply voltage of the control circuit, the maximum current that can be provided;
② Voltage and current in the controlled circuit;
③ The controlled circuit needs several groups and what form of contact. When choosing relay, the power supply voltage of general control circuit can be used as the basis of selection. The control circuit should be able to provide enough working current for the relay, otherwise the relay pull-in is unstable.
2. After consulting the relevant data to determine the service conditions, you can look up the relevant information to find out the model and specification number of the required relay. If the available information can be used to check whether the relay can be checked. Finally, consider whether the size is appropriate.
3. Pay attention to the volume of the appliance. If it is used for general electrical appliances, in addition to considering the volume of the cabinet, the installation layout of the circuit board is mainly considered for the small relay. For small electric appliances and toys, the remote control device should be selected.