What is a relay race? Concept, principle, application and function?

First, the working principle and characteristics of relay

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, these two contacts are open, and when energized, these 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. The contact group * * * has three contacts, namely the moving contact in the middle and the static contact at the top and bottom. 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 information to determine the conditions of use, you can find relevant information and find out 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.