The contact of the relay is in the state of normally open or often closed, that is, the contact that the switch is often open or often turn the signal on or off is called the contact of the relay.
Contact point is one of the most important components of the electromagnetic relay. The performance of contacts is affected by factors such as contact material, contact pressure, load type, operating frequency, atmospheric environment, contact configuration, and beating. If any of these factors cannot meet the predetermined value, there may occur such as electrochemical corrosion of the metal between contacts, contact melt welding, wear, and rapid increase in contact resistance. The rated load of the contact refers to the voltage and current that the electromagnetic relay allows to break off. The size of the load determines the size of the electromagnetic relay to control the voltage and current of the electromagnetic relay. The electromagnetic relay should not exceed these two values during use, otherwise it will easily cause damage to the relay contacts.
What are the first few basic forms of the relay contact point?
1. When the dynamic composite type (H type) coil is not switched on, the two contacts are switched on, and after the power is switched on, the two contacts are closed. It is indicated by the pinyin prefix "H".
2. When the broken type (type D) coil is not electrified, the two contacts are closed after electrification. Use the broken word pinyin prefix "D".
3. Conversion type (type Z type) This is the contact group type. This group of contacts has three contacts, namely one in the middle, and one static contact up and down. When the coil is not energized, the moving contact and one of the static contacts are disconnected and the other is closed. After the coil is electrified, the moving contact will move, so that the original disconnected state is closed and the original closed disconnected state is closed to achieve the purpose of conversion. Such a group of contacts is called the transition contacts. Use the pinyin prefix "z" of the word "turn".
Knowledge and understanding of the relay contacts
Relay is a kind of electrical appliance that controls the open and breaking current in the circuit according to the electrical signal of the external person. It can be said that it is a "switch", and the current in the control circuit depends on the relay contact "open" and "closed"
The reliability and service life of the relay work depend to a large extent on the quality of the contact work, so it is necessary to understand and understand the contact of the relay in order to use it correctly.
The working process of relay contact has: disconnection process, disconnection state, closing process, closed state, the requirement of its work is to be reliable closing, broken. The contact resistance of the contact is the contact resistance of the contact. No matter how good the contact is, it cannot have no contact resistance, so the contact resistance of the contact exists objectively.
Relay contact contact resistance, when the current through the closed contact, because the relay contact contact resistance will consume a certain power (i. e., I 2 Rj), which will increase the contact temperature, if the current is larger, the contact temperature rise, will make the contact material softening, deformation, lead to contact resistance is bigger, serious even welding fault, make the closed contact can not be disconnected.
Another form of contact resistance is "membrane resistance". Because the contacts of the relay are exposed to the air for a long time, compounds produced by dust, water vapor and chemical gas will adhere to the contact to form a thin film, which is so called "membrane resistance"; the conductivity of the contact is very poor, not even in severe cases. This is sometimes seen in the use of the scene, although a relay contact surface looks closed contact, but it controls the circuit is blocked, or suddenly broken, good and bad, not only affected the normal work of the control circuit, but also make it difficult to find the fault point.
auxiliary relay
The factors affecting the contact resistance of relay contacts are: the size of contact pressure, the selection and use of contact materials, the form of contact structure, the manufacturing process of contact, the use environment of contact and the degree of daily maintenance, etc. For relay users, in addition to the correct selection, but also to ensure that the use environment of the relay meets the requirements. Make the relay to avoid as far as possible water vapor, dust, harmful gas erosion, to take measures to reduce the contact pollution, to ensure the stability of the contact resistance, so as to improve the reliability of the contact action.
The contact point in disconnected when the relay coil is not charged is called "active close contact", also called "normally open contact"; the closed contact when the relay coil is not charged is called "dynamic break contact", also called "normally closed contact". A moving contact is often closed with a static contact and often open with another static contact, so they are called "conversion contacts". In the same relay, there may be a pair or pairs of normally open or normally closed contacts (both simultaneously) or a set or array of conversion contacts.
On this basis, according to the needs of various circuits, many relay contacts with different structures are derived to meet different applications. For relays used in high altitude areas, the change of insulation and flow capacity must also be considered. The data show that the insulation level will be reduced by 10% for every 1000m elevation, and the air density also decreases when the altitude increases. Therefore, the heat dissipation of the relay should also be considered.
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