1 Working principle and characteristics of electromagnetic relays Electromagnetic relays are generally composed of iron core, coil, armature, contacts and so on. As long as a certain voltage is applied across the coil, a current flows through the coil, thereby generating an electromagnetic effect. The armature absorbs the tension of the anti-spring against the tension of the anti-spring under the action of electromagnetic attraction, thereby driving the dynamic contact of the armature. The point 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 under the reaction force of the spring, so that the movable contact is attracted to the original static contact (normally closed contact). This is sucked and released to achieve the purpose of turning on and off the power.
For the "normally open" and "normally closed" of the relay, it can be distinguished as follows; the relay coil is not energized into the open contact, which is called the "normally open contact", and the static contact is in the on state. It is a "normally closed contact".
2 The working principle and characteristics of the 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 dry spring is determined by the temperature control characteristics of the temperature sensitive magnetic ring.
3 Solid State Relay (SSR) Working Principle The solid state relay is a four-terminal device with two terminals as the output terminals. The isolation device is used to realize the electrical isolation of the input/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.
4 Current relay working principle and characteristics The current relay is a relay that turns the circuit on or off according to the magnitude of the current in the coil. The coil of the current relay is connected in series in the circuit. In order not to affect the working condition of the circuit, the current relay attracts fewer coils and the conductor is thick. When the coil current is higher than the set value, the relay is called an overcurrent relay; when it is lower than the set value, the relay is called It is an undercurrent relay.
When the overcurrent relay is in normal operation, the current through which the current coil passes is the rated value, so the generated electromagnetic force is insufficient to overcome the reaction elastic force; the normally closed contact remains closed, and when the current passing through the coil exceeds the setting value, the electromagnetic suction force is greater than The reaction spring pulls, the iron core attracts the armature, the normally closed contact is disconnected, the normally open contact is closed, and the overcurrent fine relay is mainly used for frequent and heavy load starting occasions, as short circuit and overload protection of the motor or main circuit, undercurrent relay Commonly used for loss of magnetic protection of DC motors and magnetic chucks.
5 Thermal relay working principle and characteristics Thermal relay is a protection circuit that uses the current thermal effect industry switching circuit, and is used as overload protection of the motor in the circuit.
The working principle of the thermal relay: When the motor winding is overloaded due to overload, the heat generated by the heating element is enough to bend the main bimetal, pushing the guide to the right to push the temperature compensation piece to rotate the push rod around the axis, pushing the touch The head link separates the moving contact from the static contact, so that the contactor coil in the motor circuit is discharged and the power is cut off, thereby protecting the utility.
The temperature compensation sheet is used to compensate for the influence of the ambient temperature on the operation accuracy of the thermal relay; it is made of a bimetal of the same type as the main bimetal.
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