1. Classification by purpose, low-voltage electrical appliances are divided into control, the main electrical appliances, electrical protection, electrical distribution and implementation of electrical appliances.
2. According to the classification of executive function, low-voltage electrical appliances are divided into contacts and non-contact electrical appliances.
3. Classified by working principle, low-voltage electrical appliances are divided into electromagnetic and non-electrical control appliances.
4. Electromagnetic mechanism by attracting coil, core, armature and other parts.
5. Electromagnetic appliances are divided into DC and AC two categories, are made using the principle of electromagnets.
6. Knife switch wiring, the power into the line should be connected to the static side of the inlet side of the socket, the power equipment should be connected to the movable contact side of the outlet off.
7. The use of iron shell switch, the shell should be grounded to prevent leakage caused by electric shock accident
8. Contactor mainly by the electromagnetic system, contact system, and interrupter devices.
9. DC contactor does not produce eddy current and hysteresis loss, so do not heat.
10. Relay is a kind of automatic switching electrical control circuit according to the input signal to the outside world.
11. Compared with the relay and the contactor for switching small current control circuit and the protection circuit, so there is no relay arc extinguishing device, there is no main and auxiliary contact points.
12. The speed relay is mainly used for reverse brake control of cage induction motor.
13. The proximity switch is also called contactless travel switch.
14. Fuse mainly by the melt and melt-mounted fuse.
15. Circuit breaker is mainly composed of contacts, arc extinguishing system and release.
16. Common short-circuit protection appliances are fuses and automatic air circuit breakers.
17. Commonly used overload protection electrical thermal relay.
18. plc's hardware is composed of the host, I / O expansion module and a variety of external devices.
19. PLC's software system consists of system programs and user programs.
20. PLC process of the implementation process is divided into input sampling or input processing, program execution and output refresh or output processing three stages.
twenty one. Usually a PLC instruction consists of step number, mnemonic and part number of three parts.
twenty two. Relays in a PLC equivalent circuit are not actual relays, and they are often referred to as "soft relays" to distinguish them from actual relays.
twenty three. State transition diagram, each state provides: drive load, specify the conversion conditions, set a new state of the three functions.
24, low-voltage electrical appliances refer to the working voltage in _ DC 1500V or _ AC 1200V the following appliances.
25, according to the main contactor contacts by the type of current can be divided into DC _ contactor and AC _ contactor.
26, the relay contactor control circuit is composed of a variety of _buttons, limit switches, relays, contactors, fuses and other components, to achieve the electric drive system start, speed control, braking, reverse and other control and Protection, to meet the production process on the electric drive control requirements.
27, thermal relay is the use of current thermal effect principle to work on the protection of electrical, which is mainly used in the circuit as a three-phase asynchronous motor _ overload protection.
28, speed relay is mainly used as reverse brake control.
29, the time relay is used to achieve contact delay delay or open control _ _ electrical appliances.