PLC control three-phase ac motor and reversing control circuit is introduced Industrial control -

0 the introduction of PLC for output type transistor, the output unit to allow the work load power supply for DC 12 ~ 24 V, the standard method of direct drive AC contactor, pioneer can only ask in 12 ~ 24 V DC relay, reoccupy intermediate relay to bring AC 380 V load, thus makes the external connection become tedious, and because the traditional AC contactor for electromagnetic switch, the mechanical contact of the life and reliability of control system with PLC is far, significantly impedes the development of control system performance. Like this kind of load, therefore, we need to choose a more suitable relay to act as its controlled switching devices. 1 the characteristics of the solid state relay

solid state relay SSR is in recent years, the world's emerging control relay, the relay in a few milliamps of tiny signal can control the start and shut off of power load, are in accordance with the characteristics of the transistor output type PLC. And the input signal, Control point) And the output signal, Controlled side) Adopts photoelectric isolating circuit, ensure the noninterference input and output, the output end USES contactless power output circuit, the circuit with epoxy resin casting as a whole. Therefore, solid state relay run time no spark, no noise, no pollution, do not produce electromagnetic interference, than electromagnetic relay switch speed, small volume, long service life, resistant to shock, anti-corrosive, moistureproof, anticorrosive, output in through the instant the advantages of no vibration phenomenon, can be used under the environment of serious pollution and vibration, more has the very high sensitivity and anti-interference ability, are widely used in petroleum chemical industry equipment, lighting equipment, textile machinery, CNC lathe, entertainment facilities and other automatic control field, especially in the bad environment, such as corrosion, dustproof, explosion-proof, and frequently switch places. The classification of solid state relay

2 ac solid state relays according to points have zero voltage switch way conduction type and random conduction type; According to the output switch components have a bidirectional thyristor output type ( Ordinary) And one-way thyristor parallel type ( Enhanced) ; According to the installation points of printed circuit board with a needle type ( Natural cooling, not with the radiator) The device type and fixed on the metal base plate ( On the radiator cooling) ; Other input and wide range input ( DC 3～32 V） The constant current source type and series resistance current limiting type, etc.

single-phase active SSR for four terminal device, two of the input control side, the two outputs, for light isolation between input and output, the input and dc or pulse signal to a certain value, the output end can shift from off state to state. And three-phase ac solid state relays are integrating three single-phase ac solid state relays, and directly as a single input of three-phase load switch, can easily control the l a phase ac motor, heater, such as three-phase load, figure 1 for three-phase ac solid state relays the basic wiring diagram. Three-phase ac solid state relays facies asked, between the input and output, as well as between substrate and insulation voltage is greater than 2, 000 VAC, other basic indicators and corresponding single-phase solid state relay is the same. It should be pointed out that the actual load current is not big occasions, such as laboratory teaching, three-phase SSR use rise more convenient, but high current when the heating is also big, then use three single-phase SSR is more reliable. 1 PLC control of the three-phase ac motor and reversing control circuit

figure 2 for PLC control of the three-phase ac motor and reversing control circuit, the X1, X2, X3, respectively the PLC input, control the direction of rotation of the motor and the start-stop; Y1, Y1 said the output of PLC. When Y1 effective SSR1 input dc signal by DC24V is three-phase output from the off state into a state, three-phase ac electric motor, inversion; With be effective, Y SSR2 three-phase output terminal connected, because of A, c, reversing the motor forward. 2 Y - PLC controller control Delta step-down starting control circuit

figure 3 Y - for PLC control Delta step-down starting control circuit, in which the X1, X2, respectively PLC input, control the start-stop of the motor; Y1, Y2, Y3 said the output of PLC. When Y1 and Y3 effectively, the corresponding SSR1 and SSR3 is effective at the same time, the motor of Y type connection, delay for a few seconds, Y3, Y2 effectively, the corresponding SSR3 three-phase output disconnect, SSR2 three-phase output end closed, the motor into a delta connection, completed a delta Y step-down starting.

3 conclusions three-phase ac solid state relays are integrating three single-phase ac solid state relays, directly as a single input of three-phase load switch, and can use a few milliamps of small signal to control the starting of large power load and cut off the switch devices. Verified, it can be reliable, safe and convenient to control three phase ac motor, heater, such as three-phase load, and makes the PLC wiring simple.

technology zone of PLC control of three-phase ac motor and reversing control circuit is introduced PLC controller used in process control system of the origin of the advantages of various kinds of electromagnetic interference in PLC control system of PLC used in the design of water supply system and the principle of Siemens PLC is used in the constant pressure water supply system is introduced in this paper
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