Sequence Control Lesson

The basis of sequence control is relay control.Introduction to sequence control.Understanding relay control makes it easy to understand PLC programs.First I will explain the relay.


The above picture is a general relay.It is attached to the terminal block.So wiring can be fixed with screws.


The above picture is a from the side.The blue part is the coil.When a voltage is applied to the coil, the right contact is attracted.So the contacts will be stuck or separated. There are various kinds of coils.

I will explain with an painting.

The above painting is in normal condition.Contacts C and B are connected. And C and A are out. Supplies power to the relay.It is an AC voltage.

Then the coil attracts the contact.Contacts C and A are connected.And C and B are out.The point of contact between C and A is called "a-contact"(normal open). And the point of contact between C and B is called "b-contact"(normal close). C contacts are common.The part of A, B and C is called a terminal.

Relay is used as a terminal block.

The above painting is a general arrangement, almost the same for any manufacturer.The wiring diagram is written on the top of the relay. There are also numbers on the terminal block.Basically, the inside is a-contact.

I make an arrangement.

It is an electric sign.

Pressing the pushbutton switch will cause current to flow through the coil of the relay and the coil will operate.Relay contacts also operate.The light bulb will light up as the contact operates. Release the pushbutton switch, the contact also releases and the light bulb goes out.Actually this circuit is useless circuit meaningless.Originally you should light the bulb directly with the push button switch.

In this circuit, we changed the part of the bulb to LED.It is DC voltage for LED.Since the push button switch part is AC, LED can not be lit as it is. DC power is supplied to the LED circuit.Then operate the relay and light the LED.In this way, it is possible to change the voltage by a relay, or to operate a circuit of a different system. But yet this is not relay control.

I will explain the timer relay.Timer relay is basically the same as relay.You can change the timing at which the contacts operate arbitrarily.

There is a dial at the top of the timer relay.You can set the time with this dial. Temporarily set it to 1 second.Touch the push button switch and the contact will operate after 1 second.In other words, the lamp lights up in 1 second after pushing the push button switch.

Before explaining the relay control, we will explain signal input.I will explain how to input signals such as sensors to the relay.

Input signal

This is a Japanese reference books.

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