motorfwdpro

8/13/2019 motorfwdpro

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Motor forward and reverse direction control

using a PLC.

AIM

To achieve motor forward and reverse direction control using a PLC.

PROCEDURE

In our experiment, we wish to change the direction of motor rotation by

click of a push button, using a PLC.

Let us see the basic diagram of the circuitry:


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Ladder logic design

Now, let us see how the ladder logic of motor forward and reverse

direction control is implemented using a PLC.

Inputs to the PLC are:

Stop ( normally open push button )

Forward (normally open push button )

Reverse (normally open push button )

Outputs to the PLC are:

Motor forward circuit.

Motor reverse circuit

Forward (LED)

Reverse (LED)

Forward slow (LED)

Reverse slow (LED)

Note : Motor forward circuit (forwardmtr) and Motor reverse circuit

(reversemtr) is a circuit, which is connected to the motor, which changes

the supply polarity , which is fed to the motor. In return, changes the

direction of motor rotation.

Since the inputs and outputs are less, 8-point input module and 8

point output module is sufficient, where CPU resides in slot 0, input

module resides in slot 1 and output module in slot 2.

Let us assign the address for the input and output signals of the

PLC:

Stop (normally open push button ) : I:1/0

Forward (normally open push button) : I:1/1

Reverse (normally open push button) : I:1/2 Temp1(temporary variable) : O:2/0

forwardmtr ( Motor forward circuit ) : O:2/1

Temp2(temporary variable) : O:2/2

Forward (LED) : O:2/3

reversemtr (Motor reverse circuit ) : O:2/4

Reverse (LED) : O:2/5

Forwardslow (LED) : O:2/6

Reverseslow (LED) : O:2/7


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Let us see its ladder logic diagram:

Note : Here, the motors breaking is natural breaking. So when the

motors direction in changed, it cannot instantly change its direction.When motors supply is cut down, it will have a natural breaking, during

which its speed reduces and finally comes to rest. Our assumption is

that, the motor takes 7 seconds to completely stop. So when the motor

is instructed to change direction by the user, PLC cuts off its supply, till it

comes to rest and then, it changes its direction, using the direction

changing circuits ( forwardmtr, reversemtr ) . In order to be on the safer

side, an off-delay timer of 10 seconds ( greater than 7 seconds) is used,

to activate the motor direction changing circuits.


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c)

The above rungs are used for the reverse motor direction rotation.

d)

The above rung is executed when the motor is instructed to change

direction from reverse to forward, or from reverse to stop.

Documents

motorfwdpro