Introduction to Industrial Automation

Figure 7.72  Control of water level and dissolved chlorine of a swimming pool performed by a 

PLC.

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Basic Programming Principles of PLCs 

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343

According to the I/O connections of the PLC and the addresses listed, the required Boolean 

language program is as follows:

A

I1.0

AN I1.1

S

Q0.0

A

I1.3

R

Q0.0

AN I1.3

A

I1.0

=

Q0.0

A

I1.0

A

I1.1

AN I1.2

S

Q0.2

A

I1.2

R

Q0.2

AN I1.0

R

Q0.0

R

Q0.2

A

I1.3

AN I1.2

O

A

I1.3

AN I1.0

O

A

I1.2

AN I1.1

=

Q0.4

L

MW100

L

‘0.5’

< 

=

M3.0

L

MW100 

L

‘1.5’

> 

=

M4.0

A

I1.3

A

M3.0

=

Q0.2

A

M3.0

=

QX.X

A

M4.0

=

QY.Y

BE

Outputs QX.X and QY.Y are hypothetical that energize indications “Low Cl”

and “High Cl” correspondingly.  

Drilling machine automation. In Figure 7.73 a drilling machine is shown, for holes opening on 

objects A, which are manually placed by an operator. The machine has a movable cover to protect 

the operator from lubricating liquids, insertion of the hands, etc., during the operation of the drill-

ing head. In particular, the machine includes the following equipment:

C

1

 =  Cylinder that lowers or raises the chuck.

C

2

 =  Cylinder that lowers or raises the protective cover.

S

0

  =  Sensor detecting the lower position of the piston C

1

, that is, when the drilling has finished.

S

1

  =  Sensor detecting the presence of an object in the drilling position.

S

2

 =  Sensor detecting the lower position of the protective cover.

The stand-by control panel is the two-button control box with which the machine is set to a 

stand-by status, which means that it is ready for operation. Also, there is a light indicator express-

ing the “Stand-by ON” status.

The operation control panel is the two-button control box in a double function to start or stop 

the drilling procedure.

M = The motor of the drilling head rotation.

The following specifications are valid for the operation of the machine:

  1. The initial position of the two pistons is “up”.

  2. The machine can operate only if it is in “Stand-by ON” status, i.e., if the “Stand-by ON” 

button has been pressed and the readiness indicator lights up.

  3. Drilling can only be started if an object has been placed and has been detected by sensor S

1

.

  4. If there is an object in the drilling position and the two buttons “start drilling” are pressed 

at the same time (requires both hands of the operator for safety reasons), then the protective 

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344

 

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  Introduction to Industrial Automation

cover (activation of the relay C

2

) starts to lower. If the two buttons are released, the cover 

returns to its original position.

  5. When the protective cover is brought to its final position, it is detected by sensor S

2

 and then 

the piston C

1

 (activation of the relay C

1

) starts to lower, while simultaneously the drilling 

head (M) starts its rotation. In this phase, we do not have to press the two “start drilling” 

buttons because the protective cover has already been lowered.

  6. Piston C

1

 and the drilling head press down on the object until drilling is complete. This is 

established by the sensor S

0

 activation.

Base

Α

S

2

S

1

S

0

C

2

C

1

Protective cover

Left hand

Right hand

Start drilling

Stop drilling

Stand-by

indication

Stand-by ON

Stand-by OFF

PLC

Inputs

Outputs

0 V

+24 V DC 

0 V

+24 V DC 

I0.0

Q4.1 

Μ

I0.3

I0.4

C

1

h

Q4.4 

Q5.1 Q 

5.4

STOP

START

C

2

STOP

START

STOP

START

S

0

S

1

S

2

I0.1

I0.2

I0.5

I 2.0

I2.1  I2.2

Stand-by

Left hand

Right hand