Introduction to Industrial Automation

Figure 7.63  Conventional Y/

Δ

 automation circuit with two timers for implementation in a PLC.

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Basic Programming Principles of PLCs 

◾

 

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(defined in the program). It is also assumed that the initial number of cars at the beginning of the 

PLC operation is 350. With the reset button, the content of the counter can reset if required for some 

other reason, while the connections of the I/O devices to the PLC are shown in the same figure. The 

required Boolean language program has the following form:

A

I2.0

CU C7

A

I2.2

CD C7

A

I2.4

L

‘350’

S

C7

A

I2.6

R

C7

L

C7

L

‘950’

> 

=

Q0.4

L

C7

L

‘1000’

≥ 

=

Q0.1

BE

Electric ladder control. Figure 7.65 shows an escalator that can operate only when a person 

is approaching (and not permanently, as happens sometimes). The detection of the approaching 

person at the up-escalator is performed via a photocell. At the entrance and exit of the ladder 

there are, at appropriate points, two emergency STOP buttons for use by the public, so if any 

accident occurs during the operation, anyone can stop the movement of the ladder. In the space 

of the escalator machinery, there is a control panel with buttons and indicators for controlling the 

electric ladder during maintenance periods. Specifically, the operating specifications of the above 

installation are as follows:

PC

1

PC

2

PLC

Inputs

Outputs

0 V

Siren

+24 V DC

 

0 V

+24 V DC

Q0.1

I2.0

Q0.4

h

1

I2.2

I2.4

PC

1

PC

2

SET

RESET

I

2.

6