Introduction to Industrial Automation

Figure 7.64  The PLC controls the fullness of the parking lot.

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  Introduction to Industrial Automation

  1. By instantaneous pressing of the “Stand-by ON” button, the automation system is powered, 

and the escalator is ready to operate if someone approaches it.

  2. The readiness and hence the operation capability is removed by pressing the “Stand-by OFF” 

button.

  3. For the “Stand-by ON” status, a corresponding light indicator is activated.

  4. If the electric ladder is operating due to human presence, it stops immediately if the STOP 

button on the control panel is pressed, if one of the two emergency buttons at the entrance 

and exit of the ladder is pressed, or if the thermal overload switch of the motor is activated.

  5. If the escalator is in “Stand-by ON” status and a person is approaching, the activation of the 

photocell will cause the ladder to operate for 40 s, after which it will automatically stop.

  6. Successive arrivals of people will cause a reset to the 40-s operating time.

  7. During the maintenance period, it is necessary to operate the ladder manually. This is accom-

plished with the “momentary operation” button, which means that the ladder operates as long 

as the button is pressed, regardless of whether the system is in “Stand-by ON” status or not.

The escalator operation, based on the above specifications, is accomplished with the classic 

automation circuit shown in Figure 7.66. Two auxiliary relays and an OFF-delay timer are used. 

Relay C is the power relay that powers the motor of the escalator. Figure 7.67 shows the con-

nections of the I/O devices in the PLC and the corresponding programs in both LAD and FBD 

languages. In Boolean language, the program will have the following instructions:

A(

O

I1.0

O

M3.0

)

AN M4.0

=

M3.0

=

Q0.4

A(

O

I1.2

O

I1.4

O

I2.0

O

I2.2

O

I2.4

)

A

M3.0

=

M4.0

A

I2.6

A

M3.0

L

‘40 sec’

SF

T1

A

T1

=

M5.0

O(

A

M5.0

A

M3.0

)

O

I1.6

=

Q0.1

BE

The three programs do not constitute a perfectly direct translation of the classic automation circuit. 

For example, the logic coil M5.0 does not exist as an auxiliary relay in the classic automation circuit.

M

Stand-by ON

Stand-by OFF

Stand-by

indication

Momentary

operation

STOP

Push button

for emergency

stop 

Photocell

Control panel

Push button for

emergency stop