Page 145 - Programmable Logic Controllers, Fifth Edition - Mobile version

EXAMPLE 6-3
Figure 6-73 shows the sketch of a continuous filling opera- Hopper
tion. This process requires that boxes moving on a con-
veyor be automatically positioned and filled. PL Run
The sequence of operation for the continuous filling
operation is as follows: PL Standby

• Start the conveyor when the start button is momen-
tarily pressed. Solenoid PL Full
• Stop the conveyor when the stop button is momen- Level
tarily pressed. switch
• Energize the run status light when the process is
operating.
• Energize the standby status light when the process is
stopped.
• Stop the conveyor when the right edge of the box is Photo
first sensed by the photosensor. switch
• With the box in position and the conveyor stopped, Motor
open the solenoid valve and allow the box to fill. Filling
should stop when the level sensor goes true.
Start
• Energize the full light when the box is full. The full light
should remain energized until the box is moved clear Stop
of the photosensor. Figure 6-73 Sketch of the continuous filling operation.
Figure 6-74 shows the ladder logic program required for
the operation.

Inputs Ladder logic program Outputs
Stop Start Run
L1 L2
Stop Motor
Run

Start Run Standby Solenoid

Photo Level Photo Full Run

Full Standby
Level
Photo Run Motor
Full

Full

Run Level Full Photo Solenoid

Figure 6-74 Continuous filling operation PLC program.

126 Chapter 6 Developing Fundamental PLC Wiring Diagrams and Ladder Logic Programs

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