In this section of a factory, there is a bottle filling machine that fills the empty bottles
on a conveyor belt with liquid from this tank.
In this and the next lessons you’re going to learn how this machine works and how to
write a professional PLC program that fully controls this machine.
The components that I have for this machine include input devices and output devices.
The machine inputs include these momentary switches that I have here, this three position
selector switch here, and these three photo eye sensors.
For the purpose of controlling this machine by a PLC, these components are going to be
wired to the PLC input module.
The machine outputs include the conveyor belt motor, the drain valve, and these two signal
lamps here which are all going to be wired the PLC output module.
As you can see, this filling machine has three operation modes which are off, manual and
automatic.
These modes are determined by the three position selector switch here.
When I put the switch in the manual state, the machine is going to operate in the manual
mode and when I put the switch in the automatic state the machine is going to operate in the
automatic mode.
To be able to write a proper PLC program for this machine I need to know how exactly this
machine operates.
So let’s see how it works.
When the machine is in the manual mode and this switch is pressed, the motor rotates
in the clockwise direction.
As soon as I release the switch, the motor stops.
If I press the next switch, the motor rotates in the counter clockwise direction and stops
when I release the switch.
When this switch is pressed, the drain valve is going to be open and when I take my hand
off the switch, the valve will close.
So that’s how the machine operates in the manual mode now let’s see how it’s going
to operate in the automatic mode.
In the automatic mode, when the start switch is pressed, the motor rotates in the clockwise
direction.
When a bottle is seen in front of the sensor number 2, the motor is going to stop and this
valve will open for 7 seconds.
After 7 seconds, the valve is going to close and the motor will start rotating in the clock
wise direction.
This process continues until I press the stop switch at which time, the whole system will
shut down.
I have two additional photo eye sensors at the two ends of the conveyor belt.
Sensor number 1 is going to be used to count the number of the empty bottles on the conveyor
belt and the sensor number 3 is going to be used to count the number of the filled bottles.
There is also a RESET switch here.
This switch is going to be used to RESET the number of the bottles counted by the sensors
at the two ends of the conveyor belt.
This means the empty and filled bottles counted by the sensors will be set to zero when I
press this switch once.
As you can see, I have two signal lamps here as well.
These lamps are used to indicate whether the machine is in manual or automatic mode.
The “man” lamp will be lit in manual mode and the “auto” lamp when in automatic
mode.
Neither lamp will be lit when in the off mode.
Okay now you’re completely clear about how the machine should operate in both manual
and automatic modes but there are a few safety points that I need to take care of while I’m
writing a PLC program for this machine.