A weekend$-$only carpark has a variable capacity which ranges from $1$ to $9$ cars depending on the

numbers of spaces already occupied by monthly users. A sensor S$1$ counts the number of cars entering

the carpark and a sensor S$2$ counts the number of cars exiting the carpark. A gate solenoid $($G$)$ prevents

from cars entering the carpark when there isn$$t space available. An HMI installed at the entrance of

carpark provides relevant information to the user and offers system configuration functionalities while

in Service Mode.

Entrance

Exit

S$1$ G

S$2$

HMI

O

H

Figure $20$

Assume that the real application elements connect to the digital PLC inputs and outputs according to

the definitions from Table $1.$

Application Elements PLC Digital I$/$Os Assumptions

Entrance sensor S$1$ I$10\mathrm{.}6$ Input $=1$ when a car passes in front of the sensor

Exit sensor S$2$ I$11\mathrm{.}6$ Input $=1$ when a car passes in front of the sensor

Manual override O I$13\mathrm{.}7$ Input $=1$ when manual override is active

Through$-$beam height sensor H I$13\mathrm{.}4$ Input $=1$ if car height is above the limit

Gate solenoid G Q$5\mathrm{.}7$ Output $=1$ closes the gate

Table $1$

Develop and test a PLC solution that fulfils the following requirements:

$$ If the carpark reaches maximum capacity, then close the gate arm $($G $=1)$ and maintain it closed until

one or more parking spaces become available

$$ If the manual override function is active $($O $=1),$ then close the gate arm $($G $=1)$ and prevent it from

opening even if a vehicle approaches the entrance

$$ Use the HMI for:

$$ Informing the number of parking spaces currently available. Note: counter must not count

below $0$ or above $9$ even if in or out sensor is activated

$$ Greeting a user approaching the entrance with the message $$Welcome to Acme Carpark$$ and

displaying a virtual Green Light

RMIT University $|$ School of Engineering $|$ EEET$2105/$EEET$2388$ Industrial Automation

$13$ March $2024|$ Rev $6|$ Page: $13/21$

$$ Informing a user approaching the entrance with a blinking $(2$ seconds on$,2$ seconds off, repeat$)$

message $$Discount Rates Apply$$ if three or fewer cars are in the carpark

$$ Preventing a user approaching the entrance from entering the carpark if the vehicle is too high

$($H $=1)$ by maintaining the gate closed $($G $=1),$ showing the message $$Maximum Vehicle Height

Exceeded$$ and displaying a blinking $(4$ seconds on$,2$ seconds off, repeat$)$ virtual Red Light

$$ Advising a user approaching the entrance that the carpark is full by showing the message

$$Carpark Full$$ and displaying a virtual Red Light

$$ Entering in Service Mode via a virtual push$-$button

$$ In Service Mode, the HMI switches to a second screen which offers the possibility of entering a new

carpark capacity within the range $1$ through to $9.$ While in Service Mode, the HMI can be switched

back to Normal Mode by pressing a virtual push$-$button

Hint: For creating a second screen and navigating to and from it: on the organisation tree, go to Screen

$->$ Add new screen to create a second screen. From the Toolbox task card, choose Elements $->$

Button, and drag it to a location on the new screen. Right$-$click at the button and click Properties, and

on the Events tab, click Change $->$ Add Action and select Screens $->$ ActivateScreen, and on Screen

name, choose Root screen. Repeat these steps to insert a button in the Root screen to navigate to the

new screen.