This assignment assesses Outcome 3 as listed below.

Outcome 1:
- evaluate the design characteristics of typical programmable logic control devices
- describe different types of input and output devices
- evaluate the different types of communication links used in programmable logic control systems
- describe the internal architecture of a typical programmable logic device
- describe the operational characteristics of the CPU.

Outcome 2:
- evaluate the different forms of signal used in programmable logic control
- describe the resolution and relationship between analogue inputs and outputs and word length
- express numbers using different number systems
- compare the typical protocols used in signal communication
- evaluate networking methods and networking standards
- write programs using logic functions based on relay ladder logic.

Outcome 3:
- evaluate methods of programming programmable logic controllers
- evaluate the range and type of advanced functions of programmable logic controllers
- demonstrate methods of producing and storing text and documentation
- use and justify methods of testing and debugging hardware and software
- identify elements associated with the preparation of a programmable logic controller program
- produce and demonstrate a programmable logic controller program of at least 50 instructions for an engineering application.

EXERCISE 1 - ANNUNCIATOR

In industry, plant conditions are monitored and, if there are problems, it is necessary to have some way of indicating such problems. An indicator system of this type is called an Annunciator. A typical alarm system uses the following sequence to indicate a plant alarm condition to an operator.

(i) System healthy - no indication.

(ii) System in alarm - a flashing Amber light and audible alarm. FIGURE 1 shows the graphics simulation of the alarm system.

FIG. 1 Annunciator Simulation

1. If the operator presses the ACCEPT button when the plant is in alarm (ii above), the audible alarm stops and the flashing Amber light changes to permanently ‘ON'.

2. If the plant drops out of the alarm condition before the ACCEPT button is pressed, the panel will show a flashing Green light. The Audible alarm and Amber light will go ‘OFF'.

3. If the ACCEPT button was pressed when the plant is healthy as in 2 above, the flashing Green light will go ‘OFF'.

4. There should be a LAMP TEST button which, when pressed, will light all lamps and sound the audible alarm.

5. Write a program that will operate the Alarm Simulation, using the following inputs and outputs and whatever Timers and Flags are required.

IP0 = Plant alarm condition OP0 = Amber Lamp

IP1 = Operator accept button OP1 = Green Lamp

IP2 = Lamp test OP2 = Audible Alarm

6. Use the comments facility to describe the operation of the program.

EXERCISE 2 - CAR PARK

FIG. 2 Car Park Simulation

Consider the above diagram, FIGURE 2, of the car park. The object of this assignment is to write a program to operate the barriers to allow the cars in and out.

As you can see there is a box in which there are two condition lights for when the car park is Full, and when there are Spaces.

The entrance to the car park is on the left hand side. When a car drives into the car park there is a sensor that detects the car and this should cause the barrier to be opened to allow the car in.

On the right hand side is the exit. When a car leaves the car park it will activate a sensor inside the park to open the exit barrier.

Both the entry and exit barriers will need to be in the Up position long enough to allow the cars to enter or leave the car park. The inputs and outputs are listed as follows:

IP0 = Entry Sensor OP0 = Entry Barrier

IP1 = Exit Sensor OP1 = Exit Barrier

OP2 = Full Light OP3 = Spaces Light

When writing the program it is necessary to observe the following conditions. When the car park is not full the Spaces light should be ‘ON'. When the car park is full the Full light should be ‘ON'. As a car enters or leaves the car park the entry and exit barriers have to be held in the Up position long enough to allow the cars to pass under the barriers.

When the program is complete and the car park graphic is displayed in Simulation mode the program is operated by pointing at the car and clicking the mouse button. You will see directional pointers left and right so point at and click the direction you wish the car to travel. When you wish a car to leave the car park point at the one you wish to leave the park and click. You should explain the operation of the program, using the documentation facility.