In an ever-increasing automated environment, control systems are everywhere in our daily lives. The air-conditioning in our homes, automatic doors, traffic lights and now nearly all the products we consume pass through some sort of control system. Control systems have three basic principles at the core, INPUT, PROCESS, OUTPUT. The scale, quantity and algorithms within these three basic components determines the complexity of the system. A automatic supermarket door having just a few levels of input, a simple process and just one or a couple of outputs, compared the the Mars Opportunity Rover having a complex array of input, process and output devices and millions of lines of code running complex machine learning algorithms.
Where a simple electrical lighting circuit with a switch to turn a light on is not classed as a control system because it only has passive components to allow the flow of electricity by the press of a switch by a human to join the electrically conductive contacts and lacks the process stage. However, if a sensor was added to the system so the light would only switch on if the area is dark then this would become a very basic control system with the photo-resistor (or other light sensor) becoming the process part of the system.
Control systems often follow a closed-loop process. From being switched on to being switched off closed-loop systems constantly loop through the same process - A: (INPUT) Take an input reading - B: (Process) Check if the reading is within set parameters - C: (Output) Actuate any output needed - and repeat from A. The diagram below is a basic illustration of this closed-loop control of a supermarket door.
Basic pedestrian crossing system work by the following process control steps
STEP 1: The user presses the button to cross STEP 2: The system delays the changing of the lights (Approximately 30 seconds depending on the system) STEP 3: The lights change to RED for the cars and GREEN for the pedestrians to cross STEP 4: The lights hold this state for a pre-determined length of time STEP 5:The system goes back to idle mode and waits for the user to press the button (back to step 1)
However these systems are not very smart. Smarter pedestrian crossing systems have sensors and algorithms to allow for some of the following smarter decision making.
✓ If a pedestrian presses the button and there are not cars coming then the lights will change immediately ✓ If it is a busy school crossing time then, the lights will change quickly after the button is pressed even if there are cars coming ✓ If a pedestrian presses the button and there are cars very close to the lights but no cars in the distance approaching the lights, then the system allows for the first cars to pass before changing.
The system will monitor the person crossing or group size, for example if an elderly person is crossing slowly then the lights will give way to the pedestrian for longer.
This section looks at some real-world examples of control systems. You should be able to see that they all work from the same basic principles and these principles could be applied to answering an examination style question for any given situation.
