Open Loop Control Systems

 

Electronic systems can take control of things for us and make decisions by themselves. For instance, when we are out and about using public transport, or going into shops or buildings, we often find that doors or barriers will open in front of us automatically.

For this to happen, an electronic system will have first needed to notice you are there. Special devices or sensors will have been positioned to do this. The system must be able to work safely and respond to individuals or groups of people, walking slowly or quickly. Having a suitable control element to the system is essential for it to work properly. In the example above, the system should only start to close, when the people going through are completely clear of the doors.


Systems can also detect things and not just people. For instance, when cash is put into a vending machine, it will check the correct amount has been entered. If that condition has been met, it will then serve the requested drink or food.

Modern cars use a great number of electronic systems controlled by a central computer...

In many types of vehicles, messages (or warning lights) come on to warn the driver when the brake pads are wearing out. They may be alerted when the tyres are under pressure too.

          

It is common for the heating to be regulated automatically. (This might require more sophisticated "closed loop" systems and you can read about these via the link on the left).

Parts of an Electronic Control System

Control systems are made up from smaller subsystems. These are often connected together in this linear arrangement known as an Open Loop control system.




"Open Loop" Control System Block Diagram


INPUT Subsystem(s)

These do the sensing for the electronic system and detect when something is happening or changing.

PROCESS (CONTROL) Subsystem(s)

These act on the information provided by the input subsystem(s) and then they make decisions and "instruct" something to happen. They might use a small number of discrete electronic components for simple decision making, or a high-powered microprocessor or microcontroller when things get a bit more complicated.

An easy decision would involve a simple instruction to turn an output subsystem on and off repeatedly.

OUTPUT Subsystem(s)

These are the final part(s) of the control system and may, for example, involve a door sliding open or an LED coming-on to warn us about something.

Test Yourself:

1, What are the three main parts of an open loop control system?

2, What is the control part of the system used for?

3, List any input sensors or detectors that you know about, or have seen.

4, List as many different types of output devices that can be part of a control system. (These may be electrical or mechanical).