Control Creating a System

Giving the orders When you design a system, it’s really important that you write about it in a way that other people can follow. Imagine you are designing a system to wash cars automatically. You need to make sure the cars will get clean but won’t get damaged. Sensors can help to make sure the car is in the right place and the brushes move over the car gently without damaging it.

A simple car wash might work like this:

Watching every move You would need to draw a flow chart to explain the order that things need to happen in.

Move water/brush bar over length of car Stop no no Raise exit barrier Car in position? yes Start button pressed? yes no Drying time over? yes Lower exit barrier Start Spray foam Dryer on Move water/brush bar over length of car Move bar back to original position

Things can only get better A system like this would be tested on a computer model first, with cars of lots of different sizes, to make sure it works with all of them. That’s cheaper than damaging real cars if things didn’t work!

When the system was tested for real, each part of the process would need to be watched. Are the cars clean enough? Perhaps they need more foam Are they dry enough? Do the heaters need to be on for longer? The system needs to be evaluated to see how well it does its job. It’s important to write down exactly what is happening – if someone needs to change the system later, they need to know exactly what is happening.

Summary When designing a system it must be well documented to enable others to make changes at a later date. The order of things in a system can be documented using a flow chart. A system needs to be tested and reviewed using a computer model first to ensure it works under all conditions. This is cheaper and safer than testing the real thing. The real system still needs to be tested after the computer model. What can I remember?