Electrical systems and circuits The systems approach

What is a system?

The system is a word used to describe a collection of related components, which interact as a whole. A motorway system, the education system, and computer systems are three varied examples. A large system is often made up of many smaller systems, which in turn can each be made up of smaller systems and so on. shows how this can be represented in a visual form.

One further definition of a system: ‘A group of devices serving a common purpose’. Using the systems approach helps to split extremely complex technical entities into more manageable parts. It is important to note, however, that the links between the smaller parts and the boundaries around them are also very important. System boundaries will also overlap in many cases.

The modern motor vehicle is a very complex system and, in itself, forms just a small part of a larger transport system. It is the ability for the motor vehicle to be split into systems on many levels that aids both in its design and construction. In particular, the systems approach helps to understand how something works and, furthermore, how to go about repairing it when it doesn’t.

Open-loop systems

An open-loop system is designed to give the required output whenever a given input is applied. A good example of an open-loop vehicle system would be the headlights. With the given input of the switch being operated, the output required is that the headlights will be illuminated.

This can be taken further by saying that input is also required from the battery and a further input of, say, the dip switch. The feature that determines that a system is an open loop, is that no feedback is required for the system to operate.

Closed-loop systems

A closed-loop system is identified by a feedback loop. It can be described as a system where there is a possibility of applying corrective measures if the output is not quite what is desired. A good example of this in a vehicle is an automatic temperature control system.

The interior temperature of the vehicle is determined by the output from the heater, which is switched on or off in response to a signal from a temperature sensor inside the cabin. The feedback loop is due to the fact that the output from the system, i.e., temperature, is also an input to the system. This is represented.

The feedback loop in any closed-loop system can be in many forms. The driver of a car with a conventional heating system can form a feedback loop by turning the heater down when he or she is too hot and turning it back up when cold. The feedback to a voltage regulator in an alternator is an electrical signal using a simple wire

Cable is available in stock sizes and Table

Last word

lists some typical sizes and uses. The current rating is assuming that the cable length is not excessive and that the operating temperature is within normal limits. Cables normally consist of multiple strands to provide greater flexibility.

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