Motor

Motor

Diodes

The simplest way of describing a diode is ‘a non return valve’. The current will flow through the diode from the anode to the cathode, due to the construction of it though current cannot come back. Diodes are used to reduce the possibilities of ‘back feed’. This is where current comes through the circuit the wrong way for one reason or another. Below is the circuit symbol for a diode.

Light Emitting Diode (LED)

The light emitting diode (LED) works on the same principal as the diode. The main difference is that in the manufacturing process one of the materials is replaced by another. This replacement material has certain properties that when a certain voltage passes through it glows.

Transistor

A transistor in simplistic terms is a switch with no moving parts. The ‘switching’ is controlled by electronics and currents etc. rather than a physical switch being operated. Below is the circuit symbol for it. The example shown below is one of the most common basic type used called a ‘Bipolar’.

Field Effect Transistor (FET)

A field effect transistor (FET) is, in simplistic terms, a switch with no moving parts. The ‘switching’ is controlled by electronics and currents etc. rather than a physical switch being operated. The main difference between this and the type of transistor shown above is this one operates using a magnetic field.

Earth / Ground

For an electrical current to ‘flow’ around a circuit it has to start from a power source and go to an earth / ground. If there are any breaks in this circuit then current will not flow, this is called an ‘Open circuit’

There are 2 types of earth, Signal Earth and Chassis Earth, these are referred to sometimes as a Quiet Earth and Noisy Earth respectively.

Some sensors for example specify a Signal / Quiet Earth. While components such as pumps and motors can have a Chassis / Noisy Earth. The reason behind this is that pumps, motors and the like can generate ‘electrical noise’ by the way of their operation. Some of this ‘electrical noise can be transferred through wires, it is this ‘electrical noise’ that can have an adverse effect on sensor signals and affect the control readings.

Keeping Signal / Quiet and Chassis / Noisy earths separate reduces the effect of ‘electrical noise’ being transferred from component to component.

This symbol is a standard symbol for earths.

On the circuit diagrams some earths are shown as eyelets with the description of Earth-**** next to it, the earths also comply with the 4 digit C number. An example of this is shown below.