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\title{Assignment 2 --- Understanding Control Systems \\
Unit 24 --- Controlling Systems Using IT \\
BTEC IT Practitioner Extended Diploma}


\author{Jake Moreman}
\affil{Affiliation not available}



\date{\today}

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\section{Types of Control Systems}

There are four primary types of control systems. Below are a set of sections explaining each of them in detail.

\subsection{Command System}

The command system type is the most basic and fundamental type. It is used for sending an instruction to another system. There is no feedback whatsoever. This means that it will never know if the sent command was acknowledged and understood by the receiving end.

This type also is part of the other control systems. An example of a command system could be a television remote control. i.e. When a button is pressed, a signal is sent to the TV or similar. That is the end of the communication.

\subsection{Programmable System}

Programmable systems have a similarity to command systems. The difference is that it runs a sequence of commands, not just one. The order of commands in the sequence is already predetermined and is part of it being {\it ``programmable''}.

An example of a programmable system could be a dishwasher. A set sequence on how the items are washed in the dishwasher are executed.

\subsection{Sensing System}

A sensing system works by monitoring the environment that it is in and executing a command or a sequence of commands when a certain environmental condition is met.

An example of a sensing system could be with outside lights turning on depending on the level of lighting.

\subsection{Conditional System}

Conditional systems work by executing certain commands depending on certain conditions.

An example of this could be a central heating system, where it turns the heating system on or off depending on the temperature in the rooms (or where the sensor is). There would also be a set threshold, which is used in determining when the heating should turn on and off.

Although this does appear to be a sensing system, it isn't. This is because there is more than one condition.

\section{Characteristics of Digital and Analogue Control Systems}
\label{sec:characteristics-of-digital-analogue-control-systems}

In this section I will be explaining the differences between digital and analogue control systems. As part of this an explanations of what digital and analogue signals actually are will also be included.

\subsection{Digital Control Systems}

A digital control system is one that can only make use of digital signals. Digital signals can only be of two values --- 0 and 1. One of the biggest examples of a digital control system is a micro-controller. The key characteristics that they have include:

\begin{description}

\item[Input/Output Ports] All digital devices will have specific ports for the flow of input and output to and from the device. Usually these will be represented physically on the device. Only digital signals can be used for these ports. The number of input and output ports will depend on the amount of data that will be processed, and how it is represented. For example if the output would be shown on a display and to a form of file storage, then many output ports will be required. Sometimes more ports than what is required are included for potential expansion.

\item[Memory] Digital devices will have some form of semiconductor memory. This is used for storing the data that is used for the task(s) the device performs, the actual procedure or program that it executes. The memory of the device is commonly represented in bytes. The actual size of the memory on the device will depend on the requirements. i.e. The bigger the software program and data it processes, the more memory it will need.

\item[Speed of the device] Every digital device will have a set speed in which it can complete the program. The actual speed will depend on a few factors. The main one being the clock speed of the microprocessor. The clock speed determines how many cycles of fetching the program code and executing it can take place per second. This is measured in hertz (Hz). 1 kHz = 1 clock cycle per second For every machine code instruction (low level programming), the execution requires two clock cycles. So, if the microprocessor clock speed is 800 MHz then 400 machine code instructions can be executed per second.

\end{description}

\noindent The main differences between a digital and an analogue system is the type of signals that are processed or used by it. This obviously means that a digital system uses digital signals and analogue systems use analogue signals. Please see section \ref{sec:characteristics-of-digital-analogue-control-systems} for an in-depth explanation regarding what the difference between analogue and digital signals.

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