Analogue-to-Digital, Sonsors, Control & Monitoring

These are ICT notes from my ICT teacher. GOD BLESS HER!! Thanks to her, i might actually pass GCSE ICT :P:P:P hope these help. i was feeling nice

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  • Created on: 07-06-09 19:00
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Analogue to digital converters, sensors, control & monitoring
What is computer control?
Computer control means is using a computer to control the action or movement of an object.
This is often not done by a `computer' such as a desktop PC or laptop, it is often a processor or microchip.
A sensor is something which can measure physical quantities in the surrounding environment. An example
might be a heat sensor which measures the temperature in a room or a pressure sensor which senses when
someone has walked over it.
Once the sensor has taken a reading or measurement, it might send that reading straight back to the
computer or may store it up and take a set of readings over time and send the data back in a batch.
This data is called an `input'.
Most sensors take analogue measurements but all computers need digital data in order to be able to
understand it and process it. Digital data only has two values either 0 and 1 or On and Off.
In order for the data collected by the sensor to be understood by the computer, it needs to be converted
from an analogue signal to a digital signal. To do this, a special piece of hardware is needed called an
analogue-to-digital converter or ADC. This is called an `interface'.
Once the input data from the sensors has been received by the computer, it can then begin to process it.
The data will be compared against a set of rules which have been programmed into the control system and
a decision will be made.
For example, think about a heat control system in a greenhouse:
The system is set to keep the greenhouse at 25oC.
1. The heat sensor will take regular temperature readings in the room and send the readings back to the
2. The computer will then process the data to see if it matches 25oC.
3. If it is lower than 25oC the computer will need to respond to correct this e.g. turn a heater on
4. If it is higher than 25oC the computer will need to respond to correct this e.g. turn a heater off or open a
This stage is called processing. The computer can only follow the rules that are programmed into the
control system, it cannot make its own decisions.
Once the processing has taken place and a decision has been made, the computer will send the correct
signal to the output device - this is the output stage.
For the greenhouse, this might be to turn the heating on or off, open or shut a window or turn sprinklers on
or off.
There two types of computer control system:
1. Open loop system
2. Feedback system
Open loop system
An Open Loop System just looks at its input signal in order to decide what to do. It does not look at what is
happening to its output.
Examples of open loop systems:
a) You set the microwave oven to run for two minutes. After cooking for two minutes, the control system
turns the microwave off. It has no idea whether your food is still frozen, burnt or cooked perfectly.
b) You program the video recorder to start recording the football game at 7.30pm. However, because the
news program finished early, you miss the first vital 15 minutes of the match. Because the system is only
checking its input (time), it had no idea that the starting time of the match had changed.
Feedback system

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Most control systems carry on working continuously, they don't just stop after one decision has been made.
Take the example of the greenhouse system:
1. The sensor takes a reading of 23 degrees and sends it to the computer. The computer processes this and
sends a signal to the heating to switch on.
2. The sensor takes a reading of 24 degrees and sends it to the computer. The computer processes this and
sends a signal to the heating to remain switched on.
3.…read more

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Computer controlled lighting systems at discos and concerts
Advantages of computer controlled systems:
Can operate 24 hours a day without taking a break.
Can work without holidays or sick days
Will work without any wages.…read more

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Special software (data logging software) takes the data and analyses it
The results of the analysis are presented as graphs and tables
The results are printed out
Advantages of computer data logging:
Data Logging can be used in remote or dangerous situations
Data logging can be carried out 24 hours a day, 365 days of the year
Time intervals for collecting data can be very frequent and regular, for example, hundreds of
measurements per second
Data logging can be set up to start at a…read more

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READ temperature
IF temperature > 60
3) The temperature of the water in a fish tank is controlled using a computer connected through an
interface box to sensors and a heater.
a) The analogue data collected from the temperature sensor is converted into digital data for use by the
computer. Explain the differences between analogue & digital data with examples of their use.…read more

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