A control system uses sensors to monitor conditions, a microprocessor to process input data and compare it to preset values, and outputs to regulate the condition. Common examples are central heating, air conditioning, and refrigeration systems which use temperature sensors, microprocessors to turn heating/cooling on or off to maintain the set temperature, and fans or compressors as outputs. Control systems operate continuously and automatically but have disadvantages like cost, reliance on computer functioning, and inability to react flexibly like humans.

1. How organisations use ICT Control Systems By the end of this presentation you should be able to answer the following questions: What is a control system? Explain how an air conditioning system, refrigerator and central heating system works Describe the advantages and disadvantages of a control system

2. What is a Control System? Computer Control: Uses a computer to control the action or movement of an object. Control System: uses a computer or microprocessor to control certain physical conditions, either by keeping them over a length of time or varying them according to pre-set values

3. Control Systems Input device: Sensor A sensor is something which can measure physical quantities in the surrounding environment. Examples: heat sensor which measures the temperature in a room or a pressure sensor which senses when someone has walked over it. Once sensors have taken a reading or measurement, they might send that reading straight back to the computer or they may store it up and take a set of readings over time and send them back in a batch.

4. TASK: Types of sensors Touch Tilt Sound Smoke Pressure PH Light Infra-red Humidity Heat Where Used Measures Sensor

5. Types of sensors Computer controlled robots Detects if one object bumps into another Touch Windows in security alarm system Angle of tilt Tilt Security alarm systems Levels of sound Sound Offices Smoke in the atmosphere Smoke Burglar alarm systems, automatic doors Pressure Pressure Environmental experiments, river pollution Acid/alkali levels e.g. pH of soil PH External security lights Light levels Light Security alarm systems Infra-red radiation e.g. body heat Infra-red Swimming pool, greenhouse Water vapour in the air Humidity Living room for central heating system Temperature Heat Where Used Measures Sensor

6. ADC Most sensors take analogue measurements. This means that the measurement can have a wide range of values or be on a continuous scale. 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. The ADC is connected between the sensor and the computer’s input-output port and it is called an ‘interface’.

7. Process 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.

8. Example: central heating systems The system is set to keep the room at a constant 22 ° C. The sensor will take regular temperature readings in the room and send the readings back to the computer. The computer will then process the data to see if it matches the ideal 22 ° C. If it is lower e.g. 20 ° C, then the computer will need to identify the correct response (e.g. the heating must be turned on). If it is equal or above 22 ° C then the computer must identify the correct response (e.g. the heating must be turned off). This stage is called processing . The computer can only follow the rules that it has programmed into the control system, it cannot make its own decisions.

9. Output Once the processing has taken place and a decision has been made, the computer will send the correct signal to the output device. Example: for a central heating system, this might be to turn the heating on or off. For a greenhouse watering system this might be to turn the sprinklers on or off.

10. Open loop systems There two types of computer control system: Open loop system Closed loop system/feedback system Open Loop System: only looks at its input signal in order to decide what to do. It takes no account at all of what is happening to its output. Examples: 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.

11. Closed loop systems Most control systems carry on working continuously, they don’t just stop after one decision has been made. Example: central heating system The sensor takes a reading of 20 ° C and sends it to the computer. The computer processes this and sends a signal to the central heating to switch on. The sensor takes a reading of 21 ° C and sends it to the computer. The computer processes this and sends a signal to the central heating to remain switched on. The sensor takes a reading of 22 ° C and sends it to the computer. The computer processes this and sends a signal to the central heating to switch off. The sensor takes a reading of 21 ° C and sends it to the computer. The computer processes this and sends a signal to the central heating to remain switched on. This cycle of taking one reading and responding to it, then taking another reading and responding to it is known as ‘Feedback’.

12. Control examples Air conditioning systems Central heating systems Refrigeration Car manufacture Medical applications Process control – Batch / Continuous / Discrete

14. Air conditioning systems 1 Air conditioning systems require the use of sensors to monitor temperature ( input ). Temperature values from the sensor are then compared with a preset value by the microprocessor ( process ). Microprocessor then makes the air conditioning fan motor unit speed up or slow down by means of an actuator ( output ).

15. Air conditioning systems uses Air conditioning systems are often used in warm climates, especially in: Computer rooms Homes Offices Cars Shops Other public places

16. Refrigeration systems Inputs Temperature sensor Contact switch on door Number pad / Wheel for temperature required Process Microprocessor compares current temperature with the set value Timer calculates how long the door has been open Output LED showing temperature status Warning buzzer if door is left open Actuator turns the compressor on/off – changing the temperature

17. Refrigeration Systems 2 The compressor compresses the refrigerant gas. This raises the refrigerant's pressure and temperature (orange), so the heat-exchanging coils outside the refrigerator allow the refrigerant to dissipate the heat of pressurization. As it cools, the refrigerant condenses into liquid form (purple) and flows through the expansion valve. When it flows through the expansion valve, the liquid refrigerant is allowed to move from a high-pressure zone to a low-pressure zone, so it expands and evaporates (light blue). In evaporating, it absorbs heat, making it cold. The coils inside the refrigerator allow the refrigerant to absorb heat, making the inside of the refrigerator cold. The cycle then repeats. A: Inside a refrigerator B: Compressor C: Expansion Valve

18. Refrigeration systems uses Different sizes of refrigeration machines and different temperatures would be required in Supermarket chillers Freezers Wholesale butchers Breweries

19. Advantages of Control Systems Can operate 24 hours a day without taking a break. Can work without holidays or sick days Will work without any wages. Will repeat actions over and over and over again Can process data from sensors very quickly Can take account of hundreds of inputs at the same time Can make reliable and accurate decisions Can be used in dangerous or awkward environments where it wouldn't be a good idea to send humans to.

20. Disadvantages of Control Systems The software for the control system is specialist and may cost a lot of money to develop If the computer malfunctions the system will not work If there is a power cut the system will not work The computer can’t react to unexpected events like a human could. It can only respond in the way it has been programmed to. It can cause some concern if total control for a system and the decisions are handed over to a computer.

21. Questions What is a control system? Name 2 types of control systems Describe how a central heating system works Describe the advantages and disadvantages of a control system

22. Vocabulary – Time to fill in your electronic vocabulary list Control system Sensor Closed loop system Open loop system ADC Feedback: is where the output of a system affects the input.

23. Next lesson Exam question A computer company uses robots in their assembly line however because there could be a danger of the robots overheating the company wants to introduce a computerised air conditioning system. Describe how this system would work. Marks 3

24. Answer Sensors are needed to monitor temperature (continuously) Microprocessor compares the temperature with a preset value/range Depending on result microprocessor causes the fan motor to speed up or slow down/fan motor switched on or off

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