Английский язык. Арланова Т.Л - 40 стр.

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40
The control unit is the heart of the system. It receives and sends out signals
which control all the activities of the machine. It is also capable of diagnosing
faults which may occur, stopping the program, and informing the service
engineer what is wrong. It is a 30 small, dedicated computer which, like other
computers, uses the language of logic.
Source: P. Fowler and M. Horsley, 'Control systems in the home', CDT:
Technology
Exercise 4. Read the following text to find the answers to these questions:
1 What device is used to lock the door?
2 What provides feedback to the control unit about the door position?
Text 1
Door position
The machine will not start any program unless the door is fully closed and
locked. When the door is closed, it completes an electrical circuit which heats
up a heat-sensitive pellet. This expands as it gets hot, pushing a mechanical
lock into place and closing a switch. The switch signals the control unit that
the door is closed and locked. Only when it has received this signal will the
control unit start the wash program.
Exercise 5. Read the following texts and complete the table.
Control factor Operating device Feedback by
1 Door position heat-sensitive pellet switch
2 Water level
3 Water temperature
4 Wash and spin times
5 Drum speeds
Text 2
Water level
When a wash program first starts it has to open the valves which allow the
water in. There are usually two of these valves, one for hot water and one for
cold. Each must be controlled separately depending on the water
temperature needed for that program. The valves are solenoid operated, i.e.
they are opened and closed electrically.
The rising water level is checked by the water level sensor. This is a pressure
sensor. The pressure of the air in the plastic tube rises as it is compressed by
the rising water. The pressure sensor keeps the control unit informed as to
the pressure reached and the control unit uses the information to decide
when to close the water inlet valves.
Text 3
Water temperature
The temperature sensor, a type of thermometer which fits inside the washer
drum, measures the water temperature and signals it to the control unit. The
control unit compares it with the temperature needed for the program being

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