Английский язык. Арланова Т.Л - 42 стр.

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42
Sensor Condition Control unit action
Door Door open Machine cannot start
Door closed Machine can start
We can link these conditions and actions as follows:
1 If the door is open, the machine cannot start.
2 If the door is closed, the machine can start.
3 Unless the door is closed, the machine cannot start.
We use unless when an action cannot or will not happen if a prior condition
is not true. In example 3, Unless means If... not. We can rewrite 3 as:
If the door is not closed, the machine cannot start.
Exercise 8. Complete these sentences using Unless and your knowledge of
engineering.
1 Unless the ignition is switched on. a car cannot…
2 Unless the pilot light is on, gas central heating will not…
3 Unless the diverter valve is switched to central heating, the radiators will
not…
4 Unless there is current flowing in the primary coil of a transformer, there will
be no current in the … coil.
5 Unless there is … in the cylinders, the petrol engine will not start.
6 Unless the doors are …, a lift will not operate.
7 Unless mild steel is painted, it will …
Exercise 9. Writing Explaining a diagram
Study this diagram of a pressure sensor. Explain how it works by linking each
pair of actions with appropriate time words.
1 A wash programme first starts.
It opens the valves to allow the water in.
2 The water level in the drum rises.
The air in the plastic tube is compressed.
3 The pressure rises.
The diaphragm moves upwards.

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