SYSTEMS PREPARATION QUESTIONS 2007 - 3
V. Ryan © 2007 -2017
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The railway barrier shown below has been designed and manufactured for a model railway system. The motor inside the post drives the barrier up and down. The motor is the output to a 555 timer circuit. |
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1. There are two types of 555 timer. What is the name of the 555 circuit shown below? |
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CIRCUIT NAME: ___________________________ | ||
ANSWER | ||
CIRCUIT NAME: 555 ASTABLE | ||
2. Label the components on the circuit diagram below (A TO G). | ||
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3. The relay is causing major problems because an important component is missing. Name the component and draw its symbol in the correct position on the circuit diagram above. |
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COMPONENT NAME: ___________________________ | ||
COMPONENT NAME: DIODE | ||
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4. What is the function of the component ? | ||
ANSWER | ||
The diode protects sensitive components such as the transistors from back E.M.F. When a current to a relay is removed the relay can emit current stored in its coils. This can be sent the wrong way round the circuit damaging components. The diode operates like a one way valve preventing this from happening. |
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A second version of the railway barrier has been manufactured. This is mechanically operated by a rotating device. |
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5. What is the function of the pivot ? | ||
ANSWER | ||
The pivot allows the barrier to rotate at a specific point. In this case the barrier rotates upwards and downwards about the pivot. |
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6. Draw the mechanical device on the diagram above. | ||
ANSWER | ||
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7. Name the device and explain how it works. | ||
NAME:____________________________ | ||
HOW IT WORKS: | ||
ANSWERS | ||
NAME: ECCENTRIC CAM | ||
HOW IT WORKS: As the eccentric cam rotates in a clockwise direction the barrier is pushed upwards at a constant rate. It then descends at a constant rate back to its original position. |
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8. What is the function of the barrier stop ? | ||
ANSWER | ||
The stop prevents the barrier from dropping below the horizontal. | ||
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