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SYSTEMS PREPARATION QUESTIONS 2007 - 3 |
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V. Ryan © 2007 -2017 |
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PDF FILE - CLICK HERE FOR PRINTABLE WORKSHEET |
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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: ___________________________ |
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ANSWER |
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CIRCUIT NAME: 555 ASTABLE |
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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: ___________________________ |
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COMPONENT NAME: DIODE |
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4. What is the function of the component ? |
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ANSWER |
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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 ? |
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ANSWER |
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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. |
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ANSWER |
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7. Name the device and explain how it works. |
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NAME:____________________________ |
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HOW IT WORKS: |
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ANSWERS |
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NAME: ECCENTRIC CAM |
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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 ? |
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ANSWER |
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The stop prevents the barrier from dropping
below the horizontal. |
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