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SYSTEMS PREPARATION QUESTIONS 2008 - 7

V. Ryan 2007

 

A roller coaster track has sets of points that allow carriages to transfer from one track to another (for routine maintenance). However, in winter points can freeze and this is extremely dangerous as a carriage can be easily derailed.
The block / systems diagram shows how a heating system works. This warms up points in freezing weather ensuring that they operate safely.

 
The ice sensing part of the circuit is shown below.
1. Which component acts as a sensor in this circuit ?
 
   
ANSWER
   
Component B - Thermistor
   
2. What does the component sense ?
 
   
ANSWER
   
The component senses a change in temperature
   
3. Which component is used to adjust sensitivity of the circuit ?
 
   
ANSWER  
     
Component A - Variable resistor  
   

4. The ice sensing circuit shown above can be altered to sense heat. In the summer the points can expand due to extreme heat. This can also be dangerous. To counter this problem a cooling unit is to be fitted to the points. Complete the next circuit by adding the heat sensor.

ANSWER
5. What is the name of component C shown in the heat sensing circuit above?
   
ANSWER
   
Component C is a diode
   
6. What is its function ?
 
 
 
   
ANSWER
   

To protect the circuits components form back EMF. When current to a relay is removed the relay can emit current, sending it round the circuit in the opposite direction. This can damage sensitive components such as transistors. The diode prevents this happening.

     

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