Systems 1&2 Practice Questions

Systems and Control - Practice Questions

Here are some extra questions to help you with Outcome 1 and 2 in the lead up to your NAB.  If you click on picture for the first question you can scroll through the pictures without seeing the answers. That way you can write your own answers and then check it later.

a) Closed loop control (continuous)
b) Negative Feedback
c) Error detector - to compare the actual temperature to the set temperature and send a signal to the control.  i.e. if the temperature is higher than the set level then a negative signal will be sent to the control, if the temperature is lower than the set level then a positive signal will be sent.
d) The desired temperature is set by the user.  The error detector then compares this set level to the actual temperature in the oven, sensed by the temperature sensor.  If it is too cold the error detector will send a positive signal to the control which will turn on the oven to heat up.  When it reaches the correct temperature there will be no difference between the set temperature and the sensed temperature and so the error detector will send a 0 signal to the control which will switch off the oven.  If it is too hot then the sensed temperature will be higher than the set temperature and the error detector will send a negative signal to the control which will keep the oven off.  This system of constantly monitoring the temperature will mean that the oven will maintain a constant temperature.
e) Thermistor

a) Open Loop Control

b)

a) Sequential Control - A series of events happen one after the other.  The end of one event signals for the start of the next.  So the green traffic light switching off will send the signal to switch on the amber light.

b) Continuous Control - This is a system where the input (temperature sensor) is sending information into the system all the time and the outputs (heater) are being controlled all of the time.  A change in the input directly results in a change in the output. In this example if it is sensed to be too hot, the heater will turn down, if it is sensed to be too cold the heater will be turned up, maintaining a constant temperature.

c) On/Off Control - The system can only ever be in one state: on or off, and nothing in between. This is the type of control used in the conveyor belt.  It will keep moving until a box is sensed and then the motor will switch off, stopping the belt.