Q1. In order to prevent the greenhouses as they become too hot in the sunny weather, an automatic window can be installed. This opens automatically when the temperature reaches a pre-determined value. The higher the temperature, the more the opening becomes. Other than the heat generated by the sun, there is no external power source.

a) Research and describe how this method works.

b) Illustrate whether this is open or closed loop control, provide reasons to support your answer.

c) Represent the system with a proper block diagram.

Q2. The direct acting proportional pressure controller has a gain of 3, a range of 0-40 bar and is set up to control at 25 bar. When the measured value and the desired value are equivalent, the output signal is 60%.  Find out the input pressure needed to produce controller output values of 10% and 90%.

Q3.

a) A temperature control method consists of a first-order response with a step response time of 12 seconds. In choosing a temperature sensor for the control system for the method, for what maximum value of sensor time-constant would you be looking?

b) If your need is for a sensor appropriate for a heavy industrial application, with a linear characteristic, working in temperatures up to 300°C, what kind of sensor would you propose? Draw the symbol for the sensor and illustrate its interfacing circuit.