1. Applied Control Systems Underlying Principles
HL Sample Question
Applied Control Systems
Underlying Principles

2. Higher Level - Option 1 Question 1(a) (i)
Microprocessors may be used to conserve energy in the home by:
Monitoring a central heating system.
Monitoring the use of internal and / or external lights.
Question 1(a) (ii)
When monitoring central heating systems microcontrollers can respond to heat sensors turning on or off control valves when and where required, opening or closing vents / windows / doors / heat blinds etc.
When monitoring internal or external light systems microcontrollers can respond to light sensors / motion sensors / timers to provide light when and where required.
Microcontrollers can also be found in washing machines / dishwashers
/ microwaves and many other household appliances where they offer
opportunities to monitor and respond to temp. time etc.

3. Higher Level - Option 1 Question 1(b) (i) Egg Timer flowchart
Operation:
1. Program flows to ‘Decision Command’
2. Continues to check for a digital input on input 1
3. When input 1 is high (switch pressed), the ‘Yes’ route is followed.
4. The program turns on a LED.
5. The LED remains on for 2.
6. The LED is then turned off.
7. Program flow returns to the ‘Decision Command’ and continues to check again for input 1 to go high i.e. ‘switch pressed?’

4. Higher Level - Option 1
Question 1(b) (ii)

5. Higher Level - Option 1 Question 1 (b) (iii) Digital signal:
A digital signal can be represented by a switch which is either on or off.
As a voltage signal, it is high at logic 1 (5 V), or low at logic 0 (0 V).
There are no in between values.
Analogue signal:
An analogue signal can vary continually between high and low values.
A voltage signal responding to changes in temperature is an example.

6. Higher Level - Option 1 Question 1 (b) (iii)
The potential divided circuit shown at A will provide a digital signal to a PIC.
When the switch is off, voltage out is equal to 0V or Logic 0.
When the switch is turned on, voltage will rise to the supply voltage, Logic 1
There are only two output voltage levels possible.

7. Higher Level – Option 1 Question 1 (c) (i)
Work Envelope
A Polar robot’s work envelope can be represented by part of a sphere.
The polar robot shown has three degrees of freedom. It has a prismatic arm providing linear motion. The arm can also rotate about it’s base and tilt up and down in a semi-rotational vertical motion.
This particular robot arm is often referred to as a ‘Gun Turrett’ type.

8. Higher Level – Option 1 Question 1 (c) (i) Work Envelope
A cylindrical robot’s work envelope can be represented by a cylinder.
The cylindrical robot shown has three degrees of freedom. It is able to rotate about its base, and has two prismatic joints providing two linear movements along the Z and Y axis.

9. Higher Level – Option 1 Question 1 (c) (ii)
Stepper motor operation is dependent on the operation of a number of electromagnets in a particular sequence.
Magnet (Rotor)
Electromagnets
Energised coils
The diagram shows how a basic motor works.
The magnet in the middle is joined to the motor shaft. The four magnets on the outside represent each coil of the stepper motor. As the coils are energised the centre magnet is attracted in different directions, N will attract S etc. Reversing current direction will alternate N, S, poles.
The correct sequence of pulses will achieve motor rotation.

10. Higher Level – Option 1 Question 1(d)(i)
Electro-pneumatic control interfaces electronic circuits with pneumatic components.
This offers the possibility of electronic feedback compared to pure pneumatic feedback.
Advantages:
Allows sensors etc. to be positioned further away from pneumatic components and provides faster feedback. A reduction in mechanical components used is also achieved – lower maintenance
Possible interface with computer control systems providing flexible design options.

11. Higher Level – Option 1 Question 1 (d) (ii)
Component A is a ‘Double Acting Cylinder’
Component B is a lever operated 5 port two stage valve.
The pneumatic circuit shows the double acting cylinder in a returned position. Compressed air enters the right side of the piston through port 1 & 2 while the left side exhausts through ports 4 & 5. Exhaust port 3 is blocked.
When the 5 port valve is operated by the right hand lever, compressed air will enter the left side of the piston through ports 1 and 4 while the right side will exhaust through ports 2 & 3. Exhaust port 5 will be blocked.
The piston will remain latched in this position until the 5 port valve is returned by the left hand lever.