ELEC4123: Electrical Design Proficiency
Topic 3: Control Systems Preliminary Notes
The Control Systems Design topic in this subject is spread over 3 weeks, with 2 lab sessions in Week 6 and week 7 and 1 lab session in Weeks 8. The topic might have 5 to 6 design tasks. Unlike previous topics, you need to work through the tasks in sequence as each coming task relies on the results of the previous tasks. Tasks may be assessed individually, or two tasks may be assessed together, but you should not expect to be able to get more than 2 tasks assessed in any given lab session.
Your performance in the design tasks will be assessed in the laboratory. As indicated in the course outline, this assessment is worth 25% of the marks for this course (including its reflective task), but your mark will be calculated out of 100 at the end. The mark breakdown for all tasks is as follows:
• 48 marks for achievement of design requirements, including soft objectives (12% out of the 25%).
• 44 marks for understanding (11% out of the 25%).
• 8 marks for reflection (2% out of 25% later submitted on Moodle).
• Neatness of the code/circuit.
o This item is a double-edged sword since it can work either as a bonus mark or reduce your mark if you do not write a code that can be easily read and followed by a third person (Be careful with it!), for example consistent use of variable names with standard format (like var_1 as variable 1 or varA as variable A, using proper structure in your code, initialization of variables at the beginning, proper use of comments in the code, etc.).
You should bring to the laboratory:
1. a breadboard.
2. a bound laboratory notebook
3. a small screw-driver for adjusting trimpots
4. a USB thumb drive that can be used to transfer files to/from the laboratory computers.
Some analog circuitry is required for the Control Design topic, in particular for creating the control input signal to the actuator which controls the device/setup, known as “control rig”, and perhaps for filtering the noise from measured data coming from the sensor. Other aspects of the topic, however, involve using the computer (MATLAB/Simulink and/or Arduino microcontroller), for which you may use either the Lab computers or your own laptop – you might need to use an external peripheral to ensure that line-in and line-out functionality are available on your own laptop.
The Control Rig
All of the Control design tasks are based on a custom-made control rig which have been modified for this iteration of the course for better performance. The control rig is in fact some sort of air levitation device using a computer fan as the main actuator to provide air flow to a slotted PVC pipe such that it can raise or lower a “floater” within the pipe. A new floater has been designed and 3D printed to work with an IR sensor attached on top of the pipe to be able to measure its distance with respect to the position of the sensor. You can easily remove the cap, which is 3D-printed to house the sensor, and insert the floater inside the pipe. The apparatus with its components is illustrated Figure 1. Specifications for the computer cooling fan that powers the rig as well as the sensor datasheet may be found on the Moodle (you can also find some important information about the sensor on its vender website here). The main objective of this topic is to control the height of the floater inside the pipe through controlling air flow of the fan which is a voltage-controlled actuator. More details on the device will be provided in Task 2.
The following rules apply to your use of the control rig:
1. You may not take the control rig out of the laboratory, but each rig has an ID that will be assigned to
you so that you use the same rig in each week. Lab demos will distribute the control rig in the first lab.
Original version created by Prof David’s Taubman.
Current version is heavily changed and updated by Dr. Page | 1 Arash Khatamianfar, Term 2, 2019
Topic 3: Control Systems
2. You must keep the control rig away from the bench edge to avoid risk of dropping it.
3. Marking, modifying or defacing any part of the rig is strictly forbidden. To mark positions along the
measure tape along the slot of the PVC pipe you must use the masking tape provided in the lab.
4. You can directly connect the GND and 12V terminal to the DC power supply and test your device for
any potential issue.
5. You must avoid exceeding the rated motor supply voltage of 12V DC.
6. Please treat the floater and the sensor carefully, particularly if you need to sand the floater (the plate
of the floater, which is designed to be detected by the IR sensor, can be damaged if you put too much
pressure on the plate of the floater), and don’t lose them!
7. If you notice the floater is not moving smoothly due to friction of its edges against the slot in the PVC
pipe, you can ask for a sandpaper and smooth out the edges if required (please note that the darg
effect is different with surface friction when the floater goes down).
8. You must be careful with the sensor if you want to test it at the same time with the rig. The wires of
the sensor are colour coded, i.e., the red wire is the power (between 4.5V-5.5V, see the datasheet), the black wire is the ground, and the white wire is the output analogue voltage. We highly recommend using the fix 5V channel of the power supply and use a parallel 10F or larger capacitor across power and ground of the sensor as recommended by the manufacturer (see he datasheet as well as the Sharing Equipment section in this manual). You can connect the white wire to the multimeter to see the output analog voltage as the floater gets close to the sensor or does away from it.
Sensor
PVC pipe
Power terminals for the fan
(PWM and hall-effect sensor terminals won’t be used)
Cap
Measuring tape
Floater
Cap with locking mechanism
Floater
Sensor
Sensor wires
Fan
ID number
Plate of the floater
(a)
Figure 1: (a) The control rig, (b) the floater, the sensor and the cap housing it.
Unlike previous topics, you will be allowed to bring a populated breadboard into all but the first lab, since the first task is the only one that involves building a proper driver circuit to operate the fan. For the rest of the tasks, you will have to use the same circuit. So, it is important that once your circuit is done, you have to keep it until the end of this topic.
(b)
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ELEC4123: Electrical Design Proficiency
Also, the nature of any control system design requires to complete the tasks in sequence, as they are highly depended on each other, unlike the previous two topics. That means if you cannot have a good working circuit to power up the fan, you cannot properly run the device and collect data for deriving a dynamic model of the process, and consequently, you cannot design a proper controller for it.
Demonstrators will write down your marks and sign off on your lab book. It is your responsibility to ensure that your lab book is signed off and marked as well as the stickers remain intact over the topic.
You must have a bound laboratory notebook (not loose sheets of paper) present with you in any lab session where you expect to be assessed. Your design must be documented in this notebook in your own handwriting, including schematics, considered alternatives and design calculations. When explaining your design to a demonstrator during assessment, you must use these handwritten notes. You may not use printed materials or digital notes for this purpose as the documentary evidence for your design.
The code that you write as part of this topic must be clear and well commented so that an assessor can follow the reasoning and match it against the explanation in your lab notebook. Of course, it is strictly forbidden to copy any other student’s work, even if you have exchanged ideas with other students during the lead- up to a laboratory.
Electronic Components and Programming Platform
You would only have to use electronic components for task 1 which are provided in the task manual. You will be given an extra $2 credit to get the power MOSFET required for task 1.
For programming your control algorithm and applying the real-time control operation, you have multiple option:
• Use an Arduino board (available from Workshop for $12 out-off pocket cost, or use your own Arduino board)
• Use MATLAB or Simulink to create your code and use NI-DAQ or sound card for signal acquisition and output.
You may use Arduino packages in MATLAB/Simulink to embed your code into the Arduino board, but you need to be able to change the PWM frequency of the Arduino to a higher frequency. If, you choose to use the NI-DAQ device or sound card for signal acquisition and output, you should be aware that there is only one such device per bench, and you cannot take it home to experiment with. Also, all inputs to and outputs from the NI-DAQ and the sound card must be AC-coupled in this design topic.
You may use the remaining of your $15 credit if you need to get the Arduino from the Workshop (it comes with a USB cable). Any components you want to purchase after you finished your entitled amount should be paid by you. You may NOT use this credit to buy breadboard. You need to keep the built circuit on your breadboard after the first lab as you will be re-using it regularly for the rest of the topic.
Sharing Equipment
Due to current resource constraints, you will generally share a work bench in the laboratory with a lab partner. Despite this, your design, implementation and assessment for these tasks are all individual. Naturally, you cannot expect to have your design permanently tethered to the power supply, oscilloscope, signal generator or other laboratory equipment. You should, therefore, communicate with your lab partner and establish a good working relationship for sharing the equipment.
You may use your own laptop for this topic. However, you have to make sure that under no circumstances your circuit draws more than 200mA from Arduino’s I/O port combined, or you accidentally short circuit the power supply to the common ground while the Arduino is connected to your laptop as it may damage the USB port of your laptop (all the grounds should be connected together).
Except Task 3, the rest of the tasks will require the use of one channel of the power supply (single-ended), but to power up the sensor, it is highly recommended to use the fix 5V channel of the power supply which can be shared easily as it provides up to 5A (do not use the regulated 5V output of your Arduino so that if something happens to it, the sensor would not be damaged). You need to use a 10F capacitor or larger across power and ground of the sensor close to it to stabilize the power supply line since this sensor draws large current in short bursts even though its average current consumption is only 12 mA.
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Topic 3: Control Systems
Communication in the Lab
Although assessment is individual, you can communicate freely with your lab partner regarding the design problem. There is no expectation that your partner should help you with the construction or preliminary testing of your design, but this is permitted so long as you both agree. However, it is unacceptable for anybody other than you, your lab partner and course staff to be interacting significantly during the laboratory session, and it is totally unacceptable for any other person to come to your lab bench without the permission of a lab demonstrator.
Note: Lab demonstrators have full authority to enforce the above policy by moving the offending parties to the end of their marking list or (after a warning) by suspending them from any form of assessment during the week in which the offence occurs.
Assessment Procedure
Lab demonstrators will maintain an ordered assessment list. You may not add your name to the list until you have a solution you are prepared to have assessed. Students who have already been assessed for a task may have the opportunity to be re-assessed, during the same or a later laboratory session, but students who have not yet been assessed will be given priority over those seeking re-assessment.
Demonstrators may ask you to move to a separate area for assessment, so that your lab partner need not be disturbed. With this in mind, you should ensure that your implementation is as portable as possible, so that you can easily connect it to a separate power supply, signal generator, oscilloscope and/or lab computer, as appropriate. For tasks involving digital processing, you will be allowed to use your own laptop computer as part of the assessment process.
You must have your lab notebook with you to be assessed, and for each task your lab notebook must contain a “final” hand drawn schematic and/or algorithm description that corresponds to the design you are bringing for assessment.
For tasks that involve control system parameter design, a handwritten description of the final algorithm is particularly important, which may be presented as a flow chart and/or block diagram with sufficient detail, along with a description of key parameters and variables and the most relevant equations.
Unless otherwise stated, you cannot receive understanding marks for a design that you have not implemented.
For each task, there are three assessment items with the following grades being awarded:
• Achievement of requirements: (_____/ 0 – US – BC – SF – HG – OS)
• Soft objectives: (_____/ 0 – US – SF – HG – OS)
• Understanding: (_____/ 0 – US – BC – SF – HG – OS)
• Code Neatness (or circuit neatness): (_____/ 0 – US – SF – HG)
The grading abbreviations stands for: OS → Outstanding (±); HG → High (±); SF → Satisfactory (±); BS → Basic (±); US → Unsatisfactory (±), and 0 → Zero.
Not all the assessment items will have all the grades associated with them. The Achievement of requirements and understanding has the highest weight in the final mark of each task, respectively, followed by soft objectives and finally the neatness. However, in some tasks, the soft objectives might have a high weight which will be clearly stated in the task
In general, it is recommended to follow the guideline below for smooth assessment:
• First lab session: At least one task is recommended to be completed and assessed (not compulsory).
• For the next two lab sessions: At least one task must be completed and assessed, two tasks are
recommended to be completed and assessed, but no more than two tasks will be marked.
• Open-lab session: At least one task is recommended to be completed and assessed (not compulsory).
• Final assessment lab session: No more than two tasks will be assessed.
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ELEC4123: Electrical Design Proficiency
Task 1: Linear Voltage Driver (L11)
The purpose of this task is to design a circuit that extracts the DC value of a pulse signal with variable duty cycle (PWM signal) and converts it to a variable/controlled DC voltage. You can use the signal generator to generate the PWM signal either from its normal output or from the TTL/CMOS output. This is part of the actuator design in a control system that is used to receive the control input signal from the controller and converts it to a compatible input for the process.
Operating conditions:
1. Input PWM signal has 5V as high and 0V and low.
2. Assume a frequency of 7.8kHz or 31.3kHz for the input signal (choose one only).
3. Power supply: maximum 18V, single-ended (you have to decide on the maximum supply voltage
based on your design).
Requirements/specifications:
1. Output signal should be a time-varying DC voltage ranging between 0V and 12V (0% duty cycle or 0V should be converted to 0V and 100% duty cycle or 5V should be converted to 12V).
2. The response time of your circuit should be less than or equal to 1.5ms.
3. The amount of ripple voltage in the steady state should be less than 100mV.
4. The output of the circuit should be capable of delivering up to at least 500 mA to a 25- load resistor
at any voltage within the range of 0V-12V.
5. A simulation of your design that behaves very closely to the actual circuit (you can use any available
electronics software like PSpice or equivalent which helps with validating he response time and the voltage ripple in steady state).
Note 1: The signal generator can only generate duty cycles between 20% o 80%, but this should be enough for testing purposes.
Note 2: You can use the control rig as the load to do your testing. But it is recommended to first test the rig directly with the power supply. You will notice that the fan does not start with a voltage less than 6V at the beginning and it takes time to reach its steady state speed. But once its fully running, you can reduce the voltage up to around 4V (each fan may have different behaviour). You need to look at the behaviour of the fan when you directly apply a voltage to its power terminals in your initial testings. You will notice that as it begins to speed up at a fix initial voltage, the current goes up until it reaches steady state.
Soft objectives:
1. Accuracy of the duty cycle conversion to a variable DC value.
2. Minimising voltage ripple and the response time.
3. Some protection against short circuiting on the input side (bonus mark, not compulsory).
4. A 5-V voltage regulator with output current capacity of at least 100mA to power the sensor. (bonus
mark, not compulsory).
Components available for this task:
• Transistors: Power MOSFET IRLB8743
• Analog IC’s: LM324, LM348
• Resistors and capacitors, as found in the laboratories
• (You may use other components that only have been used in any of the Electronics Topic before)
Assessment for this task:
Marks for this task are as follows:
• Achievement of requirements: (_____/ 0 – US – BC – SF – HG – OS)
• Soft objectives: (_____/ 0 – US – SF – HG – OS)
1 L1 refers to level 1 difficulty (relatively easy), L2 refers to Level 2 difficulty (medium), and L3 refers to level 3 difficulty (challenging)
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Topic 3: Control Systems
• Understanding: (_____/ 0 – US – BC – SF – HG – OS)
• Neatness: (_____/ 0 – US – SF – HG)
Assessment timing and requirements:
You must complete this task in Weeks 6. If you cannot successfully complete this task by the end of week 6, a template circuit will be given to you to be able to work on the rest of the tasks and your Task 1 mark for requirements and soft objectives will be capped to SF-. Please note the general instructions above concerning the requirement that you present your lab notebook, with a “final” hand drawn schematic of the design you are bringing for assessment. These instructions apply to all tasks.
Task 2: System identification (L1 – L2)
— End of Topic 3 —
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