Master's Level Unit Expectations
This is a master's level unit and we expect no less than illustrating mastery from your answers. EIT strive to maintain the highest academic integrity. You may generate ideas in groups, but the work you submit must be your own effort. Wherever a source is used as basis, make a due reference to the origin.
To assist you in reaching your full potential, please note the following guidelines in answering various types of questions:
a) Programming-related questions:
The use of CODESYS is required.
ii. Failure may/probably will result in marks being lost. Marks in these kinds of questions are mostly allocated towards:
Relevant and correct assumptions listed (10%)
Correct timing / logic / language choice (25%)
Judicious screenshots of Visual Simulations to proof working (25%)
Variables and coding style / compactness (25%)
Correct interpretation / compact solution of problem (15%)
The above is a guideline and may chance as required
b) Problem-based questions:
Provide ample, relevant assumptions and comments supporting your solution.
ii. This is the only way I can effectively judge your train of thought.
c) Answers in general:
It is mostly required that apart from you answer, you also say why you chose the answer you did, to obtain full marks.
ii. The answer alone is usually not sufficient.
iii. The above being said, always aim for compact but effective solutions and answers. Long-windedness will not be rewarded.
A free version of CODESYS is available for download to your own device via the internet. You will need to register.
ii. CODESYS can also be accessed on EIT Remote Labs.
iii. Ample introduction to CODESYS is available here.
For those with additional learning appetite:
Unit code and name:
Total marks:150 (max.)
Please complete your answers on the assessment cover page document available on Moodle.
Clearly label your question numbers (there is no need to copy the full question over). Include all working out.
Question 1: (15 marks)
a) Define both risk and hazard. (4 marks)
b) What is the principle difference between a hazard and a risk? (2 marks) c) What does the Heinrich model learn in respect of the probability of a major risk occurring? (3 marks)
d) On what part of the Heinrich model should we concentrate our efforts in order to decrease the probability of a major risk and how and why will these efforts assist in lowering the major risk? (3 marks)
e) Is the Heinrich model directly applicable to heavy metal cast industry? Why or why not?
Question 2: (10 marks)
a) Define the impact of a risk. (3 marks)
b) Can risk be taken to zero? Explain. (2 marks)
c) Define the notion of a functional safety system. (2 marks)
d) List three kinds of safety systems or safety interventions apart from a functional safety system. (3 marks)
Question 3: (25 marks)
a) Name five types of events that should be logged as alarms in industrial systems. (5 marks)
b) List and describe the four typical access modes and levels of authorization found in SIS systems in a tabular format. (20 marks)
Question 4: (25 marks)
a) Explain the IP rating system for cabinets. (10 marks)
b) Choose an IP rating for a cabinet mounted outside, against a brick wall of the factory, adjacent to a garden. The cabinet contains automation equipment. Explain why you chose the particular rating. (5 marks)
c) Explain when and why you will use Aluminium conduit versus galvanised steel conduit to carry signal cables past other equipment racks on a factory floor. (5 marks) d) Explain how disturbance signals are quenched at ac and at dc contactor coils? (5 marks)
240 VAC Supply VDC Supply
Suppression Network for AC Suppression Network for DC
Question 5: (25 marks)
The picture above shows the layout of a junction between three office blocks. At night, this foyer is totally dark to save on power.
The lights in the foyer need to be switched on from any of the 3 different entrances. Three presence sensors are mounted to achieve this. One sensor at each entrance looks down the passage and is connected to inputs Il, 12 and 13 respectively, of a micro PLC. Sensors are NC and opens their contacts for 100ms when movement is detected.
It takes, on average, 1 1/2 minutes to walk through the foyer towards an exit, therefore a 2minute time window is allowed during which the foyer lights must be kept on.
If, within the current 2 min window that lights are on, someone else entering the foyer from another entrance should also experience the lights staying on for 2 minutes. Thus, from the perspective of any person walking in from any entrance, the foyer lights should be on for 2 minutes.
The cleaners are due to clean the portal every night at 19h00.
a) Write down any required assumptions and code an implementation of the required functionality in ST. (10 marks)
b) Show that your implementation achieves the required functionality by pasting various pertinent simulation results with relevant headings. (10 marks)
c) The night-shift cleaners complain that 2 minutes is not enough to clean the foyer. The facilities manager gives you cart blanche to alter only the logic (NO new physical wiring). Propose a solution that will accommodates the cleaners for 15 minutes. Fully describe the logic solution you would use. (5 marks)
Question 6: (30 marks)
The two inputs, A and B are connected to discrete inputs of a micro PLC.
A free-running time base of 200 ms per frame, is established. Arbitrary boundaries are shown in the timing diagram.
The figure shows the behavior of the output (OUT) in reaction to the inputs A and B, by means of a timing diagram.