Examination A0002N Safety 1

Examination

A0002N – Safety 1

Date

2012-01-11, 5 hours

Allowed aids

Dictionary, Calculator

_{Course book: Ericsson or Storey,}

Safety Critical Computer Systems

Teachers on call

:

Lars Furberg +46 920 4917 30

The exam contains 3 questions with a total of 80 points. Results of the exam will be

presented in the studentportal

General instructions:

- Always give explanatory answers (essay), well justified, as though the one reading them does not already know. Answers with no motives will be treated as guesses and give no point.

- Check that you have received all questions, read the entire exam through.

- Write clearly. Unreadable answers will not, of course, be taken into consideration. - Assumptions made shall be clearly stated

- The campus guard is just a guard, no interaction on the exam subjects - The guard can whenever he/she pleases inspect aids like course book

- No talking or collaboration or transmitting of materials between students are accepted, then you have to leave the exam.

- Cheating will lead to that the result will not be counted for - See the following page for the Internet rules!

Good Luck

This page is strictly for those who are taking the exam on Distance

Allowed aids

The final examination is a written test covering allot of the course. Since you will have books available at the workplace in your ordinary work with security, we have decided that the course book is allowed during the final exam. Use this opportunity! You are also allowed to use any dictionary in order to understand the essence of the questions. Not allowed aids

Any other help than these described above is not allowed. You cannot ask other persons or use Internet, USB memory, telephones, SMS, pagers, other books, noted things, documents in the course book. In the computer the only software started should be Connect pro and a wordprocessor of your choice. You are allowed to before and after exam have the e-mail running, to receive questions and to send the answers.

If we find out that you have not followed the rules, the exam for you will be disqualified.

Start

Adobe Connect examroom started

Startup E-mail again & send an email to me with your answers attached and

bio files Clear workplace, room,

stop phone, other “lock door” Adjust web camera and mic.

Ask for questions by e-mail from the guard/ me

When received questions, save it on your computer & exit the e-mail program

This page is strictly for those who are taking the exam on Distance

Exam-place for students of the course __________________

Guard: [email protected]/ [email protected]  Up to 5 hours is allowed writing time

 Have microphone attached but not on

 Have camera attached and enabled

 Allowed help course book & Dictionary

 Use private chat to guard/teacher when asking questions

 Visit to toilet are allowed after questioning

 Download the BioForensic exe file from the course room and Install it (course info folder on Fronter)

 Start the BioForensic when you start the exam

 Email to get the question sheet from the guard with email posted

 After you have received the questions close down the email system, time starts

 Just note pad/word and Adobe Connect Pro are supportive in the computer.

 When exam is over start email program again and send the answers and the bio-files to the Guard.

 We can randomly ask you to turn on microphone for inspection during the exam

 We can randomly ask you to rotate the webcam (separate or inbuilt) for inspection during the exam

 You must keep your Passport/National ID card with you during the exam and it must be shown to the examiner on demand.

 Your status in the Adobe Connect Pro exam room will be as Presenter.

 You will be able to Switch on Camera and mic by clicking on the icon on the upper left corner. A small window will appear asking you to allow sharing your camera and Mic you shall press allow button.

 You are not supposed to write public messages, use Private chat by selecting Private from the drop down list on chat menu and the receiver must be the guard.

 You shouldn’t upload any document in the main window.

 You are supposed to share your computer screen when asked by the guard.

 When you are asking the guard for the exam questions you are also agreeing on the above terms

 Cheating is prohibited and it is important to follow the rules, in case of violation of the rules, you can be suspended from education, examination or tutoring for a period of up to six months.

Question 1 (30 points)

Description of a home security alarm system

Home alarm systems typically comprise sensors, annunciators, and telecom paths. Sensors include those for fire, motion within a room, structural movement (e.g., doors and windows), sound (e.g., glass breaking), and panic buttons (e.g., medical or threat emergencies). Annunciators, which are activated when a sensor is triggered, include local audible alarms (e.g., sirens, bells, voice warnings) and messages sent using the telecom paths to an alarm call centre (a central station where operators monitor alarms from alarm service subscribers) or directly to an alarm authority (e.g., police, fire department, ambulance).

Typically, a local sensor in a multi-sensor alarm system detects fire, motion within a room, structural movement, specific sounds, operation of a panic buttons, or other state for which a sensor is designed (each such detection is an "alarm trigger") and sends a signal to a local processor ("sensor hub"), usually on premises. The sensor hub then sends a signal over a wireline (e.g., dials-up or leased telephone line, DSL, cable modem) or wireless (e.g., mobile phone network, private radio service) to an alarm call centre or alarm authority, where a response to the alarm is undertaken.

There are several problems with typical home alarm systems. Basic home alarm systems typically do not differentiate between types of alarms (e.g., fire, motion, medical). This lack of differentiation requires the alarm call centre to interpret the alarms received. Errors can be made in this interpretation, and the wrong type of alarm response dispatched. Improved home alarm systems, include a means of analyzing the local annunciator sound output (e.g., siren, bell), in essence, performing an electronic interpretation of the type of alarm. Electronic interpretations, however, are not as good as actual identification of sensor type. There is an unmet need for a home alarm system that differentiates

between types of sensor that produces an alarm trigger and communicates that information to the alarm call centre or alarm authority using one or more telecom paths.

SUMMARY OF THE INVENTION

The present automatic home alarm system and method invention comprises one or more sensors, at least one sensor hub that identifies and transmits the type of sensor or alarm trigger to a system unit, which communicates such information to an alarm call centre or alarm authority using one or more telecom paths (e.g., dial-up telephone, mobile phone) and one or more message types (e.g., voice, proprietary signalling). Sensors types used in the invention can include those for fire, motion within a room, structural movement (e.g., doors and windows), sound (e.g., glass breaking), and panic buttons (e.g., medical or threat emergencies). Annunciators used in the invention can include local audible alarms (e.g., sirens, bells, voice warnings), visible alarms (e.g., flashing lights, semaphores), and messages sent using the telecom paths to an alarm call centre or to an alarm authority.

Annunciator : one that annunciates ; specifically: a usually electrically controlled signal board or indicator

a) Do a PHA on the above defined Home alarm system choose a suitable technique and investigate at least five realistic and different hazards

Question 2 (20 points)

The reliability of a system is related to its constant failure rate  by the expressionR(t)et. Calculate the reliability of a system at a time equal to 60 % of its MTTF.

Question 3 (30 points)

A reliability block diagram of a command signal system takes the form of figure below. The probabilities shown for the events are reliabilities or the probabilities that the event will occur in the time constraint t.

Event 1 Battery Power R1=0,98 Event 5 Command signal box functions R5=0,98 Event 3 Relay 1 Closed R3=0,90 Event 2 Switch Closed R2=0,90 Event 4 Relay 2 Closed R4=0,90 Command signal

a) Compute the probability of successful or reliable functioning of the system above, show the event tree?

b) Which are the cut sets of the system above?

c) Compute the upper bound on the probability of system failure above by the cut set method?