2005 Technological Studies. Standard Grade Credit. Finalised Marking Instructions

Transcription

1 5 Technological Studies Standard Grade Credit Finalised Marking Instructions These Marking Instructions have been prepared by Examination Teams for use by SQA Appointed Markers when marking External Course Assessments.

2 . Two types of heating systems are shown below. boiler thermostat electric fire central heating system Systems can be placed into two groups, open loop or closed loop control. (a) State which group each heating system belongs to. (i) (ii) Electric fire open loop Central heating system closed loop (b) State the difference between open loop and closed loop control. OR closed loop has feedback open loop has no feedback (c) State the name of the control diagram symbol shown below. Error detector Page two

3 litres of water is pumped into a swimming pool each hour ( litre of water = kg). The water has to be added at a temperature of 5 C. (a) If the water s original temperature is 6 C, calculate the heat energy given to the water. (Show all working and units.) EH = Cm T = (5-6) = J for substitution for correct answer from given working. (b) If the input power required by the heater is W and it takes hour to heat the water, calculate the efficiency of the heating system. Power out η = (6 6) = 4 7 W = out in = 4 7 W = W Answer from (a) above (allow follow through) Answer from given working. substitution (allow follow through). 65 (65%) 4 (c) Electrical energy can be generated in a number of ways, including nuclear and fossil fuel sources. (i) State one environmental concern with the use of nuclear energy. Dangerous/long lasting waste/accidents etc. (ii) (iii) State two disadvantages of using fossil fuels. They will run out (finite). Damage to ozone layer etc. Two distinct environmental issues marks State two examples of renewable energy sources. Solar/tidal/wave/hydro/geothermal etc. not nuclear Page three

4 . Part of the logic system used to control the operation of a drinks vending machine is shown below. Coffee (X) White Coffee (A) Sweet White Coffee (B) Milk (Y) Sweet Black Coffee (C) Sugar (Z) (a) Complete the truth table for the above logic system. White Coffee (A) Sweet White Coffee (B) Sweet Black Coffee (C) Coffee (X) Milk (Y) Sugar (Z) (b) mark for each correct column With reference to the Data Booklet, state the full name and number of the integrated circuit (IC) required to complete the above logic system. Full name Number Quad input OR gate 74 Page four

5 . (continued) (c) Complete the circuit diagram for the vending machine logic system. +5V Power connections * Milk (Y) Each correct line Sugar (Z) White Coffee (A) Sweet White Coffee (B) Sweet Black Coffee (C) V (d) State the purpose of the dot on an integrated circuit (IC). To show pin. * Coffee (X) * need both power connections for 5 4 (e) When a pupil was modelling this circuit on a prototype board, LEDs were used to show the state of each output. (i) State what the letters LED stand for. Light emitting diode. When the LEDs were connected directly to the output pins of the IC, they kept blowing. (ii) State one alteration which could be made to the circuit to stop this from happening. Place a resistor before the output. (Add a resistor) (iii) LEDs are polarity conscious devices. State the meaning of the term polarity conscious. It will only work if connected the right way round. Page five

6 4. A model car has a fast and slow speed setting controlled by a microcontroller. Pulse Width Modulation is used to produce the slow speed setting. (a) Explain, with the aid of a sketch, how Pulse Width Modulation can be used to control the speed of a motor. Sketch Switching power on and off Mention of mark and space (or appropriate labelling of sketch) The following flowcharts outline the operation of the speed control of the model car. Start Slow Is Fast Selected? No Is Slow Selected? No Brakes off Yes Yes Brakes off Slow Motor forward Motor forward 5 ms delay Is Brake Selected? No Motor stop Yes Motor stop 5 ms delay Brakes on Is Brake Selected? Yes Return No Page six

7 4. (continued) The connections to the microcontroller are shown in the table below. Input Connection Brake Selector Slow Selector Fast Selector Pin Motor Fwd Brake Output Connection (b) Using the flowcharts and the table, complete the following PBASIC program. init: let dirs = % set pins 7 4 as outputs, rest inputs main: if pin = then slowsel if fast is not selected then jump to slowsel low 5 brake off high 7 motor on brakesel: if pin = then brakesel if brake not selected then jump to brakesel low 7 motor off brakeon: high 5 or let pins =... goto main brake on jump back to main slowsel: if pin = then main if slow is not selected then jump to main gosub slow (not goto) goto brakeon jump to sub-procedure slow jump to brakeon slow: low 5 brake off pwm: high 7 motor on pause 5 } 5 ms delay low 7 motor off pause 5 5 ms delay if pin = then pwm if brake is not selected then jump to pwm return (not goto main) return to main program Page seven

8 4. (continued) (c) State the full name and function of the following microcontroller terms. (i) EEPROM Full Name Electronically Erasable Programmable Read Only Memory Function To store the program. (ii) I/O Port Full Name Input Output Port Function To connect the microcontroller to the outside world. world. (d) State two advantages of microcontroller based systems over hard-wired electronic circuits. Flexible, reprogrammable, smaller circuits, reliability cheaper with justification etc Each correct answer maximum of (e) Other than a model car, state the name of two products which use microcontrollers in their operation. Washing Machine, Central Heating Programmer, Microwave, VCR, etc for each correct answer. Maximum of. Not computer Page eight

9 5. An internet mailing company uses an electro-pneumatic circuit to close and seal boxes. When a box is sensed on a conveyor belt, the belt stops and Cylinder A outstrokes. Cylinder A closes the flaps of the box before Cylinder B outstrokes to seal it with tape. Cylinder C then outstrokes to cut the tape. The cylinders instroke and the conveyor belt restarts. (a) Complete the piping of the pneumatic circuit below. Valve Cylinder B Cylinder A Cylinder C Magnetic piston Valve Component Z Signal from box sensor to start sequence Signal restart conveyor belt V (b) State the name of the actuator on the following valves. (i) Valve Solenoid (ii) Valve Roller trip (c) State the name of the Component Z, operated by the magnetic piston. Reed switch Page nine

10 6. A motorway service station has installed a number of combined hand washer/dryers in the toilets. Each washer/dryer is controlled by a microcontroller and follows the sequence shown below: the sequence starts when the user s hands are sensed warm water is released for 4 seconds soap is released for seconds a delay of 5 seconds allows the user to massage the soap into their hands warm water is released for 8 seconds to allow the user to rinse their hands the dryer switches on for seconds the sequence is then reset for the next user. Page ten

11 6. (continued) Complete the flowchart for the washer/dryer sequence. Start Are hands sensed? No warm water on 4 second delay warm water off soap release second delay } stop soap 5 second delay warm water on 8 second delay } warm water off dryer on second delay dryer off Page eleven } 6 5 4

12 7. In a shopping centre, revolving doors are controlled electronically by the circuit shown below. The doors should only operate when a person is sensed, crossing a light beam. +5 V V door motor V Y M R in V out V be V (a) (i) State the purpose of the variable resistor in the voltage divider circuit. To adjust the system s sensitivity (ii) State the purpose of the fixed resistor (R in ). To protect the transistor or to limit the current (b) (i) With reference to the Data Booklet, determine the resistance of the light dependant resistor at a light level of lux. 4 Ω (4 4) (ii) With the light level at lux and the variable resistor set to. kω, determine the output voltage, (V out ) from the voltage divider. (Show all working and units.) V V S R R T V 4 = 5 5 V = 4 5 = 5 substitution (Allow follow through) correct answer from given working. (Allow follow through) Page twelve

13 7. (continued) (c) Assuming the transistor is fully saturated and the light level is at lux, determine the reading on the voltmeter (V ). (Show all working and units.) V = V out V be = =. V (Allow follow through) correct answer units (d) The voltage divider is currently used to sense darkness. State how the circuit could be altered to sense light. Swap the LDR and V. Resister around. (e) State the name and function of Component Y shown in the circuit. Name Diode not LED Function To protect the transistor (from back EMF.) Page thirteen

14 8. A winch system used to raise a 5 N load is shown. Motor Belt Drive Windlass Simple Gear Train 5 N Load (a) If the windlass has a diameter of mm, calculate the torque produced by the load. (Show all working and units.) T = F r = 5 5 = 875 Nmm = Nm substitution correct answer from given working. Page fourteen

15 8. (continued) Motor rev/min Pulley B Gear D Pulley A Gear C Windlass Pulley A 5 mm diameter Gear C teeth Pulley B 7 mm diameter Gear D 6 teeth (b) If the motor is rotating with a speed of rev/min, calculate the rotational speed of the windlass. (Show all working and units.) Speed of B = 5 7 = 5 7 rev/min Speed of Windlass = substitution = 8 57 rev/min correct answer. (Allow follow through) The system makes use of a flat belt to connect the motor to the simple gear train. (c) (i) State one disadvantage of this type of belt. Flat belts tend to slip. (ii) State the name of two other types of belt which could be used instead of a flat belt. Vee belt Toothed belt Round belt Page fifteen

16 9. A pneumatic circuit used in an industrial spot welding machine is shown below. Valve is actuated when the machine guard is in position. Cylinder A Valve 4 Valve 5 Start Valve Valve Valve (a) Study the diagram above and, using appropriate terminology, explain how the circuit controls the cylinder. When Start Valve is actuated the pilot air changes the state of and the machine guard is in position,/ mark Valve / mark, slowly outstroking the cylinder./ mark When the cylinder is fully outstroked, it actuates Valve 4 mark which changes the state of instroke./ mark Maximum of four marks Valve./ mark Allowing the cylinder to 4 (b) The circuit is to be modified by creating a pneumatic time delay before the piston outstrokes. (i) State the name of the two pneumatic components required to produce a time delay. (Unidirectional) restrictor Reservoir (ii) Use an (X) to mark the position of the time delay sub-system on the circuit diagram above. Page sixteen

17 9. (continued) (c) State the name of the actuator on Valve 4. Plunger It has been suggested that Valve 4 should be operated by an air bleed signal. (d) (i) State the name of the actuator required in an air bleed circuit. Diaphragm (ii) Draw the symbol for this actuator below. (Allow follow through from d(i)) Valve 5 is used to control the speed of the outstroke of the cylinder. (e) Explain why Valve 5 is piped to restrict exhaust air. To stop piston judder. Page seventeen

18 . A truth table for a prototype electronic circuit is shown below. A B C Z (a) Develop the Boolean expression to describe when Z is on, in terms of A, B and C. (b) Z = (A. B. C) + (A. B. C) TTL or CMOS integrated circuits (ICs) can be used to construct the circuit. State one difference between these families of ICs. Different power supply, fan out, etc. For reasonable correct answer. [END OF MARKING INSTRUCTIONS] Page eighteen