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This question paper consists of 11 pages and a 2-page formula sheet.

ELECTRICAL TECHNOLOGY

FEBRUARY/MARCH 2016

NATIONAL SENIOR CERTIFICATE

GRAAD 12

GRADE 12

Electrical Technology 2 DBE/Feb.–Mar. 2016 NSC


INSTRUCTIONS AND INFORMATION 1. 2. 3. 4. 5. 6. 7. 8. 9.

This question paper consists of SEVEN questions. Answer ALL the questions. Sketches and diagrams must be large, neat and fully labelled. Show ALL calculations and round off answers correctly to TWO decimal places. Number the answers correctly according to the numbering system used in this question paper. You may use a non-programmable calculator. Show the units for all answers of calculations. A formula sheet is attached at the end of this question paper. Write neatly and legibly.



QUESTION 1: OCCUPATIONAL HEALTH AND SAFETY 1.1 Name ONE unsafe condition that may result in an injury in an electrical

technology workshop.

(1) 1.2 Define the term unsafe action with reference to an electrical technology

workshop.

(2) 1.3 State FOUR steps, in order of priority, that must be adhered to when helping

a person who is a victim of an electrical shock in an electrical technology workshop.

(4)

1.4 Briefly explain why productivity is considered an important work ethic in the

South African industrial context.

(3) [10] QUESTION 2: THREE-PHASE AC GENERATION 2.1 Name the instrument that is used to measure electrical energy. (1) 2.2 State TWO advantages of three-phase systems over single-phase systems. (2) 2.3 Draw a neatly labelled sketch representing the voltage waveforms of a

three-phase AC generation system.

(5) 2.4 A three-phase star-connected balanced load is supplied by a three-phase

generator. The generator supplies 20 kVA at a current of 25 A.

Given: Il

S = =

25 A 20 kVA

Calculate the: 2.4.1 Line voltage (3) 2.4.2 Phase voltage (3)



2.5 In a three-phase supply system the two-wattmeter method was used to

measure the input power to an inductive load which has a power factor of 0,8. The values indicated on the instruments are 8 kW and 4 kW respectively. The line voltage is 380 V.

Given: P1

P2 Cos Ɵ Vl

= = = =

8 kW 4 kW 0,8 380 V

Calculate the: 2.5.1 Total input power (3) 2.5.2 Line current (3) [20] QUESTION 3: THREE-PHASE TRANSFORMERS 3.1 State how eddy currents may be limited in the iron core of a transformer. (1) 3.2 Name TWO similarities between a single-phase transformer and a

three-phase transformer.

(2) 3.3 State TWO factors that may cause excessive heating in a transformer. (2) 3.4 Name TWO applications of a delta-star-connected distribution network

transformer.

(2) 3.5 Explain the function of a transformer in a distribution network. (3) 3.6 Refer to FIGURE 3.1 and answer the questions that follow.

FIGURE 3.1: THREE-PHASE TRANSFORMER Given: Vlp

Vps Ils Pout Cos Ɵ

= = = = =

6,6 kV 230 V 30 A 15 kW 0,8

LOA

D

Primary Secondary

Vlp = 6,6 kV

P = 15 kW Cos Ɵ = 0,8 Ils = 30 A Vps = 230 V



Calculate the: 3.6.1 Primary phase voltage (2) 3.6.2 Secondary phase current (2) 3.6.3 Primary phase current (3) 3.6.4 Turns ratio (3) [20] QUESTION 4: THREE-PHASE MOTORS AND STARTERS 4.1 Name ONE application of a three-phase motor. (1) 4.2 State THREE advantages of a three-phase motor compared to a single-phase

motor.

(3) 4.3 A star-delta starter is used to reduce the starting current used by a motor

when starting.

4.3.1 Describe why it is necessary to do this. (3) 4.3.2 Describe how the starter reduces the starting current. (3) 4.4 Describe the principle of operation of a three-phase squirrel-cage induction

motor.

(7) 4.5 FIGURE 4.1 represents the terminals of a three-phase induction motor.

Answer the questions that follow.

FIGURE 4.1: TERMINALS OF A THREE-PHASE INDUCTION MOTOR 4.5.1 Redraw the terminal box in FIGURE 4.1. Then draw in the motor coils

and show them connected in star.

(5) 4.5.2 A megger set on the insulation resistance setting is connected across

W1 and U2. Describe what type of reading should be expected if the motor is in good working order.

(3)

4.5.3 A megger set on the insulation resistance setting is connected across

U1 and E. If the reading on the meter shows a low resistance, describe why the motor should not be energised.

(3)

E

U1 V1 W1

W2 U2 V2



4.6 Calculate the number of pole pairs of a three-phase motor if the motor is

connected to a 50 Hz supply and has a synchronous speed of 600 r/min.

Given: f

ns = =

50 Hz 600

(3)

4.7 A three-phase delta-connected motor is connected to a 380 V/50 Hz supply.

The motor draws a current of 16 A at full load. It has a power factor of 0,85 and an efficiency of 90%.

Given: Il

Vl Pf ɳ

= = = =

16 A 380 V 0,85 90%

Calculate the: 4.7.1 Input kVA (3) 4.7.2 Power developed by the motor at 100% efficiency (3) 4.7.3 The actual output power of the motor (3) [40] QUESTION 5: RLC 5.1 Name the TWO factors that influence the reactance of a capacitor. (2) 5.2 Distinguish between the two concepts reactance and impedance. (2) 5.3 Draw the typical frequency/impedance characteristic curve of a series RLC

circuit. The graph must show the relationship between impedance and frequency, as the frequency changes. The graph must also show the resonant point of the circuit.

(4) 5.4 Calculate the Q-factor of a series RLC circuit that resonates at 6 kHz. The coil

and the capacitor each have a reactance of 4 kΩ at resonance. The coil and the capacitor are connected in series with a 50 Ω resistor.

Given: fr

Xl Xc R

= = = =

6 kHz 4 kΩ 4 kΩ 50 Ω

(3)



5.5 Refer to the circuit diagram in FIGURE 5.1.

FIGURE 5.1: SERIES RLC CIRCUIT Given: R

L C f

= = = =

30 Ω 400 mH 47 µF 50 Hz

Calculate the: 5.5.1 Inductive reactance of the coil (3) 5.5.2 Capacitive reactance of the capacitor (3) 5.5.3 Frequency at which the circuit will resonate (3) [20] QUESTION 6: LOGIC 6.1 State TWO advantages of a programmable logic controller (PLC) compared to

a hard-wired system.

(2) 6.2 Draw a block diagram of a PLC scan cycle showing the THREE steps that are

used to execute a programme. Label each step and indicate its function.

(6) 6.3 Name TWO output devices that may be connected to a PLC. (2) 6.4 Simplify the equation below using Boolean algebra: C B A C B A C B A CBAF (5) 6.5 Name THREE programming methods used to instruct a PLC. (3)

R = 30 Ω C = 47 µF L = 400 mH

V = 220 V/50 Hz



6.6 Consider the following Boolean equation and answer the questions that follow: D C B AD C B AD C B AD C B AD C B AF 6.6.1 Convert the equation into a Karnaugh map. (Remember to group.) (6) 6.6.2 Derive and write the simplified Boolean equation from the Karnaugh

map in your ANSWER BOOK.

(3) 6.7 Refer to the circuit diagram in FIGURE 6.1 and answer the questions that

follow.

FIGURE 6.1: RELAY CONTROL CIRCUIT 6.7.1 Identify the circuit in FIGURE 6.1. (2) 6.7.2 Draw the PLC ladder logic diagram that would execute the relay

control circuit in FIGURE 6.1. Your diagram must include a marker or a flag function.

(8) 6.7.3 Explain why the marker or flag is used in the drawing of the ladder

diagram in QUESTION 6.7.2.

(3) [40]

Hold in MC1(N/O)

N

L

Hold in MC2(N/O)

O/LL

Start 1 Start

2

MC1 (Lamp)

MC2 (Motor)

Stop

T

T (N/O)



QUESTION 7: AMPLIFIERS 7.1 Name TWO characteristics of an ideal op amp. (2) 7.2 Describe the term bandwidth. (3) 7.3 Describe the term positive feedback. (3) 7.4 Draw and label the circuit symbol of an op amp. Include the power terminals. (6) 7.5 With reference to the ideal op-amp circuits below, draw the given input and

output wave-form diagrams on the same y-axis. Label the wave forms.

7.5.1

FIGURE 7.1: IDEAL OP-AMP CIRCUIT (3) 7.5.2

FIGURE 7.2: IDEAL OP-AMP CIRCUIT (3) 7.6 State TWO advantages of using negative feedback in an op-amp circuit. (2)

7.7 Refer to FIGURE 7.3 and answer the questions that follow.

FIGURE 7.3: OP-AMP CIRCUIT 7.7.1 Identify the op-amp configuration. (1) 7.7.2 Draw the input and output signal on the same y-axis. Label the

wave forms.

(3) 7.7.3 Calculate the voltage gain. (3) 7.7.4 Calculate the output voltage if an input signal of 2,5 V is applied to

the op amp.

(3)

Vout

_

+_

V1

V2

Input

Output

Rin

Rf

Vin Vout

+

_ Rf = 45 kΩ Rin = 15 kΩ Vin = 2,5 V

Input

Output

Vout

V1

+_

_

V2

Input

Output



7.8 Name TWO applications of an astable multivibrator circuit. (2)

7.9 With reference to FIGURE 7.4, draw the input wave form shown in FIGURE 7.5 and the output wave form directly below it.

FIGURE 7.4: BI-STABLE MULTIVIBRATOR

FIGURE 7.5: INPUT WAVE FORM FOR THE CIRCUIT IN FIGURE 7.4 (4)

R2

R1 Vout

+

_

R3

Trigger pulse

Trigger pulse

Vout

+V

-V

0

0


Copyright reserved

7.10 With reference to FIGURE 7.6, answer the questions that follow.

7.10.1 Identify the type of feedback used in the RC phase-shift oscillator. (1) 7.10.2 State ONE application of the oscillator. (1) 7.10.3 Calculate the oscillation frequency for an RC phase-shift oscillator

that uses three RC networks. The resistors are all 15 Ω. The capacitors are all 150 nF.

(3)

7.11 With reference to FIGURE 7.7, answer the questions that follow.

7.11.1 State ONE application of the integrator circuit. (1) 7.11.2 Draw the input and output wave forms of the op-amp integrator

circuit.

(6) [50]

TOTAL: 200

FIGURE 7.6: RC PHASE-SHIFT OSCILLATOR

FIGURE 7.7: OP-AMP INTEGRATOR CIRCUIT

Rin

Vout

+

Vin _

C

R1

C1 C2 C3

R1

R2 R3 +

-

0v

Vout

Electrical Technology DBE/Feb.–Mar. 2016 NSC

Copyright reserved

FORMULA SHEET

THREE-PHASE AC GENERATION RLC CIRCUITS Star fL2Xl S

pl V3V fC2

1Xc S

pl II

(LC)21

frS

Delta

pl I 3I Series pl VV lcrt IIII

2cl2 XXRZ ~

θcosI3VP pp ll XIV θcosIV3P ll u cc XIV

ll I V3S Z IVt θsin I V3Q ll 2cl

2rt VVVV ~

SPθCos

ZVI t

t

p

pp I

VZ Z

RθCos

Two wattmeter method

t

r

VVθCos

21t PPP

RXQ l

Parallel OPERATIONAL AMPLIFIERS lcrt VVVV

amp op inverting RR

VVA Gain

in

f

in

outv ¸

¹

·¨©

§ R

VI rr

amp op inverting-non RR1

VVA Gain

in

f

in

outv

c

cc X

VI

oscillatorHartley CL2

1ft

rS

ll X

VI l

oscillator shift-phase RC RC62

1frcS

2cl2

rl I~III

)...VV(VV n21out

t

r

II

θCos

RXQ l

Electrical Technology DBE/Feb.–Mar. 2016 NSC

Copyright reserved

THREE-PHASE MOTORS AND STARTERS THREE-PHASE TRANSFORMERS Star Star

pl V3V pl V3V

pl II pl II Delta Delta

pl I 3I pl I 3I

pl VV pl VV Power Power

θ cosppI3VP θ cosppI3VP θ cos I V3P ll θ cos I V3P ll

ll I V3S ll I V3S θ sin I V3Q ll θ sin I V3Q ll

SP

θ Cos

primary p

secondary p

s

p

secondary p

primary p

II

NN

VV

in

out

PPη Efficiency

in

out

PP

η Efficiency

ηθ cosSlossesPP inout

uu

ηθ cosSlossesPP inout

uu

pf60ns

u

s

rsunit per n

nnSlip

unit persr S1nn

100%n

nn%slip

s

rs u


MARKS: 200

This memorandum consists of 15 pages.

GRAAD 12

ELECTRICAL TECHNOLOGY

FEBRUARY/MARCH 2016

MEMORANDUM

NATIONAL SENIOR CERTIFICATE

GRADE 12

Electrical Technology 2 DBE/Feb.–Mar. 2016 NSC – Memorandum


INSTRUCTIONS TO THE MARKERS 1. All questions with multiple answers imply that any relevant, acceptable

answer should be considered.

2. Calculations: 2.1 All calculations must show the formulae. 2.2 Substitution of values must be done correctly. 2.3 All answers MUST contain the correct unit to be considered. 2.4 Alternative methods must be considered, provided that the correct

answer is obtained.

2.5 Where an incorrect answer could be carried over to the next step,

the first answer will be deemed incorrect. However, should the incorrect answer be carried over correctly, the marker has to re-calculate the values, using the incorrect answer from the first calculation. If correctly used, the candidate should receive the full marks for subsequent calculations.

3.

This memorandum is only a guide with model answers. Alternative interpretations must be considered and marked on merit. However, this principle should be applied consistently throughout the marking session at ALL marking centres.



QUESTION 1: OCCUPATIONAL HEALTH AND SAFETY 1.1 Unsafe conditions include:

− Inadequate guards around machinery. − No eye protection goggles in the workshop and around the bench

grinder. − Loose and dangerous components on moving machinery.

(1)

1.2 An unsafe action is an action performed by a person/worker that could

cause: − Injury to him/herself or his/her colleagues − Cause damage to tools and equipment − Render a workplace unsafe − Lead to loss of income to the employer

(2) 1.3 Protocol to follow when discovering a person experiencing electrical shock is:

− Do not touch the victim with bare hands until the supply is turned off. − Switch off the supply. − Call a teacher or medical person for help. − If the electricity cannot be switched off and the victim is still in contact

with it push the wire away with an insulated object.

(4)

1.4 Productivity is an important work ethic to assist the growth of South Africa's

economy due to the following reasons: − Safe working procedures are more productive as less time is lost due to

injuries and downtime related to accidents. − Efficient working methods lead to less use of raw materials, thus

increasing profits. − Good ergonomics lead to cleaner and safer work environments and

promotes worker satisfaction and morale. − Workers with a high morale and a good safety record tend to follow

instructions more precisely and enact safe working procedures. − Effective monitoring and reporting systems lead to better quality

assurance of products, thus placing a better product in the market within a shorter time frame, thus promoting productivity.

(3) [10] QUESTION 2: THREE-PHASE AC GENERATION 2.1 A Kilo-watt hour meter (1) 2.2 Two advantages of three-phase systems over single-phase systems are:

− 3φ can be operated in star or delta.

− Three-phase systems can supply both three-phase and single-phase installations of power

− In generators and motors, for the same size frames, three-phase machines delivers more power than single-phase machines

(2)



2.3

(5)

Note to markers:

No additional marks are awarded for the manipulation of the formulae. Manipulation is shown to illustrate how the formula was derived.

2.4 2.4.1

A 461.88

25 x 3

20000

I x 3

SV

I V 3

L

L

LL

=

=

=

=S

(3) 2.4.2

V 267.67

1.73

462.43

3

VV

V3V

L

P

PL

=

=

=

=

(3) 2.5 2.5.1

kW 12

kW 4)(8

P21T

=+=+= PP

(3)

+Vmax

-Vmax

Ph1 or L1 or ER

1200 1200

0

Showing amplitude Showing displacement of 1200

Ph2 or L2 or Ey

Ph3 or L3 or ER



2.5.2

A 22.79

0.8 x 380 x 3

12000

Cosθ V x 3

PI

Cosθ I V 3P

L

L

LL

=

=

=

=

(3) [20] QUESTION 3: THREE-PHASE TRANSFORMERS 3.1 By laminating and insulating the laminations of the core of the transformer. (1) 3.2 Two similarities between single phase and three-phase are:

− Both have the same functional operations − Transformers are used to step down or step up the supply voltage − Both can have either the closed core type or shell core type − No electrical connections between primary and secondary windings, with

the exception of the autotransformer.

(2) 3.3 Two factors that may cause excessive heating in a transformer are:

− Insufficient ventilation − Constant overloading − Loose connections − Ineffective tap-changer contacts − Impure/carbonized/insufficient transformer oil

(2) 3.4 Applications of delta-star connected transformers in power distribution

systems are: − Single and three-phase supply to Commercial sites

− Three-phase supply to Industrial areas

− Single and three-phase supply to domestic installations − Single and three-phase supply to agricultural installations − Three-phase supply to other substations (transformers) in a ring-fed

supply network.

(2) 3.5 The function of a transformer is to 'step down' or to 'step up'

(transform) the voltage in a distribution network to the required value.

(3)



3.6 3.6.1 kV 6.6V

VV

PH

PHL

=∴=

(2) 3.6.2

A30I

II

P

PL

=∴=

(2) 3.6.3

A 1.04

6600

23030

V

VII

Ph( p)

Ph( s)Ph( s)

Ph( p)

=

×=

×=

(3) 3.6.4

1:30N:N

1.04

30

N

N

I

I

N

N

SP

S

P

PH( p)

PH( s)

S

P

=

=

=

(3) [20] QUESTION 4: THREE-PHASE MOTORS AND STARTERS 4.1 Applications of three-phase motors include:

− pumps − lifts − cranes

(1)

4.2 Advantages of a three-phase over single-phase motors:

− For the same size frame a three-phase motor delivers more power − Three-phase motors are self-starting − More robust − Simple construction

(3) 4.3 4.3.1 At start motors draw more than the motors rated current. This may

lead to unnecessary tripping of the motor and the increased current at start causes wear on switch gear.

(3) 4.3.2 The motor is started in the star mode which reduces the voltage

across each phase of the motor as in star VPH = √3 VL. As the voltage across each phase is reduced, the current in each phase will also be reduced.

(3)



4.4 The operation of three-phase squirrel cage induction motor: − Three-phase supply is such that the peak voltage of each phase is

reached at 120o intervals. − When a squirrel cage motor is connected across a three phase

alternating supply, alternating current will flow in the respective stator windings.

− As a result the alternating current will set up a magnetic field in and around the respective stator windings.

− The stator windings are however spaced 120o apart around the axis of the motor.

− The result is that the magnetic field has a rotating maximum flux density as the peak in each winding is reached at a 120o interval, resulting in a rotating magnetic field.

− A squirrel cage rotor consists of cage like conductors bound electrically with a short circuit ring at each end.

− The rotating magnetic field will sweep across the rotor conductors of the squirrel cage rotor.

− As the magnetic field sweeps over the rotor conductors, the magnetic flux will cut/cross the rotor conductors.

− Faraday's law determines that an EMF will be induced in the rotor windings due to the sweeping action of the rotating magnetic field.

− Lenz's Law will determine that the induced current will be such that its force will oppose the inducing action (from the stator), thus establishing a repelling force between the stator and rotor (due to the opposing magnetic fields), thus forcing the rotor into rotation.

− When the speed of the rotor approaches the speed of the rotating magnetic field (synchronic speed), the inducing action is reduced and the rotor tends to slow down. The result is that the rotor rotates at a speed lower than that of the rotating magnetic field (synchronic speed)

(7) 4.5 4.5.1

(5) Coil 1:U1 – U2

Coil 2: V1 – V2 Coil 3: W1 – W2 L1 , L2, L3 – 3 Phase specified N: Star is specified E – Not requested in the question

U1 V1 W1

W2 U2 V2

L1 L2 L3 N

E



4.5.2 The reading on the meter should be of a high resistive value, more than 1 MΩ, this will indicate that there is no electrical connection between the windings showing sound/good insulation.

(3)

4.5.3 A low resistance reading will indicate that there is electrical connection

between the winding and earth. This will indicate any electrical fault that may lead to an operator being shocked in the motor is energised.

(3)

4.6

5

600

50 60

N

f 60 pairs Pole

S

=

×=

×=

(3)

4.7 4.7.1

kVA 10.53

16 x 380 x 3

I V 3SLL

==

=

(3)

4.7.2

η=100%

kW 8.95

0.85 x 10.53

θ Cos x S

==

=P

(3)

4.7.3

kW 8.06

0.9 x 8.95

x PP

P

P

io

i

o

===

=

η

η

(3)

[40] QUESTION 5: RLC 5.1 Factors influencing the capacitive reactance are:

− Value of capacitance − Frequency of the supply

(2) 5.2 Reactance is the opposition of the specific reactive component to the flow

of current in AC circuits Impedance is the total opposition offered to the flow of current in an AC circuit which contains resistive and reactive components

(2)



5.3

(4) 5.4

80

50

4000

=

=

=Z

XQ

L

(3) 5.5 5.5.1

Ω=

=

=

−

73,67

1047502

1

2

1

6xxx

fCXC

π

π

(3) 5.5.2

Ω==

=−

66,125

10400502

2

3xxx

fLXL

π

π

(3) 5.5.3

Hz

LC

fr

71.36

1047104002

1

2

1

63

=

×××=

=

−−π

π

(3) [20]

Z [Ω]

R XC>XL XL>XC

fr F[Hz]



QUESTION 6: LOGIC 6.1 Advantages of a PLC over a hardwired systems are:

− Reduced space. PLCs are solid state devices and are compact and small compared to hard wire logic.

− Less maintenance PLCs have error diagnostic units making it easy to trouble shoot.

− Faster response time it can process thousands of items a second.

(2) 6.2

(6) 6.3 Output devices that can be used with a PLC are:

− Motor contactor − indicator lamps − relays − switches

(2) 6.4

C

A) A( C

AC CA

B)B( ACB)B( C A

C BA C BA C B A C BAF

=+=

+=

+++=

+++=

(5) 6.5 PLCs could be programmed using the following methods:

− Ladder diagrams − Function blocks − Sequential functions − Charts − Instructional list − Structured text

(3)

Input

Check Inputs via input interface

Process

Execute Instructions according to the program

Output

Update Outputs according to the program and inputs and starts again

Cycle Repeats



6.6 6.6.1

(6) 6.6.2 DCBDCADCBY ++= (3) 6.7 6.7.1 Sequence starter with a time delay circuit

Note to markers: The circuit cannot be star delta starter as there is no lockout function included in the circuit.

(2) 6.7.2

(8) Note to markers:

− The candidate may use inverse functions (simulating real world NO and NC switches) in the ladder circuit, which must be considered. Should it function correctly marks are to be awarded to the candidate. − Note that some labels may differ from that of the learner. − Please check that the learner utilises labelling consistently throughout the answer.

6.7.3 PLC's allow for the use of markers as the number of operands3 that

can be placed in a rung3 of the Ladder program is limited3 due to hardware design constraints. A marker/flag is a function of PLC programming that can be used as a placeholder, or a subroutine which in turn simplifies the ladder program.

(3) [40]

BA BA AB BA

DC 0 0 0 0

DC 1 1 1 0 CD 1 0 0 1

DC 0 0 0 0

Correct groupings

LAMP

O/L STOP MARKER/FLAG (MO1)

START 2

START 1 O/L STOP OUTPUT LAMP

OUTPUT MOTOR

MOTOR

MO1

TIMER

TIMER 01



QUESTION 7: AMPLIFIERS 7.1 Characteristics of ideal op-amps are:

− Open-loop voltage gain AV = infinite − Input impedance Zin = infinite − Output impedance Z0 = zero − Bandwidth = infinite − Unconditional stability − Differential inputs, i.e. two inputs − Infinite common-mode rejection

(2)

7.2 The bandwidth is the range of frequencies within which an amplifier can

amplify without distorting the output signal (retain linearity) or losing gain.

(3) 7.3 Positive feedback is obtained when the output signal of an amplifier circuit is

fed back to the input of the circuit. When the signal is fed back to the input, it is in phase with the input signal, thus added to the input signal.

(3) 7.4

(6) 7.5 7.5.1

(3)

Output

Input Amplification Cycles coincide/ same frequency Inversion

Inverting input

Non-inverting input

+Vsupply (+Vcc)

-Vsupply (-Vcc)

Output

-

+



7.5.2

(3) 7.6 Advantages of using negative feedback are:

− Bandwidth is increased. − Level of noise (hiss) is decreased. − Gain is decreased. − Deformation of the input signal is reduced.

(2) 7.7 7.7.1 Non inverting op-amp (1) 7.7.2

(3) 7.7.3

4

15x10

45x101

R

R1

V

VAV

3

3

in

f

in

out

=

+=

+==

(3) 7.7.4

V 10

2.5 x 4

V AVinvout

==

×=

(3) 7.8 The a-stable multivibrator can be used as a:

− Tone generator − Clock pulse generator − Square wave generator − Fake alarm circuit if used with two LED's

(2)

Output Amplification Cycles coincide/ same frequency Inversion due to V1 on inverting input and V2 on non-inverting input Common mode

V1 V2

Output

Input

Amplification In phase Non inversion



7.9

(4) 7.10 7.10.1 Positive feedback (1) 7.10.2 Sine wave generator

Tone Oscillator Buzzer driver

(1) 7.10.3

Hz 43.31

10 150 15 62π1

6RC2π1

f

9

RC

=×××

=

=

−

(3) 7.11 7.11.1 Timing circuit (1)

Trigger pulse

Vout

+V

+V

-V

-V

0

0


Copyright reserved

7.11.2

(6) 50

TOTAAL: 200

Vout if T=smaller

+V

+V

-V

-V

0

0

Vin= Square wave 2 Marks

Vout Alternative

if T=larger

Note: Higher order answers will show the wave starting from zero, thus receiving additional 2 marks Other answers will receive 4 marks maximum.

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