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4C : ignals checkpoints


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CHECKPOINT A

1. Calculate the frequency of waveforms with periods of (a) 10 s, (b) 5 ms, (c) 200 Ás

2. What is the period of waveforms with frequencies of (a) 20 Hz, (b) 150 kHz, (c) 0.5 hz?

3. Find values for the period, frequency, peak amplitude, peak-to-peak amplitude and rms amplitude for the sine wave shown below:

4. Use graph paper and choose appropriate scales to sketch V/t graphs for sine waves as follows:

(a) period 10 ms, peak-to-peak amplitude 5 V.
(b) frequency 250 Hz, peak amplitude 10 V.
(c) frequency 4 kHz, rms amplitude 6 V.

to ANSWERS A Back

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CHECKPOINT B

1. What is a complex waveform?

2. Can all waveforms be built up from sine waves?

to ANSWERS B Back

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CHECKPOINT C

1. Distinguish between square and pulse waveforms.

2. What duty cycle value corresponds to a mark space ratio of 0.33?

3. Draw an accurate V/t graph of a pulse waveform with a repetition rate = 100 Hz, LOW voltage = 0.2 V, HIGH voltage = 4.5 V, and mark space ratio = 0.25.

to ANSWERS C Back

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CHECKPOINT D

1. Read through the instructions for setting up and using the oscilloscope again, then complete the table to show the functions of the oscilloscope controls:

control function
INTENSITY
FOCUS
  allows the horizontal scale of the V/t graph to
be changed
VOLTS/DIV
X-POS allows the entire V/t graph to be moved from
side to side on the screen
Y-POS

2. Look carefully at the oscilloscope traces shown below and suggest which control(s) need to be adjusted to produce a clear display on the oscilloscope screen:

A

 

 

 

B

 

 

 

C

 

 

 

D

 

 

 

 

to ANSWERS D Back

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ANSWERS A

1. Use formula:

(a) 0.1 Hz, (b) 200 Hz, (c) 5 kHz

2. Use formula:

(a) 50 ms, (b) 6.7 Ás, (c) 2 s

3. period = 4 ms, frequency = 250 Hz, peak amplitude = 2.4 V, peak-to-peak amplitude = 4.8 V,
rms amplitude = 0.7 x 2.4 = 1.7 V

back to CHECKPOINT A


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ANSWERS B

1. A complex waveform is formed by adding sine waves together (fundamental + harmonics), or by adding sine waves to a DC signal.

2. Yes!

back to CHECKPOINT B


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ANSWERS C

1. A square wave has equal LOW and HIGH times and is centred around 0 V, with equal areas above and below the X-axis. A pulse waveform can have any mark space ratio and has HIGH and LOW levels between 0 V and the power supply voltage.

2. 25%

3. Pulse waveform:

back to CHECKPOINT C


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ANSWERS D

1. Completed table:

control function
INTENSITY the brightness of the spot can be increased or
decreased to give an effective display
FOCUS the spot should be focused to a bright dot for slow
TIME/DIV settings or to a thin line
TIME/DIV allows the horizontal scale of the V/t graph to
be changed
VOLTS/DIV allows the vertical scale of the V/t graph to be
changed
X-POS allows the entire V/t graph to be moved from
side to side on the screen
Y-POS allows the entire V/t graph to be moved up and
down on the screen

2. Adjusting controls:

A: The trace is off the screen at the top and can be brought back using Y-POS

B: The vertical scale is too sensitive, so VOLTS/DIV should be rotated anti-clockwise

C: The V/t graph is compressed, so that you can't see the changes taking place. Two controls need to be changed. The vertical scale is not sensitive enough, so VOLTS/DIV should be rotated clockwise. In addition, the spot is not moving fast enough across the screen. You need to rotate TIME/DIV clockwise to make the horizontal scale more 'spread out'.

D: This can happen when not all of the oscilloscope controls have been put in their 'normal' positions. All the small square buttons must be in the OUT position.

back to CHECKPOINT D


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