Transcript Measurements - Oscilloscopes

Chelmsford Amateur Radio Society
Advanced Course
(10) Measurements
Part-3 - Oscilloscopes
Chelmsford Amateur Radio Society
Advanced Licence Course
Anthony Martin M1FDE
Slide Set 23: v1.0, 13-Oct-2004
(10) Measurements-3 - Oscilloscopes
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Oscilloscopes
• Oscilloscopes can be used for
– Measuring DC voltages
– Measuring amplitude
– Measuring waveform period and frequency
– Checking waveforms
• Oscilloscopes contain
– A CRT or LCD display screen
– A horizontal timebase
– A vertical deflection input (or two)
– A timebase trigger
Chelmsford Amateur Radio Society
Advanced Licence Course
Anthony Martin M1FDE
Slide Set 23: v1.0, 13-Oct-2004
(10) Measurements-3 - Oscilloscopes
2
Oscilloscope Controls
Y-axis
X-axis
Focus
Brightness
Chelmsford Amateur Radio Society
Advanced Licence Course
Y input
Anthony Martin M1FDE
Vertical
gain
(V/div)
Horizontal
timebase
Slide Set 23: v1.0, 13-Oct-2004
(10) Measurements-3 - Oscilloscopes
(ms/div)3
Measuring Amplitude
• Check variable controls are as “cal”
• Obtain a large trace
• Read the pk-pk amplitude in divisions.
• Read the vertical gain (volts/division)
• Calculate the pk-pk voltage
• The amplitude is half the pk-pk value
• The RMS voltage is amplitude x 0.707
Chelmsford Amateur Radio Society
Advanced Licence Course
Anthony Martin M1FDE
Slide Set 23: v1.0, 13-Oct-2004
(10) Measurements-3 - Oscilloscopes
4
Measuring Frequency
• Check variable controls are as “cal”
• Display a suitable number of cycles (say 5)
1 2 3 4 5
• Read the total divisions for the cycles
• Calculate divisions for 1 cycle
• Read timebase setting (ms/division)
• Calculate period in seconds
• Calculate: Frequency = 1 / Period
Chelmsford Amateur Radio Society
Advanced Licence Course
Anthony Martin M1FDE
Slide Set 23: v1.0, 13-Oct-2004
(10) Measurements-3 - Oscilloscopes
5
Oscilloscope Probes
• Scope probes reduce input capacitance
and divide voltage, usually by 10.
• This means you must remember to
multiply voltage readings by 10.
• All probes must be adjusted to match the
’scope by connecting to ‘probe cal’ point
and tweaking for a level-topped square
wave.
Trimmer
Chelmsford Amateur Radio Society
Advanced Licence Course
Anthony Martin M1FDE
Slide Set 23: v1.0, 13-Oct-2004
(10) Measurements-3 - Oscilloscopes
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