# Using an Oscilloscope

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## How to use an oscilloscope

The position of the spot of light on the screen is affected by the pd across either pair of deflecting plated, the spot on the screen stays in the same position. If a pd is applied across the X-plates, the spot deflects horizontally. A pd across the Y-plates makes it delfect vertically. nIn both cases, the displacement of the spot is proportional to the applied pd.

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## Displaying a Waveform

• the X-plates are connected to the oscilloscope's time base circuit which makes the spot move at constant speed left to right across the screen, then back again much faster. Because the spot movesat constant speed across the screen, the x-scale can be calibrated, usually in milliseconds or microseconds per centimetre.
• the pd to be displayed is connected to the Y-plates via the Y-input so the spot moves up and down as it moves left to right across the screen. As it does so, it traces out the waveform on the screen. Because the vertical displacement of the spot is proportional to the pd applied to the Y-plates, the Y-input is calibrated in volts per centimetre (or per division if the grid on the oscilloscope screen is not a centimetre grid). The calibration value is usually referred to as the Y-sensitivity or Y-gain of the oscilloscope.
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## Measurements

• To measure the peak pd, observe the waveform height from the bottom to the top of the wave. The wave's amplitude is half of this value. Times this value by whatever the Y-gain is set at.
• To measure the frequency of the alternating pd, we need to measure the time period (T) of the waveform. We can then calculate f as f = 1/t
• The time period is the distance corresponded to by one full cycle times by the value which the time base control is set to.
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## Measuring the speed of ultrasound

• The time base circuit of an oscilloscope can be used to trigger an ultrasonic transmitter so that it sends out a short pulse of ultrasonic waves. An ultrasonic receiver canm be used to detect the transmitted pulse. If the receiver signal is applied to the Y-input of the oscilloscope, the waveform of the receiver pulse can be seen on the oscillscope screen.
• Because the pulse takes time to travel from the transmitter to the receiver, it is displayed on the screen at the point reached by the spot as it sweeps across from left to right. By measuring the horizontal distance on the screen from the leading edge of the pulse to the start of the spot's sweep, the travel time of the pulse from the transmitter to the receiver can be determined.
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