4.7- USING AN OSCILLOSCOPE Flashcards
What does an oscilloscope consist of?
specially made electron tube and associated control circuits
What does an electron gun at one end of the glass tube emit and towards where? (oscilloscope)
emits electrons in beam towards fluorescent screen at other end of tube
What is emitted where the beam hits the screen? (oscilloscope)
light emitted from spot on screen where beam hits screen
What is the position of the spot of light on the screen affected by?
pd across either pair of deflecting plates
What happens to the spot on the screen with no pd across either set of deflecting plates?
spot on the screen stays in the same position
What happens to the spot if a pd is applied across the X-plates?
spot deflects horizontally
What happens to the spot if a pd is applied across the Y-plates?
spot deflects vertically
What is the displacement of the spot proportional to?
displacement of spot proportional to applied pd
What are the X-plates connected to?
oscilloscope’s time base circuit
What does the X-plates being connected to the oscilloscope’s time base circuit do the spot?
spot moves at constant speed left to right across the screen, then back again much faster
What can be done as the spot moves at constant speed across the screen?
x-scale can be calibrated
What is the x-scale usually calibrated in? (2) (hint- unit)
milliseconds or microseconds per centimetre
What is the pd to be displayed connected to?
Y-plates via Y-input
What happens to the spot as the pd to be displayed is connected to the Y-plates via Y-input?
spot moves up and down as it moves left to right across the screen
What does the spot trace out as it moves up and down as it moves left to right across the screen?
traces out the wavefront on the screen
What is the vertical displacement of the spot proportional to?
vertical displacement of spot proportional to pd applied to Y-plates
What is the Y-plate calibrated in?
volts per centimetre (or per division if the grid on the oscilloscope screen is not a cm grid)
What is the calibration value of the Y-plate usually referred to as?
Y-sensitivity or Y-gain of the oscilloscope
How do you measure the peak pd?
observe waveform height from bottom to top
half this to get the amplitude
multiply Y-gain and amplitude to get peak pd
How do you measure frequency of alternating pd?
measure time period:
see what distance one full cycle corresponds to
multiply time base by this distance to get time period
f = 1 / T
What can the time base circuit of an oscilloscope be used to trigger? (measuring the speed of ultrasound)
ultrasonic transmitter so it sends out a short pulse of ultrasonic waves
What can be used to detect the transmitted pulse? (measuring the speed of ultrasound)
ultrasonic transmitter
How can the waveform of the receives pulse be seen on the oscilloscope screen? (measuring the speed of ultrasound)
if receiver signal applied to Y-input of oscilloscope
What happens as the pulse takes time to travel from the transmitter to the receiver? (measuring the speed of ultrasound)
it’s displayed on the screen at the point reached by the spot as it sweeps across the left to right
How can the travel time of the pulse from the transmitter to the receiver be determines? (measuring the speed of ultrasound)
by measuring the horizontal distance of the screen from the leading edge of the pulse to the start of the spot’s sweep
How to calculate the travel time? (measuring the speed of ultrasound)
pulse multiplied by time base control
What can be calculated if the distance from the transmitter to the receiver is known?
speed of ultrasound (from distance / travel time)
