Author Topic: Basic Function of an Oscilloscope  (Read 394649 times)

Fu-Kwun Hwang

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Basic Function of an Oscilloscope
« on: January 29, 2004, 10:43:07 pm »
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Like a televison screen, the screen of an oscilloscope consists of a cathode ray tube. Although the size and shape are different, the operating principle is the same. Inside the tube is a vacuum. The electron beam emitted by the heated cathode at the rear end of the tube is accelerated and focused by one or more anodes, and strikes the front of the tube, producing a bright spot on the phosphorescent screen.

The electron beam is bent, or deflected, by voltages applied to two sets of plates fixed in the tube. The horizontal deflection plates, or X-plates produce side to side movement. As you can see, they are linked to a system block called the time base. This produces a sawtooth waveform. During the rising phase of the sawtooth, the spot is driven at a uniform rate from left to right across the front of the screen. During the falling phase, the electron beam returns rapidly from right ot left, but the spot is 'blanked out' so that nothing appears on the screen.

In this way, the time base generates the X-axis of the V/t graph.

The slope of the rising phase varies with the frequency of the sawtooth and can be adjusted, using the TIME/DIV control, to change the scale of the X-axis. Dividing the oscilloscope screen into squares allows the horizontal scale to be expressed in seconds, milliseconds or microseconds per division (s/DIV, ms/DIV, µs/DIV). Alternatively, if the squares are 1 cm apart, the scale may be given as s/cm, ms/cm or µs/cm.

The signal to be displayed is connected to the input. The AC/DC switch is usually kept in the DC position (switch closed) so that there is a direct connection to the Y-amplifier. In the AC position (switch open) a capacitor is placed in the signal path. As will be explained in Chapter 5, the capacitor blocks DC signals but allows AC signals to pass.

The Y-amplifier is linked in turn to a pair of Y-plates so that it provides the Y-axis of the the V/t graph. The overall gain of the Y-amplifier can be adjusted, using the VOLTS/DIV control, so that the resulting display is neither too small or too large, but fits the screen and can be seen clearly. The vertical scale is usually given in V/DIV or mV/DIV.

The trigger circuit is used to delay the time base waveform so that the same section of the input signal is displayed on the screen each time the spot moves across. The effect of this is to give a stable picture on the oscilloscope screen, making it easier to measure and interpret the signal.

Changing the scales of the X-axis and Y-axis allows many different signals to be displayed. Sometimes, it is also useful to be able to change the positions of the axes. This is possible using the X-POS and Y-POS controls. For example, with no signal applied, the normal trace is a straight line across the centre of the screen. Adjusting Y-POS allows the zero level on the Y-axis to be changed, moving the whole trace up or down on the screen to give an effective display of signals like pulse waveforms which do not alternate between positive and negative values.
The above information are quoted from http://www.doctronics.co.uk/scope.htm


This java applet shows the basic functions of an oscilloscope.
The oscilloscope is an electronic instrument widely used in making electrical measurements.
The main component of the oscilloscope is the cathode ray tube (CRT).
The CRT is a vacuum tube in which electrons are accelerated and deflected under the influence of electric field. The electrons are deflected in various directions by two sets of plate placed at right angle to each other in the neck of the tube.
Signal for the horizontal deflection plate (X-axis) is generated by the scope
It mathematic form is Fx(t)= C t + D (default)
C : time scale
D : horizontal offset
The external signal (need to be measured) is applied to the vertical deflection plate (Y axis).
The default form for this java applet is Fy(t)=A sin(w t + B)
    You can change X or Y axis signal to either kind of signal.

It can be operated in different mode



X = C t + DX = A sin( w t + B)
Y = A sin(w t + B)default modeLissajou's figure
Y = C t + Dnot supported for an oscilloscope


For parameter B please enter value in degree.
Click within one of the knobs and drag the mouse button clockwise/countercolockwise to change values for Time/Div, Volt/Div , yOffset and xOffset.

For example: You can produce Lissajou's figure:


Registed user can get files related to this applet for offline access.
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Jeanke

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The Applet of the oscilloscope
« Reply #1 on: February 24, 2005, 08:17:38 pm »
Hi,

is it possible to download this applet?
I'm very interested, because I have to make an end work for school.

Greetz,

Jeanke

Fu-Kwun Hwang

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topic34
« Reply #2 on: February 25, 2005, 07:58:39 am »
You will find "GET APPLET FILES' button at the end of the first posted message if you are a registered user and login to the system.
When you click the button, you will get files related to the applet in your email.

bobsmith

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topic34
« Reply #3 on: May 03, 2005, 07:29:05 pm »
is possible to actually obtain the code for this in *.java format?

Fu-Kwun Hwang

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topic34
« Reply #4 on: May 04, 2005, 08:06:58 am »
You shpuld have received in your email account.
 However it was written many years ago with JDK1.0.2.
You might need to make some change to make it works with current verison JDK.

mcbeeone

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Oscope
« Reply #5 on: October 24, 2005, 09:18:46 am »
This is a very nice demo. I think I shall have my students try it BEFORE I let them touch the real thing. :)

abby

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Re: Basic Function of an Oscilloscope
« Reply #6 on: September 30, 2007, 05:27:16 am »
than you sir for this demo

raktekan

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Re: Basic Function of an Oscilloscope
« Reply #7 on: November 04, 2007, 05:37:42 pm »
thank you

jack

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Re: topic34
« Reply #8 on: November 20, 2007, 01:47:04 pm »
is possible to obtain the code for this in *.java format?

Fu-Kwun Hwang

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Re: Basic Function of an Oscilloscope
« Reply #9 on: November 20, 2007, 08:43:20 pm »
Could you let me know why you need the source code?

jack

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Re: Basic Function of an Oscilloscope
« Reply #10 on: November 26, 2007, 05:05:52 pm »
i need it for a project to my students

Fu-Kwun Hwang

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Re: Basic Function of an Oscilloscope
« Reply #11 on: November 26, 2007, 08:50:55 pm »
You should have received the source code now. However, could you tell me what you want to do with it?
Is there something need to be improved for the applet?
Let me know and may be I can help.

DolphinDream

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Re: Basic Function of an Oscilloscope
« Reply #12 on: December 28, 2007, 12:30:16 am »
Hi, I was wondering...maybe you can help me with similar program. I need to make a program that calculates frequency of, how i say it in english, coinciding of two frequencies.
For example if i had two frequencies in Hz:
__|'''''|____|'''''|____|'''''|____|'''''|____
__|''''''''|______|''''''''|______|''''''''|____
I need a program that calculates frequency when both of them are '''''.
 ;D

Fu-Kwun Hwang

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Re: Basic Function of an Oscilloscope
« Reply #13 on: December 29, 2007, 10:03:37 am »
Are you talking about the beat product from two very close frequency signal?

DolphinDream

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Re: Basic Function of an Oscilloscope
« Reply #14 on: January 07, 2008, 07:43:34 pm »
Are you talking about the beat product from two very close frequency signal?

Yes, i think so... i need a program that calculates frequency...if i put two frequencys ontop eachother, then in what frequency they are at same point (that is at max).