ASSIGNMENT: CATHODE RAY OSCILLOSCOPE Name: Faisal Ahmed Moshiur
Group: A
Batch: 10
Roll: SH-99

Name: Faisal Ahmed Moshiur
Group: A
Batch: 10
Roll: SH-99

Cathode Ray Oscilloscope (CRO):
An oscilloscope is easily the most useful instrument available for testing circuits because it allows you to see the signals at different points in the circuit. The best way of investigating an electronic system is to monitor signals at the input and output of each system block, checking that each block is operating as expected and is correctly linked to the next. With a little practice, we will be able to find and correct faults quickly and accurately.
The screen of a CRO is very similar to a TV, except it is much simpler. We will not go into the similarities except to say that the "picture tube" on a TV and the "screen" on a CRO are both a special type of valve called a Cathode Ray Tube.
It is a vacuum tube with a cathode (negative electrode) at one end that emits electrons and anodes (positive electrodes) to accelerate the electron beam up/down and left/right to hit a phosphor coating at the end of the tube, called the screen. The electrons are called cathode rays because they are emitted by the cathode and this gives the oscilloscope its full name: Cathode Ray Oscilloscope or CRO.

Internal Components 1. An indirectly heated cathode which provides a source of electrons for the beam by "boiling" them out of the cathode. 2. The anode (or plate) which is circular with a small central hole. The potential of P creates an electric field which accelerates the electrons, some of which emerge from the hole as a fine beam. This beam lies along the central axis of the tube. 3. The grid: Controlling the potential of the grid controls the number of electrons for the beam, and hence the intensity of the spot on the screen where the beam hits. 4. The focusing cylinder: This aids in concentrating the electron beam into a thin straight line much as a lens operates in optics. 5. X, Y, deflection plate pairs: The X plates are used for deflecting the beam left to right (the x direction) by means of the "ramp" voltage. The Y plates are used for deflection of the beam in the vertical direction. Voltages on the X and Y sets of plates determine where the beam will strike the screen and cause a spot of light. 6. The screen: This is coated on the inside with a material which fluoresces with green light (usually) where the electrons are striking.

As well as this tube, there are several electronic circuits required to operate the tube, all within the C.R.O. along with the tube: 1. A power supply, operated from the 220 volt 50 cycle per second electrical "mains". This supply provides all the voltages required for the different circuits within the C.R.O. for operation of the tube. 2. A "saw tooth", or "ramp" signal generator which makes the spot move left to right on the screen. External controls for this circuit allow variation of the sweep width, and the frequency of the sweep signal. Because of the persistence of our vision, this sweep is often fast enough that what we see on the screen is a continuous horizontal line. 3. Amplifiers for the internally generated ramp signal, and for the "unknown" signal which we hook up to the C.R.O. for the purpose of displaying it. 4. Shift devices which allow us to control the mean position of the beam; up or down, or left to right. 5. The synchronizer circuit: This circuit allows us to synchronize the "unknown" signal with the ramp signal such that the resulting display is a nice clear signal like a snapshot of the unknown voltage vs. time.

C.R.O. Operation: Typical front-panel controls
Front Panel 1. On-off switch. 2. INTENSITY: This is the intensity control connected to the grid G to control the beam intensity and hence the brightness of the screen spots. The intensity shouldn’t be too high, just bright enough for clear visibility. The spot is being kept sweeping left to right so that beam may not "burn" a hole in the screen. 3. FOCUS allows to obtain a clearly defined line on the screen. 4. POSITION allows to adjust the vertical position of the waveform on the screen. (There is one of these for each channel). 5. AMPL/DIV. is a control of the Y (i.e. vertical) amplitude of the signal on the screen. (There is one of these for each channel). 6. AC/DC switch. This should be left in the DC position unless we cannot get a signal on-screen otherwise. (There is one of these for each channel). 7. A&B/ADD switch. This allows to display both input channels separately or to combine them into one. 8. +/- Switch. This allows to invert the B channel on the display. 9. Channel A input 10. Channel B input 11. X POSITION: This allows to adjust the horizontal position of the signals on the screen. 12. LEVEL: This allows to determine the trigger level; i.e. the point of the waveform at which the ramp voltage will begin in time base mode. 13. ms/µs This defines the multiplication factor for the horizontal scale in time base mode. (See 15 below.) 14. MAGN: The horizontal scale units are to be multiplied by this setting in both time base and xy modes. To avoid confusion, it was left at x1 unless it was really need to change it. 15. Time/Div. This selector controls the frequency at which the beam sweeps horizontally across the screen in time base mode, as well as whether the oscilloscope is in time base mode or xy (x VIA A) mode. This switch has the following positions: (a) X VIA A In this position, an external signal connected to input A is used in place of the internally generated ramp. (This is also known as xy mode.) (b) .5, 1, 2, 5, etc. Here the internally generated ramp voltage will repeat such that each large (cm) horizontal division corresponds to .5, 1, 2, 5, etc. ms. or µs depending on the multiplier and magnitude settings. (Note also the x1/x5 switch in 14 above.) 16. The following controls are for triggering of the scope, and only have an effect in time base mode. 17. A/B selector. This allows to choose which signal to use for triggering. 18. -/+ will force the ramp signal to synchronize its starting time to either the decreasing or increasing part of the unknown signal we are studying. 19. INT/EXT this will determine whether the ramp will be synchronized to the signal chosen by the A/B switch or by whatever signal is applied to the EXT. SYNC. Input. (See 21 below.) 20. AC/TV selectors. I've never figured out what this does. 21. External trigger input

The Cathode-ray oscilloscope
Working principle
The diagram represents a soft cathode ray oscilloscope which contains an inert gas such as Argon. Electrons are produced from the filament which is heated by a low tension current represented in the diagram as originating from a battery. These electrons enter into the field between the filament and anode, the difference of potential being, in this case, 500 to 1000 volts. They are thus accelerated and passed through the hole in A with considerable energy, and on striking the fluorescent screen, they make it luminous at the point of impact. The screen marked S is usually kept at a potential a little lower than that of the filament, so that electrons which tend to diverge are made to concentrate along the center of the beam. This is an example of electrostatic focusing, and its effect is to direct more electrons through the hole in the anode.
The focusing in this case is not enough to produce a sharply defined small spot on the screen and in the soft tube additional definition results from the presence of this inert gas. The gas is ionized by the stream of energetic electrons and the electrons produced in the process add themselves to the main stream. The resulting positively charged ions produce a field which tends to keep the electrons clustered round them and so prevent spreading.
The plates, XX and YY, are arranged in pairs with the plane of one pair perpendicular to that of the other, both parallel to the direction of the electron stream, as illustrated diagrammatically in the figure. One pair of plates horizontal and the other vertical, and one pair is at a short distance from the other. By the applications of fields to these plates the electron beam is changed, and since the beam has negligible inertia it follows the variation of the field instantaneously. The character of the variation is thus portrayed on the screen by a luminescent line.
In the hard tube of focusing is of a different character. The tube is exhausted to the state of high vacuum and the focusing is obtained either by electrostatic or magnetic fields. In the case of electrostatic focusing, the filament is surrounded by the control shield in the way already described, but there is a succession of anodes. Figure illustrates a two anode focusing device.
The second anode is the main accelerating device in this case, and is at a potential of 1000 to 2000 volts above that of the filament. The first anode, which lies between the filament and second anode, is maintained at about a quarter of the potential difference. The arrangement can be described as an electron gun. For still better focusing, an additional anode is required and the best potentials to employ are indicated with the apparatus.
In the case of magnetic focusing, the anode serves as an accelerator, as described in the case of the soft tube, and a screen surrounds the filament as before. The focusing is by means of a coil of wire round the neck of the tube, which carries an electric current and thus generates a magnetic field along the axis. Any electrons not moving in this direction spiral round the lines of force, and as their velocity components at right angles to the axis of the tube are not large, they spiral in paths of small radius and tend to come to the axis along which they move with the velocity acquired by the fall between the filament and anode. It will be observed in any but the very simple forms of soft tubes that the X and Y plates are not as simple as has been illustrated so far. The form often taken in practice is illustrated in another figure. The reason for this is to eliminate a form of a distortion known as origin distortion. One of each pair of plates is divided and the parts maintained at a difference of potential. In the diagram is shown a battery supply, but in practice the required difference is obtained from the tube power pack.
Thus the average p.d. through which the electrons fall is kept on stand and the sensitivity is unaltered. Electron beam generated by the electron gun first detected by the detection plates, and then directed onto the fluorescent coating of the CRO screen, which produces a visible light spot on the face plane of the oscilloscope screen. A detailed representation of a CRT is given in Figure. The

CRT is composed of two main parts,
1. Electron Gun
2. Deflection System
Electron gun
Electron gun provides a sharply focused electron beam directed toward the fluorescent-coated screen. The thermally heated cathode emits electrons in many directions. The control grid provides an axial direction for the electron beam and controls the number and speed of electrons in the beam. The momentum of the electrons determines the intensity, or brightness, of the light emitted from the fluorescent coating due to the electron bombardment. Because electrons are negatively charged, a repulsion force is created by applying a negative voltage to the control grid, to adjust their number and speed. A more negative voltage results in less number of electrons in the beam and hence decreased brightness of the beam spot. Since the electron beam consists of many electrons, the beam tends to diverge. This is because the similar (negative) charges on the electrons repulse each other. To compensate for such repulsion forces, an adjustable electrostatic field is created between two cylindrical anodes, called the focusing anodes. The variable positive voltage on the second anode cylinder is therefore used to adjust the focus or sharpness of the bright spot.

The Deflection System
The detection system consists of two pairs of parallel plates, referred to as the vertical and horizontal detection plates. One of the plates in each set is permanently connected to the ground (zero volt), whereas the other plate of each set is connected to input signals or triggering signal of the CRO. The electron beam passes through the detection plates. A positive voltage applied to the Y input terminal causes the electron beam to detect vertically upward, due to attraction forces, while a negative voltage applied to the Y input terminal causes the electron beam to detect vertically downward, due to repulsion forces. Similarly, a positive voltage applied to the X input terminal will cause the electron beam to detect horizontally toward the right, while a negative voltage applied to the X input terminal will cause the electron beam to detect horizontally toward the left of the screen. The amount of vertical or horizontal detection is directly proportional to the corresponding applied voltage. When the electrons hit the screen, the phosphor emits light and a visible light spot is seen on the screen. Since the amount of detection is proportional to the applied voltage, actually the voltages Vy and Vx determine the coordinates of the bright spot created by the electron beam.

Graticule
The graticule is a grid of squares that serve as reference marks for measuring the displayed trace. These markings, whether located directly on the screen or on a removable plastic filter, usually consist of a 1 cm grid with closer tick marks (often at 2 mm) on the central vertical and horizontal axis. One expects to see ten major divisions across the screen; the number of vertical major divisions varies. Comparing the grid markings with the waveform permits one to measure both voltage (vertical axis) and time (horizontal axis). Frequency can also be determined by measuring the waveform period and calculating it’s reciprocal. On old and lower-cost CRT oscilloscopes the graticule is a sheet of plastic, often with light-diffusing markings and concealed lamps at the edge of the graticule. The lamps had a brightness control. Higher-cost instruments have the graticule marked on the inside face of the CRT, to eliminate parallax errors; better ones also had adjustable edge illumination with diffusing markings. (Diffusing markings appear bright.) Digital oscilloscopes, however, generate the graticule markings on the display in the same way as the trace. External graticules also protect the glass face of the CRT from accidental impact. Some CRT oscilloscopes with internal graticules have an unmarked tinted sheet plastic light filter to enhance trace contrast; this also serves to protect the faceplate of the CRT. Accuracy and resolution of measurements using a graticule is relatively limited; better instruments sometimes have movable bright markers on the trace that permit internal circuits to make more refined measurements.

Operation of a CRO
In using the cathode-ray tube the potential difference to be investigated is connected across one pair of plates known as the Y-plates. If an alternating P.D. is connected to the plates and the X-plates are at equal potentials, the spot on the fluorescent screen will move to and fro in time with the supply, the extent of the swing being a measure of the amplitude of P.D. This examination gives no indication of how the P.D. varies with time. Information on this point can be obtained if the spot is made to cross the field in a direction at right angles to the oscillations. If the motion in this direction is made at a uniform speed the fluorescent track is a displacement graph of the motion and is thus a graph of the P.D. against the time. If the spot can be caused to move back, the trace can be repeated. By synchronization of the motion due to the X-plates with that due to the Y-plates, a stationary picture is obtained for the motion is so rapid that the fluorescence persists. In this way the screen is made to present a graph of P.D. dependence on time which can be examined under static conditions. The application of the required P.D. to the X-plates in order to produce the constant sweep provides a time scale of measurement known as a time base. In order to understand the principle of time bases we begin with a simple form based on the property of the neon lamp. The apparatus necessary is described as a neon time base. The potential is applied at points A, B which are connected through a variable resistance, R and condenser C. The condenser plates are connected to the X-plates and to a neon lamp. Suppose a potential V0 applied at AB. The condenser is charged through the resistance R and taken an infinitely long time to attain the full voltage, V0 .The potential V at any time, t after the beginning of changing is V=V x (1-e-tCR )

The neon lamp ashes when a certain potential V1 is applied to it. This causes the condenser to discharge and it continues to do so until a certain potential V2 is reached, when the potential, V1 is reached the process repeated. Thus the detector plates gradually attain the potential difference, V1 and then suddenly fall to V2 the process repeating itself as long as the tension is applied. Thus the spot moves across the Plate a distance corresponding to a P.D. of V1, then is back to that corresponding to V2 .In the case of the neon lamp, these potentials are about 170volts and 130volts, so that a range of 40volts is provided. There are two disadvantages associated with this time base. The first is that the range is small and the second that the sweep is not linear. This means that the sweep is not linear. This means that the P.D. between the plates is not proportional to the time taken to acquire it.

FUNCTION GENERATOR
A function generator is a device that can produce various patterns of voltage at a variety of frequencies and amplitudes. It is used to test the response of circuits to common input signals. The electrical leads from the device are attached to the ground and signal input terminals of the device under test.
Most function generators allow the user to choose the shape of the output from a small number of options. * Square wave - The signal goes directly from high to low voltage. * Sine wave - The signal curves like a sinusoid from high to low voltage. * Triangle wave - The signal goes from high to low voltage at a fixed rate.
The amplitude control on a function generator varies the voltage difference between the high and low voltage of the output signal.
The direct current (DC) offset control on a function generator varies the average voltage of a signal relative to the ground.
The frequency control of a function generator controls the rate at which output signal oscillates.
On some function generators, the frequency control is a combination of different controls.
One set of controls chooses the broad frequency range (order of magnitude) and the other selects the precise frequency.
This allows the function generator to handle the enormous variation in frequency scale needed for signals.
The duty cycle of a signal refers to the ratio of high voltage to low voltage time in a square wave signal.

FUNCTION OF FUNCTION GENERATOR
Analog function generators usually generate a triangle waveform as the basis for all of its other outputs. The triangle is generated by repeatedly charging and discharging a capacitor from a constant current source. This produces a linearly ascending or descending voltage ramp. As the output voltage reaches upper and lower limits, the charging and discharging is reversed using a comparator, producing the linear triangle wave. By varying the current and the size of the capacitor, different frequencies may be obtained.
A 50% duty cycle square wave is easily obtained by noting whether the capacitor is being charged or discharged, which is reflected in the current switching comparator's output. Most function generators also contain a non-linear diode shaping circuit that can convert the triangle wave into a reasonably accurate sine wave. It does so by rounding off the hard corners of the triangle wave in a process similar to clipping in audio systems.
The type of output connector from the device depends on the frequency range of the generator. A typical function generator can provide frequencies up to 20 MHz and uses a BNC connector, usually requiring a 50 or 75 ohm termination. Specialized RF generators are capable of gigahertz frequencies and typically use N-type output connectors.
Function generators, like most signal generators, may also contain an attenuator, various means of modulating the output waveform, and often the ability to automatically and repetitively "sweep" the frequency of the output waveform (by means of a voltage-controlled oscillator) between two operator-determined limits. This capability makes it very easy to evaluate the frequency response of a given electronic circuit.
Some function generators can also generate white or pink noise.
More advanced function generators use Direct Digital Synthesis (DDS) to generate waveforms. Arbitrary waveform generators use DDS to generate any waveform that can be described by a table of amplitude values.

Factors affecting the frequency of digital oscilloscope: * Bandwidth specification * Oscilloscope sample rate

Bandwidth specification
The bandwidth specification determines the frequency range which the scope (oscilloscope) measures accurately in the display. As the frequency is increasing the oscilloscope accuracy decreases. The bandwidth is mainly defined as a drop of 3 decibels (dB) or sensitivity at lower frequency at 0.707. Bandwidth in Hz x rise time in seconds = 0.35 e.g. to resolve an oscilloscope pulses with the rise of 2 nanosecond would have a bandwidth of 700MHz. but for a digital oscilloscope the sampling rate would have to be ten times higher frequency to resolve e.g. 10megasample/second would measure up to 1 megahertz of signals.
Oscilloscope sample Rate
The oscilloscope sampling rate indicates on digital oscilloscopes how many samples per second the analog to digital converter can gain. The quicker it can sample, the accurate the results are displayed for fast signal. The maximum sample rate is given by MS/s which is mega samples per second. The minimum sample rate might come in handy if you need to look at signals changing slowly. The sampling rate can be change by the controls (sec/div) on the oscilloscope.
Digital storage oscilloscope
The digital storage oscilloscope is of the three digital oscilloscopes but DSO is the conventional form of digital oscilloscope. Its screen is like a computer monitor or TV screen as it uses raster type screen. By using the raster screen its helps to display images that fill the whole screen and it may include text on the screen. First you have to store the waveform in the digital format to get the raster type display on screen. As a result of storing the waveform form digitally it can be processed by the oscilloscope or by connecting to a computer. "This enables a high degree of processing to be achieved, and the required display provided very easily and often with a very cheap processing platform. It also enables the waveform to be retained indefinitely, unlike the analogue scopes for which the waveform could only be stored for a very limited time."
The operation of the digital storage oscilloscope is pretty simple, "The first stage the signal enters within the scope is the vertical amplifier where some analogue signal conditioning is undertaken to scale and position the waveform. Next this signal is applied to an analogue to digital converter (ADC)." The samples are taken at regular intervals. The sampling rate is important because it determines the resolution of the signal. The samples are taken in per second or MS/s (mega sample rate). All the samples are stored within is the oscilloscope as waveform points, and several samples of waveform make up a single waveform point. "The overall waveform is stored as a waveform record and its start is governed by the trigger, its finish being determined by the horizontal time base time."
The digital storage oscilloscope is an in the digital format which means there is a signal processor. With having a signal processor it helps to process the signal in different ways, before it passes the display memory and the display.

Oscilloscope Controls

Vertical Control (Gain)
The VERTICAL control sets the gain (ratio) in Volts/cm between the voltages of the Input Signal and the vertical deflection of the trace drawn on the screen. There is a separate Vertical Control for each input channel, similar to those shown in figure 1. Each vertical control is usually a large knob.
{CAUTION! There is usually a small knob marked VAR (or VARIABLE) that allows adjustment between the “clicks” of the VERTICAL control knob. When measuring voltages from the screen, it should be ensured that the VAR knob is in the CAL (or CALIBRATE) position!}
There are some subsidiary vertical controls that need proper care in handling:
• COUPLING: The coupling setting determines which part of the signal presented to the input is displayed on the screen. The Coupling control has three settings: DC: The full signal voltage, including any DC component that may be present, is displayed. This is the usual setting. AC: A coupling capacitor is placed in series with the input, removing any low frequency component of the signal, including the DC component. The time constant of this high-pass filter is usually about 0.1 sec. AC coupling is useful if you have to look at a small signal sitting on top of a large DC voltage. GND: The signal is removed from the input, and the input connected to +0V.
• POSITION: This moves the trace vertically on the screen. It is used in conjunction with COUPLING – GND to set the zero voltage position of the trace.

Figure 1: Typical vertical gain controls of a two-channel analog (left) and digital oscilloscope (right).

Horizontal Control (Time base)
The horizontal control sets the scale in cm/sec at which the trace is drawn on the screen. There is only one horizontal control for all input channels, as shown in Figure 2. There is also a HORIZONTAL POSITION control.
{CAUTION! There is usually a small knob marked VAR (or VARIABLE) that allows adjustment between the “clicks” of the HORIZONTAL control knob. When measuring times screen, it should be ensured that the VAR knob is in the CAL (or CALIBRATE) position!}
Note that time on an oscilloscope screen moves from left to right (unlike in a graph), so that older stuff is to the right of the screen. On some scopes there is also an “XY” setting for displaying two input channels – one channel drives the horizontal display and the other drives the vertical display. This is useful for looking at the phase, frequency or voltage relationships between two signals.

Figure 2: Typical horizontal (time base) control of an analog (left) and digital oscilloscope (right).

Triggering Control
This is the tricky bit that is hard to comprehend its functioning. Let’s imagine that the input signal to an oscilloscope is a sinusoidal voltage. The scope repeatedly draws a trace across the screen that represents the time-varying voltage. The trace is drawn hundreds or thousands of times each second. Now imagine that each time the trace is drawn across the screen, the drawing begins on a different part of the sine wave. The trace of the sine wave will flicker horizontally, backwards and forwards across the screen. To stop the flickering and “freeze” the trace on the screen, the scope must start to draw the sine wave on exactly the same part of the wave every time the wave is drawn. This is what the TRIGGERING control lets you do. Triggering works by setting a reference (DC) voltage level, which the scope compares with the input signal. When the input signal voltage reaches the trigger voltage, the scope begins drawing the trace on the screen. The trace remains rock-solid on the screen. Actually, what is happening is that every time the trace is drawn (thousands of times per second) it is drawn in exactly the same place.
Of course, there are a couple of circumstances where this will not give a stable screen trace:
• If the input signal voltage never reaches the trigger voltage, the scope never draws the trace.
• If the input signal is non-repetitive. {For this, we need a storage scope}

Here are descriptions of all the usual trigger controls:
• LEVEL: This knob allows the trigger reference voltage to be set;
• SLOPE: Sets the slope (+ or –) of the signal that will cause triggering as it crosses the level of the trigger reference voltage;
• MODE: Allows selection between NORMAL: the trace will be drawn on the screen when the trigger source signal crosses the trigger reference voltage with the correct slope; AUTO: the trace “free runs”. This is sometimes useful for looking at signals that have very little AC component, and also for signals that sometimes get very small. Both types of signals can be hard to trigger on; SINGLE: Once “armed”, the scope will trigger the next time that the input signal matches the trigger level and slope condition. This triggering option is essential for viewing non-repetitive waveforms, and is most useful when the oscilloscope is a digital storage scope.
• SOURCE: Determines which signal is compared to the trigger reference voltage.
Usually selectable between CH1, CH2, etc.: The various input signals; EXTERNAL: some other signal that is injected through a dedicated input; LINE: the AC power supply for the scope, and maybe some other options.
• HOLDOFF: is a time delay before the scope can re-trigger. It is sometimes useful when an input signal is nearly repetitive.

Figure 3: Typical trigger controls of an analog (left) and digital oscilloscope (right).

The Importance of Probes
The function of an oscilloscope is to allow you to “see” a time-varying waveform. The function of a scope probe (see Figure 4) is to transmit the waveform from the circuit node to the scope input without distortion or added noise. That is, a scope probe is not just any old bit of wire that happens to be lying around on the lab bench.
The Importance of Probes

The function of an oscilloscope is to allow you to “see” a time-varying waveform. The function of a scope probe (see Figure 4) is to transmit the waveform from the circuit node to the scope input without distortion or added noise. That is, a scope probe is not just any old bit of wire that happens to be lying around on the lab bench.

The input impedance of a scope is typically around 1MΩ in parallel with about 100pF. Even this may load the circuit under test too much, with the input capacitance distorting the measured waveform. The usual solution is to use a “10x” passive scope probe which has a resistance of 9MΩ in parallel with an adjustable capacitor of about 5pF. When the capacitor is adjusted to be 1/9th of the capacitance of the scope input plus probe lead, the probe will have an impedance of 10 MΩ at all frequencies. Loading of the circuit under test will have been reduced by a factor of 10, and waveform distortion eliminated through the process of probe compensation. In Figure 4a, the short black lead with the alligator clip is the ground connection, to be clipped to the +0V reference point in the circuit. The probe hook can be seen just above the probe itself. This style of probe hook pulls (gently!) off the probe; some styles screw off.

Grounds
A scope measures the voltage of the input signal relative to “ground”, the voltage on the outer conductor in the BNC input connector. This ground is usually tied to the oscilloscope chassis for shielding reasons. The protective earth conductor of the AC power supply (the third pin of the power plug) is also connected to the instrument chassis. In other words, one is usually forced to measure the voltage of the input signal relative to the arbitrary ground of the protective earth conductor. If a circuit under test is floating above ground, you cannot connect the probe ground clip to the circuit because this will cause a direct short circuit to protective earth through the scope. In this situation, you must make a differential measurement of the voltage between two circuit nodes by using two probes. Invert the input of one probe, then use the oscilloscope’s ADD function.

Digital Scopes
In an analogue scope, the input signal is amplified and used to deflect an electron beam that excites a phosphor to produce the screen trace – like a TV. A digital scope is quite different: it rapidly samples the input signal with an analog to digital converter, then stores the digitized samples in memory. The samples are then retrieved for display. It is clear that a digital scope is intrinsically also a storage scope, capable of capturing and displaying single, non-repetitive events. Digital scopes are therefore very useful for looking at digital signal. The foregoing has avoided much description of the form of the operator controls, since both analog and digital scopes have essentially the same controls. The only real difference is that an analog scope will have many knobs and push buttons, whereas only the most important controls on a digital scope will have dedicated knobs, and the other controls are usually implemented through screen-based “soft” keys that change in function as the user steps through menus on the screen.

Uses of Cathode Ray Oscilloscope
The cathode ray oscilloscopes have many applications. Number of applications are discussed below: * An important use of the CRO is to examine different waveforms. The electron beam produces a graph in which the amplitude of the wave is represented by the vertical displacement of the spot (Y-axis).The X-axis represents time. * Electrical Measurement: Measurement of extremely small alternation potentials or voltages, the effect of the inductance and condenser in an AC circuit, measurement of phase angle, power factor, frequency etc. ;inductance of coil, hysteresis loss and dielectric loss. * Use in radar and television equipment. * Electrical Engineering: defects in generators and motors during actual running. * Medical: To study the action of the heart (electro-cardiography). * Measurement of extremely short intervals of time(less than a micro-second). * Industrial: Study of mechanical pressure, inductor diagrams of internal combustion engines etc.

Typical Diagrams Encountered While Using Oscilloscope:

References: http://www.doctronics.co.uk/scope.html http://www.9h1mrl.org/workshop/CRO-Ebook-1/html/CRO-P1-Intro.html http://denethor.wlu.ca/pc200/scope/oscilloscope.pdf http://cnx.org/content/m11895/latest/
Horowitz, P. & Hill, W. The Art of Electronics. 2 ed., Cambridge University Press, 1989,
Appendix A: The Oscilloscope.
Tektronix. The XYZs of Oscilloscopes. Available 28 July 2002 from http://www.tek.com/Measurement/App_Notes/XYZs/03W_8605_2.pdf
Tektronix. The ABCs of Probes. Available 28 July 2002 from http://www.tek.com/Measurement/App_Notes/ABCsProbes/60W_6053_7.pdf http://en.wikipedia.org/wiki/Oscilloscope
Kularatna, Nihal (2003), "Fundamentals of Oscilloscopes", Digital and
Analogue Instrumentation: Testing and Measurement, Institution of Engineering and Technology, pp. 165208
Advanced Practical Physics for Students by B.L.Worsnop and S.R.Flint
(Page-726-732)
Evaluating Oscilloscope Fundamentals [www.agilent.com]