Presentation of cathode ray oscilloscope By : Ravi pambhar

Basic introduction of CRO The oscilloscope counts among the important measuring instruments in experimental physics. It makes it possible to observe and to measure quantitatively the course of an electric voltage UY as a function of time t or as a function of voltage UX in „real-time“. The temporal course of all physical quantities that can be converted to an electrical voltage using a suitable sensor can be displayed with an oscilloscope1. There are few restrictions regarding the amplitude and frequency of the measurable signals: if you are prepared to spend enough money, you will certainly find an oscilloscope which meets the requirements. During the introductory laboratory course, too, the oscilloscope is a frequently used measuring

instrument. In some experiments it is a fundamental component of the experimental set-up and yields the quantitative data required for the analysis. In other experiments it is used for qualitative control, i.e., whether a circuit has been correctly set up and is operative, if a sensor is providing the correct signal, ... . In order to perform the following experiments successfully, a thorough knowledge of the oscilloscope is imperative. . The experiments described in this document are divided into two laboratory sessions.

A Tektronix model 475A portable analog oscilloscope, a very typical instrument of the late 1970s

Lissajous figures on an oscilloscope, with 90 degrees phase difference between x and y inputs. One of the most frequent uses of scopes is troubleshooting malfunctioning electronic equipment. Another use is to check newly designed circuitry

Cathode ray oscilloscope tube

Working principle of CRO The electron gun or electron emitter, the deflecting system and the fluorescent screen are the three major components of a general purpose CRT.

Electron Gun: In the electron gun of the CRT, electrons are emitted, converted into a sharp beam and focused upon the fluorescent screen. The electron beam consists of an indirectly heated cathode, a control grid, an accelerating electrode and a focusing anode. The electrodes are connected to the base pins. The cathode emitting the electrons is surrounded by a control grid with a fine hole at its centre. The accelerated electron beam passes through the fine hole. The negative voltage at the control grid controls the flow of electrons in the electron beam, and consequently, the brightness of the spot on the CRO screen is controlled.

Display waveform on the screen: Figure 14-5(a) shows a sine wave applied to vertical deflecting plates and a repetitive ramp or saw-tooth applied to the horizontal plates. The ramp waveform at the horizontal plates causes the electron beam to be deflected horizontally across the screen. If the waveforms are perfectly synchronized then the exact sine wave applied to the vertical display appears on the CRO display screen.

Triangular waveform: Similarly the display of the triangular waveform is as shown in Fig. 14-5(b).

MEASUREMENTS USING THE CATHODE-RAY OSCILLOSCOPE: 1) Measurement of Frequency:

MEASUREMENTS USING THE CATHODE-RAY OSCILLOSCOPE: 2) Measurement of Phase:

TYPES OF THE CATHODE-RAY OSCILLOSCOPES: The categorization of CROs is done on the basis of whether they are digital or analog. Digital CROs can be further classified as storage oscilloscopes. 1. Analog CRO: In an analog CRO, the amplitude, phase and frequency are measured from the displayed waveform, through direct manual reading. 2. Digital CRO: A digital CRO offers digital read-out of signal information, i.e., the time, voltage or frequency along with signal display. It consists of an electronic counter along with the main body of the CRO. 3. Storage CRO: A storage CRO retains the display up to a substantial amount of time after the first trace has appeared on the screen. The storage CRO is also useful for the display of waveforms of low-frequency signals. 4. Dual-Beam CRO: In the dual-beam CRO two electron beams fall on a single CRT. The dual-gun CRT generates two different beams. These two beams produce two spots of light on the CRT screen which make the simultaneous observation of two different signal waveforms possible. The comparison of input and its corresponding output becomes easier using the dual-beam CRO.

Uses Oscilloscopes are commonly used when it is desired to observe the exact wave shape of an electrical signal. In addition to the amplitude of the signal, an oscilloscope can show distortion and measure frequency, time between two events (such as pulse width or pulse rise time), and relative timing of two related signals.

Advantages One of the advantages of a scope is that it can graphically show signals: where a voltmeter may show a totally unexpected voltage, a scope may reveal that the circuit is oscillating. Digital electronics usually operate from a clock, so a dual-trace scope which shows both the clock signal and a test signal dependent upon the clock is useful. Storage scopes are helpful for "capturing" rare electronic events that cause defective operation.