![]() The ac amplifiers, used in oscilloscopes, are required for laboratory purposes. The low-cost oscilloscopes generally use ac-coupled amplifiers.(i) AC-coupled amplifiers (ii) DC-coupled amplifiers The oscillographic amplifiers can be classified into two major categories. ![]() Considerable attention has to be paid to the design of these amplifiers for this purpose.The purpose of an oscilloscope is to produce a faithful representation of the signals applied to its input terminals.The time taken to return to its initial value is known as flyback or return time.14-6-we observe a pattern which is generally called a saw-tooth waveform. If the voltage decreases rapidly to zero-with the waveform repeatedly produced, as shown in Fig. A voltage with such characteristics is called a ramp voltage.As the beam velocity is a function of the deflecting voltage, the deflecting voltage must increase linearly with time.If the wave form is to be accurately reproduced, the beam should have a constant horizontal velocity. The CRO is used to display a waveform that varies as a function of time.If the waveforms are perfectly synchronized then the exact sine wave applied to the vertical display appears on the CRO display screen.The ramp waveform at the horizontal plates causes the electron beam to be deflected horizontally across the screen.Thus, the horizontal movement is controlled along X1OX2 line.ĭisplay 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. By changing the polarity of voltage, the beam will focus at point X1. To deflect the beam horizontally, an alternating voltage is applied to the horizontal deflecting plates and the spot on the screen horizontally, as shown in Fig.If the polarity of the deflecting voltage is reversed, the spot appears at the point Y2, as shown in Fig. If a positive voltage is applied to plate P1 with respect to plate P2, the negatively charged electrons are attracted towards the positive plate P1, and these electrons will come to focus at point Y1 on the fluorescent screen.ĭeflection Systems: The deflection is proportional to the deflecting voltage between the plates.The beam is focused at point O on the screen in the absence of a deflecting plate voltage. Let us consider two parallel vertical deflecting plates P1 and P2.The deflecting system consists of a pair of horizontal and vertical deflecting plates. Electrostatic deflection of an electron beam is used in a general purpose oscilloscope.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.The accelerated electron beam passes through the fine hole.The cathode emitting the electrons is surrounded by a control grid with a fine hole at its centre. The electrodes are connected to the base pins.The electron beam consists of an indirectly heated cathode, a control grid, an accelerating electrode and a focusing anode.In the electron gun of the CRT, electrons are emitted, converted into a sharp beam and focused upon the fluorescent screen.A detailed diagram of the cathode-ray oscilloscope is given in Fig. The electron gun or electron emitter, the deflecting system and the fluorescent screen are the three major components of a general purpose CRT.The central unit of the oscilloscope is the cathode-ray tube (CRT), and the remaining part of the CRO consists of the circuitry required to operate the cathode-ray tube.īlock diagram of a cathode-ray oscilloscope:ĬOMPONENTS OF THE CATHODE-RAY OSCILLOSCOPE: The CRO consists of the following:.CROs are used to study waveforms, and other time-varying phenomena from very low to very high frequencies. A moving luminous spot over the screen displays the signal.and strain can be converted into electrical signals by the use of transducers, and the signals can be displayed on the CRO.Many physical quantities like temperature, pressure It can measure amplitude, frequencies and phase shift of various signals. CRO is generally an x-y plotter on a single screen it can display different signals applied to different channels.The cathode-ray oscilloscope (CRO) is a multipurpose display instrument used for the observation, measurement, and analysis of waveforms by plotting amplitude along y-axis and time along x-axis.
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