In the figure on the next page is the front panel of the Hitachi V-212 Oscilloscope, which will be used in this lab. In order to use the oscilloscope effectively, you need to be somewhat familiar with the function of control knobs and switches. You will observe its effect by watching the beam sweep across the screen.) (Note: You will not see the saw-tooth pattern displayed on the screen of the oscilloscope. If the beam is moving fast enough, the spot looks like a line because the phosphor of the screen glows for a short time after the beam is gone. ![]() When the spot reaches the far right side of the screen, the Emf falls suddenly to zero and the spot almost instantaneously returns to the left side of the screen and starts across again. The steadily increasing Emf causes the spot to sweep across the tube at constant speed, the speed being selected by the knob setting. This time varying voltage allows the beam to sweep across the screen from left to right by sending a "saw-tooth" voltage to the horizontal deflection plates. The oscilloscope contains a special circuit which applies a time-varying Emf to the horizontal deflection plates (when the time/div knob is not in the XY position). The two sets of plates are connected to the vertical input and horizontal input of the scope. A similar set of plates can deflect the beam horizontally. These are called the vertical deflection plates. When an electric field is established between these plates (by connecting them to a source of Emf) the beam is deflected up or down. The first set consists of two horizontal plates. In the field-free region beyond the anode are two sets of parallel plates. This effectively reduces the number of electrons in the beam and thus reduces the intensity of the beam. However, when a small negative voltage is applied to the grid, electrons are repelled toward the cathode. Electrons normally pass freely through the grid. Very near the cathode is an open wire mesh called the grid (G). The screen glows at the point of impact of the electrons. The beam passes through the cylindrical anode into an essentially field-free region where, some 20 cm away, it strikes a fluorescent screen. Proper design and adjustment of the current flowing through these coils results in a narrow, well-focused beam of electrons. ![]() In the region on either side of the anode are coils of wire which surround the electron stream. The anode attracts the electrons which accelerate across the space between the cathode and anode, acquiring a high velocity - about 10 7 cm/s. Some 5 cm from the cathode is a positive anode (A 2) maintained at about +500 V potential. These electrons form a cloud around the cathode much like the cloud of water vapor over a heated pan of water. This surface, called the cathode (K), emits large numbers of electrons when heated. Quite near the filament is a special metal oxide surface which is in turn heated by the filament. At the base (back of the instrument case) of this tube is a small wire filament (F) which is heated to high temperature when an electric current flows through it. The nucleus of the oscilloscope is the Cathode Ray Tube (CRT) - a vacuum tube some 30 cm long which you can see in the center of the instrument. ![]() When you have completed this laboratory exercise, you should be able to: (1) describe the basic components of an oscilloscope and explain the function of each (2) use an oscilloscope to measure time intervals and potential differences (3) use an oscilloscope to display periodic voltage waveforms (4) use a dual trace oscilloscope to measure phase differences between two signals. In this lab, we will not only be concerned about the shape of some electrical waveforms, but we will also make measurements with this instrument of the frequency, period, and voltage amplitude of electrical signals of an AC nature. A fundamental element of this lab is becoming familiar with this instrument and how to use it in making measurements in a variety of situations.īecause the CRO is primarily a visual display instrument, able to display the waveform of virtually any kind of electrical signal, it is usually employed in situations where the waveform is of some interest, often with some kind of AC circuit. The CRO is the heart of the auto engine analyzer and the patient monitor in a hospital intensive care ward. ![]() The device is readily at hand in every electronics shop, every radio and TV station's engineering department, and every physics, chemistry, and engineering research laboratory. The cathode ray oscilloscope (CRO) is one of the most versatile instruments available in a modern laboratory.
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