The thin pencil beam of electrons is travelling at a high velocity when it leaves the final anode, and is therefore capable of traversing the space between the final anode and the screen. The second anode is, therefore, called the 'focusing anode'. The potential of the second anode is normally made variable, so that focusing of the electrons into the narrowest possible beam may be achieved. These are of essentially the same mechanical form as the first anode, but they are connected to progressively higher potentials.īy the time the electrons have passed through these anodes, they are concentrated into a narrow beam. One or two further anodes may be situated beyond the first anode. The electrons are attracted toward this electrode and stream through the hole at the centre. This anode is often in the form of a disc with a small hole at its centre. Beyond this electrode is an anode positively charged with respect to cathode. By biasing this electrode relative to the cathode, a variation in the number of electrons passing through the hole may be achieved, as in the case of a normal valve. Between the cathode and the anode there is a 'grid' consisting of a tube with a hole in one end, as shown above right. This cathode therefore emits electrons, which are attracted away from it by the anode A1. The left hand diagram above shows an electrostatically deflected tube.Īt the base of the tube there is a cathode heated in the same way as in an ordinary valve. This is the device which produces the picture, and therefore all the circuitry is designed around it. The heart of the oscilloscope is the cathode ray tube. The vertical axis would normally represent voltage. If the frequency of the signal were 25 Hz, and the horizontal scale were 0.5 second, 12.5 cycles would be displayed. If, for example, we were to connect our oscilloscope to a point in a circuit where a sinusoidal signal existed, a picture of the sinusoid should appear on the screen of the oscilloscope. The purpose of the oscilloscope is to draw what is virtually a graph of regularly varying electrical quantities, such as voltage or current, against a horizontal scale of time. In this 1955 article the CRT is discussed with specific application to the oscilloscope. The Cathode-Ray Tube is used in instrumentation and picture presentation. Cathode-Ray Tube Cathode-Ray Tubes CRT Power Network
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