The Cathode-Ray Oscilloscope

The electron gun consists of a cathode that emits the electrons, one or more grids by which the number of electrons in the beam can be controlled, accelerating anodes, that cause the electrons to attain rapid motion, and often a focusing arrangement, although sometimes external coils are used for focusing.

The deflecting mechanism often consists of two pairs of parallel plates between which the electrons flow. One pair is in a horizontal plane, and the other in a vertical plane. By impressing voltages between these plates the motion of the electron beam and the trace on the fluorescent screen can be controlled. Sometimes external magnetic deflecting coils are used.

The fluorescent screen consists of a suitable material deposited on the inside of the tube. The type of material used depends on the nature of the trace desired.

Many of the uses of the cathode-ray oscilloscope are so familiar as to need no review. A use mentioned on pages 172 and 174 is for measuring phase angles, as explained in Fig. 42.

Figure 42. If the phase relations between the input voltage to a circuit and the output voltage from a circuit are desired, the input voltage is impressed on one set of oscilloscope deflecting plates, and the output voltage is impressed on the other set. For angles between 0 and 180°, sinθ = B/A, the distances B and A being as shown. The figures represent the patterns on the end of the oscilloscope tube.