Patent GB-515044-A (GB)
Title: Improvements in or relating to circuit arrangements embodying cathode ray oscillographs
IPC: G01R13/30
Filed: 1938-03-23
Abstract: 515,044. Oscillographs. BLUMLEIN, A. D., HARDWICK, J., and BROWNE, C. O. March 23, 1938, Nos. 8883 and 24411. [Class 37] In order to measure phase or amplitude of a recurrent wave signal, it is impressed on a cathode-ray oscillograph and biasing means are provided whereby the deflected trace is restored to its initial position, the amount of bias giving the required measure. A recurrent electrical signal, such as a cyclically varying current or voltage, is applied to the oscillograph and a wave-form is traced upon the screen, part of the wave-form being coincident with a datum line. The wave-form is then displaced by a control current or voltage to bring another part upon the datum line, and the amplitude or duration of the signal is determined by the amount of control employed. One pair of deflecting plates Y is connected to the anodes of valves 2a, 2b arranged in push-pull similar to the amplifier described in Specification 482,740, [Group XL], and the signal under examination is applied at terminals 6. Bias for the control grid of valve 2b is taken from the junction of resistors 11, 12 in parallel with potentiometer 13, these elements 11 ... 13 and a common resistor 14 being connected across the supply. A D.C. meter is connected between the resistors 11, 12 and potentiometer slider 13a, a variable resistor 16 with earthed tapping 17 being provided for setting the range of the instrument. The output of the push-pull amplifier is taken at 20 to a further amplifier stage 23 and thence to a blocking oscillator 25 producing a sawtooth output. The oscillator 25 includes input and output condensers and resistors 28, 30 and 32, 33, the condensers being ganged, and the charging current being regulated by tapping 31a. The sawtooth output from condenser 32 is applied to an amplifier 42a, 42b, connected similarly to the valves 2a, 2b, and the other deflecting plates X are connected to their anodes. Potentiometers 50, 51 have their tappings 50a, 51a connected to the ends of leakage resistors 48, and a further potentiometer 52 is connected to potentiometer 50. The elements 50, 52 have a mid-point connection on resistor 54 that is in parallel with potentiometer 51. These potentiometers control the bias on the valves 42a, 42b. In television synchronizing signals, the peak voltage on the Y axis and the time ratio x<1>-x<2> to x<1>-x<3> on the X axis can be determined, the axes being constituted by cursors or other indicators. The datum line is first fixed by earthing the terminals 6 and obtaining a zero on the instrument 15. Measurement of peak voltage is then made by varying the slider 13a until the parts 60 of the trace coincide with the cursor on the X axis, the instrument reading then giving the value desired since the signal potential is neutralized by the bias produced on the control grid of valve 2b. The output potential developed across a push-pull amplifier can be examined on the Y axis of the oscillograph. In the measurement of pulse duration, the slider 50a is adjusted until the potential on the control grid of valve 42a is equal to that of the point 54a. Slider 51a then varies the control on valve 42b to bring the part 60a of the trace in line with the Y axis. The bias on valve 42a is then adjusted until the part 60b is brought into line with the Y axis, and by adjustment of the slider 50a the trace can be moved back and forward. A calibrated scale in association with this slider can therefore give measurements of pulse durations and intervals. The resistor 53 can be connected to give negative control to the valve 42a. Rate of change of potential can be measured if a sloping front or back is given to the pulse wave-form. Modifications of the connections of potentiometers 50 ... 52 are described, and a meter can be employed in these circuits. The resistors 4d and 44d are variable in steps to relate to gain with the voltage readings on the meters.