GB548396A - Apparatus for converting a direct voltage into a frequency proportional thereto - Google Patents

Abstract

548,396. Relaxation oscillators. TRIGGS, W. W. (Akt.-Ges. Brown, Boveri, & Cie). June 3, 1941, No. 7028. [Class 40 (v)] In a relaxation oscillator of the kind in which a condenser is discharged through a gas-filled grid-controlled tube, a positive impulse is applied to the grid to start the discharge whenever the condenser voltage exceeds the extinction voltage of the tube by a certain fixed voltage. The oscillator is particularly intended for the generation of oscillation of a frequency which is variable with the voltage applied to the charging circuit, but is unaffected by variations in the tube characteristics or in auxiliary voltage sources. As shown in Fig. 2, the condenser 2 is charged from a source 3 through a resistance 4 and is discharged through a gas-filled tube 1. The condenser 2 is connected through a fixed voltage source 14, rectifier 13, and transformer primary 12 to a condenser 10 which is kept positively charged by a connection through resistance 9 to a tapping on a potentiometer 8 across an auxiliary source 30. The circuit 9, 10 has a high time constant and the voltage on the condenser 10 is reduced to that of the condenser 2 each time the latter is discharged through the tube, the rectifier 11 permitting this equalization at the extinction voltage of the tube. When the voltage on the condenser 2 rises to a point exceeding the extinction voltage (on condenser 10) plus the fixed voltage 14, current passes through the transformer 12 and induces a pulse in the secondary which is applied to the grid of the tube 1 and causes ignition. If the voltage 3 is a variable quantity, the frequency of the generated oscillations is a measure of that voltage and the oscillations may be used for tele-metering. In the circuit shown in Fig. 3, the condenser 2 is discharged through the tube 1 and is charged from the source 30 through a hard valve 19, the grid bias of which is determined by the source 3 and by a feed-back resistance 4 in the cathode lead. The charging current is held constant by the feed-back resistance 4. The condenser 10 is maintained at the extinction voltage as in Fig. 2, and the discharge through the tube 1 is initiated as before by a pulse through the transformer 12. This pulse is, however, amplified in a valve 15 before its application to the grid of the tube 1. The battery 14 of Fig. 2 is replaced by a condenser 23 on which a steady voltage is maintained by a regulator 20. The tripping circuit 10, 11, 12, 13, 23 includes a resistance 24 to compensate for the short discharge period of the condenser 2. The output voltage across the condenser 2 may be amplified by a valve 25, and taken through a transformer 26 and suitable filters. For telemetering, a variable voltage to be transmitted is used in place of the source 3 and the resulting variations in frequency are transmitted from the output trariformer 26.