GB649840A - Improvements in automatic reset time delay relay - Google Patents

Abstract

649,840. Valve relay circuits. RADIO CORPORATION OF AMERICA. June 16, 1948, No. 16225. Convention date, June 26, 1947. [Class 40 (vi)] An automatic reset time delay relay comprises a capacitor which is charged through a resistor from a voltage source which includes a constant component and one proportional to the charging current flowing through the resistor, the timing cycle commences when the capacitor is discharged and terminates when the voltage across the capacitor on charging reaches a predetermined value. In this way the effective time constant of a given resistor and capacitor is very greatly increased. Fig. 2 shows a circuit in which the timing cycle commences when capacitor 5 has discharged through thyratron 11 which has been rendered conducting by a positive pulse at terminal 13. The grid potential of valve 27 is thus reduced to a low value, the voltage across resistor 25 which acts as a charging voltage source has a low value, thyratron 17 is non-conducting and relay 19 is released. Capacitor 5 is charged from the voltage across resistor 25 through resistor R, the effective source voltage being reduced as charging current flows, by the negative feed back action of stage 27 so that an effective time constant of considerable length is obtained. The voltage across resistor 25 which is proportional to the charge on capacitor 5 increases until valve 17 fires when relay 19 operates and terminates the timing cycle which recommences when the next positive pulse renders valve 11 conducting. In a modification, Fig. 3 (not shown), the bias batteries of Fig. 2 are replaced by cathode biassing resistors and the circuit is operated entirely from an A.C. supply. In a further modification, Fig. 4 (not shown), the effective time constant of the delay circuit is still further increased by amplifying the voltage produced across the charging circuit resistor R in a number of D.C. coupled stages before applying it to the grid circuit of the negative feed-back amplifying stage.