| 摘要 |
629,260. Variable time constant circuits. STANDARD TELEPHONES & CABLES, Ltd., McWHIRTER, E. M. S., and DUNN, R. H. June 21, 1946, No. 18737. [Class 40 (viii)] A variable time constant circuit comprises a reactive element in combination with two non-linear resistors normally biassed to a state of low conductivity but arranged so that one or other is biassed to a state of high conductivity on a rapid change of applied potential. The invention is applied to apparatus in which the rate of impulsing of a contact IP is required to be measured on a meter M. Thus the contact IP may be operated by a kilowatt-hour meter and the meter M required to register kilowatts. Contact IP alternately charges C2 negatively and discharges it into C1 which in turn discharges over the arms of the potentiometer R6 ... R10 so that the point A varies in potential about a mean determined by the rate of impulsing of IP. Condenser C1 is arranged as part of a negative feed-back circuit for the valve VI, thereby ensuring a linear relation between the depression of the mean potential of the point A and the rate of impulsing. The potential of this point is communicated to the grid of valve V2 through a time constant circuit comprising condenser C3 and a resistance comprising resistors R8, R9 and rectifiers D1, D2 in series-parallel. The standing voltages across R8, R9 are greater than the fluctuations due to the impulsing, so that for a steady rate of impulsing, when the grid of V2 has attained the potential of the point A the rectifiers D1, D2 are backbiassed to provide a high time constant and efficient smoothing. If, however, the rate of impulsing increases or decreases suddenly, the potential of the point A falls or rises compared with that of the grid of V2 and D1 or D2 becomes forward-biassed at the peaks of the fluctuations, to reduce the time constant of the circuit and permit of rapid equalization of the potentials of A and the grid of V2. Variations of the grid potential of V2 are registered on the meter M in the cathode circuit of the valve. Specifications 603,137 and 629,244, [Group XXXVI], are referred to. |
