Improved means for producing low frequency pulsating current from an alternating current supply

摘要

558,931. Frequency changing. ARNOLD, J. C. (Tyler Co., W. S.). Oct. 29, 1942, No. 15180. [Class 38 (ii)] [Also in Group XL] Means for energizing a load L such as the operating coil of a vibrating screen with impulses of lower frequency than that of the A.C. supply A, B comprises a grid-controlled valve PT in series with the load the grid being energized so as to maintain the valve blocked for intervals including at least one cycle of positive voltage on the anode by potentials derived from a timing unit comprising a condenser C discharging through a resistance R4. The timing unit also comprises a valve CT the anode circuit of which is energized from the A.C. supply A, B through a transformer T5. Thus initially the valves P, T and CT conduct simultaneously, the latter operating to charge the condenser C through a transformer T2 and rectifier RT, whereupon both valves become blocked by the condenser voltage applied to their grids. They remain blocked for an interval determined by the magnitude of resistance R4 through which the condenser discharges and which may be varied to determine the frequency of the impulses applied to the load L. One such timing unit may control a number of valves PT controlling different load circuits.