Improvements in variable resistance networks for phase shifting apparatus

摘要

913,992. Resistance networks. WELTRONIE CO. June 2, 1959 [Nov. 28, 1958], No. 18773/59. Class 40 (8). A variable resistance for use in conjunction with a non-linear device comprises a switch for increasing the resistance in different increments to obtain equal decrements of current and a fine adjustment for obtaining subdecrements, the magnitude of the sub-decrements being arranged to vary in accordance with the value of the next decrement to be selected. As shown, resistors 101R to 108R have values (generally unequal) calculated in accordance with the curvilinear law of the load to change the value of the current between terminals 52, 54 by equal decrements of 10% as contact 60 is moved by switch ISW from one tapping point to the next. In addition, by means of switch 2SW, any number of a set of ten smaller resistors 117R to 126R may be connected in series with the resistors of the coarse setting to obtain nominal current decrements of 1%. The maximum value (in current decrements) of the fine setting should amount to 10% at each position of the coarsesetting contact 60. The required variation in this value over the whole range is obtained by shunting the selected fine resistors 117R to 126R with the next succeeding one of the selected coarse resistors. This is done by means of movable contact 62 forming part of the coarse-setting switch 15W. For example, if contact 60 is set at the third position to include resistors 101R and 102R in circuit, resistor 103R is placed in parallel with the selected number of fine resistors 117R to 126R which each provide, under these conditions, a 1 % current decrement. In the embodiment, resistors 101R to 108R are made greater than their nominal values and are shunted by corresponding numbers of the set of resistors 109R to 116R selected by contact 66 of switch 1SW. The 10% decrements of current thus result from the parallel combinations of resistors selected by contacts 60 and 66. The variable resistance is incorporated in a resistive branch for one phase of a polyphase phase-shifting network whose other phases have resistive branches with similar variable resistances. The phase-shifting circuits may be those described in Specification 913,991, where they are applied to a welding controller.