| 摘要 |
1,068,346. Frequency comparators. DE HAVILLAND AIRCRAFT CO. Ltd. Nov. 12, 1963 [Nov. 12, 1962], No. 42657/62. Heading H3A. [Also in Division G3] A frequency comparator, e.g. for use in controlling the speed of a gasturbine comprises means for deriving a number of relatively phase-displaced pulse trains having a frequenoy proportional to the speed of the turbine, means for deriving a square-wave pulse train having a frequency proportional to a desired speed and means for comparing the two frequencies to derive a difference signal for adjusting the turbine speed. A tachometer generator/coupled to the turbine develops three pulse trains on lines A, D and G, which are applied, respectively, to one input of AND gates 11 and 12, 21 and 22, and 31 and 32; these pulse trains have a frequency proportional to the speed of the turbine and are relatively phase displaced by 120 degrees. A voltage controlled oscillator 3, controlled by a speed demand voltage, develops a square-wave pulse train having a frequency proportional to the required speed and this train is applied directly to the other inputs of gates 11, 21 and 31 and after inversion in unit 3A to the other inputs to gates 12, 22 and 32. The outputs of AND gates 11 and 12 respectively control the switching of a bi-stable circuit 13 to each of its stable conditions, similarly the outputs of gates 21 and 22 oontrol bi-stable circuit 23 and bi-stable circuit 33 is controlled by the outputs from gates 31 and 32. In one stable condition each of the bi-stable circuits closes an associated switch 14, 24, 34 via which windings 15, 25 and 35 of a stepping motor 6 are connected to a D.C. supply. The motor controls the supply of fuel to the turbine, to control its speed, via a throttle shaft. When the frequency proportion to the actual speed and that proportional to the required speed are equal the bi-stable circuits remain in one or another of their stable states and the motor 6 does not rotate, if, however, these frequencies differ the bi-stable circuits operate the switches 14, 24 and 34 in sequence whereby a rotating field is applied to the motor. The direction of rotation of the field and hence the motor depends on whether the actual speed of the turbine is above or below the required speed and the rate at which the stepping motor is turned is a function of the magnitude of the difference. |
