| 摘要 |
1,246,323. Frequency discriminators; monostable circuits. DYNAMIC PRECISION CONTROLS CORP. 16 Sept., 1968 [26 Sept., 1967], No. 44004/68. Headings H3A and H3T. [Also in Division G3] A system for controlling a variable, e.g. the speed of an engine or motor, comprises: means for generating a train of regularly spaced input pulses having for example a frequency proportional to speed; a monostable circuit having a variable time constant and fed with the pulse train to produce output pulses having a width dependent on frequency; and an actuator fed with the output width pulses to control the variable such that the frequency of the input pulses has a predetermined relation with pulse width. In one embodiment, Fig. 2, input pulses turn on transistor 21 to charge capacitor 33. turn off transistor 42 and turn on transistor 43. At the termination of an input pulse, transistor 21 switches off, and capacitor 33 discharges through resistor 32 until transistor 42 switches on again and transistor 43 switches off. The resulting constant width pulses are integrated by CR network 19 to provide an output which varies inversely with frequency. If the input frequency exceeds a predetermined limit the circuit 42, 43 does not have time to reset before the next input pulse and transistor 43 remains switched on giving zero output from network 19. The limit at which this occurs may be varied by resistor 32 which varies the relaxation time of the monostable circuit. In a modification, Figs. 6, 7, 8 (not shown), the capacitor 33 is arranged in shunt with the emittercollector path of transistor 21. These arrangements also include level sensing circuits connected to the output in place of network 19, which switch their state at a predetermined frequency.
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