Circuit arrangement for an electronic distance measuring device for drawing the frequency of a measuring oscillator towards a set point frequency which is higher or lower, respectively, by a certain predetermined value

Claim 1

A circuit arrangement for an electronic distance measuring device for shifting the frequency of a measuring oscillator to a set point frequency higher or lower, respectively, by a certain CERTAIN predetermined amount than the frequency of a similar measuring oscillator at a counter station, said circuit arrangement through mixing of the measuring waves of both measuring oscillators producing a differential signal, said circuit arrangement further incorporating a discrimination circuit for comparing the frequency of the differential signal with a reference frequency corresponding to the predetermined amount and upon deviation from the reference signal producing an error voltage for shifting the frequency of such controlled measuring oscillator, the improvement comprising an exclusive NOR-gate provided for said circuit arrangement and defining the discrimination circuit, said exclusive NOR-gate having at least one pair of inputs and an output, at one of said inputs of said exclusive NOR-gate there is applied the differential signal and at the other input of which there is applied the reference signal, low-pass filter means having an output, said low-pass filter means being arranged in circuit with and followIng sad exclusive NOR-gate, said low-pass filter means embodying two series connected resistors and a subsequently connected capacitor, means defining a current supply leading to the junction between one of said resistors and said capacitor, switch means controlled by the differential signal bridging said capacitor, said switch means upon the presence of said differential signal being open, an OR-circuit for conducting the momentary greater input voltage supplied thereto, said OR-circuit having a first input, a second input and an output, said first input of said OR-circuit being connected with the output of said low-pass filter means, means for applying a pre-bias voltage to the second input of said OR-circuit which shifts the measuring oscillator to a frequency which is between the fundamental frequency and the set point frequency, and a further low-pass filter means for electrically coupling said output of said ORcircuit with a frequency control input of such measuring oscillator.