GB1253390A - Arrangement for controlling and indicating the phase of an oscillation - Google Patents

Abstract

1,253,390. Photo-electric distance measuring. AGA AB. 28 Nov., 1968 [15 Dec., 1967], No. 56450/68. Heading H4D. [Also in Division G4] Apparatus for controlling and indicating the phase of an output signal from a periodic counter C (Fig. 1) includes a source of reference pulses SR of predetermined frequency coupled to the counter C so that the counter generates output signals at a submultiple of the predetermined frequency and modifying means for varying the number of pulses applied to the counter C a reversible counter PC indicating this variation which represents the phase of the output signal from the counter C. The modifying means preferably comprises switches SW1, SW2 and a further source of reference pulses SA (which may be derived from the original source SR via a delay) switch SW1 when actuated disconnecting the counter C from their reference source SR and connecting the counter PC where the pulses are accumulated negatively. Switch SW2 when activated supplies additional pulses to the counter C, these pulses being simultaneously accumulated in counter PC. To indicate the phase of the output signal from a second counter (C2, Fig. 2, not shown) relative to a first counter (C) an additional source of reference pulses (SA) may be connected via switches (SW3, SW4) to the counters (C, C2) respectively and to the decrementing and incrementing input of reversible counter (PC). The apparatus may be used to measure the distance of a remote object by emitting a modulated light beam and comparing the phase of a reflected beam with that of light which has passed over a calibration path CP (Fig. 3). Initially, the phase of a generator GH is adjusted so that the output pulses from counter C and mixer MX (receiving the signal from multiplier MU, the light modulator LM and generator GH) are in phase. The phase of a second counter C2 and the signal from photo tube PT receiving the signal over calibration path CP are then compared and either via a switch SW6 the phase of C2 is adjusted or via switch SW5, counter C and generator GH the phase of the signal from photo tube PT is adjusted to bring the inputs to a phase detector PD2 into agreement. With mirrors M1, M2 in position light reflected from the distant object is then received by tube PT and again the phases of the two inputs to detector PD2 are brought into agreement, the operation of switch SW5 or SW6 resulting in the pulses applied to C or C2 being accumulated negatively or positively respectively in counter PC. The count which is displayed represents the distance of the object.