Patent GB-552992-A (GB)
Title: Improvements in or relating to apparatus for measuring distance
IPC: G01S15/10
Filed: 1941-09-29
Abstract: 552,992. Echo-sounding and distance measuring apparatus. AGA-BALTIC AKTIEBOLAG, (formerly known as AGA-BALTIC RADIO AKTIEBOLAG). Sept. 29, 1941, No. 12592. Convention date, Oct. 1, 1940. '[Class 118 (ii)] Relates to apparatus for measuring distances by the reception of reflected sound pulses the operation being controlled by an alternating current with a continuously variable frequency. According to the invention a filter is provided which; at a predetermined value of the variable control frequency, causes the emission of a pulse with a predetermined fixed frequency different from the variable control frequency, a receiver for the reflected pulse being arranged to actuate a frequency indicator. The emitted pulses, preferably of supersonic frequency, are generated by an oscillator 10, and the oscillations are passed through an amplifier 11 to a transmitter 12. The emitted vibrations after reflection are received by a receiver 13 which is connected to an indicating instrument 15 thorugh an amplifier 14. The emission of the supersonic vibrations in the form of pulses is controlled by an oscillator 16 tuned by a condenser 18 which is rotated continuously by a motor 17. The output side of the oscillator is connected to the transmitter and the receiver through a filter 19 which suppresses all except two frequency bands, a narrow band indicated by 22 and a wide band indicated by 23. The filter is connected by a conductor 20 or with a rectifier 24 the output of which is fed to the amplifier 11. Normally the amplifier is so biassed that the output is blocked, but the reception of a narrow frequency band 22 from the rectifier 24 reduces the bias voltage and permits the passage of vibrations from the oscillator to the transmitter. Thus so pulses are transmitted periodically at intervals determined by the speed of the motor 17. The wider band of frequencies 23 is conducted through a rectifier 25 to the amplifier 14 of the receiver 13. The biassing of the amplifier 14 is so arranged that the amplifier is blocked when the biassing is reduced by the frequency band 23. The oscillator 16 is also connected through the indicator 15 through an amplifier 28 which normally is blocked, but the blocking is cancelled when amplifier 14 is freed by the reception of a frequency band 23. During this period the indicator 15 is actuated if a reflected pulse is received by the receiver 14. The output of the oscillator 16 passes through a predetermined cycle of frequencies and the bands 22, 23 are selected from the different parts of the cycle. The receiver 13 does not record the pulse received directly from the transmitter as the amplifier 14 is then blocked. The reflected pulse is received when the amplifier 14 is freed during the relatively long time represented by wide band 23 and the indicator 15 is actuated when the reflected pulse is received. A discriminator 29, interposed between the amplifier 28 and the indicator 15, and when a reflected pulse is received, the indicator responds and shows the particular frequency of the oscillator 16 at that moment. As the oscillations vary continuously through a cycle, the indicator 15 can be calibrated to show the time between the emission of a pulse and its reception after reflection, or directly in terms of distance. Provision is made for adjusting the apparatus when long distances are being measured involving a relatively long time between the emission of a pulse and the reception of the echo.