Patent GB-1349968-A (GB)
Title: Echo sounding apparatus
IPC: G01S7/60
Filed: 1971-05-24
Abstract: 1349968 Echo sounding apparatus FRIED KRUPP GmbH 24 May 1971 [25 May 1970] 16575/71 Heading H4D [Also in Division G4] In an echo sounder for analysing and displaying a succession of measurements, electrical signals generated by the returned acoustic signals update a store independently of the read out of the store for display on an echo graph type chart recorder. In Fig. 1 for each acoustic pulse transmitted at the beginning of a measuring period Lm one or more acoustic signals are returned at time intervals MO-Mp, defined by a clock driven counter 14, with values such as amplitude or duration represented by mO-mp. After A/D conversion (10) the values mo-mp are read into a store 11 via a comparator 15 and read-in device 17 at positions determined by MO-Mp. The comparator 15 compares the new values of mo-mp with the corresponding values of a previous measuring period Lm and if the difference is within a predetermined tolerance updates the store with the new value. Otherwise the new value of mi is put into a fresh storage location. Each location has a validity number, which is updated by 1, but not beyond a maximum, each time it is able to be updated. Every cycle the validity number of non-updated locations is reduced by 1, any location whose number reaches a minimum being erased. An echo graph chart recorder 19 has a number of display position numbers DO-Dq at which it can display the values gathered in the measuring period Lm (defined by numbers MO-Mp). A correlator 26 associates particular display position numbers DO-Dq with the measurement numbers MO-Mp, so that during the cycle of the recorder, displacement pulses Id, or position encoding data, passed to the correlator call for particular data from the store, whose readout cycle is much shorter than that of the recorder. The data read out at 18 is D/A converted and printed via electrode 22, the amplitude or duration of the acoustic pulse may govern the density of the recording. To be able to be read out for displaying, the store data must have the maximum value of its validity number. Switches 16a govern the read-out of data in this respect. Switch 29 can connect alternative correlators 26a-26b to control the format of the display. For example the data can be recorded in the upper or lower half of the chart or be recorded in the reverse order or can have a logarithmic relationship. The readout can be controlled to read out only acoustic signals returned from a given range of depth which range is set up manually in the apparatus. The transmission of an acoustic pulse can be initiated manually, automatically when counter 14 reaches a predetermined count, or when the first returned echo signal, usually the sea bed signal, returns. Also the pulses can be transmitted only when the survey vessel is in a vertical position. An acoustic transducer may be positioned on a fishing trawl net under water to determine the position of the sea-bed both beneath the surface and the bottom of the trawl net. Two frequencies of acoustic signal may be transmitted from the survey vessel and the apparatus set to analyse one or the other of these two frequencies.