Patent GB-986416-A (GB)
Title: Improvements in or relating to apparatus for numerically recording time intervals
Inventor: BARRAULT FRANCOIS
IPC: G01S7/527
Filed: 1962-05-04
Abstract: 986,416. Echo sounding. ELECTRICITE DE FRANCE. May 4, 1962 [May 5, 1961], No. 17322/62. Heading H4D. In apparatus for recording distances in terms of time intervals, the commencement and termination of which are defined by distinguishable electrical signals which are utilized respectively to open and close a gate circuit controlling the passage of fixed frequency pulses to a counter, the count of which is recorded (e.g. on a punched tape or on magnetic recording means), operation of the gate circuit by signals other than intended signals is prevented by means including a blocking circuit which is rendered conductive only by desired signals having a predetermined minimum duration or when desired signals are expected to occur. The invention is described in connection with ultrasonic sounding apparatus, which may include known graphic recording means, employed to study the swell of the sea and in this case the distinguishable electrical signals comprise signals generated by an electro-acoustic transducer positioned on the sea bed and signals produced by reflection of ultrasonic waves from the surface of the sea. Two embodiments of the invention are described. In the first, the gate circuit controlling the passage of the fixed frequency pulses to the counter is opened on the occurrence of a transmitted pulse and closed on reception of an echo pulse means being provided to prevent closure of the gate for at least a predetermined time determined by the depth of water after the occurrence of a transmitted pulse and also to prevent closure after this predetermined time by received pulse signals, the duration of which is less than a predetermined value. This latter discrimination arises from the fact that spurious echo signals have a shorter duration (pulse length) than that of the transmitted pulses. In a second embodiment the gate circuit controlling the passage of the fixed frequency pulses to the counter is opened by one of the transmitted pulses and closed by a received echo pulse by means of a circuit which, depending on the depth of water, is conditioned during a period when a desired echo is expected to occur, to respond to a received echo pulse and thereafter to be unresponsive to any received signals until the next desired echo pulse is expected to occur. In both embodiments the transmitted signals consist of 2 to 4 millisecond bursts of 30 kc./s. oscillatory acoustic energy with a repetition frequency of 8 bursts per second. The first embodiment is shown in Fig. 2, the signals in various parts of which are shown in Fig. 7. Referring to the latter figures, a bi-stable circuit BV is switched to one state by the trailing edge of a 15 millisecond pulse derived from output S1 of a monostable circuit U15 controlled via a trigger BS by the transmitted burst signals EE detected at DTE. On reception of an echo signal ER a Schmitt trigger CT and a monostable circuit U1 (having a reset period of one millisecond) operate via a gate PO (as described with reference to Figs. 3 to 6, not shown) to pass a received signal e2 to circuit BV if the duration of the latter exceeds a predetermined minimum value, in this case, one millisecond. Such signal then resets BV. If the duration is less than one millisecond, gate PO is opened and resetting of BV is prevented. If no echo signals are received, circuit BV is reset by a signal e<SP>1</SP> 2  derived from a monostable circuit UZ having a reset time of 100 milliseconds and supplied with the transmitted pulses from trigger BS. The leading edge of the e<SP>1</SP> 2  pulse from UZ (which coincides with a transmitted burst) triggers a bi-stable gating circuit BP to one state and the circuit is then reset at the instant that BV is reset. However, when the time intervals are to be recorded on a punched tape, the repetition frequency of the transmitted bursts (i.e. 8 per second) must be reduced. To this effect the gate BP is controlled by signals e/4 of one quarter of the repetition frequency of the transmitted bursts derived via bi-stable circuits BD1, BD2 so that output pulses Ec, Rc representative respectively of the instants of transmission and reception are produced with repetition frequency of two per second. These signals then control the passage of the fixed frequency pulses to a binary decimal coding register which controls the tape perforator (Fig. 1, not shown). The second embodiment is shown in Fig. 11, the signals in the various parts of which are shown in Fig. 13. Referring to the latter figures a gate PR 1 supplies received echo signals from a shaper CR to the series arrangement of shapers CI1, CI2 and gates PR2, PR3 and thence via monostable circuits UV1, UV2, UP to control a gate PR which passes the echo signals to a bi-stable gating circuit BP to which, as a second input, as in the case of the gate BP of Fig. 2, signals of one quarter the repetition frequency of the transmitted bursts are supplied. The gate PR1 is blocked by a pulse from a monostable circuit UVE, the duration of which may be adjusted (e.g. from 30 to 50 milliseconds) depending on the depth of water and the commencement of which occurs 110 milliseconds after the transmission of burst signal EE. Gate PR1 is thus made unresponsive to the transmitted signals. When the gate conducts to pass an echo signal the operation of the monostable circuits UV1, UV2 closes gates PR2, PR1 respectively and spurious echo signals (i.e. those which are received outside the expected time period as determined by the adjustment of UVE) are thus presented from operating gate PR. The latter is operated for a period of 5 milliseconds by monostable circuit UP commencing at the instant that UV2 resets so that the first received echo signal is a desired signal (UVE being assumed to be correctly adjusted). The reception of such signal then recloses gates PR2, PR3 as described above and prevents further (spurious) signals which occur inside the 5 millesecond open period of gate PR from reaching gate BP. In this manner by correct adjustment of UVE depending on the expected echo time (i.e. on the depth of water) the operation of the circuit is, in effect, synchronized with received echo signals. The gate BP is then employed as described in connection with Fig. 2.