FR2688891A1 - DEVICE FOR TESTING A RECEIVER GROUP. - Google Patents

Abstract

Test device for detecting failures of N sensors and their associated amplifiers. The signals supplied by the N hydrophones (10.1, 10.2, .. 10.N) are amplified by the preamplifiers (20.1, 20.2, .. 20.N). A circuit (41) is traversed by an alternating current I supplied by a current source (40) and inductively coupled to all the circuits (30.1, 30.2, .. 30.N) formed by the N hydrophones and the input of their preamplifiers. The supplied amplified signals (25.1, 25.2, .. 25.N) are used both for processing and for fault detection. Application to linear acoustic antennas, towed by a boat in the technique of underwater listening.

Description

TEST DEVICE

A RECEIVER GROUP

  The object of the present invention is a test device for detecting failures in a set of sensors each provided with a preamplifier.

  This invention applies more particularly to an acoustic antenna

  linear tick, composed of a number of hydrophones, used in underwater acoustics It is known that to detect targets at a great distance, by underwater listening, it is necessary to work at frequencies below 1000 Hz. these conditions a good angular resolution, it is necessary to use antennas of great length Thus for a frequency of 500 Hz, an angular resolution of 100, requires a

length of the order of 20 meters.

  It is known to produce linear antennas, generally composed of

  several dozens of hydrophones, with their associated electronics, enclosed in an envelope allowing the acoustic waves to pass. These antennas, which have a pipe-like shape, can be towed by a boat carrying the means for exploiting the signals.

  amplified hydrophones, to form angular channels.

  The malfunction of a single hydrophone or its electro-

  associated device, affects the entire processing chain It is therefore necessary to have a test device for rapid diagnosis of each hydrophone and its associated electronics.

  lend to the elongated structure of the system.

  It is known to test each of the hydrophones with its amplifier by a voltage source, which allows resistance bridges to bring back into the circuit of each hydrophone a low voltage at the input

of the corresponding preamplifier.

  This device has the drawback of coupling the differences between

  rents circuits formed by the hydrophone and its preamplifier There is crosstalk, that is to say that we find at the output of a preamplifier a

  parasitic signal induced by other hydrophones.

  Another disadvantage lies in the fact that this device does not lend itself to serial power supplies of the preamplifiers, which in the case

  of a large number of hydrophones, greatly facilitates electrical connections.

  cudgels. In the case of a series supply of preamplifiers, connection capacitors can be used to overcome the difference in potential between preamplifiers In applications where the frequencies are low, the capacitance values are high. of a large number of hydrophones, the potential difference becomes large and the service voltage of the capacitors is large, resulting in

  bulky capacitors In addition the reliability is reduced.

  It is also known to use photocouplers connecting the test circuit to the different hydrophones, a light emitting diode exciting a photodetector element The disadvantages of this device are the noise

  brought back by the photodetector itself and by the polarization resistors

  preamplifier, since there is one preamplifier photocoupler, the circuit volume is large and the reliability is

  bad, especially when the number of hydrophones is large.

  The device according to the invention makes it possible to remedy these drawbacks.

  According to the main characteristic, it is a test device for a set of N sensors each connected to a preamplifier, characterized in that an AC source supplies a current I to a circuit which is inductively coupled to the circuits connecting the sensors to their preamplifiers, that the output signals of these preamplifiers are used both for processing the signals detected by the sensors and

  for fault detection of a sensor or amplifier.

  Other features and advantages will emerge from the description

  which will follow, illustrated by the figures which represent: FIG. 1, a linear antenna towed by a boat; FIG. 2: a general block diagram of the supply of the processing circuits and the fault detection circuits of a linear antenna;

  FIG. 3: the circuit diagram of the hydrophones of their preamplifiers.

  and the circuit for the test voltage, according to the invention; Figure 4: the diagram of a serial power supply for the different preamplifiers; Figures 5 and 6: two assemblies for the inductive coupling of the voltage

  test in hydrophone circuits.

  FIG. 1 shows a boat 2 towing by a cable 3, an antenna 1, composed of N hydrophones 10 1, 10 2, 10 i, 10 N enclosed

  in an envelope transparent to the acoustic waves.

  The cable 3 contains conductors for applying the necessary supply voltages for the preamplifiers, as well as the test voltage. This cable 3 also contains the connections for the signals supplied by the preamplifiers, which are applied to the processing device.

edge of the boat 2.

  The processing device makes it possible to form angular channels The signals supplied by the preamplifiers are also used for the test, in order to detect a possible failure, either of a hydrophone, or of a

preamplifier.

  FIG. 2 shows the general diagram of the towed linear antenna 24 with the assembly 20 on board the boat. This assembly 20 contains, on the one hand, the formation circuits 21 of the P channels, V 1, Vp obtained from the N signals. amplified SI, SN from N hydrophones The voltage

  supply V and the test voltage U are supplied by the subassembly 23.

  The N signals 51, SN are applied on the other hand to a detection circuit

  22 providing the N test signals T ,, TN.

  FIG. 3 shows the device according to the invention N sensors, by

  For example, hydrophones 10 1, 10 2, 10 N form the linear antenna.

  Each hydrophone is connected to the input of a preamplifier.

  20 1, 20 2, 20 N have their power supplies in series as shown in Figure 4 A DC source 4 is connected to the terminals of a

  circuit containing N Zener diodes, 40 1, 40 2, 40 N, which are in series.

  The voltage at the terminals 21 1 and 21 2 of the Zener diode 40 1 is applied to the first preamplifier 20 1 of FIG. 3 The second preamplifier receives the voltage at the terminals 21 2 and 21 3 of the second Zener diode 40 2 On

  likewise feeds the other preamplifiers and finally the preamplifier

  20 N controller receives the voltage at the terminals 21 N and 21 N + 1 of the Zener diode 40.N. The N circuits 30 1, 30 2, 30 N each formed by the hydrophone and the input of the corresponding preamplifier are inductively coupled, by loops, at 50 1, 50 2, 50 1, 50 N to a circuit 41. 41 is

  traversed by an alternating current I generated by the current generator 40.

  If M is the mutual inductance due to this coupling, the alternating current I traversing the circuit 41 induces in each loop, such as 50 i, an alternating current J = 1 Md, if Z is the impedance presented by each

  Circuit 30 i At the outputs 25 1, 25 2, 25 N of the N pre-amplifiers are collected.

  an alternative signal to judge the state of good

  of the hydrophone-preamplifier unit.

  Importantly, the circuit 41 is composed of a single round trip wire connected to the current source 40. The stop of the current source 40 suppresses the injection of the test signal in the same way as if the

  Circuit 41 had been opened, the impedance becoming infinite.

  This test device, easy to implement, can be easily integrated in a linear antenna structure comprising a hundred hydrophones for example No additional electrical component intervenes thus increasing the reliability of the device This device performs a galvanic isolation between the various elements to be tested allowing serial power supplies The opening of the electrical injection circuit of the test signal eliminates any coupling between the elements to be tested, which is fundamental in the application to a linear antenna

underwater listening for example.

  Several techniques can be used to couple the circuit 41 to the different circuits 30. FIG. 5 represents an embodiment in which the test signal injection circuit 41 is twisted and forms a turn 42.i at the level of each element to be tested. circuit 30 i form one or more inner turns 50 1 to the turn formed with the

  Circuit 41 The turns are held together by clips 400.

  FIG. 6 shows another embodiment in which a cylinder 500 forming a magnetic core is inserted on a wire of the circuit 41 and allows

  maintain one or more turns 50 i of each circuit 30 i.

  Finally, a test device consisting of an electrical circuit formed of a single return and return wire without discontinuities or addition of circuits or components connected to a current source on which all the elements to be tested by induction are described is described. in a way to

obtain galvanic isolation.

Claims (4)

  1 test device for a set of N sensors each connected to a preamplifier, the output signals of the preamplifiers (20 1, 20 2, 20.N) being used both for the processing of the signals detected by the sensors (10 1 , 2 2, 10 N) and for fault detection of a sensor or preamplifier, characterized by the fact that a current source (40) supplies an alternating current I to a circuit (41), which is inductively coupled to the circuits (30 1, 30 2, 30 N) connecting the sensors (10 1, 10 2, 10 N) to   their preamplifiers (25 1, 25 2, 25 N).   2 test device according to claim 1, characterized in that the circuit (41) traversed by the current I is twisted and forms coupling turns (42 1, 42 i, 42 N) and each circuit (30 i) connecting a sensor (10 i) to its preamplifier (20 i) forms one or more turns (50 i) inside a turn (42 i) traversed by the current I. 3 test device according to claim 1, characterized in that the circuit (41) traversed by the current 1, and one or more turns (50 i) of each of the circuits (30 i) connecting a transducer (10). i) to its preamplifier (25 i) pass through cylinders (500) of magnetic material.  4 Test device according to Claim 1, characterized in that the supply voltages of all the preamplifiers (20 1, 20 2, 20 N) are obtained across N Zener diodes (40 1, 40 2, 40 N ) serial,   powered by a current generator.   Test device according to claims 1 to 4, characterized by the   the sensors are hydrophones (10 1, 10 2, 10 N) forming a linear antenna (24) towed by a boat and on board the vessel are the power supplies (23) of the test circuit (41) and of the channel formation processing circuit (21) as well as the detection circuit of breakdown (22).