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Bench characterization hydrophone sonar antennas

By C. Lachaize Thomson Marconi Sonar and X. Chabert Saphir

The objective: to measure the sensitivity and directivity of hydrophone component antennas sonar.

The solution: build a new generation of acoustic test bench, with maps of scanning signals and a dynamic software LabVIEW drivers.

Thomson Marconi Sonar is the world leader in the manufacture of sonars for different marines. The sound department of the site of Sophia Antipolis is the french site that explores, develops and manufactures antennas and transducers acoustic sonars component.

Measuring Principle
Passive sonars use a large number of hydrophones to listen to the sounds and classify submarines in the area heard. To characterize or describe these hydrophones, one performing measurements of sensitivity and Directivity. To do this, it sends an acoustic signal in the form of a train of pulses to eliminate echoes in the time domain. The signal is received by a hydrophone and the standard or the hydrophone (s) under test. The hydrophone standard used to determine the sound level received and calculate the sensitivity of the hydrophone (s) under test in V / ìPa according to the level measured electricity.

The chassis of the previous measurement using measurement devices controlled by GPIB. For a large number of signals (from 4 to> 256) are recorded on magnetic tape recorders and calculations are made in delayed time on a workstation. The new measure allows bench testing several sensors at once, with calculations performed at the same time or shortly after the test.

We have worked closely with an engineer Saphir jointly conducting the prototype in LabVIEW, which simplifies the specification phase and produces a robust and reliable code.

Implementation
To build this new chassis, called Banc Acoustics New Generation (BANG), we chose the LabVIEW software, two PCI-4451 and PCI-4452 for the issuance of four signals and receiving signals from eight. We have entrusted the implementation of the application to the company Saphir, a partner of National Instruments. We chose Sapphire for references in similar applications.
To make correct measurements, it is necessary to synchronize the signals generated and received signals. We used the RTSI bus, present on the cards to share the same clock between different cards and between input and output cards 4451.

During the tests, the antenna, composed of more than one hundred sensors, is immersed in a tank. The rotation sensor is made by a turret controlled by GPIB. For the sensitivity test, a train of pulses at a given frequency is generated by the exit of the card 4451. We measure the amplitude and phase difference between seven hydrophones under test and a standard hydrophone. Then we repeated the same test at a different frequency. The tests are performed in a frequency band ranging from 3 to 20 kHz over a thirty not about, and take just minutes.

To test the directivity, positioned on the turret with different angles relative to the source and for each position, it performs no action on several frequencies. We measure the signal attenuation compared with the optimal reception of the same hydrophone at the same frequency.

Results
The chassis works well and allows us to perform the qualification tests and acceptance on the antennas. The implementation of the bench was made in six months. We have worked closely with an engineer Saphir jointly conducting the prototype in LabVIEW, which simplifies the specification phase and produces a robust and reliable code.
We consider all of the bench as a measuring device and we have developed the procedure to measure performance (amplitude, phase, frequency and duration) for signals generated and acquired using equipment calibrated. This procedure allows us to meet our quality requirements.
In the future, we would like to implement several other benches acoustic bench giving access to more channels (8 transmit and 24 receive), without a bench portable external enclosure and a bench to cover a frequency band 20 to 500 kHz.

For more information, please contact
Xavier Chabert
Saphir
38530 BARRAUX
Tel. : 04 38 92 15 50
E-mail: info@saphir.fr
Christian Lachaize
Thomson Marconi Sonar

February 2001

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