Hydrophone Calibration System

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"The Hydrophone Calibration System based on PXI helps the user replace the limited features imported system with a customized system and new features including testing more channels and more types of tests."

- Tejeswar Jakkilinki, Digilogic Systems Pvt.

The Challenge:
Developing a digital calibration system for underwater acoustic transducers (hydrophones) for applications like ocean bottom profiling, underwater telephony, and more.

The Solution:
Replacing the imported calibration system that uses box instruments with a modular system based on PXI and using LabVIEW software to achieve high performance, including automation of the calibration process.

Author(s):
Tejeswar Jakkilinki - Find this author in the NI Developer Community

Digilogic Systems PVT. LTD. (DSPL), an ISO 9001:2008-certified company accredited by UKAS in India, provides systems, products, and solutions for defense, aerospace, automotive, and manufacturing market segments. The DSPL technical staff comprises a pool of professionals with vast experience and skill sets in developing automatic test equipment (ATE) and simulators for testing systems ranging from DC to 40 GHz, PCB diagnostics, data acquisition, and control systems with LabVIEW software. We are staffed with more than 30 engineers with an average experience of six years and in-depth LabVIEW knowledge. Our expertise varies from control systems to high-end RF and EW applications. We also work on IP developments based on LabVIEW FPGA and converting client-specific algorithms into FPGA target codes.

System Overview

A hydrophone calibration system calibrates and compares test hydrophones with the standard projector and standard receiver hydrophones using reciprocity, comparison, and directivity principles. Our Hydrophone Calibration System uses special techniques that consider various requirements of calibration principles, limitations of water medium, and frequency range of operation (limited due to water tank dimensions of 8 x 8 x 8 m).

Most hydrophone users import the Hydrophone Calibration System for their use. Maintaining such calibration systems becomes tedious as there is no local support to handle maintenance activity on the systems. Also, the vendor fixes the features of such imported systems and users cannot add or remove any new elements on their own.

One user approached us for an alternate solution for the Hydrophone Calibration System. We studied the available imported system and determined that it could be replaced with a modular instrument system based on PXI, and we could customize tests using LabVIEW software.

System Design

We proposed an alternate solution using the NI PXI platform that included a signal generator, a high-speed oscilloscope, a programmable insulation resistance measurement meter, and multiplexer switch hardware. For developing the customized application, we used LabVIEW because of the availability of most of the mathematical and signal processing functions needed for hydrophone calibration.

Figure 1. Hydrophone Calibration System Block Diagram

The reasons for a solution based on NI products:

  • Modularity and scalability of the PXI Express platform - more channels
  • Reusability and integration of available subsystems - turntable
  • LabVIEW platform - more tests
  • Local support - presence of NI Alliance Partner locally

To calibrate a hydrophone, we needed to generate the required stimulus signal by an arbitrary waveform generator (AWG) and compare the response signals from the test hydrophone with the standard hydrophone by acquiring both the stimulus and response signals through a high-speed digitizer. Both the stimulus and response signals go through amplifiers to have the signals at the desired power level. The PXI Express AWG and high-speed digitizer replace the stand-alone box instruments, which reduced the equipment space required and increased the equipment programmability.

The user needed customized test sequences and features to add new test sequences, which we could deliver since we chose LabVIEW as the calibration software development platform. Also, the multiplexer switch module helped us make the system scalable up to 64 channels for testing quickly. If needed, we could add a few more switches and enhance the number of channels to be tested with minimal software changes.

Types of tests include:

  • Reciprocity test
  • Comparison test: transmitting voltage response test up to 64 channels; free field receiving sensitivity test up to 64 channels
  • Directivity test
  • Directivity test for multiple frequencies
  • Directivity test with external trigger
  • Directivity test with external trigger for multiple frequencies
  • Insulation resistance measurement

Figure 2. Test Configuration

Figure 3. Calibration Software GUI

Features of our Hydrophone Calibration System include:

  • Can calibrate maximum of 64 hydrophones at once
  • Integrated insulation resistance measurement
  • Can generate CW burst with minimum burst duration of 0.5 ms
  • Can generate CW frequency of 2 kHz to 1 MHz
  • Pulse repetitive rate of 20 ms
  • Averaging of 1 to 20
  • Measurements, amplification/attenuation, frequency analysis, and signal processing on the fly to estimate signal parameters for further processing and analysis
  • Customized configuration and automated report generation based on the tests conducted

Author Information:
Tejeswar Jakkilinki
Find this author in the NI Developer Community

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