Overview

Hydrophone Tester.  A company that develops and manufactures hydrophones needed software that generated a signal with a sound projector and then measure the hydrophone response .    A hydrophone is an underwater microphone that detects sound.   The software needed to be able to perform a variety of different tests on the hydrophone such as Transmitting Voltage Response (TVR) and Free Field Voltage Sensitivity (FFVS).  The data acquired from the software was analyzed using MATLAB.

Open-water monitoring using a hydrophone

Solution

Hardware Overview

A NI PXI system was used to control the arbitrary waveform generator and acquire the data from the hydrophone.  A PXI data acquisition card was used to acquire the data.   A remote MXI card was used to control the PXI system so a standard PC could be used.  A Precision filter/amplifier was used to provide precise filtering and amplification of the measured hydrophone signal.  GPIB was used to communicate from the PXI chassis to the arbitrary waveform generator.

Hardware Block Diagram

Example of PXI Chassis

PXI (PCI eXtensions for Instrumentation) is a proven PC-based platform for measurement and automation systems. It provides power, cooling, and a communication bus to support multiple instrumentation modules within the same enclosure. 

Example of a Remote PXI Control using a PC

Remote controllers manages a PXI system from desktops, laptops, or server computers.

Precision Filter PF-1U-16FA

The PF-1U-FA series is a multi-channel programmable filter/amplifier system in a compact rack mountable or benchtop package. Fully programmable 8-channel and 16-channel configurations are available in high performance or standard configurations with a selection of input connector configurations.

The Keysight 33220A provides easy access to standard sine, square, ramp, triangle, and pulse waveforms plus you can create custom waveforms using the 50 MSa/s, 14 bit, 64 K-point arbitrary waveform function.  Communication to the instrument was done with GPIB.

Waveform Generation and Measurement

The software had to generate the Transmit Pulse train as seen below.  An arbitrary waveform generator was used to generate the pulse.  The user could specify amplitude, frequency, pulse width, time between pulses, and number of pulses to generate.

The software had to measure the received pulse using a PXI data acquisition card on the hydrophone between T₁ and T₂ as seen below.  The software also measured the voltage, current, and phase used to generate the pulse.

Features

Software Overview

The software was developed using LabVIEW.   LabVIEW was chosen due to the hardware connectivity required.  The software needed to be user friendly and allow the operator to adjust the test parameters. 

TVR Test 

The TVR Test captured the Time domain data for the Hydrophone, Voltage, and Current.  The software stepped through the desired frequencies and calculated TVR, TVR, Phase, Power and More.  LabVIEW had all the math functions required to make all the necessary calculations.  The data was saved to a text file to be read by MATLAB for later analysis.

Setup Screen

The setup screen allowed the user to enter what type of test to perform on the hydrophone and quickly view the test parameters.

Function Generator

The function generator dialog allowed the user to specify the waveform parameters to generate.  A manual mode was included so the operator could manually send signals to the hydrophone under test to verify the set parameters.

Options

The options dialog allowed the operator to set the hardware settings.

Result

The LabVIEW Hydrophone test system allowed the customer to successfully test their products.  The system replaced obsolete hardware that was getting harder to obtain.  The PXI platform used is still currently manufactured.  New hardware with faster sample rates and higher resolution was used to obtain more precise data.  LabVIEW had all the math functions required to analyze the data in real time. 

Over the years additional tests were added such as Harmonic distortion test, Beam pattern test, and Life test.  The software  was designed to add tests at a later time.  This made the test system adaptable to the customer's changing needs.  The system has been in use for over 15 years.

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