Measuring Underwater Environmental Variables With CompactRIO

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"The programmable CompactRIO controller acquires measurement data and transmits it to the land station. With the modular solution used in this controller and its rugged construction and low energy consumption, we optimally adjusted its configuration for required tasks."

- Ignacy Gloza, PhD (Eng.), Academy of Naval Forces, Poland

The Challenge:
Designing and building a mobile module to continuously measure underwater environmental variables in shallow water.

The Solution:
Using a special immersion casing combined with a rugged, programmable NI CompactRIO controller for data acquisition and multithreaded NI LabVIEW software, we configured a modular system that optimally works with existing environmental parameters.

Author(s):
Ignacy Gloza, PhD (Eng.) - Academy of Naval Forces, Poland
Krystian Buszman, M.Sc. (Eng.) - Academy of Naval Forces, Poland
Bogdan Iwiński, M.Sc. (Eng.) - Veritech Sp. z o.o.

Introduction

We created the smallest possible environmental-variable monitoring module capable of gathering the most information. The module is intended to go where other systems cannot—such as in shallow water, which presents difficult measuring conditions.

System Setup

The device we developed has sensors and necessary electronic equipment mounted on an underwater tripod. The whole device is connected to a second land-based component. We established the connection with a retractable cable for double-sided data transmission and a control-system power supply on the platform. The measurement platform has a power supply and all necessary instrumentation for recording and analysing sensor data.

The programmable CompactRIO controller acquires and transmits measurement data to the land station. Because this modular controller is rugged and consumes little energy, we optimally configured it for required tasks. Recording and transmitting multiple fast-changing signals requires a very efficient system. Therefore, we used an 800 MHz, 512 MB RAM configuration with a Gigabit Ethernet interface for data transmission. The system reads dynamic data on four analog channels with 51.2 kHz sampling frequency and 24-bit resolution, as well as a 1 MHz frequency channel. Measurement data continuously transmits to the computer located on a vessel or land by means of a 1 km optical fibre.

The whole device is modular, mobile, and very easy to launch in the shallow water typical of Gulf of Gdańsk. The sea floor should be relatively flat to simplify measurement tasks and later recorded signal analysis.

Data quality depends on the distance from the littoral zone, which may include noise coming from industrial, commercial, or housing areas. The littoral zone influences not only the hydroacoustic field, but also the magnetic and electric fields.

Our system consists of an underwater platform with installed sensors; a measurement console for monitoring measurements; a data analysis and recording unit (located on land or a vessel); a long cable for controlling the power supply and double-sided data transmission; and a sensor suite. The sensor suite includes hydrophones; a magnetic field sensor; a compass with a motion sensor; an electric field sensor; a water sound-velocity sensor; a hydrodynamic pressure sensor; and a hydrostatic pressure sensor.

The hydroacoustic module contains four hydrophones that monitor audible environmental noises in detail. Because we can accurately control the hydrophone locations, we can adjust the measurement system to specific current conditions. The very high converter sensitivity records even the smallest changes within the operating area.

The magnetic field sensor consists of three pairs of sensors located on the x-, y-, and z-axes, respectively. This not only measures current magnetic field component values, but also provides a gradient for all components. The sensor and an analog correction unit can calibrate the measurement system anywhere in the world.

We included a compass with a motion sensor to determine the current measurement module setting in all directions. The compass measures changes yaw value, while a motion sensor measures platform pitch and roll parameters. Such a system is necessary to precisely determine sensor location in relation to the investigated disturbance source.

The sound velocity sensor measures temporary elastic wave propagation velocity changes, depending on salinity level, hydrostatic pressure, and temperature, or by measuring the impulse transit time between the transmitter and the receiver. We need this value to be able to interpret data from the hydroacoustic system, where all sound velocity sensor data is analyzed.

The hydrostatic pressure sensor measures the current measurement platform depth. The calculation algorithm uses data received from this sensor to determine the distribution of sound velocity in water.

The hydrodynamic pressure sensors monitor changes caused by water movement near the platform. These movements include tides, water surface waves, and the displacement of objects near the measurement system.

A notebook computer controls the whole recording system with a dedicated application for basic data logging, ongoing operator-required data. It also runs online calculations for some of the parameters and displays them onscreen. The direct connection between the computer and the underwater research module using a Gigabit Ethernet network means the system can send large amounts of data and present it in real time. We selected system components because they could precisely record environmental variables in various weather conditions.

Conclusion

We used a programmable CompactRIO controller to create a device to help us research and create the physical parameters map of the Gulf of Gdańsk. It also monitors changes in these parameters through human interference in the water environment.

The investigation was supported by the Ministry of Science and Higher Education (Grant No OR00 0047 08).

For more information on this case study, contact:

Bogdan Iwiński, M.Sc. (Eng.)
ul. 1 Maja 21/3 
Ruda Slaska, Poland
Tel: +48 501 275 890
Email: b.iwinski@veritech.pl
Website: Veritech Sp. z o.o.

Author Information:
Ignacy Gloza, PhD (Eng.)
Academy of Naval Forces, Poland
Poland

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