16-MHz MicroADV Expanded Description

1. Introduction

The SonTek/YSI 16-MHz MicroADV (Acoustic Doppler Velocimeter) is a versatile, high-precision instrument used to measure 3D water velocity (Figure 1). The MicroADV is used to measure water velocity in a wide range of environments including laboratories, rivers, estuaries, and the ocean.

The MicroADV uses acoustic Doppler technology to measure 3D flow in a small sampling volume located 5 cm from the probe (Figure 2). The velocity range is programmable from ±3 to ±250 cm/s. Data can be acquired at sampling rates up to 50 Hz (higher rates are available). With no zero offset, the MicroADV can measure flow velocities from less than 1 mm/s to over 2.5 m/s.

Figure 2. Sampling Volume

The MicroADV consists of three basic elements: the probe, the signal conditioning module, and the processor. The probe is attached to the conditioning module, which contains low-noise receiver electronics enclosed in a submersible housing. The MicroADV conditioning module and probe are connected to the processing module using a custom shielded cable up to 10-m long.

The MicroADVField processor is a set of three printed circuit cards that operates from external DC power and outputs data using serial communication or a set of analog voltages. The MicroADVField can be operated from any PC-compatible computer or can be integrated with a variety of data acquisition systems.

For autonomous deployment (internal data storage and battery power), the MicroADV can be integrated as part of a SonTek Hydra system.

2. MicroADV Probe

The MicroADV probe configuration is determined by a combination of four factors: sampling volume location, coordinate resolution (3D or 2D), sensor mounting, and sensor orientation. Probes can be constructed with almost any combination of these options (See Figures 3, 4, 5, 6, and 7.)

2.1. Sampling Volume Location

The precise location of the MicroADV sampling volume is determined by probe geometry and is nominally 5 cm from the tip of the probe.

2.2. Coordinate Resolution: 3D or 2D

For most applications, a 3D velocity measurement is preferred. 2D probes are available for a number of specialized applications. A 2D side-looking probe can operate in as little as 3 cm of water; a 2D down-looking probe can be used in very narrow channels (width less than 5 cm) or for measurements along-side underwater structures.

2.3. Sensor Mounting

The acoustic sensor can be mounted on a rigid stem, either 25 or 40 cm in length, or on a 100-cm flexible cable. The 40-cm stem is common for laboratory applications, as most measurements can be made with the conditioning module out of the water (although it is completely submersible). For field applications, a 25-cm stem provides a more rigid installation. The 100-cm cable mounting provides great flexibility for probe installation, but requires a user-supplied mounting fixture to ensure reliable sensor orientation.

2.4. Sensor Orientation

The down-looking sensor orientation (standard for all systems) is ideal for measurements close to the bottom. Side-looking probes are typically used in wave flumes to avoid flow interference. If the primary interest is to measure velocity in the surface layer or under structures, an up-looking probe is preferred.

3. MicroADV Signal Conditioning Module

The standard MicroADV signal conditioning module (for MicroADVFields with no optional sensors) is a cylindrical acetyl (Delrin) housing (Figure 8). The cable to the processing module attaches using an underwater mateable connector. The probe is permanently mounted to the front of the housing.

MicroADVField systems that include optional sensors (compass/tilt, pressure, and/or temperature) use an expanded acetyl (Delrin) housing. The cable to the processing module attaches with an underwater mateable connector. The probe is permanently mounted to the front of the housing.

Figure 8.
Top: Standard Conditioning Module
Bottom: Conditioning Module with Sensors

4. MicroADV Processor

The MicroADV processor can be housed in different ways depending upon how the system will be used and whether the processor will need to be submerged.

The MicroADVField operates from DC power and is typically connected to a laptop computer running SonTek's powerful data acquisition software. It can also be integrated with a variety of data acquisition systems using either serial communication or the analog output voltages.

For applications where the MicroADV processor does not need to be submerged, the processor (Figure 9) is enclosed in a splashproof housing with connectors for the probe, power, communication, and auxiliary input/output (analog voltages and external synchronization). The splashproof housing can include an internal rechargeable battery (capacity for 6-10 hours of operation).

Figure 9. MicroADVField Splashproof Processor

The MicroADVField processor can also be housed in an underwater canister (Figure 10) with underwater mateable connectors to the probe and the external interface (power, communication, and auxiliary input/output). The power and communication cable can be up to 1500 m long for deployment in a wide range of environments.

Figure 10. MicroADVField Underwater Processor

5. Standard Features

MicroADV systems include the following standard features.

6. Options

Several options, including the following, are available for use with MicroADV systems.

Analog Outputs (MicroADVField Splashproof)

Three analog output voltages (for 3 components of velocity) for integration with an analog data acquisition system.

Internal Battery (MicroADVField Splashproof)

Rechargeable lead-acid battery for short-term field deployments (capacity for 6-10 hours operation).

Compass/Tilt Sensor (MicroADVField)

The compass and 2-axis tilt sensors allow the MicroADVField to report velocity data in Earth (East-North-Up) coordinates. The sensor has a built-in calibration feature to compensate for magnetic distortion. The user can easily re-orient the compass for up, down, or side-looking operation.

Pressure Sensor (MicroADVField)

A strain gage pressure sensor can be installed in the MicroADVField to measure wave height (PUVW for directional wave spectra) and deployment depth. The pressure sensor is available in a variety of ranges for most any environment.

Temperature Sensor (MicroADVField)

Any MicroADVField with compass/tilt or pressure sensor includes a temperature sensor to compensate for changes in sound speed. Sound speed is used to convert Doppler-shift to water velocity.

The Hydra -- Autonomous Operation

The MicroADV can be integrated with a wide range of other sensors as part of SonTek's Hydra autonomous ocean sensor system (including internal data storage and battery power). For more information on the Hydra system, go here.

• MicroADV Overview
• MicroADV Applications
• MicroADV Specifications
• MicroADV Principles of Operation
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