Hydra Principles of Operation
The Hydra can collect data from three different types of sensors. The primary type is a
SonTek/YSI Doppler velocity sensor as described below. The Hydra will also sample data from up
to four sensors using analog output voltages (A/D), as well as one serial interface
(RS232) sensor. All integrated sensors are connected using a custom splitter cable built
to user specifications.
Figure 1. Sample Hydra Configuration
SonTek/YSI 3D Doppler Velocity Sensor
The velocity sensor in each Hydra system is the SonTek/YSI Acoustic Doppler Velocimeter
(ADV). Most users select the rugged ADVOcean for deployments in the most hostile
environments -- applications requiring the finest possible spatial and temporal resolution
may use the ADV. Each velocity sensor provides a 3D measurement in a remote sampling
volume located a fixed distance from the probe. The velocity sensors support sampling
rates up to 25 Hz. Since its introduction in 1992, the ADV has become the standard for
high-quality, high-resolution velocity data. when used with the Hydra, the ADV typically
includes an integrated compass/tilt sensor to report velocity data in Earth
(East-North-Up) coordinates.
SonTek/YSI Doppler velocity sensors have a proven performance record in a wide range of
applications. Features include immunity to biofouling, invariant calibration, programmable
velocity range, and integrated diagnostic parameters.
Analog Sensors
The Hydra includes four 12-bit A/D channels that are used to sample an analog voltage
from 0 to 4V. For most applications, three of these channels are for temperature,
pressure (strain gage), and battery voltage sensors. The remaining channel can be used for
a wide variety of additional sensors. The most common sensor is the D&A Optical
Backscatter Sensor (OBS). Coupled with the acoustic signal strength from the Doppler
velocity sensor, this makes the Hydra a powerful tool for suspended sediment analysis.
The Hydra can also sample a variety of other sensors that use an analog output voltage
in the range 0 to 4V. The system can supply 12 VDC power to the external sensors, with a
maximum power draw during continuous operation of 2.0 W (excluding the velocity sensor).
For certain applications, the temperature, pressure, and/or battery voltage sensors can be
replaced with external sensors.
Serial Interface Sensors
The Hydra includes one RS232 serial port for external sensor integration. This is most
commonly used for a Paroscientific pressure sensor or a SeaBird MicroCat CTD. Other
sensors using an RS232 interface may also be integrated depending upon the requirements of
the system. As with the analog sensors, they Hydra can provide 12 VDC power to external
sensors with a maximum power draw of 2.0 W.
Other Sensors
The Hydra processor has highly flexible sampling capabilities and can be used to
integrate a wide variety of sensors. Sensors with different output data formats or power
requirements can often be integrated with modifications to the basic data sampling system.
For custom sensor applications,
contact SonTek/YSI.
More details about the Hydra can be found at:
