Mechanical installation
The DVL must be rigidly fixed to the vessel structure.
It is recommended to align the DVL forward mark toward the vessel bow.
In this case, the nominal alignment angle to enter in the inertial system configuration is +45°.
Note that the native DVL instrument frame (displayed DVLX and DVLY on the diagram) is a left handed frame whereas the SBG Systems products operate in a right handed coordinate system. Therefore we internally invert the DVLX and DVLZ velocity directly on the received sensor input before applying user alignment angles.
Following diagram shows DVL instrument frame as well as the inverted DVL-X (pink arrow) axis that is used for DVL to vessel misalignment determination.
The lever arm from the IMU to the DVL must also be measured accurately.
Electrical connections
The typical DVL electrical integration takes care of two main aspects:
- The DVL data output
- Synchronization between DVL and INS
Data output connection
Regarding the data output, a simple serial connection is generally used, by connecting the DVL serial port to one of the SBG INS available serial ports (eg. PORT A Rx), either in RS-232 or in RS-422.
Synchronization between DVL and SBG INS
DVL Master
In this mode of operation, the DVL runs on its own and can send a synchronization pulse to the SBG INS whenever a new velocity measurement is available.
The measurement rate might be not constant depending on water conditions.
To operate in this mode, the DVL synchronization output must be connected to one of the available SBG INS SYNC IN pins.
DVL Slave
In this mode of operation, the SBG INS generates a regular pulse signal to trigger each measurements of the DVL.
The measurement rate can be constant in this mode, driven by the SBG INS SYNC OUT rate.
However care must be taken in setting up the SYNC OUT Rate to mach the minimum DVL's timing requirement, based on DVL type, configuration, and maximum depth during the mission.
In other words, the DVL must be able to send a ultrasonic pulse, wait for the echo and process the data before the next trigger shall occur.
Setting the right rate
SBG Systems recommends you to contact your DVL's manufacturer to know what allowable SYNC OUT rates can be used depending on your system configuration and water environment.
As a rule of thumb, an update rate between 1Hz and 10Hz is feasible in shallow water conditions.
