Principles of Operation 13
© 2018 Nortek AS
gravity. We therefore offer the Vector with an integrated IMU (inertial measurement unit) which
operates over a larger tilt range and can be used to correct measurements for motion contamination.
This sensor is intended to help understand how the Vector's own motion influences the
measurements. The simple configuration allows one to basically record motion data simultaneously
with the Vector velocity data. Physically, the IMU is incorporated in the Vector by simply using the
magnetometer contact interface. This means the standard tilt and magnetometer are removed and
replaced with the IMU, so there is no standard Nortek compass system with the IMU integrated.
More about this sensor can be found here: Optional IMU.
Magnetometer:
Magnetoresistive (MR) magnetometers sense magnetic fields with thin strips of a metal alloy whose
electrical resistance varies with a change in applied magnetic field. These sensors have a well-
defined axis of sensitivity. The Vector's compass includes three MR sensors, one each for X, Y and
Z components.
Each compass system is calibrated at the factory to quantify the characteristic response of the
individual components and of the system as a whole. When it leaves the factory, each system can
measure its tilt and the direction of its magnetic field vector accurately, anywhere in the world.
Note: Users disturb the magnetic field near the instrument when they deploy. Adding a battery pack
and mounting the instrument with deployment hardware adds magnetic materials that change the
magnetic field measured by the instrument. The compass calibration procedure quantifies this
magnetic disturbance, and the instrument's compass algorithm then corrects for it to obtain accurate
heading.
1.5 Measurement Volume
The Velocimeters use separate transmit and receive beams and are therefore referred to as bistatic
sensors. The measurement volume is defined by the intersection zone of the three or four slanted
receivers and the central transmitter.
1.5.1 Vector
The Vector measurement volume is defined as the area where the beams intersect each other, that
is, 157 mm from the transmitter. The transmit transducer sends a short pulse that covers only about
4 mm vertically (user selectable), and the receivers listen to an echo that corresponds to about 14
mm vertically (also user selectable). Since the Vector use three receivers, all focused on the same
volume, it obtains three simultaneous velocity measurements from that very volume.
Figure: The Vector beams intersect each other at a know n
distance from the center transducer, defining the
measurement volum e.
To Next Page
Loading...
