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July 2019 – TD 304 OPERATING MANUAL – Doppler Current Profiler Sensor
9.1.3
Transducer 1 as reference when upside-down
Use the same method as when the sensor is upward looking. Rotating clockwise gives an increasing angle. The sensor
is able to sense its vertical orientation sensor and automatically correct for the upside-down orientation of the sensor.
NOTE: To check the value measured by the tilt and heading sensor refer to chapter 4.2. Viewing incoming data
in real-time.
9.1.4
Orientation/Steering pin as reference when upside-down
Now transducer 1 is 135 degrees clockwise from the orientation pin. Add 135 degrees instead of 225 degrees.
9.2
Checking the compass
First point transducer 1 towards North. The compass heading should lie close to 360°/0° (same point).
NOTE: To check the value measured by the tilt and heading sensor refer to chapter 4.2. Viewing incoming data
in real-time.
A clockwise rotation gives an increasing compass angle. Keep the sensor away from magnetic object like table legs (if
iron, these are acting as a permanent magnet magnetized by the earth magnetic field). Big objects like for example a
car outside the room where the compass is tested can affect the earth magnetic field at the point where the sensor is
placed. Also the structure of the building can influence on the earth magnetic field around the sensor.
Be aware that nearby objects may influence the magnetic field when the sensor is used. This can for example be a
problem on a buoy as described above or if hanging from a boat. The rule of thumb is that the bigger the magnetic
object is (hard and/or soft magnetic) the further away sensor should be positioned to eliminate the influence. If the
sensor is in a fixed position the fixed heading input can be used as described earlier in this chapter. On buoys the
solution is often to use an external compass which is placed on a non-magnetic mast away from the buoy.
Even alkaline batteries can be a problem if placed close enough to the sensor. When used on SeaGuardII the upper
battery compartment can give problems when using alkaline battery cells. The battery cells provided by Aanderaa do
not give problems when using the lower battery compartment. When batteries are own-built, you have to be aware of
this problem. The influence from the batteries can be checked by looking at the heading output from the sensor while
placing the batteries closer to the sensor. Moving the batteries around a hand held compass also gives a good
indication on whether the batteries are low magnetic or not. Batteries can also be degaussed to reduce the magnetic
influence from the batteries.
