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3.5 Options
3.5.1
Options > Units
Metres or Feet can be selected as the units used.
3.5.2
Options > Measure Target
Measures distance in metres or feet (depending on Options > Units selection) on the display.
3.5.3
Options > Enable Gyro
Enables the internal gyro to be used in North Up, Heading Up, Target Steering and Acquire Target modes.
3.5.4
Options > Calibrate Gyro
All gyros are sensitive to the environment (i.e. temperature, motion, earth's rotation, etc.) and will naturally drift with
time. Therefore, from time to time, it is recommended to complete a gyro calibration (in manual mode) or recalibrate
the motor (auto mode) to remove the accumulated drift.
Automatic Gyro Calibration
Imagenex Gyro enabled scanning sonars now incorporate an automatic gyro biasing feature which is selectable in
the user program. This mode continuously re-bias's the gyro in real time, accommodating for temperature
fluctuations and internal drift. See Section 3.5.5 Options > Enable Gyro Auto Bias for enabling / disabling this mode.
When first starting the sonar, the bias adjustment will be very rapid as the temperature stabilizes. While the gyro
will still internally drift, the sonar image will be coherent, allowing the operator to continue to work. Note that the
absolute heading will not be exact during this time as the sonar does not differentiate between induced drift and
real movement. After a few minutes, re-calibrate the motor to realign the sonar and the transducer. This will reset
the accumulated drift that occurred during the warmup period. It is recommended to periodically re-calibrate the
motor to reset the accumulated drift.
Manual Gyro Calibration
The information below describes the manual biasing mode which may be necessary in strong magnetic field
environments.
Do not calibrate the gyro until the internal temperature of the sonar has stabilized, approximately 30-60 minutes
underwater.
The procedure below is followed:
•
Suspend sonar operations and mount the sonar on a level stable surface or settle the ROV on a flat bottom.
•
Select Options > Calibrate Gyro.
•
The message Calibrating Gyro will appear. Calibration takes approximately 30 seconds.
•
Once the message disappears, standard operation commences.
Note: When using manual biasing, it is ESSENTIAL that the sonar is completely stationary and at constant
temperature during gyro calibration. Any movement will cause undesirable drift in the gyro.
