Directed Electronics VS102 Betriebsanweisung PDF herunterladen (Seite 39)

Chapter 3: Operation

in an environment that has high dynamics for the first five to ten minutes

instead of sitting stationary.

With the gyro enabled, the gyro is also used to update the post HTAU

smoothed heading output from the moving base station RTK GPS heading

computation. This means that if the HTAU value is increased while gyro

aiding is enabled, there will be little to no lag in heading output due to

vehicle maneuvers. Hemisphere GPS’ GPS Technical Reference includes

information on setting an appropriate HTAU value for the application.

Time Constants

The V102 incorporates user-configurable time constants that can provide a

degree of smoothing to the heading, course over ground (COG), and speed

measurements. You can adjust these parameters depending on the expected

dynamics of the vessel. For example, increasing the time is reasonable if the

vessel is very large and is not able to turn quickly or would not pitch quickly.

The resulting values would have reduced “noise,” resulting in consistent

values with time. However, if the vessel is quick and nimble, increasing this

value can create a lag in measurements. Formulas for determining the level

of smoothing are located in Hemisphere GPS’ GPS Technical Reference. If

you are unsure on how to set this value, it is best to be conservative and

leave it at the default setting.

Note: For heading and rate of turn there is no lag once the gyro is calibrated

and enabled.

Heading time constant: Use the $JATT,HTAU command to adjust the level

of responsiveness of the true heading measurement provided in the

$GPHDT message. The default value of this constant is 10.0 seconds of

smoothing when the gyro is enabled. The gyro is enabled by default, but can

be turned off. By turning the gyro off, the equivalent default value of the

heading time constant would be 0.5 seconds of smoothing. This is not

automatically done and therefore you must manually enter it. Increasing the

time constant increases the level of heading smoothing and increases lag.

Pitch time constant: Use the $JATT,PTAU command to adjust the level of

responsiveness of the pitch measurement provided in the $PSAT,HPR

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Directed Electronics VS102 Betriebsanweisung Seite 39