Time Constants; Watchdog - Hemisphere GPS V104n User Manual

V104n GPS Compass User Guide

Time Constants

The V104n incorporates user-configurable time constants that can provide a
degree of smoothing to the heading, pitch, rate of turn (ROT), 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
GNSS' 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.
Rate of Turn (ROT) time constant: The default value of this constant is
2.0 seconds of smoothing. Increasing the time constant increases the level of
ROT smoothing.
Course Over Ground (COG) time constant: The default value of this
constant is 0.0 seconds of smoothing. Increasing the time constant increases
the level of COG smoothing. COG is computed using only the primary GPS
antenna and its accuracy depends upon the speed of the vessel (noise is
proportional to 1/speed). This value is invalid when the vessel is stationary,
as tiny movements due to calculation inaccuracies are not representative of
a vessel's movement.
Speed time constant: The default value of this constant is 0.0 seconds of
smoothing. Increasing the time constant increases the level of speed
measurement smoothing.

Watchdog

The watchdog is a timer that is controlled by the software that monitors if
the heading is lost. The watchdog software is compliant with IEC 60945.
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