Operating Instructions and Installation Instructions

ComNav Vector G2/G2B Installation & Operation Operation
Document PN 29010078 V2.0 - 60 -
DRAFT #3 – 29 May 2009
Measurement
Time
Constant
Sentences Affected Usage
Course Over
Ground
COGTAU $GPVTG
• If the vessel is resistant to quick
changes in its motion, increase it.
Heading HTAU $GPHDT, HDG, HDM
• If vessel does not turn quickly,
increase it.
Rate Of Turn HRTAU $GPROT
• If vessel does not turn quickly,
increase it.
Pitch (or Roll) PTAU $PSAT,HPR
• If vessel does not pitch (roll)
quickly, increase it.
Speed SPDTAU $GPRMC, VTG, BIN 1
• If the vessel does not change
speed quickly, increase it.
Table 17 – Smoothing Time Constants
If your vessel is small and highly manoeuvrable, or if you are unsure of how changing
these values will affect your vessel (and the other navigation equipment you have
on-board), it is probably best to be conservative and leave the time constants at the
default settings.
But, if you do wish to change any of the G2’s time constants, the next table provides
some formulae for figuring out an optimal value of each constant.
For further details, please consult the GPS Technical Reference manual.
Time
Constant
Range (seconds) Formula 1
COGTAU 0.0 to 60
• default: 0.0
10
sec)/ (in course of change of ratemax °
HTAU 0.0 to 60.0
• default: 2.0
gyro ON:
sec)/ (in turn of ratemax
40
°
gyro OFF:
sec)/ (in turn of ratemax
20
°
HRTAU 0.0 to 60 sec
• default: 2.0
10
)sec/ (in turn of rate of ratemax
2
°
PTAU 0.0 to 60 sec
• default: 0.5
sec)/ (in pitch of ratemax
10
°
SPDTAU 0.0 to 60 sec
• default: 0.0
10
)sec/metres (in onaccelerati of ratemax
2
Table 18 – Time Constant Formulae
1 Speed conversions: 1 Knot = 0.51444 metres/sec & 1 Km/H = 0.53996 Knots
Note: the default value of 2.0 seconds for HTAU & HRTAU is correct
when the gyro is enabled. If the gyro is disabled, the equivalent
default value of HTAU is 0.5 seconds. But the HTAU constant is not
automatically changed if the gyro is disabled, and therefore must be
changed manually.
L CAUTION! COG is computed using the Primary GPS receiver only,
and its accuracy is dependant upon the speed of the vessel (noise in
the COG measurement is inversely proportional to speed).
L When the vessel is stationary, the value of COG is invalid!!
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