Simrad MX575D User Manual

26 |
Operation | HS80/MX575C/MX575D User Manual
Time constants
The Smart GPS compass 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. The level of smoothing maybe
adjusted manually but if you are unsure on how to set this value, it is best to be conservative
and leave it at the default setting.
¼ 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 only if the gyro is disabled.
Pitch time constant
Use the $JATT,PTAU command to adjust the level of responsiveness of the pitch
measurement provided in the $PSAT,HPR message. The default value of this constant is 0.5
seconds of smoothing. Increasing the time constant increases the level of pitch smoothing
and increases lag.
Rate of Turn (ROT) time constant
Use the $JATT,HRTAU command to adjust the level of responsiveness of the ROT
measurement provided in the $GPROT message. 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
Use the $JATT,COGTAU command to adjust the level of responsiveness of the COG
measurement provided in the $GPVTG message. 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
Use the $JATT,SPDTAU command to adjust the level of responsiveness of the speed
measurement provided in the $GPVTG message. The default value of this constant is
0.0 seconds of smoothing. Increasing the time constant increases the level of speed
measurement smoothing.
Alarm functionality
¼ Note: Alarm functionality is only valid for serial communication.
A relay is located on the Transmit Heading Device (THD) circuit board. The relay contacts are
isolated from all circuitry in the THD. The THD is connected to the coil side of the relay, but
not to the contacts that are connected to the external pins through the main IO connector.
If the THD loses power or heading, the coil voltage is lost and the relay opens and activates
the notification method employed by the user. When the heading is output, the relay
contacts remain closed, completing the circuit as an indication that the Smart GPS compass is
operational.
¼ Note: Alarm pins must be connected to an IMO type-approved device.

Simrad MX575D Specifications

General

Brand	Simrad
Model	MX575D
Category	Marine GPS System
Language	English