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V102 GPS Compass User Guide

is lost because the satellite signals were blocked. The gyro provides a

relative change in angle since the last computed heading, and, when used in

conjunction with the tilt sensor, defines the search space as a wedge-shaped

location (see Figure 3-3).

Figure 3-3: V102’s gyro aiding

The gyro aiding accurately smoothes the heading output and the rate of

turn. It provides an accurate substitute heading for a short period depending

on the roll and pitch of the vessel, ideally seeing the system through to

reacquisition. The gyro provides an alternate source of heading, accurate to

within 1º for up to three minutes, in times of GPS loss for either antenna. If

the outage lasts longer than three minutes, the gyro will have drifted too far

and the V102 begins outputting null fields in the heading output messages.

There is no user control over the timeout period of the gyro.

Calibration, which is set at the factory, is required for the gyro to remove

latency from the heading solution as well as provide backup heading when

GPS is blocked. The receiver will calibrate itself after running for a while but

it may be important to follow the manual calibration instructions if you want

to guarantee performance quickly after powering up the receiver.

The gyro initializes itself at powerup and during initialization, or you can

calibrate it as outlined in Hemisphere GPS’ GPS Technical Reference. When

the gyro is first initializing, it is important that the dynamics that the gyro

experiences during this warmup period are similar to the regular operating

dynamics. For example, if you use the V102 on a high speed, maneuverable

craft, it is essential that when gyro aiding in the V102 is first turned on, use it

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Directed Electronics VS102 Guía de usuario Pagina 38