Watson Industries, Inc.
DMS-SGP02 Rev K 03/22/2018
6
When GPS heading is selected, the Heading Angle is referenced to the fore-aft alignment of the
two GPS antennas using the True North GPS Heading (the string start label is “G”). If for any
reason this true north GPS heading is unavailable, the GPS Ground Track heading will be used (the
string start label is “T”). If GPS becomes completely unavailable, relative heading will be
maintained (the string start label is “I”).
While this DMS is "all attitude", the accuracy deteriorates rapidly when its forward direction is
within about 5 degrees of vertical. Operation for any extended period of time at more than 60
degrees from level is not recommended. If these few operational precautions are observed, the
DMS should provide very accurate data for a wide variety of applications.
Special Operation Modes
Reference Mode
This mode is usually used for calibration or diagnostics. When in reference mode, the DMS will
output data generated directly from the sensor reference signals rather than as a product of the
closed loop integration used for normal operation. This mode provides sensor information similar
to normal operation mode with the following differences:
Bank and Elevation are obtained directly from the accelerometers - no gyro stabilization.
Heading is directly from the GPS reference.
Angular Rate Sensors bias corrections are not updated.
The reference mode can be selected either through the command mode, or by an analog logic
command. Note that reference mode is never a default setting. It must be re-selected when re-
powering the unit.
Free Mode
While in Free Mode, the DMS will output data from the sensors without correction by the
references. For example, the Bank Angle data output in Free Mode is calculated directly from the
X-axis Rate Sensor. In this case, the angle is a direct integration of the roll rate. Free Mode can be
used to totally reject effects from dynamic accelerations, but accuracy degrades with time. It is
intended for use over periods of up to a minute at a time. This mode provides sensor information
similar to normal operation mode with the following differences:
Bank, Elevation and Heading are obtained directly from the rate sensors alone.
Relative Heading from last known heading is used.
Angular Rate Sensors bias corrections are not updated.
Free mode can be accessed either through command mode, or by an analog logic command. Note
that free mode is never a default setting. It must be re-selected when re-powering the unit. The
user should not enter free mode until after the DMS is initialized and its readings are stable.
Hold Mode
This mode inhibits bias adjustments to the rate sensors. It is intended for short-term use only since
leaving biases uncorrected will allow errors to accumulate over time. The accumulating bias error
will result in small attitude errors. Hold mode can provide better performance in highly dynamic
environments such as continuous circling over several minutes time. The user should not enter hold
mode until after the DMS is initialized and its readings are stable.
Command Mode
In this mode, the DMS will output sensor data normally unless it receives a valid command
character. Once a command is received, the DMS will send data in response and await the next
command. Using this mode, the user can retrieve the EEPROM map, adjust baud rates, adjust
