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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 a few minutes at a time. This mode provides sensor information
similar to normal operation mode with the following differences:
Bank and Elevation are obtained directly from the rate gyros.
No heading information is available.
Angular Rate Sensors are not close-loop bias corrected.
Free mode can be accessed either through terminal 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 gyros. 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.
Control Mode
In this mode, the DMS will output sensor data normally unless it receives a control mode
command. 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, baud rates, output formats,
and many other operational settings of this sensor. Having access to this information makes the
Control Mode useful in assisting the factory to remotely troubleshoot the certain operational
problems that can occur. For more details, see the RS-232 Input Commands section later in this
manual.
Interface
The DMS has analog, logic, and digital interface capabilities.
RS-232 Output Format
The standard RS-232 output consists of a string of decimal ASCII characters sent asynchronously
at regular intervals. Nominally, the string is sent at 9600 baud with eight data bits, one stop bit and
no parity. The mating connector for the RS-232 is a 9 Pin Male D-Sub. The number of strings sent
per second depends on the baud rate and the output format. The maximum rate is 71.11 strings per
second. See Appendix A for information on how to change the data string. The contents of a
typical string are formed as follows:
1.
A single letter and a space used to indicate the start of the data string. The letter "G"
indicates the start of an inertial data string with successful GPS data input. The letter "I"
indicates the start of an inertial data string with GPS disabled or absence of valid GPS data.
The letter "R" indicates the start of a Reference data string. If the letter is in lower case
("g","i", or "r"), an error over-range condition is indicated (see below).
2.
A seven character string representing the bank angle starting with a "+" or a "-", followed
by three digits, a decimal point, one digit and a space for up to ±179.9 degrees.
Watson Industries, Inc.
DMS-EGP01 Rev A 02/12/2015
6
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