AHRS500CA Series User’s Manual
Doc# 7430-0050-03 Rev. A
Page 9
*Note: Pin 4 on the AHRS500CA is data ground as well as power ground.
Power is applied to the AHRS500CA on pins 3 and 4. Pin 4 is ground; Pin
3 should have 10-40 VDC unregulated at 275 mA. DO NOT REVERSE
THE POWER LEADS.
3.3
Interface
The default serial interface is standard RS-232, model configurable baud
rate, 8 data bits, 1 start bit, 1 stop bit, no parity, and no flow control, and
will output at a model configurable output rate.
3.4
Measurements
The AHRS500CA Series is designed to operate as a complete attitude and
heading reference system. The default system operation is “angle” mode
with the packet and output data as described below. The AHRS500CA
operates in two other measurement modes that are for factory use only and
are not supported for general use.
The AHRS500CA acts as a complete attitude and heading reference system
and outputs the stabilized pitch, roll, and yaw angles along with the angular
rate and acceleration.
The Kalman filter operates to track the rate sensor bias and calculate the
stabilized roll, pitch, and yaw angles.
The AHRS500CA uses the angular rate sensors to integrate over your
rotational motion and find the actual pitch, roll, and yaw angles. The
AHRS500CA uses the accelerometers to correct for rate sensor drift in the
vertical angles (pitch and roll); the AHRS500CA uses the magnetometers to
correct for rate sensor drift in the yaw angle. This is the modern equivalent
of an analog vertical gyro that used a plumb bob in a feedback loop to keep
the gyro axis stabilized to vertical. The AHRS500CA takes advantage of
the rate gyros’ sensitivity to quick motions to maintain an accurate
orientation when accelerations would otherwise throw off the
accelerometers measurement of the AHRS500CA orientation relative to
gravity; the AHRS500CA then uses the accelerometers to provide long term
stability to keep the rate gyro drift in check.
The AHRS500CA uses a sophisticated Kalman filter algorithm to track the
bias in the rate sensors. This allows the AHRS500CA to use a very low
effective weighting on the accelerometers when the AHRS500CA is moved.
This makes the AHRS500CA very accurate in dynamic maneuvers.
The AHRS500CA outputs the stabilized pitch, roll and yaw angles in the
digital data packet. To convert the digital data to angle, use the following
relation:
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