Crossbow Technology AHRS400 Series User manual

AHRS400 Series User’s Manual
Models…
AHRS400CA-
AHRS400CB-
AHRS400CC-
(DMU-HDX-AHRS)
Revision A, March 2002
Document 7430-0004-01
Crossbow Technology, Inc., 41 E. Daggett Dr., San Jose, CA 95134
Tel: [phone], Fax: [phone]
email: [email protected], website: www.xbow.com
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©2001-2002 Crossbow Technology, Inc. All rights reserved. Information
in this document is subject to change without notice.
Crossbow and SoftSensor are registered trademarks and DMU is a
trademark of Crossbow Technology, Inc. Other product and trade names
are trademarks or registered trademarks of their respective holders.
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AHRS400 Series User’s Manual
Doc# 7430-0004-01 Rev. A Page i
Table of Contents
1Introduction......................................................................................................1
1.1 The AHRS Series Motion and Attitude Sensing Units....................1
1.2 Package Contents ...................................................................................2
2Quick Start .......................................................................................................3
2.1 GyroView Software ...............................................................................3
2.1.1 GyroView Computer Requirements...........................................3
2.1.2 Install GyroView...........................................................................3
2.2 Connections.............................................................................................3
2.3 Setup GyroView.....................................................................................4
2.4 Take Measurements...............................................................................4
3AHRS Details ..................................................................................................5
3.1 AHRS Coordinate System....................................................................5
3.2 Connections.............................................................................................5
3.3 Interface...................................................................................................7
3.4 Measurement Modes..............................................................................8
3.4.1 Voltage Mode................................................................................8
3.4.2 Scaled Sensor Mode.....................................................................9
3.4.3 Angle Mode..................................................................................10
3.5 Commands.............................................................................................11
3.5.1 Command List.............................................................................11
3.6 Data Packet Format..............................................................................14
3.7 Timing....................................................................................................16
3.8 Temperature Sensor.............................................................................16
3.9 Analog Output......................................................................................17
3.10 Magnetic Heading................................................................................18
4AHRS Operating Tips..................................................................................19
4.1 Mounting the AHRS............................................................................19
4.2 AHRS Start Up Procedure..................................................................20
5Appendix A. Mechanical Specifications...................................................21
5.1 AHRS400CA Outline Drawing.........................................................21
5.2 AHRS400CB Outline Drawing .........................................................22
5.3 AHRS400CC Outline Drawing .........................................................23
6Appendix B. AHRS Output Quick Reference .........................................24
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AHRS400 Series User’s Manual
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6.1 Analog Output Conversion.................................................................24
6.2 Digital Output Conversion..................................................................24
7Appendix C. Hard and Soft Iron Calibration...........................................25
7.1 Description............................................................................................25
7.2 Command List......................................................................................26
8Appendix D. AHRS Command Quick Reference...................................27
9Appendix E. Warranty and Support Information....................................28
9.1 Customer Service .................................................................................28
9.2 Contact Directory.................................................................................28
9.3 Return Procedure..................................................................................28
9.3.1 Authorization...............................................................................28
9.3.2 Identification and Protection.....................................................29
9.3.3 Sealing the Container.................................................................29
9.3.4 Marking.........................................................................................29
9.3.5 Return Shipping Address...........................................................29
9.4 Warranty................................................................................................29
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AHRS400 Series User’s Manual
Doc# 7430-0004-01 Rev. A Page iii
About this Manual
The following annotations have been used to provide additional
information.
XNOTE
Note provides additional information about the topic.
þEXAMPLE
Examples are given throughout the manual to help the reader understand the
terminology.
PIMPORTANT
This symbol defines items that have significant meaning to the user
MWARNING
The user should pay particular attention to this symbol. It means there is a
chance that physical harm could happen to either the person or the
equipment.
The following paragraph heading formatting is used in this manual:
1 Heading 1
1.1 Heading 2
1.1.1 Heading 3
Normal
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AHRS400 Series User’s Manual
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AHRS400 Series User’s Manual
Doc# 7430-0004-01 Rev. A Page 1
1Introduction
1.1 The AHRS Series Motion and Attitude Sensing Units
This manual explains the use of the AHRS400 Series of products, nine-axis
measurement system designed to measure stabilized pitch, roll and yaw
angles in a dynamic environment.
The AHRS is a nine-axis measurement system that combines linear
accelerometers, rotational rate sensors, and magnetometers. The AHRS
uses the 3-axis accelerometer and 3-axis rate sensor to make a complete
measurement of the dynamics of your system. The addition of a 3-axis
magnetometer also allows the AHRS to make a true measurement of
magnetic heading.
The AHRS is the solid-state equivalent of a vertical gyro/artificial horizon
display combined with a directional gyro.
The AHRS series units are low power, fast turn on, reliable and accurate
solutions for a wide variety of stabilization and measurement applications.
All AHRS products have both an analog output and an RS-232 serial link.
Data may be requested via the serial link as a single polled measurement or
may be streamed continuously. The analog outputs are fully conditioned
and may be connected directly to an analog data acquisition device.
Crossbow Technology DMUs employ onboard digital processing to
compensate for deterministic error sources within the unit and to compute
attitude information. The DMUs accomplish these tasks with an analog to
digital converter and a high performance Digital Signal Processor.
The AHRS uses angular rate sensors and linear acceleration sensors that are
micro-machined devices. The three angular rate sensors consist of vibrating
ceramic plates that utilize the Coriolis force to output angular rate
independently of acceleration. The three MEMS accelerometers are surface
micro-machined silicon devices that use differential capacitance to sense
acceleration. Solid-state MEMS sensors make the AHRS both responsive
and reliable. The magnetic sensors are state-of-the-art miniature fluxgate
sensors. Fluxgate sensors make the AHRS sensitive and responsive, with
better temperature performance than other technologies such as magneto-
resistive sensors.
The AHRS400 Series of products utilize a sophisticated Kalman filter
algorithm to allow the unit to track orientation accurately through dynamic
maneuvers. The Kalman filter will automatically adjust for changing
dynamic conditions without any external user input. No user intervention
or configuration is required at power-up.
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AHRS400 Series User’s Manual
Page 2Doc# 7430-0004-01 Rev. A
The AHRS should not be exposed to large magnetic fields. This could
permanently magnetize internal components of the AHRS and degrade its
magnetic heading accuracy.
1.2 Package Contents
In addition to your DMU sensor product you should have:
•1 CD with GyroView Software
GyroView will allow you to immediately view the outputs of the
AHRS on a PC running Microsoft® Windows™. You can also
download this software from Crossbow’s web site at
http://www.xbow.com.
•1 Digital Signal Cable.
This links the DMU directly to a serial port. Only the transmit,
receive, power, and ground channels are used. The analog outputs
are not connected.
•1 DMU Calibration Sheet
The Digital Calibration Sheets contains the custom offset and
sensitivity information for your AHRS. The calibration sheet is
not needed for normal operation as the AHRS has an internal
EEPROM to store its calibration data. However, this information
is useful when developing your own software to correctly scale the
output data. Save this page!
•1 DMU Data Sheet
This contains valuable digital interface information including data
packet formats and conversion factors.
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AHRS400 Series User’s Manual
Doc# 7430-0004-01 Rev. A Page 3
2Quick Start
2.1 GyroView Software
Crossbow includes GyroView software to allow you to use the DMU right
out of the box and the evaluation is straightforward. Install the GyroView
software, connect the DMU to your serial port, apply power to your unit and
start taking measurements.
2.1.1 GyroView Computer Requirements
The following are minimum capabilities that your computer should have to
run GyroView successfully:
•CPU: Pentium-class
•RAM Memory: 32MB minimum, 64MB recommended
•Hard Drive Free Memory: 15MB
•Operating System: Windows 95, 98, NT4, 2000
2.1.2 Install GyroView
To install GyroView in your computer:
1. Insert the CD “Support Tools” in the CD-ROM drive.
2. Find the GyroView folder. Double click on the setup file.
3. Follow the setup wizard instructions. You will install GyroView
and a LabView 6 Runtime Engine. You will need both these
applications.
If you have any problems or questions, you may contact Crossbow directly.
2.2 Connections
The DMU is shipped with a cable to connect the DMU to a PC
communications port.
1. Connect the 15-pin end of the digital signal cable to the port on the
AHRS.
2. Connect the 9-pin end of the cable to the serial port of your
computer.
3. The additional black and red wires on the cable supply power to
the AHRS. Match red to (+) power and black to (-) ground. The
input voltage can range from 9 -30 VDC at 275 mA for the
AHRS. For further information, see the specifications for your
unit.
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AHRS400 Series User’s Manual
Page 4Doc# 7430-0004-01 Rev. A
MWARNING
Do not reverse the power leads! Applying the wrong power to the AHRS
can damage the unit; Crossbow Technology is not responsible for resulting
damage to the unit.
XNOTE
The analog outputs from the AHRS are unconnected in this cable.
2.3 Setup GyroView
With the AHRS connected to your PC serial port and powered, open the
GyroView software.
1. GyroView should automatically detect the AHRS and display the
serial number and firmware version if it is connected.
2. If GyroView does not connect, check that you have the correct
COM port selected. You find this under the “DMU” menu.
3. Select the type of display you want under the menu item
“Windows”. Graph displays a real time graph of all the AHRS
data; FFT displays a fast-fourier transform of the data; Navigation
shows an artificial horizon display.
4. You can log data to a file by entering a data file name. You can
select the rate at which data is saved to disk.
5. If the status indicator says, “Connected”, you’re ready to go. If
the status indicator doesn’t say connected, check the connections
between the AHRS and the computer; check the power; check the
serial COM port assignment on your computer.
2.4 Take Measurements
Once you have configured GyroView to work with your AHRS, pick what
kind of measurement you wish to see. “Graph” will show you the output
you choose as a strip-chart type graph of value vs. time. “FFT” will show
you a real-time fast Fourier transform of the output you choose.
“Navigation” will show an artificial horizon and the stabilized pitch and roll
output of the AHRS.
Let the AHRS warm up for 30 -60 seconds when first turned on. This
allows the Kalman filter to estimate the rate sensor biases. Now you’re
ready to use the AHRS!
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3AHRS Details
3.1 AHRS Coordinate System
The AHRS will have a label on one face illustrating the DMU coordinate
system. With the connector facing you, and the mounting plate down, the
axes are defined as:
X-axis –from face with connector through the DMU
Y-axis –along the face with connector from left to right
Z-axis –along the face with the connector from top to bottom
The axes form an orthogonal right-handed coordinate system. An
acceleration is positive when it is oriented towards the positive side of the
coordinate axis. For example, with the AHRS sitting on a level table, it will
measure zero g along the x-and y-axes and +1 g along the z-axis.
Gravitational acceleration is directed downward, and this is defined as
positive for the DMU z-axis.
The angular rate sensors are aligned with these same axes. The rate sensors
measure angular rotation rate around a given axis. The rate measurements
are labeled by the appropriate axis. The direction of a positive rotation is
defined by the right-hand rule. With the thumb of your right hand pointing
along the axis in a positive direction, your fingers curl around in the
positive rotation direction. For example, if the AHRS is sitting on a level
surface and you rotate it clockwise on that surface, this will be a positive
rotation around the z-axis. The x-and y-axis rate sensors would measure
zero angular rates, and the z-axis sensor would measure a positive angular
rate.
The magnetic sensors are aligned with the same axes definitions and sign as
the linear accelerometers.
Pitch is defined positive for a positive rotation around the y-axis (pitch up).
Roll is defined as positive for a positive rotation around the x-axis (roll
right). Yaw is defined as positive for a positive rotation around the z-axis
(turn right).
The angles are defined as standard Euler angles using a 3-2-1 system. To
rotate from the body frame to an earth-level frame, roll first, then pitch, and
then yaw.
3.2 Connections
The AHRS400CA has a female DB-15 connector, whereas AHRS400CB
and AHRS400CC have a male DB-15 connector. The signals are as shown
in Table 1.
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AHRS400 Series User’s Manual
Page 6Doc# 7430-0004-01 Rev. A
Table 1. AHRS Connector Pin Out
Pin Signal
1RS-232 Transmit Data
2RS-232 Receive Data
3Positive Power Input (+Vcc)
4Ground
5X-axis accelerometer Analog voltage1
6Y-axis accelerometer Analog voltage1
7Z-axis accelerometer Analog voltage1
8Roll rate analog voltage2
9Pitch rate analog voltage2
10 Yaw rate analog voltage2
11 NC –factory use only
12 Roll angle/X-axis magnetometer scaled analog voltage3
13 Pitch angle/Y-axis magnetometer scaled analog voltage3
14 Yaw angle/Z-axis magnetometer scaled analog voltage3
15 NC –factory use only
Notes:
1. The accelerometer analog voltage outputs are the raw sensor output.
These outputs are taken from the output of the accelerometers.
2. The rate sensor analog voltage outputs are scaled to represent°/s. These
outputs are created by a D/A converter.
3. Actual output depends on DMU measurement mode. These outputs are
created by a D/A converter.
All analog outputs are fully buffered and are designed to interface directly
to data acquisition equipment.
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AHRS400 Series User’s Manual
Doc# 7430-0004-01 Rev. A Page 7
The serial interface connection is standard RS-232. On a standard DB-25
COM port connector, make the connections per Table 2.
Table 2. DB-25 COM Port Connections
COM Port Connector DMU Connector
Pin # Signal Pin # Signal
2TxD 2RxD
3RxD 1TxD
7GND* 4GND*
*Note: Pin 4 on the DMUis data ground as well as power ground.
On a standard DB-9 COM port connector, make the connections per Table
3.
Table 3. DB-9 COM Port Connections
COM Port Connector DMU Connector
Pin # Signal Pin # Signal
2RxD 1TxD
3TxD 2RxD
5GND* 4GND*
*Note: Pin 4 on the DMU is data ground as well as power ground.
Power is applied to the DMU on pins 3 and 4. Pin 4 is ground; Pin 3 should
have 9-30 VDC unregulated at 275 mA. If you are using the cable supplied
with the DMU, the power supply wires are broken out of the cable at the
DB-9 connector. The red wire is connected to VCC; the black wire is
connected to the power supply ground. DO NOT REVERSE THE POWER
LEADS.
The analog outputs are unconnected in the cable Crossbow supplies. The
analog outputs are fully buffered and conditioned and can be connected
directly into an A/D. The analog outputs require a data acquisition device
with an input impedance of 10kΩor greater for DAC outputs and relatively
higher input impedance for raw analog outputs.
3.3 Interface
The serial interface is standard RS-232, 38400 baud, 8 data bits, 1 start bit,
1 stop bit, no parity, and no flow control.
Crossbow will supply DMU communication software examples written in
LabView. Source code for the AHRS serial interface can be obtained via
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AHRS400 Series User’s Manual
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the web at http://www.xbow.com. The source code has a .vi file format and
requires a National Instruments LabView 5.0 or newer license to use.
The DMU baud rate can be changed per the following procedure:
1. Start with the DMU connected to the serial interface, with
your software set to the default baud rate of 38,400.
2. Send the ASCII character “b” (0x62 hex) to the DMU. In a
terminal program like Windows HyperTerminal or ProComm,
this means simply type the letter “b”. The DMU is case
sensitive. The DMU will respond “B” (0x42 hex).
3. Now change the baud rate of your terminal software.
4. Send the ASCII character “a” (61 hex). The DMU will detect
the character and automatically match the baud rate your
software is using. Upon successful operation, the DMU will
return the character “A” (0x41 hex) at the new baud rate.
5. You can now use the DMU at the new baud rate.
The new baud rate setting is not permanent; therefore, this process must be
repeated after any power reset.
3.4 Measurement Modes
The AHRS400 Series is designed to operate as a complete attitude and
heading reference system. You can also use the DMU as a nine-axis sensor
module. The AHRS can be set to operate in one of three modes: voltage
mode, scaled sensor mode, or angle (VG) mode. The measurement mode
selects the information that is sent in the data packet over the RS-232
interface. See the “Data Packet Format” section for the actual structure of
the data packet in each mode.
3.4.1 Voltage Mode
In voltage mode, the analog sensors are sampled and converted to digital
data with 1 mV resolution. The digital data represents the direct voltage
output of the sensors. The data is 12-bit, unsigned. The value for each
sensor is sent as 2 bytes in the data packet over the serial interface. A single
data packet can be requested using a serial poll command or the DMU can
be set to continuously output data packets to the host.
The voltage data is scaled as:
voltage = data*(5 V)/212
where voltage is the voltage measured at the sensor, anddata is the value
of the unsigned 16-bit integer in the data packet. Note that although the
data is sent as 16-bit integers, the data has a resolution of only 12 bits.
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The DMU rate sensor, magnetometer, and angle analog outputs are not
enabled in this mode. Only the linear accelerometer analog outputs on pins
5 -7 are enabled because these signals are taken directly from the
accelerometers. See the “Analog Output” section for a complete description
of the analog outputs.
3.4.2 Scaled Sensor Mode
In scaled sensor mode, the analog sensors are sampled, converted to digital
data, temperature compensated, corrected for misalignment, and scaled to
engineering units. The digital data represents the actual value of the
quantities measured. A calibration table for each sensor is stored in the
DMU non-volatile memory. A single data packet can be requested using a
serial poll command or the DMU can be set to continuously output data
packets to the host. The data is sent as signed 16-bit 2’s complement
integers. In this mode, the DMU operates as a nine-axis measurement
system.
The scaled sensor analog outputs are enabled in this mode. Note that
stabilized pitch, roll, and yaw angles are not available in scaled sensor
mode. See the “Analog Output” section for a complete description of the
analog outputs.
To convert the acceleration data into G’s, use the following conversion:
accel = data*(GR * 1.5)/215
where accel is the actual measured acceleration in G’s, data is the digital
data sent by the DMU, andGR is the G Range for your DMU. (The data is
scaled so that 1 G = 9.80 m s-2.) The G range of your DMU is the range of
accelerations your DMU will measure. For example, if your DMU uses a ±
2 G accelerometer, then the G range is 2.
To convert the angular rate data into degrees per second, use the following
conversion:
rate = data*(AR*1.5)/215
where rate is the actual measured angular rate in°/sec, data is the digital
data sent by the DMU, andAR is the Angular rate Range of the DMU. The
angular rate range of your DMU is the range of angular rates your DMU
will measure. For example, if your DMU uses ± 150 °/s rate sensors, then
the AR range is 150.
To convert the acceleration data into Gauss,use the following conversion:
mag = data*(MR*1.5)/215
where mag is the actual measured magnetic field in Gauss, data is the
digital data sent by the DMU, andMR is the Magnetic field Range of the
DMU. MR is 1.25 for the AHRS.
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The AHRS Kalman filter is not enabled in scaled sensor mode. Therefore,
the rate sensor bias will change slightly due to large changes in temperature
and time. If the unit is changed from angle to scaled mode, the last
estimated rate sensor bias values are used upon entering scaled mode.
3.4.3 Angle Mode
In angle mode, the DMU acts as a complete attitude and heading reference
system and outputs the stabilized pitch, roll, and yaw angles along with the
angular rate, acceleration, and magnetic field information. The angular rate,
acceleration, and magnetic field values are calculated as described in the
scaled sensor mode.
The DMU analog outputs are enabled in this mode, including stabilized
pitch, roll, and yaw angles.
The Kalman filter operates in angle mode to track the rate sensor biasand
calculate the stabilized roll, pitch, and yaw angles.
In angle mode, the DMU uses the angular rate sensors to integrate over your
rotational motion and find the actual pitch, roll, and yaw angles. The DMU
uses the accelerometers to correct for rate sensor drift in the vertical angles
(pitch and roll); the DMU 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 DMU 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 DMU orientation relative to gravity; the DMU then uses the
accelerometers to provide long term stability to keep the rate gyro drift in
check.
The AHRS400CA and AHRS400CB use a sophisticated Kalman filter
algorithm to track the bias in the rate sensors. This allows the DMU to use
a very low effective weighting on the accelerometers when the DMU is
moved. This makes the DMU very accurate in dynamic maneuvers. Unlike
other Crossbow DMU systems, the user does not need to set an erection
rate.
The AHRS outputs the stabilized pitch, roll and yaw angles in the digital
data packet in angle mode. To convert the digital data to angle, use the
following relation:
angle = data*(SCALE)/215
where angle is the actual angle in degrees (pitch, roll or yaw), data is the
signed integer data output in the data packet, and SCALEis a constant.
SCALE= 180°for roll, pitch and yaw.
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AHRS400 Series User’s Manual
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3.5 Commands
The AHRS has a simple command structure. You send a command
consisting of one byte to the DMU over the RS-232 interface and the DMU
will execute the command.
XNOTE
The DMU commands are case sensitive!
GyroView is a very good tool to use when debugging your own software.
GyroView formulates the proper command structures and sends them over
the RS-232 interface. You can use GyroView to verify that the DMU is
functioning correctly. GyroView does not use any commands that are not
listed here.
XNOTE
Certain combinations of characters not listed here can cause the unit to enter
a factory diagnostic mode. While this mode is designed to be very difficult
to enter accidentally, itis recommended that the following command set be
adhered to for proper operation.
3.5.1 Command List
Command Reset
Character(s) Sent R
Response H
Description Resets DMU to default state
Command Voltage Mode
Character(s) Sent r
Response R
Description Changes measurement type to Voltage Mode.
DMU outputs raw sensor voltage in the data
packet.
Command Scaled Mode
Character(s) Sent c
Response C
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Description Changes measurement type to Scaled Mode.
DMU outputs measurements in scaled
engineering units.
Command Angle Mode
Character(s) Sent a
Response A
Description Changes measurement type to Angle (VG) Mode.
DMU calculates stabilized pitch and roll. Also
outputs sensor measurements in scaled
engineering units.
Command Polled Mode
Character(s) Sent P
Response none
Description Changes data output mode to Polled Mode.
DMU will output a single data packet when it
receives a "G" command.
Command Continuous Mode
Character(s) Sent C
Response Data Packets
Description Changes data output mode to Continuous Mode.
DMU will immediately start to output data
packets in continuous mode. Data rate will
depend on the measurement type the DMU is
implementing (Raw, Scaled or Angle). Sending
a "G" will return DMU to Polled Mode.
Command Request Data
Character(s) Sent G
Response Data Packet
Description "G" requests a single data packet. DMU will
respond with a data packet. The format of the
data packet will change with the measurement
mode (Raw, Scaled or Angle). Sending the
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DMU a "G" while it is in Continuous Mode will
place the DMU in Polled Mode.
Command Query DMU Version
Character(s) Sent v
Response ASCII string
Description This queries the DMU firmware and will tell you
the DMU type and firmware version. The
response is an ASCII string that describes the
DMU type and firmware version.
Command Query Serial Number
Character(s) Sent S
Response Serial Number Packet
Description This queries the DMU for its serial number. The
DMU will respond with a serial number data
packet that consists of a header byte (FF), the
serial number in 4 bytes, and a checksum byte.
The serial number bytes should be interpreted as
a 32-bit unsigned integer. For example, the serial
number 9911750 would be sent as the four bytes
00 97 3D C6.
Command Request Auto Baud Rate
Character(s) Sent b
Response -
Description This starts the auto baud rate detection process.
This will allow you to change the DMU baud rate
from its default. This change will not affect the
default settings.
1. Start with communications program and
DMU at same baud rate.
2. Send "b" to the DMU. The DMU will
respond with “B”.
3. Change the baud rate of your
communications program.
4. Send "a" to the DMU. The DMU will
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AHRS400 Series User’s Manual
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respond with "A" at the new baud rate
when a successful detection of the new
baud rate is completed.
3.6 Data Packet Format
In general, the digital data representing each measurement is sent as a 16-bit
number (two bytes). The data is sent MSB first then LSB.
In voltage mode, the data is sent as unsigned integers to represent the range
0 –5 V.
In scaled and angle mode, the data generally represents a quantity that can
be positive or negative. These numbers are sent as a 16-bit signed integer in
2's complement format. The data is sent as two bytes, MSB first then LSB.
In scaled and angle mode, the timer information and temperature sensor
voltage are sent as unsigned integers.
The order of data sent will depend on the selected operating mode of the
AHRS.
Each data packet will begin with a header byte (255) and end with a
checksum. The checksum is calculated in the following manner:
1. Sum all packet contentsexcept header and checksum.
2. Divide the sum by 256.
3. The remainder should equal the checksum.
XNOTE
The header byte FF will likely not be the only FF byte in the data packet.
You must count the bytes received at your serial port and use the checksum
to ensure you are in sync with the data sent by the DMU. This is especially
critical when using the continuous data packet output mode.
Table 4 shows the data packet format for each mode.
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