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AHRS-E304  Watson Industries, Inc 

 

09/06/05 

Symmetry is very important in such mount designs (consult Watson Industries for application 
notes on this if needed). 

Environment:

   

High level AC magnetic fields, such as from large transformers, motors, or soldering guns, are to 
be avoided as being potentially damaging to the circuitry, even if the system is not powered.  
Exposure to high DC magnetic fields are to be avoided since this can produce a lingering self-
magnetization of the sensor, which can cause distortion of the heading reference. 

Power:

   

This unit has an internal regulator to allow operation over a wide voltage input range.  Best 
operation is obtained at either 12 or 24 VDC level, although operation is fully satisfactory down 
to 10 VDC and up to 30 VDC.  Power draw of the unit is about 4 Watts.  Internal capacitors are 
provided to remove a reasonable level of power line noise, however, capacitors should be added 
for long power line wiring or if noise is induced from other loads on the circuit.

 

ERROR CORRECTION 

 
The correction systems, which all aircraft attitude systems use, unfortunately also allow errors 
from the forces on a maneuvering aircraft to enter the system.  To control these effects, a balance 
of time constant and error limits are used: 
 
 

 

Limiting Factor Causing Error Reduction: 

 
Axis of  

Bank   

Elevation 

Heading 

Centrifugal 

Acceleration 

Error Limit 

Angle Error 

Angle Error 

Angle Error   Force Offset  Force Offset 

 

 

Bank   

     ±10º 

       None 

     None 

     ±5 g 

     None 

Elevation 

    None 

       ±10º 

     None  

     None 

     ±5 g 

Heading 

    None 

       None 

      ±20º  

     None     

     None 

 

It would not be a problem to cross over into these limits since the rate of deterioration from the 
original reference should be about 0.03 degrees per second.  However, prolonged strong 
maneuvers should be avoided if accuracy is to be minimized.  In normal attitudes, error is 
corrected with a 30-second time constant. 

 

While this AHRS is "all attitude", the accuracy deteriorates rapidly within about 5 degrees of 
straight up or straight down.

 

Centrifugal Force Compensation:

   

The compensation for centrifugal force is based on calculating the horizontal turn rate and 
multiplying it by the forward velocity.  The result is subtracted from the vertical reference 
accelerometers for the roll axis.  This system directly depends on the quality of the velocity 
signal.  

Delta Velocity Compensation:

   

The compensation for forward acceleration is based on calculating the changes in average 
forward velocity.  The result is subtracted from the vertical reference accelerometers for the pitch 
axis.  This is limited in unusual attitudes and the error correction system is locked out when the 

Содержание AHRS-E304

Страница 1: ...ustries Inc 09 06 05 1 ATTITUDE AND HEADING REFERENCE SYSTEM OWNER S MANUAL PART NUMBER AHRS E304 WATSON INDUSTRIES INC 3041 MELBY ROAD EAU CLAIRE WI 54703 Phone 715 839 0628 FAX 715 839 8248 email support watson gyro com ...

Страница 2: ...ERROR CORRECTION 4 Centrifugal Force Compensation 4 Delta Velocity Compensation 4 SPECIFICATIONS 5 RS 232 OUTPUT FORMAT 6 ANALOG OUTPUTS 8 OUTPUT FLAGS 8 RS 232 INPUT COMMANDS 8 ANALOG INPUTS 9 INPUT LOGIC COMMANDS 10 CONNECTIONS 11 WARNING 12 Appendix A 15 Appendix B 16 DETERMINING SETTING OUTPUT CHANNELS 16 ADJUST TIME CONSTANTS 17 SETTING OUTPUT FORMAT 17 Appendix C 17 ...

Страница 3: ...titude and heading signals are compared against three accelerometers and a triaxial fluxgate magnetometer to derive short term absolute errors These errors are filtered over a long time constant and are used to adjust biases in the system so that the long term convergence of the system is to the vertical references and the magnetic heading Compensations for centrifugal forces and velocity changes ...

Страница 4: ...effects a balance of time constant and error limits are used Limiting Factor Causing Error Reduction Axis of Bank Elevation Heading Centrifugal Acceleration Error Limit Angle Error Angle Error Angle Error Force Offset Force Offset Bank 10º None None 5 g None Elevation None 10º None None 5 g Heading None None 20º None None It would not be a problem to cross over into these limits since the rate of ...

Страница 5: ...5V South 0V West 5V North Heading 0 360º 18º V South 10V West 5V North 0V East 5V 2 Rate Accuracy Static 0 2º sec Dynamic 2 3 Attitude Accuracy Static 0 5º Dynamic 2 4 Heading Accuracy Static 1º Dynamic 2 5 Velocity Input 800 to 800 Km hr 10 to 10 Volts Forward Velocity 6 Temperature Operating 30º to 60º C Storage 40º to 85º C 7 Weight 32 Ounces 8 Power about 350 milliamps at 12 Volts DC 200 milli...

Страница 6: ...racter string representing the X axis accelerometer starting with a space then a or a followed by one digit a decimal point and two digits for up to 9 99 g 6 A six character string representing the Y axis accelerometer starting with a space then a or a followed by one digit a decimal point and two digits for up to 9 99 g 7 A six character string representing the Z axis accelerometer starting with ...

Страница 7: ...II decimal This whole message can be temporarily or permanently suppressed or restored by a command from the interfacing computer Data transmission sent by the AHRS can also be suppressed or restored by a command from the interfacing computer The error overrange condition is indicated by the use of a lower case i or r when the calculated attitude or heading error exceeds the ranges listed above In...

Страница 8: ...quired for access to this command 2 An I or i will clear the Reference Command mode if it had been set by the serial input This is the default mode at power up and is the normal operating mode This will also disable the logic input Reference Command Coast Mode Command and Invalid Velocity Command until the next time the unit is powered up Double spacebar at initialization is required for access to...

Страница 9: ...for access to this command The command calls a menu which allows any of several parameters to be set These are system time constants selection of data channels for serial output and baud rate Double spacebar at initialization is required for access to this command The commands S M X T D and are used by the Watson factory to calibrate the unit and should be used only with the assistance of the fact...

Страница 10: ... of the unit is changed so that the velocity input has no influence The same effect can be obtained by holding the velocity input to zero When not in use the pin is to be left unconnected This input is disconnected until the next power up by activating some of the RS 232 command set The Coast Mode Command input when grounded pin 25 will disconnect the references from the attitude system The main u...

Страница 11: ... Channel 1 Input 9 User Channel 2 Input 10 Velocity Error Flag 11 South Heading Flag 12 Velocity Input Command 13 Reference Output Command 14 Heading North 15 Heading South 16 Bank 17 Elevation 18 Forward Velocity Analog Input 19 User Channel 3 Input 20 Heading Rate 21 Roll Rate 22 User Channel 4 Input 23 Pitch Rate 24 Yaw Rate 25 Coast Mode Command FUNCTION SIGNAL PINOUT PIN 12 24 VDC Z X Y ...

Страница 12: ...2 Over voltage and or miswiring of this unit will cause damage 3 The non magnetic connectors supplied with the unit must be used to preserve heading accuracy The user must use non magnetic hardware to install the unit 4 This unit should be protected against prolonged exposure to high humidity and or salt air environments ...

Страница 13: ...ted to any implied warranty of merchantability or fitness for a particular purpose Excluded from any warranty given by Watson Industries are products that have been subject to abuse misuse damage or accident that have been connected installed or adjusted contrary to the instructions furnished by seller or that have been repaired by persons not authorized by Watson Industries Watson Industries rese...

Страница 14: ...ABC GYRO or 715 839 0628 Fax 715 839 8248 All sensors returned under warranty will be repaired or replaced at the sole option of Watson Industries at no cost to the customer other than shipping charge from customer to Watson Industries plus any export and transportation charges outside the United States In the case of units not under warranty a flat repair fee will be charged This fee can be deter...

Страница 15: ...er ZA 9 99 g 10 g X Angular Rate XR 99 9 º s 200 º s Y Angular Rate YR 99 9 º s 200 º s Z Angular Rate ZR 99 9 º s 200 º s Heading Rate HR 99 9 º s 200 º s X Magnetometer XM 999 mGauss 1000 mGauss Y Magnetometer YM 999 mGauss 1000 mGauss Z Magnetometer ZM 999 mGauss 1000 mGauss X inclinometer simulated XI 179 9º 180º Y Inclinometer simulated YI 89 9º 180º User Channel 1 U1 9 99 VDC 10 VDC User Cha...

Страница 16: ... again Now type 2 to set up channels The following message will appear To proceed type Y Now each channel will come up one at a time For example Type Y to output channel type N to remove channel When you get to bottom of list this message will appear To accept channels type N then hit space bar output data to resume To make this channel selection the default the next time you power the unit on typ...

Страница 17: ... to the format you want to switch into for example type _ to change into Decimal Format To make this format selection the default the next time you power the unit on type in double quote Appendix C 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 Data Word MSB LSB As the data words are received the LSB is shifted left to shift out the sign bit The MSB is then connected to the LSB as a 16 bit word This word is then...

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