AHRS Interface Control Document
Contents
1. 4 7 Set point azimuth deg float 4 Not realized yet 8 11 Average pitch deg float 4 12 15 Average roll deg float 4 16 27 Reserved byte 12 28 29 USW word 2 See section 6 5 If the Success of the current calibration run byte is zero calibration run is not successful in the AHRS answer Table 6 15 then this run will be excluded from calculations in the 2D 2T calibration procedure To complete this procedure it is necessary to perform at least two successful runs with essentially different pitch angles Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 39 inertial Labs AHRS Interface Control Document After each calibration run the AHRS sends message with payload shown in the Table 6 15 and it waits one of the next three commands from the host computer 1 StartCloRun command followed by its message see section 6 4 6 to start new calibration run Before send this command the object should be turned to the next pitch angle After sending this command the above described procedure of the calibration run with object rotation in heading should be performed 2 StopClb command see section 6 4 2 for details to finish the calibration procedure and to calculate calibration parameters After that the AHRS gives out message with the calibration results see the Table 6 14 and waits one of t2. Magnetometers are used to determine initial heading of the AHRS and to correct gyros drift in the heading angle determination Initial alignment algorithm Initial conditions Heading H Numeric integrating of the orientation equations Orientation angles estimation Pitch P Computation of correction signals Kalman filter based algorithm Magnetometers Accelerometers Gyros Fig 2 1 Operational Diagram of the Inertial Labs AHRS Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com inertial Labs AHRS Interface Control Document The base of the AHRS algorithm is robust Kalman filter which is used for estimation of the gyros bias drift and for calculation of stabilized heading pitch and roll angles The Kalman filter automatically adjusts for changing dynamic conditions without any external user input After start the Inertial Labs AHRS it requires about 60 seconds for initial alignment process At this initial orientation angles are determined as initial conditions for integration of gyros outputs Also gyros drift is estimated using Kalman filter for next compensation Therefore don t move the AHRS during initial alignment process If this requirement is not met then large errors may be occurred in orientation angles determination As the Inertial Labs AHRS uses magnetic sensors
3. 28 31 Alignment angle A2 float on the carrier object 32 35 Alignment angle A3 float degrees see Appendix B 36 43 Device ID char only read DOS 44 49 Reserved 6 3 8 LowPowerOn command The LowPowerOn command code 0xBO0 in the Payload field see the Table 6 2 switches the AHRS to low power Sleep mode At this command all AHRS sensors are switched off processor core and part of periphery are switched off No outputs are from the AHRS Its microprocessor only waits command from the host computer to exit from the Sleep mode In the Sleep mode the AHRS s indicator lamp is off 6 3 9 LowPowerOff command The LowPowerOff command code OxBA in the Payload field see the Table 6 2 awakes the AHRS from the Sleep mode and switches it to the idle mode with normal power consumption Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 32 inertial Labs AHRS Interface Control Document 6 3 10 GetVerFirmware command The GetVerFirmware command code 0x1F in the Payload field is used to read firmware version of the AHRS 50 bytes from the AHRS nonvolatile memory As answer the AHRS sends out the message with structure according to the Table 6 2 and payload shown in the Table 6 11 Table 6 11 Payload of the AHRS answer on the GetVerFirmware command B
4. Byte structure of this message is shown in the Table 6 2 where payload is the calculated check sum 1 word This check sum should be equal to the check sum in the message that was sent to the AHRS After receiving of any from these commands the AHRS starts process of initial alignment that takes usually 30 seconds This process includes the AHRS gyros drift estimation therefore don t move the AHRS during its ini tial alignment If this requirement is not met then large errors may be oc curred in orientation angles calculation Note Default time 30 seconds of the initial alignment can be changed see section 6 3 6 LoadAHRSPar command but only in agreement with developers of the Inertial Labs AHRS After completing of the initial alignment the AHRS gives out message with block of the initial data payload is 50 bytes of the data see the Table 6 8 and goes to the On Request operating mode In the On Request operating mode the AHRS sends only one data block after each request command GetDataReq see section 6 3 4 issued from host computer Data blocks have structure described in the Table 6 2 with payload depending on chosen variant of output data format see section 6 2 for details 6 3 3 NMEAcont NMEAreq commands The NMEAcont command is used to start the Inertial Labs AHRS in the Continuous operating mode with NMEA format of output data see Table 6 7 The NMEAcont command has the byte structure shown
5. ICD provides details on mechanically mounting the electrical connections powering and software interface between the Inertial Labs AHRS and host computer This document is intended for all parties requiring such information including engineers and researchers responsible for implementing the interface 3 SPECIFICATIONS Table 3 1 Inertial Labs AHRS specifications Update Rate 1 100 user settable Start up Time lt 1 Full Accuracy Data Warm up Time Range deg 0 to 360 Angular Resolution deg 0 01 Static Accuracy in Whole Temperature Range deg lt 0 4 lt 0 7 lt 1 2 Dynamic Accuracy 9 deg RMS 0 7 1 0 2 0 Noise at 100 Hz output deg RMS 0 03 Range Pitch Roll deg 90 180 Angular Resolution deg 0 01 Static Accuracy in Whole Temperature Range deg lt 0 1 lt 0 1 lt 0 4 Dynamic Accuracy deg RMS 0 3 0 3 0 8 Noise at 100 Hz output deg RMS 0 02 In run Bias Stability at Constant Temperature deg s RMS 0 02 0 02 0 02 Bias stability in whole Temperature Range deg s RMS 0 2 0 2 0 2 Scale Factor Accuracy 0 1 0 1 0 1 Random Walk deg sart hr 1 1 1 Resolution deg sec 0 02 0 02 0 01 Bandwidth Hz 50 50 50 Linear Acceleration Accelerometer range g 1 7 1 7 6 Bias stability in Whole Temperature Range mg RMS 1 1 5 Scale Factor Accuracy lt 0 1 lt 0 1 lt 0 5 Inertial Labs I
6. INTERFACE The Inertial Labs AHRS has the Binder Series 718 female 6 pin connector cordset part 79 3464 52 06 see http www binder usa com psearch_ detail php pid 28852 For electrical connection of the Inertial Labs AHRS to the host system the Binder Series 718 male 6 pin connector cordset part 79 3465 52 06 or part 79 3465 55 06 should be used see http Awww binder usa com psearch_detail php pid 28850 or Binder Series 768 male 6 pin connectors part 09 3463 00 06 09 3423 00 06 09 3423 81 06 09 3423 86 06 09 3463 81 06 09 3463 86 06 Fig 5 1 shows the Inertial Labs AHRS connector pinout Pin color fits to wire color in mating cordset Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 16 inertial Labs AHRS Interface Control Document Fig 5 1 The Inertial Labs AHRS connector pinout mating side of the connector Table 5 1 Pin diagram of the Inertial Labs AHRS connector Pi n Signal Do not connect Tx RS232 Rx RS232 GND Von Do not connect Note Do not connect anything to pins 1 and 6 that are connected to AHRS PCB for firmware updates OO O1 OO PO Table 5 2 Electrical specifications Parameter Conditions Min Typical Max Units Input Supply 5 5V 6V 6 5V Volts DC Current Vbp 6V 15 85 90 mA Power
7. Labs AHRS Interface Control Document 4 3 Mechanically mounting the Inertial Labs AHRS The Inertial Labs AHRS housing has two base surfaces A and B see Fig 4 1 that are designed for the AHRS mounting during its run and testing B A Fig 4 1 AHRS mounting surfaces A B and mounting holes 1 2 Salient bottom base surface A has 4 holes 2 6 mm on 4 lugs see Fig 4 1 positions 1 and 4 threaded holes M3x6 mm see Fig 4 1 positions 2 which are designed for the AHRS mounting Lateral base surface B is designed for the AHRS alignment during mounting The Inertial Labs AHRS is factory calibrated with respect to the base surfaces A and B thus it must be aligned within the host system carrier object with respect to these mounting surface not the device edges Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 14 inertial Labs AHRS Interface Control Document _ 65 sE 78 cad A A Cable with connector 4 holes M3x6 GI 4 holes 926 e Fig 4 2 The Inertial Labs AHRS outline drawing all dimensions are in millimeters When mounting Inertial Labs AHRS on your system please pay attention to orientation of input axes X Y Z marked on the cover of the AHRS see Fig 1 2 During the ordinary operation on the carrier object the AHRS is set on the surface A wit
8. Vpp 6V 90 510 540 mW At the Inertial Labs AHRS operations it is connected to the host system that provides command interface described in the section 6 and the AHRS powering For tests the Inertial Labs AHRS can be connected to PC by wire as Fig 5 2 shows At this for the Inertial Labs AHRS powering the AC DC adapter can be used which receives the power from the 100 240V 50 60Hz AC power source This AC DC adapter is provided by the Inertial Labs and is included in the delivery set Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 17 inertial Labs AHRS Interface Control Document Cable 1 Inertial Labs AHRS Host Computer PowerBlock 100 240V AC DC Adapter Fig 5 2 The diagram of electric connection of the Inertial Labs AHRS to host computer The delivery set for the AHRS electrical connection to PC is provided by the Inertial Labs and includes interface cable 1 for the Inertial Labs AHRS connection to the COM port of PC or another device with branch wires for the Inertial Labs AHRS DC powering COM to USB converter for connection of the AHRS to PC through the USB port ACIDC adapter Also Inertial Labs AHRS Demo software is included in the delivery set for quick evaluation of the Inertial Labs AHRS Fig 5 3 shows the diagra
9. of the Inertial Labs AHRS 4 It is necessary to set current latitude longitude altitude year month day only in two cases a if the magnetic declination is unknown so its calculation inside the AHRS is required for current place and date b before hard soft iron calibration of the AHRS magnetometers see section 6 4 6 3 7 ReadAHRSPar command The ReadAHRSPar command code 0x41 in the Payload field see the Table 6 2 is used to read block of the Inertial Labs AHRS parameters 50 bytes from the AHRS nonvolatile memory Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 31 inertial Labs AHRS Interface Control Document After receiving ReadAHRSPar command the AHRS sends out the message with structure according to Table 6 2 and payload shown in the Table 6 10 Table 6 10 Payload of the AHRS answer on the ReadAHRSPar command block of parameters read from the AHRS Byte Parameter Format Length Note 0 1 Measurement rate word 2 Hz 2 3 Initial alignment time word 2 seconds 4 7 Magnetic declination float 4 degrees 8 11 Latitude float 4 degrees 12 15 Longitude float 4 degrees 16 19 Altitude float 4 meters 20 23 Date Year Month float 4 Year Month 1 12 Day Day 365 24 27 Alignment angle A1 float Angles of AHRS mounting
10. 0 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 38 inertial Labs AHRS Interface Control Document initial alignment Default time of the initial alignment is 30 seconds and can be changed see section 6 3 6 LoadAHRSPar command but only in agreement with developers of the Inertial Labs AHRS After completing of the initial alignment the AHRS gives out the block of the initial data payload is 50 bytes of the data see the Table 6 8 and starts data accumulation during time specified in message sent after the Start2D2TClb command see the Table 6 13 Rotate object in azimuth with approximately constant pitch and roll This rotation must include one or more full 360 deg turns Please correct the time required for such rotation in the Time of data accumulation field of the message Table 6 13 to provide necessary rotation After set accumulation time is reached or Stop command is sent to the AHRS see section 6 3 5 for details the AHRS gives out message with result of the calibration run see the Table 6 15 Table 6 15 Payload of the AHRS message after each calibration run of the 2D 2T calibration Byte Parameter Format Length Note 0 Type of calibration byte 1 2 for 2D 2T calibration 1 Calibration run byte 1 Pe ere 2 Reserved byte 1 3 Calibration success byte 1 0 unsuccessful 1 successful
11. 3 are used to start the Inertial Labs AHRS in the Continuous operating mode with one of three variants of output data AHRScont1 command code 0x80 Full Output Data format Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 25 inertial Labs AHRS Interface Control Document AHRScont2 command code 0x82 Quaternion Of Orientation format AHRScont3 command code 0x83 Orientation Sensor Outputs format All these commands have the byte structure shown in the Table 6 2 Payload for all commands has length 1 byte and contains code of the command In order to identify to the host system that AHRS received one of these commands the AHRS answers back immediately on this command prior to completion of the initial alignment process The AHRS calculates the check sum of the message without its header and check sum and returns it for a checking Byte structure of this message is shown in the Table 6 2 where payload is the calculated check sum 1 word This check sum should be equal to the check sum in the message that was sent to the AHRS After receiving of any from these commands the AHRS starts process of initial alignment that takes usually 30 seconds This process includes the AHRS gyros drift estimation therefore don t move the AHRS during its ini tial alignment If this requirement is not met then l
12. Calibration of the Inertial Laobs AHRS on hard and soft iron 33 6 4 1 Start3DClb command for AHRS 3D calibration n 34 6 4 2 StopClb COMMINATA 37 6 4 3 AcceptClb command MARE RR RR AR A 37 6 4 4 ExitClb command widaaicnsiduecasdrdacaaudsdusnicadanadaciaagadueadaasdadaeaentadaanbainvatainindeaateceas 37 6 4 5 Start2D2TClb command for AHRS 2D 2T calibration n 38 6 4 6 StartClboRuNn commanb iciiri rei 41 6 4 7 Start2DClb command for AHRS 2D calibration n 41 6 4 8 ClearClb command ssi 43 6 4 9 GetClbRes COommand i i uiiiri cirie ia 43 6 5 The Unit Status Word GefiNitioN ciririi iii 44 APPENA Aerei 46 A The Inertial Labs AHRS calibration iii 46 B Variants of the Inertial Labs AHRS mounting relative to the object axes 47 C Full list of the Inertial Labs AHRS commands 49 Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com inertial Labs AHRS Interface Control Document LIST OF FIGURES Figure 1 1 The Inertial Labs AHRS 6 Figure 1 2 Coordinate system of the Inertial Labs AHRS n 7 Figure 2 1 Operational Diagram of the Inertial Labs AHRS n 8 Figure 4 1 The Inertial Labs AHRS mounting surfaces A B and mounting holes 1 2 CEE ERRE eee ener erat
13. Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 24 inertial Labs AHRS Interface Control Document with ASCII Notes USW is unit status word see section 6 5 for details Temperature is averaged value for 3 accelerometers Vdd is input voltage of the AHRS Check sum consists of a and two hex digits representing XOR of all characters between but not including and Important note The AHRS maximum data rate is limited to 50 Hz in the NMEA output format 6 3 Control of the Inertial Labs AHRS After power connection the AHRS is in the idle mode Red light of the indicator lamp near the connector signifies readiness of the Inertial Labs AHRS to receive commands from the host computer When the AHRS switches from idle to any operation mode the light indicator changes its color from red to green The next commands are used to control the AHRS e AHRSconti AHRScont2 AHRScont3 e ReadAHRSPar e AHRSreqi AHRSreq2 AHRSreg3 e LoadAHRSPar e NMEAcont NMEAreq e LowPowerOn e GetDataReg e LowPowerOff e Stop e GetVerFirmware e GetBIT All these commands have the byte structure shown in the Table 6 2 Payload for all commands has length 1 byte and contains code of the command See Appendix C for exact structure of these commands 6 3 1 AHRScont1 AHRScont2 AHRScont3 commands The commands AHRScont1 AHRScont2 AHRScont
14. RS nonvolatile memory This command can be used in the end of the 3D and 2D 2T calibration The AHRS answers on this command The AHRS calculates the check sum of the message without its header and check sum and returns it for a checking Byte structure of this message is shown in the Table 6 2 where payload is the calculated check sum 1 word 6 4 4 ExitClb command The ExitClb command code OxFE in the Payload field is used to exit from the calibration without any calculations in the AHRS and without saving any calibration parameters The AHRS stops work in operating mode and goes into the idle mode The AHRS answers on this command The AHRS calculates the check sum of the message without its header and check sum and returns it for a Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 37 inertial Labs AHRS Interface Control Document checking Byte structure of this message is shown in the Table 6 2 where payload is the calculated check sum 1 word 6 4 5 Start2D2TCIb command for AHRS 2D 2T calibration Since AHRS firmware version 4 9 1 the 2D 2T calibration is realized in the AHRS This calibration is designed for objects that operate in full azimuth range but with limited range of pitch and roll angles This calibration procedure involves a few full 360 rotations of the object in azimuth with differe
15. T OGG MONT animi 6 1 1 Description OF the System 4 ccccsecccnesesseecnsoneeneesteesencctonnneeteentenssecdnnsetnentemeniene 6 1 2 Principles of the Inertial Labs AHRS Operation 8 2 Scope and applltabilVic lot 9 Os SPEC CANOSA 10 A Mechanical MEM ACS ara 11 4 1 Where to install the Inertial Labs AHRS for tests ii 11 4 2 Where to install the Inertial Labs AHRS on the object 12 4 3 Mechanically mounting the Inertial Labs AHRS c cccccccceeseeseeseeeeseeeeeeees 14 5 Eischical INerate criari iii iaia ia 16 6 Software interface lean 19 6 1 Operational modes of the Inertial Labs AHRS ii 21 6 2 Output Data Formats of the Inertial Labs AHRS in the Operating Modes 22 6 3 Control of the Inertial Labs AHRS ii e 25 6 3 1 AHRScont1 AHRScont2 AHRScont3 commands n a 25 6 3 2 AHRSreqi AHRSreq2 AHRSreg3 commands 27 6 3 3 NMEAcont NMEAreg commandsS eeen eee nn nnnnnnnnennnen en 28 6 3 4 GetDataReq command titoli dee lenire 29 6 3 5 St0p COMMIMANING FREE I 30 6 3 6 LoadAHRSPar command 30 6 3 7 ReadAHRSPar command wciiinscisitevainscdtencasadisandasiddeadsec tendeixdtendcenblenitecddeadtes 31 6 3 8 LowPowerOn command soia iaia 32 6 3 9 LowPowerOff COMMA rici 32 6 3 10 GetVerFirmware command 33 6 3 11 GetBIT command scellerata 33 6 4
16. after the Start3DClb Start2D2TClb and Start2DClb commands the block of parameters loaded to the AHRS Byte Parameter Format Length Note 0 3 Reserved byte 4 4 5 Time of data accu word 2 Seconds mulation in one run 6 9 Latitude float 4 Degrees 10 13 Longitude float 4 Degrees 14 17 Altitude float 4 Meters 18 21 Date Year Month float 4 Year Month 1 12 Day Day 365 The AHRS calculates the check sum of received parameters and returns it for a checking Byte structure of this message is shown in the Table 6 2 where payload is the calculated check sum 1 word Then the AHRS starts process of initial alignment This process includes the AHRS gyros drift estimation therefore don t move the AHRS during its initial alignment Default time of the initial alignment is 30 seconds and can be changed see section 6 3 6 LoadAHRSPar command but only in agreement with developers of the Inertial Labs AHRS After completing of the initial alignment the AHRS gives out the block of the initial data payload is 50 bytes of the data see the Table 6 8 and starts data accumulation during time specified in message sent after the Start3DClb command see the Table 6 13 During the AHRS data accumulation the object should be rotated in full azimuth pitch and roll ranges For example the object is rotated in the horizon plane the Z axis is up with periodical stops about each 90 degr
17. arge errors may be oc curred in orientation angles calculation Note Default time 30 seconds of the initial alignment can be changed see section 6 3 6 LoadAHRSPar command but only in agreement with developers of the Inertial Labs AHRS After completing of the initial alignment the AHRS gives out message with block of the initial data payload is 50 bytes of the data see the Table 6 8 and goes to the Continuous operating mode Table 6 8 Structure of the payload of block of initial alignment data Byte Parameter Format Length Note 0 11 Gyros bias float 3 4 3 numbers in ADC codes 12 23 Average acceleration float 3 4 3 numbers in ADC codes 24 35 Average magn field float 3 4 3 numbers in ADC codes Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 26 inertial Labs AHRS Interface Control Document 36 39 Initial Heading float 4 degrees 40 43 Initial Roll float 4 degrees 44 47 Initial Pitch float 4 degrees 48 49 USW word 2 0 successful initial see section 6 5 alignment 0 unsuccessful In the Continuous operating mode set by any of above commands AHRScont1 AHRScont2 AHRScont3 the program in the AHRS microprocessor operates in the endless loop providing the process of data reading from ADC and
18. ception is done for the AHRS output in the NMEA text format see section 6 2 Table 6 2 Byte structure for all commands and messages to from the AHRS Byte n 1 0 1 2 3 4 5 6 n number n 2 Header Header Message Reser Message Check Parameter 0 1 type ved length Payload sum Length 1 byte 1 byte 1 byte 1 byte 1 word Variable 1 word Note OxAA 0x55 Equal to n Message type is equal to 0 for commands 1 for transferring data All the AHRS outputs are data therefore they have Message type 1 The Message length is the number of bytes in the message without header The Check sum is the arithmetical sum of bytes 2 n all bytes without Header In the check sum the low byte is transmitted first see Table 6 3 Table 6 3 Format of the check sum transmitting byte0 byte1 low byte high byte Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 20 inertial Labs AHRS Interface Control Document In the Table 6 2 and in all other there is denoted word unsigned 2 byte integer sword signed 2 byte integer Important note The low byte is transmitted by first in all data denoted as word sword float 6 1 Operational modes of the Inertial Labs AHRS The Inertial Labs AHRS can operate in the five modes 1 Idle mode Al
19. d Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 43 inertial Labs AHRS Interface Control Document gt 80 AHRS is calibrated by loading calibration parameters from other software e g Demo software 1 Number of used byte 1 calibration runs 2 Reserved byte 1 3 Calibration success byte 1 0 calibration is not successful 1 calibration is successful 4 39 Matrix for soft iron float 9 4 Matrix Tm_c 3x3 by correction rOWS 39 51 Matrix for hard iron float 3 4 Matrix Hm_0 3x1 correction 6 5 The Unit Status Word definition The Unit Status Word USW provides the AHRS state information The low byte bits 0 7 of USW indicates failure of the AHRS If this byte is 0 the AHRS operates correctly if it is not 0 see the Table 6 18 for type of failure The high byte bits 8 15 contains a warning or is informative for the user Status of each bit of the USW warning byte is specified in the Table 6 18 and Table 6 19 Table 6 18 The Unit Status Word description Bit Parameter Description Low O Initial Alignment 0 Successful initial alignment failure 1 Unsuccessful initial alignment due byte to AHRS moving or large changing of outer magnetic field 1 AHRS Parameters 0 Parameters are correct 1 Parameters are incorrect 2 Gyroscope Unit 0 No failure 1 Failure detect
20. d over the Z axis is down and the procedure described above should be repeated During this calibration the range of pitch and roll angles changing must be as much as possible 2D 2T calibration is designed for carrier objects that operate in full heading range but with limited range of pitch and roll angles This calibration procedure involves a few full 360 rotations of the carrier object with installed AHRS in heading with different pitch angles During each rotation pitch and roll angles should be as constant as possible Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 46 inertial Labs AHRS Interface Control Document If place of the AHRS mounting on the carrier object is changed or if the carrier object is changed then the AHRS should be re calibrated on the hard and soft iron of the carrier object B Variants of the Inertial Labs AHRS mounting relative to the object axes The Inertial Labs AHRS can be mounted on the object in any known position up to upside down upright etc relative to the object axes Such mounting doesn t change right determination of the object orientation if angles of the AHRS mounting are correctly stored in the AHRS nonvolatile memory To store angles of mounting in the AHRS please use the Inertial Labs AHRS Demo Program item Device option from the Options me
21. e 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 30 inertial Labs AHRS Interface Control Document 2 3 Initial alignment time word 2 seconds default is 30 sec 4 7 Magnetic declination float 4 degrees if Mdec gt 360 Mdec then AHRS calculates it 8 11 Latitude float 4 degrees 12 15 Longitude float 4 degrees 16 19 Altitude float 4 meters 20 23 Date Year Month float 4 Year Month 1 12 Day Day 365 24 27 Alignment angle A1 float 4 Angles of AHRS mounting 28 31 Alignment angle A2 float 4 on the carrier object 32 35 Alignment angle A3 float 4 degrees see Appendix B 36 49 Reserved 14 Should be all zeros The AHRS calculates the check sum of received parameters and returns it for a checking Byte structure of this message is shown in the Table 6 2 where payload is the calculated check sum 2 bytes Notes 1 The most easy and sure way to change above parameters is using the Inertial Labs AHRS Demo Program 2 Before using LoadAHRSPar command it is necessary to use ReadAHRSPar com mand see below to read parameters from the AHRS at first After that user can change some parameters listed in the Table 6 9 and to send back all block of parame ters to the Inertial Labs AHRS 3 Default time 30 seconds of the initial alignment can be changed but only in agree ment with developers
22. e E E 14 Figure 4 2 The Inertial Labs AHRS outline drawing c ccccecesssssesesesesessseseesesesenes 15 Figure 5 1 The Inertial Labs AHRS connector pinout mating face of the connector 17 Figure 5 2 The diagram of electric connection of the Inertial Labs AHRS to host COMPUTO RIEN ISSN 18 Figure 5 3 The diagram of the interface cable 1 for the Inertial Labs AHRS connections to the COM port of host computer and to the AC DC adapter 19 Figure B 1 Examples of the Inertial Labs AHRS mounting on the carrier object 48 LIST OF TABLES Table 3 1 Inertial Labs AHRS Specifications i 10 Table 5 1 Pin diagram of the Inertial LabsTM AHRS connector 17 Table 5 2 Electrical specifications scr ii 17 Table 6 1 COM port parameters i 20 Table 6 2 Byte structure for all commands and messages to from the AHRS 20 Table 6 3 Format of the check sum transmitting eeeeeeeeneeeeeeeeeeeeeeeeeeeeeeeeees 20 Table 6 4 The AHRS message payload at Full Output Data format at AHRScont1 or AMRSregi command solo 23 Table 6 5 The AHRS message payload at Quaternion of Orientation format at AHRScont2 or AHRSreq2 command iaia 23 Table 6 6 The AHRS message payload at Orientation Sensor Outputs format at AHRSconts or AHRSreq3 command srl 24 Table 6 7 The AHRS message in NMEA at NMEAcont or NMEAreq c
23. e Parameter Format Length Note 0 Type of calibration byte 1 2 for 2D 2T calibration 3 for 3D calibration 1 Number of used byte 1 Not used for 3D calibration runs calibration 2 Data decimation byte 1 for 3D calibration only 3 Calibration success byte 1 0 calibration is not successful 1 calibration is successful 4 39 Matrix for soft iron float 9 4 Matrix Tm_c 3x3 by correction rows 39 51 Matrix for hard iron float 3 4 Matrix Hm_0 3x1 correction Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 36 inertial Labs AHRS Interface Control Document 6 4 2 StopClb command After receiving the StopClb command code 0x20 in the Payload field the AHRS finishes data accumulation in calibration procedure and calculates the calibration parameters After that the AHRS gives out message with the calibration results see the Table 6 14 After receiving the StopClb command the AHRS waits one of the next commands e the AcceptClb command see section 6 4 3 to accept and save the calibration parameters e or the ExitClb command see section 6 4 4 to exit from calibration procedure without accepting and saving its results 6 4 3 AcceptClb command The AcceptClb command code 0x2E in the Payload field is applied to accept the calibration parameters and to save them to the AH
24. ed Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 44 InertialLabs AHRS Interface Control Document 3 Accelerometer Unit 0 No failure 1 Failure detected 4 Magnetometer Unit 0 No failure 1 Failure detected 5 Electronics 0 No failure 1 Failure detected 6 Software 0 No failure 1 Failure detected 7 AHRS mode See the Table 6 19 High 8 0 Supply voltage is not less than warning minimum level byte Incorrect Power 1 Low supply voltage detected 9 Supply 0 Supply voltage is not higher than maximum level 1 High supply voltage detected 10 0 X angular rate is within the range 1 X angular rate is outrange 11 Angular Rate 0 Y angular rate is within the range Exceeding Detect 1 Y angular rate is outrange 12 0 Z angular rate is within the range 1 Z angular rate is outrange 13 Large Magnetic 0 Total magnetic field is within the Field Detect normal range 1 Total magnetic field limit is exceeded 14 Environmental 0 Temperature is within the operating Temperature range 1 Temperature is out of the operating range 15 AHRS mode See the Table 6 19 The AHRS indicates its current mode of operation in the bits 7 and 15 as the Table 6 19 shows Inert
25. ees for tilting in pitch and roll After full 360 rotation the object with the AHRS is turned over the Z axis is down and the procedure described above should be repeated During this calibration the range of pitch and roll angles changing must be as much as possible Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 35 inertial Labs AHRS Interface Control Document After set accumulation time is reached or StopClb command is sent to the AHRS see section 6 4 2 for details the AHRS finishes data accumulation and calculates the calibration parameters After calculation of the calibration parameters that takes lt 0 5 seconds the AHRS gives out message with the calibration results see the Table 6 14 and it waits one of the next commands e the AcceptClob command see section 6 4 3 to accept and save the calibration parameters usually if the Calibration success byte in the AHRS message is equal to 1 see the Table 6 14 e or the ExitClb command see section 6 4 4 to exit from calibration procedure without accepting and saving its results usually if the Calibration success byte in the AHRS message is equal to 0 see the Table 6 14 The AHRS answers on these commands with checksum and goes to idle mode Table 6 14 Payload of the AHRS message after calibration completed Byt
26. for heading reference then it directly determines just magnetic heading The Inertial Labs AHRS also provides true North heading when the current magnetic declination is set Declination also called magnetic variation is the difference between true and magnetic North relative to a point on the Earth Declination angle vary throughout the world and changes slowly over time Declination angle can be entered directly to the Inertial Labs AHRS memory using special command see Table 6 2 or the Inertial Labs AHRS Demo Program Also the declination can be calculated by AHRS itself based on entered latitude longitude altitude and date see section 6 3 6 LoadAHRSPar command for details Both AHRS and AHRS Demo Program calculate the declination using the World Magnetic Model produced by the U S National Geophysical Data Center and the British Geological Survey http www ngdc noaa gov geomag WMM DoDWMM shtml The World Magnetic Model is the standard model of the US Department of Defense the UK Ministry of Defense the North Atlantic Treaty Organization NATO and the World Hydrographic Office WHO navigation and attitude heading referencing systems 2 SCOPE AND APPLICABILITY Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com Inertial Labs AHRS Interface Control Document This Interface Control Document
27. gnment angles are 180 90 0 degrees Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 48 InertialLabs AHRS Interface Control Document C Full list of the Inertial Labs AHRS commands All the AHRS commands have the byte structure shown in the Table 6 2 Payload for all commands has length 1 byte and contains code of the command Below Table C 1 lists all commands with their exact structure in hexadecimal numbers Table C 1 List of the AHRS commands with exact structure Command name Code Exact structure hex Commands for Inertial Labs AHRS control AHRScont1 0x80 AA 55 00 00 07 00 80 87 00 AHRScont2 0x82 AA 55 00 00 07 00 82 89 00 AHRScont3 0x83 AA 55 00 00 07 00 83 8A 00 AHRSreg1 0x84 AA 55 00 00 07 00 84 8B 00 AHRSreq2 0x86 AA 55 00 00 07 00 86 8D 00 AHRSreq3 0x87 AA 55 00 00 07 00 87 8E 00 NMEAcont 0x88 AA 55 00 00 07 00 88 8F 00 NMEAreq 0x89 AA 55 00 00 07 00 89 90 00 GetDataReq OxCA AA 55 00 00 07 00 CA D1 00 Stop OxFE AA 55 00 00 07 00 FE 05 01 LoadAHRSPar 0x40 AA 55 00 00 07 00 40 47 00 ReadAHRSPar 0x41 AA 55 00 00 07 00 41 48 00 LowPowerOn OxBO AA 55 00 00 07 00 BO B7 00 LowPowerOff OxBA AA 55 00 00 07 00 BA C1 00 GetVerFirmware Ox1F AA 55 00 00 07 00 1F 26 00 GetBIT Ox1A AA 55 00 00 07 00 1A 21 00 Commands for Ine
28. h the axis Y directed to the nose of the object Also the Inertial Labs AHRS can be mounted on the object in any known position up to upside down upright etc relative to the object axes Such mounting doesn t change right determination of the object orientation if angles of the AHRS mounting are correctly stored in the AHRS nonvolatile memory See Appendix B Variants of the Inertial Labs AHRS mounting relative to carrier object axes To obtain accurate attitude and heading please remember that mounting is very important and mounting error can cause attitude and heading errors When Inertial Labs AHRS mounting please align it on two base surfaces A B relative your system axes Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 15 inertial Labs AHRS Interface Control Document There are two variants of the Inertial Labs AHRS mounting on your system 1 Use 4 holes 2 6 mm on 4 lugs see Fig 4 1 positions 1 2 Use 4 threaded holes M3x6 mm on the bottom of AHRS see Fig 4 1 positions 2 Note It is recommended to use holes in lugs for the AHRS mounting because of threaded holes in the aluminum case of the AHRS can be damaged at multiple mounting dismounting procedures Requirements to the mounting surface of the carrier object flatness tolerance is 0 03 mm undulation is Ra 1 25 5 ELECTRICAL
29. he two commands a the AcceptClb command see section 6 4 3 to accept and save the calibration parameters usually if the Calibration success byte in the AHRS message is equal to 1 see the Table 6 14 b or the ExitClb command see section 6 4 4 to exit from calibration procedure without accepting and saving its results usually if the Calibration success byte in the AHRS message is equal to 0 see the Table 6 14 The AHRS answers on these commands with checksum and goes to idle mode 3 ExitClb command see section 6 4 4 In this case the calibration finishes without any calculations in the AHRS and without saving any calibration parameters The AHRS answers on this command with checksum and goes into the idle mode Notes 1 Rotation of the object with the AHRS in heading must include one or more full 360 turns Please correct the time required for saving data in the Accumulation time window to attain necessary rotations 2 During calibration run pitch and roll angles should be approximately constant 3 If place of the AHRS mounting on the object is changed or if the object is changed then the AHRS should be re calibrated on the hard and soft iron of this object Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 40 inertial Labs AHRS Interface Control Document 6 4 6 StartClbRun comma
30. ial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 45 inertial Labs AHRS Interface Control Document Table 6 19 Indication of the AHRS current operational modes USW bits Bit 7 Bit 15 peared 0 0 Readiness 1 1 Sleep this is in the last data block sent by the AHRS before it went to Sleep mode APPENDIX A The Inertial Labs AHRS calibration The Inertial Labs AHRS software allows to take into account influence of the carrier object soft and hard iron on the heading determination For this purpose field calibration of the AHRS magnetometers on hard and soft iron is provided This calibration does not require any additional equipment but it requires setting of the carrier object where the AHRS is mounted in specified positions There are several types of the calibration Since AHRS firmware version 4 8 1 the 3D and 2D 2T calibrations are realized in the AHRS Other types of hard soft iron calibration can be fulfilled with Inertial Labs AHRS Demo software 3D calibration is designed for carrier objects that can operate in full heading pitch and roll ranges For this calibration the carrier object is rotated in the horizon plane the Z axis is up with periodical stops about each 90 degrees for tilting in pitch and roll After full 360 rotation the carrier object with the AHRS is turne
31. ial Labs utilizes several types of field calibration depending on the carrier object type The next types of the calibration are realized in the Inertial Labs AHRS firmware e 3D calibration e 2D 2T calibration e 2D calibration since firmware version 4 9 1 6 The next commands are used for the AHRS calibration Start8DClb Start2D2T Clb Start2DClb StartClbRun StopClb AcceptClb ClearClb ExitClb GetClbRes All these commands have the byte structure shown in the Table 6 2 Payload for all commands has length 1 byte and contains code of the command See Appendix C for examples of these commands 6 4 1 Start3DCIb command for AHRS 3D calibration The 3D calibration is designed for carrier objects that can operate in full heading pitch and roll ranges At this calibration the carrier object should be rotated in all these ranges To start the 3D calibration the host computer sends to the AHRS the Start3DCIb command code 0x23 in the Payload field followed by message with block of parameters listed in the Table 6 13 This message Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 34 inertial Labs AHRS Interface Control Document have the byte structure shown in the Table 6 2 and should be sent without pause after sending the Start83DClb command Table 6 13 Payload of the message following
32. ially from 7 temperature sensors inside gyros accelerometers and magnetometers The low byte is transmitted by first Table 6 5 The AHRS message payload at Quaternion of Orientation format at AHRScont2 or AHRSreq2 command Byte ae Auber 0 1 2 3 4 5 6 13 27 29 30 31 32 33 LkO Lk1 Reser ysw Parameter Heading Pitch Roll Lk2 Lk3 ved Vdd Utermo 4x 2 byte 2 byte 2 byte 14 2byte 2 byte 2 byte Length word sword sword 2 byte bytes Word word sword sword Quaternion of Supply Temper Note aida rated n gles orientation DIR ature a 10000 fon 0 Notes USW is unit status word see section 6 5 for details Vdd is input voltage of the AHRS Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 23 inertial Labs AHRS Interface Control Document Utermo is averaged temperature in 3 accelerometers The low byte is transmitted by first Table 6 6 The AHRS message payload at Orientation Sensor Outputs format at AHRScont3 or AHRSreg3 command Byte 12 18 24 28 32 ine te eee GyroX AccX MagX Reser Parameter Heading Pitch Roll GyroY AccY MagY ed USW Vdd Utermo GyroZ AccZ MagZ 2 byte 2 byte 2 bytel 2 3 9 2 byte 2 byte 2 byte Length word
33. in the Table 6 2 where payload is one byte equal to 0x88 The NMEAreq command is used to start the Inertial Labs AHRS in the On Request operating mode with NMEA format of output data see Table 6 7 The NMEAreq command has the byte structure shown in the Table 6 2 where payload is one byte equal to 0x89 Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 28 inertial Labs AHRS Interface Control Document In order to identify to the host system that AHRS received one of these commands the AHRS answers back immediately on this command prior to completion of the initial alignment process The AHRS calculates the check sum of the message without its header and check sum and returns it for a checking Byte structure of this message is shown in the Table 6 2 where payload is the calculated check sum 1 word This check sum should be equal to the check sum in the message that was sent to the AHRS Then the AHRS starts process of initial alignment that takes usually 30 se conds This process includes the AHRS gyros drift estimation therefore don t move the AHRS during its initial alignment If this requirement is not met then large errors may be occurred in orientation angles calculation Note Default time 30 seconds of the initial alignment can be changed see section 6 3 6 LoadAHRSPar command but only in agreement wi
34. inertial Labs AHRS Interface Control Document 6 2 Output Data Formats of the Inertial Labs AHRS in the Operating Modes The next output data formats are available in the Continuous and On Request operating modes e Full Output Data e Quaternion of Orientation e Orientation Sensor Outputs e NMEA Output since AHRS firmware version 4 9 2 The default is Orientation Sensor Outputs data format It provides the AHRS output in the form of 3 orientation angles heading pitch and roll and calibrated outputs of the 9 sensors gyros accelerometers magnetometers that give information about current angular rate linear acceleration of the AHRS and components of outer magnetic field along the AHRS measurement axes see Fig 1 2 More correctly these 9 sensors output are integrated angular rate linear acceleration specific force magnetic field increments In the AHRS output these increments are divided by time step of data output so they may be interpreted as average angular rates linear acceleration and magnetic field for cycle of data output On the other hand incremental sensor data are good for the AHRS using as IMU inertial measurement unit The Quaternion of Orientation data format gives quaternion presentation of an object orientation in addition to 3 orientation angles Usually the Full Output Data format is used by the AHRS developers for full control of calculations in the AHRS mic
35. inertial Labs AHRS Interface Control Document Attitude and Heading Reference System INERTIAL LABS AHRS Interface Control Document February 2012 Revision 1 2 2012 Inertial Labs This document contains information proprietary to Inertial Labs Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com InertialLabs AHRS Interface Control Document CHANGE STATUS LOG DOCUMENT NUMBER AHRS ICD TITLE Inertial Labs AHRS Interface Control Document AFFECTED REVISION DATE PAGES REMARKS 1 0 Jan 19 2012 All Released version 1 1 Feb 06 2012 For AHRS firmware since v 4 9 1 6 35 1 Inserted 4 bytes float for set point azimuth in the AHRS message after each calibration run Table 6 14 37 38 45 2 2D calibration is realized and its description is added 39 3 Because of added 2D calibration the AHRS answer on GetClbRes command is updated Table 6 16 1 2 Feb 13 2012 For AHRS firmware since v 4 9 2 0 23 27 47 1 Added commands NMEAcont NMEAreq for new NMEA output data format and description of this format Table 6 7 Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com inertial Labs AHRS Interface Control Document TABLE OF CONTENTS I M
36. l Labs AHRS should be mounted in a physically stable location Choose a location that is isolated from excessive shock oscillation and vibration Special rotary table must be used for the Inertial Labs AHRS accuracy testing that mounted on a special testing basement which is free from the laboratory oscillations and vibrations Tests on vibrations and shocks are fulfilled separately from the main accuracy tests 4 2 Where to install the Inertial Labs AHRS on the object It is necessary to follow the recommendations listed in the section 4 1 whenever it is possible when installing the Inertial Labs AHRS on an carrier object Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 12 inertial Labs AHRS Interface Control Document e Inertial Labs AHRS should be installed on an object as far as pos sible from large ferromagnetic masses of the object and powerful sources of magnetic electrical and electro magnetic fields Inertial Labs AHRS software allows compensation of hard and soft iron effects of the carrier object on the heading measurement accuracy For this purpose field calibration of the AHRS magnetometers is provided This calibration does not require any additional equipment but it requires turns of the carrier object on which the AHRS is mounted Note that the above field calibration is correct
37. l pitch and roll angles not more than a few degrees This calibration procedure involves full 360 rotation of the carrier object in azimuth During this rotation pitch and roll angles must be as close to zero as possible To start the 2D calibration the host computer sends to the AHRS the Start2DCIb command code 0x21 in the Payload field followed by Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 41 inertial Labs AHRS Interface Control Document message with block of parameters listed in the Table 6 13 This message have the byte structure shown in the Table 6 2 and should be sent without pause after sending the Start2DClb command Note that first 4 bytes in the payload Reference azimuth do not influence on the 2D calibration as it is noted in the Table 6 13 The AHRS calculates the check sum of received parameters and returns it for a checking Byte structure of this message is shown in the Table 6 2 where payload is the calculated check sum 1 word Then the AHRS starts process of initial alignment This process includes the AHRS gyros drift estimation therefore don t move the AHRS during its initial alignment Default time of the initial alignment is 30 seconds and can be changed see section 6 3 6 LoadAHRSPar command but only in agreement with developers of the Inertial Labs AHRS After comple
38. l sensors and electronics are powered The AHRS microprocessor waits any command from the host computer to start operate in one of the next modes In the idle mode the AHRS indicator lights red 2 Continuous operating mode In this mode the AHRS operates in the endless loop providing the continuous output of calculated orientation angles and some other data according to chosen output data format see section 6 2 Data rate is set by user from 1 Hz to 100 Hz In the Continuous operating mode the AHRS s indicator lights green 3 On Request operating mode It is close to the Continuous operating mode but the AHRS sends only one data block after each Request command issued from host computer In this mode the AHRS s indicator lights green 4 Calibration operating mode In this mode the embedded calibration procedure is performed for compensation of hard and soft iron effects of the carrier object See section 6 4 for more details 5 Sleep low power mode with the minimal power consumption of the AHRS All sensors are switched off processor core and part of periphery are switched off No outputs are from the AHRS only Its microprocessor waits command from the host computer to exit from the Sleep mode In the Sleep mode the AHRS s indicator lamp is off Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 21
39. m of the interface cable 1 for the Inertial Labs AHRS connections to the COM port of host computer and to the DC power source Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 18 inertial Labs AHRS Interface Control Document Cable 1 X1 Male Cable Connector X3 COM Female Binder 718 Connector DB 9F in the case X2 Power PR 002B Fig 5 3 The diagram of the interface cable 1 for the Inertial Labs AHRS connections to the COM port of host computer and to the AC DC adapter 6 SOFTWARE INTERFACE After power connection the primary initialization of the Inertial Labs AHRS microprocessor takes place and the main program starts working The time of the device pretreatment is not more 1 second The program works in the waiting mode of the commands Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 19 inertial Labs AHRS Interface Control Document The commands are transmitted through the serial port according to the protocol RS232 Table 6 1 COM port parameters COM port parameters Baud rate 115200 Data bits 8 Parity none Stop bits 1 All commands and messages to from the Inertial Labs AHRS have the byte structure shown in the Table 6 2 Ex
40. nc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com inertial Labs AHRS Interface Control Document Random Walk m s sqrt hr 0 06 0 06 0 06 Resolution mg 0 1 0 1 0 2 Bandwidth Hz 50 50 50 Operating temperature deg C 40 to 70 Storage temperature deg C 50 to 85 Supply voltage V DC 5 5 to 6 5 Current draw e in readiness mode mA 85 85 87 e in sleep mode mA 15 15 15 Connector 6 Pin Binder 718 series Female Digital Interface RS 232 Size mm 90 x 27 x 26 Weight gram 73 including time of initial alignment It may be decreased on request in homogeneous magnetic environment for latitude up to 65 deg may depend on type of motion AHRS1 modification with 1000 deg s gyro range is also available length with mounting lugs U N 4 1 2 3 4 5 4 MECHANICAL INTERFACE 4 1 Where to install the Inertial Labs AHRS for tests The Inertial Labs AHRS has magnetometers with wide dynamic range and its sophisticated calibration algorithms allow it to operate in many environments For optimal performance however you should mount the Inertial Labs AHRS with the following considerations in mind e Locate the Inertial Labs AHRS away from local sources of magnetic fields The place for testing must not have ferromagnetic magneto susceptible materials a
41. nd If calibration procedure includes more than one run like 2D 2T calibration then the StartClbRun command code 0x2B in the Payload field is used to start each run For unification with the StartCloRun command for some other calibration types this command must be followed by message with block of parameters listed in the Table 6 16 But for the 2D 2T calibration the value of those 6 bytes does not influenced so these 6 bytes may be any for example zeros Only requirement is that this message should have the byte structure shown in the Table 6 2 and should be sent without pause after sending the StartClbRun command Table 6 16 Payload of the message following after the StartClbRun command block of parameters loaded to the AHRS Byte Parameter Format Length Note 0 3 Reserved byte 4 4 5 Measurement units word 2 0 degrees 1 mils After receiving the StartCloRun command the AHRS calculates the check sum of received parameters and returns it for a checking This check sum should be equal to the check sum in the StartCloRun command message that was sent to the AHRS Byte structure of this message is shown in the Table 6 2 where payload is the calculated check sum 1 word 6 4 7 Start2DCIb command for AHRS 2D calibration Since AHRS firmware version 4 9 1 5 the 2D calibration is realized in the AHRS This calibration is designed for carrier objects that operate in full azimuth range but with smal
42. nd the lab room itself must have the level of intrinsic magnetic and electro magnetic fields suitable for the magnetic heading system testing Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com inertial Labs AHRS Interface Control Document inside and near the lab room there must be no powerful source of magnetic electrical and electro magnetic fields The magnetic field intensity must not be different from the Earth magnetic field intensity at the test site more than 0 01 small ferromagnetic objects must be as far as 3 meters from the test table Large size ferromagnetic objects such as cars and trucks must be as far as 15 m from the table it is necessary to conduct a regular check up of the magnetic field uniformity inside the lab room It is highly recommended to degauss AHRS before heading test to remove permanent magnetization of some components in the AHRS if you accidentally expose the unit to a large magnetic field You can use a hand held degausser tape eraser to demagnetize the AHRS Most audio and video degaussing units can be used Follow the instructions for your demagnetizer If heading accuracy is not checked and only pitch and roll accuracy are tested then there are no requirements to magnetic fields and ferromagnetic materials near place of the Inertial Labs AHRS mounting e The Inertia
43. nt pitch angles To start the 2D 2T calibration the Host computer sends to the AHRS the Start2D2TCIb command code 0x22 in the Payload field followed by message with block of parameters listed in the Table 6 13 This message have the byte structure shown in the Table 6 2 and should be sent without pause after sending the Start2D2TCIb command The AHRS calculates the check sum of received parameters and returns it for a checking Byte structure of this message is shown in the Table 6 2 where payload is the calculated check sum 1 word The 2D 2T calibration procedure involves a few runs with full 360 rotations of the object with installed AHRS in heading with different pitch angles Set the object to the first pitch angle usually the minimum pitch angle is set first Then send the StartCloRun command followed by message see section 6 4 6 to start the first run of the calibration After receiving the StartCloRun command with its message the AHRS calculates the check sum of received block of parameters and returns it for checking This check sum should be equal to the check sum in the StartCloRun command message that was sent to the AHRS Byte structure of this message is shown in the Table 6 2 where payload is the calculated check sum 1 word Then the AHRS starts process of initial alignment This process includes the AHRS gyros drift estimation therefore don t move the AHRS during its Inertial Labs Inc Address 1380
44. nu or send LoadBlockPar command to the AHRS directly see structure of the message following after the LoadAHRSPar command in the Table 6 9 Angles of the AHRS position alignment angles are set in next order like heading pitch and roll setting first alignment angle sets position of the AHRS longitudinal axis Y rel ative to longitudinal axes of the object measured in the horizontal plane of the object Clockwise rotation is positive second alignment angle is equal to angle of inclination of the AHRS longitudinal axis Y relative to the horizontal plane of the object Posi tive direction is up third alignment angle is equal to inclination angle of the AHRS lateral axis X measured around AHRS longitudinal axis Positive rotation is X axis moving down All angles are set in degrees Some examples of the Inertial Labs AHRS mounting relative the carrier object are shown on Fig B 1 To check correctness of the alignment angles please run the AHRS using the Inertial Labs AHRS Demo program Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 47 inertial Labs AHRS Interface Control Document Fig B 1 Examples of the Inertial Labs AHRS mounting on the carrier object a alignment angles are 0 0 0 degrees b alignment angles are 0 0 180 degrees c alignment angles are 90 0 0 degrees d ali
45. ol Document Calibration success byte in the AHRS message is equal to 0 see the Table 6 14 The AHRS answers on these commands with checksum and goes to idle mode 6 4 8 ClearClb command The ClearClb command code 0x2F in the Payload field is used to clear parameters of the hard and soft iron calibration from the AHRS nonvolatile memory The AHRS answers on this command The AHRS calculates the check sum of the message without its header and check sum and returns it for a checking Byte structure of this message is shown in the Table 6 2 where payload is the calculated check sum 1 word You should clear parameters of the soft and hard iron calibration if you uninstall the AHRS from object to avoid incorrect azimuth determination with standalone AHRS 6 4 9 GetClbRes command The GetClbRes command code 0x2A in the Payload field can be send from the host computer to check the last calibration results of the AHRS As answer on this command the AHRS sends out the message with the data block near the same as after completing calibration with StopClb command see the Table 6 17 Table 6 17 Payload of the AHRS answer on request about calibration results Byte Parameter Format Length Note 0 Type of calibration byte 1 0 AHRS is not performed calibrated 1 2D calibration 2 2D 2T calibration 3 3D calibration Inertial Labs Inc Address 13800 Coppermine Roa
46. ommand 24 Table 6 8 Structure of the payload of block of initial alignment data 26 Table 6 9 Payload of the message following after the LoadAHRSPar command block of parameters for loading to the AHRS 30 Table 6 10 Payload of the AHRS answer on the ReadAHRSPar command block of parameters read from the AHRS i 32 Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com inertial Labs AHRS Interface Control Document Table 6 11 Payload of the AHRS answer on the GetVerFirmware command Table 6 12 Payload of the AHRS answer on the GetBIT command 33 Table 6 13 Payload of the message following after the Start3DClb and Start2D2TClb commands the block of parameters loaded to the AHRS _ 35 Table 6 14 Payload of the AHRS message after calibration completed 36 Table 6 15 Payload of the AHRS message after each calibration run of the 2D 2T Gba iaia 39 Table 6 16 Payload of the message following after the StartClbRun command block of parameters loaded to the AHRS iii 41 Table 6 17 Payload of the AHRS answer on request about calibration results 43 Table 6 18 The Unit Status Word description 44 Table 6 19 Indication of the AHRS current ope
47. orientation angles calculating Data blocks are transmitted according to chosen variant of output data in messages described in the Table 6 2 In all variants the message payload has 34 bytes of data which structure depends on chosen variant of output data see section 6 2 The update rate of data blocks is set by the user in range 1 100 Hz Default update rate is100 Hz 6 3 2 AHRSreqg1 AHRSreq2 AHRSreq3 commands The commands AHRSreq1 AHRSreq2 AHRSreq3 are used to start the Inertial Labs AHRS in the On Request operating mode with one of three variants of output data AHRSreq1 command code 0x84 Full Output Data format AHRSreq2 command code 0x86 Quaternion Of Orientation format AHRSreq3 command code 0x87 Orientation Sensor Outputs for mat All these commands have the byte structure shown in the Table 6 2 Payload for all commands has length 1 byte and contains code of the command In order to identify to the host system that AHRS received one of these commands the AHRS answers back immediately on this command prior to completion of the initial alignment process The AHRS calculates the check Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 27 inertial Labs AHRS Interface Control Document sum of the message without its header and check sum and returns it for a checking
48. rational Modes 46 Table C 1 List of the AHRS commands with exact structure 49 Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com inertial Labs AHRS Interface Control Document 1 INTRODUCTION 1 1 Description of the System The Inertial Labs Attitude and Heading Reference System AHRS is a high performance strapdown system that determines absolute orientation heading pitch and roll for any device on which it is mounted Orientation is determined with high accuracy for both motionless and dynamic applications The Inertial Labs AHRS utilizes 3 axes each of precision MEMS gyroscopes MEMS accelerometers and fluxgate magnetometers to provide accurate heading pitch and roll of the device under measure Integration of gyroscopes output provides high frequency real time measurement of the device rotation about all three rotational axes Accelerometers and magnetometers measure absolute pitch roll and magnetic azimuth at AHRS initial alignment as well as ongoing corrections to gyroscopes during operation Fig 1 1 The Inertial Labs AHRS Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com iner tial Labs AHRS Interface Control Documen
49. roprocessor Also this format can be used by user at any troubles to get full data from the AHRS for next sending them to developers Structure of the AHRS output in above output data formats corresponds to the Table 6 2 where payload depends on chosen output data format Table 6 4 Table 6 6 show these payloads where is denoted word unsigned 2 byte integer sword signed 2 byte integer Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 22 inertial Labs AHRS Interface Control Document Table 6 4 The AHRS message payload at Full Output Data format at AHRScont1 or AHRSreqi command i 0 1 2 3 4 5 6 23 24 27 28 29 30 31 32 33 number Ugyro Reser Parameter Heading Pitch Roll Uacc Gea USW Vdd Utermo Umag 9x 2 byte 2 byte 2 byte 2 byte 2 byte 2 byte Length word sword sword Py 4byte word word sword sword Raw Combi sensor ned data voltage Temper Orientation angles gyros VDC ature in NOIE deg 100 accelero 1000 each meters sensor magne tometers Notes USW is unit status word see section 6 5 for details The following data are recorded in the field Vdd sequentially the AHRS input voltage stabilized voltage supplied to the AHRS sensors In the Utermo field ADC codes are recorded sequent
50. rtial Labs AHRS calibration Start2DClb 0x21 AA 55 00 00 07 00 21 28 00 Start2D2TClb 0x22 AA 55 00 00 07 00 22 29 00 Start3DClb 0x23 AA 55 00 00 07 00 23 2A 00 StartCIbRun 0x2B AA 55 00 00 07 00 2B 32 00 StopClb 0x20 AA 55 00 00 07 00 20 27 00 AcceptClb 0x2E AA 55 00 00 07 00 2E 35 00 ExitClb OxFE AA 55 00 00 07 00 FE 05 01 Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 49 Inertial Labs AHRS Interface Control Document ClearClb Ox2F AA 55 00 00 07 00 2F 36 00 GetCloRes Ox2A AA 55 00 00 07 00 2A 31 00 Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 50
51. sword leword 2 byte 2 byte 2 byte 4 byte word Word sword sword sword sword Angular Magne Supply N Orientation angles rates ise iL voltage Tempe ote deg 100 deg s g KA fields VDC fms KG nT 10 1000 0 Notes KG 50 KA 10000 for AHRS1 1 AHRS1 2 KG 100 KA 5000 for AHRS1 3 Angular rates linear accelerations and magnetic fields are in the AHRS axes X is lateral axis Y is longitudinal axis Z is vertical axis USW is unit status word see section 6 5 for details Vdd is input voltage of the AHRS Utermo is averaged temperature in 3 accelerometers The low byte is transmitted by first At the NMEA Output the AHRS output data are transmitted in the form of sentences with printable ASCII characters like the NMEA 0183 format Each sentence starts with a sign and ends with lt CR gt lt LF gt carriage return OxD and line feed OxA symbols All data fields are separated by commas The general form of the NMEA Output sentence is the next PAHR RRRR rr PPP pp HHH hh TTT t V vv SSSS CC lt CR gt lt LF gt where PAHR is identifier and other fields are listed in the Table 6 7 Table 6 7 The AHRS message in NMEA format at NMEAcont or NMEAreq command Field RRRR rr PPP pp HHH hh TTT t V vv SSSS CC Parameter Roll Pitch Heading Temperature Vdd USW aoa Note deg deg deg C VDC hex written Inertial Labs Inc Address 13800 Coppermine Road Suite 300
52. t Fig 1 2 shows the AHRS own coordinate system OxoyoZo This coordinate system is body fixed and defined as the calibrated sensors coordinate system Non orthogonality between the axes of the body fixed coordinate system Oxoyozo is an order of 0 01 Zo Up Xo Lateral Heading Pitch Roll Yo Forward Fig 1 2 Coordinate system of the Inertial Labs AHRS Measured angles are the standard Euler angles of rotation from the Earth level frame East North Up to the body frame heading first then pitch and then roll Orientation angles measured by the Inertial Labs AHRS are not limited and are within common ranges e Heading 0 360 e Pitch 90 e Roll 180 Also the Inertial Labs AHRS provided orientation calculation in quaternion form Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com inertial Labs AHRS Interface Control Document 1 2 Principles of the Inertial Labs AHRS Operation Fig 2 1 shows the operational diagram of the Inertial Labs AHRS The AHRS uses gyros to measure absolute angular rate of the carrier object then its orientation angles heading pitch and roll are obtained by using special integration of gyros outputs Accelerometers are used to determine initial attitude of the AHRS and to correct gyros drift in the tilt angles pitch roll determination
53. th developers of the Inertial Labs AHRS After completing of the initial alignment the AHRS gives out message with block of the initial data payload is 50 bytes of the data see the Table 6 8 and goes to e Continuous operating mode in case of NMEAcont command e On Request operating mode in case of NMEAreq command In the Continuous operating mode the AHRS sends out data blocks with update rate set by user in range 1 50 Hz Default update rate is 50 Hz In the On Request operating mode the AHRS sends only one data block after each request command GetDataReq see section 6 3 4 issued from host computer In both operating modes the data blocks are transmitted in the form of sen tences with printable ASCII characters like the NMEA 0183 format see Table 6 7 6 3 4 GetDataReq command The GetDataReq command code OxCA in the Payload field see the Table 6 2 is used to get one data block from the AHRS in the On Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 29 inertial Labs AHRS Interface Control Document Request operating mode Command GetDataReq is valid if one of the AHRSreg1 AHRSreq2 AHRSreq3 NMEAreg commands was sent before As answer on the GetDataReq command the AHRS outputs one block of orientation data with structure described in the Table 6 2 and pa
54. ting of the initial alignment the AHRS gives out the block of the initial data payload is 50 bytes of the data see the Table 6 8 and starts data accumulation during time specified in message sent after the Start2DClb command see the Table 6 13 Rotate carrier object in azimuth with pitch and roll angles close to zero as possible This rotation must include one or more full 360 deg turns Please correct the time required for such rotation in the Time of data accumulation field of the message Table 6 13 to provide necessary rotation After set accumulation time is reached or StopClb command is sent to the AHRS see section 6 4 2 for details the AHRS finishes data accumulation and calculates the calibration parameters After calculation of the calibration parameters that takes lt 0 5 seconds the AHRS gives out message with the calibration results see the Table 6 14 and it waits one of the next commands e the AcceptClob command see section 6 4 3 to accept and save the calibration parameters usually if the Calibration success byte in the AHRS message is equal to 1 see the Table 6 14 e or the ExitClb command see section 6 4 4 to exit from calibration procedure without accepting and saving its results usually if the Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 42 inertial Labs AHRS Interface Contr
55. until the residual magnetic field of the object surrounding the AHRS is changed If this field is changed due to displacement of ferromagnetic masses of the object or magnetic field sources the AHRS should be re calibrated Field calibration procedure of the Inertial Labs AHRS can be performed by two means e by AHRS itself using special commands described in the section 6 4 e using the Inertial Labs AHRS Demo Program The AHRS Demo Program provides more variants of the field calibration and is more convenient for use but it requires connection of the AHRS to PC Calibration of the AHRS itself is performed without its disconnection from the host system on the carrier object More detailed description of the field calibration procedure is given in the Users Manual on the Inertial Labs AHRS Demo Program Field calibration procedure is developed by Inertial Labs after type of the object on which the Inertial Labs AHRS will be used is agreed on with a customer e It is preferable to locate the Inertial Labs AHRS as close to the centre of mass of the object as possible With such location effects of linear accelerations during oscillations on the AHRS accelerometers are reduced and therefore orientation angle determination errors are also reduced Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 13 inertial
56. yload according to the Table 6 4 Table 6 5 or Table 6 6 depending on chosen variant of output data format At the NMEA format of output data set by the NMEAreq command the AHRS outputs one block of orientation data with structure described in the Table 6 7 6 3 5 Stop command At receiving the Stop command code OxFE in the Payload field the AHRS stops work in an operating mode and goes to the idle mode At that the light indicator of the AHRS changes its color to red Important Note Before using all other commands please send the Stop command to the AHRS to switch device into the idle mode Be sure that the AHRS s light indicator is red before sending of any other commands 6 3 6 LoadAHRSPar command The LoadAHRSPar command code 0x40 in the Payload field is used to load the block of the AHRS parameters which are available for changing by user into the AHRS nonvolatile memory After sending the LoadAHRSPar command the block of the AHRS parameters must be send to the AHRS in the message shown the Table 6 2 with payload shown in the Table 6 9 This message should be sent without pause after sending the LoadAHRSPar command Table 6 9 Payload of the message following after the LoadAHRSPar command block of parameters for loading to the AHRS Byte Parameter Format Length Note 0 1 Update rate word 2 1 100 Hz default is 100 Hz Inertial Labs Inc Address 13800 Coppermine Road Suit
57. yte Parameter Format Length Note 0 49 Firmware version char 50 6 3 11 GetBIT command The Inertial Labs AHRS has continuous built in monitoring of its health In both Continuous and On Request operation modes the AHRS sends out Unit Status Word USW in each data block see Table 6 4 Table 6 6 The USW is described in the section 6 5 The USW can be got in any time if the AHRS is in ldle or On Request operation mode after AHRSreg1 AHRSreq2 or AHRSreq3 command For this the GetBIT command code Ox1A in the Payload field is used In answer the AHRS sends out the message with data according to the Table 6 12 Table 6 12 Payload of the AHRS answer on the GetBIT command Byte number 0 1 2 3 Parameter Utermo100 USW Length 2 byte word 2 byte word Utermo100 is the AHRS temperature in 1 100 C increments 6 4 Calibration of the Inertial Labs AHRS on hard and soft iron The Inertial Labs AHRS software allows compensation of hard and soft iron effects of the carrier object on the heading determination accuracy For Inertial Labs Inc Address 13800 Coppermine Road Suite 300 Herndon VA 20171 USA Tel 1 703 880 4222 Fax 1 703 935 8377 Website www inertiallabs com 33 inertial Labs AHRS Interface Control Document this purpose field calibration of the AHRS magnetometers is provided see Appendix A The AHRS calibration Inert
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