VG700MB Series User`s Manual
Contents
1. Doc 7430 0280 01 Rev D VG700MB User s Manual Command Character s Sent Response Description Command Character s Sent Response Description Command Character s Sent Response Description Crossb w DMU a Gr while it is in Continuous Mode will place the DMU in Polled Mode Set Erection Rate T lt x gt none The T command sets the vertical gyro erection rate The argument of the command lt x gt is a single binary byte that represents the value you want to set as the erection rate The units are in degrees per minute For example if you wanted to set the erection rate to 50 deg min you would send the command T lt 50 gt which in hex would be 54 32 Calibrate Rate Sensor Bias Z lt X gt Z Measure the bias on each rate sensor and set as the new zero The DMU should be still motionless during the zeroing process The argument of the command lt x gt is a single binary byte that the DMU normally ignores and hence any single byte character can be sent The zeroing command turns on the high pass filter rate estimation that takes approximately 3 minutes If lt x gt is set to 0 then the previously stored gyro biases are erased Query DMU Version v ASCII string This queries the DMU firmware and will tell you the DMU type and firmware version The response is an ASCII string The exact string will vary according to the DMU type and version Doc 7430 0280 01 Rev D Page 11 Crossb2. lt x gt is set to 0 then the previously stored gyro biases are erased S ASCII Query DMU serial number Returns serial number as String 32 bit binary number v ASCII Query DMU version ID string Returns ASCII string String B b Built in test performed result in BIT byte of next data packet Delay of 70ms occurs for this test The Gyro zeroing validity bit defaults to the high condition upon power up or any restart of the system If the previous zeroing performed was successful the user may choose to ignore the gyro zeroing validity bit Note argument of command is sent as a single hex byte not as an ASCII character Doc 7430 0280 01 Rev D Page 25 Crossb w VG700MB User s Manual 8 Appendix D Troubleshooting Tips Is the supply voltage and connections okay The VG700MB needs at least a 16V power supply for proper operation Verify that your power supply is regulated and not current limited Ensure that the supply does not fall below 16V or go above 32V Make sure that all the connections are intact Is the VG700MB mounting orientation okay The Pitch angle corresponding to 90 degree orientation are singularity points for the algorithm and you should not let the unit sit in this position for extended periods of time As a result the angles start drifting if you stay at these singularities for a long time The longer you keep the unit in a singularity position the longer it will take for the
3. 6 If the status indicator says Connected you re ready to go If the status indicator doesn t say connected check the connections between the DMU 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 DMU 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 DMU Navigation does not work with the IMU models Let the DMU warm up for at least 30 seconds when you first turn it on You should zero the rate sensors when you first use the DMU Set the DMU down in a stable place On the main control panel enter a value into the zero avg time box 3 will work well Click the Z button This measures the rate sensor bias and sets the rate sensor outputs to zero The zeroing command turns on the high pass filter rate bias estimation that takes approximately 3 minutes The DMU needs to be held still motionless during zeroing operation The zero command is discussed more in The Zero Command section Now you re ready to use the DMU Page 4 Doc 7430 0280 01 Rev D VG700MB User s Manual Crossb w 3 DMU Details 3 1 DM
4. LSB Gyro Voltage Y LSB 5 Roll Rate MSB Yaw Rate MSB Gyro Voltage Z MSB 6 Roll Rate LSB Yaw Rate LSB Gyro Voltage Z LSB 7 Pitch Rate MSB Acceleration X MSB Accel Voltage X MSB 8 Pitch Rate LSB Acceleration X LSB Accel Voltage X LSB 9 Yaw Rate MSB Acceleration Y MSB Accel Voltage Y MSB 10 Yaw Rate LSB Acceleration Y LSB Accel Voltage Y LSB 11 Acceleration X MSB Acceleration Z MSB Accel Voltage Z MSB 12 Acceleration X LSB Acceleration Z LSB Accel Voltage Z LSB 13 Acceleration Y MSB Temp Voltage MSB Temp Voltage MSB 14 Acceleration Y LSB Temp Voltage LSB Temp Voltage LSB 15 Acceleration Z MSB Time MSB Time MSB 16 Acceleration Z LSB Time LSB Time LSB 17 Temp Voltage MSB Checksum Checksum 18 Temp Voltage LSB 19 Time MSB 20 Time LSB 21 Checksum Doc 7430 0280 01 Rev D Page 15 Crossb w VG700MB User s Manual Table 4 Data Packet Format VG700MB 206 Byte VG Mode Scaled Sensor Mode Voltage Mode 0 Header OxAA Header 255 Header 255 1 Header 0x55 Roll Rate MSB Gyro Voltage X MSB 2 Roll MSB Roll Rate LSB Gyro Voltage X LSB 3 Roll LSB Pitch Rate MSB Gyro Voltage Y MSB 4 Pitch MSB Pitch Rate LSB Gyro Voltage Y LSB 5 Pitch LSB Yaw Rate MSB Gyro Voltage Z MSB 6 Relative Heading MSB Yaw Rate LSB Gyro Voltage Z LSB
5. 44 DMU Start Up Procedure sroronernvrrnvrrnvrnvrnnrrrrrnrrnrrsnrrssrenernne 21 4 5 Advanced Strategies for Adjusting the Erection Rate 22 5 Appendix A Mechanical Specifications sscsscssseeees 23 Doc 7430 0280 01 Rev D Page i Crossb w VG700MB User s Manual 5 1 VG700MB Outline Drawing oovrrornnvnernrnvenrrnvrnrrrrervreresnervseneense 23 6 Appendix B DMU Output Quick Reference ssceeee 24 6 1 Digital Output Conversion eseenrrvrnnvrerernvenrrnernverrenerernsnesvseneensee 24 7 Appendix C DMU Command Quick Reference 0 25 8 Appendix D Troubleshooting Tips eeeveeevvrsvvennvensversvernveeene 26 9 Appendix E Warranty and Support Information 28 9 1 Custonier Servicen snonsedmn eee ase nn eel areas 28 9 2 Contact Directory snirsuarmsiniisis ins estrea Ei tE EE KERESE 28 9 3 Return Procedures nise je sia a 28 9 3 1 Authorization osnrrornnnrrnvrvnnvrnnrnrrnvrrnnvennnnnrnsrrnnrsnnsnnrnsrrrnennssnnensennn 28 9 3 2 Identification and Protection srrrnnnnrrnvrvnnvvnnnnvnn ren nvrnnrnnrnnrensennn 29 9 3 3 Sealing the Container ssmssronrrvnnrnrnnnrrnvrrnnvrnnrnnrnsrrnnrsnernersrrnnesnenn 29 9 3 4 Markinan E ER EEE ERRE 29 9 3 5 Return Shipping Address ssrrnrrennrvrnvnrrnvrvnnvrnnnnvnnnnrnrrrrnrnnrnnrrnsennn 29 9 4 Warranty sereo TiS keea E ES EEEE NEEN EERE 29 Page ii Doc 7430 0280 01 Rev D VG700MB User s Manual C
6. Connect the 9 pin end of the cable to the serial port of your computer via RS422 to RS232 converter not included 3 The additional black and red wires on the cable supply power to the DMU Match red to power and black to ground The input voltage supply for the VG700MB should be 16 32 VDC The current draw is lt 0 25 A at 28 VDC See the specifications for your unit amp WARNING Do not reverse the power leads Applying the wrong power to the DMU can damage the unit Crossbow is not responsible for resulting damage to the unit Doc 7430 0280 01 Rev D Page 3 Crossb w VG700MB User s Manual 2 3 Setup GyroView With the DMU connected to your PC serial port and powered open the GyroView software 1 GyroView should automatically detect the DMU 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 DMU 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 Under DMU or DMU Controls you can set the erection rate and rate sensor zeroing time Enter a value and click the button The value is not sent until the button is clicked
7. as measured by integrating the rate gyros is forced to agree with the direction of vertical as measured by the accelerometers The erection rate is specified in degrees per minute The erection rate must be higher than the Doc 7430 0280 01 Rev D Page 19 Crossb w VG700MB User s Manual drift rate of the rate gyros or the calculated angles will drift off with increasing error If the erection rate is too high however the calculated angles will be forced to follow the accelerometers too closely This will lead to inaccuracies when the unit is under dynamic conditions One way to start is to set the erection rate about twice as fast as the worst rate gyro drift rate This is appropriate for a dynamic environment when the unit will be under significant acceleration Estimate the drift rate by looking at the offset on the rate gyro output Use the zero command first to zero the rate gyros The rate gyro output is in degrees per second the erection rate is set in degrees per minute So take the rate gyro offset multiply by 60 to turn it into degrees per minute multiply by two and use this as a starting value for the erection rate As an example if the rate sensor offset is 0 1 degrees per second we would set the erection rate to 0 1 x 60 x 2 12 The stabilized pitch and roll output will be responsive to actual rotations and relatively insensitive to linear accelerations You can set the T Setting in a qualitative way using GyroView Gra
8. unit to stabilize upon recovery Are you exceeding the range of the rate sensors causing the outputs to over range Whenever the maximum range of the rate sensors is exceeded the VG700MB algorithm strategy is based on the philosophy that any overrange inputs are purely short term disturbances lt 100ms and not commanded inputs In this case the strategy is to allow the angles to be computed through the overrange with any errors that accumulate during the overrange being quickly removed once the input is back within range All output signals continue to be available during the overrange If the rate sensors are overranged for a longer time the error accumulation will be large and may take a long time to recover Do you have extended maneuvers close to the maximum range of the rate sensors Although the VG700MB is rated to operate at 200 deg sec extended maneuvers close to the range should be avoided Prolonged rates close to the maximum range may result in larger errors due to scale factor errors on the rate sensors Do you have heavy EMI interference in the environment Heavy EMI interference can cause a bias shift of the rate sensors and hence continuous drift in calculated angles Before you install the VG700MB in the system by closely watching the rate sensor outputs you can test the effect of different potential EMI contributors strobe lights microwave transmitters alternators radio modems controllers etc by actually
9. using gyros and Bits 6 7 11 accelerometers Notes 1 The Algorithm Validity Status BIT is updated every transmitted serial packet 2 The Accelerometer Failure BIT is only updated after the BIT self test is executed 3 The Gyro Zeroing Validity BIT defaults to the high condition upon power up or any restart of the system The Gyro Zeroing Validity BIT will stay high signifying an invalid gyro zeroing result Performing another gyro zeroing can reset the BIT so the gyro zeroing should be repeated until this bit stays low If the previous zeroing performed was successful the user may choose to ignore the Gyro Zeroing Validity BIT Examples BIT Byte Interpretation 11000000 Pitch and roll at full accuracy everything OK 01000000 Angles based on accelerometer only everything OK 11010000 Pitch and roll at full accuracy Gyro zeroing invalid Accels OK Doc 7430 0280 01 Rev D Page 13 Crossb w VG700MB User s Manual 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 SV 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 fi
10. w Command Character s Sent Response Description Command Character s Sent Response Description VG700MB User s Manual Query Serial Number S Serial number packet 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 Built in Test VG700MB 206 Only B b Built in test performed result in BIT byte of next data packet Delay of 70ms occurs for this test The Gyro zeroing validity bit defaults to the high condition upon power up or any restart of the system If the previous zeroing performed was successful the user may choose to ignore the gyro zeroing validity bit See section 3 5 2 below for definition of BIT word structure Page 12 Doc 7430 0280 01 Rev D VG700MB User s Manual Crossb w Table 2 Bit Message Definition VG700MB 206 Only BIT Data Description Bit Location Accelerometer Accelerometer outputs are incorrect Bit 2 Failure Gyro Zeroing Gyro Zeroing invalid Bit 4 Validity Gyro Zeroing Gyro Zeroing in process Bit 5 Process Algorithm Not valid Bits 6 7 00 Validity Status Pitch and Roll outputs computed Bits 6 7 10 using only accelerometers Not used Bits 6 7 01 Full accuracy data
11. wires are broken out of the cable at the DB 9 connector The red wire is connected to the power supply output the black wire is connected to the power supply ground DO NOT REVERSE THE POWER LEADS 3 3 Interface The VG700MB has a standard RS 422 serial interface The unit is configured with a 38400 baud rate 8 data bits I start bit 1 stop bit no parity and no flow control 3 4 Measurement Modes The VG700MB is designed to operate as a vertical gyro however you can also use it as a six axis sensor The VG700MB 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 422 interface See Data Packet Format 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 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 2 where voltage is the voltage measured at the sensor and data is the value of the unsigned 16 bit integer in the data packet Note that although the d
12. 7 Relative Heading LSB Acceleration X MSB Accel Voltage X MSB 8 Roll Rate MSB Acceleration X LSB Accel Voltage X LSB 9 Roll Rate LSB Acceleration Y MSB Accel Voltage Y MSB 10 Pitch Rate MSB Acceleration Y LSB Accel Voltage Y LSB 11 Pitch Rate LSB Acceleration Z MSB Accel Voltage Z MSB 12 Yaw Rate MSB Acceleration Z LSB Accel Voltage Z LSB 13 Yaw Rate LSB Temp Voltage MSB Temp Voltage MSB 14 X Accel MSB Temp Voltage LSB Temp Voltage LSB 15 X Accel LSB Time MSB Time MSB 16 Y Accel MSB Time LSB Time LSB 17 Y Accel LSB Checksum Checksum 18 Z Accel MSB 19 Z Accel LSB 20 Model Number MSB 21 Model Number LSB 22 BIT MSB 23 BIT LSB 24 Checksum MSB 25 Checksum LSB Page 16 Doc 7430 0280 01 Rev D VG700MB User s Manual Crossb w 3 7 Timing In some applications using the DMU s digital output requires a precise understanding of the internal timing of the device The processor internal to the DMU runs in a loop collecting data from the sensors processing the data then collecting more data The data is reported to the user through a parallel process In continuous mode the system processor activity is repeatable and accurate timing information can be derived based purely on the overall loop rate The unit goes through three processes in one data cycle First the sensors are sampled Second the unit processes the data for output A
13. RR 200 6 1 Digital Output Conversion Data is sent as 16 bit signed integer for all but Temperature Temperature sensor data is sent as unsigned integer Roll Pitch Relative Heading Angle Mode Accel G data GR 1 5 2 1 Angle data 180 2 5 1 Acceleration Rate Temperature Rate s data RR 1 5 2 1 Temperature C data 5 4096 1 375 44 44 Page 24 Doc 7430 0280 01 Rev D VG700MB User s Manual Crossb w 7 Appendix C DMU Command Quick Reference Command Response Description ASCII Pp P R H Ping Pings DMU to verify communications r R Change to Voltage Mode c C Change to Scaled Sensor Mode A Change to Angle Mode VG Mode P None Change to polled mode Data packets sent when a G is received by the DMU C None Change to continuous data transmit mode Data packets streamed continuously Packet rate is dependent on operating mode Sending G stops data transmission G Data Get Data Requests a packet of data from the DMU Packet Data format depends on operating mode T lt 0 255 gt None 2 byte command sequence that changes the vertical gyro erection rate Z lt x gt Z Calibrate and set zero bias for rate sensors by averaging over time The argument of the command lt x gt is a single binary byte that the DMU generally ignores and hence any single byte character can be sent Unit should be still during zeroing However if
14. U Coordinate System The DMU 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 Acceleration is positive when it is oriented towards the positive side of the coordinate axis For example with the DMU 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 In a typical installation this will require the system to mount with the connector facing aft 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 DMU 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 rate and the z axi
15. VG700MB Series User s Manual Models VG700MB 200 VG700MB 206 VG700MB 208 Revision D November 2008 Document 7430 0280 01 Crossb w Crossbow Technology Inc 4145 N First Street San Jose CA 95134 Tel 408 965 3300 Fax 408 324 4840 email info xbow com website www xbow com 2003 2007 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 VG700MB User s Manual Crossb w Table of Contents 1 Introduction eeneeenneennesnnvennvennnennnennnennnennnnnnnnsnnnennnennnesnnennneenenene 1 1 1 The DMU Series Motion and Attitude Sensing Units 1 1 2 Package Contents srronvrerrrrrrrrrrrrrrrrernrernvrrnvrrnversrrrserrsersserssrrnnenn 2 2 Quick Startissuesssssssssdvsssisssassdsassekesddesesednseesesdesssdseddssekbdnssnsden 3 2 1 GyroView Software mmmmrmsrrsrrsvrrvrrsvrnsvrrrsrrrrrsrrrrrsersrernvernr 3 2 1 1 GyroView Computer Requirements 3 2 1 2 Install Gyr View oorennronnnnrnnnnnnrrrnnvnrnnnnrnnvrnnrnnnnnnrnsernnrsnnsnnrsrrsnrnnnnn 3 22 Connections sneonen E E EEEE E ESE tres 3 2 3 SEP GyroViem hisses an sbies deo a E 4 2 4 Take Measurements cccccccscecsceesceesceeeceeceseceseceeecseesseesseeeneeees 4 3 DMU Detallsvisscss
16. a small erection rate you are depending more on the rate gyros than the accelerometers with a large erection rate you are forcing the rate gyros to follow the accelerometer measurement of vertical more closely In general for dynamic measurements you will want a low erection rate But the erection rate should always be greater than the drift rate of the rate gyros The erection rate is discussed in section 4 2 in more detail Page 8 Doc 7430 0280 01 Rev D VG700MB User s Manual Crossb w The VG700MB outputs the pitch roll and relative heading in the digital data packet in angle mode To convert the digital data to angle use the following relation angle data SCALEY 2 1 where angle is the actual angle in degrees either pitch or roll and data is the signed integer data output in the data packet and SCALE is a constant SCALE 180 for roll pitch and relative heading 3 5 Commands The DMUs have a simple command structure You send a command consisting of one or two bytes to the DMU over the serial interface and the DMU will execute the command NOTE The DMU commands are case sensitive GyroView formulates the proper command structures and sends them over the serial interface You can use GyroView to verify that the DMU is functioning correctly GyroView does not use any commands that are not listed here 3 5 1 Command List Command Ping Character s Sent R Response H Description Pings DMU to veri
17. age sent in the DMU data packet The DMU temperature sensor is internal to the DMU and is not intended to measure the ambient temperature The internal temperature of the DMU may be as much as 15 C higher than the ambient temperature Doc 7430 0280 01 Rev D Page 17 Crossb w VG700MB User s Manual 3 9 Adaptive T Algorithm installed at Crossbow factory There is no one optimal erection rate for all environments A high erection rate is better when you are closer to a static situation and a low erection rate is better when you are in a dynamic situation Crossbow has developed an algorithm to automatically switch the erection rate the T parameter based on the dynamics measured by the DMU This algorithm is referred to as adaptive T and is implemented as default at the factory An overview of the algorithm is presented below note that the user still has a certain amount of control over the adaptive T function When the unit is powered up and initialized and the adaptive T Setting feature has been chosen the unit will default to adaptively tune the T Setting between a maximum T Setting of 20 and a minimum T Setting of 1 The user has the ability to change the effect of the adaptive T function through the T Setting command as follows The user selected T Setting sets the upper end of the adaptive T algorithm which then tunes the T Setting between a T Setting of I and the chosen T Setting by scaling the setting based on sensed ac
18. ata is sent as 16 bit integers the data has a resolution of only 12 bits 3 4 2 Scaled Sensor Mode In scaled sensor mode the analog sensors are sampled converted to digital data temperature compensated 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 Six axis measurement system Doc 7430 0280 01 Rev D Page 7 Crossb w VG700MB User s Manual To convert the acceleration data into G s use the following conversion accel data GR 1 5 2 1 where accel is the actual measured acceleration in G s data is the digital data sent by the DMU and GR is the G Range for your DMU The data is scaled so that G 9 80 m s The G range of your DMU is the range of accelerations your DMU will measure For example if your DMU uses a 4 G accelerometer then the G range is 4 To convert the angular rate data into degrees per second use the following conversion rate data AR 1 5y 2 1 where rate is the actual measured angular rate in sec data is the digital data sent by the DMU and AR is the Angular rate Range of your DMU The angular rate range of you
19. bow com 9 3 Return Procedure 9 3 1 Authorization Before returning any equipment please contact Crossbow to obtain a Returned Material Authorization number RMA Be ready to provide the following information when requesting a RMA e Name e Address e Telephone Fax Email e Equipment Model Number e Equipment Serial Number e Installation Date e Failure Date e Fault Description e Will it connect to GyroView Page 28 Doc 7430 0280 01 Rev D VG700MB User s Manual Crossb w 9 3 2 Identification and Protection If the equipment is to be shipped to Crossbow for service or repair please attach a tag TO THE EQUIPMENT as well as the shipping container s identifying the owner Also indicate the service or repair required the problems encountered and other information considered valuable to the service facility such as the list of information provided to request the RMA number Place the equipment in the original shipping container s making sure there is adequate packing around all sides of the equipment If the original shipping containers were discarded use heavy boxes with adequate padding and protection 9 3 3 Sealing the Container Seal the shipping container s with heavy tape or metal bands strong enough to handle the weight of the equipment and the container 9 3 4 Marking Please write the words FRAGILE DELICATE INSTRUMENT in several places on the outside of the shipping container s In all corresponde
20. by an attitude tilt change in the gravity vector or from external translational accelerations For this reason a user selectable erection rate is available which allows for the possibility of a rapidly maneuvering mission There is a tradeoff between how much error in the gyros the algorithm can overcome with a low erection setting compared to the errors induced from having a high erection rate while experiencing large maneuvering accelerations The gyro zeroing command is useful in maintaining the gyro bias errors down to a minimum which allows a lower T Setting to be used during the mission It must be noted that for the zeroing command to work properly there must be no external disturbance to the unit engine noise wind disturbance etc If the user has knowledge of the intensity of upcoming maneuvers or complete control of the flight profile and can maintain constant serial communications with the DMU unit then an adapted erection setting profile can be developed Page 22 Doc 7430 0280 01 Rev D VG700MB User s Manual Crossb w 5 Appendix A Mechanical Specifications 5 1 VG700MB Outline Drawing Hi 40F 150 433 Doc 7430 0280 01 Rev D Page 23 Crossb w VG700MB User s Manual 6 Appendix B DMU Output Quick Reference GR is the G range of the accelerometers For example if your DMU has 4 G accelerometers GR 4 RR is the rate range of the rate sensors For example if your DMU has 200 s rate sensors
21. ccvcccascssssssossccccsssnussincnssssossconsseseascesesscovasseensdiecss 5 3 1 DMU Coordinate System ssrernvrrnvrvnvrnvrrnrrrnrrrnsrrssrrssrrssrrserenesnnn 5 32 COMMECH ONS snsc ierni aiis RER E E EERE RS 5 3 3 Jnt rfac nnna ER E E ERSA 7 3 4 Measurement Modes rrnnrenvrrnvrrnvrrnrrrrnrernrrnnrrnnrnnsrnrssnvssnrsssessneensernn J 3 4 1 Voltage Mode o eeececccecccseesceesceseesceeseesecuaecaeeeseeseceaesaceeseeeeeaeeneeeneeaes 7 3 4 2 Scaled Sensor Mode snrrnvnnnvrrnnrnnnvnnnnvrnnvvrrnvnnevnrenvrrnnrsrsrnnensnrnvessnnn 7 3 4 3 Angle Mode mnnnnnnnnnnvnnnnnnnnnrnvrrnnvnnnnnennrrnnrsnnsnnensrrnarsnnrnnennerrnrsnnsnnenne 8 3 5 Commands inii R RNE 9 3 5 1 Command List sosssiesscncsecsienctavnsesseden iesdeceosvadondadunsostasudesdnieadtihiesdseerse 9 3 6 Data Packet Format ecssicisciiisisisisinesisiieisin seissy 14 3 7 Mist coy Tat ea re rer een terse opens tem ee rreer sce ron eerie tere terrae 17 3 8 Temperature Sensor ss cc scccsetscentsersecessecsdenescntsenntcdsnecssesssaese eben 17 3 9 Adaptive T Algorithm installed at Crossbow factory 18 4 DMU Operating Tips eeooevonvvvnvvennvennvennvenennnennnennnenneennvennenenneee 19 4 1 The Zero Command iisc ciccc ccccccscccsecsacesstcsadecdaetsdectecsaeeddecetseddae 19 4 2 The Erection Rate c cccccciscesssesscceasessdencsaacsaecs cdcoaedsecdsanssessdecases 19 4 3 Mounting the DMU soesnnrnvvenvrenvrrnvrraresrsnsrsnnrsnernvessvrssressrsssernn 21
22. celerations and the yaw gyro measure of the turn rate For instance during large accelerations high G maneuvers or fast turns the T setting will be set to a value of 1 and during low accelerations and straight motion the T Setting will be set to the value chosen by the user In this way the T Setting chosen controls the maximum T Setting that the algorithm will use While the adaptive T algorithm offers a hands off approach to the T Setting problem some control over the algorithm is still allowed The user should still evaluate the performance of the algorithm in each application to achieve the best results Page 18 Doc 7430 0280 01 Rev D VG700MB User s Manual Crossb w 4 DMU Operating Tips 4 1 The Zero Command The z lt x gt command is used to zero the angular rate sensor biases This command does not zero the angle output This should be an essential part of your strategy in using the DMU effectively Stabilized pitch and roll angles are calculated by integrating the output of the angular rate sensors Rate sensors are subject to small offsets in the angular rate measurement A constant offset error in angular rate will integrate into an error in angle that increases linearly with time resulting in angular drift The VG700MB uses accelerometers to correct the calculated angle but in a dynamic situation the accelerometers will be an inaccurate indication of the angle due to motional accelerations The DMU rate s
23. ensors should therefore be zeroed to maintain the best accuracy Zeroing the rate sensors allows you to use a smaller value for the erection rate T Setting which gives you better performance in dynamic environments The rate sensors need to be zeroed more often when subject to large shocks or extremes of temperature The DMU unit should be still motionless during the zeroing process but need not be level You should let the DMU warm up for 5 minutes before issuing the zero command Zeroing the DMU turns on the high pass filter rate bias estimation that takes approximately 3 minutes The zeroing command does not level the stabilized angle output NOTE Remember that the VG700MB stores the rate sensor zero calibration in non volatile memory If you cycle power to the DMU the zero calibration will not be lost However if lt x gt is set to 0 then the previously stored gyro biases are erased The Gyro zeroing validity bit defaults to the high condition upon power up or any restart of the system If the previous zeroing performed was successful the user may choose to ignore the gyro zeroing validity bit If you find that the DMU zeroing algorithm does not work well in your particular application please contact Crossbow to discuss possible options 4 2 The Erection Rate The erection rate parameter controls the weighting between the rate gyro sensors and the accelerometers This is the rate at which the direction of vertical
24. fter processing the data the DMU will make another measurement while presenting the current measurement for output Third the unit actually transfers the data out either over the serial port or onto the analog outputs A time tag is attached to each data packet The time tag is simply the value of a free running counter at the time the A D channels are sampled The clock counts down from 65 535 to 0 and a single tick corresponds to 0 79 microseconds The timer rolls over approximately every 50 milliseconds You can use this value to track relative sampling time between data packets and correlate this with external timing 3 8 Temperature Sensor The DMU has an onboard temperature sensor The temperature sensor is used to monitor the internal temperature of the DMU to allow for temperature calibration of the sensors The sensor is specified to be within 2 accurate over the DMU temperature operating range The DMU reads and outputs the temperature sensor voltage in the digital data packet with 12 bit precision The temperature sensor voltage is sent in the data packet scaled as Viemp V data 5 4096 where data is the 16 bit unsigned integer sent as the temperature information in the data packet The DMU uses two full bytes to express the data but it is really scaled to 12 bits Calculate the temperature with the following calibration T C 44 4 C V Viemp V 1 375 V where Viemp is the temperature sensor volt
25. fy communications 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 Doc 7430 0280 01 Rev D Page 9 Crossb w Description Command Character s Sent Response Description Command Character s Sent Response Description Command Character s Sent Response Description Command Character s Sent Response Description VG700MB User s Manual Changes measurement type to Scaled Mode DMU outputs measurements in scaled engineering units Angle Mode a A Changes measurement type to Angle VG Mode DMU calculates stabilized pitch and roll Also outputs sensor measurements in scaled engineering units Polled Mode P none Changes data output mode to Polled Mode DMU will output a single data packet when it receives a G command Continuous Mode C Data Packets 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 Request Data G Data Packet 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 Page 10
26. ggest a starting point based on past experience with similar applications but you should be prepared to experiment some in the beginning to find the best setup for your DMU in your application Page 20 Doc 7430 0280 01 Rev D VG700MB User s Manual Crossb w 4 3 Mounting the DMU The DMU should be mounted as close to the center of gravity CG of your system as possible This will minimize any lever effect If it is not mounted at the center of gravity then rotations around the center of gravity will cause the DMU accelerometers to measure acceleration proportional to the product of the angular rate squared and the distance between the DMU and the CG The DMU will measure rotations around the axes of its sensors The DMU sensors are aligned with the DMU case You should align the DMU case as closely as possible with the axes you define in your system Errors in alignment will contribute directly into errors in measured acceleration and rotation relative to your system axes The sides of the DMU case are used as reference surfaces for aligning the DMU sensor axes with your system The DMU should be isolated from vibration if possible Vibration will make the accelerometer readings noisy and can therefore affect the angle calculations In addition if the magnitude of the vibration exceeds the range of the accelerometer the accelerometer output can saturate This can cause errors in the accelerometer output The DMU case is weathe
27. low power fast turn on reliable and accurate solutions for a wide variety of stabilization and measurement applications The VG700MB product has an RS 422 serial link Data may be requested via the serial link as a single measurement or streamed continuously The Crossbow DMUs employ on board digital processing to provide application specific outputs and to compensate for deterministic error sources within the unit The DMUs accomplish these tasks with an analog to digital converter and a high performance Digital Signal Processor The VG700MB uses three micro electro mechanical machined MEMS accelerometers and three fiber optic gyro FOG angular rate sensors The three MEMS accelerometers are surface micro machined silicon devices that use differential capacitance to sense acceleration These solid state MEMS sensors are responsive and reliable The FOG rate sensors provide angular rate measurements that are more accurate and subject to less drift than the silicon based rate sensors Doc 7430 0280 01 Rev D Page 1 Crossb w VG700MB User s Manual 1 2 Package Contents In addition to your DMU sensor product you should have e 1 CD with GyroView Software GyroView version 2 5 or greater will allow you to immediately view the outputs of the DMU on a PC running Microsoft Windows You can also download this software from Crossbow s web site at http www xbow com e 1 Digital Signal Cable This links the VG700MB directly to a se
28. nce please refer to the equipment by the model number the serial number and the RMA number 9 3 5 Return Shipping Address Use the following address for all returned products Crossbow Technology Inc 4145 N First Street San Jose CA 95134 Attn RMA Number XXXXXX 9 4 Warranty The Crossbow product warranty is one year from date of shipment Doc 7430 0280 01 Rev D Page 29 Crossb w Crossbow Technology Inc 4145N First Street San Jose CA 95134 Phone 408 965 3300 Fax 408 324 4840 Email info xbow com Website www xbow com
29. operating them Move the VG700MB to a location where effects of such interferences are within the acceptable accuracy Page 26 Doc 7430 0280 01 Rev D VG700MB User s Manual Crossb w Is the vibration isolation adequate Large amounts of vibration will make the accelerometer readings noisy and thereby may affect the angle calculations In addition if the magnitude of the vibration exceeds the range of the accelerometer the accelerometer output can saturate This can cause errors in the accelerometer output and in turn the estimated angles The VG700MB must be installed in a location that is rigid enough to alleviate potential vibration errors induced from normal airframe vibration sources You can use vibration isolators if needed to dampen out the unwanted vibrations Doc 7430 0280 01 Rev D Page 27 Crossb w VG700MB User s Manual 9 Appendix E Warranty and Support Information 9 1 Customer Service As a Crossbow Technology customer you have access to product support services which include e Single point return service e Web based support service e Same day troubleshooting assistance e Worldwide Crossbow representation e Onsite and factory training available e Preventative maintenance and repair programs e Installation assistance available 9 2 Contact Directory United States Phone 1 408 965 3300 8 AM to 5 PM PST Fax 1 408 324 4840 24 hours Email techsupport xbow com Non U S refer to website www x
30. ph the pitch and roll Start with the T Setting at about 100 Lower the T Setting in increments of 10 20 until the roll and or pitch starts to drift When the angle outputs start to drift the T Setting is just a bit lower than the rate sensor offset Increase the T Setting by about 5 This should keep the angle outputs stable If you expect the DMU to be subject to changing temperatures or to have to operate for long periods without re zeroing you should increase the T Setting further You may have to experiment some to find the best erection rate for your situation If the DMU is used in a less dynamic environment the erection rate can be set much higher The DMU angles will stabilize quicker to the gravity vector So if the motion is slow or if you sit in one position for a long time then you should probably use a high erection rate A more advanced approach to the erection rate would take advantage of both regimes of operation Use a low erection rate when the unit is subject to dynamic motion use a high erection rate when the unit is relatively stable You can use the DMU itself to distinguish between the two cases by looking for changes in the accelerometer outputs For example in an airplane you could use a low erection rate when the airplane executes a banked turn and a high erection rate 100 when the plane is flying straight and level Unfortunately there is no single ideal erection rate for all applications We can su
31. r DMU is the range of angular rates your DMU will measure For example if your DMU uses a 200 s rate sensor then AR range is 200 3 43 Angle Mode In angle mode the DMU will act as a vertical gyro and output the stabilized pitch and roll angles along with the angular rate and acceleration information The angular rate and acceleration values are calculated as described in the scaled sensor mode It will also provide the relative heading calculation output In angle mode the DMU uses the angular rate sensors to integrate over your rotational motion and find the actual pitch and roll angles The DMU uses the accelerometers to correct for the drift in the rate sensors 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 uses the accelerometers to provide long term stability to keep the rate gyro drift in check The DMU gives you control over the weighting between the accelerometers and rate gyros through a parameter called the erection rate This term is derived from analog vertical gyros and refers to the rate at which the system can pull the gyro spin axis back to vertical as measured by gravity With
32. r proof WARNING Although the DMU is rated and tested for operating temperatures from 40 C to 71 C the temperature ramp rate must be limited to within 5 C minute The higher ramp rate could potentially result in permanent damage to the sensors M EXAMPLE 4 4 DMU Start Up Procedure As an example let s look at how the DMU might be used on an airplane Assume a VG700MB is mounted on a small twin prop plane and will be used to record the plane s attitude during flight The VG700MB is mounted near the CG of the plane and is connected to a laptop serial port during flight 1 Turn on power to the DMU and let it warm up 5 10 minutes Power can be on to all electronics but the engines should be off 2 Zero the rate sensors if you haven t already done previously Engines are off so there is no vibration Start the engines Start data collection Proceed with flight Doc 7430 0280 01 Rev D Page 21 Crossb w VG700MB User s Manual 4 5 Advanced Strategies for Adjusting the Erection Rate The DMU attitude estimation algorithm is divided into two separate entities Gyro angular rate information is integrated in time to propagate the DMU body attitude with respect to the tangent plane If the initial attitude of the vehicle was known exactly and if the gyros provided perfect readings then this integration process would suffice However the initial state is seldom known to great precision especially a vehicle s atti
33. rial port via RS422 to RS232 converter Only the transmit receive power and ground channels are used e 1 VG700MB User s Manual This contains helpful hints on programming installation valuable digital interface information including data packet formats and conversion factors Page 2 Doc 7430 0280 01 Rev D VG700MB User s Manual Crossb w 2 Quick 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 e CPU Pentium class e RAM Memory 64MB minimum 128MB recommended e Hard Drive Free Memory 20MB e Operating System Windows 2000 XP 2 1 2 Install GyroView To install GyroView in your computer I Putin CD Support Tools 2 Find the GyroView folder Double click on the setup file 3 Follow the setup wizard instructions You will install Gyro View and a LabVIEW Runtime Engine You need both 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 COM port via RS422 to RS232 converter 1 Connect the 22 pin end of the digital signal cable to the port on the DMU 2
34. rossb w About this Manual The following annotations have been used to provide additional information NOTE Note provides additional information about the topic M EXAMPLE Examples are given throughout the manual to help the reader understand the terminology IMPORTANT This symbol defines items that have significant meaning to the user 6 WARNING 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 Doc 7430 0280 01 Rev D Page iii VG700MB User s Manual Crossb w 1 Introduction 1 1 The DMU Series Motion and Attitude Sensing Units This manual explains the use of the VG700MB Series of products The VG700MB is a six axis dynamic measurement unit DMU designed to measure linear acceleration along three orthogonal axes and rotation rates around three orthogonal axes It uses three accelerometers and three angular rate sensors to make a complete measurement of the dynamics of your system In addition it is designed to provide stabilized pitch and roll in dynamic environments The VG700MB is the solid state equivalent of a vertical gyro artificial horizon display The VG700MB 206 also includes a relative heading output based upon yaw gyro information The DMU series products are
35. rst 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 DMU 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 contents except header and checksum 2 Divide the sum by 256 3 The remainder should equal the checksum The packet also contains the model type configuration number and the BIT word output Please refer to section 3 5 2 for details about the BIT word processing In scaled and voltage mode 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 contents except header and checksum 2 Divide the sum by 255 3 The remainder should equal the checksum Tables 3 and 4 show the data packet format for each mode Page 14 Doc 7430 0280 01 Rev D VG700MB User s Manual Crossb w Table 3 Data Packet Format VG700MB 200 and VG700MB 208 Byte VG Mode Scaled Sensor Mode Voltage Mode 0 Header 255 Header 255 Header 255 1 Roll Angle MSB Roll Rate MSB Gyro Voltage X MSB 2 Roll Angle LSB Roll Rate LSB Gyro Voltage X LSB 3 Pitch Angle MSB Pitch Rate MSB Gyro Voltage Y MSB 4 Pitch Angle LSB Pitch Rate
36. s sensor would measure a positive angular rate 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 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 then yaw 3 2 Connections The VG700MB has a male 22 pin circular connector The signals are as shown in Table 1 Doc 7430 0280 01 Rev D Page 5 Crossb w VG700MB User s Manual Table 1 VG700MB Connector Pin Out Pin Signal RS 422 Transmit 2 RS 422 Transmit 3 RS 422 Receive 4 Power Input Ground 5 Positive Power Input 6 Do Not Connect 7 Factory Use Only 8 Factory Use Only 9 Factory Use Only 10 Factory Use Only 11 Factory Use Only 12 Factory Use Only 13 Factory Use Only 14 Factory Use Only 15 Do Not Connect 16 RS 422 Receive 17 Signal Ground 18 Factory Use Only 19 Do Not Connect 20 Case Ground 21 Factory use only 22 Do Not Connect Page 6 Doc 7430 0280 01 Rev D VG700MB User s Manual Crossb w The VG700MB serial interface connection is standard RS 422 Power is applied to the DMU on pins 4 and 5 Pin 4 is ground Pin 5 should have 16 32 VDC unregulated at 0 5 A If you are using the cable supplied with the DMU the power supply
37. tude and the gyros usually provide corrupted data Rate gyro bias bias drift misalignment acceleration G sensitive nonlinear square term and scale factor errors will be present in the angular rate measurements The largest error is typically associated with the bias and bias drift terms Without a correction algorithm and separate independent sensors the attitude estimation algorithm would diverge off the true trajectory Accelerometers provide the separate measurements which help keep the attitude estimates on track The correction algorithm involves deriving an estimate of the roll and pitch angle from the accelerometer s gravity reference comparing this estimate to the gyro propagated quaternion Euler angles and providing a linear feedback gain to the quaternion propagation to take out the errors observed from the gyro angular rate measurements The correction feedback is also referred to as the erection rate implying that the attitude errors are erected out by moving the estimated orientation more towards the absolute attitude measurements derived from the accelerometer measurements It is also given the name T Setting to describe the user interface which allows the user to command the DMU to use a desired erection rate Sensed dynamic accelerations can introduce error into the accelerometer absolute attitude reference The angle calculation algorithm has no way of knowing whether the sensed acceleration change is being caused
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