VG700AA User`s Manual
Contents
1. 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 Let the DMU warm up for 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 Page 4 Doc 7430 0074 01 Rev A VG700AA User s Manual Crossbow during zeroing operation The zero command is discussed more in The Zero Command section Now you re ready to use the DMU Doc 7430 0074 01 Rev A Page 5 Crossbow VG700AA User s Manual 3 DMU Details 3 1 DMU Coordi2. degrees per minute For example if you wanted Doc 7430 0074 01 Rev A VG700AA User s Manual Command Character s Sent Response Description Command Character s Sent Response Description Command Character s Sent Response Description Doc 7430 0074 01 Rev A Crossbow 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 ignores and is part of the legacy code any single byte character can be sent The zeroing command turns on the high pass filter rate estimation that takes approximately 3 minutes 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 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 Pag
3. s use the following conversion accel G Vour V bias V sensitivity G V where accel is the actual acceleration measured Vout is the voltage at the analog output bias is the zero G bias voltage and sensitivity is the scale factor in units G volts Doc 7430 0074 01 Rev A Page 19 Crossbow VG700AA User s Manual For example if the x axis of your accelerometer has a zero G bias of 2 512 V a sensitivity of 1 01 G V and you measure 2 632 V at the analog output the actual acceleration is 2 632 V 2 512 V 1 01 G V 0 121 G The raw accelerometer voltages will always be available on pins 5 7 3 9 2 Scaled Accelerometer Voltage In scaled mode the DMU will create scaled analog accelerometer voltages on pins 12 14 In scaled mode these accelerations will always be in the DMU body frame These analog voltages reflect any calibration or correction the DMU applies to the accelerometer data The analog voltage is created by an internal D A converter using the digital data available to the DSP The data is scaled to the range 4 096 V with 12 bit resolution You do not need to use the calibration data that came with the DMU to use these outputs the DMU is already applying the calibration stored in its EEPROM to the data To find the acceleration in G s use the following conversion accel G GR 1 5 Vout V 4 096 V where accel is the actual acceleration measured Vout is the voltage at the analog output
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5. 7 Z axis accelerometer raw Accelerometer Scaled Mode only Accel G Vout V GR 1 5 4 096 Pin 12 X axis accelerometer Pin 13 Y axis accelerometer Pin 14 Z axis accelerometer Rate Sensor Angle Mode only Accel G Vout V RR 1 5 4 096 Pin 8 Roll rate sensor Pin 9 Pitch rate sensor Pin 10 Yaw rate sensor Page 32 Rate Sensor Scaled Mode Only Rate s Vout V RR 1 5 4 096 Pin 8 Roll rate sensor Pin 9 Pitch rate sensor Pin 10 Yaw rate sensor Roll Pitch Angle Mode only Angle Vout V 90 4 096 Pin 12 Roll Angle Pin 13 Pitch Angle Doc 7430 0074 01 Rev A VG700AA User s Manual Crossbow 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 Japan 06 6489 5868 email info xbow jp 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 Equipm
6. acquisition device 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 VG700AA 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 1 2 Package Contents In addition to your DMU sensor product you should have e 1 CD with GyroView Software Doc 7430 0074 01 Rev A Page 1 Crossbow VG700AA User s Manual Page 2 GyroView 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 1 Digital Signal Cable This links the DMU directly to a serial port Only the transmit receive power and ground channels are used The analog outputs are not connected 1 DMU Calibration Sheet The Digital Calibration Sheets contains the custom offset and sensitivity information for your DMU The calibration sheet
7. and GR is the G range of your sensors The G range is listed on the calibration sheet For example if your DMU has 2 G accelerometers GR is 2 In angle mode the X Y and Z acceleration measurements will be output on pins 8 9 and 14 For model 201 the acceleration reported will be in the earth level frame for model 202 the acceleration reported will be in the DMU body frame 3 9 3 Scaled Rate Sensor Voltage The DMU will output analog voltages representing the rate sensor measurement on pins 8 10 in scaled sensor mode In angle mode only the yaw rate sensor will be output on pin 10 The analog outputs for the angular rate signals are not taken directly from the rate sensors they are created by a D A converter internal to the DMU The output range is 4 096V with 12 bit resolution The analog data will represent the actual measured quantities in engineering units not the actual voltage at the sensor output To convert the analog output to a sensor value use the following relation rate RR 1 5 Vou V 4 096 V where rate is the actual measured rate in units s RR is the angular rate range of your sensor and Vout is the measured voltage at the analog output Page 20 Doc 7430 0074 01 Rev A VG700AA User s Manual Crossbaw NOTE RR is 200 for all VG700AAs 3 9 4 Stabilized Pitch and Roll Voltages In angle mode the DMU outputs the stabilized pitch and roll angle analog voltages on pins 12 and 13 The ana
8. is not needed for normal operation as the DMU has an internal EEPROM to store its calibration data However this information is useful when developing your own software to correctly scale the output data Save this page 1 DMU Users Manual This contains helpful hints on programming installation valuable digital interface information including data packet formats and conversion factors Doc 7430 0074 01 Rev A VG700AA User s Manual Crossbow 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 32MB minimum 64MB recommended e Hard Drive Free Memory 15MB e Operating System Windows 95 98 NT4 2000 2 1 2 Install GyroView To install GyroView in your computer 1 Insert the CD Support Tools in the CD ROM drive 2 Find the GyroView folder Double click on the setup file 3 Follow the setup wizard instructions You will install GyroView and a LabView 6 Runtime Engine You will need both these applications If you have any problems or questions you may contact Crossbow directly 2 2 Connections The DMU is shipped
9. of the highly dynamic environment A high erection rate would result in very large errors during the high acceleration maneuvers a low erection rate might not recover from a large gyro bias drift or saturation of the rate sensors because of very large dynamics Since every flight profile is different this approach necessitates careful erection rate profile planning If enough care is taken active control of the erection rate will provide the best performance Page 26 Doc 7430 0074 01 Rev A VG700AA User s Manual Crossbew 5 Appendix A Mechanical Specifications 5 1 VG700AA Outline Drawing ak HR HP Doc 7430 0074 01 Rev A Page 27 Crossbow VG700AA User s Manual 6 Appendix B DMU Output Quick Reference GR is the G range of the accelerometers For example if your DMU has 2 G accelerometers GR 2 RR is the rate range of the rate sensors RR 200 for all VG700A As 6 1 Analog Output Conversion NOTE See Appendix D for the Analog Output Conversion for Model VG700AA 202 Accelerometer Raw output Use sensitivity offset from calibration sheet Output is raw sensor voltage Pin 5 X axis accelerometer raw Pin6 Y axis accelerometer raw Pin 7 Z axis accelerometer raw Accelerometer Scaled Mode only Accel G Vout V GR 1 5 4 096 Pin 12 X axis accelerometer Pin 13 Y axis accelerometer Pin 14 Z axis accelerometer Accelerometer Angle Mode only Accel G Vout V GR
10. 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 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 Doc 7430 0074 01 Rev A Page 23 Crossbow VG700AA User s Manual 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 not weather proof You shou
11. the axis in a positive direction your fingers curl around in the positive rotation direction For example if the DMU 1s 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 axis 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 and then yaw The VG700AA coordinate definition is consistent with the SAE J670e convention on vehicle coordinate systems See Table 1 Page 6 Doc 7430 0074 01 Rev A VG700AA User s Manual Crossbew Table 1 VG700AA Submodel Definitions of Acceleration Output Acceleration Coordinate Sign SUM ode Frame positive SAE 3 2 Connections VG700AA has a male DB 15 connector The signals are as shown in Table 2 All analog outputs are fully buffered and are designed to interface directly to data acquisition equipment See Analog Output for details 15 Pin T Connector Male Pincas 0 6 6 6 6 6 6 6 v v vB j NOTE See Appendix D for the correct pin out for Model VG700AA 202 Doc 7430 0074 01 Rev A Page 7 Crossbow VG
12. 1 5 4 096 Pin 8 X axis accelerometer Pin 9 Y axis accelerometer Pin 14 Z axis accelerometer Page 28 Rate Sensor Scaled Mode Only Rate s Vout V RR 1 5 4 096 Pin 8 Roll rate sensor Pin 9 Pitch rate sensor Pin 10 Yaw rate sensor Rate Sensor Angle Mode Only Rate s Vout V RR 1 5 4 096 Pin 10 Yaw rate sensor Roll rate and Pitch rate not available in Angle Mode Roll Pitch Angle Mode only Angle Vout V 90 4 096 Pin 12 Roll Angle Pin 13 Pitch Angle Doc 7430 0074 01 Rev A VG700AA User s Manual 6 2 Digital Output Conversion Crossbow Data is sent as 16 bit signed integer for all but Temperature Temperature sensor data is sent as unsigned integer Acceleration Accel G data GR 1 5 2 Rate Rate s data RR 1 5 2 Doc 7430 0074 01 Rev A Roll Pitch Angle Mode Angle data 180 2 Temperature Temperature C data 5 4 096 1 375 44 44 Page 29 Crossbow VG700AA User s Manual 7 Appendix C DMU Command Quick Reference RJM Prrengsomsiovereommunenene R cumovageme Change to polled mode Data packets sent when a G is received by the DMU Change to continuous data transmit mode Data packets streamed continuously Packet rate is dependent on operating mode Sending G stops data transmission Calibrate and set zero bias for rate s ensors by averaging over time The argument of the command lt x gt is
13. 3 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 The DMU analog outputs are enabled in this mode including stabilized pitch and roll angles See the Analog Output section for a complete description of the analog outputs 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 Doc 7430 0074 01 Rev A Page 11 Crossbow VG700AA User s Manual The DMU uses the accelerometers to provide long termstability 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 ba
14. 700AA User s Manual Table 2 DMU Connector Pin Out Models VG700AA 201 p Pin signe Positive Power Input 0 I z E 4 E Notes 1 The accelerometer analog voltage outputs are the raw sensor output These outputs are taken from the output of the accelerometers 2 The accelerometer analog output voltages are scaled to represent g s The acceleration data is transformed from body coordinates to the earth level frame coordinates These outputs are created by a D A converter 3 The yaw rate sensor analog voltage output is scaled to represent s This output is created by a D A converter 4 The pitch and roll angle analog outputs are scaled to represent degrees These outputs are created by a D A converter Page 8 Doc 7430 0074 01 Rev A VG700AA User s Manual Crossbow The serial interface connection is standard RS 232 On a standard DB 25 COM port connector make the connections per Table 3 Table 3 DB 25 COM Port Connections COM Port Connector a DMU Connector GE ELLE o TxD Note Pin 4 on the DMU is data ground as well as power ground On a standard DB 9 COM port connector make the connections per Table 4 Table 4 DB 9 COM Port Connections COM Port Connector a DMU Connector 00 e mw ee Jar ll low Note Pin 4 on the DMU is data ground as well as power ground Power is applied to the DMU on pins 3 and 4 Pin 4 is ground Pin 3 should have 10 to 30 VDC unregulated at 0 75 A
15. Appendix D VG700AA 202 Analog Outputs eecossvesseesesees 31 8 1 Model VG700AA 202 Connector Pin Out srerennrenvvrnnrvenvesenseennernn 31 8 2 Model VG700AA 202 Analog Output Conversion 1 32 9 Appendix E Warranty and Support Information 33 9 1 Customer SEN Loren 33 9 2 COMPACT Die TOY EEE AR RE oE 33 9 3 Return PV OCS CUES os da veec arenes consautaucercnncwsrsaetantsns ERR ESSENSEN 33 93 1 AUOT O ERE EE 33 252 Identification and Protection srnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn 34 9 3 3 Sealing th Container xx ao SEE DEREK NAS 34 9 3 4 Ge LO ERE EN 34 9 3 5 Return Shipping Address errnnrrnnnrnrrnnnnrrrnnnnnnnnnnnnrrnrvnrnnnnnsnrnnnnnneneee 34 Ve 34 Page ii Doc 7430 0074 01 Rev A VG700AA User s Manual Crossbaw About this Manual The following annotations have been used to provide additional information NOTE Note provides additional information about the topic vi 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 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 0074 01 Rev A Pa
16. If you are using the cable supplied with the DMU the power supply wires are broken out of the cable at the DB 9 connector The red wire is connected to the positive power input the black wire is connected to the power supply ground DO NOT REVERSE THE POWER LEADS The analog outputs are unconnected in the cable we supply The analog outputs are fully buffered and conditioned and can be connected directly to an A D The analog outputs have a I kQ resistor in series with each output to protect the outputs from a short circuit This should be taken into account when using data acquisition devices with moderate input impedances less than 10 KQ Doc 7430 0074 01 Rev A Page 9 Crossbow VG700AA User s Manual 3 3 Interface The serial interface is standard RS 232 38400 baud 8 data bits I start bit I stop bit no parity and no flow control Crossbow will supply DMU communication software examples written in LabView Source code for the DMU serial interface can be obtained via the web at http www xbow com The source code has a vi file format and requires a National Instruments LabView 5 0 license to use 3 4 Measurement Modes The VG700AA is designed to operate as a vertical gyro however you can also use it as a six axis sensor The VG700AA can be set to operate in one of three modes voltage mode scaled sensor mode or angle VG mode The DMU must be in VG mode to output the acceleration data in the earth level reference fra
17. NE eee senere 18 3 8 Temperature Sheep 18 3 9 MIT Et eaer EEEE 19 3 9 1 Raw Accelerometer Voltage rrmrrrrrnrrrrnrnnnnnnnnnnrnnrrrrnvrnrernnnnnnenerr 19 3 9 2 Scaled Accelerometer Voltage rrrrrrnnnnnrvnnnnnrrnnnnnnnnnenenrnrrrrnnnnnvnnnnn 20 3 9 3 Scaled Rate Sensor Voltage rrrrnnnnnnnnnnnrnnrnnrnrnnnnnnnnnennnrerrrrnnnnnsnnnnn 20 3 9 4 Stabilized Pitch and Roll Voltages rrrnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn 21 3 10 Adaptive T Algorithm installed at Crossbow factory 21 4 DMU MIN 22 4 1 The 20 Command sesasi El oe 22 4 2 The Fe Re 22 Doc 7430 0074 01 Rev A Page i Crossbow VG700AA User s Manual 4 3 Mounting the DMU Grease 23 4 4 DMU Start Up Proces CULE accra civoussicdniiesiannsusencsntsaceadsenctewnsndsadetautastennsncees 24 4 5 Advanced Strategies for Adjusting the Erection Rate 24 4 6 Adapted Flight Profile T Setting 0 eeseesesseeetessteeseeseeeseeeees 25 5 Appendix A Mechanical Specifications scccsscssssees 27 5 1 VG700AA Outline Drawing sresonveenvrennvesnvrsnnsesnvssensssnnsennsssnvssnnsesnnenen Zi 6 Appendix B DMU Output Quick Reference 6 28 6 1 Analog Output Conversion s esesssessesssrssreseeseersesssessesseeseeseresressesee 28 6 2 Digital Output CoOnversion ssersnvernverenrrennerenrssnverensvsnrssnnrsensssnnsssnsesen 29 7 Appendix C DMU Command Quick Reference 30 8
18. VG700AA User s Manual VG700AA DMU FOG AUTO Rev A September 2002 Document 7430 0074 01 2002 2003 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 VG700AA User s Manual Crossb w Table of Contents LT 1 1 1 The DMU Series Motion and Attitude Sensing Units 1 12 Package COMES Luer i 2 Ot 3 2 Gyro View SOTEW ANC ne ann Ee EEA a E EE 3 2 1 1 GyroView Computer Requirements cccccccccscccccccscccecceesceeseceeeeeeeess 3 Ve Install GyroView orrornnnrnnnnnnnnnnrnnnrornnrnnnnnnnnnnnnnnnnnesenrnrnnnnnnnnnnnnnnnnnnene 3 22 ENN 3 23 FONN 4 2 4 Take Measurements rrrrnnnrrnrrnnnnnnnsernnnnnnsrnnnnnnnennnvnennnnnnrnnnsnnnnnnesennnnnessenns 4 3 DMU DG tal S eieren 6 3 1 DMU Coordinate Syse ssc sccesstacnseassaccdaceedes vacesebenscashiastacie stander intense 6 3 2 Ce EE SEERE REESE aise 7 3 3 Mi 10 3 4 Measurement Modes rrronnnrronnnrnrnnnnrrrennrnsnnnrnernnnnessennnesnnnressnnnnssnnnnsnnnn 10 3 4 1 LAL EEE EEE 10 3 4 2 Scaled SCNSOT NTG 10 3 4 3 MMS II 3 5 COMIN ATIGS 52h seo ssissecbassaenancancesvanstacseenseasesasieanasaeacoosnnaeineeeevenoeeasneiaeys 12 3 5 1 COT EEE ENE 13 3 6 Data Packet POT ab air 16 3 7 PUPA EEE
19. a single binary byte that the DMU ignores and is part of the legacy code any single byte character can be sent Unit should be still during zeroing Query DMU serial number Returns serial number as 32 bit binary number Query DMU version ID string Returns ASCII string Note argument of command is sent as a single hex byte not as an ASCII character Page 30 Doc 7430 0074 01 Rev A VG700AA User s Manual Crossbaw 8 Appendix D VG700AA 202 Analog Outputs 8 1 Model VG700AA 202 Connector Pin Out p Pin 8g Positive Power Input 5 e VarsecslrometerAnaogvolege e oeo e memon Notes 1 The accelerometer analog voltage outputs are the raw sensor output These outputs are taken from the output of the accelerometers 2 The rate sensor analog voltage output is scaled to represent s This output is created by a D A converter 3 The pitch and roll angle analog outputs are scaled to represent degrees These outputs are created by a D A converter Doc 7430 0074 01 Rev A Page 31 Crossbow VG700AA User s Manual 8 2 Model VG700AA 202 Analog Output Conversion GR is the G range of the accelerometers For example if your DMU has 2 G accelerometers GR 2 RR is the rate range of the rate sensors RR 260 for all VG700A As Accelerometer Raw output Use sensitivity offset from calibration sheet Output is raw sensor voltage Pin 5 X axis accelerometer raw Pin6 Y axis accelerometer raw Pin
20. after the data processing step is over In the case of the digital data the data is transferred only if the previous data packet is cleared 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 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 accurate within 2 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 C V Viemp V 1 375 V where Viemp is the temperature sensor voltage sent in the DMU data packet Page 18 Doc 7430 0074 01 Rev A VG700AA User s Manual Crossbaw The DMU temperature sensor is internal to the DMU and is not intended to measure the ambient te
21. aled 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 Page 13 Crossbow Command Character s Sent Response Description Command Character s Sent Response Description Command Character s Sent Response Description Command Character s Sent Response Description Page 14 VG700AA User s Manual 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 DMU a G 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
22. ccelerations 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 no external disturbance to the unit engine noise wind disturbance etc and it would be advised to perform a gyro zeroing in the initial phase of the mission when only electrical power is available 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 An example follows vi EXAMPLE 4 6 Adapted Flight Profile T Setting 1 Vehicle electric power is applied to the DMU while the vehicle is out of external disturbances within the hanger for instance Doc 7430 0074 01 Rev A Page 25 Crossbow VG700AA User s Manual 2 Following a warm up period 10 minutes should suffice a gyro zeroing command is sent to the unit to average out the gyro biases 3 Senda T setting command t
23. ck to vertical as measured by gravity With 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 1s discussed in section 4 2 in more detail The VG700AA outputs the pitch and roll angles in the digital data packet in angle mode To convert the digital data to angle use the following relation angle data SCALE 2 where angle is the actual angle in degrees either pitch or roll datais the signed integer data output in the data packet and SCALE is a constant SCALE 180 for roll and pitch With the VG700AA 201 in angle mode the acceleration measurements will be rotated into the earth level coordinate frame This is the acceleration that would have been measured if the DMU was kept level relative to the gravity The DMU uses its pitch and roll angle measurement to translate the acceleration between the DMU body frame and the level frame You can check this by graphing the acceleration output and slowly tilting the DMU You will see that the X and Y axis components of acceleration remain near zero while the Z axis component stays at I g If you have a VG700A A 202 the acceleration measurement will a
24. e 15 Crossbow VG700AA 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 O 5 V In scaled and angle mode the data generally represents a quantity that can be positive or negative These numbers are sent as a 16 bit signed integer in 2 s complement format The data is sent as two bytes MSB first then LSB In scaled and angle mode the timer information and temperature sensor voltage are sent as unsigned integers The order of data sent will depend on the selected operating mode of the DMU Each data packet will begin with a header byte 255 and end with 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 Table 5 shows the data packet format for each mode Page 16 Doc 7430 0074 01 Rev A VG700AA User s Manual Crossbaw Table 5 Data Packet Format v1 2 EN Header 255 Header 255 Header 255 1 Roll Angle MSB Roll Rate MSB 2 Roll Angle LSB Roll Rate LSB Pitch Angle MSB Pitch Rate MSB Gyro Voltage Y MSB Pitch Angle LSB Pitch Rate LSB Gyro Voltage Y LSB Roll Rate MSB Yaw Rate MSB Gyro Voltage Z MSB Roll Rate LSB Yaw Rate LSB Gyro Voltage Z LSB Ya
25. ent Serial Number e Installation Date e Failure Date e Fault Description e Will it connect to GyroView Doc 7430 0074 01 Rev A Page 33 Crossbow VG700AA User s Manual 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 93 4 Marking Please write the words FRAGILE DELICATE INSTRUMENT in several places on the outside of the shipping container s In all correspondence please refer to the equipment by the model number the serial number and the RMA number 93 5 Return Shipping A New unit warranty in J apan is 6 month Consult Silicon Sensing Sys J apan at SSSJ Spp co jp or phone 06 6489 5868 Page 34 Doc 7430 0074 01 Rev A Crossb w Crossbow Technology Inc
26. ge iii Crossbow VG700AA User s Manual Page iv Doc 7430 0074 01 Rev A VG700AA User s Manual Crossbaw 1 Introduction 1 1 The DMU Series Motion and Attitude Sensing Units This manual explains the use of VG700AA The VG700AA is a Crossbow Technology Dynamic Measurement Unit DMU designed for automotive testing and measurements The VG700AA is a six axis measurement system designed to measure linear acceleration along three orthogonal axes and rotation rates around three orthogonal axes This device 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 VG700AA is the solid state equivalent of a vertical gyro artificial horizon display The VG700AA has the unique ability to use the stabilized angle information to translate the acceleration measurement fromthe DMU body frame to the local earth level frame This removes the effect of tilt and gravity from the accelerations reported The DMU series units are low power fast turn on reliable and accurate solutions for a wide variety of stabilization and measurement applications All DMU products have both an analog output and an RS 232 serial link Data may be requested via the serial link as a single measurement or streamed continuously The analog outputs are fully signal conditioned and may be connected directly to a data
27. 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 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 Page 22 Doc 7430 0074 01 Rev A VG700AA User s Manual Crossbaw 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 Graph the pitch and roll Zero the rate sens
28. isalignment 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 by an attitude tilt change in the gravity vector or from external translational a
29. ld protect the DMU from moisture and dust vi EXAMPLE 4 4 DMU Start Up Procedure As an example look at how the DMU might be used in a car Assume a VG700AA is mounted in an automobile and will be used to record the vehicle s attitude during a drive The test will be about hour long The VG700AA is mounted near the CG of the vehicle and is connected to a laptop serial port during the test 1 Turn on power to the DMU and let it warm up 5 10 minutes Power can be on to all electronics but the car engine should be off if it causes vibration to the DMU Zero the rate sensors The engine is off so there is no vibration 3 Change the T Setting After zeroing you should be able to set the T Setting in the range 5 10 fora VG700AA Start the engine 5 Start data collection 6 Proceed with test 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 Page 24 Doc 7430 0074 01 Rev A VG700AA User s Manual Crossbow known to great precision especially a vehicle s attitude and the gyros usually provide corrupted data Rate gyro bias bias drift m
30. log pitch and roll outputs are created by the DMU internal D A The voltage output will be in the range 4 096 V with 12 bit resolution The output is scaled so that full scale is 90 for both roll and pitch To convert the voltage to an actual angle use the following conversion angle 90 Vout V 4 096 V where angle is the actual pitch or roll angle in degrees and Vout is the analog pitch or roll voltage measured 3 10 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 0 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
31. lways be reported in the DMU body coordinate frame The DMU will output the actual acceleration measured along each coordinate axis You can check this by graphing the acceleration output and slowly tilting the DMU You will see that the X or Y axis component of acceleration will go towards g depending on which axis you tilt the unit while the Z axis component goes to Og 3 5 Commands The VG700AA has a simple command structure You send a command consisting of one or two bytes to the DMU over the RS 232 interface and the DMU will execute the command NOTE The DMU commands are case sensitive Page 12 Doc 7430 0074 01 Rev A VG700AA User s Manual Crossbow Gyro View is a very good tool to use when debugging your own software GyroView formulates the proper command structures and sends them over the RS 232 interface You can use GyroView to verify that the DMU is functioning correctly GyroView does not use any commands that are not listed here 3 5 1 Command List Command Character s Sent Response Description Command Character s Sent Response Description Command Character s Sent Response Description Command Character s Sent Response Description Doc 7430 0074 01 Rev A Ping R H Pings DMU to verify communications Voltage Mode r R Changes measurement type to Voltage Mode DMU outputs raw sensor voltage in the data packet Scaled Mode C Changes measure ment type to Sc
32. me The measurement mode selects the information that is sent in the data packet over the RS 232 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 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 Vy 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 data is sent as 16 bit integers the data has a resolution of only 12 bits The DMU rate sensor and angle analog outputs are not enabled in this mode Only the linear accelerometer analog output on pins 5 7 will be enabled because these signals are taken directly from the accelerometers See the Analog Output section for a complete description of the analog outputs 3 4 2 Scaled Sensor Mode In scaled sensor mode the analog sensors are sampled converted to digital data temperature compensated and scaled to engineering units The digital data represents the actual value of the quantities measured A calib
33. mperature The internal temperature of the DMU may be as much as 15 C higher than the ambient temperature 3 9 Analog Output NOTE See Appendix D for the correct pin out for Model VG700AA 202 The DMU provides six fully conditioned analog outputs in scaled mode three accelerometer voltages and three rate sensor voltages In angle mode the scaled accelerometer voltages are replaced with the pitch and roll analog voltages In all modes the raw accelerometer sensor output is also available The analog signals can be connected directly to an A D or other data acquisition device without further buffering The analog outputs all have a I kQ resistor in series to protect against short circuits This should be taken into account when using data acquisition systems with moderate input impedances 10 kQ The circuit diagram for the raw accelerometer outputs Pin 5 6 and 7 is shown below EO Accel Fin 7 Outpat me _ 3 pl The DMU must be set to scaled sensor mode or angle mode to enable the scaled analog signals 3 9 1 Raw Accelerometer Voltage The analog outputs from the accelerometers are taken directly from the sensor through a buffer They are raw in the sense that they do not represent a calculated or calibrated value You will need the zero bias point and scale factor given on the DMU calibration sheet to turn the analog voltage into an acceleration measurement To find the acceleration in G
34. n Fate 59 Yow Fate 58 11 Acceleration Z MSB Accel Voltage Z MSB e pemen ives T Toro vae 66 Tero vase DR e owes fm fT mea cm TTT NOTE The header byte FF will likely not be the only FF byte in the data packet You must count the bytes received at your serial port and use the checksum to ensure you are in sync with the data sent by the DMU This is especially critical when using the continuous data packet output mode Doc 7430 0074 01 Rev A Page 17 Crossbow VG700AA User s Manual 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 loop collecting data from the sensors processing the data and 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 After 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 RS 232 port or onto the analog outputs In the case of the analog output the data is presented immediately on the analog output pins
35. nate System The DMU will have a sticker on one face illustrating the DMU coordinate system With the connector facing you and the mounting plate down the axes are defined as X axis from face with connector through the DMU Y axis along the face with connector from left to right Z axis along the face with the connector from top to bottom The axes form an orthogonal right handed coordinate system An acceleration is positive when it is oriented towards the positive side of the coordinate axis For example with the DMU sitting on a level table it will measure zero g along the x and y axes and 1 g along the z axis If you slide the DMU forward this is an increase in velocity along the positive direction of the x axis so this is a positive acceleration and the DMU will report a positive acceleration On some models the acceleration reported will be in the DMU body frame and in some models the acceleration reported will be in the earth level coordinate frame On some models the definition of positive acceleration is the opposite of the above See the table below to reference the available output options for the acceleration 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
36. o set the erection rate at a high setting T setting 100 which should remove any initial attitude errors or drifts Engine turn on and rollout onto the runway 5 Maneuver I Takeoff and climb to desired altitude set the erection rate to a low setting T setting 7 6 Maneuver 2 1 Coast Phase set the erection rate to a high setting T setting 100 7 Maneuver 3 45 degree heading change set the erection rate to a low setting T setting 7 8 Maneuver 4 Ci Coast Phase set the erection rate to a high setting T setting 100 9 Maneuver 5 180 degree turn and altitude change very fast 20 second maneuver set the erection rate to an even lower setting since the maneuver is short and the dynamics are large T setting 4 10 Maneuver 6 3 Coast Phase set the erection rate to a very high setting to remove any gyro saturation or acceleration saturation from the previous high dynamic maneuver T setting 150 and then set the erection rate back to a high setting T setting 100 11 Maneuver 7 Altitude descent and landing set the erection rate to a low setting T setting 7 12 Maneuver 8 Runway taxi and stop set the erection rate to a high setting T setting 100 The profile above can be used as an example to produce an adapted erection rate profile to achieve the best possible performance from the DMU A constant erection rate would not allow the DMU to perform as well because
37. ors 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 each time 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 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 1s flying straight and level Unfortunately there is no single ideal erection rate for all applications We can suggest a starting
38. ration 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 Page 10 Doc 7430 0074 01 Rev A VG700AA User s Manual Crossbow signed 16 bit 2 s complement integers In this mode the DMU operates as a 1X axiS Measurement system The scaled sensor analog outputs are enabled in this mode Note that stabilized pitch and roll angles are not available in scaled sensor mode See the Analog Output section for a complete description of the analog outputs To convert the acceleration data into G s use the following conversion accel data GR 1 5 2 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 exampk if your DMU uses a 2 G accelerometer then the G range is 2 To convert the angular rate data into degrees per second use the following conversion rate data RR 1 5 2 where rate is the actual measured angular rate in sec data is the digital data sent by the DMU and RR is the Angular rate Range of your DMU The angular rate range of your DMU is the range of angular rates your DMU will measure NOTE RR is 200 for all VG700AAs 3 4
39. uation the accelerometers will be an inaccurate indication of the angle due to motional accelerations The DMU rate sensors 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 Remember that the DMU does not store the rate sensor zero calibration in non volatile memory If you cycle power to the DMU it loses the zero calibration Ideally you would issue the zero command every time you power on the DMU Also ideally you would let the DMU warm up for 5 minutes before zeroing the rate sensors 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 as measured by integrating the rate
40. which then tunes the T Setting between a T Setting of 0 and the chosen T Setting by scaling the setting based on sensed accelerations 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 0 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 Doc 7430 0074 01 Rev A Page 21 Crossbow VG700AA User s Manual 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 constant offset error in angular rate will integrate into an error in angle that increases linearly with time resulting in angular drift The VG700AA uses accelerometers to correct the calculated angle but in a dynamic sit
41. with a cable to connect the DMU to a Serial port of the PC 1 Connect the 15 pin end of the digital signal cable to the port on the DMU 2 Connect the 9 pin end of the cable to the serial port of your computer 3 The additional black and red wires on the cable supply power to the DMU Match red to power and black to ground The input voltage can range from 10 30 VDC at 0 75 A See the specifications sheet for the VG700AA for details Doc 7430 0074 01 Rev A Page 3 Crossbow VG700AA User s Manual 6 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 NOTE The analog outputs from the DMU are unconnected in this cable 2 3 Setup GyroView With the DMU connected to your PC serial port and powered open the Gyro View software I 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 FFT displays a fast fourier transform of the data Navigation shows an artificial horizon display 4 You can log data to a file by entering a data file name You can select the rate at which data is saved to disk 5
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