DMU User`s Manual
Contents
1. 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 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 Maneuver 7 Altitude descent and landing set the erection rate to a low setting T setting 7 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 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 Page 26 Doc 7430 0070 01 Rev B DMU User s Manual Crossbew If enough care is taken active control of the erection rate will provide the best performance Doc 7430 0070 01 Rev B Page 27 Crossbew DMU User2. s Manual 5 Appendix A Mechanical Specifications 5 1 IMU700CA and VG700CA Outline Drawing Page 28 Doc 7430 0070 01 Rev B DMU User s Manual Crossbew 6 Appendix B DMU Output Quick Reference GR is the Grange of the accelerometers For example if your DMU has 2 G accelerometers GR 2 RR is the rate range of the rate sensors For example if your DMU has 200 s rate sensors RR 200 6 1 Analog Output Conversion Accelerometer Use sensitivity offset from Rate Sensor calibration sheet Output is raw Rate s sensor voltage Vou V RR 1 5 4 096 Pin5 X axis accelerometer raw Pin 8 Roll rate sensor Pin6 Y axis accelerometer raw Pin 9 Pitch rate sensor Pin 7 Z axis accelerometer raw Pin 10 Yaw rate sensor Accelerometer Scaled Mode only Accel G Roll Pitch Angle Mode only Vout V GR 1 5 4 096 Angle Vout V 90 4 096 Pin 12 X axis accelerometer Pin 12 Roll Angle Pin 13 Y axis accelerometer Pin 13 Pitch Angle Pin 14 Z axis accelerometer 6 2 Digital Output Conversion Data is sent as 16 bit signed integer for all but Temperature Temperature sensor data is sent as unsigned integer Acceleration Roll Pitch Angle Mode Accel G data GR 1 5 2 Angle data 180 2 Rate Temperature Rate s data RR 1 5 2 Temperature C data 5 4 096 1 375 44 44 Doc 7430 0070 01 Rev B Page 29 Crossbew DMU User s Manual 7 Appen
3. 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 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 GyroViewto 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 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 Page 4 Doc 7430 0070 01 Rev B DMU User s Manual Crossbew approximately 3 minutes The DMU needs to be held still motionless during zeroing operation The
4. 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 1 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 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
5. critical when using the continuous data packet output mode Doc 7430 0070 01 Rev B Page 17 Crossbew DMU 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 a loop collecting data from the sensors processing the data then collecting more data The data is reported to the user through a parallelprocess 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 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 a
6. 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 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 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 5 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 2 G accelerometer then the G range is 2 To convert the angular rate data into degrees per second use the following conversion rate data AR 1 5 2 3 where rate is the actual measured angular rate in sec data is
7. 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 0070 01 Rev B Page 21 Crossbew DMU 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 A constant offset error in angular rate will integrate into an error in angle that increases linearly with time resulting in angular drift The VG7600AA 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 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 i
8. the digital data sent by the DMU and AR 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 For example if your DMU uses a 200 s rate sensors then AR range is 200 Page 10 Doc 7430 0070 01 Rev B DMU User s Manual Crossbew NOTE RR is 200 for all VG700CA and IMU700CAs 3 43 Angle Mode VG700CA Only 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 ina 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 t
9. COM port 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 supply for the VG700CA and IMU700CA should be 10 30 VDC at 0 75 A See the specifications for your unit 6 WARNING Do not reverse the power leads Applying the wrong power to the DMU Doc 7430 0070 01 Rev B Page 3 Crossbew DMU User s Manual 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 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 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 Under DMU or DMU Controls
10. DMU User s Manual Models I MU700CA VG700CA DMU FOG Revision B September 2002 Document 7430 0070 01 Crossb w Crossbow Technology Inc 41 E Daggett Dr San Jose CA 95134 Tel 408 965 3300 Fax 408 324 4840 email info xbow com website www xbow com 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 DMU User s Manual Crossbew Table of Contents I Introduction esessoseeenesnsnnnnnnnennnnnnennnnnennenennnsnnnnnnnnenneneneeeee 1 1 1 The DMU Series Motion and Attitude Sensing Units 1 1 2 Package Contents s c cscc sv cctstscei berg ER ELERS EET Edgar 1 2 Quick Start EOE E E O E 3 2 1 Gyro View Software niren EEEE 3 2 1 1 GyroView Computer Requirements ororrnnrnnrnrnvrnrnnrnvrnrvnvrnvvnrvernerne 3 2 1 2 Install GyroView 22 COMME CTIONS ssc Mise vesscaveses lerende EA EARE 2 3 Setup Gyro VIEW vescsssisesentssasseadicsssscessucscacutseaentnsanscecatseetecseasscdentsvavedatanseed 4 2 4 Take Measurements cecsessseccssseeccseseseecseseseeceeaeseecsearseecasarseeeaearseeenee 4 3 DMU Details ceeeeevevevevnvnvevevensnnnnnnenenveeenennnennnnnnenennennnnnnnnnee 6 3 1 DMU Coordinate System srenrnrvvrvavenvvvrvev
11. U measurement mode The pitch and roll analog outputs are scaled to represent degrees The accelerometer analog outputs are scaled to represent G s These outputs are created by a D A converter Doc 7430 0070 01 Rev B Page 7 Crossbew DMU User s Manual The serial interface connection is standard RS 232 On a standard DB 25 COM port connector make the connections per Table 2 Table 2 DB 25 COM Port Connections COM Port Connector DMU Connector Dmu cones GE E 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 3 Table 3 DB 9 COM Port Connections COM Port Conne ctor DMU Connector ECOC Pree Sins e ser 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 30 VDC unregulated at 0 75 A If you are using the cable supplied with the DMU the power supply wires are broken out of the cable at the DB 9 connector The red wire is connected to VCC the black wire is connected to the power supply ground DO NOT REVERSE THE POWER LEADS The analog outputs are unconnected in the cable we supply The analog outputs are fully buffered and conditioned and can be connected directly to an A D The analog outputs have a k resistor in series with each output to protect the outputs from a short circuit This should be taken into account when us
12. 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 Page 12 Ping R H Pings DMU to verify communications Voltage Mode T R Changes measurement type to Voltage Mode DMU outputs raw sensor voltage in the data packet Scaled Mode c C Changes measurement type to Scaled Mode DMU outputs measurements in scaled engineering units Angle Mode a Doc 7430 0070 01 Rev B DMU User s Manual Response Description Command Character s Sent Response Description Command Character s Sent Response Description Command Character s Sent Response Description Command Character s Sent Doc 7430 0070 01 Rev B Crossbew 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 ou
13. dix C DMU Command Quick Reference A None Change to polled mode Data packets sent when a G is received by the DMU H C None Change to continuous data transmit mode Data packets streamed continuously Packet rate is dependent on operating mode Sending G stops data transmission Data Get Data Requests a packet of data from the DMU Packet Data format depends on operating mode T lt 0 None 2 byte command sequence that changes the vertical yro erection rate 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 ignores and is part of the legacy code any single byte character can be sent Unit should be still during zeroing Autobaud detection Send b change baud rate baud rate send a DMU will send A when new baud rate is detected Query DMU serial number Returns serial number as String 32 bit binary number ASCII Query DMU version ID string Returns ASCII string String Note argument of command is sent as a single hex byte not as an ASCII character Page 30 Doc 7430 0070 01 Rev B DMU User s Manual Crossbew 8 Appendix D Warranty and Support Information 8 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 representa
14. ection 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 sensors 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 if you have a VG700CA 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 situa
15. erm 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 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 The VG700CA outputs the pitch and roll 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 and data is the signed integer data output in the data packet and SCALE is a constant SCALE 180 for roll and pitch Doc 7430 0070 01 Rev B Page 11 Crossbew 3 5 Commands DMU User s Manual The DMUs have 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 GyroView is
16. et 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 e 1 DMU Users Manual This contains helpful hints on programming installation valuable digital interface information including data packet formats and conversion factors Page 2 Doc 7430 0070 01 Rev B DMU User s Manual Crossbew 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 Gyro View software connect the DMU to your serial port apply power to your unit and start taking measurements 2 11 GyroView Computer Requirements The following are minimum capabilities that your computer should have to run GyroView successfully e CPU Pentiumclass e RAM Memory 32MB minimum 64MB recommended e Hard Drive Free Memory 15MB e Operating System Windows 95 98 Me NT4 2000 2 1 2 Install GyroView To install GyroView in your computer 1 Putin CD Support Tools 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 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
17. evenssveveveresvavavenvsvsvevesesvsesese 6 3 2 Connections sr enhe HARER REES 6 3 3 mene 42424424 9 3 4 Measurement Modes rnenvsvrnrnvrsvrnrnnsvrnenrsrnsensnenrsnsnrnenssrrnenssrssenesssrsnsnsnens 9 3 4 1 Voltage Mode screenet eders eN bes eani ik 9 3 4 2 Scaled Sensor Mode iscenirao non 10 3 4 3 Angle Mode VG700CA ONLY sccsccssceseeseesseseeseeeseeseeseeseesseaseaeeaeens 11 3 5 COMMANA S eirese eierne are E eee 12 3 5 1 Command Lis bases siver isen sages Ths tea E E ad ede eden 12 3 6 Data Packet Fora aser autieinte anken 3 7 Timing eres veese 3 8 Temperature Sensor 3 9 Analog Output eororovovevvvrvvrvversrveversevevevenvavavssevensrserenvavevevvevnvavesernseer 19 3 9 1 Raw Accelerometer Voltage 19 3 9 2 Scaled Accelerometer Voltage 19 3 9 3 Scaled Rate Sensor Voltage rnernrvnrnernnnrnnrvnnnevnnvrrnerrenernevsenervenssne 20 3 9 4 Stabilized Pitch and Roll Voltages VG models sc 20 3 10 Adaptive T Algorithm for VG700 Series installed at CLOSSDOW LAClOLY csesssisssssescesccsenssasitnapttsspereccsesg ia gs eas deca aaa veaes 21 4 DMU Operating Tips eeoevevevevevevevevevevevevevevevevevevesevevevesereee 22 4 1 The Zero Command 5 s5 ccssstesssssessaesispncessescssevseustesascesenseesensenseseon 22 Doc 7430 0070 01 Rev B Page i Crossbew DMU User s Manual 4 2 The Erection Rate VG700CA only renerrrvrerersrvrervrrrerererererervrrsereren 22 4 3 Mounting the DMU soeonvonservvererv
18. gacy 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 Doc 7430 0070 01 Rev B DMU User s Manual Crossbew DMU will respond with a serial number data packet that consists of a header byte FF the serial number in 4 bytes and a checksum byte The serial number bytes should be interpreted as a 32 bit unsigned integer For example the serial number 9911750 would be sent as the four bytes 00 97 3D C6 Command Request Auto Baud Rate Character s Sent b Response Description This starts the auto baud rate detection process This will allow you to change the DMU baud rate from its default This change will not affect the default settings 1 Start with communications program and DMU at same baud rate Send b to the DMU 3 Change the baud rate of your communications program 4 Send a to the DMU The DMU will respond with A at the new baud rate when a successful detection of the new baud rate is completed 3 6 Data Packet Format In general the digital data representing each measurement is sent as a 16 bi
19. he Container Seal the shipping container s with heavy tape or metal bands strong enough to handle the weight of the equipment and the container 8 3 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 8 3 5 Return Shipping Address Use the following address for all returned products Crossbow Technology Inc 41 E Daggett Drive San Jose CA 95134 Attn RMA Number XXXXXX 8 4 Warranty The Crossbow product warranty is one year from date of shipment Page 32 Doc 7430 0070 01 Rev B Crossb w Crossbow Technology Inc 41 E Daggett Drive San Jose CA 95134 Phone 408 965 3300 Fax 408 324 4840 Email info xbow com Website www xbow com
20. however you can also use them as six axis sensors The VG700CA can be set to operate in one of three modes voltage mode scaled sensor mode or angle VG mode The IMU700 Series of products do not support angle mode 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 I 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 Doc 7430 0070 01 Rev B Page 9 Crossbew DMU User s Manual The voltage data is scaled as voltage data 5 Vvy 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 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
21. ing data acquisition devices with moderate input impedances less than 10 kQ Page 8 Doc 7430 0070 01 Rev B DMU User s Manual Crossbew 3 3 Interface The serial interface is standard RS 232 38400 baud 8 data bits 1 start bit 1 stop bit no parity and no flow control Crossbow will supply DMU communication software examples written in LabView Source code for the 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 The DMU baud rate can be changed To change the baud rate follow this procedure 1 Start with the DMU connected to the serial interface with your software set to the default baud rate of 38400 2 Send the ASCII character b 62 hex to the DMU Ina terminal program like Windows HyperTerminal or ProComm this means simply type the letter b The DMU is case sensitive 3 Now change the baud rate of your terminal software Send the ASCII character a The DMU will detect the character and automatically match the baud rate your software is using Upon successful operation the DMU will return the character A at the new baud rate 5 You can now use the DMU at the new baud rate The new baud rate setting is not permanent therefore this process must be repeated after any power reset 3 4 Measurement Modes The VG700CA is designed to operate as vertical gyros
22. nce 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 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 pro
23. nce 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 0070 01 Rev B Page iii Crossbew DMU User s Manual Page iv Doc 7430 0070 01 Rev B DMU User s Manual Crossbew 1 Introduction 1 1 The DMU Series Motion and Attitude Sensing Units This manual explains the use of the IMU700CA and the VG700CA The IMU700CA is six axis measurement systems 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 The VG700CA has similar sensor architecture as the IMU700CA but is designed to provide stabilized pitch and roll in dynamic environments The VG700CA is the solid state equivalent of a vertical gyro artificial horizon display The AHRS Series products are nine axis measurement systems that combine accelerometers rate sensors and magnetometers to create a complete attitude and heading reference system The operation of the AHRS models are covered in separate user s manuals The Dynamic Measurement Unit DMU series 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 outputs and an RS 232 se
24. on 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 then yaw 3 2 Connections The IMU700CA and VG700CA have a male DB 15 connector The signals are as shown in Table 1 All analog outputs are fully buffered and are designed to interface directly to data acquisition equipment See Analog Output for details Page 6 Doc 7430 0070 01 Rev B DMU User s Manual Crossbew 15 Pin D Connector Male Pinout se oe e e e e e e 0 0 0 Table 1 DMU Connector Pin Out KO ORNE 0 ee ERE TET Roll analog voltage VG Series only X axis accel scaled analog voltage Pitch analog voltage VG Series only Y axis accel scaled analog voltage 14 Unused Z axis accel scaled analog voltage NC factory use only Notes 1 The accelerometer analog voltage outputs are the raw sensor output These outputs are taken from the output of the accelerometers 2 The rate sensor analog voltage outputs are scaled to represent s These outputs are created by a D A converter 3 Actual output depends on DM
25. or output is also available The analog signals can be connected directly to an A D or other data acquisition device without further buffering The input impedance of your data acquisition device should be greater than 10 kQ for the DAC outputs and relatively higher impedance for raw analog outputs The circuit diagram for the raw accelerometer outputs Pin 5 6 and 7 is shown below Accel EKO Pin 5 6 7 Outpat i BAK RS ip 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 s use the following conversion accel G Vau 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 For example if the x axis of your accelerometer has a zero G bias of 2 512 V asensitivity 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 a
26. ot the actual voltage at the sensor output To convert the analog output to a sensor value use the following relation rate AR 1 5 Vout V 4 096 V where rate is the actual measured rate in units s AR is the angular rate range of your sensor and Vout is the measured voltage at the analog output For example if your DMU has a 200 s rate sensor and the analog output for that sensor is 1 50 V the value of the measurement is 200 s 1 5 1 50 4 096 109 86 s NOTE AR is 200 for all VG700CA and IMU700CAs 3 9 4 Stabilized Pitch and Roll Voltages VG models In angle mode the DMU outputs the stabilized pitch and roll angle analog voltages on pins 12 and 13 The analog 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 180 for roll 90 for VG700CA and 90 for the pitch To convert the voltage to an actual angle use the following conversion angle FA Vou V 4 096 V Page 20 Doc 7430 0070 01 Rev B DMU User s Manual Crossbew where angle is the actual pitch or roll angle in degrees FA is the full scale angle and Vout is the analog pitch or roll voltage measured FA is 90 for roll and pitch 3 10 Adaptive T Algorithm for VG700 Series installed at Crossbow factory There is no one optimal erection rate for all environments A high erection rate is better when you
27. perly 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 Doc 7430 0070 01 Rev B Page 25 Crossbew DMU User s Manual M EXAMPLE 4 6 10 11 12 Adapted Flight Profile T Setting Vehicle electric power is applied to the DMU while the vehicle is out of external disturbances within the hanger for instance Following a warm up period 10 minutes should suffice a gyro zeroing command is sent to the unit to average out the gyro biases Send a T setting command to 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 Maneuver 1 Takeoff and climb to desired altitude set the erection rate to a low setting T setting 7 Maneuver 2 1 Coast Phase set the erection rate to a high setting T setting 100 Maneuver 3 45 degree heading change set the erection rate to a low setting T setting 7 Maneuver 4 io Coast Phase set the erection rate to a high setting T setting 100 Maneuver 5
28. portional 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 should protect the DMU from moisture and dust M EXAMPLE 4 4 DMU Start Up Procedure As an example look at how the DMU might be used on an airplane Assume a VG700CA is mounted on a small twin prop plane and will be used to record the plane s attitude during flight Flights will be 2 6 hours long The VG700CA 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 Zero the rate senso
29. pproximately 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 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 CC V Viemp Y 1 375 V where Vtemp is the temperature sensor voltage 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 Page 18 Doc 7430 0070 01 Rev B DMU User s Manual Crossbew 3 9 Analog Output 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 sens
30. rial 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 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 VG700CA and IMU700CA use the same accurate reliable MEMS acceleration sensors as the IMU300 Series IMU400 Series The VG700CA and IMU700CA use fiber optic gyros to 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 GyroView will allow you to immediately view the outputs of the DMU ona PC running Microsoft Windows You can also download this software from Crossbow s web site at http www xbow com Doc 7430 0070 01 Rev B Page 1 Crossbew DMU User s Manual e 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 e 1DMU Calibration Sheet The Digital Calibration Sheets contains the custom offset and sensitivity information for your DMU The calibration she
31. rrsvarenrvrsvevevessveverervsvavavesvsvevevesesvssene 4 4 DMU Start Up Procedure 4 5 Advanced Strategies for Adjusting the Erection Rate VG models 4 6 Adapted Flight Profile T Setting 5 Appendix A Mechanical Specifications ssosooeseeesssssoo 28 5 1 IMU700CA and VG700CA Outline Drawing eee 28 6 Appendix B DMU Output Quick Reference 00 29 6 1 Analog Output Conversion 6 2 Digital Output Conversion 7 Appendix C DMU Command Quick Reference 30 8 Appendix D Warranty and Support Information 31 8 1 Customer SEIVICE aeiee AE E E EGEE 31 8 2 Contact Directory oniro ee ee ee 31 8 3 Return Procedure 8 3 1 Authorization 8 3 2 Identification and Protection 32 8 3 3 Sealing the Container ss snennrvvnnvnrvvvnnvrvenvnnvronnvnnrnennvrennvnnerennvvevesnne 32 8 3 4 Markin sienna RRE RENEE O EE EE 8 3 5 Return Shipping Address 8 4 Warranty Page ii Doc 7430 0070 01 Rev B DMU User s Manual Crossbew About this Manual The following annotations have been used to provide additional information 4 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 cha
32. rs Engines are 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 for a VG700CA 4 Start the engines 5 Start data collection 6 Proceed with flight 4 5 Advanced Strategies for Adjusting the Erection Rate VG models 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 Page 24 Doc 7430 0070 01 Rev B DMU User s Manual Crossbew readings then this integration process would suffice However the initial state is seldom known to great precision especially a vehicle s attitude 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 refere
33. ssuing 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 p lease contact Crossbow to discuss possible options 4 2 The Erection Rate VG700CA only 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 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 0070 01 Rev B DMU User s Manual Crossbew One way to start is to set the er
34. t number two bytes The data is sent MSB first then LSB In voltage mode the data is sent as unsigned integers to represent the range 0 5 V In scaled and angle mode the data generally represents a quantity that can be positive or negative These numbers are sent as a 16 bit signed integer in 2 s complement format The data is sent as two bytes MSB first then LSB In scaled and angle mode the timer information and temperature sensor voltage are sent as unsigned integers The order of data sent will depend on the selected operating mode of the DMU Doc 7430 0070 01 Rev B Page 15 Crossbew DMU User s Manual 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 Table 4 shows the data packet format for each mode Page 16 Doc 7430 0070 01 Rev B DMU User s Manual Crossbew Table 4 Data Packet Format v1 2 Co her ee Co Rot Faw 188 vavnaetsB Gyovotago2Z 056 gt romere Aeon X58 acce ote X58 Co YewRae wss Acton 5 ne Teve TS mu poo mes es iP 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
35. tion 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 suggest 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 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 0070 01 Rev B Page 23 Crossbew DMU User s Manual will cause the DMU accelerometers to measure acceleration pro
36. tion e Onsite and factory training available e Preventative maintenance and repair programs e Installation assistance available 8 2 Contact Directory United States Phone 1 408 965 3300 7 AM to 7 PM PST Fax 1 408 324 4840 24 hours Email techsupport xbow com Non U S refer to website www xbow com 8 3 Return Procedure 8 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 Gyro View Doc 7430 0070 01 Rev B Page 31 Crossbew DMU User s Manual 8 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 8 3 3 Sealing t
37. tput 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 VG Series only T lt x gt Page 13 Crossbew Response Description Command Character s Sent Response Description Command Character s Sent Response Description Command Character s Sent Response Description Page 14 DMU User s Manual 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 Xx 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 le
38. vailable 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 These analog voltages reflect any calibration or correction the DMU applies to the accelerometer data The analog voltage is created Doc 7430 0070 01 Rev B Page 19 Crossbew DMU User s Manual 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 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 3 9 3 Scaled Rate Sensor Voltage The DMU will output analog voltages representing the rate sensor measurement on pins 8 10 in both scaled sensor mode and angle mode 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 n
39. zero command is discussed more in The Zero Command section Now you re ready to use the DMU Doc 7430 0070 01 Rev B Page 5 Crossbew DMU User s Manual 3 DMU Details 3 1 DMU 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 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 rotati
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