VG700AA/AB User's Manual
Contents
1. Connect the 15 pin end of the digital signal cable to the port on the DMU Connect the 9 pin end of the cable to the serial port of your computer 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 AB for details 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 The Crossbow Inertial Systems have an EMI filtered connector The issue with grounding EMI shield is very important because the EMI filter capacitively couples the signals together if it is left floating The solution is to provide a good ground for the DMU connector shell This can be accomplished by soldering a wire between ground pin Pin 4 and the cable metal part that contacts the DMU connector eg backshell 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 DMU2. C6 In general the digital data representing each measurement is sent as a 16 bit number two bytes The data is sent MSB first then LSB In voltage mode the data is sent as unsigned integers to represent the range 0 5V 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 a checksum The checksum is calculated in the following manner 1 Sum all packet contents header and checksum 2 Divide the sum by 255 3 The remainder should equal the checksum Table 5 shows the data packet format for each mode 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 In some applications using the DMU s digital output requires a precise understanding of the internal timing of the device The processor int
3. 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 properl
4. 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 Ifthe 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 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 at least 5 minutes when you first turn iton You should zero the rate sensors when you first use the DMU Set the DMU down in a stable place On the main control panel enter a value into the zero avg time box 3 will work well Click the Z button This measures the rate sensor bias and sets the rate sensor outputs to zero The zeroing command turns on the high pass filter rate bias estimation that takes approximately 3 minutes The DMU needs to be held still motionless during zeroing operation The zero command is discussed more in The Zero Comm
5. information about the topic Examples are given throughout the manual to help the reader understand the terminology This symbol defines items that have significant meaning to the user 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 Normal Introduction This manual explains the use of VG700AA AB The VG700AA AB is a Crossbow Technology Dynamic Measurement Unit DMU designed for automotive testing and measurements The VG7OOAA AB 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 AB is the solid state equivalent of a vertical gyro artificial horizon display The VG700AA AB has the unique ability to use the stabilized angle information to translate the acceleration measurement from the 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 stabi
6. refer to website www xbow com 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 Name Address Telephone Fax Email Equipment Model Number Equipment Serial Number Installation Date Failure Date Fault Description Will it connect to GyroView 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 Seal the shipping container s with heavy tape or metal bands strong enough to handle the weight of the equipment and the container Please write the words 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 Use the following address for all returned products Crossbow Technology Inc 4145 N First Street San Jose CA 9513
7. 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 x EE where is the actual measured acceleration in G s is the digital data sent by the DMU and is the G Range for your DMU The data is scaled so thatl G 9 80 m 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 1 5 2P where is the actual measured angular rate in sec is the digital data sent by the DMU and 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 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 d
8. 4 Attn RMA Number XXXX The Crossbow product warranty is one year from date of shipment Crossbgw
9. G700AA AB 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 E DS where is the actual angle in degrees either pitch or roll is the signed integer data output in the data packet and is a constant 180 for roll and pitch With the VG700AA AB 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 1 g If you have a VG700AA AB 202 the acceleration measurement will always 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 1 g depending on which axis you tilt the unit while the Z axis component goes to 0 g The VG7OOAA AB has a simple command structure You send a command consisting of one or two bytes to the DMU over the RS 232 interfac
10. VG700AA AB User s Manual VG700AA VG700AB Revision C February 2007 Document 7430 0074 05 Crossbow Technology Inc 4145 N First Street San Jose CA 95134 Tel 408 965 3300 Fax 408 324 4840 email info xbow com website www xbow com This product has been developed by Crossbow exclusively for commercial applications It has not been tested for and Crossbow makes no representation or warranty as to conformance with any military specifications or that the product is appropriate for any military application or end use Additionally any use of this product for nuclear chemical biological weapons or weapons research or for any use in missiles rockets and or UAV s of 300km or greater range or any other activity prohibited by the Export Administration Regulations is expressly prohibited without the written consent of Crossbow and without obtaining appropriate US export license s when required by US law Diversion contrary to U S law is prohibited 2002 2007 Crossbow Technology Inc All rights reserved Information in this document is subject to change without notice Crossbow and SoftSensor are registered trademarks and DMU is a trademark of Crossbow Technology Inc Other product and trade names are trademarks or registered trademarks of their respective holders 1 1 12 2 1 2 2 2 3 2 4 3 1 3 2 3 3 3 4 3 5 3 6 3 7 3 8 3 9 3 10 4 1 42 Table of Contents The DMUTM Series Motion and Attitud
11. and section Now you re ready to use the DMU 3 DMU Details 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 from face with connector through the DMU along the face with connector from left to right 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
12. e Sensing Units 1 Package Contents ceo sedi ie re e eds 2 Gyro VIEW Software sedeo il eta ie 3 Connections en 3 Setup GyrOVIeW inei ee Der 4 Take Measurements se BEE GE et RERO peer AG 4 DMU Coordinate System essere 6 Connections dete there idas 7 Interface wih socal esatto Ae Was meis 9 Measurement Modes eese nennen 9 Commands RR EE GE WERE 12 Data Packet Format ees ee se ee ee GR ee ee GR Re ee ee GR Re ee 15 Tuming Be rise OBERE aet 17 Temperature Sensor nett bte roter a 17 Analog Output 5 iege eer a Ee Ee 18 Adaptive T Algorithm installed at Crossbow factory 20 The Zero Command esses enne 21 The Erection Rate iese ese ee ee ee Re RR RR RA RA ener 21 43 4 4 4 5 5 1 6 1 6 2 9 1 9 2 9 3 9 4 Mounting the DMU seen rennen 23 DMU Start Up Procedure sse 23 Advanced Strategies for Adjusting the Erection Rate 24 VG700AA AB Outline Drawing eene 26 Analog Output Conversion eee 27 Digital Output Conversion esee 28 Customer ServIGe x onte ei e D sabi eed 32 Contact Directory snot e E ep eee edes 32 Return Proced re onto tee RE AE 32 About this Manual The following annotations have been used to provide additional information Note provides additional
13. e 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 Get Wye yy G V where is the actual acceleration measured is the voltage at the analog output is the zero G bias voltage and 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 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 2 0 121 G The raw accelerometer voltages will always be available on pins 5 7 The sign convention for the raw accelerometer analog outputs may be different from the DMU coordinate system as illustrated on the label This is due to the mechanical mounting constraints of the accelerometers inside 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 90 V 4 096 V where angle is the actual pitch or roll in degrees and is the analog pitch or roll voltage measured There is no one optimal erection rate for all environments A high erection rate is be
14. e and the DMU will execute the command The DMU commands are case sensitive 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 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 C Changes measurement type to Scaled Mode DMU outputs measurements in scaled engineering units Angle Mode a A Changes measurement type to Angle VG Mode DMU calculates stabilized pitch and roll Also outputs sensor measurements in scaled engineering units Polled Mode P none Changes data output mode to Polled Mode DMU will output a single data packet when it receives a G command Continuous Mode C Data Packets Changes data output mode to Continuous Mode DMU will immediately start to output data packets in continuous mode Data rate will depend on the measurement type the DMU is implementing Raw Scaled or Angle Sending a G will return DMU to Polled Mode Request Data G Data Packet G requests a single data packet DMU will respond with a data packet The format of the data packet will change with the measurement mode Raw Scaled or Angle Sending the DMU a G while it is in Continuous Mode will place the DMU i
15. ernal to the DMU runs in a 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 A time tag is attached to each data packet The time tag is simply the value of a free running counter at the time the A D channels are sampled The clock counts down from 65 535 to 0 and a single tick corresponds to 0 79 microseconds The timer rolls over approximately every 50 milliseconds You can use this value to track relative sampling time between data packets and correlate this with external timing 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 prec
16. escription 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 The DMU uses the accelerometers to provide long term stability to keep the rate gyro drift in check The DMU gives you control over the weighting between the accelerometers and rate gyros through a parameter called the erection rate This term is derived from analog vertical gyros and refers to the rate at which the system can pull the gyro spin axis back to vertical as measured by gravity With 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 V
17. gital Calibration Sheets contains the custom offset and sensitivity information for your DMU The calibration sheet 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 This contains helpful hints on programming installation valuable digital interface information including data packet formats and conversion factors 2 Quick Start 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 The following are minimum capabilities that your computer should have to run GyroView successfully CPU Pentium class RAM Memory 32MB minimum 64MB recommended Hard Drive Free Memory 15MB Operating System Windows 95 98 NT4 2000 XP To install GyroView in your computer 1 2 3 Insert the CD Support Tools in the CD ROM drive Find the Gyro View folder Double click on the setup file Follow the setup wizard instructions You will install Gyro View and a LabVIEW Runtime Engine You will need both these applications If you have any problems or questions you may contact Crossbow directly The DMU is shipped with a cable to connect the DMU to a Serial port of the PC 1
18. ision The temperature sensor voltage is sent in the data packet scaled as V 5 4096 where 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 2444 C V V 1 375 V where 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 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 havealk resistor in series to protect against short circuits This should be taken into account when using data acquisition systems with moderate input impedances 10k The circuit diagram for the raw accelerometer outputs Pin 5 6 and 7 is shown below 1k Pin 5 6 7 T MAAN n The DMU must be set to scaled sensor mode or angle mode to enable the scaled analog signals Th
19. lization 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 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 AB 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 In addition to your DMU sensor product you should have 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 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 The Di
20. me 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 4 DMU Operating Tips 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 VG700AA AB 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 at least 5 minutes before issuing the zero command Zeroing the DMU turns on the high pass filter ra
21. n Polled Mode Set Erection Rate T lt x gt none The T command sets the vertical gyro erection rate The argument of the command lt x gt is a single binary byte that represents the value you want to set as the erection rate The units are in degrees per minute For example if you wanted to set the erection rate to 50 deg min you would send the command T lt 50 gt which in hex would be 54 32 Calibrate Rate Sensor Bias Z lt x gt Z Measure the bias on each rate sensor and set as the new zero The argument of the command lt x gt is a single binary byte that the DMU normally ignores and hence any single byte character can be sent The zeroing command turns on the high pass filter rate estimation that takes approximately 3 minutes However if lt x gt is set to O then the previously stored gyro biases are erased Query DMU Version v ASCII string This queries the DMU firmware and will tell you the DMU type and firmware version The response is an ASCII string The exact string will vary according to the DMU type and version 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
22. of your right hand pointing along the axis in a positive direction your fingers curl around in the positive rotation direction For example if the DMU is sitting on a level surface and you rotate it clockwise on that surface this will be a positive rotation around the z axis The x and y axis rate sensors would measure zero angular rate and the z 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 VG7OOAA AB coordinate definition is consistent with the SAE J670e convention on vehicle coordinate systems See Table 1 enabled because these signals are taken directly from the accelerometers See the Analog Output section for a complete description of the analog outputs 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
23. on 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 The DMU should be mounted as close to the center of gravity CG of your system as possible This will minimize any lever effect If it is not mounted at the center of gravity then rotations around the center of gravity will cause the DMU accelerometers to measure acceleration proportional to the product of the angular rate squared and the distance between the DMU and the CG The DMU will measure rotations around the axes of its senso
24. rs 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 Although the DMU is rated and tested for wide operating temperature ranges refer to the data sheet the temperature ramp rate must be limited to within 1 C minute The higher ramp rate could potentially result in permanent damage to the sensors As an example look at how the DMU might be used in a car Assume a VG700AA AB is mounted in an automobile and will be used to record the vehicle s attitude during a drive The test will be about 1 hour long The VG700AA AB 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 electronic
25. s but the car engine should be off if it causes vibration to the DMU 2 Zero the rate sensors if you haven t already done previously 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 for a VG700AA AB Start the engine 5 Start data collection 6 Proceed with test The DMU attitude estimation algorithm is divided into two separate entities Gyro angular rate information is integrated in time to propagate the DMU body attitude with respect to the tangent plane If the initial attitude of the vehicle was known exactly and if the gyros provided perfect readings then this integration process would suffice However the initial state is seldom known to great precision especially a vehicle s 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 reference
26. t 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 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 erecti
27. te bias estimation that takes approximately 3 minutes The zeroing command does not level the stabilized angle output Remember that with Firmware Rev 03 and later the DMU stores the rate sensor zero calibration in non volatile memory If you cycle power to the DMU the zero calibration will not be lost However if lt x gt is set to 0 then the previously stored gyro biases are erased If your firmware is older than Rev 03 the Zeroing command is not stored in EEPROM and has to be issued every time you power up the unit Contact Crossbow for information on firmware upgrade If you find that the DMU zeroing algorithm does not work well in your particular application please contact Crossbow to discuss possible options 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 One way to start is to set the erection rate about twice as fas
28. tter 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 O 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 O 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 so
29. y there must be no external disturbance to the unit engine noise wind disturbance etc If the user has knowledge of the intensity of upcoming maneuvers or complete control of the dynamic profile and can maintain constant serial communications with the DMU unit then an adapted erection setting profile can be developed 5 Appendix A Mechanical Specifications Large amounts of vibration will make the accelerometer readings noisy and thereby may affect the angle calculations In addition if the magnitude of the vibration exceeds the range of the accelerometer the accelerometer output can saturate This can cause errors in the accelerometer output and in turn the estimated angles The VG700AA AB must be installed in a location that is rigid enough to alleviate potential vibration errors induced from normal airframe vibration sources You can use vibration isolators if needed to dampen out the unwanted vibrations 9 Appendix E Warranty and Support Information As a Crossbow Technology customer you have access to product support services which include Single point return service Web based support service Same day troubleshooting assistance Worldwide Crossbow representation Onsite and factory training available Preventative maintenance and repair programs Installation assistance available United States Phone 1 408 965 3300 8 AM to 5 PM PST Fax 1 408 324 4840 24 hours Email techsupport xbow com Non U S
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