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Inertial+ User Manual

1. Inertial Configuration xX GPS Selection Inertial 7 Choose the external GPS receiver connected to the Inertial Inertial and GPS ii Manufacturer Model Navigation C amp C Technologies C Nav 3050 7 C o Step 2 of 10 Leica GPS1230 E NavCom SF 3050 Read Config Novatel OEM3 e Novatel OEM4 Orientation External Antenna Novatel OEMV P Secondary Antenna Omnistar 4305 HP gt Wheel Config Topcon GB 500 a Odometer Input V Use advanced settings Options Commit Advanced settings Save Finish Baud Rate 9600 x Data Bits s Mi Parity None Mi Stop bits 1 X Format NMEA x Confidentty Use intemal GPS Accurately Dev ID 120817 14ce E Enlish lt Back Next gt Cancel For some GPS receivers it is necessary to change the port settings so that the External GPS port on the Inertial matches the port settings on the GPS receiver Use the Advanced Settings to change the port settings 28 Oxford Technical Solutions Inertial User Manual Qoxrs Inertial GPS The advanced settings can also be used to change the format of the receiver being used For example if a Novatel OEMV receiver is being used using NMEA then select the OEMV from the top but change to the NMEA format at the bottom Mixing receivers and formats is not recommended unless directed by OxTS The Inertial has an internal GPS receiver that can be
2. Inertial Configuration Inertial Options Options to improve performance Inertial and GPS x 5 Option Setting Navigation Initialisation Speed 5 m s Output Displacement Disabled Step 8 of 10 Camera Trigger Disabled Heading Lock Normal Read Config Output Lock Disabled GPS Selection Output Smoothing Disabled Orientation Altitud Ellipsoidal External Antenna m ipsoidal Serial 1 Qutput NCOM Secondary Antenna Wheel Config Serial 2 Output Disabled Odometer Input Ethernet Output NCOM GPS Control Default Commit GPS Weighting Medium Save Finish Advanced Disabled Confidenthy Accurately Dev ID 110826 14ce ERgenaish x o m EI Oxford Technical Solutions Inertial User Manual Qoxrs Inertial GPS Initialisation Speed Option The default starting speed for the Inertialt t is 5m s However some slow vehicles cannot achieve this speed For these vehicles adjust the Jnitialisation Speed to a different value If a speed less than 5m s is selected then care should be taken to make sure that the Inertial is travelling straight when it initializes The accuracy of some GPS receivers is not good enough to initialize at very low speeds Output Displacement Option The Inertial can displace or move its outputs to another location in the vehicle This simulates the Inertial being mounted at the new location rather than at its actual location This function displaces all of the outputs
3. TNC Connector Date 23 07 09 Part 201 990146 789 Document Magnetic GPS Antenna
4. Qty Qty Description Inertial Inertial 2 1 1 Inertial System Unit 1 2 GPS Antenna AT575 70 1 1 Serial Cable 1 1 Ethernet Cable cross over 1 1 CD ROM with Manual and Software 1 1 User Manual 1 1 Calibration Certificate In addition to the components supplied the user will require a laptop to configure the Inertial An external GPS receiver is needed for high accuracy the internal GPS can be used for low accuracy applications Revision 120928 o Figure 1 Typical Inertial system in transit case 10 Oxford Technical Solutions Inertial User Manual Qoxrs Inertial GPS Warranty Oxford Technical Solutions Limited warrants the Inertial products to be free of defects in materials and workmanship subject to the conditions set forth below for a period of one year from the Date of Sale Date of Sale shall mean the date of the Oxford Technical Solutions Limited invoice issued on delivery of the product The responsibility of Oxford Technical Solutions Limited in respect of this warranty is limited solely to product replacement or product repair at an authorised location only Determination of replacement or repair will be made by Oxford Technical Solutions Limited personnel or by personnel expressly authorised by Oxford Technical Solutions Limited for this purpose In no event will Oxford Technical Solutions Limited be liable for any indirect incidental special or consequential damages whether t
5. After the changes have been made to the Inertial the Inertial will automatically reset Press Commit to save the configuration to the Inertial and reset it Saving a copy of the settings locally Before finishing it is possible to save a copy of the settings in a folder on your computer This can then be reloaded next time The Finish screen also lets you know if the settings have been committed successfully to the Inertial or not Figure 20 below shows the Finish screen Figure 20 it config Finish Screen Inertial Configuration X e Finish Inertial TEN i Save configuration in a folder Inertial sar ahd You have not yet committed your changes to the Inettial Go back to Commit Navigation to retry Step 10 of 10 Read Config GPS Selection Orientation External Antenna Secondary Antenna Wheel Config Odometer Input Options Commit Preserve these settings in folder C Data nertial Cfg Confidenthy Accurately Te _REet To save a copy of the settings in a local folder check the Preserve these settings in folder check box and enter the folder name The settings will be saved before the software finishes Revision 120928 Ea Inputs and Outputs This section describes the connectors and the signals on the Inertial The layout of the front panel of the Inertial is shown in Figure 21 below Figure 21 Inertial Front Panel Axes Neima oP Ons e
6. This option extracts the configuration used at run time Read Initial Settings from Inertial If the Inertial is connected to the computer via Ethernet then it is possible to read the initial settings directly from the Inertial The initial settings are the settings that the Inertial starts up with before it makes any improvements Select this radio button and enter the correct IP address of your Inertial The drop down box will list all of the Inertial systems that are connected to this computer this function does not work if Enginuity or other software is using the Inertialt UDP port unless the OxTS UDP Server is running Revision 120928 a If the IP address of the PC is not correct for the Inertial then it config can try to change the IP address of the computer This cannot work under all conditions If the IP address is changed then it will be restored after it config finishes Type of GPS receiver connected It is essential to select the correct external GPS receiver so that the Inertial can interpret its data correctly An integration document giving details on how to connect and configure the external GPS receiver is available This gives essential information on the GPS receiver and it should be followed carefully in order to obtain the best performance The integration manual can be opened by clicking on the icon if the computer has software for viewing PDF files Figure 5 itconfig GPS Selection Screen
7. ones that do not get power from the GPS receiver Revision 120928 a LED Definitions The front panel of the Inertial has three LEDs Table 8 LED Descriptions WETICE Description SdNav Strapdown Navigator State GPS Position Solution from GPS Power Pwr Power Comms Strapdown Navigator LED States The Strapdown Navigator LED shows the state of the Strapdown Navigator in the system Table 9 below gives the states of this LED Table 9 Strapdown Navigator LED States Colour Description Off The operating system has not yet booted and the program is not yet running This occurs at start up Red The operating system has booted and the program is running The Inertial GPS receiver has Flash not yet output a valid time Yellow The internal GPS receiver has locked on to time but the external GPS receiver does not Flash have valid position and velocity Red The external GPS receiver has locked on to satellites and has a valid position and velocity The Strapdown Navigator is ready to initialize If the vehicle is travelling faster than 5 m s then the Strapdown Navigator will initialize and the system will become active Yellow The Strapdown Navigator has initialized and data is being output but the system is not real time yet It takes 10 seconds for the system to become real time after start up Green The Strapdown Navigator is running and the system is real time Red The Inertial is asleep password locked if
8. 2 will show some error the size of the error depends on the multipath in the environment Table 6 below lists the error you can expect when stationary with a 1m base line Table 6 Typical Heading Error for when Stationary in different Environments Complete Open Sky 0 45 degrees 0 3 degrees 10 Near Trees Buildings 1 degrees Next to Trees Buildings 2 degrees Typical figures using a 1m base line For accuracy specification of 0 15 degrees RMS a 2m separation is required Using a 2m base line can halve the figures shown here a Oxford Technical Solutions Inertial User Manual Qoxrs Inertial GPS Using an antenna splitter In many cases it is possible to use an antenna splitter with the Inertial so that only one antenna is needed or two antennas for dual antenna systems If an antenna splitter is used then there are a few important points to consider The Inertial supplies a 5V output to the antenna with up to 100mA supply This is probably enough to power both the antenna and the antenna splitter If the Inertial is supplying the power to the antenna splitter then both the antenna and the antenna splitter need to work correctly from a 5V supply The Inertial has an extremely sensitive GPS receiver in it High gain antennas can sometimes have a signal that is too large for the Inertial Antenna splitters often contain some additional gain to overcome cable and connector losses Having an antenna with a gain of more
9. Read Config Right x 0 000 m GPS Selection z Orientation Below M 1 000 m External Antenna Secondary Antenna Se Wheel Config Overall accuracy 0 100 m M Step 7 of 10 C Specify each accuracy separately Options Commit Save Finish Pulses per metre 100 00 pulses per metre to within fi 0 00 a Confidently Accurately Dev ID 110826 14ce EEEn x The distance from the measurement point on the Inertial to the measurement point of odometer should be input If the odometer is from a prop shaft then the distance should be measured half way between the two wheels Revision 120928 EJ Inertial GPS Ideally the measurements would be made to an accuracy of 10cm Using higher precision for the measurement does not improve the results Using an accuracy figure worse than 20cm will increase the drift of the Inertial Use the accuracy fields to select or specify the accuracy of the measurements Enter the pulses per metre of the odometer The Inertial will improve the accuracy of this measurement and so it does not need to be very accurate Use a value that is accurate to 10 unless you know the figure more accurately for example from a previous calibration run using the Inertial Setting the Correct Options The Options Page includes some important settings for getting the best results from your Inertial system Figure 13 below shows the Options screen Figure 13 i config Options Screen
10. biases up to 5 s Table 17 Angular Rate Measurement Specifications Rotation Angular Rate Measurement Y ve Zero Zero X direction should indicate positive rotation others are small ve Zero Zero X direction should indicate negative rotation others are small Zero ve Zero Y direction should indicate positive rotation others are small Zero ve Zero Y direction should indicate negative rotation others are small Zero Zero ve Z direction should indicate positive rotation others are small Zero Zero ve Z direction should indicate negative rotation others are small It is hard to do a more exhaustive test using the angular rate sensors without specialised software and equipment For further calibration testing it is necessary to return the unit to OxTS Note that the Inertial is capable of correcting the error in the angular rate sensors very accurately It is not necessary to have very small values for the angular rates when stationary since they will be estimated during the initialisation process and warm up period This estimation process allows the Inertial to go for long periods without requiring recalibration Testing the Internal GPS and other Circuitry To check that all the internal circuits in the Inertial are working correctly and that the navigation computer has booted correctly use the following procedure EI Oxford Technical Solutions Inertial User Manual Qoxrs Inertial GPS 1 Connect power to t
11. car projected in to the horizontal plane d Down This is the down direction of the car along the gravity vector For example the velocity in the forward direction of the car would be written as Vf EI Oxford Technical Solutions Inertial User Manual Qoxrs Inertial GPS Figure 24 Level Frame Definition Lateral Forward Q Lateral 0 F Forward Vehicle Frame The Vehicle Frame is attached to the body of the vehicle It is related to the Inertial through the rotations in the Orientation page of i config It can be changed while the Inertial is running using the Quick Config page of Enginuity The definitions of the Vehicle Frame are listed in Table 22 and shown in Figure 25 Table 22 Vehicle Frame Definition Axis Description X This is the forward direction of the car y This is the right direction of the car Z This is the down direction of the car For example the acceleration in the x direction would be written as Ax Figure 25 Vehicle Frame Definition y Revision 120928 Revision History Table 23 Revision History Revision Comments 080107 080213 090108 091009 100721 110901 120928 Initial Version Update including images from the software Added RMC message available in German split wheel and odometer input Added Inertial 2 Output Displacement other small changes Added NMEA GSV GSA messages Added undulation options for altitude Added Javad
12. drivers turn the steering wheel while not moving Output Lock The output of the Inertial will continue to change even when the vehicle is stationary For some video systems this leads to ambiguous results The position and orientation can be locked by the Inertial automatically when the vehicle becomes stationary 40 Oxford Technical Solutions Inertial User Manual Qoxrs Inertial GPS While the outputs are locked the Kalman filter continues to run and accumulate errors When the vehicle moves the Kalman filter will quickly return to the new solution The drift rate can be controlled using the Output Smoothing option Output Smoothing Figure 15 shows the Output Smoothing window Figure 15 itconfig Output Smoothing window Output Smoothing x Enable Output Smoothing Smoothing Position 0 2 m Velocity 0 5 m s Angle 0 1 deg Time Limit Position s Velocity s Angle s Ok Cancel When the Kalman filter in the Inertial determines that there is some error to correct this error is applied smoothly rather than as a jump The output smoothing controls how fast the correction is applied to the outputs The smoothing of the position velocity and orientation corrections can be controlled independently Enter the maximum correction that can be applied every second For example if 0 1m is entered for the position smoothing then the Inertial will only correct a position error by a ma
13. output for faster RTK relock Added reverse polarity clarification Added specification for internal GPS receiver Updated for the new software Added improved settings Clarification on co ordinate frames Updated for the new software Added GPPPS messages Two new receivers added Updated Conformance Notices Added section on ECCN Added Software Disclaimer Added section on Ethernet output Updated Inertial drawing EI Oxford Technical Solutions Inertial User Manual Qoxrs Inertial GPS Drawing List Table 24 below lists the available drawings that describe components of the Inertial system Many of these drawings are attached to the back of this manual Note that the x following a drawing number is the revision code for the part If you require a drawing or different revision of a drawing that is not here then contact Oxford Technical Solutions Table 24 List of Available Drawings Drawing Description 14A0040x Inertial System Outer Dimension Drawing AT575 70B GPS Antenna Revision 120928 EE 77 Heyford Park Upper Heyford Oxfordshire OX25 5HD www oxts co uk Copyright Oxford Technical Solutions 2007 oi O The information in this document is confidential and must not be ey es ze published or disclosed either wholly or in part to other parties or used to DXG 3 Me rte 6 _ build the described components Red A i g without t
14. position velocity acceleration to this new location To enable Output Displacement select this option and enter the offsets to the new location in the vehicle The Output Displacement window is shown in Figure 14 Figure 14 itconfig Output Displacement Properties Output Displacement ey General Ahead x 0 000 m Right m 0 000 m Below 0 000 m Note that the noise in the acceleration outputs will be much higher when Output Displacement is used Typical installations in moving vehicles have angular vibrations of about 2 radians s this equates to 2m s of additional vibration of a 1m output displacement It will be necessary to filter the data if Output Displacements are used Revision 120928 EZ Camera Trigger The Inertial can generate a regular pulse based on distance for example one pulse every 10m of travel This can be used to trigger a camera so that a picture can be taken on a regular basis Enter the distance between pulses or leave disabled default Heading Lock Option The heading of the Inertial can drift when it remains stationary for long periods of time To solve this the Inertial includes an option to lock the heading to a fixed value when stationary This option cannot be used if the vehicle can turn on the spot i e on a boat With Heading Lock enabled the Inertial can remain stationary for indefinite periods of time without any problems Th
15. than 40dB is not recommended This may be 35dB for the antenna and 5dB for the antenna splitter Cable loss may increase the amount of gain that can be used In dual antenna configurations only one antenna splitter is required if the antenna splitter does not cause a significant phase change to the signal Both antennas need to be of the same design or the dual antenna system will not work Cable lengths should not be significantly different E g 1m on one antenna and 15m on the other is not recommended OxTS has tried and tested an antenna splitter from GPS Networking in a dual antenna configuration and we could not find a reduction in the performance The details of the product tested are listed in Table 7 Table 7 GPS Networking Antenna Splitter Website http www gpsnetworking com Model HIALDCBS1X2 Description GPS Hi isolation amplified antenna splitter 2 outputs TNC Gain option 3dB Note By default this antenna splitter comes with an 18dB gain It must be ordered with a 3dB gain for use with the Inertial otherwise the overall gain is likely to be too high This gain cannot be ordered through the web and GPS Networking must be contacted directly in order to have the 3dB gain We have tested the hi isolation version by default which minimises the possibility of interference between the GPS receivers This is the version that we would recommend We have also successfully used active antenna splitters from GPS Networking i e
16. then the Inertial will only be able to output the ellipsoidal altitude A constant altitude offset can be specified by entering a value in to the box Serial 1 and Serial 2 The Seriall and Serial2 output ports can be configured for different message types Figure 16 shows the configuration pages for the Serial 2 output which is the same as the Serial 1 output window Figure 16 itconfig Serial Output window 7 Serial 2 Output oa Serial 2 Output _ X General NMEA General NMEA Packet NMEA X Message Type Periodic Falling Rising Camera Baud 57600 GPGGA 1 Hz a O O o GPHDT 1Hz z GPVTG Disabled xi _ GPZDA Disabled v B GPGST Disabled a O O O PASHR Disabled bd GPRMC Disabled nA GPGSV Disabled X GPGSA lDisabedmmm N 0 N 7 Baud Rate 57600 Z Maximum chars s 101 Available chars s 5760 Allow extended length messages E Output approximate values before initialisation o cance C ok E Canca 2 Oxford Technical Solutions Inertial User Manual Qoxrs Inertial GPS NCOM is a proprietary format from OxTS Please contact OxTS for a description of this format The IPAQ mode is the NCOM format at a lower data rate and should be used with Pocket PC systems NMEA is a standard format that is found on many different systems The NMEA tab will only be enabled w
17. used The internal GPS receiver is a low cost receiver and it not capable for giving good position measurements It is useful for debugging or trying the Inertial Orientation of the Inertial in the vehicle The Inertial can be mounted at any angle in the vehicle The outputs can be rotated so that the measurements can be referenced to the vehicle co ordinate frame For correct initialisation it is also necessary to get the heading orientation correct The Inertial gets its initial heading by assuming that the vehicle is travelling forwards in a straight line If the definition of the vehicle s X axis forward direction is incorrect in the Inertial then it will not initialize correctly when the vehicle drives forwards The Inertial 2 can initialize while stationary though this can be unreliable in poor GPS conditions It is still better to configure the vehicle axes correctly The orientation of the Inertialt in the vehicle is normally specified using three consecutive rotations that rotate the Inertial to the vehicle s co ordinate frame The order of the rotations is Heading Z axis rotation then Pitch Y axis rotation then Roll X axis rotation The Inertial co ordinate conventions are listed in Figure 23 and Table 19 It is important to get the order of the rotations correct When using the Oxford Technical Solutions RT Strut the orientation will need to be changed The default orientation of the RT Strut has the Y axis poin
18. 2 The Inertial 2 will lock on to satellites but it cannot estimate heading so it cannot start Either motion or static initialisation can be used to initialize the Inertial 2 3 The vehicle drives forward at about 12mph or Initialization Speed the Inertialt 2 assumes that the heading and track are similar and initializes heading to track angle If the Inertialt 2 is mounted in the vehicle with a large heading offset then the initial value of heading will be incorrect This can also happen if the Inertial 2 is initialized in a turn This can lead to problems later 4 When the combined accuracy of heading plus the Orientation Accuracy figure for the Secondary Antenna see configuration software is sufficiently accurate then the Inertial 2 will solve the RTK Integer problem using the inertial heading There is no need for the Inertialt 2 to solve the RTK Integer problem by searching If the antennas angle is offset from the Inertial 2 by a lot then the RTK Integer solution that is solved will be incorrect It is essential to get the Inertial 2 orientation and the Secondary Antenna orientation to within 5 degrees preferably within 3 degrees This becomes more critical as the separation becomes larger 5 Once the RTK Integer solution is available the Inertial 2 can start to use the dual antenna solution to improve heading The level of correction that can be applied depends on how accurately the angle of the Secondary GPS Antenna is k
19. Inertial Inertial and GPS Measurement System User Manual Confidently Accurately Legal Notice Information furnished is believed to be accurate and reliable However Oxford Technical Solutions Limited assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use No license is granted by implication or otherwise under any patent or patent rights of Oxford Technical Solutions Limited Specifications mentioned in this publication are subject to change without notice and do not represent a commitment on the part of Oxford Technical Solutions Limited This publication supersedes and replaces all information previously supplied Oxford Technical Solutions Limited products are not authorised for use as critical components in life support devices or systems without express written approval of Oxford Technical Solutions Limited All brand names are trademarks of their respective holders The software is provided by the contributors as is and any express or implied warranties including but not limited to the implied warranties of merchantability and fitness for a particular purpose are disclaimed In no event shall the contributors be liable for any direct indirect incidental special exemplary or consequential damages including but not limited to procurement of substitute goods or services loss of use data o
20. a with a high accuracy better than lcm so that the Inertial will not move the antenna position If the Inertial does not compute the correct position of the antenna then the Javad receiver will not be able to use the measurements correctly Ethernet Output The Ethernet output of the Inertial can be configured for different data rates Figure 17 shows the Ethernet Output page Figure 17 itconfig Ethernet Output Configuration r General Output packet Ncom Data Rate 100 Hz x E Output on falling edge of tigger Output on rising edge of trigger Output on camera trigger The Ethernet output can either output NCOM or be disabled by using the Output Packet dropdown list box When NCOM is selected the NCOM data rate can be selected by using the Data Rate dropdown list box The Inertial can output Ethernet messages when an event rising or falling edge is input on the Event input pin It can also output Ethernet messages when the wheel speed output is configured in camera output mode by selecting a distance longer than about 1m between pulses These messages are interpolated to the time when the event occurred To enable these messages select the Output on checkbox It is essential to o Oxford Technical Solutions Inertial User Manual Qoxrs Inertial GPS enable these messages if the events have a data rate higher than 1Hz otherwise the NCOM output cannot communicate all o
21. al drift when GPS is not available and to improve the heading accuracy When combined with an odometer input see Odometer Input screen the drift of the Inertialt when GPS is not available is drastically reduced Figure 11 below shows the Wheel Configuration screen Revision 120928 EZ Figure 11 itconfig Wheel Configuration Screen i Inertial Configuration a Oe Wheel Configuration Inertial a 4 Specify the position of a non steered axle Inertial and GPS Navigation Measured from the Inertial How far ahead or behind is the non steered axle Step 6 of 10 Ahead m 0 000 m Read Config How far left or right is the centre of the vehicle GPS Selection Right 0 000 m Orientation j g External Antenna How far below or above is the ground Secondary Antenna Below x 1 000 m Odometer Input C Specify each accuracy separately Options Overall accuracy 0 100 m x Commit Save Finish Confidently Devio 110628 Me EEEren Measure from the Inertial to the centre of the non steered wheels Ideally this would be measured to an accuracy of 10cm Enter the value and select whether the wheels are ahead or behind the Inertial Measure from the Inertial to the centreline of the vehicle Ideally this would be measured to an accuracy of 10cm Enter the value and select whether the centreline is left or right of the Inertial Measure from the Inertial to the ground Ideally this wou
22. and run the visual display software ENGINUTIY EXE 3 Orient the Inertialt in the following ways and check that the accelerations measurements are within the specifications shown in Table 16 below Table 16 Acceleration Measurement Specifications Orientation Acceleration Measurement Y Flat Flat Down Z Acceleration between 9 7 and 9 9m s Flat Flat Up Z Acceleration between 9 7 and 9 9m s Down Flat Flat X Acceleration between 9 7 and 9 9m s Up Flat Flat X Acceleration between 9 7 and 9 9m s Flat Down Flat Y Acceleration between 9 7 and 9 9m s Flat Up Flat Y Acceleration between 9 7 and 9 9m s This test is sufficient to ensure that the accelerometers have not been damaged Typically a damaged accelerometer will read full scale about 100m s or 100m s or will not change its value Gyro Test Procedure To check that the gyros angular rate sensors are working correctly follow this procedure Revision 120928 EI 1 Use the default orientation configuration in i config 2 Connect power to the system connect the system to a laptop computer and run the visual display software ENGINUTIY EXE 3 Rotate the Inertial according to Table 17 below and check that the angular rate measurements occur 4 With the unit stationary check that all the angular rates are within 5 s In general they will be within 0 5 s but the algorithm in the Inertial will work to specification with
23. because in very dynamic conditions or when used on land vehicles the heading accuracy is better than the heading that the dual antenna system can provide When stationary in open sky conditions the accuracy will be 0 15 degrees RMS for a 2m antenna separation GPS Antenna Operating Temperature The GPS antennas have a much wider operating temperature range from 55 C to 85 C allowing them to be used on the outside of vehicles Revision 120928 15 Export Control Classification Number Export control regulations change and so the classification number of the Inertialt may also change The information here relates to the time when the manual was published The Inertial products can fall under two different export control categories depending on the type of accelerometer fitted internally The type of accelerometer does not affect the specification of the product only the export control classification number ECCN The ECCN can be found on the invoice delivery note and also on the label of your Inertialt system The label shows a code used by OxTS to identify the type of accelerometer and is used because the ECCN numbers can change in the future Table 5 shows the current ECCN numbers for the different label text on the Inertial Table 5 ECCN Number and Inertial Label Text Label Text Current ECCN Number EXCT 1 7A003d EXCT 2 7A103a 16 Oxford Technical Solutions Inertial User Manual Qoxrs Inertial GPS Co
24. conditions many GPS products do not achieve 1cm accuracy Revision 120928 Ea Table 3 Typical Performance Specification for Inertial 2 Parameter 2cm 20cm Internal L1 L2 GPS L1 Float GPS GPS Positioning L1 L2 L1 Kinematic Differential SPS SPS Kinematic OmniStar HP OmniStar VBS Position Accuracy 2cm lo 20cm 0 4m CEP 1 8m CEP 3 0m CEP 10cm for HP Velocity Accuracy 0 05 km h 0 08 km h 0 1 km h 0 1 km h 0 2 km h RMS RMS RMS RMS RMS Acceleration Bias 10 mm s lo 10 mm s lo 10 mm s lo 10 mm s lo 10 mm s lo Linearity 0 01 0 01 0 01 0 01 0 01 Scale Factor 0 1 lo 0 1 lo 0 1 lo 0 1 lo 0 1 lo Range 100 m s 100 m s 100 m s 100 m s 100 m s Roll Pitch 0 03 lo 0 04 lo 0 05 lo 0 05 lo 0 15 lo Heading 0 1 lo 0 1 lo 0 1 lo 0 1 lo 0 2 lo Angular Rate Bias 0 01 s lo 0 01 s lo 0 01 s lo 0 01 s lo 0 01 s lo Scale Factor 0 1 lo 0 1 lo 0 1 lo 0 1 lo 0 1 lo Range 100 s 100 s 100 s 100 s 100 s Track at 50km h 0 07 RMS 0 1 RMS 0 15 RMS 0 15 RMS 0 25 RMS Dual Antenna Yes Yes Yes Yes Yes Note 1 The operating temperature range for the antenna is much wider since it can be mounted outside the vehicle See specification below Note 2 Some manufacturers specify L1 L2 GPS to be more accurate than 2cm in which case the Inertial will also be more accurate However it is assumed that the Inertial will be used in dynamic conditions and under these con
25. d window on the Options page It will tell the ambiguity resolution algorithm to only search within 15 degrees of the horizontal Note that this is the angle between the antennas and it is independent of the height offset entered in to the software The static initialisation algorithms degrade rapidly in non ideal conditions They should only be used in open sky environments Using a shorter separation or using the pitch constraint can improve the accuracy in non ideal conditions It is possible to use long antenna separations and obtain higher heading accuracy The limiting accuracy is about 0 05 degrees using an antenna separation of 5 0m or more However we only recommend using a separation up to 2 0 metres Above 2 0m metres the static initialisation algorithms changes and will take considerably longer Also above 2 0m it becomes even more critical that the angle is measured accurately and it may take a long time before the direct solving of the ambiguities works Contact Oxford Technical Solutions support team if you want to use separations above 2 0m Configuring the Wheel Position Specifying the position of the non steered wheels makes a huge difference to the lateral drift performance of the Inertial when GPS is not available The wheel configuration can only be used on land vehicles with non steered wheels Aircraft and marine vehicles cannot use this option The Inertial uses the position of the non steered wheels to reduce the later
26. ditions many GPS products do not achieve 1cm accuracy Common Specifications The specifications in Table 4 apply regardless of the GPS receiver attached to the products n Oxford Technical Solutions Inertial User Manual Qoxrs Inertial GPS Table 4 Specifications that are common to all the products Inertial Inertial 2 Update Rate 100 Hz Calculation Latency 3 5 ms Power 9 18 V d c 15W Dimensions mm 234 x 120 x 76 excluding connectors Weight 2 3 kg Operating 10 to 50 C Temperature Vibration 0 1 g Hz 5 500 Hz Shock Survival 100G 11ms Internal Storage 2GB Dual Antenna Heading Accuracy The heading accuracy that can be achieved by the dual antenna system in the Inertial is 0 3 degrees lo per meter of separation in ideal open sky conditions The maximum recommended separation is 2m giving an accuracy of 0 15 degrees lo in static conditions In dynamic conditions the accuracy tends to be better than this since the multipath error is constantly changing and the algorithms remove the noise from this constantly changing error A separation more than 2m can be used with the Inertial 2 but a special calibration run will be required The limit of accuracy that can be achieved by the Inertial 2 is about 0 05 degrees 1o using a 5m antenna separation Non ideal mounting of the GPS antennas will reduce the heading accuracy The heading accuracy listed here is better than 0 15 degrees for dual antenna systems
27. e Heading can be locked to three different levels Normal Tight and Very Tight For most applications the best setting to use is the Normal setting This is the one that is least likely to cause problems to the Kalman filter The Tight and Very Tight options are better when trying to reduce position drift in poor GPS environments and traffic jams Table 12 i config Heading Lock Options Heading Lock Description Normal This option assumes that the Heading of the vehicle does not change by more than 2 degrees while the vehicle is stationary The Heading accuracy recovers quickly when the vehicle moves Tight This option assumes that the Heading of the vehicle does not change by more than 0 5 degrees while the vehicle is stationary The recovery is fast if the Heading of the vehicle does not change but will be slow if the vehicle turns before it moves Very Tight The option assumes that the Heading of the vehicle does not change by more than 0 3 degrees while the vehicle is stationary The recovery is fast if the Heading of the vehicle does not change but will be slow if the vehicle turns before it moves This option can cause problems during the warm up period if the vehicle remains stationary for a long time and then drives suddenly Note The Heading of most vehicles does change if the steering wheel is turned while the vehicle is stationary Junctions and pulling out of parking spaces are common places where
28. ecify the orientation and height offset Getting the angle wrong by more than 3 degrees can lead the Inertial 2 to lock on to the wrong heading solution The performance will degrade or be erratic if this happens If the angle between the antennas cannot be estimated within a 3 degree tolerance then contact OxTS we have some techniques for identifying the angle of the antennas EI Oxford Technical Solutions Inertial User Manual Qoxrs Inertial GPS The Inertial 2 does not estimate the distance between the two antennas It is essential to get this right yourself otherwise the system will not work correctly and the performance will be erratic The measurement needs to be accurate to 5mm preferably better than 3mm The Inertial 2 products are able to initialize when static This option is useful on slow moving vehicles or where it is essential to start the Inertial 2 running before moving for example in autonomous vehicles Static initialisation is 99 reliable in open sky the reliability decreases in environments with high multipath Static initialisation is also faster when the antenna separation is smaller If you can guarantee that the antennas are level always within 15 degrees of horizontal during static initialisation then the following advanced command can also speed up static initialisation and make it more reliable gps_pitch15 0 This is a pitch constraint or tilt constraint Enter this text in to the Advance
29. en pitch and finally roll that transform a vector measured in the navigation co ordinate frame to the body co ordinate frame The navigation co ordinate frame is the orientation on the earth at your current location with axes of North East and Down If V is vector V measured in the navigation co ordinate frame and V p is the same vector measured in the body co ordinate frame the two vectors are related by Vn l bn Vb cos y sin y 0 cos 0 o sin 0 1 0 0 V n sincy cos w of 0 1 0 ff0 cos o sin gt V 0 0 1 sin 0 o cos 0 sin d cos d where y is the heading angle O is the pitch angle and is the roll angle Remember heading pitch and roll are usually output in degrees but the functions sin and cos require these values in radians EI Oxford Technical Solutions Inertial User Manual Qoxrs Inertial GPS Co ordinate Frame Conventions The Inertial uses a co ordinate frame that is popular with most navigation systems Figure 23 below shows how the axes relate to the Inertial box Figure 23 Inertial Co ordinate Frame Definition Table 19 lists the directions that the axes should point for zero heading pitch and roll outputs when the default mounting orientation is used Table 19 Direction of Axes for zero Heading Pitch and Roll outputs X North Forward Y East Right Z Down Down If the axes of the Inertial and the Vehicle Axes are not the same as those listed in Table 19 then
30. evision 120928 Ea Changing the Configuration It will be necessary to configure the Inertial for you application before using it for the first time The program i config can be used to do this This section describes how to use i config and gives additional explanations on the meanings of some of the terms used It is only possible to change the Inertial configuration using Ethernet It is necessary to have the Ethernet on your computer configured correctly in order to communicate with the Inertial and change the settings Overview In order to give the best possible performance the Inertialt needs to know the following things e The type of GPS receiver fitted e The orientation that the Inertial is mounted at in the vehicle e The position of the external GPS antenna compared to the Inertial e The position of the Rear Wheels or non steering wheels compared to the Inertial e The position of the odometer compared to the Inertial e The orientation of the dual antenna system Selecting the Operating Language The i config software can operate in several languages To change language select the language from the drop down menu at the bottom of the page The language is hot swappable making it easy and fast to switch between languages The software will use the regional settings of the computer to choose whether numbers are represented in the English or European format dot or comma for the decimal separator The
31. f metres travelled between pulses The output has 0 8V or less for a low and 2 4V or more for a high There is no protection on this output no more than 10mA should be used on this output EI Oxford Technical Solutions Inertial User Manual Qoxrs Inertial GPS Reverse Polarity Protection The Inertial products have limited reverse polarity protection Reversing the polarity on the power inputs for short periods of time is unlikely to damage the product Causing a short circuit through the Inertial will damage the product A short circuit will be created if the polarity is reversed and another connector has ground connected In this condition the ground input of the power supply will be connected to the positive power supply this causes a high current to flow through the circuits in the Inertial and it will damage several internal components Revision 120928 ER Ethernet Configuration To configure the Inertial it is necessary to use the Ethernet connection The operating system at the heart of the Inertial product allows connection to the unit via FTP Configuration files for alternative configurations require FTP to put the configuration files on to the Inertial The Inertial outputs its data over Ethernet using a UDP broadcast The use of a UDP broadcast allows everyone on the network to receive the data sent by the Inertial The data rate of the UDP broadcast is 100Hz It is advisable to use the Inertial on its own
32. f the events and some will be lost GPS Control Figure 18 shows the window for the GPS Control Figure 18 itconfig GPS Control window i GPS Control These settings control how long the INS will ignore unexpected GPS measurements before being forced to believe them X GPS Position updates oj O Never believe unexpected measurements Start believing measurements after unexpected GPS update GPS Velocity updates Use firmware defaults Never believe unexpected measurements Start believing measurements after unexpected GPS update The Inertial will reject GPS updates that it believes are not correct However there is a limit on the number of GPS measurements that the Inertial will reject Once this limit has passed the Inertial accepts the GPS update The GPS Control determines how long the Inertial should wait before forcing the GPS to be accepted In the default state the Inertial will reject up to 10 seconds of GPS measurements before it forces the GPS to be accepted However in high multi path environments and when odometer measurements are used it may be desirable to reject up to 60 seconds of GPS measurements Both the velocity and the position can be controlled separately GPS Weighting The Inertial can place different emphasis on the GPS receiver s measurements Using the High GPS Weighting the Inertial believes the GPS receiver more and using the Low We
33. for other measurements that have already been entered into i config For example if the orientation in the vehicle has been changed then it is not clear whether the external GPS antenna should be rotated or not In general i config will rotate the configurations that the Kalman filter can derive external antenna lever arm and secondary antenna orientation but it will not change the user measured configurations wheel config wheel speed input The improvement to orientation should only be applied if the change in the orientation is small less than 5 degrees If the change in orientation is large then it is likely that the original configuration was wrong or has not been loaded into i config You are very likely to get poor results if the orientation is changed by a large amount Specifying the Position of the External Antenna It is essential to measure the position of the external GPS antenna the antenna connected to the external GPS compared to the Inertial accurately Getting these measurements incorrect is one of the main reasons for poor results from the Inertial so it is important to be careful with the measurements When the internal GPS receiver is used then the position of the primary GPS antenna should be used The distance should be made from the measurement point on the Inertial to the phase centre of the GPS antenna The measurement point of the Inertial is shown on the drawing at the end of the manual The measurements sh
34. g a low and 2 4V or more representing a high No more than 10mA should be drawn from this output There is no protection on this output protection circuitry would disturb the accuracy of the timing Event Input The Event Input can be used to time events like the shutter of a camera or a brake switch The Event Input has a pull up resistor so it can be used with a switch or as a CMOS input A Low Voltage requires less than 0 8V on the input and a high voltage requires more than 2 4V on the input There is no protection on this input protection circuitry would disturb the accuracy of the timing Keep the input in the range of OV to SV The maximum event rate is 1 per second Odometer Input The Odometer Input accepts TTL pulses from an encoder on a single wheel An encoder from a gearbox should not be used and simulated TTL pulses e g from a CAN bus should not be used The timing of the Odometer Input pulses is critical and nothing should cause any delay in the Odometer Input pulses The Odometer Input requires less than 0 8V for a low pulse and more than 2 4V for a high pulse Limited protection is provided on this input however the input voltage should not exceed 12V The wheel that is used should not steer the vehicle The Inertial will assume that this wheel travels straight Camera Trigger Output The Camera Trigger Output generates a pulse for a fixed distance travelled The configuration software can change the number o
35. h Primary ya Secondary Eye Serial 2 Output Serial HHE gS Power air Ethernet Sifide le Digital 0 WWW AXTS L8 0K Pin Assignments Table 13 RS232 Pin Assignments Serial 1 Serial 2 and External GPS Pin Direction Description 2 Input Data Receive Other pins not connected internally 48 Oxford Technical Solutions Inertial User Manual QObxrs Inertial GPS Table 14 Digital I O Pin Direction Description 1 Output 1PPS from Internal GPS receiver 2 Input Event Input 3 Input Odometer Input from Tacho on a single wheel 4 Output Camera Trigger Output 5 Output 100Hz IMU Sample 6 Ground 7 Ground 8 Reserved 9 Reserved See additional information in Digital Inputs and Outputs Section Table 15 Power Pin Assignments Pin Direction Description 1 Input Power In 9 to 18V d c 2 Input Power In 9 to 18V d c 3 Ground 4 Ground Digital Inputs and Outputs 1PPS Output The 1PPS output is a pulse from the internal GPS receiver The falling edge of the pulse is the exact transition from one second to the next in GPS time The pulse is low for Ims then high for 999ms and repeats every second The 1PPS is only output when the internal GPS has a valid position measurement Revision 120928 a Figure 22 1PPS Waveform Falling edge denotes GPS time 1000ms crossing second boundary lt r e 1ms 4 ae The output is a Low Voltage CMOS output with 0 8V or less representin
36. he prior written consent of pact a s nertial GPS www Ooxts co uk Exces Oxford Technical Solutions mano pues ron O aia Print Size A4 Scale Not to Scale Units mm Tolerances 5mm SPELL Projection 3rd Angle Material Alu Finish Anodised Notes A M4 x 10 Tapped Hole B 2mm dia x 3 hole Date 04 10 2012 Part 14A0040A Document Inertial Outer Dimensions Oxford Technical Solutions 77 Heyford Park Upper Heyford Oxfordshire OX25 5HD www oxts co uk Copyright Oxford Technical Solutions 2007 The information in this document is confidential and must not be published or disclosed either wholly or in part to other parties or used to build the described components without the prior written consent of Oxford Technical Solutions 0 10 20 30 Print Size A4 Scale Units mi Tolerances 1mm Projection 3rd Angle
37. he system connect the system to a laptop computer and run the visual display software ENGINUTIY EXE 2 Use Table 18 below to check that the status fields are changing Table 18 Status Field Checks Field Increment Rate IMU Packets 100 per second IMU Chars Skipped Not changing but not necessarily zero GPS Packets Between 2 and 20 per second depending on system GPS Chars Skipped Not changing but not necessarily zero GPS2 Packets Between 2 and 20 per second depending on system GPS2 Chars Skipped Not changing but not necessarily zero Note 1 The GPS2 related fields will only increase on the Inertial 2 systems These checks will ensure that the signals from the internal GPS and from the Inertial Sensors are being correctly received at the navigation computer Revision 120928 EZ Using the Orientation Measurements This section has been provided to clarify the definitions of Heading Pitch and Roll that are output by the Inertial The Inertial uses quaternions internally to avoid the problems of singularities and to minimise numerical drift on the attitude integration Euler angles are used to output the heading pitch and roll and these have singularities at two orientations The Inertial has rules to avoid problems when operating close to the singularities if you regenerate the rotation matrices given below then they will be correct The Euler angles output are three consecutive rotations first heading th
38. hen the NMEA packet type is selected Select the NMEA messages GPGGA GPHDT GPVTG GPZDA GPGST PASHR and GPRMC GPGSA GPGSV GPPPS to output on the serial port of the Inertial by ticking the tick box and select the data rate for each message type NMEA messages can be generated by falling or rising voltages on the event inputs and from pulses on the camera output These messages use interpolation to compute the values at the exact time of the event so the messages do not necessarily have a timestamp that coincides with a normal measurement To enable these messages check the appropriate checkbox Note that it is easy to overload the serial port if there are too many events The software will assume that the events are at 50Hz and so it is likely to generate a warning if you know the maximum rate of events then you can work out if it will overload the serial port or not The NMEA messages from the Inertialt can either conform to the NMEA specification but this limits the number of fields that can be output in the GGA and RMC messages To output full GGA and RMC messages which are longer than the NMEA specification allows select the Allow extended length messages option The Inertial can output approximate values before initialisation Currently just the position is output and this is the position of the antenna not the inertial measurement unit Select the Output approximate values before initialisation option to enable t
39. his feature Note that there will be a jump from the antenna to the inertial measurement unit when initialisation occurs The number of characters that can be output over the serial port is limited The software computes the number of characters that will be out each second and displays this at the bottom of the window A serial port data overflow warning message will appear if the messages data rates are too high for the selected baud rate to fix this it is necessary to lower the data rate of the selected NMEA messages or increase the baud rate The NMEA description manual gives details on the different fields that are output in the NMEA messages The Javad I RTK output can be used with Javad receivers With this output the Inertial outputs a special set of messages in Javad s GREIS format which the Javad receiver can use to relock the RTK Integer position faster after bridges or other obstructions This is a tight coupling of the Inertial with the Javad GNSS receiver The tight coupling of the Inertial with the Javad GNSS receivers was introduced in January 2010 and firmware after this date is required in the Javad receiver Revision 120928 Ea In order to use the Javad I RTK output it is essential to configure the output displacement so that the output of the Inertial is at the GPS antenna position You should also make sure that the position of the external GPS antenna is known accurately and configure the position of the antenn
40. hrough tort contract or otherwise This warranty is expressly in lieu of all other warranties expressed or implied including without limitation the implied warranties of merchantability or fitness for a particular purpose The foregoing states the entire liability of Oxford Technical Solutions Limited with respect to the products herein Revision 120928 Lt Specification The specification of the Inertial depends on the GPS receiver connected Typical figures are listed in Table 2 and Table 3 These specifications are listed for operation of the system under the following conditions e After a warm up period of 15 minutes continuous operation e Open sky environment free from cover by trees bridges buildings or other obstructions The vehicle must have remained in open sky for at least 5 minutes for full accuracy e The vehicle must exhibit some motion behaviour Accelerations of the unit in different directions are required so that the Kalman filter can estimate the errors in the sensors Without this estimation some of the specifications degrade e The distance from the system to the external GPS antenna must be known by the system to a precision of 5mm or better The vibration of the system relative to the vehicle cannot allow this to change by more than 5mm The system can estimate this value itself in some dynamic conditions e The heading accuracy is only achieved under dynamic conditions Under slow and static conditions
41. ighting the Inertial believes the inertial sensors more In urban environments it is better to believe the inertial sensors more whereas in open sky the GPS receiver should be believed more Revision 120928 a Advanced The Advanced option is used to set special commands for the Inertial This should only be done with special instructions from OxTS Committing the Configuration to the Inertial The changes to the Inertial settings must be performed using Ethernet It is necessary to configure your computer s Ethernet settings so it is on the same network as the Inertial If necessary ask your system administrator to help Figure 19 below shows the Commit screen Figure 19 itconfig Commit Screen Inertial Configuration I 7 Commit Inertial a Commit configuration to the Inertial Inertial ELLELE IP Address of Inertial Navigation 1950 0138 Step 9 of 10 Read Config GPS Selection Orientation External Antenna Secondary Antenna Wheel Config Odometer Input Options Save Finish Confidently Accurately Dev ID 110826 14ce Ex enoish x Enter the IP address of the Inertial that you want to configure The drop down box will list all of the Inertial systems that are connected to this computer this function does not work if Enginuity or other software is using the Inertial UDP port 46 Oxford Technical Solutions Inertial User Manual Qoxrs Inertial GPS
42. ld be measured to an accuracy of 10cm Enter the value and select whether the ground is above unlikely or below the Inertial Typically the measurements would all be made to an accuracy of 10cm Selecting a better accuracy than 10cm does not improve results Using an accuracy figure worse than 20cm will increase the drift of the Inertial Use the accuracy fields to select or specify the accuracy of the measurements e Oxford Technical Solutions Inertial User Manual Qoxrs Inertial GPS Configuring the Odometer Input Using an odometer makes a huge difference to the longitudinal drift performance of the Inertial when GPS is not available As with the wheel configuration the odometer input can only be used on land vehicles Aircraft and marine vehicles cannot use this option The odometer input cannot be used on a steered wheel it must be used on a wheel that is measuring the forward direction of the vehicle The best odometer to use is from a wheel Optical sensors and Doppler radar sensors can also be used It is better to use a front wheel drive vehicle and put the odometer on the rear wheels The odometer pulses from driven wheels are less accurate Figure 12 below shows the Odometer Input screen Figure 12 itconfig Odometer Input Screen G TE Inertial Configuration a Inertial Inertial and GPS Navigation Measured from the Inertial Where is the measurement point of the Odometer Ahead m 0 000 m
43. n missing data Other important measurements such as heading pitch and roll can also be measured The Inertial is a true inertial navigation system INS that is aided by the external GPS An inertial sensor block with three accelerometers and three angular rate sensors is used to compute all the outputs A WGS 84 modelled strapdown navigator algorithm compensates for earth curvature rotation and Coriolis accelerations while measurements from the external GPS receiver update the position and velocity navigated by the inertial sensors This innovative approach gives the Inertial several distinct advantages over systems that use GPS alone e All outputs remain available continuously during GPS blackouts when for example the vehicle drives under a bridge e The Inertial recognises jumps in the GPS position and ignores them e The position and velocity measurements that the GPS makes are smoothed to reduce the high frequency noise e The Inertialt t makes many measurements that GPS cannot make for example acceleration angular rate heading pitch roll etc e The Inertial takes inputs from a wheel speed odometer DMI in order to improve the drift rate when no GPS is available e The Inertial has a high 100Hz update rate and a wide bandwidth e The outputs are available with very low 3 5ms latency The Inertial system processes the data in real time The real time results are output via RS232 and over 10 100 Base T Etherne
44. nformance Notices The Inertial complies with the radiated emission limits for 47CFR15 109 2010 class A of Part 15 subpart B of the FCC rules and with the emission and immunity limits for class A of EN 55022 These limits are designed to provide reasonable protection against harmful interference in business commercial and industrial uses This equipment generates uses and can radiate radio frequency energy and if not installed and used in accordance with the instructions may cause harmful interference to radio communications However there is no guarantee that interference will not occur in a particular installation If this equipment does cause harmful interference to radio or television reception which can be determined by turning the equipment off and on the user is encouraged to try to correct the interference by one or more of the following measures Re orient or relocate the receiving antenna Increase the separation between the equipment and the receiver The Inertial incorporates a GPS receiver Any GPS receiver will not be able to track satellites in the presence of strong RF radiations within 70 MHz of the GPS frequency 1575 MHz L1 The Inertial conforms to the requirements for CE Regulator Testing Standards e 47CFR15 109 2010 class A radiated emissions e EN 300 440 1 2008 test methods 8 3 2 conducted emissions and 8 3 3 radiated emissions EN55022 class A according to standard EN 301 489 1 2008 c
45. ng the Initial Configuration 26 Revision 120928 Fa Type of GPS receiver connected 28 Orientation of the Inertial in the vehicle 29 Specifying the Position of the External Antenna 32 Configuring the Secondary Antenna 33 Configuring the Wheel Position 35 Configuring the Odometer Input 37 Setting the Correct Options 38 Initialisation Speed Option 39 Output Displacement Option 39 Camera Trigger 40 Heading Lock Option 40 Output Lock 40 Output Smoothing 41 Altitude 42 Serial 1 and Serial 2 42 Ethernet Output 44 GPS Control 45 GPS Weighting 45 Advanced 46 Committing the Configuration to the Inertial 46 Saving a copy of the settings locally 47 Inputs and Outputs 48 Pin Assignments 48 Digital Inputs and Outputs 49 1PPS Output 49 Event Input 50 Odometer Input 50 Camera Trigger Output 50 Reverse Polarity Protection 51 Ethernet Configuration 52 Laboratory Testing 53 Accelerometer Test Procedure 53 Gyro Test Procedure 53 Testing the Internal GPS and other Circuitry 54 a Oxford Technical Solutions Inertial User Manual QOaxrs Inertial GPS Using the Orientation Measurements 56 Co ordinate Frame Conventions 57 Navigation Frame 58 Level Frame 58 Vehicle Frame 59 Revision History 60 Drawing List 6l Revision 120928 e Introduction The Inertial is an add on for GPS receivers to improve reliability and accuracy The Inertial uses accelerometers and angular rate sensors gyros to smooth the jumps in GPS and fill i
46. nical Solutions Inertial User Manual Qoxrs Inertial GPS Installation It is essential to install the Inertial rigidly in the vehicle The Inertial should not be able to move or rotate compared to either GPS antenna otherwise the performance will be reduced In most circumstances the Inertial should be mounted directly to the chassis of the vehicle If the vehicle experiences high shocks then vibration mounts may be required OxTS has a quick mounting system called the RT Strut which can be used to fit the Inertial in to a vehicle quickly Do not install the Inertial where it is in direct sunlight which in hot countries may cause the case to exceed the maximum temperature specification For single antenna installations the position of the primary GPS antenna is not critical it can have a partial view of the sky as long as it has enough satellites to operate For dual antenna installations it is essential for both the primary and the secondary antenna to be mounted in a good open location and on a suitable ground plane such as the roof of a vehicle The antennas cannot be mounted on non conducting materials or near the edges of conducting materials If the antennas are to be mounted with no conductor below them then different antennas must be used Dual antenna systems For best performance of the dual antenna systems it is necessary to fit the secondary antenna to the system The system is very sensitive to incorrect fit
47. nown compared to the inertial sensors 6 The Kalman filter tries to estimate the angle between the inertial sensors and the Secondary GPS Antenna The default value used in the configuration software 5 degrees is not accurate enough so that the Inertial 2 can improve the heading using this value If you want the vehicle heading to 0 1 degrees but you only know the angle of the two GPS antennas to 5 degrees then the measurements from the antenna are not going to be able to improve the heading of the car Driving a normal warm up with stops starts and turns helps the Kalman filter improve the accuracy of the Secondary GPS Antenna angle The accuracy of this angle is available in the Status information On aircraft or marine vehicles some turns are needed to help the Kalman filter estimate the relative angle of the antennas compared to the Inertial 2 7 In the unlikely event that the RTK Integer solution is incorrect at the start then the Kalman filter can update the Secondary Antenna Orientation incorrectly If this happens then things start to go wrong The Kalman filter becomes more convinced that it is correct so it resolves faster but it always solves incorrectly Solving incorrectly makes the situation worse Revision 120928 ai To avoid the Kalman filter from getting things wrong it is possible to drive a calibration run then enter the secondary antenna angle back in to the configuration software The estimated angle and accu
48. od In particular the Inertial will try to improve the external GPS antenna position the orientation of the dual antennas the yaw orientation of the Inertial in the vehicle and the wheel speed calibration values For applications where the Inertial is installed permanently in the vehicle it can be beneficial to use the values that the Inertial has learned next time you use the Inertial It can make the results more consistent e Oxford Technical Solutions Inertial User Manual Qoxrs Inertial GPS You should not use this feature if there is a risk that the Inertial will rotate in the vehicle or a risk that the GPS antennas can move even by a few millimetres Before the configuration can be improved the current configuration should be read into it config on the Read Configuration page To read the improved values from the Inertial click the button to the right of the text The Improved configuration from Inertial window will appear as shown in Figure 7 Figure 7 it config Improved configuration from Inertial window F i Improved configuration from Inertial F Read Improved Configuration Inertial Choose where to read the configuration from Inertial and GPS Navigation Read configuration from Ethernet iv Step 1 of 2 Settings Select IP address Confidently The configuration can be read from two sources From an NCOM file If an NCOM file has been saved to di
49. onducted emissions EN6100 4 3 criterion A according to standard EN 301 489 1 2008 radiated immunity e 1SO7637 2 criterion B 12V according to standard EN 301 489 1 2008 vehicular transients and surges immunity Older Inertial systems do not conform to this standard contact OxTS for further details EN60950 1 2006 safety e A11 2009 safety Revision 120928 Ka Connections The connection of the Inertial and Inertial 2 is shown in Figure 2 Figure 2 Connection Example External Secondary Primary Antenna Antenna Antenna a kiaii oo k we i Extena lt Serial 4 Power erla Serial 2 Power Ethernet The external GPS receiver is connected to the Inertial using a serial connection Power is supplied directly to the Inertial Seriall Serial2 and Ethernet outputs are available from the Inertial The Inertial has its own internal GPS receiver This receiver is required to synchronise the inertial measurements to GPS time The position and velocity measurements from this receiver are not normally used It is possible to use an antenna splitter and feed the GPS signal in to both the External GPS and Inertial When using an Inertial 2 the Secondary GPS Antenna should be fitted The Inertial 2 will operate as an Inertial if this antenna is not connected Further details on the connections may be found in the Integration Manual for the GPS receiver being used e Oxford Tech
50. or the other Do not extend the cable even using special GPS signal repeaters that are designed to accurately repeat the GPS signal Cable length options are available in 5m 15m and 30m lengths 6 Mount both antennas where they have a clear unobstructed view of the whole sky from all angles 7 Ttis critical to have the Inertialt 2 mounted securely in the vehicle If the angle of the Inertial 2 can change relative to the vehicle then the dual antenna system will not work correctly This is far more critical for dual antenna systems than for single antenna systems The user should aim to have no more than 0 05 degrees of mounting angle change throughout the testing If the Inertial 2 is shock mounted then the Inertial 2 mounting will change by more than 0 05 degrees this is acceptable but the hysteresis of the mounting may not exceed 0 05 degrees How the Inertial 2 uses the Dual Antenna Measurements It is often useful to have an understanding of how the Inertial 2 uses the measurements from the dual antenna system This can lead to improvements in the results obtained 1 To use the measurements properly the Inertial 2 needs to know the angle of the GPS antennas compared to the angle of the Inertial 2 This cannot be measured accurately by users without very specialised equipment the Inertial 2 needs to measure this itself as part of the warm up process EI Oxford Technical Solutions Inertial User Manual Qoxrs Inertial GPS
51. ould be made to an accuracy of a Oxford Technical Solutions Inertial User Manual Qoxrs Inertial GPS 5cm or better When using a lcm accurate GPS receiver the Inertial will be able to improve the measurements of the antenna itself Some GPS receivers can compensate for the height difference between the phase centre and the antenna base This option should not be used with the Inertialt The GPS receiver assumes that the roll and pitch of the antenna are zero in order to do the compensation The Inertial can perform the compensation correctly even when the roll and pitch are not zero Figure 9 below shows the External Antenna screen Figure 9 i config External Antenna Screen m Inertial Configuration Inertial Inertial and GPS Navigation Measured from the Inertial Where is the measurement point of the GPS Antenna Ahead m 0 000 m Step 4 of 10 Pi iv 0 000 m Read Config i m 1 000 m GPS Selection Orientation C Specify each accuracy separately Secondary Antenna Wheel Config Odometer Input Options Commit Save Finish Overall accuracy 0100m Confidenthy Accurately ES ey 110825 Ace 4 Configuring the Secondary Antenna On the Inertial 2 the position of the secondary antenna compared to the primary antenna needs to be specified accurately If the dual antenna page is not enabled then the Inertialt 2 will ignore
52. private network This will help avoid loss of data through collisions on the network In general the IP address of the Inertial is related to the serial number The IP address will be 195 0 0 x where x is the last two digits of the serial number Enginuity will display the IP address of any Inertial systems that are connected Note that it is possible to change the IP address of Inertial systems If the IP address has been changed then Enginuity should still be able to identify the IP address that the Inertial is using as long as the PC has a valid IP address and this is not the same as the Inertial s IP address When selecting an IP address for the PC that will communicate with the Inertial you can use any IP address in the same subnet For example 195 0 0 200 should be available since this IP address is never used by the Inertial by default EI Oxford Technical Solutions Inertial User Manual Qoxrs Inertial GPS Laboratory Testing There are several checks that can be performed in the laboratory to ensure that the system is working correctly The most fragile items in the system are the accelerometers the other items are not subject to shock and do not need to be tested as thoroughly Accelerometer Test Procedure To check that the accelerometers are working correctly follow this procedure 1 Use the default orientation configuration in i config 2 Connect power to the system connect the system to a laptop computer
53. r the dual antenna product offers almost constant heading performance under all conditions whereas the single antenna system has reduced heading accuracy on aircraft boats or in low speed land vehicles GPS only dual antenna systems require open sky environments to operate because they can take several minutes to acquire heading lock Advanced processing in the Inertial 2 allows relock to occur after 5s of a sky obstruction in this time the Inertial 2 s heading will not have significantly degraded The fast relock time is made possible because the Inertial 2 s own heading is used to resolve the ambiguities in the GPS measurements Resolution of these ambiguities is what normally takes several minutes The heading software in the Inertial 2 enables significantly better performance and coverage compared to GPS only solutions Ea Oxford Technical Solutions Inertial User Manual Qoxrs Inertial GPS Scope of Delivery The Inertial products are supplied with cables GPS antenna software and manual In the standard configurations magnetic mount antennas are provided but other antenna types are available please enquire for more details An external GPS receiver is required for best performance In land vehicles an external wheel speed odometer DMI is recommended to reduce drift rates Table 1 lists all the items that are delivered with the Inertial and Inertial 2 Table 1 Summary of the Inertial and Inertial 2 system components
54. r profits or business interruption however caused and on any theory of liability whether in contract strict liability or tort including negligence or otherwise arising in any way out of the use of this software even if advised of the possibility of such damage Copyright Notice Copyright 2012 Oxford Technical Solutions Revision Document Revision 120928 See Revision History for detailed information Contact Details Oxford Technical Solutions Limited Tel 44 0 1869 238 015 77 Heyford Park Fax 44 0 1869 238 016 Upper Heyford Oxfordshire http www oxts com OX25 5HD mailto info oxts com England a Oxford Technical Solutions Inertial User Manual QOaxrs Inertial GPS Table of Contents Introduction 6 Easy Operation 7 Self Correcting 7 Flexible Accuracy 7 Drop In Component 7 Inertial vs Inertial 2 7 Scope of Delivery 9 Warranty 11 Specification 12 Common Specifications 14 Dual Antenna Heading Accuracy 15 GPS Antenna Operating Temperature 15 Export Control Classification Number 16 Conformance Notices 17 Regulator Testing Standards 17 Connections 18 Installation 19 Dual antenna systems 19 How the Inertial 2 uses the Dual Antenna Measurements 20 Multipath Effects on Dual Antenna Systems 22 Using an antenna splitter 23 LED Definitions 24 Strapdown Navigator LED States 24 Position 25 Power Pwr LED 25 Changing the Configuration 26 Overview 26 Selecting the Operating Language 26 Readi
55. racy can be found in the Calibration window of Enginuity This step can only be done if the Inertial 2 is permanently mounted in a vehicle and the antennas are bolted on Any movement of either the Inertial 2 or the antennas will upset the algorithms Multipath Effects on Dual Antenna Systems Dual antenna systems are very susceptible to the errors caused by multipath This can be from buildings trees roof bars etc Multipath is where the signal from the satellite has a direct path and one or more reflected paths Because the reflected paths are not the same length as the direct path the GPS receiver cannot track the satellite signal as accurately The dual antenna system in the Inertialt2 works by comparing the carrier phase measurements at the two antennas This tells the system the relative distance between the two antennas and which way they are pointing the heading For the heading to be accurate the GPS receivers must measure the relative position to about 3mm The level of accuracy can only be achieved if there is little or no multipath In an ideal environment with no surrounding building trees road signs or other reflective surfaces the only multipath received is from the vehicle s roof The antennas supplied with the RT are designed to minimise multipath from the vehicle s roof when the roof is made of metal For use on non metallic roofs a different type of antenna is required When stationary the heading from the Inertial
56. selected language does not change the format used for numbers Reading the Initial Configuration The i config Read Configuration screen gives several options for reading the configuration from different places as shown in Figure 4 EJ Oxford Technical Solutions Inertial User Manual Qoxrs Inertial GPS Figure 4 i config Read Configuration Screen g Sa i Inertial Configuration x aa i Inertial Read Configuration 4 Choose where the initial settings should be read from Inertial iid Use Default Settings Navigation Read Settings from a folder Step 1 of 10 Read Settings from an RD file Read Settings from an Inertial GPS Selection Orientation External Antenna Secondary Antenna Wheel Config Odometer Input Options Commit Save Finish Confidently Accurately Dev ID 110826 14ce EfEnish x Nem _ _ Cancel Use Default Settings To use the default settings select this radio button The following pages will contain the default settings that the Inertial was delivered with Read from a folder It is possible to store a configuration in a folder The configuration requires several files so it is tidier to keep it in a folder by itself To read the configuration from a folder select this radio button A group box will appear and the folder can be selected Read Settings from an RD file The Inertial writes the configuration it is using to the internally stored RD file
57. sk or processed using the post process utility then this file can be read and the settings extracted from it Use this setting if you have an NCOM file Do not use an NCOM file that has been combined from forward and backwards processing of the inertial data e From an Inertial connected by Ethernet This will get this information that the Inertial is using at the moment and load it into the configuration software Use this setting if the Inertial is running has initialised and has warmed up Once the source has been selected the software will find which configurations can be read from the source Configurations that cannot be read will be shown in grey this may be because the Inertial was not calculating these values at present Figure 8 shows the configurations that can be read with some in grey in this example Revision 120928 i Figure 8 i config Improved configuration from Inertial window la e i Improved configuration from Inertial A 7 Select Configuration Inertial Choose which settings should be used Inertial and GPS Items Description Navigation i Step 2 of 2 Wheel speed input Source Select All Clear All Confidently You may update several parameters at once Check the checkbox next to each item in order to read the Kalman filter s best estimate and transfer it to the configuration in i config If the Orientation in vehicle is used then this has consequences
58. t using a UDP broadcast Outputs are time stamped and refer to GPS time The measurements are synchronised to the GPS clock Ey Oxford Technical Solutions Inertial User Manual Qoxrs Inertial GPS Easy Operation Installation and operation of the Inertial could not be simpler A simple configuration wizard is used to configure the Inertialt t The configuration can be saved to the Inertial so it can operate autonomously without user intervention A lot of work has been put into the initialisation of the inertial algorithms so that the Inertial can reliably start to navigate in the vast majority of situations For example the Inertial can initialize during flight without problems To make installation easier the Inertial contains its own low cost GPS receiver This receiver is used to synchronise the inertial measurements to the external GPS receiver Using this technique the Inertial is able to precisely time align the measurements from the external GPS giving much more accurate results The single unit contains the inertial sensors low cost GPS receiver data storage and CPU A laptop computer can be used to view the results in real time Often an antenna splitter can be used to split the signal from the external GPS receiver and feed it to the GPS receiver in the Inertial Self Correcting Unlike conventional inertial navigation systems the Inertial uses GPS to correct all its measurements GPS makes measurements of posi
59. the SDNav LED alternates between red and Green green The Inertial needs to be woken up by an external command Contact OxTS for more information on this feature In current versions of the software the Strapdown Navigator will not leave Green and return to any other state This may change in future releases EI Oxford Technical Solutions Inertial User Manual Qoxrs Inertial GPS Position The GPS LED shows what type of GPS solution is currently being used by the Kalman filter to update the Strapdown Navigator Table 10 below gives the states of this LED Table 10 Position Solution LED States Colour Description Off The GPS receiver is not sending data Red The GPS receiver is sending data to the Inertial This is an operational check for the GPS Flash receiver Red The GPS receiver has a standard position solution SPS Yellow The GPS receiver has a DGPS or kinematic floating position solution 20cm accuracy Green The GPS receiver has a kinematic integer position solution 2cm accuracy Power Pwr LED The Power Pwr LED shows the state of the internal 5V power supply and the state of the TX line of the J2 connector Table 11 below gives the states of this LED Table 11 Power Comms LED States Colour Description Off There is no power to the system or the system power supply has failed Green The 5V power supply for the system is active Orange The system is outputting data on connector J2 R
60. the performance will degrade a Oxford Technical Solutions Inertial User Manual Table 2 Typical Performance Specification for Inertial Parameter 2cm 20cm Internal L1 L2 GPS L1 Float GPS GPS Positioning L1 L2 L1 Kinematic Differential SPS SPS Kinematic OmniStar HP OmniStar VBS Position Accuracy 2cm lo 20cm 0 4m CEP 1 8m CEP 3 0m CEP 10cm for HP Velocity Accuracy 0 05 km h 0 08 km h 0 1 km h 0 1 km h 0 2 km h RMS RMS RMS RMS RMS Acceleration Bias 10 mm s lo 10 mm s lo 10 mm s lo 10 mm s lo 10 mm s lo Linearity 0 01 0 01 0 01 0 01 0 01 Scale Factor 0 1 lo 0 1 lo 0 1 lo 0 1 lo 0 1 lo Range 100 m s 100 m s 100 m s 100 m s 100 m s Roll Pitch 0 03 lo 0 04 lo 0 05 lo 0 05 lo 0 15 lo Heading 0 1 lo 0 1 lo 0 1 lo 0 1 lo 0 2 lo Angular Rate Bias 0 01 s lo 0 01 s lo 0 01 s lo 0 01 s lo 0 01 s lo Scale Factor 0 1 lo 0 1 lo 0 1 lo 0 1 lo 0 1 1o Range 100 s 100 s 100 s 100 s 100 s Track at 50km h 0 07 RMS 0 1 RMS 0 15 RMS 0 15 RMS 0 25 RMS Dual Antenna No No No No Yes Note 1 The operating temperature range for the antenna is much wider since it can be mounted outside the vehicle See specification below Note 2 Some manufacturers specify L1 L2 GPS to be more accurate than 2cm in which case the Inertial will also be more accurate However it is assumed that the Inertial will be used in dynamic conditions and under these
61. the secondary antenna and will not use it to compute a Revision 120928 a heading solution Enable the dual antenna in order to use the dual antenna capability of the Inertial 2 Figure 10 itconfig Secondary Antenna Configuration Screen Inertial Configuration Inertial Inertial and GPS Navigation Total distance between the Primary and 1 000 m Secondary antenna Step 5 of 10 Measured from the Primary Antenna Where is the Secondary Antenna Read Config GPS Selection Orientation External Antenna C Enable static initialisation Position of the Antenna Behind Wheel Config C Use advanced settings Odometer Input Options Commit Save Finish Confidenthy A at NE Dey 1D 110826 Tae BES eroisn v It is best to mount the two antennas on the top of the vehicle Although it is possible to mount one on the roof and one on the bonnet hood in reality the multi path reflections from the windscreen will degrade the performance of the system On aircraft it is best to mount both antennas on the main aircraft fuselage if the Inertial is mounted in the aircraft fuselage itself If the Inertial is mounted on a pod under the wings then mounting the antennas on the pod may give the best results If the antennas are mounted at significantly different heights or if the mounting angle is not directly along a car axis forward or right then use the advanced settings to sp
62. they can be aligned by reconfiguring the Inertial for a different mounting orientation using the i config software If you are using the RT Strut to mount the Inertial in the vehicle then you will have to use i config to configure the orientation or the Inertial will not work correctly Revision 120928 EZ Navigation Frame The Navigation Frame is used by the Inertial Navigation System to integrate the acceleration to velocity and to integrate the velocity to position The definition of the Navigation Frame is listed in Table 20 Table 20 Navigation Frame Definition Axis Description Diagram n North The north axis n is perpendicular to the gravity vector and in the direction of the north pole along the earth s surface North e East The east axis e is perpendicular to gravity perpendicular to the north axis and is in the east direction d Down The down axis d is along the gravity vector East For example the velocity in the north direction would be written as Vn Level Frame The Level Frame is attached to the vehicle but does not rotate with the roll and pitch of the vehicle It rotates by the heading of the vehicle The definition of the level frame is listed in Table 21 and shown in Figure 24 Table 21 Level Frame Definition Axis Description f Forward This is the forward direction of the car projected in to the horizontal plane l Lateral This is the lateral right direction of the
63. ting and operation of the secondary antenna and these instructions should be followed carefully otherwise it is unlikely that the system will operate correctly Before fitting the secondary antenna bear the following information in mind 1 In the default configuration the primary antenna should be at the front of the vehicle s roof and the secondary antenna should be at the rear 2 The antenna separation must be correct to 3mm or better 3 Itis essential to orientate the antennas the same way Always have the cable exiting from each antenna in the same direction See Figure 3 below Revision 120928 B Figure 3 Dual Antenna Orientations Correct Wrong 4 For good multipath rejection the antennas must be mounted on a metal surface using the magnetic mounts provided no additional gap may be used Multipath affects stationary vehicle more than moving vehicles and it can lead to heading errors of more than 0 5 degrees RMS if the antennas are mounted poorly on the vehicle Mounting the antennas within 30cm of the edge of the metal surface can also reduce the performance 5 For both single antenna systems and dual antenna systems it is essential that the supplied GPS antenna cables are used and not extended shortened or replaced This is even more critical for dual antenna systems and the two antenna cables must be of the same specification Do not for example use a 5m antenna cable for one antenna and a 15m antenna cable f
64. ting right and the Z axis pointing backwards though other configurations are possible Figure 6 below shows the orientation screen of i config Revision 120928 EX Figure 6 i config Orientation Screen i Inertial Configuration x Orientation Inertial ae 4 Specify how you have mounted the Inertial in the vehicle Inertial and GPS Navigation Y axis points Right Z axis points Down _ Use advanced settings Step 3 of 10 Read Config GPS Selection External Antenna Secondary Antenna Wheel Config Odometer Input a 2 Options 4 warmed up correctly operating Inertial will have improved Commit configurations Read improved configuration from the Save Finish Inertial Confidently Dev ID 110826 14ce EE Enaiish x To work out the direction that the Inertial is mounted at look to see which directions the Y axis and the Z axis are pointing Then enter these directions in to the software The greyed out Advanced Settings will change to show the three rotations associated with orientation chosen To make small adjustments use the advanced settings This allows the user to zero any heading pitch or roll offsets Also included on the orientation page is the ability to read the configuration settings that the Kalman filter in the Inertial has computed This is useful if a calibration run has been done and the Kalman filter s values are known to be go
65. tion and velocity Using these measurements the Inertial is able to keep other quantities such as roll pitch and heading accurate Flexible Accuracy The Inertial takes GPS accuracy measurements into account and uses them to obtain the best possible output accuracy When using a lcm accurate GPS receiver the Inertial will give 1cm accurate results Drop In Component The Inertial has been made so that it is a drop in component in many applications The NMEA input and NMEA output means that the original GPS output can be connected to the Inertial and the Inertial output can be connected to the final application Inertial vs Inertial 2 The Inertial 2 is a dual antenna version of the Inertial On the Inertial 2 the external GPS gives high accuracy position information and two internal GPS receivers give high accuracy heading information Revision 120928 Ea The advanced algorithm in the Inertial 2 software means that most road vehicle customers are able to use a single antenna system The Heading Lock and Advanced Slip features mean that the Inertial can maintain accurate heading while stationary and while driving with low vehicle dynamics Applications on aircraft or at sea may require a dual antenna system to maintain high accuracy heading Take care while reading the specifications The single antenna product can achieve heading accuracies that are equivalent to the dual antenna product in some conditions Howeve
66. ximum rate of 0 1m per second If a large error is accumulated for example if GPS is not available for a long period of time then it may take a very long time to apply the correction Under these circumstances it may be preferable to jump the measurement to the correct value quickly By specifying a Time Limit for the correction the Inertial will jump the measurement if it will take too long to correct For example if the position has drifted by 5m after a period without GPS and the smoothing is set to 0 05m then it will take at least 100s to correct the 5m drift If the Revision 120928 a time limit is set to 20s then the Inertial will apply the 5m correction immediately because the predicted time to correct the position is longer than the time limit Care should be taken not to make the smoothing too small If these parameters are too small then the Inertial will not be able to make suitable corrections to the outputs and it will not work correctly Altitude The altitude option can be used to change the default altitude output between the ellipsoidal altitude of WGS84 and the geoidal altitude given by adding undulation from a lookup table Outputs where the altitude type is specifically defined e g NMEA GGA are not affected outputs where the altitude type is not defined NCOM are affected The geoid table used will come from the external GPS receiver if the external GPS does not supply undulation or geoid height

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