Sparton Digital Compass Frequently Asked Questions (FAQ)1. Will the compass provide a True North indicator?2. How does the compass know where I am geographically to use the appropriate declination? 3. Will the accuracy of the digital compass be different at the North/South Pole versus the Equator? 4. Are the X, Y, and Z axis considered body centered (relative to the board) or are they relative to the earth? 5. How should the compass board be oriented? 6. How is Pitch, Roll, X, and Y defined? 7. Can you measure 360 degrees of tilt? 8. What is the data sampling rate of the compass? 9. Is there anyway of slowing down the output rate of the heading in the software so that it is easier to read? 10. Can we access tilt data from the accelerometers? 11. What does “platform tilt" mean? 12. What is the difference between storage and operating temperature range? 13. Is there any advantage of using the SPI interface verses the UART interface? 14. How do you factory calibrate the compass? 15.Does the compass require a calibration cycle before use? 16. Does the Customer need to move the compass in a circle to calibrate its readings? 17. How are the tilt measurements and magnetic compass heading measurements affected by dynamic motion and vibration? 18. What is the optimal filter value setting? 19. Does the digital compass software do the filtering or is this a command to the hardware which then applies a filter to its output? 20. Will metal encasings or nearby computer chips influence the unit negatively? 21. Will batteries or motors affect compass performance? 22. Please recommend the best way to mount the compass on a mobile Vehicle. 23. Do you have any quantitative data about how much error is created by ferrous metal or external magnetic fields around the compass? 24. Does the magnetic calibration reset command reset the entire compass? 25. Can you explain the term magnetic gradient as it pertains to measurements taken and calibration performed inside a building? The impression is that as long as the SP3003D is calibrated in the presence of the magnetic anomalies, and the magnetic anomalies don't change the heading will remain accurate. 26. I noticed that Sparton's SP3004D compass offers 2-D manual calibration capability in addition to the standard, 3-D calibration. What is the advantage of being able to perform a 2-D calibration and how is it performed? Is there a separate procedure for performing a 2-D manual calibration? 27. I have a ground robotics application in which all the electronics are in close proximity to the ground. I was wondering if I installed a digital compass in the robotic vehicle, would the rebarb normally embedded within concrete floors and other structures such as ceilings and walls create problems as the vehicle passes in close proximity? 28. The Magnetic Error bar on the display which is shown in the graphical user interface (GUI) of the development kit software shows values ranging from 0 to 1,000. In the user document, the error given by the compass ranges from 0 to 10,000. Does the software scale 0-10,000 down to 0-1,000 (ex. divide by 10 before charting) or does it ignore error above 1,000 and just show the error as 1,000 until it goes below 1,000? 1. Will the compass provide a True North indicator? Sparton digital compasses provide both Magnetic and True North indicators. Top of Page 2. How does the compass know where I am geographically to use the appropriate declination? The Sparton digital compasses will accept inputs of Latitude, Longitude, Date, Time, and Altitude information and calculate the magnetic variation based on your position. The compasses will then use the magnetic variation to provide a True North output. Top of Page 3. Will the accuracy of the digital compass be different at the North/South Pole verses the Equator? All compasses will experience performance degradation with latitude. At the North/South magnetic poles, the magnetic field is vertical and gives no indication of direction. Therefore, compasses will be more accurate at the equator than at the poles. Top of Page 4. Are the X, Y, and Z axis considered body centered (relative to the board) or are they relative to the earth? The X, Y, and Z axis are relative to the compass board. Refer to the Sparton Digital Compass User Document for more information. Top of Page 5. How should the compass board be oriented? The Sparton digital compasses are designed such that they can be mounted either vertically or horizontally. This is a User-Selectable feature. The compass will indicate the heading which corresponds to the angle between Magnetic North and the North direction of the compass board. Refer to the Sparton Digital Compass User Document for more information. Top of Page 6.How is Pitch, Roll, X, and Y defined? Pitch is associated with rotation about the Y-axis. It is measured using the X-axis accelerometer to measure Tilt. Similarly, Roll is associated with rotation about the X-axis and is measured using the Y-axis accelerometer. Refer to the Sparton Digital Compass User Document for more information. Top of Page 7. Can you measure 360 degrees of tilt? Yes. Roll can be +/-180 degrees (or a full 360 degrees). Pitch can be +/- 90 degrees. Top of Page 8. What is the data sampling rate of the compass? The sample rate is approximately 10Hz. This is mainly limited by the magnetic measurements. Top of Page 9. Is there anyway of slowing down the output rate of the heading in the software so that it is easier to read? The only way to slow down the output is by increasing the filter value. Top of Page 10. Can we access tilt data from the accelerometers? Pitch and Roll data can be requested by sending the proper native or NMEA command. The compass will respond back with the Pitch and Roll of the compass platform. Refer to the Sparton Digital Compass User Document for more information on this feature. Top of Page 11. What does “platform tilt" mean? This is the absolute tilt of the platform from vertical and is derived from both the Pitch and Roll. Top of Page 12. What is the difference between storage and operating temperature range? Operating temperature range means that the compass, in a powered up and functioning condition, will continue to function properly within the stated temperature range. Storage temperature means that the compass, in a non-powered state, can be safely stored within the stated temperature range and then will be fully functional in a powered condition when the temperature returns within the operating limits. Top of Page 13. Is there any advantage of using the SPI interface verses the UART interface? The SPI port is intended for embedded applications. It allows for simple synchronous communication between the digital compass and a microcontroller or DSP. Data is transmitted in byte format which simplifies the processing of information since there is no text strings to be converted. The UART is intended for remote applications or situations where a spare UART is available. It provides 9600 baud asynchronous communication as a default setting on our SP3003D compass and a user selectable baud rate of 1200 -115200 on our latest design, the SP3004D. The UART can communicate in a byte format (NATIVE mode) similar to the SPI interface. It also offers a NMEA text format communication making interfacing easier with a simple text terminal. The UART is more flexible as it can handle both the NATIVE and NMEA type data format but is slower and requires more data to be transmitted for a given command. The SPI only handles NATIVE or byte-formatted commands but is faster and more efficient in transmitting data. The selection of SPI vs. UART will depend on your application and the resources available to interface with the digital compass. Top of Page 14. How do you factory calibrate the compass? The compass is factory calibrated in a computer-controlled environment. Known magnetic fields are generated and the compass error is measured in 3-dimensions. Both hard and soft magnetic distortions are calculated, corrected, and downloaded into the digital compass. Our exact equations and methods are proprietary. Top of Page 15. Does the compass require a calibration cycle before use? Depends on accuracy requirements and whether your particular operating environment is free of magnetic fields. Sparton digital compasses offer automatic, 3-dimensional in-field calibration. Sparton digital compasses use a proprietary adaptive algorithm to monitor the magnetic field conditions and automatically calibrate for hard and some soft magnetic distortions. Top of Page 16. Does the Customer need to move the compass in a circle to calibrate its readings? Yes, if it is desired to perform a Manual calibration. However, Sparton digital compasses also provide automatic, in-field calibration. See User Document for more details of this feature. Top of Page 17. How are the tilt measurements and magnetic compass heading measurements affected by dynamic motion and vibration? Most compasses measure the gravitation of the Earth to determine the horizontal plane. This measurement is important in calculating an accurate magnetic heading. Accelerometers by nature are motion sensitive. Sparton digital compasses are affected by dynamic motion and vibration. Our compasses have been configured with user-selectable digital filtering to reduce these effects, but this can also decrease the responsiveness of the compass. Sparton digital compasses have been designed to be more tolerant of motion-induced errors by how they process the magnetic and acceleration data. Top of Page 18. What is the optimal filter value setting? Most compasses measure the gravitation of the Earth to determine a horizontal reference. This measurement is important in calculating an accurate magnetic heading and is typically accomplished using accelerometers. Since accelerometers are, by nature, motion sensitive, most compasses will be affected by dynamic motion and vibration. Sparton digital compasses have been designed to be more tolerant of motion-induced errors by how they process the magnetic and acceleration data. Top of Page 19. Does the digital compass software do the filtering or is this a command to the hardware which then applies a filter to its output? The software implements a single-pole digital IIR filter. Top of Page 20. Will metal encasings or nearby computer chips influence the unit negatively? If the metal has magnetic properties, then yes. Magnetic material should be kept away from any compass for best performance. Sparton digital compass products are calibrated in-house to remove any magnetic anomalies associated with the compass itself. Our compasses also come equipped with in-field calibration functions to help compensate for nearby magnetic material. Top of Page 21. Will batteries or motors affect compass performance? Yes, batteries typically contain a magnetic signature and electric motors generate magnetic fields that will affect compass performance. It is recommended that these items be placed as far away as possible from the compass. Top of Page 22. Please recommend the best way to mount the compass on a mobile Vehicle. Mount the Sparton digital compass away from strong magnetic fields or highly magnetic material. Sparton digital compasses provide calibration in full 3-dimensions and re-adjust the calibration parameters as the vehicle is used. Top of Page 23. Do you have any quantitative data about how much error is created by ferrous metal or external magnetic fields around the compass? It is difficult to quantify this error because there are many factors that affect it: - Amount and shape of magnetic material - Location and orientation relative to compass - The degree of magnetization (which can change over time) - Uniformity of the magnetization across the material Top of Page 24. Does the magnetic calibration reset command reset the entire compass? No. The magnetic calibration reset only resets the magnetic calibration parameters back to the factory default settings. It only affects the magnetics.Top of Page 25. Can you explain the term magnetic gradient as it pertains to measurements taken and calibration performed inside a building? The impression is that as long as the SP3003D is calibrated in the presence of the magnetic anomalies, and the magnetic anomalies don't change the heading will remain accurate. The compass corrects for any magnetic anomalies that move with the compass (i.e. the platform or vehicle on which the compass is mounted). Stationary magnetic anomalies that don't move relative to magnetic north (i.e. the building) will not be calibrated out by the compass. This is true for any compass because the Earth's magnetic vector will be distorted by the building and without a true reference, the compass can only act on what it measures. When the magnetic anomaly is attached to the compass platform, the compass now sees the distortion moving relative to the Earth's magnetic field and can compensate accordingly. A gradient field is a field that changes in intensity and/or direction relative to position (i.e. the magnetic field is not uniform). As the compass is moved, the sensors see different field intensities/directions based on the compass position and orientation. It becomes difficult to calibrate a compass in this situation because the magnetic field is not constant. Top of Page 26. I noticed that Sparton's SP3004D compass offers 2-D manual calibration capability in addition to the standard, 3-D calibration. What is the advantage of being able to perform a 2-D calibration and how is it performed? Is there a separate procedure for performing a 2-D manual calibration? The 2-D calibration was developed primarily for applications which have limited pitch and roll capability. When manual in-field calibration is performed, the compass will analyze the data and determine by itself if there is enough data for a 3-D calibration. If not, it will perform the 2-D calibration. The actual selection is transparent to the user. In order to perform the 2-D cal, you would rotate the compass in a level, horizontal plane a full 360 degrees. If you give the compass your latitude and longitude before the calibration, it will compute the magnetic field parameters at your location and use that information during the 2-D cal to improve the overall calibration accuracy. Top of Page 27. I have a ground robotics application in which all the electronics are in close proximity to the ground. I was wondering if I installed a digital compass in the robotic vehicle, would the rebarb normally embedded within concrete floors and other structures such as ceilings and walls create problems as the vehicle passes in close proximity? Yes, as the vehicle passes in close proximity to the magnetic material, magnetic effects on the compass may momentarily degrade compass accuracy. The degree of degradation will vary depending on the distance to and quantity of the ferrous material. Top of Page 28. The Magnetic Error bar on the display which is shown in the graphical user interface (GUI) of the development kit software shows values ranging from 0 to 1,000. In the user document, the error given by the compass ranges from 0 to 10,000. Does the software scale 0-10,000 down to 0-1,000 (ex. divide by 10 before charting) or does it ignore error above 1,000 and just show the error as 1,000 until it goes below 1,000? If the compass reports error above 1,000, the graphical error bar will max out at 1,000 just as you may have noticed on your display, however, the digital display below the bar will still show the actual reported magnetic error. Top of Page Each application is going to be different. Actual performance measurements are best measured in the end application after calibration. |
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Sparton Electronics - 5612 Johnson Lake Road - DeLeon Springs, Florida 32130 - 386-740-5472 |
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