Frequently Asked Questions

  1. How do I know if my IMU is connected properly?

    1. Refer to the VERSION log. If your IMU is communicating with a SPAN enabled receiver, the IMU details will be included in the log.

    2. When powered, the HG-1700 IMU makes a noticeable humming sound. If no sound is heard, check that the cable between the receiver and IMU is connected properly.

    3. Most IMUs do not make noise. Check that the IMU interface cable is properly connected to the receiver.
      For the IMU-ISA-100C, IMU-FSAS, IMU-CPT, IMU-HG1900, IMU-LN200, IMU-µIMU-IC, IMU-P1750 and IMU-KVH1750, ensure the IMU interface cable is connected to an RS-422 capable port and the port is configured to use RS-422.

    4. If the cable is connected properly, check the flex cable mounted on top of the IMU. Refer to the instructions in this manual on proper IMU installation to ensure that the cable is seated properly on the IMU pins. See HG1700 IMU in Universal Enclosure or LN-200 IMU in Universal Enclosure for more details.

    5. Check the input power supply. A minimum of 12 V should be supplied to the system for stable IMU performance. The supply should also be able to output at least 12 W over the entire operating temperature range.

  2. What is the minimum configuration I need to do to get the system running?

    1. Set the IMU type and IMU communication port with the CONNECTIMU command.

    2. Specify the translational offset between the IMU center of navigation and the primary GNSS antenna phase center with the SETINSTRANSLATION command.

    3. Specify the rotational offset between the IMU Body frame and the Vehicle frame, with the SETINSROTATION command.

  3. What types of IMUs are supported?

    SPAN currently supports the following IMUs:

    • ADIS-16488 from Analog Devices

    • EG320N and EG370N from Epson

    • HG1700, HG1900, HG1930 and HG4930 from Honeywell

    • IMU-FSAS from iMar

    • KVH 1750, KVH P-1750 and IMU-CPT from KVH

    • ISA-100C and µIMU from Northrop Grumman LITEF

    • LN-200 from Litton

    • STIM300 from Sensonor

    Use the CONNECTIMU command to specify the type of IMU used.

  4. Why don’t I have any INS data?

    1. By default, the raw IMU data begins flowing at system start up. If there is no INS data, check that the system has been configured properly.

    2. If the INSCOMMAND command has been set to START_FINE_TIME, the RAWIMU logs are not available until the system has solved for time. This requires that an antenna is attached and satellites are visible to the system. You can verify that time is solved by checking the time status in the header of any standard header log such as BESTPOS. When the time status reaches FINETIME, the inertial filter starts and IMU data is available.

  5. How can I access the inertial solution?

    The GNSS+INS solution is available from a number of specific logs dedicated to the inertial filter. The INSPOS log, INSPVA log, INSVEL log, INSSPD log and INSATT log are the most commonly used logs for extracting the INS solution. These logs can be logged at any rate up to the rate of the IMU data (100, 125, 200 or 400 Hz depending on your IMU model). The solution can also be triggered by the mark input signal by requesting the MARKxPVA logs.

  6. Can I still access the GNSS-only solution while running SPAN?

    The GNSS only solution used when running the OEM7 receiver without the IMU is still available when running SPAN. Logs such as the PSRPOS log and RTKPOS log are still available. The BESTGNSSPOS log is also available to provide the best available GNSS only solution. To manage processor load, any non-INS logs should be logged at a maximum rate of 5 Hz when running SPAN. Only INS-specific logs should be logged at rates higher than 5 Hz when running SPAN.

  7. What will happen to the INS solution when I lose GNSS satellite visibility?

    When GNSS tracking is interrupted, the INS solution bridges through the gaps with what is referred to as free-inertial navigation. The IMU measurements are used to propagate the solution. Errors in the IMU measurements accumulate over time to degrade the solution accuracy. For example, after one minute of GNSS outage, the horizontal position accuracy is approximately 2.5 m when using an HG1700 AG58. The SPAN solution continues to be computed for as long as the GNSS outage lasts, but the solution uncertainty increases with time. This uncertainty can be monitored using the INSSTDEV log or INSSTDEVS log.

  8. Why can SPAN not align with my IMU-KVH1750 or IMU-P1750?

    SPAN requires that the IMU-KVH1750 and IMU-P1750 be configured with non-default settings. If you have obtained your IMU-KVH1750 or IMU-P1750 directly from KVH, or have manually changed the IMU configuration, refer to IMU-KVH1750 and IMU-P1750 Baud Rate Conversion for information about configuring the IMU for operation with SPAN.