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SPAN-CPT Commonly Asked Questions

Q: Why don't I have any INS logs?

A: On start-up, the INS 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 SPAN log such as BESTPOS.
When the time status reaches FINESTEERING, the inertial filter starts and INS messages are

Q: My SPAN-CPT does not power up, I can't communicate with it.

A: Check that your power supply is stable and meets the required 9 to 18V DC specification.  Use a separate power supply such as a deep cycle battery whenever possible.  Avoid connecting the SPAN-CPT directly to your vehicle's power supply as they are usually too noisy to sustain stable power to the unit.

If you are using a known clean power supply but cannot communicate with the SPAN-CPT, check the amount of current being drawn by the unit.  The maximum power consumption of the SPAN-CPT is 15W.  If you are using a 12V power supply, the SPAN-CPT should be drawing 1.25A (P = IV).  If the SPAN-CPT is drawing significantly more or less than the expected current draw, you will have to send the unit back in to NovAtel for repair.

If the current draw is correct, but you still can't communicate with the SPAN-CPT, then check that all communication cables are securely connected.  If you are using a USB connection, make sure you have the proper USB drivers installed.  You can download the latest USB driver along with NovAtel Connect Software.

If you are using a USB to serial converter, make sure that the converter's driver is properly installed.  You may want to remove this converter and troubleshoot using a direct USB or serial connection to eliminate the converter as a source of error.

If you are using an RS-232 serial connection, avoid using any converters or gender changers when troubleshooting.  Connect to COM1 directly, or use a straight DB-9 extension cable from COM1, to see if you can establish communication.

Q: My SPAN-CPT's alignment resets in the middle of data collection.  It goes from INS_SOLUTION_GOOD to INS_INACTIVE.  What's going on?

A: There are two reasons why an alignment would reset.  The most common reason is an inadequate or noisy power supply.  NovAtel receivers have a voltage ripple spec of 100mV.  If your power source dips or jumps above 100mV, the receiver will reset, and you will have to perform the alignment again.  Please make sure that the power supply used is stable, and fits within the requirement of 9 - 18V DC.

The second possible reason is if there is a large inertial error that is unaccounted for.  This could be a poor lever arm, poor initial alignment, anything that will lead the filter to think there is a massive error.  You will first notice erratic attitude values being output, then the alignment resets to try and recover from this error.  If this happens, re-examine your setup.  Ensure that the lever arm values and rotation angles (if any) are entered correctly.  Do not use SETINITAZIMUTH or SETINITATTITUDE to speed up an alignment if the initial azimuth or attitude values are not accurate.  If you are in any doubt, please contact NovAtel support for assistance at

Q: My data does not look right.  There are lots of position jumps, or my IMU is not aligning at all.

A: Log a RAWIMU log and check the raw IMU status.  The status of a SPAN-CPT is 00000077 if it is healthy.  If you are seeing anything other than 00000077, please contact NovAtel support with your raw data.  We will likely need to send the IMU back for repair.

If your IMU is healthy, check the tracking condition of your data.  You can plot your carrier to noise (C/No) ratio using the Waypoint Toolbox here:

Your C/No should be between 37 db-Hz to 52 db-Hz from lowest elevation satellite to highest.  Are your signals coming in at a low C/No?  Is it too high?  Do you see a regular pattern of complete dropout?  Do you see a regular pattern of signal strength drop?  All of these are indications that there is a tracking issue.  Check your antenna placement and make sure it can see the sky from horizon to horizon.  Eliminate any sources of interference nearby the antenna.  If you are using two GNSS antennas, make sure they are at least 0.5m apart to avoid antenna coupling affect.

Q: I have a dual antenna setup and my IMU is not aligning.

A: First of all, check that you have both lever arm values entered either through the SPAN Alignment Wizard, or using the commands SETIMUTOANTOFFSET and SETIMUTOANTOFFSET2.  Aided transfer alignment will not start unless you have both lever arms entered.  Check that both antennas are at a location where they have good view of the sky.  Move to a location with an unobstructed view of the sky prior to doing your alignment.  Dual antenna SPAN-CPT requires good satellite tracking to perform an aided transfer alignment.

Q: I've got my wheel sensor plugged in but I'm not getting any TIMEDWHEELDATA log, or I'm seeing negative cumulative tick counts.

A: Check that you have all the proper pins connected as documented in the SPAN-CPT User Manual:

The wheel sensor must also meet the following requirements:

Input range less than or equal to 45 KHz
Input duty cycle is symmetric 40%-60%
Active input voltage is greater than or equal to 2.5 VDC with a max input voltage of 50 VDC
Inactive voltage is less than or equal to 1 VDC
Input current is approximately 3.5 mA at 5 VDC with a maximum of 5 mA at 50 VDC
Ensure input current does not exceed 5 mA. There is a current limiting diode that can dissipate 800 mW on the input opto-isolator
Quadrature, pulse and direction type odometers are compatible

If you are seeing negative tick counts, it is not an issue as SPAN and Waypoint post processing software use the change in number of ticks to calculate distance and velocity.  It only looks at the magnitude of the change, not the direction.

Q: I'm seeing a lot of INS_BAD_GPS_AGREEMENT.  Is this some sort of warning message?

A: INS_BAD_GPS_AGREEMENT means that your GNSS solution does not agree with the INS solution.  This usually happens when you are in a situation where there's a poor view of the sky, or under high multipath environment.  When this status appears, it means that the solution is going on INS only solution, and will go back to a GNSS/INS solution when a position update is available.  This is not an error or warning message.

Q: I'm seeing constant biases in my solution.  What could cause this?

A: Constant biases can be caused by lever arm errors or alignment errors.  Ensure that your lever arm is accurately known in all directions.  When you perform a kinematic alignment, do not back up, do not perform your alignment on a slope, and while there's a crab angle.  The SPAN filter assumes that during alignment, your vehicle heading is constant, the vehicle is moving forward, and the roll and pitch are close to zero.

Q: My roll and pitch angles appear to be swapped, or look like they are negative instead of positive:

A: You likely didn't mount your IMU in its default orientation of Y forward, Z up, X to the right.  Take a look at your IMU mounting and take into account any rotations.  If you have your IMU mounted so that the Z axis is not pointing up, check to see if it matches with any one of the pre-defined IMU orientations in the SETIMUORIENTATION command.  Select the closest one to your setup.  It may not match exactly if you have additional rotations to take into account.  Measure any additional rotations from the vehicle, to the SPAN body frame, and use the VEHICLEBODYROTATION command to enter them.  If you want your INS logs to output your solution in the vehicle frame, use the command APPLYVEHICLEBODYROTATION ENABLE.

If you require assistance from NovAtel support, please send the following data from your SPAN-CPT prior to contacting us to expedite support: