The Inertial Labs designs and develops high-quality products with the best price-performance ratio in the world. Our team continuously researches and creates cutting-edge solutions to provide the best possible performance for our devices. However, hardware and software errors sometimes occur, as in any technical product. The purpose of the article is to learn more about the causes of hardware and software failures and their effects on the device’s work. This knowledge will help customers avoid many issues with the Inertial Labs devices during operation.
The Inertial Labs developers implemented the Unit Status Word (USW) to firmware to control the INS state information. The USW is an uint16 that contains information about the software status and state of each hardware unit of the device. The low byte (bits 0 – 7) of USW indicates failure of the INS. The high byte (bits 8 – 15) either contains a warning or is informative for the user. If the byte is 0, the INS operates correctly; if not 0, it indicates failure. The description of each bit of the USW is specified in the table below.
The causes of the USW failures
1. Unsuccessful initial alignment (Bit 0) failure occurred if even one of the following actions took place during the process of initial alignment:
- Angular rotation is detected (if the instant angular rate exceeds the threshold). The default threshold is 10 deg/s.
- Magnetic disturbance is detected (if the span of the measured magnetic field exceeds the threshold). The default threshold is 10000 nT
2. Software status (Bit 1) is set to 1 (failure) if incorrect data appears at calculations. For example, INF or NaN appeared in calculations. INF means infinity, and its value is higher than any other value. NaN is Not a Number, and its value can’t be expressed as a number in calculations.
3. Gyroscope unit (Bit 2) failure can happen in the following cases:
- During initial alignment: if gyro data are unstable (if the span of measured angular rate is less than the threshold). The default threshold differs for different IMUs; contact Inertial Labs specifying the device serial number to get the necessary information.
- During INS operation, if more than ten gyro packages in the row are skipped.
- During INS operation, if the gyro unit reports its failure.
- During initial alignment: if accelerometer data are unstable (if the span of measured acceleration is less than threshold 0.1 mg).
- During initial alignment: if the module of measured acceleration is less than threshold 0.1 g.
- During INS operation, if more than ten accelerometer packages in the row are skipped.
- During INS operation, if the accelerometer unit reports its failure.
5. Magnetometer unit (Bit 4) failure can happen in the following cases:
- During initial alignment: if the measured total magnetic field is less than threshold 2000 nT.
- If INS does not receive magnetometer data.
6. Electronics (Bit 5) failure can happen if a 3.3V stabilized voltage is out of range (3.0-3.4V).
7. GNSS receiver (Bit 6) failure occurs if the receiver did not provide the data to the INS for more than five samples in a row.
8. Incorrect power supply (low voltage) (Bit 8) is set to 1 (warning) if the supply voltage is less than the minimum level. It can be increased by the Volt1min parameter
9. Incorrect power supply (high voltage) (Bit 9) is set to 1 (warning) if the supply voltage is greater than the maximum level. It can be decreased by the Volt1max parameter.
10. Angular rate exceeding detect (Bit 10,11,12) is set to 1 (warning) if the span of the measured angular rate is higher than the threshold. Bit 10 corresponds to the X-axis, Bit 11 – Y-axis, and Bit 12 to the Z-axis. The default threshold differs for different IMUs; contact Inertial Labs specifying the device serial number to get the necessary information.
11. Large magnetic field detect (Bit 13) is set to 1 (warning) if the measured total magnetic field exceeded threshold. The default threshold is 80000 nT.
12. Environmental temperature (Bit 14) failure occured, if measured temperature is out of range (-40 … +80 C deg).
The INS has an additional Unit Status Word – USW2. The USW2 is a word (uint8) that contains information about the state of other INS sensors and the status of INS additional operations. The description of each bit of the USW is specified in the table below.
The causes of the USW2 failures
1. Acceleration exceeding detect (Bit 0,1,2) is set to 1 (warning) if the span of the measured acceleration is higher than the threshold. Bit 0 corresponds to the X-axis, Bit 1 – Y-axis, and Bit 2 to the Z-axis. The default threshold differs for different IMUs; contact Inertial Labs specifying the device serial number to get the necessary information.
2. Baro altimeter (Bit 3) failure occurred if even one of the ADU status bits #0, 2, 4, or 8 (description below) equals 1.
3. Differential pressure sensor (Bit 4) failure occured if even one of the ADU status bits #1, 3, 5, or 9 (description below) equals 1.
4. Automatic 2D calibration of magnetometers (Bit 5) is set to 1 (failure) if the 2D calibration procedure is in progress.
5. Automatic 3D calibration of magnetometers (Bit 6) is set to 1 (failure) if the 3D calibration procedure is in progress.
6. GNSS receiver input to the INS algorithm (Bit 7) is set to 1 (failure) if the customer switched off the GNSS receiver input.
7. Differential pressure input to the INS algorithm (Bit 8) is set to 1 (failure) if the customer switched off the differential pressure input.
8. GNSS position validity (Bit 10) is set to 1 (failure) if the INS algorithm detected an invalid position from the GNSS receiver.
The description of each bit of the ADU status is specified in the table below.
The effects of software and hardware failure
1. If initial alignment failure occurred, the appropriate USW bit becomes equal to 1 and cannot be reset during operation. The device should be power cycled and restarted to allow proper initial alignment (the device must be static during the initial alignment process).
2. If a hardware error occurred (hard fault or non-maskable interrupt (NMI)), then all USW bits become equal to 1. If so, before running the device again, it should be power cycled. Also, hardware error can be detected with the LED indicator when it blinking red or yellow. The LED behavior description is specified in the table below.
If a hardware error (hard fault or NMI) occurs during the device run, then the payload bytes of the chosen data format will be replaced by 0xFF, and the data rate will switch to 4 Hz. The INS algorithm will restart if the device receives the GNSS receiver solution.
3. If gyroscope unit or accelerometer unit failure occurred at the initial alignment, the appropriate USW bit becomes equal to 1 and cannot be reset during operation. The device continues to output the data, but the Inertial Labs cannot guarantee the accuracy specified in the datasheet. The device should be power cycled to provide the best possible performance. The device stops after 3 seconds if a gyroscope unit or accelerometer unit failure happens during the INS operation.
4. If magnetometer failure occurred, the appropriate USW bit becomes equal to 1 and cannot be reset during operation. The device should be power cycled to provide high-accuracy performance.
5. The electronics failure resets if the 3.3V stabilized voltage sets to the range.
6. The GNSS receiver failure resets if the INS algorithm gets the solution from the GNSS receiver.
7. All bits of USW high byte and all bits of USW2 have information for the user or contain a warning. They don’t stop device operation but can affect the accuracy.
If you have any questions or require further information about the device failures, please don’t hesitate to reach out. Our dedicated team of experts is here to help you. We value your curiosity and are committed to providing comprehensive answers and guidance to address your needs. Your success is our priority, and we look forward to hearing from you.