A wheel speed sensor is a useful tool that can be used to improve the accuracy of the INS by providing speed updates from the wheel. In the absence of GNSS, they can reduce drift and maintain trajectory.
The guide linked below highlights the performance improvements from using a wheel speed sensor.
How to use the wheel speed sensor
- Install the RT as normal and ensure the user cable has a digital port.
- Install the WSS as per the manufacture instructions. This must be on a non-steering wheel.
- Connect the WSS output to the digital I/O. The digital I/O does not carry power, so an external power supply is needed.
- For optimal performance, configure the RT with dual antenna and no-slip options.
- Under 'Advanced settings' enable Wheel speed input.
- Measure the Wheel speed sensor lever arms as well as the tyre diameter. When measuring the lever arms, the measurement point is where the tyre touches the ground.
- Find the sensor pulse per revolution in the WSS manual. Input the information into the 'wheel speed input' page.
- Commit the configuration.
- Open NAVdisplay and go to the digital widgets tab. Search for 'Wheel speed count' and select this widget, this will be used to confirm the setup is working. It is also good practice to select the 'wheel speed speed' option.
- As you drive the wheel speed count should increase. The count is signed if both the WSS and the RT support "quadrature" input. Quadrature input is supported on units that run XBNS firmware. The count can increase or decrease depending on the direction of travel (and the side on which the WSS is mounted). The sign has no impact on the performance, as long as it is sensible (increases in one direction, decreases in the opposite). If not signed, the count should always increase. If driving in a straight line, the 'wheel speed speed' should be similar to the 'horizontal speed' of the vehicle.
- Perform a warmup as normal and apply an improved configuration, this will optimise the pulses per metre.