Feature Guide: Wheel Speed Input

Overview

The Wheel Speed Interface feature enables OXTS systems to use a directly connected wheel speed sensor (WSS) to improve navigation accuracy. By providing reliable speed updates, the wheel speed sensor helps reduce drift and maintain trajectory during GNSS outages.

The performance impact of a WSS is demonstrated in this article: Performance test in GNSS outages.

This guide explains how to:

• Correctly install and configure a wheel speed sensor with an OXTS device

• Tune and optimise key setup parameters

• Verify that the wheel speed input is functioning correctly in NAVdisplay

Requirements

Before beginning, ensure you have:

• An OXTS unit with a digital I/O port available

• A compatible wheel speed sensor (WSS)

• External power supply for the sensor (digital I/O does not provide power)

• Access to NAVsuite software installed

• The WSS manual, to obtain the pulse-per-revolution (PPR) specification

Configuration

Step 1 — Install Hardware

1. Install the OXTS unit as normal, ensuring the user cable includes a digital I/O connector.

2. Install the WSS according to the manufacturer’s instructions.

   • The WSS must be installed on a non-steering wheel.

3. Connect the WSS output to the digital I/O port on the OXTS unit.

4. Provide external power to the WSS.

Step 2 — Configure Wheel Speed Input

You can configure the wheel speed input under Advanced → Wheel Speed Input tab in NAVconfig.

1. Enable Wheel Speed Input.

2. Enter the linear offsets from the IMU to the point where the tyre contacts the ground.

3. Set the following parameters:

   • Pulses per revolution (PPR): From the WSS manual.

   • Tyre diameter: Measured directly from the installed wheel.

   • Direction / quadrature: If supported, enable to detect forward and reverse motion.

Your OXTS unit is now configured to ruse wheel speed data from the digital input interface.

Verifying Wheel Speed Operation

To confirm the wheel speed sensor is functioning correctly and providing valid data to the OXTS system:

1. Open NAVdisplay and connect to your OXTS device.

2. Open the following measurements as digital widgets:

   • Wheel Speed Count — displays the live pulse count from the WSS.

   • Wheel Speed Speed — shows the calculated speed from the WSS.

3. Observe the live data:

   • As the vehicle moves, the Wheel Speed Count should increase.

   • If quadrature input is enabled, the count will increase or decrease depending on the direction of travel.

   • When driving in a straight line, the Wheel Speed Speed value should closely match the Horizontal Speed.

If the count does not change or the speed remains zero:

• Check the WSS power supply.

• Verify wiring and digital input selection.

• Reconfirm configuration settings in NavConfig.