LED Reflective distance sensors (RDS) measure the distance to an object using an infrared light emitting diode and a photodetector. When the distance between the sensor and reflective surface changes, so does the intensity of the reflective light. This is measured as a change in voltage.

Reflective distance sensors had previously been shown to be capable of measuring distances with an accuracy of one micron when the target is stationary. This project aimed to assess their suitability for monitoring distances in a rotating, translating environment. The suitability of reflective distance sensors to distance measurement in such dynamic environments was tested by mounting the sensor on a wheel of the System Health Lab’s model truck.

Testing found that the sensor was highly susceptible to thermal drift, meaning the measured distance increase by up to 106 micrometres over a 30 minute period. However, if this thermal drift could be eliminated, the sensor would have an accuracy of 36 microns.

The project also found thermal drift and angular misalignment could have a significant impact on the accuracy of calibration curves obtained for the sensor. These findings will allow for readings to be taken from the reflective distance sensor with increased accuracy, both in static and dynamic environments. The increased accuracy will be beneficial to other applications looking into using reflective distance sensors such as strain gauges and blood pressure monitors.