A High-Resolution Ultrasonic Distance Measurement System Using Vernier Caliper Phase Meter

An ultrasonic distance measurement system for use in air is presented. The measurement is based upon the two-frequency continuous-wave (TFCW) phase-shift method. In the system, two Vernier caliper phase meters are used to measure the phase-shift data. The phase meter circuit developed to emulate the Vernier caliper to measure the phase shift is able to eliminate the measuring error and produce higher resolution results without increasing the clock frequency. A single-chip microprocessor is used to control the TFCW phase-shift measurement and send the data to a personal computer for distance calibration and examination. The experimental results show that the accuracy of the system is ±0.1362 mm and the distance resolution is 0.04% of the wavelength corresponding to the 40-kHz ultrasonic wave at a range of 50-200 mm. Therefore, the main advantages of this system are high resolution, high accuracy, low cost, and ease of implementation.