Study of the Errors in Interpolated Fast Fourier Transform for Interferometric Applications

Frequency estimation is often the basis of various measurement techniques, among which optical distance measurement stands out. One of the most used techniques is interpolated fast Fourier transform due to its simplicity, combined with good performance. In this work, we study the lim-its of this technique in the case of real signals, with reference to a particular interferometric tech-nique known as self-mixing interferometry. The aim of this research is the better understanding of frequency estimation performances in real applications, together with guidance on how to im-prove them in specific optical measurement techniques. An optical rangefinder, based on self-mixing interferometry, has been realized and characterized. The simulation results allow us to explain the limits of the interpolated fast Fourier transform applied to the realized instrument. Fi-nally, a method for overcoming them is proposed by decorrelating the errors between the meas-urements, which can provide a guideline for the design of frequency-modulated interferometric distance meters

High-speed rangefinder for industrial application

The proposed work aims to improve one of the most used telemetry techniques to make absolute measurements of distance: the time of flight telemetry. The main limitation of the low-cost implementation of this technique is the low accuracy (some mm) and measurement rate (few measurements per second). In order to overcome these limits we modified the typical setup of this rangefinder exploiting low-cost telecommunication transceivers and radiofrequency synthesizers. The obtained performances are very encouraging, reaching a standard deviation of a few micrometers over the range of some meters

Differential pressure based liquid level measurement in sloshing condition

To achieve a reliable and accurate liquid level detection, a differential pressure based liquid level measuring instrument is proposed in this paper. The phase-sensitive demodulation of the signal is performed by discrete Fourier transform through microcontroller. Pressure measurement in both DC and AC stimulation provides means to study and compare proposed instrument reliability and robustness not only in steady state condition but also in case of experiencing turbulence on the surface of the liquid. Good linearity in both AC and DC has been observed. As results show, AC based level sensing demonstrated reliable and robust level detection to compare with DC in both steady state condition and experiencing turbulence on the surface

Remote Reflectivity Sensor for Industrial Applications

A low-cost optical reflectivity sensor is proposed in this paper, able to detect the presence of objects or surface optical properties variations, at a distance of up to 20 m. A collimated laser beam is pulsed at 10 kHz, and a synchronous digital detector coherently measures the back-diffused light collected through a 1-inch biconvex lens. The sensor is a cost-effective solution for punctual measurement of the surface reflection at different distances. To enhance the interference immunity, an algorithm based on a double-side digital baseline restorer is proposed and implemented to accurately detect the amplitude of the reflected light. As results show, the sensor is robust against ambient light and shows a strong sensitivity on a wide reflection range. The capability of the proposed sensor was evaluated experimentally for object detection and recognition, in addition to dedicated measurement systems, like remote encoders or keyphasors, realized far from the object to be measured

Short-Range Contactless Laser Sensor

In this paper is shown all the process is needed to build a laser sensor, developed specifically for very short distance with a very compact size. Only the laser chip, a red VCSEL laser without any lens, makes the sensor. Features of this contactless sensor is a dynamic of measurement of 3 mm starting at 2 mm up to 5 mm with a resolution of 10 µm measuring continuously at 6.6 kHz. This sensor can be exploited in applications in harsh environments where the size of the sensor is challenging