Temperature-compensated fiber-optic gas flow speed sensor based on the ‘Hot-wire’ principle

Abstract

Compared with the use of other types of sensors, there are significant advantages in making measurements of low speed gas flows by using a fiber-optic ‘hot-wire’ sensor. Measurements of this type using intrinsically safe fiber optic technology play an important role in industry, especially in coal mine gas clearance, roadway ventilation and fire safety warning. However, the ‘line-diameter ratio’ of the fiber-optic ‘hot-wire’ wind speed sensor described in previous work is far smaller than that for the traditional electronic hot-wire sensor and this requires investigation and optimization. To do that necessitates considering the combined influence of factors such as forced convection, natural convection, radiation heat transfer and heat conduction on the operation of the sensor probe, especially on the heat transfer between the sensor element and the base, when analyzing the performance of the fiber-optic ‘hot-wire’ gas flow speed sensor and in modelling its characteristics. Based on the results of the model of electronic hot-wire sensor created, this paper presents a method to improve and indeed further enhance the performance of the sensor, having a focus on the proportion of convective heat transfer to the total energy dissipation under different ambient and different wind speed conditions, as well as the influence of different ambient temperatures on the sensor probe. The results of the numerical simulation and the experimental verification carried out show that the measurement error was less than ±0.2 m/s, when used within the gas flow speed range of 0−6 m/s. Compared with the situations before the compensation was applied, the measurement error in the use of the sensor is reduced and the sensor performance significantly improved.