Thermistor based, low velocity isothermal, air flow sensor

Abstract

The semiconductor thermistor technology is applied as a flow sensor to measure low isothermal air velocities (<2 ms−1). The sensor is subjected to heating and cooling cycles controlled by a multifunctional timer. In the heating stage, the alternating current of a main AC power supply source guarantees a uniform thermistor temperature distribution. The conditioning circuit assures an adequate increase of the sensors temperature and avoids the thermal disturbance of the flow. The power supply interruption reduces the consumption from the source and extends the sensors life time. In the cooling stage, the resistance variation of the flow sensor is recorded by the measuring chain. The resistive sensor parameters proposed vary significantly and feature a high sensitivity to the flow velocity. With the aid of a computer, the data transfer, storage and analysis provides a great advantage over the traditional local anemometer readings. The data acquisition chain has a good repeatability and low standard uncertainties. The proposed method measures isothermal air mean velocities from 0.1 ms−1 to 2 ms−1 with a standard uncertainty error less than 4%.

MEMS technology and applications in geotechnical monitoring: a review

“…In flight flow sensors, transition of a thermal pulse between a heater and a sensing element is used to monitor thermal variances [49]. Thermal flow sensors provide higher accuracy and sensitivity than conventional sensors, but their performance is limited to low flow velocities and they are prone to suffer from heat loss [202,203]. As such, it is recommended to use thermal flow sensors in non-corrosive environment to avoid degradation and irreversible damage [201].…”

Design and applications of MEMS flow sensors: A review

“…It appears that one of the most important limitations on accuracy applying to the conventional temperature-based flow sensors is maintaining the temperature on the sensing element accurately [32]. Another challenge associated with thermal flow sensors is their inability to measurement low flow velocities [33]. Sensing elements in traditional hot-wire and hot-film sensors have a high specific heat capacity making it hard to follow the weak heat convection transfer resulting a poor frequency response.…”

Ultra-High Frequency Surface Acoustic Wave Sensors for Temperature Detection

“…Currently, many electrical and optical temperature sensor components have been developed for ambient temperature detection, e.g., thermocouple sensors [ 1 ], thermistor sensors [ 2 ], jet temperature sensors [ 3 ], infrared temperature sensors [ 4 ], and so on. These detection techniques’ inherent optical and electrical properties limit their use in industrial production and aerospace applications.…”