A Thermal Flow Sensor Based on Printed Circuit Technology in Constant Temperature Mode for Various Fluids

Abstract

We present a thermal flow sensor designed for measuring air as well as water flow velocities in heating, ventilation, and air conditioning (HVAC) systems. The sensor is designed to integrate the flow along the entire diameter of the pipe also quantifying the volume flow rate of the streaming fluid where the calorimetric principle in constant temperature operation is utilized as a readout method. In the constant temperature mode, a controller keeps a specific excess temperature between sensing elements at a constant level resulting in a flow dependent heater voltage. To achieve cost-effective sensors, the fabrication of the transducer is fully based on printed circuit board technology allowing low-cost mass production with different form factors. In addition, 2D-FEM simulations were carried out in order to predict the sensor characteristic of envisaged setups. The simulation enables a fast and easy way to evaluate the sensor’s behaviour in different fluids. The results of the FEM simulations are compared to measurements in real environments, proving the credibility of the model.

clamp-on AND transit time difference AND smart meter

“…Thermal differential methods are also used to measure flow from the outside of a thin walled metal pipe, by attaching a heat source and one or more thermal sensors to the pipe and measuring how flow affects the temperature distribution on the outer wall of the pipe [2,3]. This method can yield a crude measurement of flow, and reliable quantitative measurements of flow rate are not possible, but it does have applications in water supply management where measurement accuracy is not vital, such as pathogen control [4].…”

High-Speed and High-Temperature Calorimetric Solid-State Thermal Mass Flow Sensor for Aerospace Application: A Sensitivity Analysis

“…TMFS designs exist that do not rely on this technique to build the heater element; examples include the design of Glatzl et al, which operates at low temperatures to avoid thermal conductivity issues that can collapse the sensor, or those of Kaltsas et al, Petropoulos et al, Kim et al, Mayer et al, and Bruschi and Piotto, which make use of flow channels to ensure that the fluid flow is laminar, consequently reducing the power demand from the heater once the flow volume is controlled by the tube diameter. However, these are not suitable for the proposed application due to the aforementioned ice condition [24][25][26][27][28][29][30][31].…”

MEMS thermal gas flow sensor with self-test function

“…In the past 30 years, many researchers have worked on improving the performance of thermal flow sensors through optimization of the flow sensor material [9][10][11], structure [12][13][14][15], peripheral circuits [16][17][18][19] and packaging methods [20][21][22][23]. For example, Kang et al improved the sensitivity of the MEMS-based thermal flow sensors by investigating the effect of the distance ratio between the heater and thermopiles on the measurement performance [14].…”

“…Mehmood et al systematically studied the effect of membrane shape, membrane size, heater/hot-film length and membrane (size) to heater (hot-film length) ratio on sensors' conductive heat losses and improved the performance of the thermal flow sensor by minimizing membrane conductive heat losses [15]. Moreover, various peripheral test circuits such as constant current (CC) [19], constant temperature (CT) [16], constant voltage (CV) [17] and constant power (CP) [18] are used to better characterize the performance of thermal flow sensors. Besides, advanced packaging methods are also adopted to improve the performance of flow sensors [20][21][22][23].…”