How Thermal Mass Flow Meters Work
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Thermal Mass Flow Meters How Thermal Mass Flow Meters Work Thermal mass flow meters are used almost entirely for gas flow applications. As the name implies, thermal mass flow meters use heat to measure flow. Thermal mass flow meters introduce heat into the flow stream and measure how much heat dissipates using one or more temperature sensors. This method works best with gas mass flow measurement. It is difficult to get a strong signal using thermal mass flow meters in liquids, due to considerations relating to heat absorption. While all thermal flow meters use heat to make their flow measurements, there are two different methods for measuring how much heat is dissipated. One method is called the constant temperature differential. Thermal flow meters using this method have two temperature sensors — a heated sensor and another sensor that measures the temperature of the gas. Mass flow rate is computed based on the amount of electrical power required to maintain a constant difference in temperature between the two temperature sensors. A second, and less popular concept, is called a constant current method. Thermal mass flow meters using this method also have a heated sensor and another one that senses the temperature of the flow stream. The power to the heated sensor is kept constant. Mass flow is measured as a function of the difference between the temperature of the heated sensor and the temperature of the flow stream. Both methods are based on the principle that higher velocity flows result in a greater cooling effect. Both measure mass flow based on the measured effects of cooling in the flow stream. |
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