Thermal mass flow meters use thermal dispersion technology for flow measurement. The measuring probe contains two temperature detection elements (platinum RTDs), RTD1, RTD2 and a constant heat source HTR.
RTD1 is used to measure the temperature of the fluid medium itself, and it is used as the reference temperature. RTD2 is placed close to the constant heat source HTR to measure the temperature of the constant heat source surface after the heat is taken away by the fluid medium. The temperature difference between the two temperature detection elements is a function of the mass flow rate. The change in fluid flow rate directly affects the degree of heat diffusion, and then affects the size of the temperature difference between the two temperature measuring elements. When the flow rate is zero, the temperature difference is the largest; and as the flow rate increases, the heat taken away by the constant heat source HTR increases, the temperature measured by RTD2 decreases, and the temperature difference decreases.
The temperature difference signal is converted into a 4-20mA standard signal output by the conversion circuit. The relationship between temperature difference and flow rate is as follows: Pv=K(Q/△T) where p is the fluid density (kg/m3); v is the fluid flow rate (m/h); K is the calibration constant; Q is the heat flow (J/h); △T is the temperature difference (℃). It can be seen from the above formula that the function of gas flow rate and heat dissipation capacity is directly related to the mass flow rate, which is the basic principle formula of thermal gas mass flowmeter.
Thermal mass flowmeter consists of a sensor and a transmitter. There are two types of sensors, namely plug-in type and straight-through type. When the process pipe diameter is small, the straight-through type is generally selected; when measuring large pipe diameters, the insertion type is generally selected. Either way, the temperature detection element and constant heat source are sealed inside the sensor and are not in direct contact with the fluid medium. Therefore, the heating and temperature measuring elements will not be damaged. The flow meter can be used for a long time, which also reduces the user's maintenance requirements.
The above is the thermal gas mass flow meter manufacturer's sharing of "How thermal mass flow meters are measured". Thank you for watching. If you have any questions, you can consult online or leave us a message. We will answer you wholeheartedly.
Hangzhou Economic Development Area，Hangzhou 310018，China
