I、The technology principle of the The EPI thermal type gas mass flowmeter ：
1.1 The basic working principle of Single point thermal gas mass flow meter
The thermal type gas mass flowmeter has a strong, cleanable sensor combination for thermal mass flow . The combination is composed of two RTD (resistance temperature detector) sensor components, its material is platinum resistance and ceramic with precision level. Two platinum resistance sensor on ceramic substrate, and a long thin stainless steel protective sleeve. This combination of the sensor is for temperature compensation, and not sensitive to pressure changes,no pressure correction.The gas mass flow through the heated sensing components is measured by the heat transfer quantity of the sensing components.Gas rate increases, the sensor passed to the fluid’s heat increased,so need to supply more current,in order to maintain the constant temperature difference △T of the sensing component.The quality of heat transfer is proportional to the gas flow velocity (density * velocity). The transmitter output current corresponding to the flow or velocity. The flow transmitter is composed of sensor, bridge amplifier, shell and probe.Signals from the transmitter through calibration processing are converted to linear signal , linear output signal is set for 0 to 5 VDC and 4-20 ma.
1.2 Multipoint probe flowmeter and the average probe flowmeter working principle of the product technology.
In the actual gas mass flow measurement,because of the pipe sectional area is large, or there is irregular flow section, need to use two or more probe point, in order to achieve the real average traffic signal readings. Based on the demand, the EPI company designed and developed the multipoint gas mass flow meter. It is composed of two main units, the flow transmitter probe combination and special display controller. Flow transmitter probe combination is the core of the system, it is composed of two or more flow sensor (at most 12 probes). Flow transmitter has two sizes, they are the transmitter can direct output average traffic signal for multiple probes and output the traffice signal for each probe. Display controller convert the input signal to 0 to 5 VDC and 4-20 mA output signal  is used to direct reading.In addition to the multi-point flowmeter, Average probe (Flow Average Tube) flowmeter is the latest original creation technology by EPI company,probe through the pipeline, the unique porous structure probe to Average the gas Flow velocity, especially suitable for large diameter pipeline measurement (can improve accuracy and reduce the length of the straight pipe before and after the installation requirements, and in the actual use 1 d long straight pipe can satisfy the measurement requirements), price is well matched the single point of flowmeter, but has better accuracy and stability compare to the single point flowmeter.