Thermal mass flow measurement
for gases
As shown in figure A a part of the gas flows through the sensor, and is warmed up by heater RH. Consequently the measured temperatures T1 and T2 drift apart, as shown in figure B. The formulas for dT demonstrate that the temperature difference is directly proportional to mass flow. Electrically, temperatures T1 and T2 are in fact temperature dependent resistors RT1 and RT2.
figure A
figure B
In figure A it is shown how the signals measured in the sensor are amplified to electric signals. The sensor is mounted as a by-pass to the main channel, where a patented flow resistance splitter takes care of proportional flow division, also under varying process conditions. This laminar flow element consists of a stack of stainless steel disc with high-precision etched flow channels, having similar characteristics as the flow sensor.
for liquids
Liquid mass flow meters of the LIQUI-FLOW® series are built around a stainless steel tube without any moving parts or obstructions. The heater/sensor assembly is arranged around the tube and, by following the anemometric principle, a constant difference in temperature (dT) is created and the energy required to maintain the dT is dependent on the mass flow rate. Due to the benefits of the unique patented sensor, the fluid will be warmed to a maximum of 5°C, thereby making the LIQUI-FLOW® Series suitable for fluids with low boiling points. | 
