This measurement principle for mass flow is also described as the Inline-sensor-measurement principle. In contrast to the bypass measurement principle this measurement is carried out directly in the gas flow.
The mass flow meters and controllers consist of a metal body with a straight through-flow path. Two sensors are encased with stainless steel and protrude inside this bore; one is designed as a heater and the other one is designed as a temperature probe. A constant difference in temperature (ΔT) is created between the two sensors.
The heater energy required to maintain this ΔT is dependent on the mass flow. The working principle is based on King’s law of the ratio between the mass flow and the heater energy. That means the higher the flow, the more energy is required to maintain the chosen ΔT.
The pressure drop over the instruments’ D-6300 and D-6200 measurement chamber is almost comparable to a straight run of pipe of the same diameter and is thus almost negligible. However, to make the instruments more insensitive to upstream piping configurations, special mesh screens are required to condition the flow profile. These meshes create a certain pressure drop. Also the often used compression type connections cause a significant additional pressure loss.
By reducing the number of mesh screens and using an inlet pipe the pressure loss can be minimised as an option. In addition we recommend the use of fittings with maximised internal diameter.