Liquid Mass Flow Control - Measurement Principles

The flow rate sensor in the LF-F/LV-F series of fine mass flow controllers for liquids consists of an electronic cooling element (Peltier element) that is in contact with a capillary tube, as well as several temperature detection elements. When the liquid is flowing, the sensor detects the temperature rise (⊗T) corresponding to the flow rate and displays it as a flow rate. Unlike methods where heat is added, this cooling method enables flow rate measurement of liquids with low boiling points. It also prevents problems with interference due to the influence of secondary discharge (vaporization) and makes accurate flow rate measurements possible.

The LV-F series of mass flow controllers are similar to the LF-F series of mass flow meters, but also have a piezo actuator valve and an internal comparison control circuit. They compare the flow rate setting signal and the flow rate output signal and automatically control the valve aperture so that the two signals will match. Since they use a feedback control system, there are no flow rate variations as a result of external factors, and, therefore, stable, accurate control is possible. The use of a piezo actuator valve, which is both stable and does not generate heat, as the control valve makes these units ideal for flow control of liquids with low boiling points.