The maximum flow through the sensor is limited to a small proportion of the total flow of the mass flow controller. Therefore, a bypass element is used to divide the flow into two paths by creating a pressure drop that increases linearly with flow. The gas through the sensor tube is designed to have a small Reynold's number in the laminar regime.

HORIBA STEC employ a laminar flow element as the bypass in order to obtain identical flow characteristics to the sensor tube. Therefore, the flow characteristics of the sensor and bypass are comparable with respect to the flow as a function of temperature and pressure. This results in high accuracy, repeatability and stability.

Mount-Free Sensor Configuration.

The mount-free sensor is an option in some of our mass flow controllers, it uses a new type of sensor (patent pending) that theoretically solves the problem of the inclination effect. An equivalent heater is used in a sensor configuration that prevents heat convection from occurring. The MF sensor is well suited for use in mass flow controllers used on such gases as C2F6, C3F6,C4Fe, SF6 and SiF4.

Control Valve

Mass flow controllers use various method to control the flow, these fall into various categories. Typical examples includes a thermal, solenoid and piezo electric actuator type control valve. HORIBASTEC are one of a very small number of manufactures who use the piezo actuator method, for critical control this allows:

• Extremely high resolution/sub micron precision - 100V Piezo instead of 15V solenoid actuator
• Significant reduction in movement (just 30µm) generates less particles
• Not affected by magnetic fields & RF noise
• Low power consumption with minimal heat generation
• Not affected by orientation
• Large power/torque generation