The SF-1U/2U combines precision volumetric tubes with a soap film detector (patented) that allows it to measure the flow of a high number of gases accurately. It measures the amount of time required for the movement of soap film through a known portion of the volumetric tubing (a standard volume), and determines the gas flow rate using that time value. The SF2 measures the atmospheric pressure and temperature thus compensating for these prior to calculating the actual flow. Suitable for a range of gas flow rates by using one of the four volumetric units (VP series). The SF-2U features an internal atmospheric pressure sensor.

Operating principles
The SF series of precision film flow rate meters use a combination of precision volumetric tubing and soap film detector (patented) to measure the flow rate.

When the start switch is pressed, the film pick up operates, and a soap film is generated at the bottom of the volumetric tubing. The soap film is moved up into the volumetric tubing by the flow of the gas.

The time it takes the film to pass two detectors installed a set distance apart is measured. The value for the volume between the two detectors has been determined precisely, thus the volume is known.

The time it takes for the film to pass between the detectors, along with the temperature and atmospheric pressure are processed in the microcomputer. Calculations to correct for vapor pressure are performed automatically, and the flow rate, converted to standard 25degC and 1013hPa, is displayed.