The Aalborg GFM mass flow meter is a low cost solution to thermal mass flow metering for gases. The design of the Aalborg GFM mass flow meter combines the convenience and accuracy of a conventional mass flow meter with low costs previously unattainable.

Each Aalborg GFM mass flow meter incorporates an advanced straight tube sensor in conjunction with flow passage elements constructed of aluminum and brass for non-corrosive gases or 316 stainless steel for corrosive applications.

Compact, self-contained Aalborg GFM mass flow meters are designed to read flow rates of gases. The rugged design coupled with instrumentation-grade accuracy provides versatile and economical means of flow control. Aluminum or stainless steel models with readout options of either engineering units (standard) or 0 to 100% displays are available.

The mechanical layout of the Aalborg GFM mass flow meter's design includes an LCD readout built into the top of the transducer. This readout module is tiltable over 90 degrees to provide optimal reading comfort. It is connected to the transducer by a standard modular plug, and is also readily removable for remote reading installations. Transducers without LCD readout are offered for OEM applications.
Aalborg GFM mass flow meters are available with flow ranges from 10 sccm to 1000 sL/min N2. Gases are connected by means of 1/4", 3/8", and 1/2" compression fittings and 3/4" FNPT fittings. Optional fittings are available. The Aalborg GFM mas flow meter may be used as a benchtop unit or mounted by means of screws in the base.

Transducer power supply ports are fuse and polarity protected.

The Aalborg GFM mass flow meter offers a leak integrity of 1 x 10-9 smL/sec of helium maximum to the outside environment.

Principles of Operation
Metered gases are divided into two laminar flow paths, one through the Aalborg GFM mass flow meter's primary flow conduit and the other through a capillary sensor tube. Both conduits are designed to ensure laminar flows; therefore, the ratio of their flow rates is constant.

Two precision temperature sensing windings on the sensor tube are heated, and when flow takes place, gas carries heat from the upstream to the downstream windings. The Aalborg GFM mass flowmeter's resultant temperature differential is proportional to the change in resistance of the sensor windings.

The Aalborg GFM mass flow meter has a Wheatstone bridge design to monitor the temperature dependent resistance gradient on the sensor windings which is linearly proportional to the instantaneous rate of flow. Output signals of 0 to 5Vdc and 4 to 20mA are generated indicating mass molecular-based flow rates of the metered gas.

Flow rates are unaffected by temperature and pressure variations within stated limitations.