Air flow measurement by differential pressure

The air flow monitoring system measures the longitudinal air flow at 2, 4 or 6 points in a tunnel cross section. The method allows to optionally remove all electronic components from the tunnels driving area to maintain a measurement also under high temperatures.

Two differential pressure pitot tubes are mounted on opposite tunnel walls. Measuring the air flow at 2 points allows to calculate a representative average air flow over the tunnel cross section.

Measurement is based on high-precision differential pressure measure­ment (Pitot tubes) which results in accurate flow measurement of the air through the tunnel. The data from the separately mounted field transmitters are transferred digitally into the evaluation unit (RS 485).

High-precision measurement of differential pressure is based on recurring automatic reset (autozero method) as well as on a high-resolution digital to analog converter.

Depending on the design, the differential pressure measurement in the transmitter takes place directly on the pitot tube or, for high-temperature applications, remotely in the controller.

Following outputs are available: air velocity, direction of air flow, air temperature.