TMS2000 - Principle of measurement

The ventilation of road tunnels ensures that noxic gases (above all carbon monoxide) and dirt particles are removed from the tunnel. The ventilation will become efficient and economic if it can be controlled using the flow rate of the air. Flow measurement systems TMS2000 measure the exact flow rate in the longitudinal direction of the tunnel. Local turbulences constantly caused by traffic in the tunnel have no influence.

TMS2000 averages the flow rate vz in the longitudinal direction of the tunnel (z-direction) through the tunnel crosssection and, thus, measures the actual volumetric flow rate of the air through the tunnel.Transversal components vx and vy that are not involved in air transportation in the longitudinal direction z of the tunnel don‘t contribute to the measuring signal.

Even larger traffic density in a tunnnel cannot affect the measurement. The former can lead to significant measurement errors in ultrasound measurements with time-of-flight method.

The measurement is implemented with the help of two special differential pressure chambers made of stainless steel that are measuring the flow velocity in z-direction due to their form.

According to Bernoulli equation the differential pressure which is proportional to the squared flow velocity is fed through two pressure lines to the electronic evaluation unit that calculates the flow rate.

High-precision measurement of differential pressure is based on recurring automatic reset (autozero method) as well as on the automatic switching of the measuring range (dual-range method). Therefore, the flow rate can be measured with a very high resolution (< 0.1 m/s).

Measurement of differential pressure is carried out in the evaluation unit. This means that there are no moving mechanical parts or electronic devices in the driving area. This is very advantageous for easy servicing: Pitot tubes are designed in such a way that infi ltrating soiling or water cannot interfere with the measurement. Even in an extreme case of fire the measurement is not disturbed and resists hot gases with the temperature of 1200 °C up to. This guarantees safe and continuous control of the fan almost under any operating conditions.