Accurate ultrasonic air flow measuring system based on different transition times of ultrasonic pulses. Reliably measures the average air flow over the whole tunnel cross section.


Air flow measurement based on difference of transition times of ultrasonic pulses

The air flow monitoring system measures the air flow based on different transmission times of ultrasonic pulses sent in one or the other direction. This cross section measurement delivers the average air speed more reliable and meaningful than methods that measure only one or two points on the tunnel wall.

Two sensors are mounted below the tunnel ceiling, cross section with an angle of 30° to 60° (usually 45°) such that a vector component of the air flow overlaps the direction of the ultrasonic sound pulses exchanged by the two sensors.

Air flow in the tunnel influences the transition time of the pulses between sender and receiver. Based on the difference in transition times of ultra-sonic pulses sent in one or the other direction the measured values are calculated. Measured values are air speed, air flow rate, direction of air flow and air temperature.


  • Accurate ultrasonic air flow measuring system based on different transition times of ultrasonic pulses
  • Measurement of average air flow over the whole tunnel cross section
  • Sensor setup via service interface
  • • Suitable for tunnel cross sections up to 18 m (Measuring path up to 25 m)
  • Connection to tunnel control system either via analogue output and relaysor via RS-485 MODBUS RTU
  • Visible LEDs to indicate sensor status
  • Corrosion-resistant non-wearing polyamide membranes
  • Optional, remote touch operating unit to display measured values and to modify parameters



  • Two sensors (master & slave)with mounting clamps mounted below the tunnel ceiling in an angle of30° to 60° to the tunnel axis
  • Terminal box for master to connect the power supply and the connections to the tunnel control system and the slave
  • Terminal box for slave
  • Optional remote touch operating unit



  • Specifically designed for application in tunnels
  • No control unit required
  • Easy configuration
  • Corrosion resistant against aggressive tunnel atmosphere
  • Sensors can be replaced quickly with no tools and no realignment required
  • Proven in high speed train tunnels with train speeds up to 350 km/h
  • No expendables (e.g. ultrasonic membranes)
  • Extremely low maintenance requirements


Technical Specifications:

Measuring method Determination of direction dependant differential transition times of ultrasonic pulses
Measured values Air velocityVolume flow

Direction of air flow


Measuring range -40 .. 40 m/s
Resolution 0.1 m/s, accuracy dependent upon measuring distance, flow profile, installation, typically 170.000 h
within service life if used within specifications
IP rating IP 67
Dimensions 270 x 130 x 95 mm
Weight Sensor approx. 2.2 kg each + wall bracket 1.6 kg
Material Stainless steel 1.4571 (AISI 316Ti)
Polyamide RAL5017, Flammability rating: B1 (UL 94 V0)
Type t/FL-US-TB-SS-A and t/FL-US-TB-SS-B
Operating voltage 90 .. 264 VAC, 48 .. 62 Hz
Power consumption approx. 30 VA (for master, for slave only optionally)
IP rating IP 69K
Dimensions / Weight 160 x 250 x 110 mm / 3.2 kg (Master)
160 x 160 x 110 mm / 1.9 kg (Slave)
Material Stainless steel 1.4404 (AISI 316L)
Mounting incl. mounting clamp made from stainless steel 1.4404 for wall mounting
Electrical standards 2014/35/EU Low Voltage Directive (LVD)
2014/30/EU Electromagnetic compatibility (EMC)
IEC 61326-1:2012
IEC 61010-1:2010
Tunnel safety AT: RVS 09.02.22 and ASFiNAG PlaPB
DE: RABT 2006
CH: ASTRA RL 13001 and FHB BSA


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