The Air Flow Monitor (AFM) uses ultrasonic technology to measure air velocity. A single transmitter and an array of four receivers are contained in the measuring head. Air velocity and direction are computed from measurements of the phase shifts from the ultrasonic signals at the receivers. The sensor is compact, contains no moving components, requires no routine maintenance and is unaffected by interruptions from passing vehicles and acoustic reflections within the tunnel.

- Quality and Construction
  Designed to withstand the harshest of tunnel environments