Technology

Through the operating principle of the ultrasonic transit time method, our flow measurement is non-invasive, meaning without direct contact to the medium

em-tec's non-invasive flow measurement method is based on the ultrasonic transit time method. This method determines the transit time difference of ultrasound signals through a measuring section and is used to evaluate volumetric flow rates. A typical transit time flow measurement system incorporates two piezo ceramics that act as both ultrasonic transmitter and receiver. The flow measurement is conducted by sending ultrasonic pulses from one ceramic to the other (i.e. with and against the flow direction) and by measuring the transit time difference that it takes for the pulse to travel between them.

For a higher accuracy, our Clamp-On Transducers incorporate two pairs of sound transducers. They consist of four piezo ceramics and are arranged in an X configuration around the tube containing the measured flow.

 

Clamp-On Transducer_EN-blue



Upstream Transducer

When sending ultrasonic sound signals through the measuring section, the transit time difference depends on the flow direction of the medium:

  • If the ultrasonic sound signals are sent along the flow direction, the downstream signal needs less time
  • If the ultrasonic sound signals are sent against the flow direction, the upstream signal needs more time

Consequently, the transit time difference is measured for every pulse. The difference between upstream and downstream measurements is proportional to the volumetric flow rate.

 




em-tec Transmitter and Receiver

The picture on the left shows the transmitting impulses and the resulting received signals. Through the difference in the received signals, the transit time difference can be determined.

Since the difference in transit time is very slight (picoseconds), the calculation is done with a multi-step correlation method.

With an increasing flow, the transit time difference of the received signals increases as well. By adjusting the sensor, it is possible to convert the transit time difference into a volumetric flow.