EN
2
Description of the Measurement Principle
The function of the BioProTT
TM
Clamp-On SL is based on an acoustic measurement principle and utilizes the
transit time method to determine the flow. A typical transit time flow measurement system incorporates two
piezo ceramics that act as both ultrasonic transmitter and receiver. The measurement system, consisting of
an evaluation device and a BioProTT
TM
Clamp-On SL, operates by alternately transmitting and receiving an
ultrasonic pulse between the piezo ceramics and measuring the transit time difference that it takes for the
pulse to travel between them.
This method determines the transit time difference of ultrasonic signals through a measuring section and is
used to estimate volumetric flow rates. There are at least two transducers, i.e. ceramics, required in order to
send and receive ultrasonic pulses both with and against the flow direction. For a higher accuracy, our
BioProTT
TM
Clamp-On SLs incorporate two pairs of transducers, i.e. four piezo ceramics in total, which are
arranged in an X-configuration around the tube containing the measured flow.
When sending ultrasonic signals through the measuring section, the transit time difference depends on the
flow direction of the medium:
•
The ultrasonic sound signals that are sent along the flow direction and volume flow of the medium, i.e.
downstream, need less time to travel the measuring section
than
•
the ultrasonic sound signals that are sent against the flow direction, i.e. upstream.
The transit time difference is measured for every pulse. The difference between upstream and downstream
measurements is proportional to the volumetric flow rate of the liquid in the tube. Therefore, by accurately
measuring the difference between upstream and downstream transit time T
up
and T
down
, we are able to
determine the flow velocity. The calculation as such is carried out by the evaluation device.
Figure 1: Sensor Structure
BioProTT™ Clamp-On SL
Copyright em-tec GmbH
Page 5
D162-704 BioProTT™ Clamp-On SL – User Manual– V4.0
DocuSign Envelope ID: BE88571C-E493-4DFB-AF9A-864EB3FC3D75
