TECHNICAL DESCRIPTION
ULTRAFLOW
®
54 DN150-250
5512-876 GB/04-2012/Rev. F1
29
8
Functional description
8.1
Ultrasound combined with piezo ceramics
Flow sensor manufacturers have been working on alternative techniques to replace the mechanical principle.
Research and development at Kamstrup has proven that ultrasonic measuring is the most viable solution.
Combined with microprocessor technology and piezo ceramics, ultrasonic measuring is not only accurate but also
reliable.
8.2
Principles
The thickness of a piezo ceramic element changes when exposed to an electric field (voltage). When the element
is influenced mechanically, a corresponding electric charge is generated. In this way the piezo ceramic element
can function either as sender or receiver or both.
Within ultrasonic flow measuring there are two main principles: the transit time method and the Doppler method.
The Doppler method is based on the frequency change which occurs when sound is reflected by a moving particle.
This is very similar to the effect you experience when a car drives by. The sound (the frequency) decreases when
the car passes by.
8.3
Transient time method
The transit time method used in ULTRAFLOW
®
utilizes the fact that it takes an ultrasonic signal emitted in the
opposite direction of the flow longer to travel from sender to receiver than a signal sent in the same direction as
the flow.
The transient time difference of a flow sensor is very small (nanoseconds). Therefore, the time difference is
measured as a phase difference between the two 1 MHz sound signals in order to obtain the necessary accuracy.
PHASE DIFFERENSE
S
IG
N
A
L
T
Upstream
Downstream
t
Diagram 8