MULTICAL® 302
Kamstrup A/S · Technical Description · 5512-1334_F1_GB_12.2016
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9
Flow sensor
9.1
Ultrasound combined with piezo ceramics
For more than 20 years ultrasonic measurement has proved the most long-term stable measuring principle for heat
measurement. Experience with ultrasonic meters in operation as well as repeated reliability tests carried out in
Kamstrup’s accredited long-term test equipment and at AGFW in Germany have documented the long-term stability of
ultrasonic meters.
9.2
Principles
The thickness of a piezoceramic element changes when exposed to an electric field (voltage). If the element is
influenced mechanically, it generates a corresponding electric charge. Therefore, the piezoceramic element can
function as both transmitter and receiver.
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 as the car passes
by.
9.3
Transient time method
The transient time method used in MULTICAL
®
302 utilizes the fact that it takes an ultrasonic signal sent in the
opposite direction of the flow longer to travel from transmitter 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.
Diagram 4
S
IG
N
AL
t
PHASE DIFFERENCE
T
Against the flow
With the flow