SMERI PLUR Series, Руководство пользователя, Страница: 4 / 25

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1.4 Measuring principle: Time-of-flight method
The probe is mounted on the top of the flume, and ultrasonic pulses is
transmitted by the probe to the surface of the monitored material. There,
they are reflected back and received by the pro be. The host measures the
time t between pulse transmission and reception. The host uses the time t
(and the velocity of sound c) to calculate the distance d between the sensor
bottom and the monitored liquid surface: d = c •t/2. As the host knows the
installation height H from parameters setting, it can calculate the level as
follows: h = H – d .
Since speed of sound through air is affected by changes in temperature, the
PLUR has integrated a temperature senor to improve accuracy.
An integrated temperature sensor compensates for changes in the velocity of
sound caused by temperature changes. Calibration Enter the empty distance
H and the span F to calibrate the device.
Blind zone:
Level echo from the blind zone cannot be evaluated due to the
transient characteristics of the sensor. Span F may not extend into the
blanking distance B.