Appendix Prosonic T
54 Endress+Hauser
11.2 Measuring principle
L00-FMU30-15-00-00-xx-001
BD Blocking distance D Distance from sensor membrane - product surface
E Empty distance F Span (full distance)
L Level
11.2.1 Time-of-flight method
The sensor of the instrument transmits ultrasonic pulses in the direction of the product surface.
There, they are reflected back and received by the sensor. The instrument measures the time t
between pulse transmission and reception. The instrument uses the time t (and the velocity of sound
c) to calculate the distance D between the sensor membrane and the product surface:
D = c t/2
As the device knows the empty distance E from a user entry, it can calculate the level as follows:
L = E - D
An integrated temperature sensor compensates for changes in the velocity of sound caused by
temperature changes.
11.2.2 Interference echo suppression
The interference echo suppression feature on the instrument ensures that interference echos (e.g.
from edges, welded joints and installations) are not interpreted as a level echo.
11.2.3 Calibration
Enter the empty distance E and the span F to calibrate the device.
11.2.4 Blocking distance
Span F may not extend into the blocking distance BD. Level echos within the blocking distance
cannot be evaluated due to the transient characteristics of the sensor.
Sensor BD Max. range fluids Max. range bulk materials
1½" 0.25 m (0.8 ft) 5 m (16 ft) 2 m (6.6 ft)
2" 0.35 m (1.1 ft) 8 m (26 ft) 3.5 m (11 ft)
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