Technical information

Ultrasonic Level Sensor LUC-M**

Function and system design

DOCT-0805F 01/2010 185414

Function and system design

Measuring principle

E: empty distance; F: span (full distance); D: distance from sensor membrane - product surface;

L: level; BD: blocking distance

Time-of-flight method

The sensor of the LUC-M** transmits ultrasonic pulses in the direction of the product surface.

There, they are reflected back and received by the sensor. The LUC-M** 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 x 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.

Interference echo suppression

The interference echo suppression feature on the LUC-M** ensures that interference echoes

(e. g. from edges, welded joints and installations) are not interpreted as a level echo.

Calibration

Enter the empty distance E and the span F to calibrate the device.

Blocking distance

Span F may not extend into the blocking distance BD. Level echoes from the blocking distance

cannot be evaluated due to the transient characteristics of the sensor.

Sensor BD Max. range fluids Max. range bulk materials

LUC-M10 0.25 m (9.8 in) 5 m (16.4 ft) 2 m (6.6 ft)

LUC-M20 0.35 m (13.8 in) 8 m (26.2 ft) 3.5 m (11.5 ft)

LUC-M30 0.6 m (23.6 in) 15 m (49.2 ft) 7 m (23 ft)

LUC-M40 0.4 m (15.7 in) 10 m (32.8 ft) 5 m (16.4 ft)

20 mA

100 %

4 mA

0 %