Calibration; Ultrasonic Level Calibration; Dry Calibration - ABB LST300 Operating Instruction

Calibration

An easy-to-use calibration enables the best possible accuracy
by calibrating the measurement to two known good points .

Ultrasonic level calibration

There are two types of errors: offset and gradient .
Offset error
The error at a close range is equal to the error at maximum
range . In this case the c value in the equation y=mx+c must be
corrected .
3.07 m
0.307 m
0.30 m
Gradient error
A small error at a close range becomes larger as the range
increases . In this case the m value in the equation y=mx+c must
be corrected .
3.07 m
0.307 m
0.30 m
The speed of sound is linear, enabling calibration to be
performed using only two known points . This provides
sufficient information to calibrate LST300 .
Calibration can be performed in position if the tank dimensions
are known . This gives best results as it ensures the instrument
is calibrated to the intended installation . Alternatively, the
calibration can be performed before installation by pointing
the sensor at a known target .
There are two kinds of calibration for LST300 . One is for wet
calibration and the other is for dry calibration .

Dry calibration

Dry calibration can be done when we have two known target
levels available, and have the actual measurements at those
known points from LST300 .
L S T 3 0 0 | C O M PA C T U LT R A S O N I C L E V E L T R A N S M I T T E R | L S T 3 0 0 – E N R E V. E
y = mx + c
3.0 m
y = mx + c
3.0 m
Before starting the calibration procedure, gather the required
measurements that will be used as inputs to the dry calibration
function .
Parameter Description
Lower Sensor Point LST300 measurement for the level position
closest to the bottom of the tank
Upper Sensor Point LST300 measurement for the level position
closest to the top of the tank
Lower Level Point The expected level value at the level position
closest to the bottom of the tank
Upper Level Point The expected level value at the level position
closest to the top of the tank
Figure 28 Upper calibration point measured
Figure 29 Lower calibration point measured
As shown in the above figures, values in the following table are
used as an example .
Parameter Value
Lower Sensor Point 0.410 m is measured
Upper Sensor Point 2.990 m is measured
Lower Level Point 0.400 m is expected
Upper Level Point 3.000 m is expected
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