Calibration Of Weight Measurement; Determination Of Zero Point; Span Calibration By Weight - Siemens SIWAREX WP241 Manual

8.5

Calibration of weight measurement

The incoming analog measured value from the load cells is converted by an analog-to-digital
converter into a digital value ("Digits"). A weight is calculated using this digital value. All
functions of the electronic weighing system use the weight value to calculate the material
flow rate, totalizing, and the status.
The characteristic curve of the measuring system must be defined before the weight can be
calculated from the digital value. The characteristic is defined by points 0 and 1. Working
point "0" is defined by the dead weight of the empty scale (no load).
The ADC digits are subsequently determined for the scale loaded with a test weight.
8.5.1

Determination of zero point

The load cells return a voltage measurement to the electronic weighing system as a result of
the weight of the scale itself, even if the belt is empty. Following analog-to-digital conversion
of the signal, the zero point (displayed weight = 0) is assigned to the digital value (calibration
digits for the zero point). The measurement is carried out with an empty, running, and
warmed-up belt. At least one complete belt revolution is required. The zero point of the scale
is determined more accurately if several belt revolutions are used.
The command "Start initial zero calibration" (60) is triggered with the empty belt. The zero
point is then determined for the parameterized number of belt revolutions. The status display
in DR30 indicates that the calibration is running.
The result is displayed in DR4. You can apply the result using the command "Apply initial
zero calibration digits" (88). The zero point is then imported in DR3.
8.5.2

Span calibration by weight

Carrying out the calibration
If the scale is loaded with a defined test weight (e.g. 50% of the measuring range), the test
weight is assigned to the new digital value returned by the analog-to-digital converter.
Step 1
The belt is warmed-up and the zero point has been determined.
1. Stop the belt.
2. Enter a test weight appropriate to the measuring range in DR3 (e.g. 50% of the
3. Attach this test weight to the scale or place it onto the scale.
SIWAREX WP241
Manual, 04/2014, A5E33713528A
measuring range).
Scale parameters and functions of the belt scale
8.5 Calibration of weight measurement
83