# CALIBRATING PRECISION ELECTRONIC SCALES: THE PROCEDURE TO FOLLOW

scales is precisely their degree of precision: if in fact the most precise scales are in class I, the scales with the least number of divisions fall into class IV.

### What is the procedure for calibrating and calibrating electronic scales?

Whether it is industrial scales (such as platforms, piece counters, axle scales, floor or table scales) or retail scales, such as those offered by Celmi, there is a standard procedure that guarantees that you have a perfectly electronic scale. calibrated. Let’s see this procedure together and in detail:

• Preparations: Before moving on to the actual calibration phase, it is good to make all the necessary preparations. A general advice is always to study the maximum capacity of the scale to be calibrated, as well as to understand its accuracy requirement and the type of adjustment to be made in case the procedure fails.

Good practice is to turn on the scale at least 30 minutes before carrying out the calibration and stabilize its temperature with that of the weights to be used, which must be of the horizontal type, especially in the case of precision measurements. Then proceed by carrying out some pre-tests.

• Eccentricity test: this first test is carried out to evaluate the variation of the measurement according to the variation of the position of the load (obviously with the same weight during the entire duration of the test). This procedure allows you to predict the margin of error in normal use, when it is likely that the load will not be positioned perfectly in the center of the precision instrument.

But how is this test done? The sample weight must be placed in four / five different areas of the scale, which obviously can have different shapes (round, rectangular, square, etc). In this case it is good to consult the OIML R76 and EN 45501 standards to view the different procedures to be followed according to the different forms.

• Repeatability test: this second test instead measures the degree of repeatability of the scale. In other words, it is observed how much the same measurement, repeated several times, can vary under the same conditions of the instrument, load and position.

The procedure is carried out by repeating the same weighing at least five times in a row, observing the margin of error of the scale. As a rule, the measuring instrument must be zeroed each time and therefore, only afterwards, the load can be placed, once the measurement has been taken, the same procedure is repeated.

• Weighing test: the objective of this other test is to observe the accuracy of the scale to be measured over its entire range, by increasing and decreasing the weight of the load in a series of different steps.

Proceed by zeroing the weighing instrument, then setting the load on the first point and recording the weigh; with each measurement we proceed by increasing the load weight (which are usually between 5 and 10 loads) and once the maximum is reached, we start to reduce the loads through the decreasing test points. This type of test is very useful for detecting any linearity problems, i.e. when the instrument does not measure with the same precision along the entire range.

• Minimum weight test: this last test is not necessarily required for the success of the sizing procedure, except for the weighings of the pharmaceutical industry. Specifically, this test allows to identify the minimum weight that can be measured, while always finding satisfactory results in terms of accuracy. In fact, in normal situations, the smaller the load to be weighed, the more the result tends to be inaccurate and unreliable. It is therefore good practice to be careful not to measure loads weighing less than the minimum load measurable by the instrument.

### The right calibration frequency

It is actually not that simple to determine a standard time interval in which to calibrate precision electronic scales. In deciding the calibration frequency, in fact, it is always good to keep in mind a series of considerations, such as the value of the product to be weighed: the higher its value, the greater the calibration frequency required. Or again, the greater the severity of the impact of an incorrect weighing process, the greater the frequency of calibrations. Finally, this frequency will be higher if a scale has to carry out many weighings in the course of a day and if the environmental conditions in which this scale operates are far from ideal (for example with frequent temperature changes, presence of fine particles, vibrations or displacement of air).

If you are looking for assistance with installing your scale electronics, be it industrial scales, load cells or other weighing instruments, by relying on Celmi you will receive a professional, quality and precision service. Our team of professionals is highly qualified to assist you and respond to your every need, be it assembly, testing, calibration or even product training !