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SCALES

WHAT IS THE DIFFERENCE BETWEEN SCALE AND BALANCE?

The difference in mechanical scales is a function of their principle of operation. The scales measure the force exerted by an object subject to the force of gravity, while the scales measure the weight of an object comparing it with a known scale. As the scale is used to weigh large and bulky masses, the balance is used to weigh smaller masses of only a few kilos, being usual for example in laboratories. When we speak of scales or electronic scales, the difference is not clearly defined. In general terms, the scales are used to weigh large masses, although the precision (d) is lower. In the balance instead, the opposite happens. It is quite common that the scales have a platform at ground level, where it is easy to place the mass to be weighed. In general terms, it is usually accepted that up to 30Kg capacity, the instrument is a scale. For larger capacities, it is considered a scale.

WHAT IS A MULTI-RANGE SCALE?

The weighing range of a balance is divided. Start with a fine range that has greater precision (d1). When this fine range is exceeded, the reading automatically goes to the next range (d2) which is usually a lower step (2 x d1). The two-range scales can have a defined fine range, or the fine range can move through the full range. For example, in a scale model of 2Kg capacity in which the first 300g the sensitivity is 0.01g. When exceeding 300g, the sensitivity of the balance automatically goes to 0.1g. Now, suppose we put a 500g container on the plate, we tare it and then add weight. If the fine range can be displaced through the entire capacity of the balance, the reading will have a sensitivity of 0.01g. Otherwise, it would be 0.1g. Usually it is usually expressed as for example 15 / 6Kg 5 / 2g. This means that from 0 to 6Kg the balance shows the fraction of 2 in 2 grams, while from 6Kg to 15Kg it does of 5 in 5 grams.

WHAT IS A MICRO BALANCE AND A SEMI-MICRO BALANCE?

A micro balance is an analytical balance with precision d = 0.001 mg. A semi-micro balance is an analytical balance with precision d = 0.01 mg.

WHAT IS THE DIFFERENCE BETWEEN INTERNAL AND EXTERNAL CALIBRATION?

External calibration requires the use of an external standard mass. During an external calibration, the calibration is adjusted with respect to the constants of the external standard mass. The internal calibration does not require an external standard mass. With internal calibration, the calibration constants of the instrument are adjusted with respect to precise references existing on the same scale or scale. These scales have a small internal motor that puts the internal weight in and calibrates and removes it. This process of autocalibration is carried out automatically every time we turn on the balance.

WHAT IS THE UNCERTAINTY OF A BALANCE?

From the point of view of metrology, uncertainty is defined as the characteristic associated with the result of a measurement, which defines the bidirectional space centered on the value offered by the measurement instrument, within which the value is found with a certain statistical probability. measured This type of uncertainty is calculated through calibration, obtaining statistical data from a series of comparisons of the calibrated measuring instrument, against a reference standard with nominal and known uncertainty, which has demonstrable documentary traceability to internationally accepted measurement standards. The expression of the measure of any magnitude, should not be considered complete, if it does not include the evaluation of uncertainty associated with its measurement process. Since even the advanced digital load cells are not perfect, imperceptible deviations can occur both upwards and downwards if the same weight is repeated several times. Therefore, the law contemplates a maximum permissible deviation.

WHAT IS TRACEABILITY?

Traceability is the property of the result of a measure by which this result can be related or refer to patterns or references at the highest level and through these to the fundamental units of the International System (IS) through an uninterrupted chain of comparisons When the chain is traversed in the opposite direction, that is, from top to bottom, we speak of dissemination of the unit. So there is a pyramidal structure in which the base is the instruments used in the current measurement operations of a laboratory. Each step or intermediate step of the pyramid is obtained from the one that precedes it and gives rise to the next one by means of a calibration operation. At each step there are instruments and patterns that in turn act as patterns or references of the following. As each comparison of the chain introduces new causes of error that originate new contributions to the uncertainty of the result, which add to the uncertainty with which the value of the starting pattern is known, it is required that the uncertainty of the primary standards be very high. lower than those required in ordinary applications. This pyramidal grouping is what is called the calibration and validation plan, which will ensure that all equipment and patterns have the appropriate traceability to national or international standards.

WHY IS IT IMPORTANT TO CALIBRATE?

The aging of the components, the changes of temperature and the mechanical stress that the equipment supports deteriorate their functions little by little. When this happens, the trials and measurements begin to lose confidence and both the design and the quality of the product suffer. This reality can not be circumvented, but it can be detected and limited, through the calibration process. The correct calibration of the equipment provides the assurance that the products or services offered meet the required specifications. The reasons that lead manufacturers to calibrate their measuring equipment are becoming more numerous, in order to: * Maintain and verify the proper functioning of the equipment * Respond to the requirements established in the quality standards * Guarantee reliability and traceability of the measures. The calibration of an instrument allows to determine its uncertainty, fundamental value, within a quality system, for the grouping of the instruments in metrological categories for their later use. The result of a calibration is what is included in the calibration certificate.

WHAT IS CALIBRATION?

Calibration is simply the procedure of comparison between what an instrument indicates and what it "should indicate" according to a reference standard with a known value. Also known as adjustment. In fact, the process of adjustment or calibration consists of placing a standard mass on the scale or scale (the device will visualize what it thinks the standard mass weighs, and this is based on the previous calibration) type the real weight of the standard mass placed and memorize it. The weight shown will change to the real calibrated and from this moment the balance or scale will be governed by this new reference pattern to determine what weighs what we place on the plate.

THE LOAD CELL

The load cell is a structure designed to withstand loads of compression, tension and bending and thus be able to determine a weight, inside which is one or several deformation sensors called Strain Gauges that detect the values ​​of deformation. The load cell is formed by 4 strain gages in the form of Wheatstone bridge that detect this signal which is proportional to the force or torsion exerted by the weight. From 0 mVolts in vacuum up to 20 mVolts at full load. These millivolts generated by the torsion are amplified by the digital load cell or by the general plate of the unit and allow to be visualized as Kg in the display of the balance.

Documentation

WHAT IS THE DIFFERENCE BETWEEN A VERIFIABLE BALANCE AND ANOTHER THAT IS NOT?

Technically they can be the same or similar, but the verifiable scales are equipped with small legal details such as protected Software or additional inscriptions. Many times they are built with higher quality materials and incorporate passive and active filters so that radio interference, electromagnetic, wireless, mobile devices can not affect or alter the weight.

WHAT IS A CE VERIFICATION?

The EC verification is the procedure by which the manufacturer or his representative established in the Community assures and declares that the products subject to the provisions of paragraph 4 are in conformity with the type described in the EC type-examination certificate and meet the requirements of present Royal Decree that are applicable to you.

WHAT BALANCES ARE THE EC VERIFICATION TO HAVE?

In Spain, according to Order of December 22, 1994, which determines the conditions of non-automatic weighing instruments (BOE No. 2, of January 3, 1995, with correction of errors in No. 31, of February 6, 1995), in Article 3 appended to, must have the CE verification, those instruments that are used for the following purposes. * Realization of commercial transactions. * Calculation of fees, duties, taxes, bonuses, fines, compensation, compensation and other types of similar fees. * Application of rules or regulations, as well as the performance of judicial expert opinions. * Weighing of patients for reasons of control, diagnosis and medical treatment. * Pharmaceutical preparation of medicines by order, as well as carrying out analyzes carried out in medical and pharmaceutical laboratories. * Determination of the price or total amount in the direct sale to the public and the preparation of pre-packages. If you want additional information on the verification of scales, or do not know if you need a verifiable balance, you can refer to the Verification Office in your country. In Spain you can go to the Spanish Metrology Center (www.cem.es)