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Micro scale measurement - 58 Pages

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R/A\D W/A\G RADWAG BALANCES AND SCALES ADVANCED WEIGHING TECHNOLOGIES Micro Scale Measurement

Sławomir Janas MICRO SCALE MEASUREMENT Installation at the workstation • Usage precautions • The best measuring capacity Ambient conditions effect • Optimization as a balanced process SOP – monitoring of metrologically important parameters • Diagnostics measures Weighing applications (filter weight measurement, light loads measurement, measuring liquids) Conformity with regulations (legal metrology and practice, GMP, pharm

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Author’s note Contemporarily manufactured equipment provides intuitive operation holding the users back from thorough analysis of its operation. This phenomenon is evident and at the same time desired, owing to rapid and dynamic technological development. New inventions and PC software stand for ergonomics of use and simplicity, both of which are a result of advanced know-how involving group of engineers. When it comes to determination of sample weight by means of high resolution balance, the case is likewise. The balance seems to be unsophisticated measuring device, whereas in practice it...

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1. Introduction Measurement usually lacks accuracy which is mainly caused by imprecision of measuring equipment and applied methods. Such situation concerns electronic balances too, regardless of their design or resolution. Satisfying results do not depend on the construction exclusively, the ambient conditions and used methods are of the great importance here as well. The users practically do not notice any problems while using low resolution balances (< 2 000 000 d). In contrast, for measurement performed by means of high resolution equipment, it happens that user expectations collide...

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2.1. Workstation Workstation localization is usually determined in advance, it is a rare treatment that a user may decide himself/herself where to place it. It is more frequent to optimize the workplace using draft shields rather than to move the balance elsewhere. While selecting a respective place for the balance, microbalance especially, it is necessary to take the following into account:  The workstation cannot be located near air conditioning devices being a source of air drafts. A solution to strong drafts might be air stream dispersion, performed by means of more than one discharge...

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In course of installation balance indications and working conditions are observed. One of the most significant issues is the amount of time needed for balance acclimatization. The said time is a period within which balance temperature becomes stable for a particular place of operation. The greater the difference between balance temperature and workplace temperature, the longer the temperature stabilization period. Actually the period about few hours long, therefore PRECISE weighing tests are possible to be performed on the next day. The below figure presents balance temperature variation in...

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Throughout acclimatization both of these parameters may not be comprised within permissible limits. Certain instability of indication may be expected, its degree dependent on temporary drifts. Upon taking the load of a weighing pan the balance indication does not have to equal zero. The noticed deviations are not too high, few reading units usually. While operating the balance during acclimatization it is recommended to use zeroing button more often. More frequent adjustment is as much required, this owing to possible change of balance sensitivity (internal heating process). It is assumed...

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3. Operating Conditions By operating conditions one shall understand any factors relating to the balance working environment, these are:  Temperature variation dynamics,  Moisture content variation dynamics,  Speed and direction of air flow,  Possibility of vibrations occurrence,  Unbalanced electrostatic charges around balance and a sample. Some technical documents contain information on the above listed factors, unfortunately not many users are able to record dynamics of their variations. Such detailed control is not necessary for most measuring devices. This influences the adopted...

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4. Measuring Capacity – how to obtain precise measurement This seemingly simple issue turns out to be a bit sophisticated problem in reality. It is due to the fact that measuring capacity, understood as “ACCURATE” and “PRECISE” measurement, is a sum of many factors. Fig. 7. Accuracy and precision in metrology In order to determine sample weight, one has to assume that the obtained result is both, real and accurate. In order to provide confirmation for the above mentioned, it is necessary to check balance indications by means of mass standards. The procedure is quite simple. First, balance...

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New design of Q.C Test Report

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Estimation of measurement precision is much easier since it is characterized by repeatability of indications. It is possible to speak about a precise measurement when exactly the same or insignificantly different results are obtained. This test is performed by means of mass standards, although it may be carried out using any object of constant over time weight. This is an ideal solution for those who want to determine repeatability of indication for a packaging, glass flask, initial sample weight (differential weighing), clean filter (differential weighing) etc. usually 6-10 measurements...

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There are two decisive parameters when it comes to measuring capacity: repeatability of indications and linearity. Problem of eccentricity may be omitted owing to adopted testing methodology - i.e. the sample has to be placed in the very centre of a weighing pan each time. It is assumed that the eccentricity error for such methodology is relatively small, few reading units. Deviation being a result of indefinite drifts of zero indication may be minimized and this is carried out through zeroing procedure prior each measurement. Effect of weighing result variation resulting from sensitivity...

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