Precisa 350-8182-000, Operating Instructions Manual

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390 System Settings
Precisa Gravimetrics AG 52
minimum weight which is required is determined on the basis of the QM criteria and of the
statistical data from repeated weighing procedures.
If the weight is below the minimum weight a warning is appears on the balance display warning you
of this; these values are also marked in the printout.
The required minimum weights should be determined on the basis of the QM specifications by
means of the statistical analysis of certain series of measurements.The balance's own „Statistics“
function could be used for this purpose, for example. It is used to perform and subsequently log the
requisite series of measurements. Once the minimum weight(s) has/have been determined, it/they
can be input into the balance. Up to three tare ranges can be defined with the corresponding
minimum weights.
The balance's weighing modes, as well as measuring time and stability, are also fixed in such a way
as to guarantee compliance with tolerances in future measurements. Tare ranges, minimum weights
and weighing modes cannot be changed by the user.
The values which are input can be logged by means of an configuration status print and could,
along with the report on the statistical measurement series, be used as a QM certificate.
If work is performed on the basis of the minimum weight application, this serves to ensure that the
weighing results conform to the certificate specifications and, thus, to your QM guidelines.
The minimum weight is dependent on the ambient conditions. Therefore, it must be determined on-
site and must be reviewed periodically.The following parameters influence the minimum weight:
Calculation of the Minimum Weight = k * R / U
R: Repeatability means the calculated standard deviation of at least 10 measurement of the
same small weighed on-site. For USP the value must always be at least 0.41d.
K: The extension factor. The factor is defined by the user or is defaulted. (USP = 2)
U: Relative uncertainty (USP = 0.1 %)
6.7.1 USP Chapter 41, Determinatin, Calculation
Minimum Weight = k * R / U
To determine and calculate the minumium weight according USP 41 the following settings have to
be taken for k=2 and U=0.1 %. In addition, no value <0.41d may be used for the determined
repeatability. "d" corresponds to the last digit on the right of the weight display of the balance or for
a balance with a readability of 1 mg, d = 1 mg and W would therefore be R > = 0.41 mg.