BrandTech Scientific EASYCAL 4.0 - Manual (Page 26)

26 EASYCAL ™ User Guide Version 4.0 · Status: June 2008
EASYCAL
™
User Guide
7.2 Basics
The values obtained by weighing during the gravimetric test are only the mass values of the dispensed volume. In
order to obtain the actual volume, an adjustment calculation must be carried out.
The necessary number of tests depends primarily upon the skill of the tester. Generally, one test should suf-
fice in the case of volumetric instruments made of glass/plastic; at least in case of instruments calibrated “IN”
(to contain). In case of instruments calibrated “EX” (to deliver), to be on the safe side, it is advisable to use
the mean value resulting from 3 measurements.The scatter of the individual results should not be greater than
1/ 4 of the admissible error limit of the measuring instrument. (Example: error limit of a 10 ml bulb pipette is ±0.020
ml. The scatter of measuring results must be below ±0.005 ml. If the scatter is greater, the testing procedure
should be revised, and the test should be repeated.)
Liquid Handling instruments are normally tested at 100%, 50% and 10% of their nominal volume. For each partial
volume, 10 measurements are required. The standard ISO 4787 describes the testing of volumetric instruments
and provides the following general equation for calculations:
Since this equation is rather cumbersome to work with, requiring a multitude of tables, we are providing a simplified
calculation in these Testing Instructions.
V
20
= (W
2
- W
1
) · z
Monitoring of measuring instruments, made easy:
The parameters are: V
20
[ml]: volume of the instrument at 20 °C
W
1
[g]: weight of the empty instrument
W
2
[g]: weight of the filled instrument
z [ml/g]: factor resulting from united parameters (see Tables)
To simplify the list of measuring instruments even further, we recommend to use conformity-certified BLAUBRAND ®
volumetric instruments marked with batch number or individual serial number. The initial testing of certified volumetric
instruments can be omitted since the testing results are already confirmed in the certificate.
V
20
= (W
2
- W
1
) ( 1 ) ( 1 -
ρ
L ) ( 1 -
γ ( t - 20 °C))
ρ
W
-
ρ
L
ρ
G