Brochure

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to convert the measuring results to a constant fluid temperature and a
constant speed.
To ensure a measuring result which is representative for the pump, the
test bed takes up more measurements and calculates an average value.
ISO09906 has an instruction of how the test makes a representative aver-
age value seen from a stability criteria. The stability criteria is a simplified
way to work with statistical normal distribution.
6.5.2 Overall uncertainty
The repetition precision on a test bed is in general better than the collected
precision. During development where very small dierences in performance
are interesting, it is therefore a great advantage to make all tests on the
same test bed.
There can be significant dierence in the measuring results between several
test beds. The dierences correspond to the overall uncertainty.
6.5.3 Measurement of the test bed’s uncertainty
Grundfos has developed a method to estimate a test beds’ overall uncer-
tainty. The method gives a value for the standard deviation on the QH curve
and a value for the standard deviation on the performance measurement.
The method is the same as the one used for geometric measuring instru-
ments, e.g. slide gauge.
The method is outlined in the Grundfos standard GS 241A0540: Test bench-
es and test equipment.
6.6 Summary
In this chapter we have introduced the hydraulic tests carried out on com-
plete pumps and their hydraulic components. We have described which
sizes to measure and which problems can occur in connection with planning
and execution of a test. Furthermore, we have described data treatment,
e.g. head and NPSH value.