Total tolerance
The total tolerance is the combined manufacturing tolerance and measurement uncertainty for measurements that are taken to provide proof of a guarantee.
The acceptance test codes in DIN EN ISO 9906 contain tolerance factors that make it easier to apply the combined manufacturing tolerance and measurement uncertainty that always have to be taken into account during the acceptance test for the individual operating parameters. These tolerance factors for the flow rate (± tQ), pump head (± tH) and pump efficiency (± tη) must be applied to the guaranteed point. See Fig. 1 Total tolerance
Variable | Symbol | Class 1 % | Class 2 % |
Volume flow rate | tQ | ± 4,5 | ± 8 |
Pump discharge head | tH | ± 3 | ± 5 |
Pump efficiency | η | -3 | -5 |
The head and flow rate guarantee is fulfilled if the H/Q curve determined from the measurements intersects or at least touches the vertical and horizontal bar of the tolerance cross. See Fig. 2 Total tolerance
The efficiency is derived from the point where the measured H/Q curve intersects the straight line running through the agreed operating point QG, HG and the zero point of the H/Q axis as well as from the point where a vertical is intersected by the η(Q) curve calculated from the measurements. The guarantee condition for efficiency is deemed to be within the tolerance limits if the value of this quantity is greater than or at least equal to the value for ηG ∙ (1 − tη) at this intersection point.
In the new version of DIN EN ISO 9906, the classes for assessing a pump measurement and the measurement results have been extended from 2 to 5. This also results in changes to the relevant total tolerance. See Fig. 3 Total tolerance
In accordance with this extended classification system, diagrams are available to illustrate the conditions for fulfilling the guarantee. See Fig. 4 Total tolerance
