Flow Estimation Accuracy - Grundfos MAGNA3 25-80 Installation And Operating Instructions Manual

7.6 Flow estimation accuracy

The internal sensor estimates the difference in pressure between
the inlet and outlet port of the pump. The measurement is not a
direct differential-pressure measurement, but by knowing the
hydraulic design of the pump, you can estimate the differential
pressure across the pump. The speed and power give a direct
estimation of the actual duty point at which the pump is running.
The calculated flow rate has an accuracy specified as ± xx % of
Q . The less flow through the pump, the less accurate the
max
reading will be. The typical accuracy of the flow reading is ± 5 %
of the specific pump's maximum flow. In extreme cases, such as
closed valve operation, the accuracy can be up to ± 10 % of the
maximum flow.
See also section 7.9.5 Heat energy
Example:
H
Min.
Fig. 42 Q
max
1. MAGNA3 65-60 has a Q
max
Typically 5 % accuracy means 2 m
3
m /h.
2. This accuracy is valid for the entire QH area. If the pump
3
indicates 10 m /h, the measurement is 10 ± 2 m
3. The flow rate can be from 8-12 m
The use of a mixture of water and ethylene-glycol will reduce the
accuracy.
If the flow is less than 10 % of Q
28
monitor.
Max.
Q
Q
max
3
of 40 m /h.
3
/h inaccuracy of Q ± 2
max
3
/h.
3
/h.
, the display shows a low flow.
max