Method and apparatus for adjusting a pump drive so that a pump flow corresponds with an incoming flow

1. A method in connection with a pump drive connected to a container, wherein a frequency converter is arranged to supply power to a pump such that a pump flow (Q p ) is responsive to an estimated mean incoming flow (Q est ) to the container, wherein the method comprises:

draining the container;

allowing the container to fill for a predefined filling time (t fill ) while the pump is inactive;

draining the container again at a known pump flow (Q p,nom );

measuring a drainage time (t drain );

calculating the estimated mean incoming flow (Q est ) on a basis of the drainage time (t drain ) and the filling time (t fill ) and known pump flow (Q p,nom ) of the pump; and

setting a power supplied by the frequency converter to the pump such that the pump flow (Q p ) corresponds to the estimated mean incoming flow (Q est ).

2. A method as claimed in claim 1 , wherein an estimation of an emptiness of the container comprises:

defining a motor torque from the power supplied by the frequency converter to the pump; and

judging that the container is empty, if the torque is smaller than a predefined percentage of an assumed torque defined for the pump flow (Q p ).

3. A method as claimed in claim 1 , comprising:

determining the estimated mean incoming flow (Q est ) on a basis of the filling time (t fill ) and drainage time (t drain ) and known pump flow (Q p,nom ) as follows:

Q

est

=

-

Q

p

,

nom

·

t

drain

t

fill

+

t

drain

.

4. A method as claimed in claim 1 , comprising:

updating information on a size of the estimated mean incoming flow (Q est ) by repeating a measuring cycle at predefined measuring intervals (t meas ) or when drainage of the container is detected.

5. A method as claimed in claim 1 , comprising:

activating a sleep mode of the frequency converter, during which the pump is not in use, when the estimated mean incoming flow (Q est ) is lower than a predefined minimum limit value (Q p,min ).

6. A method as claimed in claim 5 , comprising:

returning the frequency converter from the sleep mode for a new measuring cycle.

7. A method as claimed in claim 5 , wherein the container comprises a measuring sensor indicating top limit data of material level, the method comprising:

returning the frequency converter from the sleep mode to normal operation due to a top limit indication from the measuring sensor.

8. A method as claimed in claim 1 , comprising:

draining the container for a first time during a measuring cycle using a nominal flow of the pump;

measuring an initial drainage time (t drain,0 ); and

using the initial drainage time with the known pump flow (Q p,nom ) and the estimated mean incoming flow (Q est ) to estimate a material volume (v est ) in the container before the measuring cycle as follows:

v est =−( Q est +Q p,nom )· t drain,0

wherein the estimated mean incoming flow Q est is defined by using measuring results according to a present measuring cycle.

9. A method as claimed in claim 8 , comprising:

returning, at the end of the measuring cycle, the material volume (v) in the container to a desired level by allowing the container to fill while the pump is inactive for a time of a second filling time (t fill,1 ), wherein the second filling time (t fill,1 ) is obtained using an equation:

t

fill

,

1

=

v

Q

est

.

10. A method as claimed in claim 8 , comprising:

calculating a filling factor of the container by dividing the estimated material volume (v est ) by a known nominal material volume of the container.

11. A method as claimed in claim 2 , comprising:

determining the estimated mean incoming flow (Q est ) on a basis of the filling time (t fill ) and drainage time (t drain ) and known flow (Q p,nom ) of the pump as follows:

Q

est

=

-

Q

p

,

nom

·

t

drain

t

fill

+

t

drain

.

12. A method as claimed in claim 2 , comprising:

updating information on a size of the estimated mean incoming flow (Q est ) by repeating a measuring cycle at predefined measuring intervals (t meas ) or when drainage of the container is detected.

13. A method as claimed in claim 11 , comprising:

updating information on a size of the estimated mean incoming flow (Q est ) by repeating a measuring cycle at predefined measuring intervals (t meas ) or when drainage of the container is detected.

14. A method as claimed in claim 2 , comprising:

activating a sleep mode of the frequency converter, during which the pump is not in use, when the estimated mean incoming flow (Q est ) is lower than a predefined minimum limit value (Q p,min ).

15. A method as claimed in claim 13 , comprising:

activating a sleep mode of the frequency converter, during which the pump is not in use, when the estimated mean incoming flow (Q est ) is lower than a predefined minimum limit value (Q p,min ).

16. A method as claimed in claim 6 , wherein the container comprises a measuring sensor indicating top limit data of material level, the method comprising:

returning the frequency converter from the sleep mode to normal operation due to a top limit indication from the measuring sensor.

17. A method as claimed in claim 15 , wherein the container comprises a measuring sensor indicating top limit data of material level, the method comprising:

returning the frequency converter from the sleep mode to normal operation due to a top limit indication from the measuring sensor.

18. A method as claimed in claim 2 , comprising:

draining the container for a first time during a measuring cycle by using a nominal flow of the pump;

measuring an initial drainage time (t drain,0 ); and

using the initial drainage time with the known pump flow (Q p,nom ) and the estimated mean incoming flow (Q est ) to estimate a material volume (v est ) in the container before the measuring cycle as follows:

v est =−( Q est +Q p,nom )· t drain,0

wherein the estimated mean incoming flow Q est is defined by using measuring results according to a present measuring cycle.

19. A method as claimed in claim 17 , comprising:

draining the container for a first time during a measuring cycle by using a nominal flow of the pump;

measuring an initial drainage time (t drain,0 ); and

using the initial drainage time with the known pump flow (Q p,nom ) and the estimated mean incoming flow (Q est ) to estimate a material volume (v est ) in the container before the measuring cycle as follows:

v est =−( Q est +Q p,nom )· t drain,0

wherein the estimated mean incoming flow Q est is defined by using measuring results according to a present measuring cycle.

20. A method as claimed in claim 19 , comprising:

returning, at the end of the measuring cycle, the material volume (v) in the container to a desired level by allowing the container to fill while the pump is inactive for a time of a second filling time (t fill,1 ), wherein the second filling time (t fill,1 ) is obtained using an equation:

t

fill

,

1

=

v

Q

est

.

21. A pump drive system, comprising:

a pump;

a container for a liquid to be pumped;

a frequency converter arranged to supply power to the pump such that a pump flow (Q p ) is responsive to an estimated incoming flow (Q est ) to the container; and

a processor coupled to a memory arranged as a controller, the controller configured to:

drain the container by using the pump;

allow the container to fill for a predefined filling time (t fill ) while the pump is inactive;

drain the container again at a known pump flow (Q p,nom );

measure a drainage time (t drain );

calculate an estimated mean incoming flow (Q est ) on the basis of the drainage time (t drain ) and the filling time (t fill ) and known flow (Q p,nom ) of the pump; and

supply power to the pump via the frequency converter such that the pump flow (Q p ) corresponds to the produced estimated mean incoming flow (Q est ).