METHOD FOR DETECTING A PUMP OR MIXER OPERATING IN PART LIQUID AND PART GAS

Abstract

A method for detecting the occurrence of snoring during operation of a machine configured for transporting liquid. The machine includes an impeller and an electric motor, operatively connected to a control unit. The method includes operating the machine in order to transport liquid on the condition that the instantaneous power of the machine is directed towards a set power level. The instantaneous power of the machine is allowed to fluctuate within a set power level range defined upwards by a max-factor times the set power level and defined downwards by a min-factor times the set power level. The method further includes determining the machine is snoring by the control unit when the instantaneous power of the machine is below a snoring level equal to a snoring-factor times the set power level by monitoring at least one of the operational parameters of power, current, or power factor of the machine.

Claims

1-18. (canceled)

19. A method for detecting the occurrence of snoring during operation of a machine configured for transporting liquid, the machine comprising an impeller and an electric motor, operatively connected to a control unit, the method comprising the steps of: defining a max-factor equal to [100+Xup] %; defining a min-factor equal to [100−Xdown] %; defining a snoring-factor equal to [100−(Xdown+W)]%, wherein W is more than 0 and equal to or less than 25; operating the machine to transport liquid such that an instantaneous power of the machine is directed towards a set power level (Pset) and allowed to fluctuate within a set power level range (Prange) defined upwards by the max-factor times the set power level (Pset) and defined downwards by the min-factor times the set power level (Pset); and with the control unit, determining the instantaneous power of the machine by monitoring at least one of operational parameters: power [P], current [I] or power factor [cos φ] of the machine, and determining that the machine is snoring when the instantaneous power of the machine is below a snoring level (Psnor) equal to the snoring-factor times the set power level (Pset).

20. The method of claim 19, wherein the step of operating the machine to transport liquid further includes: the control unit controlling the operation of the machine to direct the instantaneous power towards the set power level (Pset).

21. The method of claim 19, wherein Xup is in a range from greater than or equal to 3 to less than or equal to 25.

22. The method of claim 19, wherein Xdown is in a range from greater than or equal to 3 to less than or equal to 25.

23. The method of claim 19, wherein the defined snoring-factor is equal to or more than 70%.

24. The method of claim 19, wherein the instantaneous power of the machine is determined as being below the snoring level (Psnor) when the instantaneous power of the machine is below the snoring level (Psnor) a plurality of times during a predetermined period of time [t] equal to or less than 3 seconds.

25. The method of claim 19, wherein the set power level (Pset) is a predetermined target value.

26. The method of claim 19, wherein the set power level (Pset) is a measured target value determined during snoring-free operation of the machine.

27. The method of claim 26, wherein the measured target value is determined as an average of the instantaneous power of the machine during a predetermined period of time [t].

28. The method according to claim 27, wherein the predetermined period of time [t] is in a range from greater than or equal to 1 second to less than or equal to 30 seconds.

29. The method according to claim 28, wherein the predetermined period of time [t] range is equal to or more than 3 seconds, and equal to or less than 10 seconds.

30. The method according to claim 27, wherein the average of the instantaneous power of the machine is based on a plurality of samples [m] evenly distributed over the predetermined period of time [t].

31. The method according to claim 30, wherein the number of samples [m] is equal to or less than 50.

32. The method according to claim 31, wherein the number of samples [m] is in a range of from greater than or equal to 10 to less than or equal to 20.

33. The method of claim 19, wherein the method further comprises: stopping the machine due to snoring by means of the control unit, when the instantaneous power of the machine is determined as being below the snoring level (Psnor).

34. The method of claim 33, wherein the method further comprises: after stopping the machine due to snoring, keeping the machine inactive inactive a predetermined pause time.

35. The method of claim 33, wherein the method further comprises: after stopping the machine due to snoring, keeping the machine inactive until the control unit obtains a start-signal from a sensor.

36. The method of claim 19, wherein the control unit comprises a variable frequency drive.

37. The method of claim 19, wherein the machine comprises a submersible machine, such as a submersible pump or a submersible mixer.

38. A computer program product comprising at least one non-transitory computer-readable storage medium having computer-readable program code portions embedded therein, the computer readable program code portions configured to cause a control unit for a machine configured for transporting liquid to execute the steps of the method according to claim 19 to detect snoring during operation of the machine.

Description

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0020] The present invention relates to a method for controlling the operation of a machine suitable for transporting liquid, such as sewage/wastewater, liquid comprising solid matter, slurry, clean water, etc. The machine is constituted by a submersible sewage/wastewater pump, a submersible drainage/dewatering pump, or a submersible sewage/wastewater mixer, i.e. a machine comprising an impeller/propeller configured to transport liquid. The present invention relates specifically to a method for detecting the occurrence of snoring during operation of such a machine, i.e. an operational condition wherein the impeller operates/rotates partly in air and partly in liquid. The machine is operatively connected to a control unit or controller, wherein the control unit is configured to at least monitor at least one of the operational parameters power [P], current [I] and power factor [cos φ] of the machine/motor, and to detect when the machine is snoring.

[0021] When snoring is detected, this information can be used to stop the machine, to notify an operator, be used as input in another control method associated with the machine, to calibrate different sensors used in connection with the machine, etc.

[0022] According to the invention, the method comprises the steps of:

[0023] operating the machine in order to transport liquid, the machine being operated on the condition that the instantaneous power of the machine is directed towards a set power level (Pset), wherein the instantaneous power of the machine is allowed to fluctuate within a set power level range (Prange) defined upwards by a max-factor [100+Xup] % times the set power level (Pset) and defined downwards by a min-factor [100−Xdown] % times the set power level (Pset), and

[0024] by means of the control unit determining that the machine is snoring when the instantaneous power of the machine is below a snoring level (Psnor) equal to a snoring-factor [100−(Xdown+W)] % times the set power level (Pset).

[0025] It shall be pointed out that the term “set power level” is construed to mean a predetermined/preset value/threshold of the actual electric power consumed by the machine/pump, and the term “snoring level” is construed to mean a value/threshold of the actual electric power consumed by the machine/pump below which snoring is considered determined.

[0026] It shall be pointed out that the term “when”, in connection with snoring detection, is construed to mean “as soon as”. It shall also be pointed out that the present invention can be used in parallel to other snoring detection methods. The term “power of the machine” is construed to mean the power consumption of the machine/motor at the present operational condition. The term “current of the machine” is construed to mean the current consumption of the machine/motor at the present operational condition. Depending on which operational parameters/quantities that are monitored the occurrence of decreasing power consumption is determined directly or indirectly/correspondingly, which is considered equivalent for the skilled person. Thus, if current is the monitored quantity, the instantaneous current is compared with a current level that corresponds to the power level at snoring, i.e. when the instantaneous current passes said current level at snoring the instantaneous power consumed by the machine passes the snoring level.

[0027] The present invention is especially intended for applications wherein the instantaneous power of the machine will fluctuate greatly within the set power level range (Prange) in normal snoring-free operation and/or when the degree of normal fluctuation is unknown. For instance due to varying nature of the transported liquid, a slow control loop, etc.

[0028] The present invention is applicable to direct-online machines, i.e. a machine that is operated by a constant frequency, i.e. the frequency Hz of the power mains. Thereby the machine is operated such that the instantaneous power of the machine is directed towards the set power level (Pset) during snoring-free/normal operation of the machine. The control unit is configured to monitor at least one of the power and current drawn by the machine and to detect when the instantaneous power of the machine is below the snoring level (Psnor). The monitoring can be performed continuously or intermittently.

[0029] The present invention is also applicable to more sophisticated or intelligent machines. The machine is operatively connected to a control unit, and according to a preferred embodiment the control unit is built-in into the machine. In such applications, the machine is driven in operation by the control unit, i.e. the machine is operated by means of the control unit to transport liquid, wherein the control unit controls the operation of the machine on the condition that the instantaneous power of the machine is directed towards a set power level (Pset). Thus, the control unit strives to keep the instantaneous power of the machine at a constant level by adjusting the operational speed of the machine. In a preferred embodiment the control unit is constituted by a Variable Frequency Drive [VFD] which is configured to regulate the operational speed of the machine, for instance by regulating the frequency Hz of the alternating current supplied to the electrical motor of the machine. Thus, the control unit is configured to monitor/regulate/control the operational speed of the machine, and the control unit is also configured to monitor at least one of the operational parameters power and current drawn by the machine. The monitoring can be performed continuously or intermittently. The control unit is also configured to detect when the instantaneous power of the machine is below the snoring level (Psnor).

[0030] According to a one embodiment the machine is stopped directly after it is determined that the machine is snoring, and according to another embodiment the machine is stopped after a predetermined time period has elapsed after it is confirmed that the machine is snoring, depending on application of use. The stopping of the machine comprise ramping down the operational speed of the machine or a direct/abrupt stop of the operational speed of the machine, for instance by setting the operational speed equal to zero in the control unit or by operatively disengaging the machine from the power mains.

[0031] After the machine has been stopped due to snoring, the machine is kept inactive until a new start criterion/condition is present. According to one embodiment the machine is kept inactive a predetermined pause time, or according to another embodiment the machine is kept inactive until the control unit obtains a start-signal from a sensor or the operator. Thereafter the machine is once again active until it is stopped manually, due to snoring, by a stop-signal from a level sensor, etc.

[0032] According to a preferred embodiment the Xup-element in the max-factor [100+Xup] % is equal to or more than 3 and equal to or less than 25. Preferably the Xup-element is equal to or more than 5 and equal to or less than 20. Thereto, it is preferred that the Xdown-element in the min-factor [100−Xdown] % is equal to or more than 3 and equal to or less than 25. Preferably the Xdown-element is equal to or more than 5 and equal to or less than 20.

[0033] Thereto, according to the invention the W-element in the snoring-factor [100−(Xdown+W)] % is strictly more than 0 and equal to or less than 25. Preferably the W-element is equal to or more than 3 and equal to or less than 10. It is preferred that superior to the above limits, the snoring-factor [100−(Xdown+W)] % is equal to or more than 70%, preferably equal to or more than 80%.

[0034] Thus, fluctuations/deviations of the instantaneous power of the machine within the power level range (Prange) are normal and only when the instantaneous power of the machine is below the offset snoring level (Psnor) the machine is determined as snoring. According to a preferred embodiment, the instantaneous power of the machine is determined as being below the snoring level (Psnor) when the instantaneous power of the machine is below the snoring level (Psnor) a plurality of times/samples during a predetermined period of time [t], equal to or less than 3 seconds.

[0035] The Xup-element and Xdown-element may be predetermined values, or may be values determined/measured during snoring-free operation of the machine. Thereto, the set power level (Pset) may be a predetermined target value, or may be target values determined/measured during snoring-free operation of the machine.

[0036] In the embodiment where the set power level (Pset) is a measured target value, it is preferably determined as an average of the instantaneous power of the machine during a predetermined period of time [t]. The predetermined period of time [t] is equal to or more than 1 second and equal to or less than 30 seconds. Preferably the predetermined period of time is equal to or more than 3 seconds and equal to or less than 10 seconds. The average of the instantaneous power of the machine is preferably based on a plurality of samples [m] evenly distributed over the predetermined period of time [t]. The number of samples [m] is equal to or less than 50 and equal to or more than 10. Preferably the number of samples [m] is equal to or less than 20. It shall be pointed out that a target value of the set power level (Pset) measured/determined during snoring-free operation of the machine may be used as a predetermined target value during subsequent operation of the machine.

[0037] In another aspect of the invention it is provided a computer program product comprising at least one non-transitory computer-readable storage medium having computer-readable program code portions embedded therein, wherein the computer-readable program code portions are configured to execute the steps of the described method when run in a control unit detecting the occurrence of snoring during operation of a machine intended for transporting liquid.

FEASIBLE MODIFICATIONS OF THE INVENTION

[0038] The invention is not limited only to the embodiments described above, which primarily have an illustrative and exemplifying purpose. This patent application is intended to cover all adjustments and variants of the preferred embodiments described herein, thus the present invention is defined by the wording of the appended claims and the equipment may be modified in all kinds of ways within the scope of the appended claims.

[0039] It shall also be pointed out that even thus it is not explicitly stated that features from a specific embodiment may be combined with features from another embodiment, the combination shall be considered obvious, if the combination is possible.