METHOD FOR DETERMINING A FLOW VOLUME OF A FLUID DELIVERED BY A PUMP

Abstract

A method for determining a flow volume of a fluid delivered by a pump, wherein the flow volume is determined as a function of predefined pump information depending on a pump geometry, rotation speed information, which correlates with the rotation speed of the pump, and pressure information, which correlates with a differential pressure at the pump.

Claims

1. A method for determining a flow volume of a fluid delivered by a pump, wherein the flow volume is determined as a function of predefined pump information, which is dependent on a pump geometry, a rotation speed information, which correlates with the rotation speed of the pump, and pressure information, which correlates with a differential pressure at the pump.

2. A method according to claim 1, wherein the flow volume is calculated by subtracting a leakage volume flow determined as a function of the pressure information from a theoretical delivery volume flow determined as a function of a pump volume predefined by the pump information and the rotation speed information.

3. A method according to claim 1, wherein, as additional information, a temperature and/or a viscosity and/or a density of the fluid, and/or an operating current and/or a shaft torque of the pump are registered, wherein the flow volume and/or the leakage volume flow are determined as a function of the additional information.

4. A method according to claim 1, wherein at least one pressure sensor, and/or at least one force sensor which registers a force acting on a pump component, in particular on a bearing, are used to determine the pressure information.

5. A method according to claim 1, wherein, by a vibration sensor, a vibration of at least one component of the pump is registered, wherein the rotation speed information is determined in dependence on sensor data of the vibration sensor.

6. A method according to claim 1, wherein the pump information describes a pump volume which indicates a theoretical delivery volume per revolution of the pump.

7. A method according to claim 1, wherein, for the determination of the flow volume and/or of the leakage volume flow, the pump geometry is described by a maximum of four parameters.

8. A method according to claim 7, wherein at least one of the parameters describing the pump geometry is defined by evaluating measurement data of at least two calibrating measurements which are performed on the pump at mutually different differential pressure.

9. A method according to claim 1, wherein, as a function of the rotation speed information and/or the pressure information and/or the additional information and/or the leakage volume flow and/or the flow volume, in particular as a function of the temporal progression of the rotation speed information and/or the pressure information and/or the additional information and/or the leakage volume flow and/or the flow volume, wear information, which indicates whether wear on the pump reaches or exceeds a predefined limit value and/or which indicates a severity of the wear and/or which describes a change in the pump geometry or in the pump information due to the wear, is determined.

10. A pump for delivering a fluid, wherein it is designed to implement the method according to claim 1, wherein it comprises at least one sensor device, which is designed to register the rotation speed information and/or the pressure information and/or the additional information, and a processing device, which is designed to determine the flow volume in dependence on at least the pump information, the rotation speed information and the pressure information.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0046] In the drawing:

[0047] FIG. 1 shows an illustrative embodiment of a pump according to the invention,

[0048] FIG. 2 shows the information processing in an illustrative embodiment of the method according to the invention,

[0049] FIG. 3 shows the determination of parameters relating to a pump geometry in the method explained with reference to FIG. 2, and

[0050] FIG. 4 shows a flow chart for determining a wear variable in an illustrative embodiment of the method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0051] FIG. 1 shows a pump 1, in the example a screw pump. This comprises a motor 2, which, via a shaft 3, drives a main screw 4. The main screw 4 is also referred to as the drive screw. This is arranged adjacent to the secondary screws 6, 7, which are also referred to as running screws, so that, in a resulting interspace 5 which is jointly formed by the main screw 4 and the secondary screws 6, 7, upon rotation of the shaft 3, fluid is delivered from the fluid inlet 8 to the fluid outlet 9. Operating parameters of the pump 1 are registered by a plurality of sensor devices 43 to 49. Screw pumps are well known in the prior art and shall therefore not be explained in detail.

[0052] In many applications, a flow volume delivered from the fluid inlet 8 to the fluid outlet 9 is intended to be determined. Options for this are set out below with additional reference to FIG. 2. In principle, it would be possible to completely disregard a leakage volume flow 11, i.e. a backflow of fluid through gaps 16 in the pump 1. In this case, a theoretical delivery volume flow 12 could be directly determined as the flow volume, by multiplying a predefined pump volume 14 or a theoretical delivery volume per revolution of the pump by rotation speed information 41 describing the rotation speed 13. The geometric pump volume 14, of which account is taken as the pump information 17 or part of this pump information 17, can be directly determined by the parameters of the pump design. For instance, it can be determined as a function of the screw diameter, the screw pitch and of predefined geometry factors. It is herein also possible to measure in detail the concrete shape of the screws or of the casing 18 in order to more accurately define the volume. Alternatively, a cycle of measurements can be performed, for instance, at various pressures falling at the pump 1, and a theoretical delivery volume per revolution can hereby be extracted from the actual flow volume.

[0053] The rotation speed 13 can anyway be known if the processing device 10 controls the motor 2 such that a predefined rotation speed is set. It is also possible for the rotation speed to be registered directly by a rotation speed sensor 14. In some embodiments, it can also be advantageous to determine the rotation speed by registering, via a vibration sensor 15, sensor data 19 relating to a vibration of a component of the pump 1, for instance the casing 18. The vibrations or sensor data 19 typically have a strong frequency contribution at at least an integer multiple of the rotation speed 13, in particular at double the rotation speed 13. By analyzing the frequencies arising in the sensor data 19, the rotation speed 13 can thus likewise be defined.

[0054] The theoretical delivery volume flow 12 is typically, however, heavily flawed. By additionally taking into account the differential pressure 20 at the pump 1, a flow volume 21 can be calculated with considerably improved accuracy. In particular, the leakage volume flow 11 is calculated as a function of the differential pressure 20 or of pressure information 42 describing this differential pressure 20, and subtracted from the theoretical delivery volume flow 12 in order to define the flow volume 21. The differential pressure 20 can be determined by an inflow-side pressure sensor 33 determining a first pressure value 22 and an outflow-side pressure sensor 23 determining a second pressure value 24, wherein the pressure values 22, 24 are subtracted one from the other in order to calculate the differential pressure 20. Alternatively, a differential pressure sensor could, for instance, be utilized to directly determine the differential pressure.

[0055] As already explained with reference to equation (1), the leakage volume flow 11 can depend on up to three further parameters 25, 26, 27, for instance the above-discussed parameters a, b and , which are provided as part of the pump information 17. As will be explained later in still closer detail, these can be determined by calibrating measurements on the pump 1 or on further pumps.

[0056] As additional information 28, in particular a density 29 and a viscosity 30 of the delivered fluid can be taken into account. The density 29 and the viscosity 30 could be determined, for instance, via special measuring devices, which can be disposed in a bypass duct 31. Where an always substantially same fluid is used at substantially always same temperature, these variables can also be assumed and predefined to be constant.

[0057] In particular, if a direct determination of the density 29 or viscosity 30 is intended to be dispensed with, it can be advantageous to additionally register the temperature 32 of the fluid via a temperature sensor 33. This temperature can in particular be evaluated to define, with the aid of a look-up table or a known mathematical correlation, a temperature-dependent viscosity 30 and/or density 29 of the respective fluid.

[0058] Moreover, it can be advantageous to monitor, by a current sensor 35, a current 36 supplied to the motor 2 or a power supplied to the motor 2. Jointly with the rotation speed 13, a torque 37 at the shaft 3 can be calculated herefrom. Alternatively, this torque 37 could be registered by a torque sensor 38. As will further be explained later with reference to FIG. 4, a registration of the torque can in particular be advantageous in order to be able to detect wear on the pump 1 or in order to adapt at least one of the parameters 25, 26, 27 to take account of a corresponding wear situation. Moreover, as has already been explained with reference to the equations (2) and (3), an evaluation of the shaft torque 37 can be utilized to define the viscosity 30, or at least to detect changes in the viscosity 30.

[0059] If, as set out above, the parameters 25, 26, 27 are chosen such that they correspond to the variables a, b and explained with reference to equation (1), then these parameters, or at least parts of these parameters, are determined by calibrating measurements on the pump. This is represented below, by way of example, in FIG. 3. If the relationship

a=a.Math..sup.3b(4)

in equation (1) is used, then it is evident that, in the double-logarithmic plotting, shown in FIG. 3, of the specific leakage volume flow against the specific differential pressure, the measuring points of all calibrating measurements 39, 40 should lie on a straight line 50. The Y-intercept herein corresponds to the parameter a, and the parameter b corresponds to the gradient of the straight line 50. It can thus already be sufficient to determine two specific leakage volume flows Q.sub.L.sup.+ at various specific differential pressures p.sup.+ in order to determine the parameters a and b. As already explained with reference to equation (1), these parameters would already be sufficient to describe the correlation between leakage volume flow and differential pressure at the pump 1. The splitting of the parameter a into the parameters a and can be advantageous, since the parameter can be chosen, by appropriate choice of the parameter a, such that it can intuitively be construed as a measure of a gap.

[0060] FIG. 4 shows a flow chart of a method for determining wear on the pump 1. This can be considered as part of the previously described method for determining a flow volume, yet can also be utilized separately herefrom. For the detection of wear, use is made of the fact that a mechanically hydraulic loss torque M.sub.mh, as already set out above, can be represented as follows:

[00004]$\begin{array}{cc}{M}_{m.Math.h}=R_{.Math.p}.Math..Math.p.Math.V+R_V.Math.\frac{V.Math..Math..Math..Math.\mathrm{nV}}{}+R_{}.Math.n^2.Math.V^{5/3}& \left(3\right)\end{array}$

[0061] The three summated loss therms respectively depend on another power of the rotation speed n. In order to make use of this, in step S1 the shaft torques 37 are firstly determined at a plurality of rotation speeds and given otherwise same measurement parameters. The measurements at the individual rotation speeds are herein realized quasi-statically, that is to say a rotation speed is firstly set and is maintained at least until such time as the shaft torque 37 has stabilized. Contributions to the increase in or reduction of the rotation speed are thus not taken into account.

[0062] In step S2, an analysis of the measurement data registered in step S1 is performed, wherein, in particular, a fit or a regression is performed in order to distinguish between contributions to the shaft torque 37 which are not dependent on the rotation speed n, are linearly dependent on the rotation speed n, and are quadratically dependent on the rotation speed n. In the shown illustrative embodiment, in step S3 solely the torque contributions independent of n are taken into account, from which, in step S4, in particular the parameter R.sub.p can be determined or a change in this parameter can be detected. A change in the parameter R.sub.p can in particular indicate that wearing is leading to increased loss of friction in a bearing of the pump 1.

[0063] In step S5, by contrast, solely those torque contributions which are linearly dependent on the rotation speed are taken into account. From these, in step S6, under the assumption that R.sub.v is constant, a change in the clearance , or a concrete value for this variable, can be determined. Thus a change in gap geometry as a result of deposits or as a result of material removal can likewise be detected. In particular, the parameter determined in this way can be taken into account, as part of the pump information 17, in a subsequent determination of the flow volume 21. Thus it is potentially not only possible to detect the presence of wear in order, for instance, to alert a user to a necessary exchange or necessary maintenance of the pump, but even concrete effects of the wear on the flow measurement can be determined and taken into account.

[0064] While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.