Controller for controlling a frequency inverter and control method

Abstract

A controller for controlling a frequency inverter of a positive displacement pump motor of a positive displacement pump. The controller comprises a control unit configured to produce a control variable (Ys) for a frequency inverter of a positive displacement pump motor depending on a reference variable (W) and a first actual operating parameter (X). According to the invention, the control unit is associated with logical means having a first threshold value defining means that are designed to determine at least one first threshold value (YGrenzmax, YGrenzmin) depending on the first actual operating parameter (X) and/or at least one further actual operating parameter (XH, YH, YHH) that could lead to a failure state of the positive displacement pump when exceeded or fallen short of.

Claims

1. A controller for controlling a frequency converter of a positive displacement pump motor of a positive displacement pump, comprising: a logic unit configured to execute the following instructions: generate a manipulated variable (YS) for the frequency converter as a function of a reference input variable (W) and a first actual operating parameter (X), the manipulated variable (YS) generated to control, at least in part, output of the frequency converter; determine at least one first limit value having a first maximum limit and a first minimum limit as a function of the first actual operating parameter (X), and at least one additional actual operating parameter (XH, YH, YHH), such that in response to exceeding the first maximum limit or falling below the first minimum limit of the at least one first limit value, a defect state of the positive displacement pump is determined; compare the manipulated variable (YS), or a first previously corrected manipulated variable (YS, YS), or a comparative value with the first maximum limit and the first minimum limit of the at least one first limit value, wherein when the manipulated variable (YS) is determined to exceed the first maximum limit or fall below the first minimum limit of the at least one first limit value, the defect state of the positive displacement pump is determined; output a first corrected manipulated variable (YS, YS) in response to exceeding the first maximum limit or falling below the first minimum limit of the at least one first limit value by a predetermined amount, the first corrected manipulated variable (YS, YS) generated to control, at least in part, output of the frequency converter; determine at least one second limit value having a second maximum limit and a second minimum limit as a function of the first actual operating parameter (X) and the at least one additional actual operating parameter (XH, YH, YHH), such that in response to exceeding the second maximum limit or falling below the second minimum limit of the at least one second limit value, a negative effect on a quality parameter of delivery fluid conveyed by the positive displacement pump is determined; compare the manipulated variable (YS), or the first corrected manipulated variable (YS, YS), or a second previously corrected manipulated variable (YS, YS), or the comparative value with the second maximum limit and the second minimum limit of the at least one second limit value, wherein when the manipulated variable (YS) is determined to exceed the second maximum limit or fall below the second minimum limit of the at least one second limit value, the negative effect on the quality parameter of delivery fluid conveyed by the positive displacement pump is determined; and output a second corrected manipulated variable (YS, YS) in response to exceeding the second maximum limit or falling below the second minimum limit of the at least one second limit value by a predetermined amount, the second corrected manipulated variable (YS, YS) generated to control, at least in part, output of the frequency converter; wherein the at least one first limit value is dynamically determinable subject to change during operation of the positive displacement pump as a function of the first actual operating parameter (X) and the at least one additional actual operating parameter (XH, YH, YHH).

2. The controller according to claim 1, wherein the first actual operating parameter is a measured actual controlled variable (X) comprising an actual pressure, an actual pressure difference or an actual volume flow of the delivery fluid.

3. The controller according to claim 1, wherein the at least one additional actual operating parameter (XH, YH, YHH) is at least one of the following: a measured actual controlled variable (X) comprising an actual pressure, an actual pressure difference or an actual volume flow of the delivery fluid; a measured auxiliary manipulated variable (YH) calculated on the basis of the actual or measured value of a rotational frequency setpoint value of the frequency converter or a torque setpoint value of the frequency converter; a measured auxiliary controlled variable (XH) calculated on the basis of a rotational speed of the positive displacement pump motor or a torque of the positive displacement pump motor; a measured delivery fluid temperature or a storage temperature of the positive displacement pump; a measured vibration value or a measured or calculated delivery fluid viscosity; and a measured leakage rate.

4. The controller according to claim 1, wherein the logic unit determines the comparative value on the basis of the functional relationship from the manipulated variable (YS) or from the first or second corrected manipulated variable (YS, YS) or from the first actual operating parameter (X) and the at least one additional actual operating parameter (XH, YH, YHH).

5. The controller according to claim 4, wherein at least one geometry parameter (GP) is accounted for in determining the comparative value, the geometry parameter being specific to the positive displacement pump assigned to the controller, the geometry parameter stored in a memory for determining the comparative value within the context of the functional relationship, or to take into account the shear properties of the delivery fluid from a delivery fluid parameter (FP) stored in the memory.

6. The controller according to claim 1, wherein the logic unit is configured to further execute: determining at least one of the at least one first limit value and the at least one second limit value as a function of a gap width or a spindle diameter assigned to the controller and stored in a memory, or to determine the at least one of the at least one first limit value and the at least one second limit value as a function of a delivery fluid parameter (FP) stored in the memory; and determining the first or second corrected manipulated variable (YS, YS) as a function of the gap width or the spindle diameter, or as a function of the delivery fluid parameter (FP) stored in the memory, the delivery fluid parameter (FP) comprising shear properties of the delivery fluid.

7. The controller according to claim 1, wherein the logic unit is configured to further execute: determining at least one of the at least one first limit value and the at least one second limit value as a function of a minimum or maximum shear rate in the positive displacement pump, which is stored in a memory and is specific for the positive displacement pump assigned to the controller, or as a function of at least one of an actual shear rate, and determining the first or second corrected manipulated variable (YS, YS) as a function of at least one shear rate in the positive displacement pump, which is stored in the memory, and is specific for the positive displacement pump assigned to the controller, or as a function of actual shear rate.

8. The controller according to claim 1, wherein the controller has at least one input for the first actual operating parameter (X) and has multiple inputs for the at least one additional actual operating parameter (XH, YH, YHH).

9. The controller according to claim 1, wherein in a nonvolatile memory comprising an EEPROM, different system parameter data records for different positive displacement pumps or different delivery fluid parameters (FP) are stored for manually selection via a selection menu.

10. The controller according to claim 1, wherein the logic unit is configured to determine or to signal a maintenance need of the positive displacement pump as a function of at least one of the first actual operating parameter (X), the at least one additional actual operating parameter (XH, YH, YHH), and a parameter that is specific for the positive displacement pump assigned to the controller.

11. The controller according to claim 1, wherein the controller is configured to communicate via a CAN bus system.

12. The controller according to claim 1, wherein the controller has a memory configured and controlled to save at least one of the first actual operating parameter (X), the at least one additional actual operating parameter (XH, YH, YHH), the reference input variable (W), comparative value, the at least one first limit value, and the at least one second limit value with a time stamp.

13. The controller according to claim 1, further including a key for configuration of the controller.

14. The controller according to claim 1, further including at least one of a display and an LED lamp.

15. A positive displacement pump system, comprising a positive displacement pump, a positive displacement pump motor for driving the positive displacement pump, and the controller and frequency converter of claim 1, wherein reference input variable specifying units are assigned to the controller for supplying the controller with the reference input variable (W).

16. The system according to claim 15, wherein the reference input variable specifying units are configured for at least one of monitoring, controlling and regulating a plurality of system units, the system units comprising positive displacement pumps.

17. The system according to claim 15, wherein multiple positive displacement pumps are provided with respective ones of said controllers.

18. The system according to claim 15, wherein the controllers are configured to communicate with at least one of a process control room and multiple controllers with one another over a CAN bus system.

19. The system according to claim 15, wherein the controllers have a signal-conducting connection to at least one sensor for receiving the first actual operating parameter (X) or the at least one additional measured actual operating parameter (XH, YH, YHH); and the controllers have a signal-conducting connection to the frequency converter for receiving the first actual operating parameter (X) or the at least one additional measured actual operating parameter (XH, YH, YHH), the at least one additional measured actual operating parameter comprising a positive displacement pump motor rotational speed or a rotational frequency setpoint value of the frequency converter or a torque setpoint value of the frequency converter.

20. The controller of claim 1, wherein the logic unit is configured to further execute: outputting the first maximum limit or the first minimum limit of the at least one first limit value in response to exceeding the first maximum limit or falling below the first minimum limit of the at least one first limit value.

21. The controller of claim 1, wherein the logic unit is configured to further execute: outputting the second maximum limit or the second minimum limit of at least one the second limit value in response to exceeding the second maximum limit or falling below the second minimum limit of the at least one second limit value.

22. A method for controlling a frequency converter of a positive displacement pump motor of a positive displacement pump, comprising: generating a manipulated variable (YS) for the frequency converter of the positive displacement pump motor as a function of a reference input variable (W) and of a first actual operating parameter (X), the manipulated variable (YS) generated to control, at least in part, output of the frequency converter, determining by a logic unit a first limit value having a first maximum limit and a first minimum limit as a function of the first actual operating parameter (X), and at least one additional actual operating parameter (XH, YH, YHH), such that, in response to exceeding the first maximum limit or falling below the first minimum limit of the at least one first limit value, a defect state of the positive displacement pump is determined, comparing by the logic unit the manipulated variable (YS) or a first previously corrected manipulated variable (YS, YS), or a comparative value with the first maximum limit and the first minimum limit of the at least one first limit value, wherein when the manipulated variable (YS) is determined to exceed the first maximum limit or fall below the first minimum limit of the at least one first limit value, the defect state of the positive displacement pump is determined; outputting by the logic unit a first corrected manipulated variable (YS, YS) in response to exceeding the first maximum limit or falling below the first minimum limit of the at least one first limit value by a predetermined amount, the first corrected manipulated variable (YS, YS) generated to control, at least in part, output of the frequency converter, determining by the logic unit at least one second limit value having a second maximum limit and a second minimum limit as a function of the first actual operating parameter (X) and the at least one additional actual operating parameter (XH, YH, YHH), such that in response to exceeding the second maximum limit or falling below the second minimum limit of the at least one second limit value, a negative effect on a quality parameter of delivery fluid conveyed by the positive displacement pump is determined, comparing by the logic unit a manipulated variable (YS), or the first corrected manipulated variable (YS, YS), or a previously second corrected manipulated variable (YS, YS), or the comparative value with the second maximum limit and the second minimum limit of the at least one second limit value, wherein when the manipulated variable (YS) is determined to exceed the second maximum limit or fall below the second minimum limit of the at least one second limit value, the negative effect on the quality parameter of delivery fluid conveyed by the positive displacement pump is determined; and outputting by the logic unit a second corrected manipulated variable (YS, YS) in response to exceeding the second maximum limit or falling below the second minimum limit of the at least one second limit value by a predetermined amount, the second corrected manipulated variable (YS, YS) generated to control, at least in part, output of the frequency converter; wherein the at least one first limit value is dynamically determinable subject to change during operation of the positive displacement pump as a function of the first actual operating parameter (X) and the at least one additional actual operating parameter (XH, YH, YHH).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Additional advantages and details of the invention are derived from the following description of preferred exemplary embodiments and the drawings, which show:

(2) FIG. 1 is an embodiment of a controller configured to compare a manipulated variable generated by a regulator with a first (pump protection) limit value;

(3) FIG. 2 is an alternative embodiment of a controller configured to compare a manipulated variable generated by a regulator with a (delivery fluid protection) limit value;

(4) FIG. 3 is another embodiment a controller in which the manipulated variable generated by the regulator is to be compared with a first limit value and/or a second limit value and can optionally be corrected;

(5) FIG. 4 is an exemplary NPSH diagram; and

(6) FIG. 5 is a diagram illustrating the physical relationship between the delivery fluid pressure, measured at the pressure connection of the pump, the delivery fluid viscosity (medium viscosity) and the pump rotational speed, namely here a minimum rotational speed of the pump.

DETAILED DESCRIPTION

(7) The present embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which some embodiments are shown. The subject matter of the present disclosure, however, may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the subject matter to those skilled in the art. In the drawings, like numbers refer to like elements throughout.

(8) In the figures, the same elements and elements having the same function are all labeled with the same reference numerals.

(9) Exemplary Embodiment According to FIG. 1

(10) FIG. 1 shows schematically the design of a positive displacement pump system 1, which comprises a positive displacement pump 2, designed as a single-spindle pump or as a multi-spindle pump, in particular a triple-spindle pump in the embodiment shown here. The positive displacement pump 2 is operatively connected to a motor shaft of a positive displacement pump motor 3, designed as an electric motor comprising a frequency converter 4, which controls and/or regulates the flow of electricity to the motor windings of the positive displacement motor pump 3 as a function of a manipulated variable Y.sub.S generated by the regulator 6 or a corrected manipulated variable Y.sub.S or a manipulated variable Y.sub.S, optionally been corrected multiple times.

(11) To generate the manipulated variable YS or a corrected manipulated variable YS, the positive displacement pump system 1 comprises a controller 5 formed by a microcontroller, for example, including a regulator 6, as mentioned above, as well logic means 7.

(12) Reference input variable specifying unit 8, for example, a process-controlled panel supplying reference input variables W to the controllers 5, are provided upstream from the controllers 5, where the reference input variable supplied is an electric voltage signal representing a setpoint volume flow or a setpoint pressure, for example.

(13) The reference input variable W and a first actual operating parameter X supplied from the outside are sent to the regulator 6, more specifically to a subtracter 9 of the regulator 6 which calculates the difference XW. The actual regulator 6, which is embodied as PI regulator or a PID regulator, for example, thus determines a manipulated variable YS, on the basis of the reference input variable W and the first actual operating parameter X, which is measured here. This manipulated variable YS, is not sent directly to the frequency converter 4, as in the state of the art, but instead first passes through the logic means 7, comprising first comparator means 10 in the exemplary embodiment shown here. The comparator means compare the manipulated variable YS generated by the regulator 6 with at least one first limit value, preferably a maximum first limit value Ylimit max to be maintained and/or a minimum limit value Ylimit min to be maintained. Instead of the direct comparison of the manipulated variable YS with the at least one first limit value, a comparative value that is functionally related to the manipulated variable YS may be calculated with the help of (optional) comparative value specifying unit (not shown here) on the basis of the manipulated variable YS, such that at least one actual operating parameter, for example, the first actual operating parameter X, and at least one additional actual operating parameter to be explained in greater detail below, may also enter into the calculation of same according to a functional relationship. The comparative value specifying unit may also take into account a geometry parameter of the positive displacement pump and/or a delivery fluid parameter according to a functional relationship for calculation of the comparative value, said parameter(s) then also having to be taken into account further in taking into account the limit value. In the exemplary embodiment shown here, this additional comparative value calculation step is eliminated, however, and the manipulated variable YS is compared directly with at least one first limit value Ylimit max and/or Ylimit min, such that the at least one first limit value is a positive displacement pump protection limit value which when exceeded or not met will or could result in a defect in the positive displacement pump.

(14) A first function unit 11 is assigned to the comparator means 10, including an addition to first limit value specifying unit 12, first correction means 13. The function unit 11 calculates the at least one first limit value Ylimit max, Ylimit min, which is sent to the comparator means 10 in addition to the manipulated variable YS generated by the regulator 6. The comparator means then check on whether the manipulated variable YS drops below a maximum first limit value Ylimit max and/or whether the manipulated variable YS exceeds a minimum first limit value Ylimit min. If this is the case, then the manipulated variable YS is an allowed manipulated variable, which does not pose a threat for the positive displacement pump and can be supplied for additional comparisons and correction routines that are not shown here or may be sent directly, as shown here, as an input signal to the frequency converter 4 which then triggers the positive displacement pump motor 3 on this basis.

(15) To calculate the at least one first limit value, the first actual operating parameter X is sent to the first function unit 11, and another measured or calculated actual operating parameter YH and/or XH is also sent to the function unit, such that the actual operating parameter YH in the exemplary embodiment shown here is an auxiliary manipulated variable of the frequency converter, for example, a rotational frequency setpoint value or a torque setpoint value of the frequency converter. These are not measured values but instead are values that are calculated, in particular simulated, based on at least one actual parameter, for example, based on a current control measurement calculated by the frequency converter. The additional actual operating parameter XH in the exemplary embodiment shown here is an auxiliary controlled variable, for example, a motor rotational speed and/or a positive displacement pump rotational speed or a torque, which is preferably measured directly on the motor 3. Thus, in each case, an operating parameter, for example, the first actual operating parameter, namely here the actual value of the controlled variable from the process control system 14, is taken into account by the first limit value specifying unit 12 for calculating the at least one pump protection limit value, and at least one additional actual operating parameter YH, XH or one main manipulated variable YHH, preferably a measured variable for the process controlled variable X, for example, a pressure or a volume flow is also taken into account.

(16) For the case when the comparator means find that the maximum first limit value Ylimit max has been exceeded and/or the minimum first limit value Ylimit min has not been met, this is reported to the first function unit 11 whose first correction means 13 then calculate a corrected manipulated variable YS, taking into account the first actual operating parameter X and one of the aforementioned additional actual operating parameters YH, XH, YHH. This corrected manipulated variable YS may then be sent as shown here to the comparator means as an input variable for comparison with a first limit value Ylimit max and/or Ylimit min or sent for another comparison and correction procedure, bypassing the comparator means (not shown) or sent directly as an input signal to the frequency converter 4.

(17) From a memory 19, preferably nonvolatile, specific geometry parameters GP for the positive displacement pump assigned to the controller 5 and/or specific delivery fluid parameters FP for the delivery fluid such as, for example, the shear properties of the delivery fluid may be sent to the first limit value specifying unit 12 and/or to the first correction means 13 so that they enter into the calculation of the first limit values Ylimit max, Ylimit min and/or the corrected manipulated variable YS within the context of a functional relationship.

(18) In the exemplary embodiment presented here, the corrected manipulated variable YS is the maximum or minimum allowed first limit value Ylimit max, Ylimit min, to approximate the manipulated variable YS generated by the regulator as closely as possible. To this extent, the first limit value specifying unit 12 and the first correction means 13 include a shared computer (computer means), because the corrected manipulated variable YS in the exemplary embodiment presented here corresponds to a first limit value Ylimit max, Ylimit min. The manipulated variable YS generated by the regulator is overwritten by the corrected manipulated variable YS.

(19) In particular when the corrected manipulated variable YS should not correspond to the first limit value, the first correction means 13 and the first limit value specifying unit 12 may be implemented as completely separate units, i.e., each with its own computation means, i.e., in separate function units. This is of course also possible for the case presented above, namely when the corrected manipulated variable YS should correspond to a first limit value, so that in this case, as shown in FIG. 1, the limit value specifying unit 12 and the correction means 13 are fused together, i.e., they have a shared computation routine.

(20) The exemplary embodiment according to FIG. 1 is described in greater detail below on the basis of exemplary variants of concrete embodiments that are not restricted.

(21) First Example

(22) The first actual operating parameter X corresponds to the actual controlled variable, namely in the exemplary embodiment shown here, a pressure measured in bar. It is assumed that the reference input variable X is a pressure and amounts to at least 20 bar. Likewise, the actual operating parameter X is measured as 20 bar.

(23) Then there is a change in the reference input variable. The reference input variable X changes from 20 bar to 10 bar, for example, due to a corresponding stipulation. This results in a system deviation of WX=10 bar.

(24) The regulator 6 determines a new manipulated variable YS, namely in this case a voltage value, which is proportional to the rotational speed and is much smaller than that in a previous run and/or in a previous calculation. The first limit value specifying unit 12 calculates a minimum allowed limit value Ylimit min, which represents a minimum allowed rotational speed in the exemplary embodiment presented here. It is desirable to maintain a minimum allowed rotational speed in order to avoid the risk of a lubricant failure if the rotational speed drops below this minimum allowed rotational speed.

(25) The minimum allowed rotational speed, i.e., the minimum allowed limit value Ylimit min is calculated on the basis of the following functional relationship:

(26) $\mathrm{Ylimit}\min =n_{\mathrm{allowed}}={\left(\frac{X}{k*b*c*v^a}\right)}^2$

(27) In this functional relationship, Ylimit max corresponds to the minimum allowed limit value. This is a minimum allowed rotational speed (nallowed).

(28) In this case, the first actual operating parameter X is the measured controlled variable, namely here the new actual pressure of 10 bar. The factor V.sup. is another operating parameter, namely a measure of the operating viscosity of the delivery fluid, which is determined by a temperature measurement of the delivery fluid, and/or for the influence of the viscosity on the maximum allowed pressure. This value amounts 10.sup.0.32 for the specific medium in question in the exemplary embodiment shown here. The constant k is the correction value for the lubricating ability of the medium, which amounts to 0.75, for example, for the specific medium.

(29) The constant b is a correction value for the tribological load-bearing capacity of the pump housing. In the exemplary embodiment shown here, this amounts to 1. The pump-specific characteristic value c is a characteristic value for the rotor diameter under a radial load. This amounts to 0.55, for example, in the exemplary embodiment shown here.

(30) The minimum allowed limit value Ylimit min is sent to the first comparator means 10, which compares the manipulated variable YS determined by the regulator 6 with the minimum allowed limit value. Depending on the result of the comparison, either the manipulated variable YS determined by the regulator is transmitted to the frequency converter or a corrected manipulated variable YS is calculated by the first correction means, preferably corresponding to the minimum allowed limit value Ylimit min calculated previously (or calculated anew).

(31) Second Example

(32) The first actual operating parameter X corresponds to the actual controlled variable, namely here a pressure. An actual pressure of 20 bar is measured. Based on a corresponding stipulation, the setpoint value of the controlled variable changes, i.e., the reference input variable W changes from 20 bar to 30 bar. At the same time, there is a change in the disturbance variable. It is assumed that the flow resistance increases as a result of a smaller flow-through area, i.e., a smaller flow-through diameter, for example, due to a change in tool.

(33) In practice, this results in the actual operating variable X, i.e., the actual pressure definitely does exceed or would exceed the reference input variable W, because the pump is still operating at an unchanged rotational speed, but in the meantime the flow resistance has increased significantly due to the tool replacement.

(34) The resulting system deviation at the difference forming output then leads to a significant decline, i.e., reduction in the manipulated variable YS. For the case when this is transmitted to the frequency converter 4 as a setpoint stipulation without correction, this would result in a risk to the pump with regard to the allowed pressure at a reduced low rotational speed. To prevent this, the aforementioned manipulated variable YS is compared with the calculated with the minimal limit value Ylimit min (first limit value) which represents the minimum allowed rotational speed. The calculation is made on the basis of the functional relationship described in the first exemplary embodiment. The manipulated variable YS falls below the minimum allowed limit value Ylimit min, i.e., the minimum allowed rotational speed, so a corrected manipulated variable YS, which is transmitted instead of the manipulated variable YS to the frequency converter, is then output by the first correction means 13.

(35) The corrected manipulated variable YS preferably corresponds to the calculated minimum allowed limit value Ylimit min.

(36) Third Example

(37) The reference input variable W is a volume flow measured in L/min. The first actual operating parameter X is a measured volume flow. It is assumed that the volume flow demand increases during operation. In the example shown here, the reference input variable should double namely from 1500 L/min to 3000 L/min. The regulator 6 determines a manipulated variable YS, namely a rotational speed in this case, from the resulting system deviation WX. This manipulated variable YS, i.e., the rotational speed preselected by the regulator 6, is compared by the comparator means 10 with a maximum allowed rotational speed, i.e., a first limit value Ylimit max. This maximum allowed rotational speed is determined on the basis of the NPSHavailable, i.e., on the basis of the available NPSH and/or the holding pressure level of the system. In the exemplary embodiment shown here this amounts to 8 m H2O (meters of water column). Then Ylimit max, i.e., the maximum allowed rotational speed, is determined on the basis of the NPSHavailable and another measured actual operating parameter, in this case the viscosity of the medium. This is done on the basis of the diagram shown in FIG. 4, for example, or alternatively, on the basis of a polynomial based on the following calculation principle and stored in a nonvolatile memory:
NPSH=f(pump size(da),spindle angle of slope,viscosity v,rotational speed n)

(38) which makes it possible to calculate the axial velocity of the medium within the pump, which is applicable for a certain design size and a certain angle of slope based on the pump size as a function of the spindle diameter da and the spindle angle of slope, so that the following relationship is obtained in simplified terms:
NPSH=f(vax size spindle slope angle,viscosity v,rotational speed n) Consequently, it is true that
vax allowed size NPSH=f(v,n) so that by means of the relationship
vax=S*n or n=vax/S ultimately the relationship
Ylimit max=nallowed size NPSH=vax allowed size NPSH/S can be established.

(39) Thus, an allowed pump rotational speed nallowed size NPSH can be calculated for a pump of a certain pump size with a certain spindle angle of slope and a certain NPSH value.

(40) In the diagram according to FIG. 4, the NPSH is shown on the left vertical ordinate in meters of water column (m H2O). The right ordinate shows the rotational speed in revolutions per minute. The horizontal axis shows the axial velocity of the fluid in m/s. This diagram relates to an exemplary pump having a model size of 20 and an angle of slope of the spindle of 56. The linear rise of the line characterizes the axial velocity vax of the medium (delivery fluid) as a function of the rotational speed.

(41) To determine the first limit Ylimit max, i.e., the maximum allowed rotational speed, it is necessary to move to the right in the diagram starting from an NPSH of 8 m H2O up to the curve that is characteristic of the measured viscosity of 500 mm2/s. At the point of intersection with this curve, it is necessary to move upward in the diagram up to the linear line. At the point of intersection with this line, the maximum allowed rotational speed, i.e., the first limit value Ylimit max, can thus be read on the ordinate at the right. For the measured viscosity, i.e., the additional actual operating parameter, this amounts to about 3800 revolutions per minute.

(42) As mentioned in the introduction, the reference input variable doubles, i.e., the required volume flow is doubled, which amounts to 3000 l/min from the assumed 1500 l/min, based on the linear relationships of a change in the manipulated variable. Since this manipulated variable YS of 3000 l/min is smaller than the first limit value Ylimit max of approx. 3800 l/min, the manipulated variable YS can be transmitted to the frequency converter 4 as an input variable.

(43) If the reference input variable were not only doubled but instead were tripled, for example, this would yield a manipulated variable of 4500 l/min, which would be larger than the first limit value Ylimit max so that the correction means 13 would exceed the manipulated variable YS stipulated by the regulator 6 by the amount of a corrected manipulated variable YS, which would correspond to the first limit value, for example, i.e., 3800 l/min in the present example.

(44) Exemplary Embodiment According to FIG. 2

(45) The exemplary embodiment according to FIG. 2 differs from the exemplary embodiment according to FIG. 1 only in that the manipulated variable YS generated by the regulator 6 is not compared with at least one first limit value representing and/or ensuring the positive displacement pump protection but instead is compared with one second limit value that ensures the delivery fluid quality. The exemplary embodiment presented here relates to a second limit value.

(46) The at least one second limit value Ylimit max, Ylimit min ensures that the delivery fluid quality is maintained. In the exemplary embodiment shown here, only a single maximum second limit value Ylimit max is supplied by the second limit value specifying unit 15, whereby as an alternative multiple second limit values, e.g., also a minimal limit value Ylimit min which ensures the quality of the delivery fluid can also be calculated.

(47) At any rate, the second comparator means 16 compare whether the manipulated variable YS generated by the regulator 6 or a corrected manipulated variable already corrected in a previous additional correction procedure not covered here exceeds the second limit value Ylimit min by a certain measure. If the manipulated variable YS is less than or equal to the maximum limit value, then the manipulated variable YS generated by the regulator 6 and/or supplied to the comparator means 16 is made available (calculated) as an input variable to the frequency converter 4.

(48) Otherwise, with the help of second correction means 18, comprising a second function unit 17 in addition to the second limit value specifying unit 15, a corrected manipulated variable YS is made available with which the manipulated variable YS is overwritten. To calculate the at least one second limit value Ylimit min, the second limit value specifying unit 15 take into account the first actual operating parameter X on the basis of a functional relationship and also take into account at least one additional (other) actual operating parameter, for example, an auxiliary manipulated variable YH, an auxiliary controlled variable XH and/or a main manipulated variable YHH. For geometry parameters GP of the positive displacement pump and/or delivery fluid parameters FP as well as the vibration to be taken into account additionally in the calculation.

(49) Fourth Example

(50) The fourth example relates to the protection of the medium, i.e., the second limit value is determined so that no negative effect of a quality parameter of the delivery fluid conveyed with the positive displacement pump (delivery medium) results from the manipulated variable.

(51) In the concrete example, there should be assurance that there is no unacceptable shearing in the delivery medium. The maximum allowed shearing rate of the medium therefore enters into the calculation of the second limit value. Again, a rotational speed regulation is to be implemented so that the second limit value corresponds to a maximum allowed rotational speed. This means that the first operating parameter X is a volume flow of the process system. In addition to the medium-specific limits to the maximum allowed shear rate, function factors of the pump enter into the determination of the second limit value, i.e., weight, velocity ratios are taken into account namely the difference in the angular velocity of the rotating positive displacement rotors (spindles) in comparison with the stationary pump housing. The velocity ratios in the gaps are directly proportionally dependent on the pump rotational speed and there is an inverse direct proportional relationship to the size of the function gap, i.e., to the respective current linear shear rate. This function gap is first of all dependent on the pump-specific conditions namely on the prevailing actual radial gap, i.e., the fixed pump rotor radial gap and also the current operating conditions namely the respective current compressive load on the delivery fluid as well as the respective prevailing viscosity of the delivery fluid. The two latter additional actual operating parameters are measured and taken into account in the calculation of the second limit value Ylimit max, i.e., in the calculation of the maximum allowed rotational speed.

(52) Thus, for example, a delivery fluid with a dynamic viscosity of 5 Pas is pumped. This corresponds to a kinematic viscosity v of 5000 mm2/s, such that with an assumed density of 1000 kg/m3 a maximum allowed shear rate Dallowed of 20,000 sec1 is obtained for the delivery fluid in a certain pump while maintaining the maximum allowed shear stress of 100,000 N/m2. This is characterized by a rotary diameter of Da=70 mm and by a radial gap S=h0, which depends on the differential pressure, yielding a value of 0.021 mm at p=5 bar. This yields a maximum allowed rotational speed, i.e., a second limit value Ylimit max of 191 1/min. As long as the manipulated variable YS preselected by the regulator 6 is below the aforementioned value, the manipulated variable YS can be forwarded directly to the frequency converter 4otherwise, the manipulated variable YS is overwritten by a manipulated variable YS that is corrected and/or limited by second correction means 18.

(53) The example described above is based on the following computation principles: It follows from
e.g., allowed=D* and =v* for Newtonian fluids that
Dallowed=allowed/(v*p) In addition, it holds that
nallowed=Wallowed/(Da**60). By inserting this into
Wallowed=Dallowed*S and/or into Dallowed=Wallowed/S and by combining all the constants that occur in k, the maximum allowed rotational speed can be calculated as follows:
Dallowed=(Da**n)/(k*S).fwdarw.nallowed=(Dallowed*k*S)/(Da*n)

(54) The maximum allowed rotational therefore corresponds to the limit value Ylimit max.

(55) For the case when the delivery fluid (medium) to be pumped does not have Newtonian properties, first the Reynolds number in the pump function gap, the shear rate and the resulting representative viscosities must be calculated according to known physical relationships for intrinsically viscous delivery fluids. In this way, the allowed relationships for these fluids can be monitored and maintained in the same way as in the case of Newtonian delivery fluids.

(56) Exemplary Embodiment According to FIG. 3

(57) The exemplary embodiment according to FIG. 3 negates the exemplary embodiments according to FIG. 1 and FIG. 2, i.e., the controller 5 are designed so that the manipulated variable YS output by the regulator 6 can be compared with at least one first limit value (pump protection limit value) as well as with at least one second limit value (medium protection limit value). In the exemplary embodiment presented according to FIG. 3, the manipulated variable YS generated by the regulator 6 is first compared with a first limit value and then with a second limit value, but the reverse order may of course also be implemented, i.e., by comparing the manipulated variable first with a second limit value and then with a first limit value.

(58) It is characteristic of the exemplary embodiment according to FIG. 3 that the output value of the first comparison forms the input variable for the second comparison where the output variable of the first comparison cannot be the corrected manipulated variable YS, namely when there is nothing going beyond the limit value in the first comparison and thus YS is not corrected, or alternatively, when it is a manipulated variable YS corrected by the first comparator means 10.

(59) YS or YS is then the input variable for the second comparator means 16. If no correction is performed here, the input value for the second comparison YS or YS is sent to the frequency converter 4 or in the case of a correction the corrected manipulated variable YS is sent to the frequency converter.

(60) In the exemplary embodiment presented here, the first and second decision means 20, 21 are provided. These decision means determine whether a pump protection comparison and/or a medium protection comparison is to be performed. The respective decision can be predefined in the software, for example, so that as an alternative the user need only perform a pump protection comparison or a medium protection comparison or may perform both comparison operations.

(61) Exemplary Embodiment According to FIG. 5

(62) This exemplary embodiment is a protected exemplary embodiment for implementation of pump protection. The manipulated variable is a rotational speed signal for the pump, where the pump rotational speed is plotted on the left ordinate in the diagram. The delivery pressure measured at the pressure connection of the pump enters into the calculation of the first limit value as the first actual operating parameter, with the delivery fluid pressure being plotted on the right ordinate. The delivery fluid viscosity (medium viscosity) enters into the calculation of the first limit value as an additional actual operating parameter, wherein the medium viscosity is plotted on the horizontal lower axis. Alternatively, the delivery fluid volume flow and/or the pump rotational speed or the delivery fluid pressure is considered here as the reference input variables. In the concrete exemplary embodiment, it is assumed that the delivery fluid pressure is the reference input variable.

(63) In the example shown here, it is assumed that the delivery fluid viscosity (medium viscosity) drops from 12 mm2/s to 9 mm2/s, to 6 mm2/s, to 4 mm2/s and then (incrementally) to 2 mm2/s because of a corresponding change in medium. The delivery fluid volume flow may fluctuate. The reference input variable, i.e., the process pressure (delivery fluid pressure) should initially be kept at 10 bar, then at 20 bar, etc., i.e., it should increase incrementally by 10 bar at a time up to max. 50 bar.

(64) In other words, the reference input variable changes incrementally from 10 bar initially to 50 bar. The regular outputs a manipulated variable (YS) as a function of the reference input variable (W). The first limit value specifying unit calculate a first limit value, which in the present case is a minimum rotational speed Ylimit min as a function of the first actual operating parameter, which here is the delivery fluid pressure and in addition, the actual operating parameter which here is the medium viscosity such that in the concrete exemplary embodiment the medium viscosity is determined indirectly based on the delivery fluid temperature. In the present exemplary embodiment, failure to conform to the first limit value, i.e., the minimum rotational speed would have resulted in a defect status of the positive displacement pump. The comparator means in the concrete exemplary embodiment compare the manipulated variable preselected by the regulator, i.e., a rotational speed signal, with the first limit value calculated by the first limit value specifying unit. If the manipulated variable in the exemplary embodiment presented here is above this first limit value, then the manipulated variable is forwarded to the frequency converter as an input signal. If the manipulated variable falls below the first limit value, then in the exemplary embodiment presented here a corrected manipulated variable is ascertained and/or determined as the input variable and is forwarded to the frequency converter where the first limit value determined by the limit value specifying unit is forwarded as a corrected manipulated variable from the first correction means in the exemplary embodiment presented here.

(65) The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments of and modifications to the present disclosure, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are in the tended to fall within the scope of the present disclosure. Furthermore, although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes. Thus, the claims set forth below should be construed in view of the full breadth and spirit of the present disclosure as described herein.