PUMP SYSTEM

Abstract

The invention relates to a pump system comprising a positive-displacement pump module, preferably a screw pump, a drive module which can be exchanged separately from the positive-displacement pump module, said drive module comprises an electric drive motor and a frequency converter associated therewith for controlling or adjusting a drive motor speed, control means comprising a controller for producing an adjustment variable (Y.sub.S) for the frequency converter in accordance with a reference variable (W) and a first actual operational parameter (X) and logistic means associated with the controller, and reference variable defining means for providing the reference variable (W) for the control means. According to the invention, the control means are provided in a control module separately from the drive module, and the drive module can be exchanged separately from the control module, and the drive module does not have a designed and/or controlled controller for producing the adjustment variable (Y.sub.S).

Claims

1. A method for operating a positive displacement pump, comprising: operating a positive displacement pump module; controlling a drive motor rotational speed by a drive module including an electric drive motor and a frequency converter, the drive module being separately replaceable with respect to the positive displacement pump module; and generating a first actual operating parameter (X) and a manipulated variable (YS) as a function of a reference input variable (W) by a controller having a regulator, the manipulated variable (YS) being receivable by the frequency converter, such that the manipulated variable (YS) is convertible by the frequency converter of the drive module through a corresponding energization of winding into the drive motor rotational speed; wherein the drive module is replaceable separately from a control module.

2. The method according to claim 1, wherein the manipulated variable (YS) is receivable by the frequency converter via a logic unit associated with the regulator.

3. The method according to claim 1, further comprising supplying the reference input variable (W) by a control room for the controller.

4. The method according to claim 1, wherein the controller is provided in the control module separate from the drive module.

5. The method according to claim 1, further comprising determining, or signaling, or both, by the logic unit, a maintenance need of the positive displacement pump as a function of at least one of the first actual operating parameter (X), 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.

6. The method according to claim 5, wherein the maintenance need is at least one of determinable and signalable by the logic unit a period of time before the positive displacement pump requires maintenance.

7. The method according to claim 2, wherein the logic unit has first limit value specifying means configured to determine at least one first limit value as a function of the first actual operating parameter (X), and the at least one additional actual operating parameter (XH, YH, YHH); having first comparator means configured to determine the manipulated variable (YS) or a corrected manipulated variable (YS, YS), or to compare a comparative value determined according to a functional relationship from the manipulated variable (YS), or the corrected manipulated variable (YS, YS) with the at least one first limit value; having first correction means configured to output a corrected manipulated variable (YS, YS) in response to the first comparator means detecting that the manipulated variable exceeds or falls below the at least one first limit value a certain amount, the corrected manipulated variable corresponding to the first limit value is determined by the first limit value specifying means; and the logic unit having second limit value specifying means designed to determine at least one second limit value as a function of the first actual operating parameter (X) and at least one additional actual operating parameter (XH, YH, YHH); having second comparator means designed to compare the manipulated variable (YS), or a corrected manipulated variable (YS, YS), or a comparative value determined according to a functional relationship from the manipulated variable (YS) or the corrected manipulated variable (YS, YS) with the at least one second limit value, and having second correction means configured to output a corrected manipulated variable (YS, Y) in response to the second comparator means detecting that the manipulated variable exceeds or falls below at least one second limit value a certain amount to output the corrected manipulated variable (YS, YS), corresponding to the second limit value, determined by the second limit value specifying means.

8. The method according to claim 7, wherein the first actual operating parameter is a measured actual control variable (X) selected from the list consisting of an actual pressure, an actual pressure difference and an actual volume flow of the delivery fluid.

9. The method according to claim 7, wherein the at least one additional actual operating parameter comprises at least one of: a measured actual control variable (X) selected from the list consisting of an actual pressure, an actual pressure difference and an actual volume flow of the delivery fluid; a measured auxiliary manipulated variable (YH) calculated on the basis of the actual value or measured, the measured auxiliary manipulated variable (YH) comprising a rotational frequency setpoint value of the frequency converter or a torque setpoint value of the frequency converter; a measured auxiliary control variable (XH) calculated on the basis of an actual value, the measured auxiliary control variable (XH) comprising a rotational speed of the positive displacement pump motor or a torque of the positive displacement pump motor; or a measured temperature, in particular a delivery fluid temperature or a storage temperature of the positive displacement pump; a measured vibration value; a measured or calculated delivery fluid viscosity; and a measured leakage rate.

10. The method according to claim 7, wherein the logic unit comprises at least one comparative value determination means configured to determine on the basis of at least one of: a functional relationship from the manipulated variable (YS); the corrected manipulated variable (YS, YS); and the first and the at least one additional actual operating parameter (XH, YH, YHH) to determine the comparative value.

11. The method according to claim 10, wherein the comparative value determination means are configured to at least one of: take into account the specific geometry parameters (GP) of a gap width or a spindle diameter which are specific to the positive displacement pump assigned to the control means and are stored in a memory within the context of the functional relationship; and take into account in particular the shear behavior of the delivery fluid from a delivery fluid parameter (FP) stored in a memory.

12. The method according to claim 7, wherein at least one of the first and second limit value specifying means are configured to: determine at least one of the first and second limit values as a function of the at least one specific geometry parameter (GP) a gap width or a spindle diameter assigned to the controller and stored in a memory; or determine these values as a function of a delivery fluid parameter (FP) stored in a memory, wherein the delivery fluid parameter comprises the shear behavior of the delivery fluid; and wherein at least one of the first and second correction means are configured to determine the corrected manipulated variable (YS, YS) as a function of at least one specific geometry parameter (GP), a gap width and a spindle diameter that is specific for the positive displacement pump assigned to the controller and stored in a memory and/or as a function of a delivery fluid parameter (FP) stored in a memory.

13. The method according to claim 7, wherein at least one of the first and the second limit value specifying means are configured to determine at least one of the first and second limit values as a function of at least one of: a minimal or maximal shear rate in the positive displacement pump stored in a memory and specific for the positive displacement pump assigned to the controller; the first or second correction means are designed to determine the corrected manipulated variable (YS, YS) as a function of at least one 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; and as a function of actual shear rate.

14. The method according to claim 7, wherein at least one of the first and second comparator means are configured to compare at least one of: (1) the first actual operating parameter (X), (2) the at least one additional actual operating parameter (XH, YH, YHH), (3) a value calculated according to a functional relationship from the first actual operating parameter (X), (4) the at least one additional actual operating parameter (XH, YH, YHH), (5) a manipulated variable (YS) of the regulator, (6) a corrected manipulated variable, (7) a comparative value calculated on the basis of the manipulated variable (YS), and (8) the corrected manipulated variable (YS, YS), with at least one limit value stored in a memory of the logic unit, and the first and/or second correction means are designed to output a corrected manipulated variable (YS, YS) when the first comparator means detects that the at least one defined limit value goes beyond the first limit value.

15. The method according to claim 7, wherein in a nonvolatile memory at least one of different system parameter data records for different positive displacement pumps and different delivery fluid parameters (FP) are stored for manual selection.

16. The method according to claim 7, wherein the controller includes a memory for storing at least one of the first actual operating parameters (X), the at least one additional operating parameter (XH, YH, YHH), the reference input variables (W), the comparative values, and the limit values, each with a time stamp.

17. The method according to claim 7, wherein the process control room is configured for at least one of monitoring, controlling and regulating the positive displacement pump.

18. The method according to claim 7, wherein the controller includes a signal-conducting connection to a sensor for receiving at least one of the first actual operating parameter (X) and at least one additional measured actual operating parameter (XH, YH, YHH) and wherein the controller have a signal-conducting connection for the frequency converter to receive at least one of the first actual operating parameter (X) and the at least one additional measured actual operating parameter (XH, YH, YHH); wherein the additional measure actual operating parameter (XH, YH, YHH) is selected from the list consisting of a positive displacement pump motor rotational speed, a rotational frequency setpoint value of the frequency converter, and a torque setpoint value of the frequency converter.

19. A method for operating a positive displacement pump, comprising: operating a drive motor of a first pump module; generating a rotational speed by a frequency converter based on a rotational speed output by a first control module for the operation of the drive motor; determining a manipulated variable (YS) as a function of a reference input variable (W) being delivered to the first control module; and controlling the drive motor by an actual operating parameter (X) and the determined manipulated variable (YS), the determined manipulated variable (YS) being delivered to the frequency converter, such that the manipulated variable (YS) is convertible by the frequency converter of the drive module through a corresponding energization of winding into the drive motor rotational speed; wherein the drive module is replaceable separately from the control module.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Additional advantages and details of the invention are derived from the following description of preferred exemplary embodiments and on the basis of the drawings, which show:

[0073] FIG. 1 a possible design of a pump system having two control modules, each of which is assigned a drive module and a pump module, such that the two control modules have an optional higher level control room,

[0074] FIGS. 2 to 5 different result scenarios on the example of the pump system according to FIG. 1, and

[0075] FIG. 6 a possible embodiment of control means in the form of control modules designed to compare a manipulated variable generated by a regulator with a first (pump protection) limit value, in particular for a system according to FIGS. 1 to 5,

[0076] FIG. 7 an alternative embodiment of control means, which are in the form of control module(s) designed to compare a manipulated variable generated by the regulator with a (delivery fluid protection) limit value, in particular for a system according to FIGS. 1 to 5,

[0077] FIG. 8 another embodiment variant of control means in the form of control modules for a positive displacement pump system, such as that shown as an example in FIGS. 1 to 5, such that the manipulated variable generated by the regulator can be compared and optionally corrected with a first limit value and/or a second limit value and such that the sequence of comparisons may also be different than that illustrated in FIG. 8, i.e., may be implemented in the opposite order,

[0078] FIG. 9 a NPSH diagram and

[0079] FIG. 10 the physical relationship in a diagram 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

[0080] 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.

[0081] The positive displacement pump system 1 shown in the figures comprises a first and a second control module 202, 203, the control module of which (first control module 202) shown at the left of the drawing is equipped as a so-called master box having signaling means 204, namely in the form of a display screen 205 and an LED lamp.

[0082] In addition to the signaling means 204, the first control module 202 (master box) is designed as a data memory unit (data logger), in contrast with the second control module 203, this data memory unit being connected to the second control module 203 in a signal-conducting manner and data transmitted by same, for example, the actual operating parameters, reference input variables or predefined rotational speeds are saved and are preferably provided with a time code. The signaling means 204 serve to signal control units or to display the need for maintenance and proposed times for performing the maintenance detected by the first control module 202 and/or the second control module 203 or optionally additional control modules (not shown).

[0083] A drive module 207 comprising an electric drive motor 3 designed here as an asynchronous motor; a frequency converter 4, which is assigned to the former and is shown separately here merely for the purpose of better illustration, preferably being arranged directly on the drive motor 3, is provided for the first control module 202.

[0084] The drive module 207, or more specifically the drive motor 3 of the drive module 207, is operatively connected by a coupling 210 to a first pump module 211 designed as a helical spindle pump.

[0085] A sensor module 212 for detecting an actual operating parameter X is arranged on the first pump module 211. In the exemplary embodiment shown here the sensor module is equipped with a vibration sensor to be able to detected unacceptable vibrations, which are then analyzed by the first control module 202, more specifically by integral logic means 7, in particular by comparison with information stored in an integral database of the control 202.

[0086] As shown in FIG. 1, the first sensor module 212 has a signal-conducting connection to the first control module 202 via a bus system 213, which is a CAN bus system here.

[0087] Logic means 7, which are mentioned above but are not shown here, are integrated into the first control module 202, and a regulator 6, which is also not shown for reasons of simplicity, but is designed as a PID regulator in the exemplary embodiment shown here, for generating a manipulated variable, which is to be described in greater detail below, or a corrected manipulated variable for the first frequency converter 4, which is not designed or alternatively is not used and/or controlled and/or supplied with actual system parameters to generate a setpoint rotational speed signal itself as a function of a pressure signal and/or a flow rate signal and/or a vibration sensor signal and/or a temperature sensor signal and/or a torque signal.

[0088] The first control module 202 like the second control module 203 has a plurality of inputs and outputs which are emphasized in the diagram for better visualization. The first control module 202 comprises analog inputs 214 by which the first control module 202 has a signal-conducting connection to a higher level control room (reference input variable specifying means 8). A reference input variable W or alternatively a manipulated variable can be transmitted from the control room over a connection which is designed here as an analog connection 216, such that the manipulated variable, for example, is looped through the first control module 202 and is sent to the first frequency converter 4 via one of preferably several analog outputs 217. As will be explained in greater detail below, however, the first control module 202 is also capable of independently generating a manipulated variable, in particular a rotational speed setpoint signal as a function of a reference input variable W, an actual operating parameter X and at least one additional operating parameter with which the first frequency converter is controlled.

[0089] In addition to the analog inputs 214, there is a plurality of digital inputs 218.

[0090] In addition, there is also a plurality of digital outputs 219 over which the data signals and other data can be transmitted to the control room.

[0091] It can be seen that the first control module 202 not only communicates with the sensor module 212 and/or receives data from it over the bus system 213 but also is connected to the second control module 203 via the bus system 213 which is designed as a CAN bus system. This second control module like the first control module 202 comprises (second) digital output 220, (second) digital inputs 221, (second) analog inputs 222 and (second) analog outputs 223 for transmitting a manipulated variable generated by the second control module 203 as a function of a reference input variable preselected by the control room or a manipulated variable preselected by the control room to the frequency converter (not shown separately) of a second drive module 224, which is operatively connected via a second coupling 225 to a second pump module 226, also designed as a positive displacement pump to which a second sensor module 227 is also assigned and by which the bus system 213 communicates with the second control module 203.

[0092] The control room (example of reference input variable specifying means 8) can transmit a motor-on signal and a motor-off signal via a digital connection 228 to the second control module 203, so that the second control module 203 controls the drive module 224 on the basis of this signal.

[0093] Instead of the sensor modules 212, 227, which are designed as vibration sensor modules and are shown here, additional sensors and/or sensor modules may additional or alternatively each be provided with one or more sensors to detect a wide variety of actual system parameters in the area of the respective pump module 211, 226.

[0094] A computer 229 which preferably communicates with the control modules 202, 203 via the bus system 213 may be provided for output and/or programming.

[0095] As shown in FIG. 1, the first control module 202 also comprises, in addition to the signaling means 204, input means 230 for performing input, preferably via menu control. The second control module 203 is not designed as a data memory unit for storing data received from other control modules, in contrast with the first control module 202, but instead in the exemplary embodiment shown here the second control module is only a second LED light and is not a display, so that one embodiment may also be implemented completely without signaling means.

[0096] Different scenarios that may occur during operation of the pump system 1 are described below with reference to FIGS. 2 through 5.

[0097] In the scenario shown in FIG. 2, the drive motor 3 of the first pump module 211 runs at a rotational speed generated by the frequency converter on the basis of a rotational speed output by the first control module 202. The corresponding and/or fundamental reference input variable W is fed via the analog connection 216 into one of the analog inputs 214 of the first control module 202, which determines a manipulated variable that is output via a analog output 217 and is sent to the first frequency converter 4 which controls the first drive motor 3 in accordance with the manipulated variable, doing so on the basis of the reference input variable W as well as taking into account an actual operating parameter. All the monitored actual system parameters, in particular a vibration signal determined by the first sensor module 212, which is sent to the first control module 202 via the bus system 213, are below the warning levels stored in a database of the logic unit of the first control module 202. A green LED 231 of the LED lamp 206 lights up.

[0098] In a second scenario which is illustrated in FIG. 3, an actual operating parameter, namely the total vibration of the first pump module 211 determined by the first sensor module 212, reaches a first warning threshold stored in the aforementioned database of the logic unit of the first control module 202, with the result that the first logic unit controls the first signaling means 204 in such a way that a yellow LED 232 of the first LED lamp 206 lights up. Furthermore, a corresponding warning and/or information is/are displayed on the display screen 205 as the signaling means 204. In the software of the logic unit of the first control module 2 it is stipulated that on reaching the first warning threshold, the first pump module 211 is to be operated at a slower rotational speed in order to maintain the allowed maximum vibration levels. The logic unit of the first control module 202 subsequently determines a manipulated variable that has been corrected downward and then is sent over the analog output 217 to the first frequency converter 4 of the first drive module 207. In addition, corresponding information is also output to the control room over one of the digital outputs 219. Depending on the programming, it can also be stipulated that the control room will decide whether the setpoint rotational speed specification set by the control room and determined by the actual process or the setpoint rotational speed specification of the second control module 203 will be routed to the frequency converter.

[0099] The scenario depicted in FIG. 4 is a result of the scenario described above with reference to FIG. 3. The reason for the increased vibration values has been eliminated. The fault elimination was acknowledged in the first control module 202, so the logic unit causes the green LED 231 on the first control module 202 to light up. It is stipulated in the logic unit of the second control module 203 in conjunction with the integrated PID regulator of the second control module 203 that now the first pump module 202, or more specifically its upstream drive motor 3 can continue operating with the setpoint rotational speed preselected by the control room. Furthermore, the fact that the fault has been eliminated is reported by the logic unit to the control room via one of the digital outputs 219 and the correspondence of the setpoint rotational speed signal preselected by the control room is eliminated.

[0100] With the scenario depicted in FIG. 5, a sudden rise in pressure on the pressure side is detected and/or measured via a pressure sensor module 233 and is transmitted over an analog connection 234 to one of the analog inputs 214 of the second control module 203. The logic unit of the second control module 203 detects by database comparison that an allowed limit value has been exceeded (warning threshold) and causes a red LED 235 on the second control module 203 to flash. In addition, a corresponding item of information is transmitted over the bus system 213 to the first control module 202, where the integral logic unit ensures that the control case is signaled via a red LED 236. In addition, a corresponding message is sent to the control room from the logic unit of the second control module 203 over a digital output 19. It is stipulated in the logic unit inside the second control module 203 that in the present case the drive motor 3 is shut down so that the second pump module will not be damaged. The motor protection is triggered accordingly via a digital output 221, which results in the drive motor 208 being shut down.

[0101] Then with references to FIGS. 6 to 8 different exemplary embodiments of positive displacement pump systems are described, each of which has a control module which is designed as a separate unit and is spaced a distance away from the drive module and is accommodated in a separate housing. On the basis of the exemplary embodiments, the functioning of the control means, which are in the form of the control module, is described in detail. This functioning of the control module shown can also be implemented by the control modules shown in FIGS. 1 through 5.

[0102] The functions described with reference to FIGS. 1 through 5 in conjunction with the control modules shown there may additionally or alternatively also be implemented in the control module shown in FIGS. 6 through 9.

[0103] Exemplary Embodiment According to FIG. 6

[0104] FIG. 6 shows schematically the design of a positive displacement pump system 1, comprising a positive displacement pump 2, which is designed in the embodiment shown here as a single-spindle pump or a multi-spindle pump, in particular a triple-spindle pump. The positive displacement pump 2 is operatively connected to a motor shaft of a positive displacement pump motor 3, which is 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 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 which has optionally been corrected multiple times. The positive displacement pump motor and the frequency converter form a drive module 207.

[0105] To generate the manipulated variable Y.sub.S or a corrected manipulated variable Y.sub.S, the positive displacement pump system 1 comprises control means 5 formed by a microcontroller, for example, including a regulator 6 as mentioned above as well a logic means 7. The control means 5 are in the form of a control module 202, which is separate from the drive module 207 and has its own housing.

[0106] Reference input variable specifying means 8, for example, a process-controlled panel supplying reference input variables W to the control means 5 are provided upstream from the control means 5 and are preferably separate from the latter, where the reference input variable supplied is an electric voltage signal representing a setpoint volume flow or a setpoint pressure, for example.

[0107] 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 difference forming unit 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 Y.sub.S, on the basis of the reference input variable W and the first actual operating parameter X, which is measured here; this manipulated variable Y.sub.S, 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 Y.sub.S generated by the regulator 6 with at least one first limit value, preferably a maximum first limit value Y.sub.limit max to be maintained and/or a minimum limit value Y.sub.limit min to be maintained. Instead of the direct comparison of the manipulated variable Y.sub.S with the at least one first limit value, a comparative value that is functionally related to the manipulated variable Y.sub.S may be calculated with the help of (optional) comparative value specifying means (not shown here) on the basis of the manipulated variable Y.sub.S, 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 means 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 Y.sub.S is compared directly with at least one first limit value Y.sub.limit max and/or Y.sub.limit 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.

[0108] A first function unit 11 is assigned to the comparator means 10, including an addition to first limit value specifying means 12, first correction means 13. The function unit 11 calculates the at least one first limit value Y.sub.limit max, Y.sub.limit min, which is sent to the comparator means 10 in addition to the manipulated variable Y.sub.S generated by the regulator 6. The comparator means then check on whether the manipulated variable Y.sub.S drops below a maximum first limit value Y.sub.limit max and/or whether the manipulated variable Y.sub.S exceeds a minimum first limit value Y.sub.limit min. If this is the case, then the manipulated variable Y.sub.S is an admissible 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.

[0109] 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 Y.sub.H and/or X.sub.H is also sent to the function unit, such that the actual operating parameter Y.sub.H 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 being simulated, on the basis of at least one actual parameter, for example, on the basis of a current control measurement by the frequency converter. The additional actual operating parameter X.sub.H in the exemplary embodiment shown here is an auxiliary control variable, for example, a motor rotational speed and/or a displaced 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 control variable from the process control system 14, is taken into account by the first limit value specifying means 12 for calculating the at least one pump protection limit value, and at least one additional actual operating parameter Y.sub.H, X.sub.H or one main manipulated variable Y.sub.HH, preferably a measured variable for the process control variable X, for example, a pressure or a volume flow is also taken into account.

[0110] For the case when the comparator means finds that the maximum first limit value) Y.sub.limit max has been exceeded and/or the minimum first limit value Y.sub.limit 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 Y.sub.S taking into account the first actual operating parameter X and one of the aforementioned additional actual operating parameters Y.sub.H, X.sub.H, Y.sub.HH. This corrected manipulated variable Y.sub.S may then be sent as shown here to the comparator means as an input variable for comparison with a first limit value Y.sub.limit max and/or Y.sub.limit min or sent to another comparison and correction procedure bypassing the comparator means (not shown) or sent directly as an input signal to the frequency converter 4.

[0111] From a memory 19, preferably nonvolatile, specific geometry parameters GP for the positive displacement pump assigned to the control means 5 and/or specific delivery fluid parameters FP for the delivery fluid such as, for example, the shear behavior of the delivery fluid may be sent to the first limit value specifying means 12 and/or to the first correction means 13 so that they enter into the calculation of the first limit values Y.sub.limit max, Y.sub.limit min and/or the corrected manipulated variable Y.sub.S within the context of a functional relationship.

[0112] In the exemplary embodiment presented here, the corrected manipulated variable Y.sub.S is the maximum or minimum allowed first limit value Y.sub.limit max, Y.sub.limit min, to approximate the manipulated variable Y.sub.S generated by the regulator as closely as possible. To this extent the first limit value specifying means 12 and the first correction means 13 include a common computer (computer means), because the corrected manipulated variable Y.sub.S in the exemplary embodiment presented here corresponds to a first limit value Y.sub.limit max, Y.sub.limit min. The manipulated variable Y.sub.S generated by the regulator is overwritten by the corrected manipulated variable Y.sub.S.

[0113] In particular when the corrected manipulated variable Y.sub.S should not correspond to the first limit value, the first correction means 13 and the first limit value specifying means 12 may be implemented as completely separate units, i.e., with their own computation means, i.e., in separate function units. This is of course also possible for the case presented above, namely wherein the corrected manipulated variable Y.sub.S should correspond to a first limit value, so that in this case as shown in FIG. 1, the limit value specifying means 12 and the correction means 13 are fused together, i.e., they have a shared computation routine.

[0114] 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.

First Example

[0115] The first actual operating parameter X corresponds to the actual control 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.

[0116] Then there is a change in the reference input variable. The reference input variable X changes, for example, from 20 bar to 10 bar due to a corresponding stipulation. This results in a controlled deviation of WX=10 bar.

[0117] The regulator 6 determines a new manipulated variable Y.sub.S, 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 means 12 calculate a minimum allowed limit value Y.sub.limit 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.

[0118] The minimum allowed rotational speed, i.e., the minimum allowed limit value Y.sub.limit min is calculated on the basis of the following functional relationship:

[00002]$Y_{\mathrm{limit}.Math..Math.\min }=n_{\mathrm{allowed}}={\left(\frac{p}{k.Math.b.Math.c.Math.v^a}\right)}^2$

[0119] In this functional relationship, Y.sub.limit max corresponds to the minimum allowed limit value. This is a minimum allowed rotational speed (n.sub.allowed).

[0120] The first actual operating parameter X in this case is the measured control variable, namely here the new actual pressure of 10 bar. The factor .Math. 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. In the exemplary embodiment shown here, this value amounts to 10.sup.0.32 for the specific medium in question. 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.

[0121] 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 an ideal load. In the exemplary embodiment shown here, this amounts to 0.55, for example.

[0122] The minimum allowed limit value Y.sub.limit min is sent to the first comparator means 10 which compares the manipulated variable Y.sub.S determined by the regulator 6 with the minimal allowed limit value. Depending on the result of the comparison, either the manipulated variable Y.sub.S determined by the regulator is transmitted to the frequency converter or a corrected manipulated variable Y.sub.S is calculated by the first correction means, preferably corresponding to the minimum allowed limit value Y.sub.limit min calculated previously (or calculated anew).

Second Example

[0123] The first actual operating parameter X corresponds to the actual control variable, namely here a pressure. An actual pressure of 20 bar is measured. Based on a corresponding stipulation, the setpoint value of the control 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.

[0124] In practice this results in the actual operating variable X, i.e., the actual pressure definitely exceeding the reference input variable W or it would exceed it because the pump is still operating at an unchanged rotational speed but in the mean time the flow resistance has increased significantly due to the tool replacement.

[0125] The resulting control deviation at the difference forming output then leads to a significant decline, i.e., reduction in the manipulated variable Y.sub.S. For the case when this is transmitted uncorrected to the frequency converter 4 as a setpoint stipulation, this would result in a risk to the pump with regard to the admissible pressure at a reduced low rotational speed. To prevent this, the aforementioned manipulated variable Y.sub.S is compared with the calculated with the minimal limit value Y.sub.limit 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 Y.sub.S falls below the minimum allowed limit value Y.sub.limit min, i.e., the minimum allowed rotational speed, so a corrected manipulated variable Y.sub.S, which is transmitted instead of the manipulated variable Y.sub.S to the frequency converter, is then output by the first correction means 13.

[0126] The corrected manipulated variable Y.sub.S preferably corresponds to the calculated minimum allowed limit value Y.sub.limit min.

Third Example

[0127] 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 Y.sub.S, namely a rotational speed in this case, from the resulting control deviation WX. This manipulated variable Y.sub.S, 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 Y.sub.limit max. This maximum allowed rotational speed is determined on the basis of the NPSH.sub.available, 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 H.sub.2O (meters of water column). Then Y.sub.limit max, i.e., the maximum allowed rotational speed is determined on the basis of the NPSH.sub.available and another measured actual operating parameter, in this case the viscosity of the medium. This is done, for example, on the basis of the diagram shown in FIG. 4 or alternatively on the basis of a polynomial based on the following calculation principle and stored in a nonvolatile memory:

NPSH=f(pump size(d.sub.a),spindle angle of slope, viscosity v, rotational speed n)

[0128] 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 d.sub.a and the spindle angle of slope, so that the following relationship is obtained in simplified terms:

NPSH=f(v.sub.ax size spindle slope angle,viscosity v,rotational speed n)

[0129] Consequently, it is true that

v.sub.ax admissible size NPSH=f(v,n)

[0130] so that by means of the relationship

v.sub.ax=S*n or n=v.sub.ax/S

[0131] ultimately the relationship

Y.sub.limit max=n.sub.admissible size NPSH=v.sub.ax admissible size NPSH/S

[0132] can be established.

[0133] Thus an admissible pump rotational speed n.sub.admissible 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.

[0134] In the diagram according to FIG. 4 the NPSH is shown on the left vertical ordinate in meters of water column (m H.sub.2O). 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 v.sub.ax of the medium (delivery fluid) as a function of the rotational speed.

[0135] To determine the first limit Y.sub.limit 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 H.sub.2O up to the curve which is characteristic of the measured viscosity of 500 mm.sup.2/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) Y.sub.limit max can thus be read on the right ordinate. For the measured viscosity, i.e., the additional actual operating parameter, this amounts to approx. 3800 revolutions per minute.

[0136] 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 Y.sub.S of 3000 l/min is smaller than the first limit value Y.sub.limit max of approx. 3800 l/min, the manipulated variable Y.sub.S can be transmitted to the frequency converter 4 as an input variable.

[0137] 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 Y.sub.limit max so that the correction means 13 would exceed the manipulated variable Y.sub.S stipulated by the regulator 6 by the amount of a corrected manipulated variable Y.sub.S, which would correspond to the first limit value, for example, i.e., 3800 l/min in the present example.

[0138] Exemplary Embodiment According to FIG. 7

[0139] The exemplary embodiment according to FIG. 7 differs from the exemplary embodiment according to FIG. 6 only in that the manipulated variable Y.sub.S 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. In FIG. 7 the control means are again present as a control module that is separate from the drive module.

[0140] The at least one second limit value Y.sub.limit max, Y.sub.limit min ensures that the delivery fluid quality is maintained. In the exemplary embodiment shown here, only a single maximum second limit value Y.sub.limit max is supplied by the second limit value specifying means 15, whereby as an alternative multiple second limit values, e.g., also a minimal limit value Y.sub.limit min which ensures the quality of the delivery fluid can also be calculated.

[0141] At any rate, the second comparator means 16 compare whether the manipulated variable Y.sub.S 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 Y.sub.limit min by a certain measure. If the manipulated variable Y.sub.S is less than or equal to the maximum limit value, then the manipulated variable Y.sub.S 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.

[0142] Otherwise with the help of second correction means 18, comprising a second function unit 17 in addition to the second limit value specifying means 15, a corrected manipulated variable Y.sub.S is made available with which the manipulated variable Y.sub.S is overwritten. To calculate the at least one second limit value Y.sub.limit min, the second limit value specifying means 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 Y.sub.H, an auxiliary control variable X.sub.H and/or a main manipulated variable Y.sub.HH. 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.

Fourth Example

[0143] 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.

[0144] 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 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 pressure 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 Y.sub.limit max, i.e., in the calculation of the maximum allowed rotational speed.

[0145] Thus, for example, a delivery fluid with a dynamic viscosity of 5 Pas is pumped. This corresponds to a kinematic viscosity v of 5000 mm.sup.2/s, such that with an assumed density of 1000 kg/m.sup.3 a maximum allowed shear rate D.sub.admissible of 20,000 sec.sup.1 is obtained for the delivery fluid in a certain pump while maintaining the maximum allowed shear stress of 100,000 N/m.sup.2. This is characterized by a rotary diameter of D.sub.a=70 mm and by a radial gap S=h.sub.0, 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 Y.sub.limit max of 191 l/min. As long as the manipulated variable Y.sub.S preselected by the regulator 6 is below the aforementioned value, the manipulated variable Y.sub.S can be forwarded directly to the frequency converter 4otherwise, the manipulated variable Y.sub.S is overwritten by a manipulated variable Y.sub.S that is corrected and/or limited by second correction means 18.

[0146] The example described above is based on the following computation principles:

[0147] It follows from

[0148] e.g., .sub.admissible=D* and =v* for Newtonian fluids that

D.sub.admissible=.sub.admissible/(v*)

[0149] In addition, it holds that

n.sub.admissible=W.sub.admissible/(D.sub.a**60).

[0150] By inserting this into

W.sub.admissible=D.sub.admissible*S and/or into D.sub.admissible=W.sub.admissible/S

and by combining all the constants that occur in k, the maximum allowed rotational speed can be calculated as follows:

D.sub.admissible=(D.sub.a**n)/(k*S).fwdarw.n.sub.admissible=(D.sub.admissible*k*S)/(D.sub.a*)

[0151] The maximum allowed rotational therefore corresponds to the limit value Y.sub.limit max.

[0152] For the case when the delivery fluid (medium) to be pumped does not have Newtonian behavior, 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.

[0153] Exemplary Embodiment According to FIG. 8

[0154] The exemplary embodiment according to FIG. 8 negates the exemplary embodiments according to FIG. 6 and FIG. 7, i.e., the control means 5 are designed so that the manipulated variable Y.sub.S 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 Y.sub.S 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.

[0155] It is characteristic of the exemplary embodiment according to FIG. 8 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 Y.sub.S, namely when there is nothing going beyond the limit value in the first comparison and thus Y.sub.S is not corrected, or alternatively, when it is a manipulated variable Y.sub.S corrected by the first comparator means 10.

[0156] Y.sub.S or Y.sub.S is then the input variable for the second comparator means 16. If no correction is performed here, the input value for the second comparison Y.sub.S or Y.sub.S is sent to the frequency converter 4 or in the case of a correction the corrected manipulated variable Y.sub.S is sent to the frequency converter.

[0157] 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.

[0158] Exemplary Embodiment According to FIG. 10

[0159] 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.

[0160] In the example shown here, it is assumed that the delivery fluid viscosity (medium viscosity) drops from 12 mm.sup.2/s to 9 mm.sup.2/s, to 6 mm.sup.2/s, to 4 mm.sup.2/s and then (incrementally) to 2 mm.sup.2/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. In other words, the reference input variable changes incrementally from 10 bar initially to 50 bar. The regular outputs a manipulated variable (Y.sub.S) as a function of the reference input variable (W). The first limit value specifying means calculate a first limit value, which in the present case is a minimum rotational speed Y.sub.limit 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 means. 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 means is forwarded as a corrected manipulated variable from the first correction means in the exemplary embodiment presented here.

[0161] 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.