EP2145112B1 - Device and method for fault monitoring - Google Patents

Description

The invention relates to a device for fault monitoring of a centrifugal pump driven by a variable speed electrical motor, which device detects, stores and maintains operating values of the engine prior to activation of the fault monitoring and compares current engine operating values with the stored values during a fault monitor, and a method for fault monitoring with such a device.

For variable speed drive motors, it must be ensured that the drive shuts down in case of failure. The speed change is generally done with so-called frequency converters, which allow by changing the frequency of the frequency converter provided by the voltage system, a nearly continuous speed control of the centrifugal pump. In systems in which centrifugal pumps equipped with such a variable-speed motor are integrated, system malfunctions can cause impermissible operating states. This can lead to a fault in the system, for example, due to a pipe break, incorrect operation of valves, too low a delivery rate or the like. Among other things, this may be idling, dry running or falling below a predetermined minimum delivery.

In systems filled with a pumped medium, it is known, for example, to integrate sensors with the aid of which the flow rate or the presence of a fluid is registered. If the specified values are undershot, then with the aid of a signal supplied by the sensor causes a shutdown of the drive motor. The use of such sensors, however, represents a considerable additional expense.

It is also known to use for disturbance monitoring electrical engine variables such as power and speed. Usually, a limit value monitoring of the power takes place. Although such a type of performance monitoring is easy to implement, it has the disadvantage that it does not meet changing plant conditions, such as those that occur in open systems due to, for example, a changing admission pressure of a centrifugal pump or varying quantities on the pressure side.

The EP-A-0978657 discloses a pump assembly having an enclosed motor and a frequency converter, a detector for detecting a frequency and a current value, a frequency and a current value in actual operation with a program provided in the frequency converter for indicating the relationship between the frequency and the current value is to be compared. The frequency generated by the frequency converter is changed to correct the current value generated by the frequency converter with the predetermined program to a desired operating point. The pump arrangement of D1 is a regulation to a specific, predetermined flow rate.

The EP-A-0150068 discloses a method and a device for controlling various operating parameters, in particular the delivery head H, the delivery flow Q, the power requirement P and the rotational speed n, for pumps and compressors, preferably centrifugal pumps and fans. The control takes place according to characteristic curves of the operating parameters according to the desired operating mode, wherein the measurement of individual operating parameters for calculating the manipulated variable takes place outside of the pumped medium. For describing the characteristic curves or characteristic diagrams used, the rotational speed n and the power requirement P are used as electrical measured variables.

From the DE 100 17 861 A1 For example, there is known a method and apparatus for fault monitoring whereby a fault monitoring device before activation of the fault monitor undergoes a learning function in which operating values of the engine are detected and stored. After storing the operating values recorded in the learning function, the fault monitoring device is activated. In this case, a comparison of the current operating data of the engine with the stored values. When these stored values are reached and / or fallen below, the motor switches off. However, the method described requires a predetermined startup procedure. Thus, for a performance monitoring in a learning process prior to activation of the fault monitoring in a specially set limit state of the system, for example, shut off conveyor system according to all possible operating conditions, approached several different speed ranges and each detected and stored the corresponding power outputs of the drive motor.

The invention has for its object to develop a device and a method for fault monitoring for centrifugal pumps, which can be used with low startup effort even with changing system conditions.

The solution to this problem is that the device evaluates a current engine operating point with respect to a limited operating range of the engine and detects a fault when leaving the operating range, the limited operating range is formed by engine operating points. The limited operating range is expediently formed by individual, characteristic engine operating points. By means of this range based on individual, characteristic engine operating points, the fault monitoring is carried out. Measurements in the pumped medium are therefore as little to perform as the acquisition and storage of series of measurements of electric motor sizes during a commissioning phase. For speed-controlled drives, moreover, the motor sizes are usually internal Measured values of a frequency converter known, so that additional measurements are unnecessary.

An illustrative embodiment of the invention provides that the operating range in an engine size diagram is limited by at least one, in each case two engine operating points-containing, in particular starting and ending points connecting, limiting curve. During operation of the centrifugal pump with variable-speed drive, the current engine operating point and its position in the engine size diagram are then analyzed continuously or periodically. Upon leaving the limited and / or predetermined range, a fault is detected and a suitable response can occur.

A bounding curve may optionally be formed by a linear, quadratic or cubic polynomial. This allows easy adaptation to different plant conditions.

The device according to the invention comprises means for inputting and / or reading in input and / or parameter values. Thus, characteristic engine operating points and types of curves can be entered. The necessary parameters for the definition of the limited operating range can be input manually regardless of their origin or can be read in by other suitable means, which are used, for example, in the context of a parameter transmission. The parameter values are, for example, manually or by means of a measuring device during a learning process in which the electric power of the drive motor is determined at minimum and maximum frequency when the pressure valve is closed and / or open, or determined by means of calculations.

According to an advantageous embodiment of the limited operating range of the engine and / or the characteristic engine operating points are derived from an allowable operating range of the centrifugal pump. A permissible operating range of the centrifugal pump is from their characteristics, plotted against a delivery rate Q of the centrifugal pump, in particular the delivery height characteristics H (Q) known. From this, a limited operating range of the engine is derived according to the invention. Usually, a permissible operating range of a centrifugal pump is defined by characteristic characteristic points, such as minimum or maximum delivery rate of a centrifugal pump. According to the invention, a limited operating range of the motor used for the disturbance monitoring is defined by transmission, for example mathematically, in an engine size diagram and connecting the respective start and end points by limiting curves.

It has proven to be advantageous for two curves in a power frequency diagram to define the limited range. The fault monitoring takes place by evaluation of electrical power and frequency values. A permissible power value P at a frequency f which is between a first, for example minimum, frequency f _min and a second, for example maximum, frequency f _max must lie within the range defined by the characteristic engine operating points and the limiting curves. Together with the configuration according to which the limited operating range of the engine and / or the characteristic engine operating points are derived from an admissible operating range of the centrifugal pump, additional advantages result. Typically, the delivery height characteristic of a centrifugal pump is known. Characteristic characteristic points define a permissible operating range of the centrifugal pump. By transforming these characteristic points into a power frequency diagram, referred to here as the Pf diagram, and two connecting curves, an image of a permissible operating range is created in the power frequency diagram and thus a simple fault monitoring by evaluation of electrical power and frequency values.

Typically, in the power frequency diagram, a first boundary curve connects a pair of points (P _{min, min} , f _min ), (P _{min, max} , f _max ) and a second boundary curve a pair of points (P _{max, min} , f _min ), (P _{max, max} , f _max ). It indicates at the power P of first index a first, for example minimum, or second, for example maximum, power at a frequency corresponding to the second index.

The points in the power frequency diagram are expediently from transformation of characteristic points (Q _{min, min} , n _min ), (Q _{min, max} , n _max ), (Q _{max, min} , n _min ), (Q _{max, max} ; n _max ) derived a delivery height characteristic of the centrifugal pump. In this case, in the flow Q, the first index indicates a first or second flow at a speed corresponding to the second index. Thus, from already known, characteristic characteristic points of the delivery height characteristic in the power frequency diagram spans an area which serves for a simple fault monitoring. A current power value needs to be evaluated during operation of a centrifugal pump only in terms of its limits at a current frequency. In this case, the limit values are determined from the predefined, stored boundary curve course and / or by interpolation of interpolation points stored in a memory device before a fault monitoring.

It is also contemplated that the points in the power-frequency diagram of transformation of characteristic points (Q _min; n _nominal), (Q _max; n _nominal) minimum and maximum delivery rate at nominal operation of the centrifugal pump are derived.

Additional benefit is achieved by an embodiment whereby the device comprises means for selectively setting an action of the device upon detection of a fault. Upon detection of a fault, a warning or alarm message is optionally generated and / or operation of the centrifugal pump is continued or stopped. It is also thought that an action does not take place immediately upon detection of a fault, but already in the run-up to an impending disturbance. Thus, for example, can be warned against imminent leaving the limited operating range.

Advantageously, the device for fault monitoring is integrated into a control or regulating device, a switching device, a display and / or a diagnostic device acting on the motor. The means necessary for carrying out the method, such as microcomputer, memory device and / or display means and required instructions in the form of computer programs can be integrated into existing control, regulating, display, diagnostic devices, switching devices and / or other electronic devices or arranged in separate devices. Such a device is also able to perform a recording of measured variables and calculated values in addition to a current fault monitoring.

It is also contemplated that a frequency converter powers the motor and / or that it constitutes or includes the fault monitoring device. All engine sizes required for fault monitoring, in particular power and frequency delivered to the engine, are available in any case during operation of the frequency converter, so that fault monitoring according to the invention requires no additional measured variables.

In an inventive method for fault monitoring of a rotary pump driven by a variable speed electric motor, it is provided that a current engine operating point is evaluated with respect to a limited operating range of the engine and a fault is detected when leaving the operating range, the limited operating range being formed by engine operating points , Conveniently, the limited operating range is formed by individual, characteristic engine operating points.

In this case, according to one embodiment, the operating range in an engine size diagram is limited by at least one limit curve, which includes two engine operating points in each case and in particular connects the start and end points. The bounding curve can be formed by a linear, quadratic or cubic polynomial.

A simple method of fault monitoring is obtained when two curves in a power frequency diagram define the limited range. A first limiting curve in the power frequency diagram expediently combines a pair of points (P _{min, min} f _min ), (P _{min, max} , f _max ) and a second limiting curve a pair of points (P _{max, min} ; f _min ), (P _{max, max} , f _max ).

• (Q_min,min; n_min), minimal zulässiger Durchfluss Q_min bei Minimaldrehzahl n_min,
• (Q_min,max; n_max), minimal zulässiger Durchfluss Q_min bei Maximaldrehzahl n_max,
• (Q_max,min; n_min), maximal zulässiger Durchfluss Q_max bei Minimaldrehzahl n_min,
• (Q_max,max; n_max) maximal zulässiger Durchfluss Q_max bei Maximaldrehzahl n_min.

As already stated above, it is advantageous if the limited operating range of the engine and / or the characteristic engine operating points are derived from a permissible operating range of the centrifugal pump and / or the points in the power frequency diagram by means of transformation of characteristic points (Q _{min, min} ; n _min ), (Q _{min, max} ; n _max ), (Q _{max, min} ; n _min ), (Q _{max, max} ; n _max ) of the delivery head characteristic of the centrifugal pump are derived. In this case, in the flow Q, the first index indicates a first or second flow at a speed corresponding to the second index. A use of the following points has proved to be useful:

• (Q _{min, min} ; n _min ), minimum allowable flow Q _min at minimum speed n _min,
• (Q _{min, max} , n _max ), minimum allowable flow Q _min at maximum speed n _max ,
• (Q _{max, min} ; n _min ), maximum permissible flow Q _max at minimum speed n _min,
• (Q _{max, max} , n _max ) maximum permissible flow Q _max at maximum speed n _min .

The points in the power-frequency chart can also by means of transformation of characteristic points (Q _min; n _nominal), (Q _max; n _nominal) minimum and maximum delivery rate at nominal operation of the centrifugal pump are derived. The required conversion to other speeds or frequencies can be done by affinity laws.

In addition, it is provided that when a fault is detected, a warning or alarm message is generated and / or an operation of the centrifugal pump is continued or stopped becomes. Also, an action may be taken before or after leaving the limited operating range.

Fig. 1

eine erfindungsgemäße Einrichtung zur Störungsüberwachung, die

Fig. 2

ein Ablaufdiagramm eines erfindungsgemäßen Verfahrens vor Aktivierung einer Störungsüberwachung, die

Fig. 3

ein Ablaufdiagramm eines erfindungsgemäßen Verfahrens während einer Störungsüberwachung, und die

Fig. 4

ein erfindungsgemäßes Motorgrößendiagramm (Leistungs-Frequenz-Diagramm) und diesem zu Grunde liegende Förderhöhenkennlinie.

Embodiments of the invention are illustrated in the drawings and will be described in more detail below. It show the

Fig. 1

an inventive device for fault monitoring, the

Fig. 2

a flowchart of a method according to the invention prior to activation of a fault monitoring, the

Fig. 3

a flowchart of a method according to the invention during a fault monitoring, and the

Fig. 4

an inventive engine size diagram (power frequency diagram) and this underlying conveying height characteristic.

The Fig. 1 shows a device according to the invention 1 for fault monitoring, consisting of microcomputer 2 with memory device 3, display means 4, and means for entering 5 and means for reading 6 of input, parameter and / or other values.

The device 1 has two inputs 7, 8 for reading current power and frequency data of a drive motor, not shown here, of a centrifugal pump. The device 1 can be connected with their inputs 7, 8, for example, to a serial data bus. The centrifugal pump is driven by an electric motor, which is powered by a frequency converter, for example, with variable speed. In addition, the device 1 is equipped with outputs 9, 12, 13. Before activating a fault monitoring, operating values of the motor are recorded. This can be done, for example, by entering four individual, characteristic engine operating points (P _{min, min} , f _min ), (P _{min, max} , f _max ) and (P _{max, min} , f _min ), (P _{max, max} , f _max ) via the means for inputting 5.

Furthermore, the curves of the limiting curves are input via the means for inputting 5. About the memory device 3 is a defined, predetermined, limited operating range, here the operating range in a P-f diagram, stored and maintained for a fault monitoring.

Alternatively, it is provided to derive the characteristic engine operating points from an admissible operating range of the centrifugal pump. The means for inputting 5 may for this purpose also, for example, characteristic points (Q _{min, min,} n _min), (Q _{min, max,} n _max), (Q _{max, min,} n _min), (Q _{max, max} n _max ) of a delivery line characteristic H (Q) of the centrifugal pump or characteristic points (Q _min ; n _nenn ), (Q _max ; n _nenn ) minimum and maximum delivery rate at rated operation of the centrifugal pump and minimum and maximum speeds or frequencies are entered, resulting in transformation of the characteristic points four points can be determined in the power frequency diagram with which the fault monitoring is carried out. In the memory device 3, the necessary calculation instructions in the form of algorithms available for the microcomputer 2 are stored for this purpose.

Likewise, a desired action of the device 1 upon detection of a fault can be set via the means 5, whether a warning or alarm message is generated when a fault is detected and / or an operation of a centrifugal pump is continued or stopped.

All the input and / or parameter values and algorithms required in the device 1 can be transmitted via the digital read-out interface 6 via a digital data interface.

The device 1 evaluates with its microcomputer 2 during a fault monitoring a current engine operating point, known here via the input quantities power P and frequency f, with respect to the limited operating range of the engine.

In this case, a current power value P is evaluated only with regard to its limit values at a current frequency f, wherein an exceeding or falling below a respective limit means leaving the limited operating range and leads to the detection of a fault.

Results of the fault monitoring or also all data available in the microcomputer 2 are displayed via the display means 4, such as a display 10 or an LED display 11, and provided via the outputs 9, 12, 13 external equipment for further processing. The outputs 12, 13 can be used, for example, for a warning or alarm message by external devices. In Fig. 1 the device 1 for fault monitoring is shown as a separate device. It is equally possible that the device is integrated in a control or regulating device, a switching device and / or a display and / or diagnostic device acting on the motor. It is also provided that a frequency converter, in which the current power and frequency values are permanently determined in any case, even contains or contains the device for fault monitoring.

1. A = (Q_min,min; n_min), minimal zulässiger Durchfluss Q_min bei Minimaldrehzahl n_min,
2. B = (Q_min,max; n_max), minimal zulässiger Durchfluss Q_min bei Maximaldrehzahl n_max,
3. C = (Q_max,min; n_min), maximal zulässiger Durchfluss Q_max bei Minimaldrehzahl n_min,
4. D = (Q_max,max; n_max) maximal zulässiger Durchfluss Q_max bei Maximaldrehzahl n_min.

In the Fig. 2 a flowchart of a method according to the invention prior to activation of a fault monitoring is shown. First, in a step 21, a first and a second engine frequency are determined by means of the parameters f _min and f _max . As a rule, this will be the minimum and the maximum permitted motor frequency, so that subsequent embodiments specifically describe such a case, without this being a limitation of the invention to this. The parameters can be entered into a proposed device by operator actions or are made available as part of a parameter set of the device during a parameterization process. In the same way, in FIG. 22, limiting characteristic points become a permissible operating range of a centrifugal pump. Ideally, these are the following, characteristic characteristic points, here designated A to D, a delivery head characteristic of the centrifugal pump, which define the permissible operating range together with the system characteristic curve:

1. A = (Q _{min, min} ; n _min ), minimum allowable flow Q _min at minimum speed n _min,
2. B = (Q _{min, max} , n _max ), minimum allowable flow Q _min at maximum speed n _max ,
3. C = (Q _{max, min} ; n _min ), maximum permissible flow Q _max at minimum speed n _min,
4. D = (Q _{max, max} , n _max ) maximum permissible flow Q _max at maximum speed n _min .

If a fault monitoring with respect to an operating limit, which is described for example by a minimum allowable flow Q _{min of} the centrifugal pump, it is of course sufficient to define a subset of the above characteristic points, such as A, B.

In a next step 23, the curves of the limiting curves are determined. For example, a limiting curve connects, in an engine size diagram, start and end points A "and B" or C "and D", which are derived from the characteristic operating points of the centrifugal pump defining characteristic points A and B or C and D respectively. Expediently, further parameters for the curve of a first limiting curve between point A "and B" and a second limiting curve between C "and D" are provided for this purpose, by means of which linear, quadratic or cubic curves can be selected. The different courses serve to adapt the fault monitoring to different plant conditions.

• A" = (P_min,min; f_min), minimale Leistung bei minimaler Motorfrequenz,
• B" = (P_min,max; f_max), minimale Leistung bei maximaler Motorfrequenz,
• C" = (P_max,min; f_min), maximale Leistung bei minimaler Motorfrequenz,
• D" = (P_max,max; f_max), maximale Leistung bei maximaler Motorfrequenz.

Once the parameters have been determined, in step 24, the characteristic points A to D are transformed into the corresponding start and end points A "to D" of the limiting curves. A "to D" represent, for example, start and end points in a power frequency diagram, in short Pf diagram, in detail mean:

• A "= (P _{min, min} ; f _min ), minimum power at minimum motor frequency,
• B "= (P _{min, max} , f _max ), minimum power at maximum motor frequency,
• C "= (P _{max, min} ; f _min ), maximum power at minimum motor frequency,
• D "= (P _{max, max} , f _max ), maximum power at maximum motor frequency.

The relationships of a transformation of the characteristic points A to D into the corresponding start and end points A "to D" of the limiting curves are later still in Fig. 4 graphically illustrated on the basis of a power frequency diagram and the underlying delivery height characteristic.

According to the invention, it is also possible to calculate the points A "to D" in a separate device or to obtain them in another way and then to transmit the values into a device 1 for fault monitoring.

Between respective values of minimum and maximum frequency, ie between A "and B" and between C "and D", the limiting curves are calculated in a further step 25 according to the desired curve profile. This is done, for example, in which a certain number of calculated curve intermediate values are stored in a kind of value table. Alternatively, it is sufficient to store the points A "to D" and the type of curves between these points. In any case, a limited range in the engine size diagram is clearly defined by the start and end points and these connecting limiting curves, together with their given curve curves, and can be used for a subsequent fault monitoring.

In a modification of the illustrated method, it is also possible according to the invention, the four points A "to D" in the power frequency diagram of transformation of the characteristic points (Q _min ; n _nenn ), (Q _max ; n _nenn ) minimum and maximum flow to get at nominal operation of the centrifugal pump. This can be done, for example, by means of a preceding transformation of the points A to D from the characteristic points (Q _min ; n _nenn ), (Q _max ; n _nenn ). In addition, the limited Operating range of the engine also be derived from other points and defined.

As already in Fig. 1 In addition, and in contrast to the method described here, it is provided that the points A "to D" of the limiting curves in the motor size diagram are directly specified. These can be determined manually by measuring device during a learning process, by means of calculations, graphic methods or by other suitable methods. During a learning process, for example, with a closed and / or open pressure-side valve, the electrical power of the drive motor can be measured at a minimum and maximum frequency in a system and thus the points A ", B" and / or the points C ", D" can be determined.

Fig. 3 shows a typical flow of fault monitoring during operation of a centrifugal pump. A fault monitoring according to the invention can, after appropriate preparation steps according to the in Fig. 2 be activated described and realize during operation of a centrifugal pump, inter alia, a no-load, dry running, minimum flow and / or overload protection function. In this case, in step 31, current or periodic engine operating values such as electric motor power and motor frequency or speed of the drive motor are detected or determined. These values are either detected by suitable sensor means or are obtained from a speed controller which powers the motor. In a frequency converter, for example, the current power and frequency values are permanently determined anyway and are available. These are used for fault monitoring without additional measurement effort. It is envisaged that the frequency converter itself represents or contains the device for fault monitoring. Likewise, other Leistungsermittlungsgeräte are suitable.

By the currently determined engine operating values, a current engine operating point in an engine size diagram can be determined in step 32. In an inventive Pf diagram with a previously determined, predetermined, limited range is such an engine operating point already defined by the current electrical power and the current engine frequency. During trouble-free operation of the centrifugal pump or centrifugal pump assembly, the engine operating point is within the limited range. In the event of a malfunction, the engine operating point under- or overshoots the first or second limiting curve, ie, is outside the limited range. The actual fault monitoring 33 consists in a simple evaluation of the position of the engine operating point in the engine size diagram. For this purpose, the current power value is evaluated with regard to its limit values at a current frequency f. The limit values for a specific frequency can be determined from the predefined, stored limiting curve course. For stored curves in the manner of a value table, the corresponding curve values for the current frequency value f are determined, if necessary, by means of interpolation methods. Other possibilities for this are known and need not be detailed here.

It is determined, as shown in FIGS. 34, 35, whether the engine operating point is within, above or below a limited range. The specification of minimum time periods t _o or t _u , for which the engine operating point must be outside the recommended range, before detection of a fault, reduces the susceptibility to incorrect measurements. In addition, only briefly pending disturbances are ignored. When an actual malfunction 36 is detected, optionally a warning or alarm message is optionally set and an operation of the centrifugal pump is continued or stopped.

Fig. 4 shows a power frequency diagram (Pf diagram) 41 as an engine size diagram according to the invention together with an underlying this basis height curve H (Q) in an HQ diagram 42 of a centrifugal pump. Shown are a characteristic curve for maximum speed 43 and a characteristic curve for minimum speed 44 and system characteristics 45 and 46 at minimum or maximum permissible pump flow Q _min or Q _max . Due to a system pressure present in the system, all characteristic curves in the HQ diagram 42 are at a height level 47. The characteristic points A to D define an admissible operating range 48 of the centrifugal pump. If the characteristic points in the HQ diagram 42 are not available, it is also possible to fall back to corresponding points A 'to D' of a characteristic P (Q) 49. By way of example, an operating point 50 of the centrifugal pump is plotted in the region of the characteristic curve 51 of an optimum degree of pump flow Q _opt .

A transformation of the characteristic points A to D into the points A "to D" in the P-f diagram 41 is graphically illustrated. Here, a transformation from the H-Q diagram 42 into the P-Q diagram 49 and then into the P-f diagram 41 is shown stepwise. Also, available points A 'to D' of a P-Q diagram 49 may be transformed. In the engine size diagram 41, a limited area 52 is defined by the points A "to D", which is used for fault monitoring. The points A "and B" are connected by a first limiting curve 53 and the points C "and D" by a second limiting curve 54. In this illustration, the limiting curves 53, 54 are linear. Other gradients, such as square or cubic, can be selected depending on the system conditions.

By evaluating a current engine operating point 55 and its position in the engine size diagram 41 and leaving the limited area 52, a disturbance 36 is detected. It is also readily possible to monitor the disturbance only with respect to one of the two limiting curves 53, 54, ie in the specific case either to perform overload or underload monitoring.

In addition, it is provided that a determination of a fault and / or a warning and / or alarm message only takes place if the curves derived from the limit curves are exceeded and / or undershot. Here, curves 56, 57 and 58, 59 derived by correction factors from the limiting curve 54 and 53 are shown, exceeding and / or falling below a warning or alarm message result.

The limited operating range need not - as described here - be bounded by the points A "to D", but the limited operating range may be formed from other engine operating points and / or from other suitable characteristic points of a centrifugal pump characteristic, in particular a HQ diagram or a PQ Diagram to be derived.

The embodiments in the figure description are essentially limited to an example with power frequency diagram. The described method with device 1 for fault monitoring is transferable to other engine size diagrams, in particular to a power-speed diagram.

Even if it is not discussed in detail, it should be noted that in a device 1 according to the invention for fault monitoring, all variables detected or calculated within a life cycle of the centrifugal pump and fault states can be stored, retrieved and output to peripheral devices.

Claims (23)

1. Device for fault monitoring of a centrifugal pump which is driven by a variable rotation speed electric motor, wherein the device provides means for recording, storing and keeping available the operating values of the motor in order, during fault monitoring, to compare instantaneous operating values of the motor with the stored values, characterized in that the device (1) provides means for evaluating an instantaneous motor operating point (55) with respect to a bounded operating range (52) of the motor, in order to detect a fault (36) on leaving the operating range, wherein the bounded operating range (52) is formed by motor operating points.
2. Device for fault monitoring according to Claim 1, characterized in that the bounded operating range (52) is formed by individual, characteristic motor operating points.
3. Device for fault monitoring according to Claim 1 or 2, characterized in that the operating range (52) is bounded on a motor variable diagram (41) by at least one boundary curve (53, 54) which in each case contains two motor operating points and in particular connects start and end points.
4. Device for fault monitoring according to Claim 3, characterized in that a boundary curve (53, 54) is formed by a linear, quadratic or cubic polynomial.
5. Device for fault monitoring according to one of Claims 1 to 4, characterized in that the device (1) has means for inputting (5) and/or reading (6) input values and/or parameter values.
6. Device for fault monitoring according to one of Claims 1 to 5, characterized in that the bounded operating range (52) of the motor and/or the characteristic motor operating points are/is derived from a permissible operating range (48) of the centrifugal pump.
7. Device for fault monitoring according to one of Claims 3 to 6, characterized in that two curves on a power/frequency diagram define the bounded range (52).
8. Device for fault monitoring according to Claim 7, characterized in that a first boundary curve (53) on the power/frequency diagram connects a pair of points P_min,min; f_min, P_min,max; f_max, and a second boundary curve (54) connects a pair of points P_max,min; f_min, P_max,max; f_max.
9. Device for fault monitoring according to Claim 8, characterized in that the points on the power/frequency diagram are derived from transformation (24) of characteristic points Q_min,min; n_min, Q_min,max; n_max, Q_max,min; n_min, Q_max,max; n_max of a feed rate characteristic (42, 43, 44) of the centrifugal pump.
10. Device for fault monitoring according to Claim 9, characterized in that the points on the power/frequency diagram are derived from transformation (24) of characteristic points Q_min; n_rated, Q_max; n_rated for a minimum and maximum feed rate during rated operation of the centrifugal pump.
11. Device for fault monitoring according to one of Claims 1 to 10, characterized by means for selective cessation of an action of the device (1) when a fault (36) is detected.
12. Device for fault monitoring according to Claim 11, characterized in that the device (1) is integrated in an open-loop or closed-loop control device which acts on the motor, in a switching apparatus, in a display device and/or in a diagnosis device.
13. Device for fault monitoring according to Claim 11 or 12, characterized in that a frequency converter feeds the motor and/or represents or contains the device (1) for fault monitoring.
14. Method for fault monitoring of a centrifugal pump which is driven by a variable rotation speed electric motor, wherein, before activation of the fault monitoring, operating values of the motor are detected, stored and kept available, and instantaneous operating values of the motor are compared with the stored values during fault monitoring, characterized in that an instantaneous motor operating point (55) is evaluated with respect to a bounded operating range (52) of the motor and a fault (36) is detected on leaving the operating range (52), wherein the bounded operating range (52) is formed by motor operating points.
15. Method for fault monitoring according to Claim 14, characterized in that the bounded operating range (52) is formed by individual, characteristic motor operating points.
16. Method for fault monitoring according to Claim 14 or 15, characterized in that the operating range (52) is bounded on a motor variable diagram (41) by at least one boundary curve (53, 54) which in each case contains two motor operating points and in particular connects start and end points.
17. Method for fault monitoring according to Claim 16, characterized in that a boundary curve (53, 54) is formed by a linear, quadratic or cubic polynomial.
18. Method for fault monitoring according to one of Claims 14 to 17, characterized in that the bounded operating range (52) of the motor and/or the characteristic motor operating points are/is derived from a permissible operating range (48) of the centrifugal pump.
19. Method for fault monitoring according to one of Claims 16 to 18, characterized in that two curves on a power/frequency diagram define the bounded range (52).
20. Method for fault monitoring according to Claim 19, characterized in that a first boundary curve (53) on the power/frequency diagram connects a pair of points P_min,min; f_min, P_min,max; f_max, and a second boundary curve (54) connects a pair of points Pmax,min; f_min, P_max,max; f_max.
21. Method for fault monitoring according to Claim 20, characterized in that the points on the power/frequency diagram are derived from transformation (24) of characteristic points Q_min,min; n_min, Q_min,max; n_max, Q_max,min; n_min, Q_max,max; n_max on a feed rate characteristic (42, 43, 44) of the centrifugal pump.
22. Method for fault monitoring according to Claim 20, characterized in that the points on the power/frequency diagram are derived from transformation (24) of characteristic points Q_min; n_rated, Q_max; n_rated for a minimum and maximum feed rate during rated operation of the centrifugal pump.
23. Method for fault monitoring according to one of Claims 14 to 22, characterized in that, when a defect (36) is detected, a warning message or alarm message is produced and/or operation of the centrifugal pump is continued or stopped.

Images