Method and device for monitoring a centrifuge

Abstract

The invention relates to a method and a corresponding device (VO) for monitoring a centrifuge (Z) for solid-liquid separation of a suspension (SUS), comprising a centrifuge drum (T), which is connected to at least one frequency-controlled drive for generating a rotation of the centrifuge drum (T), wherein during operation of the centrifuge a plurality of variables and parameters of the drive are determined time-dependently over the course of the separating process, and operating modes (I, II, III, IV) of a cycle of the centrifuge operation are derived from the correlation of the variables and parameters, and information relating to the separating process is automatically acquired depending on the derived operating mode.

Description

[0001] Description

[0002] Method and device for monitoring a centrifuge

[0003] The invention relates to a method and a corresponding device for monitoring a centrifuge for solid-liquid separation of a suspension. Furthermore, the invention relates to a corresponding computer program product.

[0004] Centrifuges are technical devices used for material separation. Centrifuges operate based on centrifugal force, which is generated by the uniform circular motion of the material being centrifuged. Particles or media with a higher density migrate outward due to their greater inertia. In doing so, they displace the lower-density components, which then move to the center.

[0005] Centrifuges such as peeler centrifuges are frequently used in the pharmaceutical or food industry (e.g. in sugar production) for the solid-liquid separation of a suspension. Such centrifuges are generally operated according to a preset time program: Suspension is fed from a vessel into the centrifuge via a time-controlled valve, with the time being limited by the risk of overfilling based on empirical values. The centrifuge has a centrifuge bowl which is filled with the suspension as the feed material at the beginning of each processing step. The centrifuge initially rotates at a first speed (filling speed DZI, see Fig. 2). The centrifuge bowl is then accelerated to a second speed (spin-off speed DZ2, Fig. 2), which is significantly higher than the first speed. This speed is maintained until the desired drying progress is achieved in the feed material.The so-called filter cake remains on the filter cloth. The centrifuge drum is then slowed to a peeling speed (DZ3, Fig. 2), and the contents are removed from the centrifuge drum using a scraping device. After a certain number of passes of this type, the filtration resistance caused by a clogged filter cloth or a non-removable base layer is usually so high that thorough cleaning is necessary. These types of centrifuges (screen centrifuges, peeler centrifuges) are generally used for batch production of substances in the pharmaceutical industry.

[0006] The throughput of a centrifuge depends on the filtration resistance, which in turn depends on the particle size distribution. Small fluctuations in particle diameter lead to significantly different separation times. A time control system must therefore be parameterized very precisely. The parameters required for optimal centrifuge operation, such as the mass fed into the material separation and the speed used, are traditionally set manually for each batch by centrifuge operators based on empirical values. Conventional condition monitoring, in which the technical condition of the unit is regularly or permanently recorded using sensors and the resulting sensor data is analyzed for further use, is difficult with centrifuges because attaching a sensor in the separation chamber within the centrifuge bowl is equally difficult.In addition, conventional sensors are always exposed to large amounts of contamination from the suspension.

[0007] Some peeler centrifuges have a type of "paddle" which, using a position sensor, glides on the rotating liquid or the filter cake separated from it, thus allowing the fill level of the centrifuge to be estimated. Unfortunately, these mechanical sensors can transmit incorrect values ​​due to caking suspension and, for example, jam. Exact monitoring of the separation process or the condition of the centrifuge is therefore not possible. Non-contact optical sensors using lasers or ultrasound are also susceptible to failure due to contamination with a high solid content and are difficult to use. There is therefore a need for contact-free yet precise monitoring of centrifuge operation in order to ensure a smooth, error-free separation process without having to install complicated sensors on the centrifuge itself or unnecessarily short filling times orsetting spin times that are too long and thus reducing the throughput of the centrifuge.

[0008] The object of the invention is to provide an improved method for monitoring centrifuges and the separation process to be carried out, in which no sensors have to be installed in or on the centrifuge.

[0009] This object is achieved by the features of independent patent claim 1. Advantageous developments of the invention are described in the dependent claims, and claim 9 describes a computer program product.

[0010] The core idea of ​​the invention is to evaluate variables and parameters of the centrifuge drive already available for controlling and regulating the centrifuge in such a way that they can be used to monitor the separation process. These can be physical variables such as current, voltage, speed (angular velocity) or torque, or variables derived therefrom with the corresponding parameters such as the rotational moment of inertia, the angular momentum of the centrifuge drum or the mass inflow. The method according to the invention is therefore based both on simple metrologically accessible data such as current or voltage, and on computationally determined data.

[0011] Accordingly, a method is proposed for monitoring a centrifuge for solid-liquid separation of a suspension, with a centrifuge drum which is connected to at least one frequency-controlled drive for generating rotation of the centrifuge drum, wherein during operation of the centrifuge a large number of variables and parameters of the drive are determined as a function of time over the course of the separation process, and operating modes of a cycle of centrifuge operation are derived from the relationships between the variables and parameters of the drive, and information about the separation process is automatically determined as a function of the derived operating mode.

[0012] The advantage of the method according to the invention is that monitoring of both the separation process and the centrifuge itself can be provided based on existing drive variables and parameters, without the need for additional sensors. The invention therefore does not require any special additional measuring instruments, but rather makes do with the instrumentation typically found in frequency converters.

[0013] The method can advantageously be implemented in software or firmware at the control level or in a cloud environment, making it flexibly adaptable. In principle, any type of centrifuge can be equipped with "smart" monitoring software based on the method according to the invention. Only a suitable software module for evaluation is required. However, the method is particularly suitable for peeler centrifuges or sieve centrifuges with batch-based operation, in which different operating modes can be derived within an operating cycle.

[0014] In a first embodiment, the filling level of the centrifuge drum can advantageously be determined or the mass contained therein can be determined. In this embodiment, the centrifuge is monitored in such a way that, in order to derive a filling mode, the speeds of the drum rotation and at least the drive energy required to maintain a speed of drum rotation are recorded as a function of time. From this, an increase in the rotational moment of inertia of the drum due to the filling is derived. From this, the (rotating) mass of the filling of the centrifuge drum can be easily determined. This embodiment is particularly suitable for the operating mode in which the centrifuge drum rotates at the filling speed. First, the power consumed by the centrifuge when empty at a constant speed is determined, and from this the rotational moment of inertia of the empty drum can be derived.The centrifuge is then filled (the valve for the mass inflow of the suspension is opened). When the bowl is filled, the incoming mass flow must be accelerated to its angular velocity and the additional energy required to accelerate an additional (inflowing) mass is recorded via the power consumed by the frequency converter (at constant angular velocity). This additional energy is used to determine the mass filling the bowl. The feed valve is then closed. The power consumption of the frequency converter therefore increases significantly during the filling process. The integral of the current consumption above the idle current consumption at this speed is therefore a measure of the mass filled. The moment of inertia of the centrifuge bowl can therefore be easily determined from the electrical energy required by the drive, given a known speed.When determining the rotational moment of inertia, the centrifuge drum can always be considered as a hollow cylinder, since the radius of the centrifuge is usually very large compared to the almost negligible layer thickness of the filling material in the drum.

[0015] The advantage of this design variant is that the filling level of the centrifuge can be determined very easily yet quite precisely. Based on the current or electrical power trends, the energy required to accelerate the rotating mass can be precisely measured and is characteristic of a filling process. The virtual mass increase during the filling process is characteristic of the process.

[0016] For further analysis, it is essential to determine the empty moment (or rotational moment of inertia of the drum when empty) or the dead weight of the drum. This involves determining the additional energy required to increase the rotational moment of inertia for the centrifuge drum in the empty state during the transition from a first speed (preferably the peeling speed) to a second speed (preferably the filling speed). This is then used to determine the (rotating) mass of the empty drum. This is particularly important when the filling level of the filled centrifuge drum is not determined by an increase in energy alone. In this way, the dead weight of centrifuge drums, which are often very heavy and large, such as those found in the sugar industry, can be determined very easily.

[0017] In another advantageous design variant, the fill level of the centrifuge can be determined easily and precisely. This design variant is particularly suitable for high speeds, i.e. for speeds in the operating mode in which the centrifuge drum rotates at the spinning speed. The "dry spinning" operating mode is first determined from the relationships between the recorded variables and drive parameters. The drum rotation speed is then varied cyclically over time, and the change in angular velocity over time is measured. From this, the energy for accelerating and decelerating the drum is derived, and the drum's rotational moment of inertia is calculated. If the zero mass is known (which results from the centrifuge's rotational moment of inertia when empty), the fill level of the centrifuge drum can be determined using the rotational moment of inertia of the rotating mass.

[0018] The advantage of this design variant is that the small variation in speed has no effect on the separation process, while the energy change caused by the acceleration and deceleration of the drum is easily measurable through the temporal change in angular velocity. As in the first design variant, the energy change is used to determine the moment of inertia of the drum and subsequently the filling level.

[0019] In a further advantageous embodiment, the residual moisture content of a filter cake is determined at high speed by comparing the rotating masses from at least two cycles of speed variations. In this embodiment, the speed of the centrifuge drum is first varied, the rotating mass is determined, and the process is then repeated at least once. If the mass determined in this way no longer changes, the filter cake in question no longer has enough moisture to be spun off. The determined mass remains constant when the moisture is completely removed. In this way, the residual moisture content of the filter cake can be determined very efficiently without interfering with the separation process, e.g. by taking a sample. Furthermore, there are no additional operating costs for the centrifuge.Firstly, the determination of residual moisture content is advantageously integrated into the centrifuge's current operating mode according to this design. Secondly, the centrifuge's spinning process can be terminated when a certain degree of dryness of the filter cake is reached. This design variant can even reduce the operating costs of the centrifuge if the spinning process is terminated earlier than originally specified based on empirical values.

[0020] In a particularly advantageous variant of the invention, the energy required to maintain or change the rotation of the centrifuge drum is determined by means of integrators in the frequency-dependent converter. Additional sensors are not necessary. The existing measurement setup is thus optimally utilized.

[0021] All embodiments of the method according to the invention lead to improved monitoring of centrifuges, since the evaluation of existing parameters provides greater accuracy and can be fully automated. The method according to the invention can be provided as a stand-alone application in a process plant or in a local or remote computer system ("cloud"), e.g., by a service provider as "software as a service."

[0022] The described developments relate both to the method according to the invention and to the device.

[0023] The invention and / or any further development described can also be implemented by a computer program product, in particular a software application, which has a storage medium on which a computer program is stored which carries out the invention and / or the further development.

[0024] The computer program product can advantageously be transferred to a working memory of a computing unit and executed from there with the aid of at least one CPU. The computer program product can advantageously be stored on a data storage device such as a USB stick, a hard disk, or a CD-ROM / DVD-ROM and from there can be retrieved or installed on the computing unit.

[0025] In the following, the invention is described and explained in more detail with reference to the exemplary embodiments shown in the figures.

[0026] In it, each in a simplified schematic representation:

[0027] FIG. 1 is a block diagram of a horizontal centrifuge and a device for monitoring the centrifuge

[0028] FIG. 2 shows a curve diagram with various temporal profiles of variables for monitoring a centrifuge over a cycle of centrifuge operation in connection with the various embodiments of the present invention

[0029] FIG. 3 shows a time profile of the inflow rate and the required motor current in the operating mode of the filling level determination of a centrifuge drum according to a first embodiment of the invention

[0030] FIG. 4 shows a time profile of a rotational speed of a centrifuge according to a further embodiment of the invention

[0031] FIG. 1 shows, by way of example and in a simplified representation, a block diagram of a horizontal centrifuge Z for the solid-liquid separation of a suspension SUS. The centrifuge Z has a centrifuge drum T into which the suspension SUS is fed via a pipe that can be closed by a valve V. The centrifuge drum T has an axis of rotation A which coincides with the axis of symmetry of the centrifuge drum and is arranged horizontally in FIG. 1. The centrifuge has at least one bearing per point at any two points on the axis of rotation for support.

[0032] In the design shown, the suspension SUS is introduced into the interior of the centrifuge drum T via a so-called filling blade. During spinning operation, the filling material lies more or less evenly against the cylindrical wall of the drum due to centrifugal forces. The horizontal centrifuge accelerates in order to force the liquid through the so-called filter cake. Spinning continues until the desired residual moisture content of the filter cake is reached. At reduced speed, a peeling knife SM pivots into the filter cake and, in this design variant, peels the product P vertically downwards via a discharge device.

[0033] To operate the centrifuge Z, it is connected to a frequency-controlled drive to generate rotation of the centrifuge drum T. The frequency-controlled drive comprises at least one frequency converter (FU), which generates a suitable alternating voltage for a motor from a supply alternating voltage. The frequency converter (FU) is connected on the one hand to a three-phase motor M, and on the other hand to a programmable logic controller (PLC) to control motor operation. The frequency converter has a speed control D, so that any speed of the rotational axis (physically: angular speed w) of the centrifuge drum can be set.

[0034] A device VO according to the invention for monitoring the centrifuge, shown as an example in FIG. 1, comprises at least one interface (S1, S2, S3) for receiving and exchanging signals from at least one of the units of the motor M, the frequency converter FU, and / or the programmable logic controller SPS. Alternatively, the device VO can also have a single interface designed to receive any desired signals and / or data.

[0035] The device VO further comprises an evaluation device AS which is designed to carry out the method according to the invention and, on the basis of the signals supplied during operation of the centrifuge Z, to record a large number of variables and parameters of the drive as a function of time over the course of the separation process, and to derive operating modes of the centrifuge from the relationships between the variables and parameters and to automatically determine information about the separation process and / or a centrifuge status depending on the derived operating mode. The evaluation device thus functions as a monitoring device and, by being connected to a display device, can show a user the previously determined information. According to the present invention, this can be the filling level of the centrifuge or the residual moisture content of the filter cake.In principle (not further explained here), it can also be information about the wear of parts of the centrifuge, such as the bearings of the centrifuge drum or an existing imbalance (= a non-rotationally symmetrical distribution of the mass in rotating bodies).

[0036] For this purpose, the evaluation device AS further comprises at least one processor unit P, at least one memory or archive Sp for storing the received signals, and at least one memory R in which a program PR with instructions is stored, the execution of which carries out one of the methods described above by means of the processor unit P. The invention implemented as a computer program PR can, for example, be stored in the main memory R or loaded into it and executed from there with the aid of the at least one processor P.

[0037] The device may further comprise or be connected to a display unit configured to monitor the centrifuge of a process plant on a user interface (GUI). A user can interact with the evaluation device (AS) of the device (VO) as desired via the graphical user interface.

[0038] Figure 2 shows a curve diagram with various temporal profiles of variables for monitoring a centrifuge over a cycle of centrifuge operation in connection with the various embodiments of the present invention. The abscissa represents the time t in ms. The ordinate shows various variables associated with an operating cycle of a peeler centrifuge for batch operation, each of which is indicated by its own axes with the corresponding scales. The lowest curve represents the measured rotational speed UMi. st of the centrifuge drum. This is given in number n per minute (rpm revolutions per minute) and is proportional to the physical quantity of the angular velocity a. Superimposed on this is the specified setpoint value of the revolutions of the centrifuge drum UM son in the same unit . Furthermore, the diagram shows the time course of the motor current I M in A, which is required to drive the centrifuge drum T, and the required electrical power P ei in kW . For a further understanding of centrifuge operation, the temporal progression of the torque of the drum M T in Nm compared with the curves of the other variables. During operation of the centrifuge, a variety of variables and drive parameters can be determined and analyzed over time over the course of the separation process.

[0039] By comparing the variables relevant to centrifuge operation, the relationships between the variables and parameters are revealed, from which the individual operating modes of a centrifuge operation cycle can be derived. These are marked in Fig. 2 with Roman numerals I to IV. For each of these operating modes, information about the separation process can now be automatically determined, for example, by evaluating the corresponding signals from the motor and frequency converter. The time series of the drive variables and parameters in relation to one another are characteristic for each operating mode (cf. differences in the curves of the operating modes "Spinning" II and "Trough Spinning" III).

[0040] In operating mode I, the centrifuge is filled. The empty drum initially rotates at a speed DZ3, which often corresponds to the peeling speed from the previous operating cycle. At the beginning of the filling mode, in this example, the empty drum is accelerated from approximately 50 to approximately 175 rpm. The latter is the filling speed DZ I. The measured actual value of the speed of the centrifuge drum UMi st follows the setpoint UM so n time-delayed . In particular, it can be clearly seen that immediately after the signal ramp of the setpoint, pronounced maxima of the motor current I M , the required electrical power P ei and the torque of the drum M Toccur which result from the fact that energy is required to accelerate the empty centrifuge drum from a first speed to a second speed. According to the invention, in the region of the first maximum of operating mode I, the area below the curve of the electrical power as a function of time can be determined using an integrator. From this (from the electrical energy used to increase the rotational energy of the centrifuge drum), the rotational moment of inertia of the centrifuge drum in the empty state, the empty moment, can be determined.

[0041] Subsequently, the filling valve V is opened and the suspension enters the drum. When the drum is filled, the incoming mass flow must be accelerated to its angular velocity, thus the power consumption of the centrifuge increases significantly during the filling process. At the end of range I, a second distinct maximum of the motor current I is therefore shown in Fig. 2.M to be recognized, as well as maxima of the required electrical power P ei and the torque of the drum M T The integral of the current consumption above the idle current consumption at this speed is therefore a measure of the energy required to accelerate the incoming mass flow to the angular velocity until the centrifuge is finally sufficiently filled. The time integral over the incoming mass flow (= mass) is proportional to the integral of the power consumption of the centrifuge drum (= electrical work). This energy balance can be used to determine the rotational moment of inertia and from this the mass of the filling (rotating mass) of the now filled drum.

[0042] At the end of operating mode I, the filling of the centrifuge drum, the filling valve is closed and the speed is "increased" to the spin-off speed DZ2. In this exemplary embodiment, a setpoint value Usoii of 1000 rpm is specified for the spin-off speed. The "spin-off mode" can be divided into two phases. In operating mode II, the centrifuge requires a lot of energy to reach the setpoint speed U so ii, which can be seen in Fig. 2 by the increasing curve of the required electrical power. At the same time, the filling material loses mass, since the liquid of the suspension is thrown off. The actual speed UM is t increases linearly until the majority of the liquid has been separated. As soon as the actual speed UM is t the target speed UM so n , no additional energy is required to rotate the drum and the motor current I M , the electrical power P eiand the torque of the drum M T fall abruptly. The "spin-off" operating mode is thus terminated.

[0043] Finally, in operating mode III, the contents are spun dry at a constant speed of 1000 rpm. This offers the possibility of determining the residual moisture content by slightly varying the rotation speed. As soon as no more moisture escapes from the filter cake, the rotational moment of inertia of the drum approaches a lower limit, and the end of the "spin dry" process can thus be determined. Details can be found in the figure description for Fig. 4.

[0044] After operating mode III (dry spinning), in this example a setpoint UM son of 50 ppm. This is the peeling speed DZ3 for peeling the filter cake. In this operating mode IV, the measured actual value also follows the speed of the centrifuge drum Ui. S t the setpoint UM so n is delayed until it finally remains at the initial level at the peeling speed DZ3. After this operating mode, a new centrifuge operation cycle begins.

[0045] Figure 3 shows an example of the time course of the inflow rate dm / dt of a centrifuge and the required motor current I M in the filling operating mode (cf. area I of Fig. 2) of a centrifuge drum according to a first embodiment of the invention. In area I ' of Fig. 3, the centrifuge drum is empty (mass flow rate dm / dt = 0). The motor current I Mdoes not change, since the drum is driven at a constant speed against a constant frictional resistance. The rotational moment of inertia Jieer of the centrifuge drum in the empty state can be determined (as already noted in the description of Fig. 2) from a speed jump by accelerating the drum from the peeling speed to the speed when filled (J = 2*Erot / a 2 with Erot = rotational energy = electrical energy (U*I M*t) and a = angular velocity). In the area I' ' of Fig. 3 the centrifuge drum is filled (dm / dt > 0). In order to keep the speed constant, the centrifuge requires additional power to accelerate the incoming mass flow to the respective angular velocity of the drum. In the area I ' ' ' in Fig. 3 no further mass is added to the drum. The additional energy required is proportional to the area of ​​the integral of the power consumption over time. This can be determined, for example, using an integrator in the frequency converter of the drive (see Fig. 2). According to this embodiment, a software application in which the specified method is implemented would provide a user with information about the fill level when a function "determination of the fill level" is called, without a special sensor having to be installed in the centrifuge drum.

[0046] Figure 4 shows a temporal progression of a rotational speed UM of a centrifuge according to a further embodiment of the invention. The drum rotation is varied slightly cyclically at a high rotational speed RDM (here at DZ2 = 1500 rpm) in relation to this rotational speed. This can be, for example, a sine wave or a sawtooth wave. This occurs particularly in the dry spin range (see operating mode III in Fig. 2). The change in angular velocity is measured. When accelerating the drum, the motor must generate energy. This can be derived from the motor's required current. When decelerating the drum, the motor acts like a generator and converts the machine's mechanical energy back into electrical energy. The converter must then "get rid of" the energy, which can be measured by the voltage drop across the resistors in the converter. Here, too, the rotational moment of inertia of the drum can be determined using the energy balances. If, as shown in Fig.4 If the centrifuge is run cyclically between two speeds with a defined acceleration or braking energy, the rotational moment of inertia can be measured periodically. This requires cyclical querying of the frequency converter power or an electricity meter. To implement this query, this query would have to be implemented in the system control system. For the separation process, a small variation of, for example, + / - 50 rpm in relation to a speed of 1500 rpm is not important. With dozens of kilograms of additional weight of the separated solids from a suspension and at several thousand revolutions, the acceleration energy of the rising ramp or the braking torque of the falling ramp can be used to determine the moment of inertia during the drying process. According to the invention, easily measurable energy must be used for acceleration or controlled braking energy, and the change in angular velocity dw / dt over time must be recorded.Using the sawtooth curve shown in Fig. 4, a change in energy over time can be brought about by either accelerating or braking the drum with a constant force and using the change in angular velocity to calculate the rotational moment of inertia, or by specifying the change in angular velocity as a function of time and determining the power required for this. The exemplary embodiment shown in Fig. 4 shows two cycles or variations in speed at different times. A comparison of the rotating mass (inertial mass) determined in each cycle can be used to determine the residual moisture in the filter cake. If residual moisture is still present, the rotating mass decreases over time. Ultimately, the residual moisture will approach a limit over time, whereupon the spinning process (if necessary) is stopped.earlier than originally set) and the filter cake can be mechanically removed once the peeling speed (DZ3) has been reached. In pharmaceutical applications and fine chemicals, the dehumidified solid is the valuable product (which is further processed) and the separated liquid is the waste. The aim here is to keep the residual moisture as low as required and this residual moisture should therefore be monitored. The invention and the described developments are preferably realized in software as well as in firmware or in a microchip, for example using a special electrical circuit, or implemented in a combination of software and hardware such as a software module which can be read into the control of the frequency converter.

Claims

Patent claims 1. Method for monitoring a centrifuge (Z) for solid-liquid separation of a suspension (SUS), with a centrifuge drum (T) which is provided with at least one frequency-controlled drive for generating a rotation of the centrifuge drum (T), wherein during operation of the centrifuge a plurality of variables and parameters of the drive are determined time-dependently over the course of the separation process, characterized in that operating modes (I, II, III, IV) of a cycle of centrifuge operation are derived from the relationships between the variables and parameters of the drive and information about the separation process is automatically determined as a function of the derived operating mode.

2. Method according to claim 1, characterized in that, in order to derive a filling mode (I), speeds of the drum rotation (DZ3, DZI) and at least the energy of the drive (EU) required to maintain a speed (DZI) of the drum rotation are recorded as a function of time, and from this an increase in a rotational moment of inertia of the drum due to the filling is derived, and from this the rotating mass of the filling of the centrifuge drum (T) and its contained mass are determined.

3. Method according to claim 1, characterized in that the operating mode "dry spinning" (III) is determined from the relationships between the recorded variables and parameters of the drive and at a high speed (DZ2) the speed of the drum rotation is varied cyclically over time, and the temporal change of the angular velocity is measured, that the energy for the acceleration and deceleration of the drum is derived therefrom, and the rotational moment of inertia of the drum is calculated and from this the rotating mass and taking into account the empty moment of the drum, the filling level of the centrifuge drum is determined.

4. Method according to claim 3, characterized in that at the high speed (DZ2) a residual moisture content of a filter cake is determined by comparing the rotating masses of at least two cycles of the speed variations, which becomes constant upon complete dehumidification.

5. Method according to one of the preceding claims, characterized in that the energy required to maintain or change the rotation of the centrifuge drum is determined by means of integrators in the frequency-dependent converter.

6. Device (VO) for monitoring a centrifuge (Z) for solid-liquid separation of a suspension (SUS), with a centrifuge drum (T) which is connected to at least one frequency-controlled drive (FU) for generating a rotation of the centrifuge drum (T), - with at least one interface (SI, S2, S3) for receiving signals from the frequency-controlled drive, and - with an evaluation device (AS) which has a data memory (Sp) which is designed to store the signals received from the interfaces (SI, S2, S3), wherein the evaluation unit (AS) is designed to carry out a method according to one of claims 1 to 5.

7. Device according to claim 6, wherein the evaluation unit (AS) and the data storage (SP) are implemented in a cloud-based environment.

8. A computer program product comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to one of claims 1 to 5.

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