Condition monitoring for rotating element

Abstract

The invention relates to state monitoring for a rotating element, in particular an electric machine. In particular, a first measurement variable dependent on the rotational position of the rotating element is acquired by means of a first sensor of a rotational speed acquisition unit and a rotation signal corresponding to the first measurement variable is output; determining a clock rate for acquiring the first measured variable by means of a processing unit of the rotational speed acquisition unit or by means of a separate evaluation unit; acquiring a second measurement variable different from the first measurement variable by means of a second sensor of the rotational speed acquisition unit, the second sensor having a clock input, by means of which a clock rate of the acquisition of the second measurement variable can be adjusted, and outputting a measurement signal corresponding to the second measurement variable; adjusting the acquired clock rate of the second measurement variable taking into account the determination of the clock rate of the first measurement variable acquired by the processing unit or by a separate evaluation unit; the condition of the rotating element is monitored using the rotation signal and a measurement signal suitable for the rotation signal.

Description

Technical Field

[0001] The invention for monitoring the state of a rotating element relates to a rotation speed acquisition unit, which is in particular a rotary encoder. The invention also relates to a technical unit having a rotating element and a rotation speed acquisition unit. The invention also relates to a system having a rotation speed acquisition unit or a technical unit and a separate acquisition unit. The invention also relates to a method for monitoring the state of a rotating element, which is in particular an electric motor. Background Art

[0002] Rotary encoders are used to measure the distance, speed or rotation angle of a rotating object connected to the rotary encoder. For this purpose, the rotary encoder has a sensor for detecting the rotational position or the change in the rotational position. Such rotary encoders can detect the rotation angle with a very high rotation angle resolution, for example with a resolution of 0.1°.

[0003] In the industrial environment, rotary encoders are used, for example, in machine tools, in operating technology and in automation technology, as well as on measuring and testing devices.

[0004] The rotary encoder can be, for example, an encoder which detects an absolute rotation angle position and outputs a corresponding coded signal. The rotary encoder can also be an incremental rotary encoder which, for example, outputs two signals which are offset by 90° from each other. The relative change in the rotation angle can be determined from the two encoder signals.

[0005] Incremental encoders are also known, which output a reference signal at a predetermined rotation angle. By evaluating this signal, the absolute rotation angle can be derived.

[0006] For example, rotary encoders can be based on the photoelectric principle or the magnetic principle. In the former case, a light beam, usually generated by an LED, is guided to a photoelectric sensor (usually a phototransistor) via a scanning plate equipped with lines or slots. As the scanning plate rotates, the light beam between the LED and the phototransistor is cyclically modulated. The modulation signal from the phototransistor can generate a corresponding rotary encoder signal.

[0007] Such a rotary encoder can be attached to, for example, the rotor shaft end of an electric motor to collect changes in the rotational position of the rotor shaft. The encoder can also be connected to the rotor shaft via a toothed belt. Rotary encoder signals are usually required to monitor and / or control the electric motor. The electric motor can be, for example, an electric motor or a generator. It can be an asynchronous machine or a synchronous machine.

[0008] "Condition Monitoring" is particularly applicable in industrial environments for condition-based maintenance of rotating machines. Since failures in monitored machines can lead to safety-critical situations and major costs (not only for the machine itself but also, above all, for the subsequent processes) condition monitoring is used to prevent such failures.

[0009] Based on the data obtained by condition monitoring, the condition of the monitored machine can be analyzed, and the service, repair and replacement of the machine can be facilitated in a condition-oriented manner.

[0010] This creates enormous potential for cost savings, since the lifespan of critical machine components can be exploited more effectively and necessary maintenance measures can be scheduled in conjunction with production planning at the same time.

[0011] Vibration and other sensor signals are evaluated in order to monitor the state of rotating systems. For this purpose, specific frequencies are analyzed in the spectrum of the sensor signal. The frequencies to be considered depend largely on the rotational speed of the rotating machine. In this respect, the basic condition for calculating the spectrum and analyzing the frequencies to be considered is that the rotational speed is constant over a relatively long period of time. However, this is often not the case in practice.

[0012] One possibility to avoid this problem is order analysis. This means that multiples of the rotational speed are analyzed instead of selected frequencies. This order analysis is possible even if the rotational speed changes during the observation period. To achieve this, however, the rotational speed must be known continuously during the observation period. Thus, the sensor value can be based on the rotational speed instead of on time.

[0013] In order to perform condition monitoring on rotating machines, even during dynamic operation, a condition monitoring system with additional speed acquisition was previously required. However, the cost of such a system was in the four- to five-figure range, and such condition monitoring was only possible for rotating machines in the high-end range.

[0014] If the motor is controlled via an encoder, speed detection and a digital interface for data transmission are already available.

[0015] From DE 10 2006 041 056 A1 it is known that an encoder interface can be used to transmit additional sensor data. However, the basic problem is that the assignment of the sensor data to the rotational speed must be done with very high precision, which cannot be achieved by digitizing the measured values ​​in parallel to the encoder position without synchronization.

[0016] One possibility is to use a sensor that provides data at the same rate as the encoder. However, conventional sensors are run by internal, relatively inaccurate clocks. For this reason, it is not feasible to select a sensor with the same data rate as the encoder clock. And even if the sensor's internal clock is more accurate, the small difference between the encoder clock and the sensor clock will of course lead to serious inaccuracies in condition monitoring.

[0017] Typically, sensors indicate that a new signal has been acquired by setting an interrupt signal. In this respect, the data rate of the sensor can be measured very easily by measuring the period between two or more interrupts, for example via a capture input of a µController (microcontroller). The encoder clock can be adapted to this data rate in order to achieve synchronized data acquisition of encoder and sensor. However, the encoder signal is used to control the rotating machine. Continuously adjusting the data rate encoder clock of the sensor would clearly hinder this control and therefore does not constitute a viable solution. Summary of the invention

[0018] The invention is based on the object of specifying a cost-effective and reliable method for monitoring the rotational speed of a rotating element.

[0019] This object is achieved by a rotation speed acquisition unit according to the invention, which is in particular a rotary encoder. In addition, this object is achieved by a technical unit according to the invention. In addition, this object is achieved by a system according to the invention and a method according to the invention for monitoring the state of a rotating element.

[0020] The rotation speed acquisition unit according to the present invention comprises a first sensor for acquiring a first measured variable depending on the rotational position of a rotating element and a second sensor for acquiring a second measured variable different from the first measured variable, wherein the rotation speed acquisition unit has a first signal output for outputting a rotation signal corresponding to the first measured variable, and wherein the rotation speed acquisition unit has a second signal output for outputting a measurement signal corresponding to the second measured variable. The first signal output and the second signal output can physically separate the signal output component. However, the same signal output component can also be used for the first measured variable and the second measured variable, however, it is feasible for the measured variables to be used to distinguish signals from each other, for example, by corresponding modulation. For example, the digital DRIVE-CLiQ interface of SIEMENS can be used as a shared signal output component.

[0021] The rotation speed acquisition unit is characterized in that the second sensor has a clock input via which the clock rate of the acquisition of the second measured variable can be adjusted. In addition, it is characterized in that the rotation speed acquisition unit has a processing unit which is designed to determine the clock rate of the acquisition of the first measured variable and to adjust the clock rate of the acquisition of the second measured variable taking into account the determined clock rate of the acquisition of the first measured variable. In this case, the processing unit is part of the rotation speed acquisition unit. It is also possible to carry out the clock rate of the acquisition of the first measured variable and to adjust the second clock rate by a separate processing unit, which is described below.

[0022] In addition to the actual rotation speed sensor (first sensor), the rotation speed acquisition unit also has at least one other sensor, through which another measured variable can be acquired. The first measured variable and the second measured variable are different from each other. Therefore, the second measured variable is not the rotation speed of the rotating element, but another measured variable connected to the rotating element or related to it. The second sensor can be, for example, a temperature sensor, a vibration sensor, an acceleration sensor, a microphone, a pressure sensor, a force sensor, a torque sensor, a displacement sensor, a magnetic field sensor, a voltage sensor or a current sensor. Acquiring temperature, vibration, acceleration or other variables can draw conclusions about the condition of the rotating element, which can be advantageously used for condition monitoring.

[0023] The rotation speed acquisition unit particularly advantageously has a second sensor having a clock input. Via the clock input, the processing unit can adjust the clock rate of the acquisition of the second (additional) measured variable to the clock rate of the acquisition of the first measured variable by the first sensor. Such (second) sensors with a clock rate that can be adjusted by external specifications have not been known for a long time and are particularly advantageously used in the context of the present invention so that the clock rate of the second sensor is adjustable. This has the advantage that the second sensor can be synchronized with the first sensor (and not vice versa).

[0024] Providing such a second time-capable sensor on the speed detection unit allows the detection of additional data, such as acceleration data, absolutely synchronously with the speed of the rotating element. This enables a direct order analysis evaluation of the condition monitoring. Until now, this required cost-intensive additional systems, with limitations associated with this, since there was no direct coupling between the additional sensor data and the speed of the rotating element.

[0025] The first sensor and / or the second sensor can be connected to the processing unit via a bus interface. A particular advantage of this embodiment is that the sensor with a standardized plug can be easily plugged into a corresponding bus connection socket of the speed acquisition unit. This reduces the assembly workload. Another advantage is that the measured variables acquired by the sensor are usually transmitted to the bus interface of the speed acquisition unit in the form of digital measured values. The bus interface can be, for example, a standardized USB interface. The USB plug and the corresponding socket advantageously have compact dimensions. Alternatively, a known FireWire interface based on the IEEE 1394 standard, a CAN bus or an I 2 C bus interface.

[0026] However, the connection can also be via a terminal strip or a connector which is arranged in or on the rotational speed detection unit. The corresponding cable ends of the sensor can be pushed or plugged in and then fixed in the terminal strip or the connector.

[0027] Preferably, the processing unit is a microcontroller, an FPGA (field programmable gate array), an ASIC (application-specific integrated circuit), a discrete circuit or a microprocessor. These components can be flexibly adapted to the needs of the rotation speed acquisition unit.

[0028] Particularly preferably, the rotation speed acquisition unit has a housing, in which the first sensor and the second sensor are arranged. For example, the housing can be made of aluminum or plastic. However, the second sensor can also be arranged outside the housing.

[0029] In the context of a preferred development of the invention, the processing unit is designed to determine the clock rate for the acquisition of the first measured variable at the start of the condition monitoring and to repeat this at specific points in time during the condition monitoring process. The processing unit can thus determine potential changes in the clock rate of the first sensor during its operation and update the clock rate of the second sensor accordingly. This further increases the reliability of the condition monitoring.

[0030] The object is also achieved by a technical unit, preferably an electric machine, in particular an electric motor or a transmission, having a rotating element and a rotational speed detection unit according to the invention for detecting a first measured variable and a second measured variable.

[0031] Furthermore, the object is achieved by a system comprising:

[0032] a rotation speed detection unit, in particular a rotary encoder, having a first sensor for detecting a first measured variable which is dependent on the rotational position of the rotating element and a second sensor for detecting a second measured variable which is different from the first measured variable,

[0033] - wherein the rotation speed acquisition unit has a first signal output terminal for outputting a rotation signal corresponding to the first measured variable,

[0034] - and wherein the rotation speed acquisition unit has a second signal output terminal for outputting a measurement signal corresponding to a second measurement variable,

[0035] - and wherein the second sensor has a clock input, via which the clock rate of the acquisition of the second measured variable can be adjusted; or a technical unit as described above,

[0036] and a separate evaluation unit which is connected to the rotational speed detection unit and is designed to determine a clock rate for the detection of the first measured variable and to adjust the clock rate for the detection of the second measured variable taking into account the determined clock rate for the detection of the first measured variable.

[0037] The above-described system therefore comprises a rotational speed detection unit and a separate (ie external) evaluation unit, or a technical unit and a separate evaluation unit.

[0038] The separate evaluation unit is implemented separately from the rotational speed acquisition unit. For example, it can be implemented in a cloud-based environment (with evaluation and control functionality). However, it can also be implemented in a unit that is implemented at a clock rate that is specified for the acquisition of the first measured variable. This simplifies the acquisition of the clock rate for acquiring the first measured variable, since the unit specifies the clock rate itself.

[0039] Furthermore, the object is achieved by a method for monitoring the state of a rotating element, in particular an electric machine, comprising:

[0040] a) acquiring a first measured variable dependent on the rotational position of the rotating element by means of a first sensor of the rotational speed acquisition unit and outputting a rotation signal corresponding to the first measured variable,

[0041] b) determining a clock rate for the acquisition of the first measured variable by means of a processing unit of the rotational speed acquisition unit or by means of a separate evaluation unit,

[0042] c) acquiring a second measured variable different from the first measured variable by means of a second sensor of the rotation speed acquisition unit and outputting a measurement signal corresponding to the second measured variable, wherein the second sensor has a clock input terminal, via which the acquisition of the clock rate of the second measured variable can be adjusted,

[0043] d) taking into account a determined clock rate for the acquisition of the first measured variable by the processing unit or by a separate evaluation unit in order to adjust the clock rate for the acquisition of the second measured variable,

[0044] e) Using the rotation signal and a measurement signal adapted to the rotation signal to monitor the condition of the rotating element.

[0045] The clock rate for the acquisition of the first measured variable is determined by the processing unit or a separate evaluation unit at the start of the condition monitoring and can be repeated at specific points in time during the condition monitoring process. For example, the clock rate for the acquisition of the first measured variable can be specified by a control unit of a converter for an electric machine as a technical unit.

[0046] During the acquisition of the second measured variable, in the case where the second sensor supports the clock rate for the acquisition of the first measured variable as its own clock rate, then during the scope of the adjustment of the clock rate for the acquisition of the second measured variable, the clock rate for the acquisition of the first measured variable is used as the clock rate for the acquisition of the second measured variable. Usually, the second sensor supports a certain bandwidth in its clock rate for the acquisition of the second measured variable. If the clock rate for the acquisition of the first measured variable is within this frequency band, the clock rate for the acquisition of the first measured variable can therefore simply be used as the clock rate for acquiring the second measured variable. The measurement signals of the first sensor and the second sensor can therefore be synchronized particularly easily and the data of the second measured variable can be directly correlated with the data of the first measured variable for condition monitoring.

[0047] During the acquisition of the second measured variable, in the case where the second sensor supports a multiple of the clock rate for the acquisition of the first measured variable as its own clock rate, then during the adjustment of the scope of the clock rate for the acquisition of the second measured variable, the multiple of the clock rate for the acquisition of the first measured variable is used as the clock rate for the acquisition of the second measured variable. For example, if the first clock rate is 100 Hz, but the bandwidth of the second sensor ranges from 150 Hz to 250 Hz, then 200 Hz is used as the clock rate of the second sensor, and this is twice the clock rate of the first sensor.

[0048] For condition monitoring, only certain parts of the rotation signal and / or the measurement signal can be considered. In the previously described example with a first clock rate of 100 Hz and a second clock rate of 200 Hz, the data of the measurement signal can extract the data of the rotation signal. Specifically, this means that only every two sensor data of the second sensor are evaluated.

[0049] Advantageously, the rotation signal and / or the measurement signal can be subjected to frequency-dependent filtering in order to prevent false identifications. In the previous example, this is the case for the measurement signal, since the measurement signal is extracted while the rotation signal is used in its original state.

[0050] However, for the purpose of condition monitoring, it is also possible to perform an interpolation of the data of the rotation signal and / or the measurement signal. In the previously described example with a first clock rate of 100 Hz and a second clock rate of 200 Hz, the data of the rotation signal can be interpolated so that the data of the rotation signal are also present for the condition monitoring at the time of the data of the measurement signal. All data of the measurement signal and all data of the rotation signal as well as the additional interpolated data of the rotation signal are thereby evaluated.

[0051] The multiple does not have to be an integer. For example, a ratio of 4 / 3 or 7 / 5 between the two clock rates can also be selected. For condition monitoring, the data of the rotation signal and the measurement signal can be interpolated so that the two signals have a clock rate that is the least common multiple of the clock rate of the acquisition of the first measurement variable or the clock rate of the acquisition of the second measurement variable. For example, in the case where the ratio between the rotation signal clock rate and the measurement signal clock rate is 4 / 3, three data will have to be inserted between the data of the acquired measurement signal and two data will have to be inserted between the data of the acquired rotation signal. For a better understanding, reference is made to the description of the embodiments and the accompanying drawings.

[0052] If during the acquisition of the second measured variable the second sensor supports a fraction of the clock rate for the acquisition of the first measured variable as its own clock rate, then during the period of adjustment of the clock rate for the acquisition of the second measured variable a fraction of the clock rate for the acquisition of the first measured variable is used as the clock rate for the acquisition of the second measured variable. For example, if the first clock rate is 100 Hz, but the bandwidth of the second sensor ranges from 25 Hz to 75 Hz, then 50 Hz can be used for the clock rate of the second sensor, and this corresponds to half the clock rate of the first sensor. Analogously to the previous statement, the data of the measurement signal can be interpolated for condition monitoring or the data of the rotation signal can be extracted.

[0053] The above characteristics, features and advantages of the present invention and the manner of achieving the same will be more clearly and understandably combined with the following description of embodiments, which will be explained in more detail in conjunction with the accompanying drawings, in which: BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 A schematic diagram of a rotation signal acquisition unit according to the present invention is shown;

[0055] Figure 2 shows a comparison of the time of the rotation signal and the measurement signal according to the first aspect;

[0056] Figure 3 shows a comparison of the time of the rotation signal and the measurement signal according to the second aspect;

[0057] Figure 4 shows a comparison of the time of the rotation signal and the measurement signal according to the third aspect;

[0058] Figure 5 shows a comparison of the time of the rotation signal and the measurement signal according to the fourth aspect;

[0059] Figure 6 shows a comparison of the time of the rotation signal and the measurement signal according to the fifth aspect; and

[0060] Figure 7 A comparison of the time of the rotation signal and the measurement signal according to the sixth aspect is shown. DETAILED DESCRIPTION

[0061] Figure 1 The structure of a rotation speed acquisition unit according to the invention is schematically shown, which is implemented as a rotary encoder 1. The rotary encoder 1 has a rotary sensor as a first sensor 2, which is used to acquire a measured variable that depends on the rotational position of a rotating element 3. The measured variable can be, for example, an angle in degrees. The reference symbol A indicates the rotation axis of the rotary encoder 1 or the rotating element 3. For the sake of clarity, the rotating element 3 is not shown. The object can be, for example, a motor shaft, a turntable, etc.

[0062] The rotary encoder 1 also has a processing unit 4, a first connection 5 for a first further sensor and a second connection 6 for a second further sensor. Furthermore, the rotary encoder 1 has a voltage input 7 for the first sensor 2, a signal output 8 and two signal outputs 9 for the further sensors 5, 6. The processing unit 4 serves in a circuit manner to distribute the input-side signals of the voltage source 7, the first sensor 2 and the further sensors 5, 6 to the output-side signal outputs 8, 9. The processing unit 4 has a microcontroller.

[0063] From the modulation signal of one of the two phototransistors (not shown) of the first sensor 2, a rotational position-dependent rotation signal and a direction-dependent rotation signal can be generated, which are provided at the sensor output 8. Thus, the measurement signal is provided by the further sensors 5, 6 at the further signal output 9. The further first sensor 5 is a temperature sensor with temperature as measured variable, while the further second sensor 6 is an acceleration sensor with acceleration as measured variable. The further sensors 5, 6 are preferably attached to the locations in the motor to be monitored, for example in the winding ends or in the area of ​​the motor bearings. Both sensors 5, 6 have external clock inputs 12, 13, via which the processing unit 4 can variably set and change the acquisition of the clock rate of the respective measured variables of the two sensors 5, 6.

[0064] Obviously, only a single further sensor 5 can be connected to the processing unit 4 .

[0065] Figure 2The time sequence of the rotation signal 10 (at the top of the figure) tapped at the first signal output 8 and the measurement signal 11 (acceleration or temperature, at the bottom of the figure) tapped at the second signal output 9 is shown. The processing unit 4 has determined the clock rate for the acquisition of the first measured variable and has adjusted the clock rate of the second sensor 5 (or the third sensor 6) accordingly. The clock rate of the further sensors 5, 6 can be set to twice the clock rate of the first sensor 2.

[0066] For condition monitoring, it is possible to associate each data of the measurement signal 11 with exactly one data of the rotation signal 10. Thus, every two data of the measurement signal 11 can be extracted and not taken into account for this (by Figure 3 ), or every two data of the rotation signal 10 can be interpolated (by Figure 4 denoted by the dashed arrow in FIG.

[0067] Figure 5 A further time sequence of a rotation signal 10 tapped at the first signal output 8 (at the top of the figure) and a measurement signal 11 (acceleration or temperature, at the bottom of the figure) tapped at the second signal output 9 is shown. It can be seen that the ratio of the clock rates of the measurement signal 11 and the rotation signal 10 is 4:3. The data of the measurement signal 11 and the rotation signal 10 are interpolated here to a data rate that represents the least common multiple of the two data rates. Thus, the measurement signal 11 is interpolated to three times the clock rate, the rotation signal 10 to four times the clock rate, and it can be seen that the ratio of the clock rates of the measurement signal 11 and the rotation signal 10 is 4:3. Figure 6 was identified.

[0068] Or, if Figure 7 As shown, partial data of the rotation signal 10 and the measurement signal 11 can also be decimated. A hybrid form of decimation and interpolation is also possible.

Claims

1. A rotation speed acquisition unit (1), in particular a rotary encoder, comprising a first sensor (2) for acquiring a first measured variable which is dependent on the rotational position of a rotating element (3) and a second sensor (5) for acquiring a second measured variable which is different from the first measured variable, in, The rotation speed acquisition unit (1) has a first signal output terminal (8), the first signal output terminal being used to output a rotation signal (10) corresponding to the first measured variable. Furthermore, the rotation speed acquisition unit (1) has a second signal output terminal (9), and the second signal output terminal is used to output a measurement signal (11) corresponding to the second measurement variable. It is characterized in that The second sensor (5) has a clock input (12, 13) via which a clock rate for the acquisition of the second measured variable can be adjusted. Furthermore, the rotational speed detection unit (1) has a processing unit (4) which is designed to determine a clock rate for the detection of the first measured variable and to adjust a clock rate for the detection of the second measured variable taking into account the determined clock rate for the detection of the first measured variable.

2. The rotation speed acquisition unit (1) according to claim 1, wherein: The first sensor and / or the second sensor (5, 6) are connected to the processing unit (4) via a bus interface.

3. The rotation speed acquisition unit (1) according to any one of the preceding claims, wherein: The processing unit (4) is a microcontroller, an FPGA, an ASIC, a discrete circuit or a microprocessor.

4. The rotation speed acquisition unit (1) according to any one of the preceding claims, wherein: The second sensor (5, 6) is implemented as a temperature sensor, a vibration sensor, an acceleration sensor, a microphone, a pressure sensor, a force sensor, a torque sensor, a displacement sensor, a magnetic field sensor, a voltage sensor or a current sensor. 5 . The rotational speed detection unit ( 1 ) according to claim 1 , comprising a housing in which the first sensor ( 2 ) and the second sensor ( 5 , 6 ) are arranged.

6. The rotation speed acquisition unit (1) according to any one of the preceding claims, wherein: The processing unit (4) is designed to carry out a determination of a clock rate for recording the first measured variable at the beginning of the condition monitoring and to repeat the determination at specific points in time during the condition monitoring process.

7. A technical unit, preferably an electric machine or a transmission, the electric machine being in particular an electric motor, comprising a rotating element (3) and a rotational speed detection unit (1) according to any one of the preceding claims, the rotational speed detection unit being used to detect a first measured variable and a second measured variable.

8. A system, The system comprises a rotation speed detection unit (1) or a technical unit according to claim 7, the rotation speed detection unit being in particular a rotary encoder, the rotation speed detection unit having a first sensor (2) for detecting a first measured variable which is dependent on the rotational position of the rotating element (3) and a second sensor (5) for detecting a second measured variable which is different from the first measured variable, in, The rotation speed acquisition unit (1) has a first signal output terminal (8), the first signal output terminal being used to output a rotation signal (10) corresponding to the first measured variable. Furthermore, the rotation speed acquisition unit (1) has a second signal output terminal (9), and the second signal output terminal is used to output a measurement signal (11) corresponding to the second measurement variable. and wherein the second sensor (5) has a clock input (12, 13) via which a clock rate for the acquisition of the second measured variable can be adjusted, The system further comprises a separate evaluation unit which is connected to the rotational speed detection unit and which is designed to determine a clock rate for the detection of the first measured variable and to adjust the clock rate for the detection of the second measured variable taking into account the determined clock rate for the detection of the first measured variable.

9. The system according to claim 8, wherein: The evaluation unit is implemented in a cloud-based environment.

10. The system according to claim 8, wherein: The evaluation unit is implemented in a unit which is implemented to specify a clock rate for the acquisition of the first measured variable.

11. A method for monitoring the state of a rotating element (3), in particular an electric motor, comprising: a) acquiring a first measured variable dependent on the rotational position of the rotating element (3) by means of a first sensor (2) of a rotational speed detection unit (1) and outputting a rotation signal (10) corresponding to the first measured variable, b) determining a clock rate for the acquisition of the first measured variable by means of a processing unit of the rotational speed acquisition unit (1) or by means of a separate evaluation unit, c) acquiring a second measured variable different from the first measured variable by means of a second sensor (5, 6) of the rotational speed acquisition unit (1) and outputting a measurement signal (11) corresponding to the second measured variable, wherein the second sensor (5, 6) has a clock input (12, 13) via which a clock rate for acquiring the second measured variable can be adjusted, d) adjusting the clock rate for the acquisition of the second measured variable taking into account the clock rate for the acquisition of the first measured variable determined by the processing unit (4) or by the separate evaluation unit, e) using the rotation signal (10) and a measurement signal (11) matched to the rotation signal (10) to monitor the condition of the rotating element (3).

12. The method according to claim 11, wherein: The clock rate for the acquisition of the first measured variable is determined at the beginning of the condition monitoring and is repeated at specific points in time during the condition monitoring process.

13. The method according to claim 11 or 12, wherein: In the case where the second sensor (5, 6) supports the clock rate for the acquisition of the first measured variable as the clock rate of the second sensor itself during the acquisition of the second measured variable, the clock rate for the acquisition of the first measured variable is used as the clock rate for the acquisition of the second measured variable during the process of adjusting the clock rate for the acquisition of the second measured variable.

14. The method according to claim 11 or 12, wherein: In the case where the second sensor (5, 6) supports a multiple of the clock rate for the acquisition of the first measured variable as the clock rate of the second sensor itself during the acquisition of the second measured variable, during the process of adjusting the clock rate for the acquisition of the second measured variable, the multiple of the clock rate for the acquisition of the first measured variable is used as the clock rate for the acquisition of the second measured variable.

15. The method according to claim 11 or 12, wherein: In the case where the second sensor (5, 6) supports a fraction of the clock rate for the acquisition of the first measured variable as the clock rate of the second sensor itself during the acquisition of the second measured variable, during the process of adjusting the clock rate for the acquisition of the second measured variable, the fraction of the clock rate for the acquisition of the first measured variable is used as the clock rate for the acquisition of the second measured variable.

16. The method according to any one of claims 11 to 15, wherein: In order to prevent aliasing, the rotation signal (10) and / or the measurement signal (11) are subject to frequency-dependent filtering.

17. The method according to any one of claims 11 to 16, wherein: For condition monitoring, only certain parts of the rotation signal (10) and / or the measurement signal (11) are taken into account.

18. The method according to any one of claims 11 to 17, wherein: An interpolation of the data of the rotation signal (10) and / or the measurement signal (11) is performed for condition monitoring.

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