F1ELD

Various example embodiments relate to an arrangement for measuring a temperature of a rotating shaft, and to a method for measuring a temperature of a rotating shaft.

BACKGROUND

lt is commonly known that the shaft temperature corresponds to a roller bearing inner ring temperature and further to a bearing condition lt is also commonly known that the temperature of the shaft may correspond to an operation condition of a machine (such as a blower or pump) lf the shaft or roller bearing inner ring temperature is measured, the information can be used for predictive maintenance purposes or to detect a failure or other abnormal operation of the system. However, accurate temperature measurement from the rotating shaft is a difficult task. Pyrometers can be used in some special applications, but those are expensive, and the measurement set-up requires detailed design.

BRIEF DESCRIPTION

According to an aspect, there is provided an arrangement as specified in claim 1.

According to another aspect, there is provided a method as specified in claim 10.

One or more examples of implementations are set forth in more detail in the accompanying drawings and the description of embodiments.

The invention may provide one or more of the following advantages: a reliable and cost effective solution for shaft temperature measurement, which, when combined with shaft displacement measurement, may provide more accurate information about the condition of the shaft system.

L1ST OF DRAW1NGS

Some example embodiments will now be described with reference to the accompanying drawings, in which

Figure 1 illustrates example embodiments of an arrangement for measuring a temperature of a rotating shaft;

Figure 2 illustrates example embodiments of a circuit board; Figures 3A, 3B and 3C illustrate further example embodiments of the circuit board; and

Figure 4 illustrates example embodiments of a method for measuring a temperature of a rotating shaft. DESCRIPTION OF EMBOD1MENTS

The following embodiments are only examples. Although the specification may refer to "an" embodiment in several locations, this does not necessarily mean that each such reference is to the same embodiment(s), or that the feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments. Furthermore, words "comprising" and "including" should be understood as not limiting the described embodiments to consist of only those features that have been mentioned and such embodiments may contain also features/structures that have not been specifically mentioned.

Let us study simultaneously both Figure 1, which illustrates example embodiments of an arrangement for measuring a temperature 140 of a rotating shaft 104, and Figure 4, which illustrates example embodiments of a method for measuring the temperature 140.

ln an example embodiment, the rotating shaft 104 is a part of a rotating machine 100. The rotating machine 100 may be a rotating electric machine (such as an electric motor, electrical generator, or the like) or another type of rotating machine. However, the rotating shaft 104 may be a part of another type of a shaft system.

The method of Figure 4 starts in 400.

The arrangement comprises a capacitive measurement sensor 110A,

HOB configured and positioned to measure 402, 404 a first capacitive shaft displacement 132 of a radial x-axis of the rotating shaft 104 and/or a second capacitive shaft displacement 130 of a radial y-axis of the rotating shaft 104.

ABB Finland has a developed a capacitive measurement sensor 110A, HOB as a primary motivation for accurate control of active magnetic bearing (AMB) rotors. The commercially available eddy current sensors’, such as Bently Nevada 3300 XL’s, major flaws are their sensitivity to rotor shaft surface’s roughness, non-concentricity and inhomogeneities, which result in reduced resolution and disturbances with the rotational frequency or its harmonics. The capacitive measurement sensor 110A, 110B can disregard the impact of roughness by using four different capacitive plates, which results in an averaging effect. The capacitive displacement measurement sensor’s 110A, HOB operating principle is based on equation

where C is capacitance, e is permittivity, A is the area between a plate and metal surface (shaft surface) and d is the distance between the surfaces. The capacitance is inversely proportional to the distance, which affects the impedance of the resonance circuit and furthermore specifies the channel’s voltage amplitude that is measured in later stages.

The capacitive measurement sensor’s 110A, HOB operation is based on measuring the resonance circuit’s RMS voltage lt may comprise four different capacitive plates, each of them paired with a plate connected to ground, resulting in eight different metallic plates in total. The capacitive measurement sensor 110A, HOB is capable of measuring displacement of radial X- and y-axes in a resolution of 0,16 gm. The measurement range is in -1. . .1 mm in each axis.

The capacitive shaft displacement measurement sensor 110A, HOB may measure shaft 104 displacement against a stationary frame. The sensor 110A, HOB may comprises a ring-shaped frame (and circuit board, see Figures 2, 3A, 3B and 3C) comprising capacitive measurement electrodes mounted around the rotating shaft 104. The sensor 110A, HOB measures the distance between the sensor head and the surface of the shaft 104. The sensor 110A, HOB may measure the capacitive shaft displacement parameter 130, 132 from an interaction with an electrically conducting part 106 of the rotating shaft 104. The electrically conducting 106 part of the rotating shaft 104 may be achieved by a special coating or material mixture, or, naturally, the whole rotating shaft 104 may be electrically conducting (as it is made of metal).

Two other patent applications by the applicant, EP 2918964 and PCT/EP2017/078198, are incorporated herein by reference in all jurisdictions where applicable. They may be consulted in order to find a further enabling disclosure, especially for the capacitive measurement sensor 110A, HOB and its use for measuring the capacitive displacement parameters 130, 132.

The arrangement also comprises one or more processing units 112 communicatively coupled with the capacitive measurement sensor 110A, HOB.

The one or more processing units 112 may be implemented with a processor (such as a microprocessor or a microcontroller), memory and software, as an integrated circuit, as an application-specific integrated circuit (ASIC), or as any other way of implementing a device that is capable of the described measurement data processing. A circuit board 200 positionable by the shaft 104 may comprise the one or more processing units 112 and the sensor 110A, HOB. However, the one or more processing units 112 may be located near the circuit board 200, in a same housing with the sensor 110A, HOB or in a separate housing, or even at a greater distance, such as in a controller, a server or a computing cloud, for example.

The communication between the different actors 112, 110A, HOB may be implemented with appropriate wired/wireless communication technologies and standard/proprietary protocols. The wired communication may be implemented with a suitable communication technology utilizing coaxial cable, twisted pair or fibre optic, and LAN (Local Area Network) or the Ethernet, for example. The wireless communication may be implemented with a suitable cellular communication technology such as GSM, GPRS, EGPRS, WCDMA, UMTS, 3GPP, 1MT, LTE, LTE-A, 2G/3G/4G/5G, or with a suitable non-cellular communication technology such as Bluetooth, Bluetooth Low Energy, Wi-Fi, WLAN (Wireless Local Area Network).

The capacitive measurement sensor 110A, HOB and the one or more processing units 112 are configured to cause the execution of the method of Figure 4. The method forms the backbone of an algorithm running in the one or more processing units 112.

ln 406, a diameter 134 (or a radius) of the rotating shaft 104 is calculated based on the first capacitive shaft displacement parameter 132 and/or the second capacitive shaft displacement parameter 130.

ln 408, a temperature 140 of the rotating shaft 104 is calculated based on the diameter 134 (or a radius), a coefficient 136 of thermal expansion of the rotating shaft 104, and a calibrated diameter 138 of the rotating shaft 104 in a known calibration temperature.

The shaft 104 diameter may be calculated based on the sum value of the displacement measurements 132, 134. The only parameter that affects the shaft 104 diameter 134 is the temperature. As long as the initialization of the sensor 110A, HOB is done in known temperature and the coefficient 136 of the thermal expansion ofthe rotating shaft 104 material is known, the displacement values 132, 134 may be directly used for continuous shaft 104 temperature 140 measurement.

There is also a possibility of using the capacitive sensor’s 110A, HOB displacement data 132, 134 to estimate the shaft 104 temperature 140 if its radius at an ambient temperature is known using thermal expansion equation ri ⁼ b[( i ^— T ^’ o) oc +1] (2) from which the temperature 140 Ti can be solved as wherein:

To is the known calibration temperature;

ri is a radius of the rotating shaft 104 at the temperature Ti 140;

ro is a radius of the rotating shaft 104 at the known calibration temperature To; and

a is the coefficient 136 of the thermal expansion of the rotating shaft

104 as a thermal expansivity multiplier (in 10 ⁶ / K).

Using these equations, only the shaft radius ri is measured and that is acquired from the capacitive sensor 110A, HOB. The average of signal amplitudes is potentially an indicator for the radius expansion. For a generic steel shaft 104, the thermal expansivity multiplier is 12-10 ⁶ / K. For example, a temperature change of 50 °C in 3 58,55 mm diameter shaft 104 results in an expansion of 16,9 gm and 100 ° C marks a variation of 35,1 gm.

ln an example embodiment illustrated in Figure 2, the capacitive measurement sensor 110A, HOB is placed on a circuit board 200, which is configured and positioned adjacent to the rotating shaft 104. The circuit board 200 may gave been machined from a circuit board blank 202. ln an example embodiment, the circuit board 200 is rigid, such as a printed circuit board.

ln an example embodiment shown in Figure 2, also the one or more processing units 112 are placed on the circuit board 200. However, the one or more processing units 112 may be located near the circuit board 200, in the same housing or in a separate housing, or even at a greater distance, such as in a server or a computing cloud, for example.

ln an example embodiment, the calibration procedure may also include a temperature of the circuit board 200 itself lf the temperature of the circuit board 200 during the measurement, also the distance between the capacitive measurement sensor 110A, HOB and the rotating shaft 104 changes. This may lead to some inaccuracy in the shaft temperature calculation. This inaccuracy may be avoided by compensating for the thermal expansion of the circuit board 200. During the calibration and the measurement, the temperature of the circuit board 200 is measured or obtained by other means, so that the thermal expansion may be calculated. This leads to higher accuracy of the rotating shaft temperature measurement.

ln an example embodiment, a voltage thermal linearity of the electrical components on the circuit board 200 is considered in a similar fashion to compensate for inaccuracy due changes in the voltage thermal linearity.

ln an example embodiment shown in Figures 2 and 3A, the circuit board

200 comprises an arched shape 210 configured and positioned adjacent to the rotating shaft 104 and dimensioned and configured to receive the electrically conducting part 106 of the rotating shaft 104. ln an example embodiment, the arched shape 210 is implemented as a mounting hole in the circuit board 200. Such an arched shape 210 is configured and dimensioned to receive the rotating shaft 104 with a desired fitting tolerance.

ln an example embodiment illustrated in Figure 3B, the arched shape 210 comprises a partial circle of at least 90 degrees extending perpendicularly through the circuit board 200 to receive the electrically conducting part 106 of the rotating shaft 104. With such a partial circle, the placing of the rigid circuit board 200 adjacent to the rotating shaft 104 is simplified (as the rotating shaft 104 need not be able to be pushed through a mounting hole, for example).

ln an example embodiment illustrated in Figure 3C, the circuit board 200 comprises two parts 200A, 200B, which are configured to be separable so as to be placeable around the electrically conducting part 106 of the rotating shaft 104 and attachable to each other thereafter. Such a structure eases placing of the circuit board 200 adjacent to the rotating shaft 104 as well, during manufacturing or maintenance, for example.

Although Figures do not illustrate it, the circuit board 200 is, naturally, fixed adjacent to the rotating shaft 104. This may be implemented by attaching the circuit board 200 by suitable fixing means (such as glue, screws, rack, bracket, stand, support, etc.), to the rotating machine 100 or to a suitable location nearby (such as floor, wall, etc.). Furthermore, the circuit board 200 may be protected by a suitable housing (made of metal, plastic, and/or composite), which may be waterproof and/or dustproof. A suitable electric energy source, such as a mains connection or a battery may be placed in the housing as well. The method ends in 416 after the processing is finished, or the operation loops 418 back from the operation 408 (or 410/412/414) to 402 in order to continue the processing as long as required.

Now that the basic measurement sequence 402-404-406-408 has been explained, let us study further augmenting example embodiments.

ln an example embodiment, the capacitive measurement sensor 110A, HOB is configured and positioned adjacent to a bearing 102 of the rotating shaft 104. ln this way, the condition of the bearing 102 may be evaluated, as a rising temperature 140 of the shaft 104 may indicate a problem or wearing of the bearing 102 or another malfunction of the shaft system. The bearing 102 may be an antifriction bearing (such as a rolling bearing including a ball bearing and a roller bearing, or a magnetic bearing, for example), or another type of bearing.

ln an example embodiment, the one or more processing units 112 are configured to perform the following: evaluating 410 a condition 142 related to the rotating shaft 104 based on the first capacitive shaft displacement 132, and/or the second capacitive shaft displacement 130, and the temperature 140. ln addition to the temperature 140, the displacement parameters 130, 132 may also indicate a problem or wearing of the bearing 102 or other abnormalities in the shaft system like unbalance.

The condition 142 (and/or the temperature 140) may be indicated in two ways. The arrangement may comprise a user interface 114 communicatively coupled with the one or more processing units 112, and the one or more processing units 112 are configured to perform the following: outputting 412 the condition 142 via the user interface 114. The arrangement may comprise a data communication interface 116 communicatively coupled with the one or more processing units 112, and the one or more processing units 112 are configured to perform the following: communicating 414 the condition 142 via the data communication interface 116.

ln an example embodiment, an installation (in a factory, ship, etc.) comprises the rotating shaft 104, the antifriction bearing 102 and the measurement arrangement.

lt will be obvious to a person skilled in the art that, as technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the example embodiments described above but may vary within the scope of the claims.