WO2015162159A1

WO2015162159A1 - Apparatus and method to determine displacement of a continuous surface of a rotating rotor

Info

Publication number: WO2015162159A1
Application number: PCT/EP2015/058674
Authority: WO
Inventors: Stefano Cioncolini; Filippo Gerbi; Chiara Cinelli; Maria Vittoria BORGHESI
Original assignee: Nuovo Pignone SRL
Current assignee: Nuovo Pignone SRL
Priority date: 2014-04-23
Filing date: 2015-04-22
Publication date: 2015-10-29
Anticipated expiration: 2016-10-23

Abstract

Is described an apparatus for determining displacement of a continuous surface (51) of a rotating rotor (50), the apparatus comprising: at least a first proximity probe (20) facing said continuous surface (51), and adapted to repeatedly provide distance data of the area (11, 26) of said continuous surface during rotation of the rotor (50); a reference probe (5) adapted to detect a reference (10) on said rotor (50) and to provide reference phase data based on the rotations of the rotor (50); an electronic processing unit (6) connected to said proximity probe (20) and to said reference probe (5), and configured to carry out a selective sampling of distance data on the basis of reference phase data; wherein said selective sampling is programmed to obtain displacement information of at least a predetermined area (12) of said continuous surface (51) during rotation.

Description

APPARATUS AND METHOD TO DETERMINE DISPLACEMENT OF A CONTINUOUS SURFACE OF A ROTATING ROTOR

DESCRIPTION

FIELD Embodiments of the subject matter disclosed herein relates to an apparatus and a method to determine displacement of a continuous surface of a rotating rotor.

BACKGROUND ART

In the Oil & Gas industries, turbo machines are used to carry out various functions, for example to compress gases or transport fluids. Such turbo machines comprise in general static and rotating parts, each of them in turn comprising various components. Monitoring these parts, particularly rotating parts, during the work cycle is imperative. Monitoring procedure occurs acquiring data on performances and data on functioning. Then, operators process these data to derive wearing status of such parts, and possibly take proper actions to avoid cracks or extend their life cycle.

A solution known from the prior art is the use of "Tip Timing" software to analyze flectional deformation of parts like rotating blades. Such blades extend outwardly from the hub and rotate at certain speed, usually measured in terms of number of rotations per minute. One or more sensors are installed at one or more points of the static part of the turbo machine; these sensors, furthermore, are connected to an electronic processing unit.

During its rotations, the tip of the blade passes near these sensors at a certain time. The time in which the tip of blade passes near a certain sensor is so called time of arrival of the tip of the blade. In normal condition and for a fixed number of rotations per minute, such time of arrival is a constant value (within a certain range): is the same for each rotation. For example, the tip of a blade rotating at 18Ό00 rpm arrives at a certain sensor on the statoric part every 3,33 ms.

Flexional and/or torsional defornnations during rotation of the blade cause a different time of arrival, detected by the sensors. The different time of arrival is stored on the electronic processing unit to be further processed. Acting on the number of rotations per minute of the blade, the flexional and/or torsional deformations are excited. Thus, the respective time of arrival are detected and flexional and/or torsional deformations determined. Post processing the different time of arrival stored on the electronic unit allows to determine a vibration mode of the blade.

The same monitoring needs to exist for other rotating elements like impellers of centrifugal compressors, disks bearing blades and shrouded blades. Such elements does not have any part (like the tip of a blade) easily recognizable by a contactless sensor at each rotation, and then determine for such part its displacement.

According to solutions known from the state of art, on the surface of these rotating elements are installed strain gauges, a cabled probe that provide displacement data of the part of the surface in which is installed. Cabled probes on a rotating element like an impeller require a careful and long preparatory work, to be made before the probe is functioning, and in case adapt part of the impeller or the turbo machine to allow the passage of the cables.

Solution known from the state of art provide use of contactless probes for measuring displacement of a rotating disk. However such measure furnishes rigid displacement of the whole rotating disk with respect to its ideal (or initial) conditions; thus a measure on its alternate deformations is not furnished nor indirectly derivable. Therefore, there is a need for an apparatus for determining displacement of a continuous surface of a rotating rotor by mean of contactless probes, by which to derive its alternate deformations.

SUMMARY According to first exemplary embodiments, there is an apparatus for determining displacement of a continuous surface of a rotating rotor, the apparatus comprising:

- at least a first proximity probe facing said continuous surface, and adapted to provide distance data of the area of said continuous surface during rotation of the rotor,

- a reference probe adapted to detect a reference on said rotor and to provide reference phase data based on the rotations of the rotor,

- an electronic processing unit connected to said proximity probe and to said reference probe, and configured to carry out a selective sampling of said distance data on the basis of said reference phase data; wherein said selective sampling is programmed to obtain displacement information of at least a predetermined area of said continuous surface during rotation.

According to second exemplary embodiments, there is a method for determining displacement of a continuous surface of a rotating rotor, wherein is provided: a first proximity probe facing said continuous surface, and adapted to provide distance data of the area of said continuous surface during rotation of the rotor; a reference probe adapted to detect a reference on said continuous surface and to provide reference phase data based on the rotations of the rotor; the method comprising the following steps:

A) acquire distance data of the area of said continuous surface by mean of said first proximity probe; B) acquire reference phase data based on the rotations of the rotor by mean of said reference probe;

C) sample said distance data, on the basis of said reference phase data, to obtain displacement information of a predetermined area of said continuous surface during rotation.

According to third exemplary embodiments, there is a system for determining alternate deformations information in a rotary machine, in particular a multi stage centrifugal compressor, adapted to monitor and signal alternate deformations of at least one impeller, such system comprising an apparatus for determining displacement as described.

BRIEF DESCRIPTION OF THE DRAWINGS.

The present invention will become more apparent from the following description of exemplary embodiments to be considered in conjunction with accompanying drawings wherein: Figure 1 shows a first embodiment of an apparatus for determining displacement of a continuous surface of a rotating rotor;

Figure 2 shows an embodiment of an apparatus for determining displacement in a first condition;

Figure 3 shows the embodiment of figure 2 in a second condition; Figure 4 shows a second embodiment of an apparatus for determining displacement of a continuous surface of a rotating rotor;

Figure 5 shows a third embodiment of an apparatus for determining displacement of a continuous surface of a rotating rotor;

Figure 6 shows some components of an apparatus for determining displacement with some part removed for more clarity; Figure 7A shows an apparatus for determining displacement in a first detecting condition;

Figure 7B shows a graph with some quantities detected by the apparatus in the first detecting condition of Figure 7A; Figure 8A shows an apparatus for determining displacement in a second detecting condition;

Figure 8B shows a graph with some quantities detected by the apparatus in the second detecting condition of Figure 8A;

Figure 9A shows an apparatus in a third detecting condition; Figure 9B shows a graph with some quantities detected by the apparatus in the third detecting condition of Figure 9A;

Figure 10A shows an apparatus in a fourth detecting condition;

Figure 10B shows a graph with some quantities detected by the apparatus in the fourth detecting condition of Figure 10A; Figure 1 1 shows a schematic view of an embodiment of a data structure storing data produced by embodiments of an apparatus.

Figure 12 shows a schematic view of data produced and stored by embodiments of an apparatus.

DESCRIPTION The following description of exemplary embodiments refer to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. Reference throughout the specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases "in one embodiment" or "in an embodiment" in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

Figure 1 shows a first embodiment of an apparatus for determining displacement of a continuous surface 51 of a rotating rotor 50. Such rotating rotor 50 typically comprises an impeller 53 of a turbo machine, and the surface 51 belongs to the impeller. The apparatus thus comprises:

- at least a first proximity probe 20 facing the continuous surface 51 , and adapted to repeatedly provide distance data of the area 1 1 , 26 of the continuous surface during rotation of the rotor 50;

- a reference probe 5 adapted to detect a reference 10 on said rotor 50 and to provide reference phase data based on the rotations of the rotor 50,

- an electronic processing unit 6 connected to the proximity probe 20 and to the reference probe 5, and configured to carry out a selective sampling of the distance data on the basis of said reference phase data; wherein such selective sampling is programmed to obtain displacement information of at least a predetermined area 12 of the continuous surface 51 during rotation.

Typically, distance data of the area 1 1 , 26 - provided by the first proximity probe 20 - are measured repeatedly by the first proximity probe 20 itself during rotation of the rotor 50. In other words, during rotation of the rotor 50 the first proximity probe 20 measures repeatedly the distance from the continuous surface 51 and each time provides distance data accordingly. In other embodiments, the measurements and distance data may be related in different fashions. The first proximity probe 20 is known from the state of art, is installed without contact facing the continuous surface 51 . The probe 20 is fix with respect to the rotor 50; according to one embodiment, such probe 20 is installed on the statoric part of the turbo machine (both statoric part of the turbo machine and the turbo machine itself are not shown in the figure).

According to one embodiment, reference probe 5 is a keyphasor probe adapted to provide reference phase data based on the rotations of the rotor 50. In particular, the keyphasor probe is adapted to identify a reference 10, for example a notch on the shaft 52. The shaft is integral with the impeller, thus at each rotation of the shaft corresponds a rotation of the continuous surface 51 . According to one embodiment, the reference probe 5 provides reference phase data that identify each rotation of the of the continuous surface 51 .

Dashed lines in figures 1 , 4 and 5 show the impeller 53 with no area displaced. The electronic processing unit 6 is connected to the first probe 20 and to the reference probe 5. The electronic processing unit 6 thus receives distance data of the area of the continuous surface 51 measured by the first proximity probe 20 and reference phase data based on the rotations of the rotor 50. The electronic processing unit 6 is configured to carry out a selective sampling of the distance data on the basis of said reference phase data.

According to one embodiment, the processing unit 6 further comprises at least a processor and a memory, and performs the following steps:

A) stores on its memory the distance data of the area of continuous surface 51 provided by the probe 20 and the reference phase data provided by the reference probe 5;

B) carries out a selective sampling of the distance data of the area of continuous surface 51 stored on the basis of the reference phase data; C) deternnines displacement information of at least a predetermined area of the surface 51 on the basis of the selective sampling occurred at the previous step B).

In one embodiment, the probe 20 acquires distance data of the continuous surface 51 according to his frequency of functioning. Such frequency of functioning is related to a certain rotation of the rotor 50, namely the probe 20 acquires distance data of the continuous surface 51 each certain number degrees of rotation of the rotor 50. For example the frequency of functioning of the probe 20 may occur for each 2 degrees of rotation of the rotor 50. Thus the distance data of the surface 51 provided by the probe 20 and stored on the memory of the processing unit 6 are in form of a plurality of samples each referring to a corresponding area on the surface 51 . However only one predetermined area among the ones that define the continuous surface 51 is analyzed during various rotations of the surface 51 itself. Thus only samples referring to that predetermined area has to be considered. In case of more than one area analyzed during various rotations of the surface 51 , only the groups of samples, each of one referring to a predetermine area, has to be considered. The "predetermined area" is a subarea of the continuous surface 51 to analyze (in terms of displacement information) during rotations of the surface 51 itself. As will be clearer afterwards, typically is interesting analyze more than one predetermined area on the surface 51 .

The selective sampling, on the basis of the reference phase data, allows to consider only those samples referring to the predetermined area(s). Such selective sampling then obtains displacement information of said predetermined area(s).

According to one embodiment, displacement information comprise the plurality of the distance data of the predetermined area for each rotation of the rotor 50. According to another embodiment, on the basis of the displacement information are determined alternate deformation information of the continuous surface 51 .

In one embodiment, alternate deformation information of the continuous surface 51 are obtained on the basis of a combination of the displacement information of the predetermined area(s).

Thus the operating flow is the following: obtain displacement data of the area of the surface 51 through the probe 20; obtain displacement information of a predetermined area of the surface 51 through the selective sampling; obtain alternate deformation information through a post processing of the displacement information.

As said, the reference phase data allows to distinguish each rotation of the continuous surface 51 .

In one embodiment, the probe 20 and the reference probe 5 are synchronized in an initial configuration step, so that the distance data may be associated to the right rotation of the continuous surface 51 . The probe 20 thus repeatedly provides distance data of the area of the surface 51 and the angle at which the respective distance data has been acquired. In one embodiment, the probe 20 provides distance data between a first acquisition and a second next acquisition after an angle according his resolution of acquisition.

Thus distance data refers to each rotation of the continuous surface 51 by means of reference phase data provided by the reference probe 5, and to the angle at which each of the distance data is provided. For example, let's consider an alternate deformation analysis of rotor through an embodiment of an apparatus for displacement measuring. Such rotor with a continuous surface rotating at 18Ό00 rpm for which only one predetermined area is of interest. As an hypothesis, such analysis is conducted for 2 minutes. The probe 20 of this example acquires distance data of the continuous surface every 2 degrees of rotation of the rotor. During a complete rotation of 360 degrees, the probe 20 will provide 180 distance data, that are referred to the complete rotation occurred by reference phase data of the reference probe 5. Only 1 of these 180 samples refers to the predetermined area, that will be considered by means of the selective sampling.

During the analysis time, the rotor 50 performs 36Ό00 rotations, thus the overall numbers of samples which constitute the distance data are 6'480'000. The selective sample extracts for each rotation one sample among the 180, thus the displacement information in view of the selective sampling will be an array of 36Ό00 samples, each of one referring to displacement data of the predetermined area at a certain rotation of the rotor. Analyzing and combining such 36Ό00 samples, the alternate deformation information are obtained.

According to one embodiment the electronic processing unit 6 comprises a computer readable medium having computer executable instructions adapted to perform such selective sampling.

Figures 2 and 3 show one embodiment of an apparatus, with focus on the area each time detected by the proximity probe 20, and for which repeatedly provide distance data. In figure 2, the rotor 50 is still. In this condition the probe 20 thus "sees" (namely, provide distance data of) the area 1 1 of the continuous surface 51 . The area 1 1 "seen" by the probe 20 is determined by the features of the probe 20 itself and the distance from the surface 51 at which is installed. As shown in figure 3, the rotor 50 rotates around his axis and according to the direction ω. The probe 20 thus provides distance data of the area of the continuous surface 50. According to one embodiment, the probe 20 provides distance data of a plurality of subareas 1 1 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24, 25, 26 of the area of the surface 51 . These subareas are a plurality of little areas for which the probe 20 repeatedly provide distance data due to the fact that the probe 20 works intermittently with a frequency of functioning. According to different embodiments, the number of subareas may be increased and in one case may coincide with area of the surface 51 itself.

The number of subareas (and their extension) depends on the features of the probe 20 and in particular from his frequency of functioning, from the activation frequency imposed (by the electronic processing unit 6) and the distance from the surface 51 at which is installed. Such number must match with the number of predetermined areas, even if in most cases the number of subareas is greater than the number of the predetermined area.

As shown in Figure 4, according to one embodiment the apparatus comprises a second proximity probe 21 facing the continuous surface 51 . Such second probe is adapted to repeatedly provide distance data of the area 1 1 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24, 25, 26 of the continuous surface 51 during rotation of the rotor 50. The second probe is adapted to repeatedly provide distance data of the continuous surface 51 measured each time by the second proximity probe 21 itself during rotation of the rotor 50.

Typically, distance data of the area 1 1 , 26 - provided by the second proximity probe 21 - are measured repeatedly by the second proximity probe 20 itself during rotation of the rotor 50. In other words, during rotation of the rotor 50 the second proximity probe 21 measures repeatedly the distance from the continuous surface 51 and each time provides distance data accordingly. In other embodiments, the measurements and distance data may be related in different fashions.

As shown, the electronic processing unit 6 is further connected to the second proximity probe 21 . According to one embodiment, the selective sampling carried out by the electronic processing unit 6 is programmed to obtain displacement information of the predetermined sector for which distance data are provided by the first probe 20 and by the second probe 21 . The angular position of a predetermined area during rotation of the rotor influences the displacement of the predetermined area itself.

For example, for a predetermined area is important to know his displacement information when - during a rotation - is at 15° and at 75° with respect of a common reference. This allows to establish, in view of further processing of displacement information, alternate deformations of the surface 51 .

According to one embodiment the second probe 21 is installed with a certain angle with respect to the first probe 20 (this angle evaluated in projection on the surface 21 ). This configuration allows to determine displacement information of the predetermined area in different condition of the rotor 50.

According to one embodiment the electronic processing unit 6 samples first distance data provided by the first probe 20 and second distance data provided by the second probe 21 .

Thus, according to one embodiment, such processing unit 6 obtains displacement information on the basis of first and second distance data. For a certain rotation, such displacement information refers to displacement information of the predetermined area at a particular first relative angular position and displacement information of the same predetermined area at a particular second relative angular position. For example, at a certain rotation, first distance data of the predetermined area are provided by the first probe 20 at 20° and second distance data of the same predetermined area are provided by the second probe at 100°. The electronic processing unit 6, on the basis of reference phase data provided by the reference probe 5, selective samples first distance data obtaining first displacement information and second distance data obtaining second displacement information. Such first and second displacement information can then be combined, for example to obtain the trend of displacement of that area in function of his relative angular position. As shown in figure 5, according to one embodiment the apparatus comprises a third proximity probe 22 facing the continuous surface 51 . Such third probe is adapted to repeatedly provide distance data of the area 1 1 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24, 25, 26 of the continuous surface 51. The third probe is adapted to repeatedly provide distance data of the continuous surface 51 measured each time by the third proximity probe 22 itself during rotation of the rotor 50.

Typically, distance data of the area 1 1 , 26 - provided by the third proximity probe 22 - are measured repeatedly by the third proximity probe 22 itself during rotation of the rotor 50. In other words, during rotation of the rotor 50 the third proximity probe 22 measures repeatedly the distance from the continuous surface 51 and each time provides distance data accordingly. In other embodiments, the measurements and distance data may be related in different fashions. As shown, the electronic processing unit 6 is further connected to the third probe 22.

According to one embodiment, the selective sampling carried out by the electronic processing unit 6 is programmed to obtain displacement information of the predetermined area for which distance data are provided by the first probe 20 and/or by the second probe 21 and/or by the third probe 22.

Two or three of the first probe 20, of the second probe 21 and of the third probe 22 are installed around a circumference.

In the embodiment shown in figure 6, the apparatus comprises three proximity probes (the first probe 20, the second probe 21 and of the third probe 22) installed around a circumference 30.

This configuration allows to obtain multiple displacement information obtained from distance information of one or more area(s) 1 1 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24, 25, 26 of the surface 51 . The reference probe 5 is not shown for clarity sake. Such reference probe 5 is intended to detect the reference 10, thus his angular displacement with respect to the other probes is to be known for correct sample the distance data furnished by the probes 20, 21 and 22. According to one embodiment, the first 20, second 21 and third 22 proximity probes are installed on the circumference 30 according to predetermined spacing angles ε, λ between them. In particular, the first probe 20 is spaced of an angle ε with respect to the second probe 21 . The second probe 21 is in turn spaced of an angle λ with respect to the third probe 22. All the three probes 20, 21 and 22 are spaced of a fixed angle (not shown in figure) with respect to reference probe 5.

Figures from 7A to 10B show an embodiment of an apparatus comprising a first proximity probe 20 and a second proximity probe 21 and in which a displacement measuring is conducted. The displacement measuring in the embodiment is aimed to detect displacement of one the predetermined area with the reference number 12, (represented with a dashed line) even if a plurality of predetermined areas are shown, that won't be considered to the end of the example.

In figure 7A the rotor 50 is in a first initial position, corresponding to the begin of measurement test. In figure 8B the rotor 50 in a measurement position in which the area 12 to be assessed is "under/seen by" the first probe 20.

Similarly, in figure 9A the rotor 50 is in a first initial position, corresponding to the begin of measurement test. In figure 10A the rotor 50 in a measurement position in which the area 12 to be assessed is "under/seen by" the second probe 21 .

As said, the reference probe 5, the first probe 20 and the second probe 21 are synchronized to properly measure displacement of the area of the surface 51 . For this embodiment is assumed that probes 20 and 21 have a resolution of measure of δ grades. In other words, each δ grades of rotation of the rotor 50 the corresponding probe provides the distance information of the respective area "seen". Furthermore, let assume that probe 20 is angularly spaced from the reference probe 5 of an angle β, and probe 21 is angularly spaced from the reference probe 5 of an angle γ.

In figure 7A, the focus is on the probe 20 and on the relative distance information provided.

Figure 7B shows a diagram of the samples comprising distance information provided by the first probe 20. As shown, the only sample is 16s1 , when the rotor 50 did not rotate yet, thus at an angle of 0 degrees.

The graph in figure shows the distance data on the Y-axis provided each δ degrees by the first probe 20. As said, the area of interest in this embodiment is the area 12. In figure 8A the displacement measuring goes on, in fact for further areas (15, 14, 13, 12) of the rotor 50 the corresponding distance measures are provided by the first probe 20. As shown on the graph in figure 8B, there are several samples (16s1 , 15s1 , 14s1 , 13s1 , 12s1 ) corresponding to areas of the continuous surface 51 of the rotor 50. From the samples provided by the first probe 20 the one of interest is that corresponding to the area 12. Such sample occurs at 45° corresponding to the angle β (angular distance from the reference probe 5 to the first probe 20) minus the angle a (angular distance from the reference notch 10 to the predetermined are 12). The angle β - a is the angle of rotation of the rotor 50 from the initial position (figure 7A) to the measuring position in which the area 12 is "under/seen by" the first probe 20 (figure 8A).

The selective sampling is programmed with the parameters of the spacing angle β between the reference probe 5 and the first probe 20 and the spacing angle between the reference 10 and the predetermined area of interest (in this case the area 12). The electronic processing unit 6 stores the sample 16s1 , 15s1 , 14s1 , 13s1 , 12s1 provided by the probe 20; eventually the selective sampling extracts the sample 12s1 as displacement information for the rotation under test of the predetermined area 12, such sample extracted when occurred at the angle β - a (as the selective sampling is programmed).

Figures from 9A to 10B represent the same measuring condition, but with focus on the second probe 21 . The graph in figure 9B shows that for the first 35°, no area of interest arrives under the second probe 21 . As shown in figure 10A, the distance data of the area 16 is the first one to be provided by the probe 21 after 45° of rotation of the rotor 50. As shown in figures 10A and 10B, the distance data of the area 12 (sample 12s2) are instead provided by the second probe 21 after 85° of rotation of the rotor 50, corresponding to the angle γ - a of rotation of the rotor from his initial position (figure 9A) from the measuring position in which the area 12 is under/seen by the probe 21 (figure 10A).

Figure 1 1 shows an embodiment of a data structure adapted to store distance data and the sample such data to obtain displacement information. Each of the samples (12s1 , 13s1 , 14s1 , 15s1 , 16s1 ; 16s2, 15s2, 14s2, 13s2, 12s2, referring to figure 7A to 9B) are A) stored in a memory of the electronic processing unit; B) associated to the number of the rotation of the rotor 50 (for example the 2189^th rotation) and C) associated to the probe providing such measure. According to one embodiment, for each rotation the first probe 20 and the second probe 21 work in parallel. First and second distance data respectively provided are then stored (for example in a memory of the electronic processing unit 6).

The first detection of the reference phase data indicates that a rotation is began; the record ref-b in figure 9 refers to this detection, in fact is the first stored in the embodiment of the data structure shown. After the first detection, a plurality of displacement data 72 are provided by one or more probes. Such displacement data 72 are stored after record ref-b. A second detection of the reference phase data indicates that the rotation has ended, the record ref-e refers to this detection, in fact is the last stored in the embodiment of the data structure shown. Thus, all the records of the distance data 72 between the records 71 (records 71 are the first and second detection of the reference phase, namely ref-b and ref-e) refer to one rotation of the rotor 52. According to one embodiment, distance data 72 may furnish the value of the distance V and indication of the probe # that provided such value.

The electronic processing unit 6 will then select the sample S among the displacement data 72 corresponding to the predetermined area of interest . In on embodiment, the electronic processing unit 6 will select one record S from the records 72.

Figure 12 shows an embodiment of samples provided by one proximity probe after two rotations of the rotor 50 (and thus of the continuous surface 51 ) of three predetermined areas.

The rotations of the rotor are determined by the reference phase data 71 a, 71 b and 71 c. The first reference phase data 71 a is detected when the first rotation begins. The probe provide a plurality of samples, but only some of these refer to the three predetermined areas of interest. In particular, for the first rotation the sample provided by the first probe referring to the first predetermined area is the 73a; the sample provided by the probe referring to the second predetermined area is the 73b and the sample provided by the probe referring to the third predetermined is the 73c. According to one embodiment, displacement information sampled from displacement data provided by the probe referring to the first area are stored on a first displacement information array 76; displacement information sampled from displacement data provided by the probe referring to the second area are stored on a second displacement information array 77 and displacement information sampled from displacement data provided by the probe referring to the third area are stored on a third displacement information array 78. According to one embodiment, the displacement data not sampled (thus not referring to the first, second or third area) are discarded. When the first rotation ends, and the second begins, a second reference phase data 71 b is detected, and the same actions of the first rotation occur. Displacement information 73a and 73b form the first displacement information array 76. The record 73a comprises displacement data of the first predetermined area at the first rotation of the rotor 50, the record 73b comprises displacement data of the first predetermined area at the second rotation of the rotor 50. Displacement information 74a and 74b form the second displacement information array 77. The record 74a comprises displacement data of the second predetermined area at the second rotation of the rotor 50, the record 74b comprises displacement data of the second predetermined area at the second rotation of the rotor 50.

Displacement information 75a and 75b form the third displacement information array 78. The record 75a comprises displacement data of the third predetermined area at the second rotation of the rotor 50, the record 75b comprises displacement data of the third predetermined area at the second rotation of the rotor 50.

According to another embodiment, processing unit 6 is configured to convert said displacement information according to a predetermined formula. In particular, the displacement information are converted in a time of arrival information adapted to be given as input of a so-called "Tip Timing" software to carry out further modal vibrational analysis.

According to another embodiment is a method for determining displacement of a continuous surface of a rotating rotor; wherein is provided: a first proximity probe facing said continuous surface, and adapted to provide distance data of the area of said continuous surface during rotation of the rotor; a reference probe adapted to detect a reference on said continuous surface and to provide reference phase data based on the rotations of the rotor; the method comprising the following steps: A) acquire distance data of the area of said continuous surface by mean of said first proximity probe;

B) acquire reference phase data based on the rotations of the rotor by mean of said reference probe; C) sample said distance data, on the basis of said reference phase data, to obtain displacement information of a predetermined area (14) of said continuous surface during rotation.

The first proximity probe repeatedly provide distance of the area of said continuous surface measured each time by said first proximity probe during rotation of the rotor.

According to another embodiment is a system for determining alternate deformations in a rotary machine, in particular a multi stage centrifugal compressor, adapted to monitor and signal alternate deformations of at least one impeller, such system comprising an apparatus for determining displacement as described. In case of more than one impeller, an embodiment of an apparatus for each impeller may be provided; in another embodiment may be provided a set of probes (reference probe and one or more proximity probes) for each impeller and a shared electronic processing unit 6 between the sets of probes. The system thus provide alternate deformations information of the impeller(s) on the basis of displacement information provided by the apparatus. Such alternate deformations information may be processed to obtain status information of the impeller(s).

Claims

CLAIMS:

1 . Apparatus, for determining displacement of a continuous surface (51 ) of a rotating rotor (50), comprising:

- at least a first proximity probe (20) facing said continuous surface (51 ), and adapted to repeatedly provide distance data of the area (1 1 , 26) of said continuous surface during rotation of the rotor (50),

- a reference probe (5) adapted to detect a reference (10) on said rotor 50 and to provide reference phase data based on the rotations of the rotor (50),

- an electronic processing unit (6) connected to said proximity probe (20) and to said reference probe (5), and configured to carry out a selective sampling of said distance data on the basis of said reference phase data; wherein said selective sampling is programmed to obtain displacement information of at least a predetermined area (12) of said continuous surface (51 ) during rotation.

2. Apparatus according to claim 1 comprising a second proximity probe (21 ) facing said continuous surface (51 ), and adapted to repeatedly provide distance data of the area (1 1 , 26) of said continuous surface (51 ) during rotation of the rotor (50), wherein said electronic processing unit (6) is further connected to said second proximity probe (21 ) and wherein said selective sampling is programmed to obtain displacement information of at least said predetermined sector (12) from distance data provided by said first probe (20) and distance data provided by said second probe (21 ).

3. Apparatus according to claim 2 comprising a third proximity probe (22) facing said continuous surface (51 ), and adapted to repeatedly provide distance data of the area (1 1 , 26) of said continuous surface (51 ) during rotation of the rotor (50), and wherein said electronic processing unit (6) is further connected to said third proximity probe (22) and wherein said selective sampling is programmed to obtain displacement information of at least said predetermined sector (12) from distance data provided by said first probe (20), distance data provided by said second probe (21 ) and distance data provided by said third probe (22).

4. Apparatus according to any of the preceding claims wherein said selective sampling is programmed to obtain displacement information of a plurality of predetermined areas (12, 14, 15) from distance data provided by said first probe (20) and/or distance data provided by said second probe (21 ) and/or distance data provided by said third probe (22).

5. Apparatus according to any of the preceding claims wherein two or three of said first (20), second (21 ) and third (22) proximity probes are installed around a circumference (30).

6. Apparatus according to any of the preceding claims wherein said first (20) and/or second (21 ) and/or third (22) proximity probes and/or said reference probe (5) are installed according to predetermined spacing angles (ε, λ) between them.

7. Apparatus according to claim 6 wherein said selective sampling is further carried out on the basis of said spacing angles (ε, λ).

8. Apparatus according to any of the preceding claims wherein said processing unit (6) further comprises at least one processor and at least one memory, wherein said processor is configured to process said distance data provided by said first (20) and/or second (21 ) and/or third (22) proximity probes to obtain displacement information of said continuous surface (51 ) and said memory is configured to store said displacement information.

9. Apparatus according to claim 10 wherein said processing unit (6) is configured to convert said displacement information into time of arrival information according to a predetermined formula.

10. Apparatus according to any of the preceding claims wherein the proximity probe/s (20, 21 , 22) is/are arranged substantially parallel to the rotational axis of the rotating rotor (50).

1 1 . Apparatus according to any of the preceding claims wherein the continuous surface (51 ) of a rotating rotor (50) is transversal with respect to the rotational axis of the rotating rotor (50).

12. Method for determining displacement of a continuous surface of a rotating rotor, wherein there is provided: a first proximity probe facing said continuous surface, and adapted to repeatedly provide distance data of the area of said continuous surface during rotation of the rotor; a reference probe adapted to detect a reference on said continuous surface and to provide reference phase data based on the rotations of the rotor; the method comprising the following steps:

A) acquiring distance data of the area of said continuous surface by means of said first proximity probe;

B) acquiring reference phase data based on the rotations of the rotor by means of said reference probe;

C) sampling said distance data, on the basis of said reference phase data, to obtain displacement information of a predetermined area (14) of said continuous surface during rotation.

13. Method for determining displacement of a continuous surface of a rotating rotor according to claim 12, further comprising an initial configuration step in which the proximity probe (20) and the reference probe (5) are synchronized for associating the distance data to the rotation of the continuous surface (51 ).

14. System for determining alternate deformations in a rotary machine, in particular a multistage centrifugal compressor, adapted to monitor and signal alternate deformations of at least one impeller of the rotary machine, the system comprising an apparatus for determining displacement according to any of the claims from 1 to 1 1 .