WO1998025123A2

WO1998025123A2 - Sealless pump rotor position and bearing monitor

Info

Publication number: WO1998025123A2
Application number: PCT/US1997/022121
Authority: WO
Inventors: Palmer H. Beam; David J. Belanger; George J. Eilers; Joseph Imlach
Original assignee: Sundstrand Corp; Sundyne LLC
Current assignee: Sundstrand Corp; Sundyne LLC
Priority date: 1996-12-05
Filing date: 1997-12-05
Publication date: 1998-06-11
Anticipated expiration: 1999-06-05
Also published as: CA2273888A1; US5955880A; CA2273888C; WO1998025123A3; EP0943082B1; JP2001505310A; EP0943082A2

Abstract

A bearing monitor for use with a canned motor pump having a wound stator and a rotor drivably coupled to an impeller, the rotor being mounted on radial journal bearings and axial thrust bearings within a containment can comprises a first and a second target embedded in an outer periphery of the rotor in axial proximity to a first and a second end of the rotor. The monitor includes a plurality of sensors mounted external to the containment can in axial proximity to each of the two targets and radially displaced approximately equally around the periphery of the containment can. A plurality of magnetic field generators create local magnetic fields coupled through the containment can, process fluid, rotor, and at least a portion of one target to one of the sensors. In response to each field, each sensor generates an output signal which varies as a result in a change in the magnetic circuit reluctance caused by bearing wear. A monitor circuit is coupled to the sensors and compares their output signals to generate a scaled output which is approximately linearly related to bearing wear. The output of sensors in the same axial plane are utilized to determine bearing wear in a radial direction, while the output of sensors in different axial planes are utilized to determine bearing wear in an axial direction. Electromagnetic shielding may be used depending on the environmental and operating conditions.

Description

SEALLESS PUMP ROTOR POSITION AND BEARING MONITOR

Field of the Invention

The instant invention relates generally to rotor position and bearing wear monitors, and

more particularly to rotor position and bearing wear monitors utilizing inductive coil sensors capable of detecting axial and radial bearing wear for sealless motor pumps.

Background Art

Process industries today are faced with increasingly stringent environmental regulations with regard to fluid leakage and containment of process fluids. At the same time, demands for increased productivity require higher reliability equipment to minimize down time. In an effort to meet both of these challenges, many in the process industry have moved from a conventional

centrifugal motor/pump configuration to sealless motor/pumps. This movement is precipitated in

part due to the problem of wear of the mechanical seals required by the conventional centrifugal

motor/pumps. This seal wear may result in increased leakage rates of the process fluid or massive

failure.

A canned motor/pump assures total fluid containment by eliminating any moving part extending through the primary containment or can, therefore eliminating the seal wear/leakage problem of the conventional centrifugal motor/pumps. The canned motor/pump, as its name implies, comprises a sealed housing (primary containment) or can into which is placed the rotor portion of the drive motor. The rotor shaft is coupled to and drives the pump impeller at the

pump end of the machine. The can is open to the pump end of the machine, and hence process

fluid is allowed to circulate through the can and around the rotor. The rotor is supported within

this can by its shaft on radial journal and axial thrust bearings which are lubricated by the circulating process fluid within the can.

While sealless pumps solve the seal wear/leakage problems of conventional motor/pumps, they are susceptible to catastrophic failure This catastrophic failure is most often the result of

excessive bearing wear, dry run, or high vibration As stated above, a typical sealless or canned

motor pump has its motor rotor supported on radial journal and axial thrust bearings lubricated with process fluid These bearings are made of a relatively soft carbon or wear resistant ceramic

material Lubrication is marginal for most operating conditions due to the nature of the process

fluid and flow paths within the can Two key factors that impact carbon bearings wear are abrasives in the fluid and intermittent dry operation If the bearings wear beyond a prescribed limit, contact can occur between the rotor and stator causing severe damage to the pump On the other hand, motors with ceramics bearings can fail due to dry operation which results in thermal shock and sudden failure of the brittle bearing material Excessive shaft vibration due to rotor

imbalance or bearing instability can also result in accelerated bearing wear Incorrect direction of

rotation results in reduced pump performance and potential bearing failure due to lack of cooling or lubricating fluid flow

Since the bearings in a canned motor pump are contained within the sealed can, visual

inspection for excessive wear is impossible without shutting down the pump and dismantling the

machine An external mechanical bearing wear monitoring device, such as shown in United States Patent No 3,991,701, entitled Bearing Wear Detecting Device for Canned Motor Driven Pumps, issued to Sato, has been used to warn of impending failure in a canned motor pump This device, however, detects only when the bearings have worn approximately two-thirds of the allowable

wear The wear detector of the Sato '701 patent does not indicate progressive wear or, which

bearing is being worn Indication of wear of the bearing on the shaft end opposite the bearing

wear monitor is not always reliable It also cannot indicate dry run operation excessive vibration or reverse rotation which are also causes of bearing failure Additionally, once this type of device activates, it must be replaced These features are no longer acceptable to customers in the industry

In recognition of the problems and dissatisfaction associated with such devices, electronic

bearing monitoring devices which allow the detection and indication of progressive bearing wear

began to be utilized by canned pump manufacturers One such device is shown in British Patent No 1,480,848 issued to Considine, for Improvements in or Relating to Bearing Wear Detection

Devices, on October 8, 1973 The Considine '848 device utilizes a single electronic coil positioned completely around a bobbin which is drivably coupled to the motor shaft of a canned motor pump The bobbin is mounted within an outer housing which is mounted on the end of the housing for the canned motor pump The bobbin contains permanent magnets, and any eccentricity in rotation will induce an emf in the coil This emf signal is passed through an

aperture in the can, which is filled with encapsulating resin after final assembly, to a detection

circuit

While this device allows for detection of progressive bearing wear, it does so only for

bearing wear in a radial direction on one end Disadvantageously, axial bearing wear is not

detected by the eccentric rotation of the bobbin Additionally, the addition of an outer housing on

the end of the canned motor pump is disadvantageous The end where the bobbin is to be mounted is normally closed as part of the containment can for the motor pump The addition of the outer housing requires the addition of a gasket to seal the junction between the containment can and the outer housing This introduces one more point of possible leakage for the sealless motor pump Additionally, in many processing plant operations, the installation envelope of a

canned motor pump is limited, and the addition of the bobbin's outer housing increases the overall

length of the machine One manufacturer of canned motor pumps, Teikoku U.S.A., Inc., also utilizes electronic

monitoring devices known as the Teikoku Rotary Guardian (TRG). One aspect of the TRG Monitor is disclosed by United States Patent No. 4,211,973, for an Apparatus for Detecting

Faults to be Occurred or Initially Existing in a Running Electric Rotary Machine, issued to Sato et

al., on July 8, 1980. This electronic monitoring device detects eccentric rotation of the rotor due to radial bearing wear. It comprises two coils specially located within the stator slots of the main stator and coupled in series. Energization of the main stator windings provides the magnetic flux which is utilized by the detector windings. The coils are coupled in series to cancel the

fundamental component of the stator energization and to allow detection of eccentric rotation.

Unfortunately, this detection circuitry cannot detect bearing wear in a thrust or axial direction.

Additionally, it cannot be used with a conventional canned motor pump configuration, but requires that the fundamental structure of the motor must be adapted to allow cooperation with

the detector coils. This greatly limits its ability to be added as a retrofit to existing canned motor

pumps already in operation in the process industry.

The other patent referenced by advertisements for TRG is United States Patent No. 4,334,189, for Operation Supervisory Apparatus, issued to Sato, on June 8, 1982. This patent discloses a similar bearing wear detector utilizing two coils interposed in the stator slots as

disclosed in the Sato et al. '973 patent. In addition to the bearing wear monitor, this reference

additionally adds a direction of rotation monitor of conventional design, and a combining circuit

to output the larger of the two monitor's outputs. As with the '973 reference, however, the

bearing monitor only monitors wear in a radial direction. No monitoring is provided for bearing

wear in an axial or thrust direction. Additionally, the ability to easily retrofit existing canned

motor pumps to incorporate these detectors is greatly reduced due to the location of the monitor

coils (within the stator slots), and due to the requirement of a specific rotor/stator structure to allow cooperation of the detector coils.

In recognition of the deficiencies of the foregoing references in failing to provide indication of bearing wear in both an axial and a radial direction, bearing monitors which were

capable of detecting both directions of wear were developed. One such bearing wear monitor is

disclosed in United States Patent No. 5,189,763, issued to Konishi, for an Apparatus for

Monitoring the Axial and Radial Wear on a Bearing of a Rotary Shaft, on March 30, 1993. This

monitoring device utilizes a single contactless distance sensor and an axial groove or ridge and a

helicial groove or ridge. Alternatively, Konishi '763 discloses that other devices such as a light source and a photo sensor may be used in a similar manner. The grooves or ridges are formed on a rotor shaft end nut, and the distance sensor is placed in close proximity to the end nut, within the containment can. While this device provides both axial and radial bearing wear indication, it still requires that the containment can be penetrated by a probe containing the distance sensor and

electrical leads. While this probe is not in motion, sealing and potential leaks are still a problem.

It is a primary objective of the instant invention, therefore, to solve the aforementioned problems by providing accurate and continuous monitoring of progressive radial and axial rotor

position and progressive bearing wear when the shaft is moving eccentrically or concentrically,

measurement of excessive rotor vibration, and detection of incorrect direction of rotation without

penetrating the containment can of a canned motor pump, and without requiring a change in the fundamental structure of the rotor and stator of a canned motor pump. It is also an objective of the instant invention to provide data on demand for the purpose of diagnostic or trend analysis to aid users in the process industry in planning maintenance activity.

It is a further objective of the instant invention to sense and display the progressive axial

bearing wear in both directions along the axis of rotation. It is an added objective to indicate in

which of these two directions axial wear is actually occurring. It is a still further objective of the instant invention to sense and display progressive radial bearing wear for each end of the rotor shaft. It is a further objective of the instant invention to provide a non-invasive means to sense both progressive bearing wear in both directions of axial wear and radial wear on both ends of the

rotor shaft simultaneously. It is additionally an objective of the instant invention to provide a

means for sensing this type of bearing wear which is easily retrofitable on existing motor pumps currently being utilized in the process industry. It is also an objective of the instant invention to

provide an effective means of sensing this bearing wear in an extremely electromagnetically noisy

environment. It is also an objective of the instant invention to provide a sensor means that is low cost to manufacture.

Summary of the Invention

The instant invention provides a bearing wear monitor for use with a sealless motor pump

having a wound stator and a rotor drivably coupled to an impeller. The rotor of this sealless motor pump is typically mounted on radial journal bearings and axial thrust bearings within a

containment can. This rotor as well as the bearings are exposed to the process fluid which is

being pumped by the sealless motor pump. The wound stator, on the other hand, is mounted

external to the containment can and isolated from the process fluid. A preferred embodiment of

this bearing wear monitor comprises a target which is embedded in an outer periphery of the rotor in axial proximity to a first end of the rotor. This target is magnetic, and preferably has a different magnetic permeability than the adjacent rotor material, such as for example aluminum end rings. The monitor further comprises a first and a second sensor mounted external to the containment

can. These two sensors are positioned in axial proximity to the target, and are radially displaced

approximately equally around the periphery of the containment can. The instant invention further

includes a magnetic field generating means, such as a coil energized by a high frequency source, operatively coupled to the two sensors. The magnetic field generators produce a first and a

second local magnetic field, each being coupled through the containment can, process fluid, rotor,

and at least a portion of the target to each of the sensors. The sensors, in turn, each generate an

output signal in response to its respective magnetic field. A monitor circuit is also included in the instant invention. This circuit is coupled to each of the sensors, and compares their output signals. The monitor circuit generates a scaled output in response to a difference between these two signals which is approximately linearly related to bearing wear in a radial direction on the first end of the rotor.

To monitor the bearing wear on the other end of the rotor, the instant invention includes a second target embedded in an outer periphery of the rotor in axial proximity to the second end of the rotor. As with the first target, this second target is magnetic, and preferably has a different

magnetic permeability than the adjacent rotor material, such as for example the aluminum end

rings. A third and a fourth sensor are then mounted external to the containment can and

positioned in axial proximity to this target, and are radially displaced approximately equally around the periphery of the containment can. On this second end, the instant invention includes a magnetic field generating means, such as a coil energized by a high frequency source, operatively coupled to the two sensors. The magnetic field generators each produce a local magnetic field which is coupled through the containment can, process fluid, rotor, and at least a portion of the

target to each of these sensors. The sensors, in turn, each generate an output signal in response

to its respective magnetic field. The monitor circuit is also coupled to each of these sensors, and

compares their output signals. The monitor circuit generates a scaled output in response to a

difference between these two signals which is approximately linearly related to bearing wear in a

radial direction on the second end of the rotor. Additional sensors may be added orthogonal to

the other sets, and in a like manner monitor radial bearing wear along a second axis. Bearing wear in an axial direction may also be monitored by the instant invention. This is

accomplished by comparing the sensor output from sensors in two different axial planes.

Additional sensors may be added to accomplish this function, or the outputs from the existing

sensors may be combined and differentially compared to determine the axial bearing wear. In a

preferred embodiment, two sensors are mounted external to the containment can in an axial plane displaced from the first and second sensors described above. The two new sensors are radially displaced approximately equally around the periphery of the containment can, and radially aligned with the first and second sensors. The magnetic field generators are also operably coupled to these two new sensors for generating a two new local magnetic fields. The two new sensors each

generate an output signal in response to the magnetic fields as described above. The monitor circuit is also coupled to these sensors, and differentially combines their output signals to form a

first axial output signal (indicating radial displacement with axial sensitivity in a first axial plane). The monitor circuit further differentially combines the output signal from the first sensor with the

output signal from the second sensor to form a second axial output signal (indicating radial displacement with axial sensitivity in a second axial plane). The monitor circuit generates a scaled output in response to a difference between the first and second axial output signals which is approximately linearly related to bearing wear in an axial direction.

Brief Description of the Drawings

While the specification concludes with claims particularly pointing out and distinctly

claiming that which is regarded as the present invention, the organization, the advantages, and

further objects of the invention may be readily ascertained by one skilled in the art from the

following detailed description when read in conjunction with the accompanying drawings in

which: FIG. 1 is a simplified block diagram of the bearing wear monitor system of the instant invention;

FIG. 2 is a cross sectional illustration of a sealless motor pump, specifically a sealless canned motor pump, constructed in accordance with an embodiment of the instant invention;

FIG. 3 is a simplified end view of the canned motor pump of FIG. 2 illustrating the placement of bearing wear monitor sensors and their generation of local magnetic fields;

FIG. 4a is a top view of a pole piece utilized in an embodiment of the instant invention with the bearing wear monitor sensors;

FIG. 4b is a front view of a pole piece utilized in an embodiment of the instant invention with the bearing wear monitor sensors;

FIG. 4c is a side view of a pole piece utilized in an embodiment of the instant invention with the bearing wear monitor sensors;

FIG. 5 illustrates a coil mounting ring which is an alternated embodiment of the mounting pole piece of FIGs. 4;

FIG. 6a is external view simplified block diagram of the bearing wear monitor sensor placement of an embodiment of the instant invention;

FIG. 6b is external view simplified block diagram of the bearing wear monitor sensor

placement of an alternate embodiment of the instant invention;

FIG. 6c is external view simplified block diagram of the bearing wear monitor sensor

placement of an alternate embodiment of the instant invention;

FIG. 6d is external view simplified block diagram of the bearing wear monitor sensor

placement of an alternate embodiment of the instant invention;

FIG. 7 is a single line interconnect sensor wiring diagram of the embodiment of the instant

invention illustrated in FIG. 6a; FIG. 8 is a graphical representation of the output frequency spectrum of the bearing wear monitor sensors of the instant invention;

FIG. 9a is a graphical illustration of the bearing wear monitor sensor outputs from the radial sensors utilized to calculate axial displacement with a radial displacement of 20 mils up from radial center of the embodiment of FIG. 6d;

FIG. 9b is a graphical illustration of the combined bearing wear monitor sensor outputs

from the radial sensors of FIG. 9a indicating axial displacement with a radial displacement of 20

mils up from radial center;

FIG. 10a is a graphical illustration of the bearing wear monitor sensor outputs from the

radial sensors utilized to calculate axial displacement with a radial displacement of 10 mils up from radial center of the embodiment of FIG. 6d;

FIG. 10b is a graphical illustration of the combined bearing wear monitor sensor outputs from the radial sensors of FIG. 10a indicating axial displacement with a radial displacement of 10 mils up from radial center;

FIG. 1 la is a graphical illustration of the bearing wear monitor sensor outputs from the

radial sensors utilized to calculate axial displacement with no radial displacement from radial

center of the embodiment of FIG. 6d;

FIG. 1 lb is a graphical illustration of the combined bearing wear monitor sensor outputs

from the radial sensors of FIG. 1 la indicating axial displacement with no radial displacement from

radial center;

FIG. 12a is a graphical illustration of the bearing wear monitor sensor outputs from the radial sensors utilized to calculate axial displacement with a radial displacement of 10 mils down

from radial center of the embodiment of FIG. 6d;

FIG. 12b is a graphical illustration of the combined bearing wear monitor sensor outputs from the radial sensors of FIG. 12a indicating axial displacement with a radial displacement of 10 mils down from radial center;

FIG. 13a is a graphical illustration of the bearing wear monitor sensor outputs from the radial sensors utilized to calculate axial displacement with a radial displacement of 20 mils down from radial center of the embodiment of FIG. 6d;

FIG. 13b is a graphical illustration of the combined bearing wear monitor sensor outputs

from the radial sensors of FIG. 13a indicating axial displacement with a radial displacement of 20 mils down from radial center;

FIG. 14 is a cross sectional view of a rotor target configuration and sensor placement in accordance with an embodiment of the instant invention;

FIG. 15 is a cross sectional view of a rotor target configuration and sensor placement in accordance with an embodiment of the instant invention;

FIG. 16 is a cross sectional view of a rotor target configuration and sensor placement in accordance with an embodiment of the instant invention;

FIG. 17 is a cross sectional view of an embodiment of the instant invention utilizing a

conical electromagnetic shield in accordance with an embodiment of the instant invention;

FIG. 18 is a cross sectional view of an embodiment of the instant invention utilizing a flat

plate electromagnetic shield in accordance with an embodiment of the instant invention;

FIG. 19 is a pictorial illustration of the bearing wear monitor output display in accordance

with an embodiment of the instant invention; and

FIG. 20 is a pictorial illustration of the bearing wear monitor output display in accordance with an alternate embodiment of the instant invention. Description of the Preferred Embodiments

As illustrated in the simplified block diagram of FIG 1, inductive sensors 104 are provided on the motor 100 which is powered by a power supply, preferably a three phase power supply 102, to sense internal bearing wear The inductive sensors 104 are excited at a frequency

sufficiently high enough to avoid interference from the motor excitation frequency In a preferred

embodiment, the excitation circuitry 106 excites at a frequency in the range of 1 kHz to 4 kHz

This circuitry 106 is powered from a power supply 108 which may be internal to the motor 100 or the controller 108 The output of the inductive sensors 104 is input through an amplifier/filter 110 to a synchronous detector 112 The synchronous detector 112 is also fed the excitation

frequency from the excitation circuitry 106 The output of the synchronous detector 112 is output to an analog to digital converter 114 which outputs the converted signal to the microprocessor 116 for processing The controller 108 includes memory circuitry 118 and a communications interface as illustrated by the RS 485 circuitry 120, although other

communication means may be used as appropriate or desired The controller 108 outputs

information to a display 122 for maintenance or other personnel to observe, and controls a relay

124 which may, for example, de-energize the motor 100 in the event of a sensed failure

In a preferred embodiment of the instant invention, the direction of rotation is also

monitored by circuitry 126 known in the art which monitors the three phase power which drives

the motor This monitored direction of rotation is also fed to the microprocessor 116 which

outputs the information to the display 122 Additionally, at least one ultrasonic sensor 128 coupled through an ultrasonic circuit 130 to the microprocessor 116 may be provided to detect dry bearing operation of the motor The particulars of the ultrasonic sensor are disclosed in co-

pending application serial number , filed on and incorporated herein by reference.

A detailed partial cross section of the motor 100 of FIG. 1 is illustrated in FIG. 2. More particularly, FIG. 2 illustrates a detailed partial cross section of a specific application of the instant invention in a canned motor pump as described above. As may be seen, the pump impeller 132 is

driven by shaft 134 by rotor 136. The rotor is enclosed by a stator can 138 which provides a fluid

seal for the process fluid which is being pumped by the impeller 132 and which lubricates and cools the rotor 136 and its bearings 140. The stator can 138 is preferably made from a non¬

magnetic material with a relative high volume resistivity. The stator can 138 is surrounded by a non-magnetic back-up sleeve 142 which provides additional strength for the stator can 138 to

resist internal pressure. In this way, the windings 144 of the stator 146 are separated from the process fluid.

In a preferred embodiment of the instant invention, the bearing wear inductive sensors 104 are located near either end of the canned motor stator 146 beneath the stator windings 144 to

facilitate interchangeability with existing stators and rotors. The sensors 104 are attached to the

back-up sleeve 142 equidistant around the outer periphery along an axial axis to avoid any

circumferential stress imposed by deformation of the stator can 138 when exposed to internal fluid

pressure. The ends of the sensors 104 project through the back-up sleeve 142 and may be

swaged or otherwise upset to increase the pole cross sectional area for increased signal strength.

A rotor target 148 is located on either end of the motor rotor 136. The rotor target 148 is preferably of magnetic material such as soft iron. Preferably, the rotor target is of a different magnetic permeability than the surrounding material. Note that the sensor 104 centerline is offset from the target 148 axis in this preferred embodiment by a specified amount, typically one half the

axial thickness of the target 148. The target 148 is separated from the process fluid by a thin,

non-magnetic rotor can 150 with relatively high volume resistivity. FIG. 3 is an end view cross section of the motor 100 illustrating the equidistant placement

of the bearing sensors 104. Each sensor 104 comprises a set of dual coil sub-assemblies. Each

coil sub-assembly 152a and 152b is wound with a suitable number of turns with two or three separate wires, forming two or three individual windings per pole (the exact number of windings being dependant on the specific configuration as described below). The dual coil assemblies 152a, 152b are mounted on the pole pieces 154. Detail of the pole pieces 154 is shown in FIGs. 4A, 4B, and 4C and described below. Each of the sensors 104 generate a local magnetic field 156 when excited by the excitation circuit 106 of FIG. 1. Each of the local magnetic fields 156 are

coupled through the containment can 138, process fluid, rotor 136, and the target 148 to each of

the other sensor coil assemblies 152a, 152b. As the rotor 136 changes position, either due to

vibration or bearing wear, the reluctance of the magnetic path 156 associated with each of the

four sensors 104 changes. When one of the targets 148 moves toward or away from a given

sensor 104 as the result of radial displacement, the reluctance of that sensor's magnetic path increases or decreases in response. Likewise, when one of the targets 148 moves towards or away from the four sensors 104 located on one end of the rotor 136 as a result of axial displacement, the reluctance of those sensor's magnetic paths increase or decrease in response.

The reluctance of the magnetic path 156 associated with a sensor 104 determines the inductance

of its dual coil assembly windings 152a, 152b and this inductance in turn determines the voltage

induced in the windings when the coils are excited by a high frequency signal. Comparing the

voltages induced in windings 152a, 152b located on opposite ends of the rotor 136 along a

diameter provides an indication of radial displacements of the rotor 136. Similarly, comparing

voltages induced in windings located in two different axial planes provides an indication of axial

displacement of the rotor 136. Both of these comparisons and the synchronous detection which allows for them are discussed more fully below with regard to FIG. 7 et seq. The pole pieces 154 for the sensors are shown in greater detail in FIG 4 A, 4B, and 4C As may be observed, the pole pieces preferably have two longer legs 158a, 158b which form the poles for the coil sub-assemblies (not shown) The pole pieces also have two shorter legs 160a, 160b which are used to mount the sensors on the back-up sleeve An alternate coil mounting

means is shown in FIG 5 This coil mounting ring 162 may be made from solid material or

laminated electrical steel The four sets of dual coils 152 are located on pole salients 164 as

shown The mounting ring 162 is attached to the back-up sleeve in the same relative position as the aforementioned pole pieces 154

FIG 6 A, 6B, 6C, and 6D illustrate exemplary sensor mounting configurations of the

instant invention In FIG 6A, four sensors 104 are mounted equidistant about the outer periphery of the containment can 138 at either end of the motor 100 Each of the four sensors 104 on each end of the motor 100 are located in the same axial plane 166a and 166b For this configuration, the sensing of radial displacements for a particular end of the motor 100 utilizes the sensors 104

located in one axial plane 166a for that end The sensors are paired with the sensor on the

opposite sides of the motor along a diameter and are connected in series opposing one another

If the voltages induced by the local magnetic field in the radial winding of these sensors 104 are

equal, no net output then results because the voltage from one coil exactly cancels the voltage

from the opposite coil A radial displacement of the rotor upsets this balance, causing the voltage

induced in one coil to increase, while the voltage induced in the other coil decreases The resulting imbalance produces a net signal whose amplitude depends upon the amount of the displacement and whose phase depends upon the direction of displacement The dependence of

net output voltage upon radial displacement is approximately linear

For sensing axial displacements with the configuration of FIG 6a, the four axial sense

coils of sensors 104 located at one end of the rotor in axial plane 166a are connected in series aiding one another. The four axial sense coils of sensors 104 located at the opposite end of the

rotor in axial plane 166b are likewise connected in series aiding one another Finally, the four coils on one end and the four coils on the opposite end are connected in series opposing one another. If the rotor is located symmetrically with respect to the coils in two different axial planes 166a, 166b, the voltage induced in these coils are equal and they cancel producing no net output An axial displacement upsets this cancellation, producing a net signal whose amplitude depends

upon the amount of the displacement and whose phase depends upon the direction of the

displacement Since an axial displacement effects the voltage induced in all four coils at each end

of the rotor (in each axial plane 166a, 166b), it also effects the radial sensitivity The coils at the

end towards which the rotor is displaced become more sensitive to radial displacements while the

coils located at the opposite end become less sensitive to radial displacements This phenomena is easily corrected by the associated microprocessor which has at its disposal both the radial and the axial output signals The axial output signal is used by the microprocessor to sense the axial displacement and apply it as a scaling factor to the radial output signals A schematic representation of this axial and radial sensor configuration is illustrated in FIG 7 Each coil sub-

assembly 152 consists of three windings 168a, 168b, 168c One winding 168a of each coil is used

for excitation and one each for radial 168b and axial 168c sensing By interconnecting the coils

from either end of the motor 100 according to FIG 7, the sensors provide both axial position and

radial position of the rotor (not shown) Fig 8 shows a typical frequency spectrum of the net

output signal from a pair of radial or axial sensing windings The spectrum is seen to include a set of low frequency components 170 which are unavoidably induced by the motor excitation fields These frequency components 170 exist at the motor excitation frequency and multiples thereof In most situations, these undesirable components 170 are confined to a range below 1 kHz and are rejected by the synchronous detector 112 of FIG 1 Centered around the sensor excitation frequency 172 is yet another group of components 174a, 174b that relate to the dynamic

displacement of the rotor. At exactly the excitation frequency, there is a single component 172

whose magnitude depends upon the static or average displacement of the rotor. The synchronous detector 112 (see FIG. 1) is a well known electronic system for resolving this component into a

DC voltage representing the displacement of the rotor. For a rotor whose displacement varies

sinusoidally at the rotation frequency of the rotor, as is often the case, there will be two

components 174a, 174b spaced apart from the excitation frequency by the rotor rotation frequency. This spacing is designated F in the FIG. 8. It is also well know that the synchronous detector will convert this frequency spectrum into an output signal that varies sinusoidally in direct correspondence with the sinusoidally varying displacement. Displacements that are not sinusoidal may also be present producing a more complex spectrum. The synchronous detector

within the frequency limits of its output filter will also correctly resolve this more complex spectrum into a non-sinusoidally varying output signal corresponding to the non-sinusoidally

varying displacement of the rotor.

The configuration of FIG. 6b utilizes an axially staggered sensor assembly which uses 4

sensors located every 90 degrees like the configuration of FIG. 6a, but with the four sensors 104

located in two different axial planes 166a, 166c on the same end of the motor 100. The 4 sensors are paired, with 2 of them in one axial plane 166a and the other 2 in a different axial plane 166c. The axial distance between them is dependent upon the width of the target. The radial outputs from this configuration are the same as the original configuration previously disclosed. The axial

output is now based on an appropriate combination of all 4 sensors in two axial planes similar to

that described above. Here, the axial output from the two sensors in one axial plane 166a are

added together, as is the axial output from the two sensors in the other axial plane 166c. These

two summed outputs are then differentially summed to generate an axial displacement signal. For this configuration, the sensors 104 in the axial plane 166b no longer need to include the axial displacement sense coils, reducing the cost of these sensors.

The configuration of FIG. 6c uses a total of 6 sensors, 4 every 90 degrees in one axial plane 166a and 2 in another axial plane 166c at 180 degrees, radially aligned with 2 of the other 4 in axial plane 166a. This configuration senses radial displacement on either end of the motor 100 using the 4 sensors in each axial plane 166a and 166b respectively. The axial displacement is

determined by combining the axial output windings of the 4 radially aligned sensors in different axial planes 166a and 166c. Here, the axial output from the two sensors in one axial plane 166a

are added together, as is the axial output from the two sensors in the other axial plane 166c.

These two summed outputs are then differentially summed to generate an axial displacement

signal. The alignment of the sensors to the target is the same as before, with the edge of the target aligned with the center of the sensor. This configuration, unlike the configuration of FIG. 6b, maintains both axial and radial symmetry of the sensors.

The configuration of FIG 6d utilizes two radial displacement signals to produce the axial displacement, and is particularly useful in environments having high electromagnetic interference.

As discussed above with regard to the embodiment of FIG. 6a, the alignment of the target with

the sensor is such that the radial sensors are sensitive to both radial and axial displacement. In

fact it is this characteristic that is utilized with the configuration of FIG. 6d to determine the axial

displacement. This configuration also eliminates the need to correct the radial signal due to its

axial sensitivity as discussed above. Using the physical configuration of FIG. 6c, the 4 sensors that

previously provided a single axial output (2 sensors in axial plane 166a and the 2 sensors in axial plane 166c which are radially aligned with the first sensors) are used to provide 2 radial outputs that are sensitive to axial displacement. That is to say, each sensor pair in one axial plane produces a radial displacement signal whose output is sensitive to an axial displacement of the rotor target However, since the rotor target will move toward one pair and away from the other,

the effect of the axial displacement is opposite for these two radial outputs (i e , one pair becomes more sensitive to radial displacement as the rotor target moves toward them while the other pair

becomes less sensitive to radial displacement as the rotor target moves away from them)

This may better be understood by reference to FIGs 9 through 13 FIGs 9a, 10a, 11a,

12a, and 13a graphically illustrate the 2 radial outputs at a fixed radial position with axial displacement as the variable Note that the sign of the slope of Y-Front 176 (the sensors in axial plane 166a) and Y-Rear 178 (the sensors in axial plane 166c) change with up or down displacement in the radial axis Note also from FIG 1 la that with zero radial displacement the 2 outputs are essentially flat lines with no sensitivity to axial displacement To determine the radial position, the average DC offset of the two radial signals 176, 178 is determined and compared to

the DC offset with zero radial and axial displacement The DC offset will be positive or negative

depending upon the direction of the radial displacement Once the radial position is determined,

the two radial outputs 176, 178 are combined to provide the axial displacement 180 as indicated

by FIGs 9b, 10b, l ib, 12b, and 13b

Although the data shown in figures 9a through 13a indicate that the 2 radial outputs criss¬

cross at approximately zero axial displacement, due to manufacturing tolerances they may not To accommodate for this the 2 sets of radial data 176, 178 need to be Normalized about zero EU (an EU is one count out of the 8 bit A/D converter 114 of FIG 1, with 0 to 255 EU 's being full scale and corresponding to 0 to 5 volts ) Normalization is accomplished by subtracting the actual

value of Y-Front 176 and Y-Rear 178 from their respective calibrated zero values The calibrated

zero values would be taken as the values with zero radial and axial displacement Once the two

data points have been normalized Y-Front 176 is subtracted from Y-Rear 178 Knowing the

radial displacement as calculated above indicates what sensitivity each sensor has to axial displacement, and therefore, which curve 180 (FIGs. 9b, 10b, 1 lb, 12b, and 13b) is required. As an example, assume the radial position is determined to be 20 mills up and that the difference between Y-Front 176 and Y-Rear 178 is 15 counts. With reference to FIG. 9b, it can be determined that the axial displacement 180 is -40 mills from zero.

With this configuration (see FIG. 6d) only two windings are needed on the sensor assembly, the excitation coils and the radial sense coils. As stated above, this configuration uses 4 sensors on one end and 6 on the other with 2 windings per sensor, but only requires 4 connections

per winding. Certainly reducing the number of interconnections is a benefit to reliability and

based on the elimination of the need for a separate axial sense winding, the size of the sensor 104

may be reduced, or the number of turns may be increased to correspondingly increase the sensitivity. Just by reducing the number of coils on the winding the cost for the windings is also

reduced. Another benefit of this configuration is that since there is no longer any reason to have three of the four radial sensors sensitive to axial position, the sensors may be positioned appropriately over their respective targets thereby eliminating any need within the software to correct their output based on axial position.

An embodiment of the target 148 used with the above configuration (see FIG. 6d) is

illustrated in FIG. 14. This target configuration is a simple ring with the ends trimmed off square.

The edges 184 of this target 148 must be aligned with the center line of the two sensors 104 as

illustrated in FIG. 14. An alternate target configuration is illustrated in FIG. 15. In this alternate

embodiment, the target 148 is longer than that illustrated in FIG. 14, with both a straight 186 and

a conical 188 section. Both sensors 104 completely cover the target 148, one over the straight section 186 and one over the conical section 188. The sensor output from the use of this target configuration would now have one sloped line and one flat line (reference FIGs. 9a, 10a, 11a, 12a, and 13a). In yet a further alternative target configuration, as illustrated in FIG. 16, the target 148 is a little longer than the configuration of FIG. 14 so that one radial sensor is not sensitive to

axial displacement and the other one is sensitive.

The above described sensor configuration (see FIG. 6d) provides accurate axial and radial

displacement data, even in environments with high electromagnetic interference, due to the axial

and radial symmetry of the sensor placement and the differential connections of the sensor pairs. If the electromagnetic interference from the motor windings becomes excessive, however, it may be required to shield the sensors 104 from the stator winding 144 radiated noise. FIG. 17

illustrates an embodiment of the instant invention which allows placement of the sensors 104 in axial proximity to the stator windings 144 by using a conical shield 180. This conical shield 180 substantially reduces the electromagnetic interference from the stator windings 144, and allows the synchronous detector 112 (see FIG. 1) to operate properly. FIG. 18 illustrates an alternate embodiment which utilizes a plate shield 182 to separate the sensor 104 from the stator winding

radiated noise. In this embodiment the sensors 104 are positioned in a separate axial plane than the stator windings 144 which further reduces the effect of the radiated noise on the sensors 104.

As the axial and radial displacement of the rotor is determined by the above described

embodiments, an incremental display of this information is provided to allow maintenance

personnel monitor ongoing bearing wear. This allows them to schedule maintenance and avoid excessive down time due to unrecognized excessive bearing wear. FIG. 19 illustrates an embodiment of the display 122 used in accordance with the instant invention. This display 122 provides an incremental display for each area of bearing wear, including an incremental display

190 to illustrate radial bearing wear on the pump end, an incremental display 192 to illustrate

radial bearing wear on the motor end, and an incremental display 194 to illustrate the extent and

the direction of axial bearing wear. These incremental displays include several green indicators

196 which indicate incremental acceptable bearing wear, a few yellow indicators 198 which indicate incremental bearing wear beyond an acceptable amount which now requires maintenance, and at least one red indicator 200 which indicates that the incremental bearing wear has now become excessive. To further aid the maintenance personnel, the incremental displays 190, 192, and 194 are positioned on an outline of the canned motor pump in proximity to the bearings

monitored. FIG. 19 illustrates the display configuration for a horizontal type canned motor pump,

while FIG. 20 illustrates the display configuration for a vertical type canned motor pump. Indication is also provided for a dry run condition 202, and for a direction of rotation condition

204.

Numerous modifications and alternative embodiments of the invention will be apparent to those skilled in the art in view of the foregoing description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the best mode of carrying out the invention. The details of the structure may be varied substantially without departing from the spirit of the invention, and the exclusive use of all modifications which

come within the scope of the appended claims is reserved.

Claims

CLAIMSWe claim:

1. A bearing monitor for use with a canned motor pump having a wound stator and a rotor drivably coupled to an impeller, the rotor being mounted on radial journal bearings and

axial thrust bearings within a containment can and exposed to process fluid being pumped

by the canned motor pump, the wound stator being mounted external to the containment can and isolated from the process fluid, comprising:

a first target embedded in an outer periphery of the rotor in axial proximity to a first end of the rotor;

a first and a second sensor mounted external to the containment can in axial proximity to said first target and radially displaced approximately equally around the periphery of the containment can; a magnetic field generating means operatively coupled to said first and said second sensors for generating a first and a second local magnetic field, each local

magnetic field being coupled through the containment can, process fluid, rotor,

and said first target to each of said sensors, said first and said second sensors each

generating an output signal in response thereto;

a monitor circuit coupled to said first and said second sensors, said monitor circuit

comparing said output signal from said first sensor with said output signal from said second sensor, said monitor circuit generating a scaled output in response to a difference therebetween, said difference being approximately linearly related to bearing wear in a first radial direction on the first end of the rotor.

The bearing monitor of claim 1, further comprising a second target embedded in an outer periphery of the rotor in axial proximity to a second end of the rotor, a third and a fourth sensor mounted external to the containment can in axial proximity to

said second target, said third and said fourth sensors radially displaced approximately equally around the periphery of the containment can, and wherein said magnetic field generating means is also operably coupled to said third and

said fourth sensors for generating a third and a fourth local magnetic field, said

third and said fourth sensors each generating an output signal in response thereto,

and wherein said monitor circuit is also coupled to said third and said fourth sensors, said monitor circuit comparing said output signal from said third sensor with said output signal from said fourth sensor, said monitor circuit generating a scaled output in response to a difference therebetween, said difference being

approximately linearly related to bearing wear in a second radial direction on the

second end of the rotor

The bearing monitor of claim 2, further comprising

a fifth and a sixth sensor mounted external to the containment can in an axial plane with

said first and said second sensors, said fifth and said sixth sensors radially displaced approximately equally around the periphery of the containment can, equally displaced from said first and said second sensors, and wherein said magnetic field generating means is also operably coupled to said fifth and said sixth sensors for generating a fifth and a sixth local magnetic field, said fifth

and said sixth sensors each generating an output signal in response thereto; and

wherein said monitor circuit is also coupled to said fifth and said sixth sensors, said monitor circuit comparing said output signal from said fifth sensor with said

output signal from said sixth sensor, said monitor circuit generating a scaled

output in response to a difference therebetween, said difference being approximately linearly related to bearing wear in a third radial direction orthogonal to said first radial direction on the first end of the rotor

4. The bearing monitor of claim 3, wherein said first and said second sensors are in a first axial

plane, and wherein said fifth and said sixth sensors are in a second axial plane axially

displaced from said first axial plane

5 The bearing monitor of claim 4, wherein said monitor circuit combines said output signals

from said first and said second sensors to form a first axial signal, and from said fifth and

said sixth sensors to form a second axial signal, said monitor circuit further comparing said first axial signal with said second axial signal, said monitor circuit generating a scaled output in response to a difference therebetween, said difference being approximately linearly related to bearing wear in an axial direction

6 The bearing monitor of claim 5, further comprising an electromagnetic shield interposed

between said sensors and said wound stator

7. The bearing monitor of claim 6, wherein said sensors are positioned in axial proximity with

windings of the wound stator, and wherein said electromagnetic shield is conically positioned between said sensors and the windings.

8. The bearing monitor of claim 6, wherein said sensors are positioned in separate axial planes

than windings of the wound stator, and wherein said electromagnetic shield is positioned

in an axial plane separating said sensors from the windings.

9. The bearing monitor of claim 3, further comprising: a seventh and an eighth sensor mounted external to the containment can in an axial plane

with said third and said fourth sensors, said seventh and said eighth sensors

radially displaced approximately equally around the periphery of the containment

can, equally displaced from said third and said fourth sensors; and wherein said magnetic field generating means is also operably coupled to said seventh and

said eighth sensors for generating a seventh and an eighth local magnetic field, said

seventh and said eighth sensors each generating an output signal in response

thereto; and wherein said monitor circuit is also coupled to said seventh and said eighth sensors, said monitor circuit comparing said output signal from said seventh sensor with said output signal from said eighth sensor, said monitor circuit generating a scaled

output in response to a difference therebetween, said difference being

approximately linearly related to bearing wear in a fourth radial direction

orthogonal to said second radial direction on the second end of the rotor.

10. The bearing monitor of claim 9, wherein said monitor circuit combines said output from said first, said second, said fifth, and said sixth sensor to form a first axial output signal and combines said third, said fourth, said seventh, and said eight sensor to form a second axial

output signal, said monitor circuit generating a scaled output in response to a difference therebetween, said difference being approximately linearly related to bearing wear in an axial direction.

11. The bearing monitor of claim 10, further comprising an electromagnetic shield interposed

between said sensors and said wound stator.

12. The bearing monitor of claim 11, wherein said sensors are positioned in axial proximity with windings of the wound stator, and wherein said electromagnetic shield is conically positioned between said sensors and the windings.

13. The bearing monitor of claim 11, wherein said sensors are positioned in a separate axial plane than windings of the wound stator, and wherein said electromagnetic shield is positioned

in an axial plane separating said sensors from the windings.

14. The bearing monitor of claim 9, further comprising: a ninth and a tenth sensor mounted external to the containment can in an axial plane displaced from said first and said second sensors, said ninth and said tenth sensors radially displaced approximately equally around the periphery of the containment

can, radially aligned with said first and said second sensors; and

wherein said magnetic field generating means is also operably coupled to said ninth and said tenth sensors for generating a ninth and a tenth local magnetic field, said ninth

and said tenth sensors each generating an output signal in response thereto; and

wherein said monitor circuit is also coupled to said ninth and said tenth sensors, said

monitor circuit combining said output signal from said ninth sensor with said output signal from said tenth sensor to form a first axial output signal, said monitor circuit further combining said output signal from said first sensor with said output signal from said second sensor to form a second axial output signal, said monitor circuit generating a scaled output in response to a difference between said first and said second axial output signals, said difference being approximately

linearly related to bearing wear in an axial direction.

15. The bearing monitor of claim 14, further comprising an electromagnetic shield interposed

between said sensors and said wound stator.

16. The bearing monitor of claim 15, wherein said sensors are positioned in axial proximity with windings of the wound stator, and wherein said electromagnetic shield is conically positioned between said sensors and the windings.

17. The bearing monitor of claim 15, wherein said sensors are positioned in separate axial planes

than windings of the wound stator, and wherein said electromagnetic shield is positioned in an axial plane separating said sensors from the windings.

18. The bearing monitor of claim 9, further comprising:

a ninth and a tenth sensor mounted external to the containment can in an axial plane

displaced from said first and said second sensors, said ninth and said tenth sensors radially displaced approximately equally around the periphery of the containment can, radially aligned with said first and said second sensors; and wherein said magnetic field generating means is also operably coupled to said ninth and said tenth sensors for generating a ninth and a tenth local magnetic field, said ninth and said tenth sensors each generating an output signal in response thereto; and

monitor circuit differentially combining said output signal from said ninth sensor with said output signal from said tenth sensor to form a first axial output signal, said monitor circuit further differentially combining said output signal from said

first sensor with said output signal from said second sensor to form a second axial

output signal, said monitor circuit generating a scaled output in response to a difference between said first and said second axial output signals, said difference being approximately linearly related to bearing wear in an axial direction.

19. The bearing monitor of claim 18, further comprising an electromagnetic shield interposed

between said sensors and said wound stator.

20 The bearing monitor of claim 19, wherein said sensors are positioned in axial proximity with

windings of the wound stator, and wherein said electromagnetic shield is conically

positioned between said sensors and the windings.

21. The bearing monitor of claim 19, wherein said sensors are positioned in separate axial planes than windings of the wound stator, and wherein said electromagnetic shield is positioned

in an axial plane separating said sensors from the windings.

22. The bearing monitor of claim 18, wherein said first target comprises a ring having a first and a second square end.

23. The bearing monitor of claim 22, wherein said first and said second sensors are located in an axial plane defining said first square end of said first target, and said ninth and said tenth sensors are located in an axial plane defining said second square end of said first target.

24. The bearing monitor of claim 22, wherein said first and said second sensors are located in an

axial plane defining said first square end of said first target, and said ninth and said tenth

sensors are located in axial proximity to said first target displaced from said second square

end of said first target.

25. The bearing monitor of claim 18, wherein said first target comprises an elongated ring having

a constant diameter section and a conical section, and wherein said first and said second sensors are positioned in axial proximity to said conical section, and wherein said ninth and said tenth sensors are positioned in axial proximity to said constant diameter section.

26. A bearing monitor for a motor having a wound stator and a rotor, the rotor being mounted

on radial journal bearings and axial thrust bearings within a containment housing, the

wound stator being mounted external to the containment housing, comprising: first means positioned external to the containment housing for sensing a radial displacement of the rotor, said first means generating a first scaled output signal

approximately linearly related to wear of the radial journal bearings;

second means positioned external to the containment housing for sensing an axial

displacement of the rotor, said second means generating a second scaled output signal approximately linearly related to wear of the axial thrust bearings; and

third means responsive to said first scaled output signal and to said second scaled output signal for displaying an incremental amount of bearing wear in both an axial and a radial direction.

27. The bearing monitor of claim 26, wherein said first means comprises a plurality of radial sensor assemblies positioned radially equidistant about either end of the rotor by sensor

mounting means, said radial sensor assemblies comprising a means for generating a local magnetic field and at least one radial sense coil, and wherein said local magnetic field

induces a voltage in said at least one radial sense coil, said induced voltage varying with

radial displacement of the rotor.

28. The bearing monitor of claim 27, wherein said sensor mounting means comprises a spider pole piece having a first pair and a second pair of legs, said first pair of legs being mounted along an axial axis of said containment housing, said second pair forming a pole piece for said means for generating a local magnetic field and for said at least one radial

sense coil.

29. The bearing monitor of claim 27, wherein said sensor mounting means comprises a spider pole piece having a first pair and a second pair of legs, said first pair of legs being mounted along an axial axis of said containment housing, said second pair forming a pole piece, and wherein said radial sensor assembly comprises two radial sense coils electrically additively coupled and mounted on said second pair of legs, and wherein said means for

generating a local magnetic field comprises two excitation coils electrically additively

coupled and mounted on said second pair of legs.

30. The bearing monitor of claim 27, wherein said means for generating a local magnetic field

comprises at least one excitation coil coupled to a source of excitation.

31. The bearing monitor of claim 30, wherein said source of excitation operates at a frequency to minimize electromagnetic effects of motor excitation frequency and harmonics thereof.

32. The bearing monitor of claim 30, wherein said source of excitation operates at a frequency of

approximately 1 kHz to 4 kHz.

33. The bearing monitor of claim 27, wherein said sensor mounting means comprises a laminated

steel mounting ring attached about an outer periphery of said containment housing, said

mounting ring defining notches therein forming a plurality of pole pieces for said means for generating a local magnetic field and for said radial sense coil.

34. The bearing monitor of claim 26, wherein said first means comprises at least four radial

sensor assemblies positioned radially equidistant about either end of the rotor by sensor

mounting means, said radial sensor assemblies comprising a means for generating a local magnetic field and at least one radial sense coil, and wherein said local magnetic field induces a voltage in said at least one radial sense coil, said induced voltage varying with radial displacement of the rotor, and wherein radial displacement is sensed along one axis as a difference between said induced voltage from a first of said at least four radial sensor

assemblies and said induced voltage of a second of said at least four radial sensor

assemblies positioned along a diameter of the rotor from said first, and wherein radial displacement is sensed along an orthogonal axis as a difference between said induced

voltage from a third of said at least four radial sensor assemblies and said induced voltage of a fourth of said at least four radial sensor assemblies positioned along a diameter of the rotor from said third.

35. The bearing monitor of claim 26, wherein said second means comprises a plurality of axial sensor assemblies positioned radially equidistant about either end of the rotor by sensor mounting means, said axial sensor assemblies comprising a means for generating a local

magnetic field and at least one axial sense coil, and wherein said local magnetic field

induces a voltage in said at least one axial sense coil, said induced voltage varying with

axial displacement of the rotor.

36. The bearing monitor of claim 35, wherein axial displacement is sensed as a difference between a sum of said induced voltages from said plurality of axial sensor assemblies on one end of said rotor and a sum of said induced voltages from said plurality of axial sensor assemblies on an opposite end of said rotor.

37. The bearing monitor of claim 35, wherein said first means and said second means are positioned by the same mounting means.

38. The bearing monitor of claim 26, wherein said first means comprises a plurality of radial sensor assemblies positioned radially equidistant about a first end and a second end of the rotor by sensor mounting means, said radial sensor assemblies comprising a means for

generating a local magnetic field and at least one radial sense coil, and wherein said local

magnetic field induces a voltage in said at least one radial sense coil, said induced voltage varying with radial displacement of the rotor, and wherein said second means comprises a plurality of axial sensor assemblies positioned radially equidistant about said first end of the rotor by said sensor mounting means, said axial sensor assemblies comprising at least one axial sense coil, and wherein said local magnetic field induces a voltage in said at least one axial sense coil, said induced voltage varying with axial displacement of the rotor, and

wherein said sensor mounting means are positioned in two axial planes on said first end of

said rotor.

39. The bearing monitor of claim 27, wherein said second means comprises a plurality of axial sensor assemblies positioned radially equidistant in a first and a second axial plane about a

first end of the rotor by sensor mounting means, said axial sensor assemblies comprising a means for generating a local magnetic field and at least one axial sense coil, and wherein said local magnetic field induces a voltage in said at least one axial sense coil, said induced voltage varying with axial displacement of the rotor.

40. The bearing monitor of claim 39, wherein said axial sensor assemblies in said first axial plane

are radially aligned with said axial sensor assemblies in said second axial plane.

41. The bearing monitor of claim 40, wherein said axial sensor assemblies in said first axial plane

are electrically combined with said axial sensor assemblies in said second axial plane to

produce an axial output voltage displacement signal which varies with axial displacement of the rotor.

42. The bearing monitor of claim 40, wherein a first and a second axial sensor assemblies are

positioned in said first axial plane, said first and said second axial sensor assemblies being

differentially combined to produce a first output, and wherein a third and a fourth axial

sensor assemblies are positioned in said second axial plane, said third and said fourth axial sensor assemblies being differentially combined to produce a second output, said first and

said second outputs being differentially combined to produce said second scaled output.

43. The bearing monitor of claim 26, further comprising a target embedded in an outer periphery of the rotor in axial proximity to a first end of the rotor, and wherein said first and said second means are mounted in axial proximity to said target.

44. The bearing monitor of claim 43, wherein said target comprises a ring having a first and a

second square end.

45. The bearing monitor of claim 44, wherein said target comprises an elongated ring having a constant diameter section and a conical section.

46. The bearing monitor of claim 26, further comprising an electromagnetic shield interposed

between said first and said second means and the wound stator.

47. The bearing monitor of claim 46, wherein said first and said second means are positioned in

axial proximity with windings of the wound stator, and wherein said electromagnetic shield is conically positioned between said first and said second means and the windings.

48. The bearing monitor of claim 46, wherein said first and said second means are positioned in separate axial planes than windings of the wound stator, and wherein said electromagnetic shield is positioned in an axial plane separating said first and said second means from the windings.

49. A method of monitoring incremental bearing wear for a motor having a wound stator and a

rotor, the rotor being mounted on radial journal bearings and axial thrust bearings within a

containment housing and having a target mounted on the outer periphery of the rotor, the

wound stator being mounted external to the containment housing, comprising the steps of: generating a first and a second local magnetic field on an outer periphery of the containment housing, said first and said second local magnetic field flowing in a first and a second magnetic circuit each penetrating the containment housing and

incorporating at least a portion of the target; sensing a change in reluctance of said first and said second magnetic circuits, said change in reluctance being indicative of incremental bearing wear.

50. The method of claim 49, further comprising the step of displaying said change in reluctance incrementally.

51. The method of claim 49 wherein said first and said second local magnetic fields are located in

a first axial plane, further comprising the step of differentially comparing said change in

said first and said second magnetic circuits, said differential being indicative of incremental bearing wear in a radial direction.

52. The method of claim 49 wherein said first and said second local magnetic fields are located in a first and a second axial plane, further comprising the step of differentially comparing said change in said first and said second magnetic circuits, said differential being indicative of incremental bearing wear in an axial direction.