ASTM D7685-11(2016)

Standard Practice for In-Line, Full Flow, Inductive Sensor for Ferromagnetic and Non-ferromagnetic Wear Debris Determination and Diagnostics for Aero-Derivative and Aircraft Gas Turbine Engine Bearings

SIGNIFICANCE AND USE
4.1 This practice is intended for the application of in-line, full-flow inductive wear debris sensors. According to (1), passing the entire lubrication oil flow for aircraft and aero-derivative gas turbines through a debris-monitoring device is a preferred approach to ensure sufficient detection efficiency.  
4.2 Periodic sampling and analysis of lubricants have long been used as a means to determine overall machinery health (2). The implementation of smaller oil filter pore sizes for machinery operating at higher rotational speeds and energies has reduced the effectiveness of sampled oil analysis for determining abnormal wear prior to severe damage. In addition, sampled oil analysis for equipment that is remote or otherwise difficult to monitor or access is not practical. For these machinery systems, in-line wear debris sensors can be very useful to provide real-time and near-real-time condition monitoring data.  
4.3 In-line full-flow inductive debris sensors have demonstrated the capability to detect and quantify both ferromagnetic and non-ferromagnetic metallic wear debris. These sensors record metallic wear debris according to size, count, and type (ferromagnetic or non-ferromagnetic). Sensors are available for a variety of oil pipe sizes. The sensors are designed specifically for the protection of rolling element bearings and gears in critical machine applications. Bearings are key elements in machines since their failure often leads to significant secondary damage that can adversely affect safety, operational availability, or operational/maintenance costs, or a combination thereof.  
4.4 The main advantage of the sensor is the ability to detect early bearing damage and to quantify the severity of damage and rate of progression of failure towards some predefined bearing surface fatigue damage limiting wear scar. Sensor capabilities are summarized as follows:  
4.4.1 In-line full flow non-intrusive inductive metal detector with no moving parts.  
4.4.2 Det...
SCOPE
1.1 This practice covers the minimum requirements for an in-line, non-intrusive, through-flow oil debris monitoring system that monitors ferromagnetic and non-ferromagnetic metallic wear debris from both industrial aero-derivative and aircraft gas turbine engine bearings. Gas turbine engines are rotating machines fitted with high-speed ball and roller bearings that can be the cause of failure modes with high secondary damage potential.  (1)2  
1.2 Metallic wear debris considered in this practice range in size from 120 μm (micron) and greater. Metallic wear debris over 1000 μm are sized as over 1000 μm.  
1.3 This practice is suitable for use with the following lubricants: polyol esters, phosphate esters, petroleum industrial gear oils and petroleum crankcase oils.  
1.4 This practice is for metallic wear debris detection, not cleanliness.  
1.5 The values stated in SI units are to be regarded as standard. The values given in parentheses are provided for information only.  
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 30-Sep-2016
• ICS: 49.050 - Aerospace engines and propulsion systems
• Technical Committee: D02 - Petroleum Products, Liquid Fuels, and Lubricants
• Drafting Committee: D02.96.07 - Integrated Testers, Instrumentation Techniques for In-Service Lubricants

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D7685 − 11 (Reapproved 2016)
Standard Practice for
In-Line, Full Flow, Inductive Sensor for Ferromagnetic and
Non-ferromagnetic Wear Debris Determination and
Diagnostics for Aero-Derivative and Aircraft Gas Turbine
Engine Bearings
This standard is issued under the fixed designation D7685; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
In-line wear debris sensors have been in operation since the early 1990s. There are now thousands
ofthesedevicesoperatinginawidevarietyofmachineryapplicationsaccruingmillionsofoperational
hours. Wear debris sensors provide early warning for the abnormal conditions that lead to failure.
Improved machine reliability is possible due to the enhanced sensor data granularity, which provides
better diagnostics and prognostics of tribological problems from the initiating event through failure.
1. Scope 1.6 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This practice covers the minimum requirements for an
responsibility of the user of this standard to establish appro-
in-line, non-intrusive, through-flow oil debris monitoring sys-
priate safety and health practices and determine the applica-
tem that monitors ferromagnetic and non-ferromagnetic metal-
bility of regulatory limitations prior to use.
lic wear debris from both industrial aero-derivative and aircraft
gas turbine engine bearings. Gas turbine engines are rotating
2. Terminology
machines fitted with high-speed ball and roller bearings that
2.1 Definitions of Terms Specific to This Standard:
can be the cause of failure modes with high secondary damage
2.1.1 condition monitoring, n—field of technical activity in
potential. (1)
which selected physical parameters associated with an operat-
1.2 Metallic wear debris considered in this practice range in
ing machine are periodically or continuously sensed, measured
size from 120 µm (micron) and greater. Metallic wear debris
and recorded for the interim purpose of reducing, analyzing,
over 1000 µm are sized as over 1000 µm.
comparing and displaying the data and information so obtained
and for the ultimate purpose of using interim result to support
1.3 This practice is suitable for use with the following
decisions related to the operation and maintenance of the
lubricants: polyol esters, phosphate esters, petroleum industrial
machine. (2)
gear oils and petroleum crankcase oils.
2.1.2 control unit, n—electronic controller assembly, which
1.4 This practice is for metallic wear debris detection, not
processes the raw signal from the sensor and extracts informa-
cleanliness.
tion about the size and type of the metallic debris detected.
1.5 The values stated in SI units are to be regarded as
2.1.2.1 Discussion—A computer(s), accessories, and data
standard. The values given in parentheses are provided for
link equipment that an operator uses to control, communicate
information only.
and receive data and information.
2.1.3 full flow sensor, n—monitoring device that installs
in-line with the lubrication system and is capable of allowing
This practice is under the jurisdiction ofASTM Committee D02 on Petroleum thefullflowofthelubricationfluidtotravelthroughthesensor.
Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcom-
Also referred to as a through-flow sensor.
mittee D02.96.07 on Integrated Testers, Instrumentation Techniques for In-Service
2.1.4 inductive debris sensor, n—device that creates an
Lubricants.
Current edition approved Oct. 1, 2016. Published November 2016. Originally
electromagnetic field as a medium to permit the detection and
approved in 2011. Last previous edition approved in 2011 as D7685 – 11. DOI:
measurement of metallic wear debris via permeability for
10.1520/D7685-11R16.
ferromagnetic debris and eddy current effects for non-
The boldface numbers in parentheses refer to a list of references at the end of
this standard. ferromagnetic debris.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7685 − 11 (2016)
2.1.4.1 Discussion—A device that detects metallic wear
debris that cause fluctuations of the magnetic field. A device
that generates a signal proportional to the size and presence of
metallic wear debris with respect to time.
2.1.5 machinery health, n—qualitative expression of the
operational status of a machine sub-component, component or
entire machine, used to communicate maintenance and opera-
tional recommendations or requirements in order to continue
operation, schedule maintenance or take immediate mainte-
nance action.
2.1.6 metallic wear debris, n—in tribology, metallic par-
ticles that have become detached in a wear or erosion process.
2.1.7 sensor cable, n—specialized cable that connects the
sensor output to the electronic control module.
FIG. 1 Wear Debris Characterization
2.1.8 trend analysis, n—monitoring of the level and rate of
change over operating time of measured parameters.
4.4 The main advantage of the sensor is the ability to detect
early bearing damage and to quantify the severity of damage
3. Summary of Practice
and rate of progression of failure towards some predefined
3.1 A full flow sensor is fitted in the oil line to detect
bearing surface fatigue damage limiting wear scar. Sensor
metallic wear debris. The system counts wear debris, sizes
capabilities are summarized as follows:
debris, and calculates debris mass estimates as a function of
4.4.1 In-linefullflownon-intrusiveinductivemetaldetector
time. This diagnostic information is then used to assess
with no moving parts.
machine health relative to cumulative debris count, or esti-
4.4.2 Detects both ferromagnetic and non-ferromagnetic
mated cumulative debris mass warning and alarm limits, or a
metallic wear debris.
combination thereof. From this information, estimates of
4.4.3 Detects 95 % or more of metallic wear debris above
remaining useful life of the machine can also be made.
some minimum particle size threshold.
4.4.4 Counts and sizes wear debris detected.
4. Significance and Use
4.5 Fig.1presentsawidelyuseddiagram (2)todescribethe
4.1 This practice is intended for the application of in-line,
progress of metallic wear debris release from normal to
full-flow inductive wear debris sensors. According to (1),
catastrophic failure. It must be pointed out that this figure
passing the entire lubrication oil flow for aircraft and aero-
summarizes metallic wear debris observations from all the
derivative gas turbines through a debris-monitoring device is a
different wear modes that can range from polishing, rubbing,
preferred approach to ensure sufficient detection efficiency.
abrasion, adhesion, grinding, scoring, pitting, spalling, etc. As
4.2 Periodic sampling and analysis of lubricants have long
mentioned in numerous references (1-11), the predominant
been used as a means to determine overall machinery health failure mode of rolling element bearings is spalling or macro
(2). The implementation of smaller oil filter pore sizes for
pitting.Whenabearingspalls,thecontactstressesincreaseand
machinery operating at higher rotational speeds and energies cause more fatigue cracks to form within the bearing subsur-
has reduced the effectiveness of sampled oil analysis for
face material. The propagation of existing subsurface cracks
determining abnormal wear prior to severe damage. In and creation of new subsurface cracks causes ongoing deterio-
addition, sampled oil analysis for equipment that is remote or
ration of the material that causes it to become a roughened
otherwise difficult to monitor or access is not practical. For
contact surface as illustrated in Fig. 2. This deterioration
these machinery systems, in-line wear debris sensors can be process produces large numbers of metallic wear debris with a
very useful to provide real-time and near-real-time condition
typical size range from 100 to 1000 microns or greater. Thus,
monitoring data. rotating machines, such as gas turbines and transmissions,
which contain rolling element bearings and gears made from
4.3 In-line full-flow inductive debris sensors have demon-
hard steel tend to produce this kind of large metallic wear
strated the capability to detect and quantify both ferromagnetic
debris that eventually leads to failure of the machines.
and non-ferromagnetic metallic wear debris. These sensors
record metallic wear debris according to size, count, and type 4.6 In-line wear debris monitoring provides a more reliable
(ferromagnetic or non-ferromagnetic). Sensors are available and timely indication of bearing distress for a number of
for a variety of oil pipe sizes. The sensors are designed reasons:
specifically for the protection of rolling element bearings and 4.6.1 Firstly, bearing failures on rotating machines tend to
gears in critical machine applications. Bearings are key ele- occur as events often without sufficient warning and could be
ments in machines since their failure often leads to significant missed by means of only periodic inspections or data sampling
secondary damage that can adversely affect safety, operational observations.
availability,oroperational/maintenancecosts,oracombination 4.6.2 Secondly, since it is the larger wear metallic debris
thereof. that are being detected, there is a lower probability of false
D7685 − 11 (2016)
FIG. 3 Sensor Major Components (3)
conditioning electronics process the raw signal from the sensor
and extract information about the size and type of the metallic
debris detected. The sensor electronics perform several func-
tions including: data processing, communication control, and
Built-In-Test (BIT). Ferromagnetic and non-ferromagnetic
wear debris counts are binned according to size. Signal
conditioning using a threshold algorithm is used to categorize
the metallic wear debris that pass through the sensor on the
FIG. 2 Typical Bearing Spall
basis of size. Several size categories can be configured which
allow the tracking of the distribution of debris.
6.2 Principle of Operation—The sensor operates by moni-
indicationfromthenormalrubbingwearthatwillbeassociated
toring the disturbance to the alternating magnetic field caused
with smaller particles.
by the passage of a metallic wear debris particle through the
4.6.3 Thirdly, build or residual debris from manufacturing
magnetic coil assembly as shown in Fig. 4 (12). The particle
or maintenance actions can be differentiated from actual
couples with the magnetic field to varying degrees as it
damage debris because the cumulative debris counts recorded
traverses the sensing region, resulting in a characteristic output
due to the former tend to decrease while those due to the latter
signature. The magnitude of the disturbance measured as a
tend to increase.
voltage defines the size of the metallic wear debris and the
4.6.4 Fourthly, bearing failure tests have shown that wear
phase shift of the signal defines whether the wear debris is
debris size distribution is independent of bearing size. (2-5)
ferromagnetic or non-ferromagnetic. When a ferromagnetic
and (11).
particle passes by each field coil, it strengthens the magnetic
5. Interferences
field of that coil due to the high magnetic permeability of the
particle relative to the surrounding fluid (oil). This disrupts the
5.1 Wear debris counts may be invalid due to excessive
balance of the fields seen by the sense coil, resulting in a
noise from environmental influences. See 7.4.
characteristic signal being generated as the particle passes
6. Apparatus through the entire sensing region of the sensor. The signal
3 looks much like one period of a sine wave where the amplitude
6.1 Sensor —Asensorsystemisidentifiedthatisathrough-
of the signal is proportional to the apparent size of the particle
flow device that installs in-line with the lubrication oil system.
and the period of the signal is inversely proportional to the
The subsections in this section provide examples for a certain
speed at which the particle passes through the sensor. For a
type of inductive debris sensor system. The sensor has no
ferromagnetic particle, the size, shape, and orientation of the
moving components.As seen in Fig. 3, the sensor incorporates
particle and the magnetic susceptibility of the material deter-
a magnetic coil assembly and signal conditioning electronics
mine the magnitude of the signal. When a non-ferromagnetic
that are capable of detecting and categorizing metallic wear
(conductive) particle passes by each field coil, the principle is
debrisbysizeandtype.Themagneticcoilassemblyconsistsof
similar except that the presence of the particle in the magnetic
three coils that surround a magnetically and electrically inert
fieldweakensthefieldduetotheeddycurrentsgeneratedinthe
section of tubing. The two outside field coils are driven by a
particle.Thisresultsinadifferenceinthesignalphaseallowing
high frequency alternating current source such that their
the processing electronics to differentiate between ferromag-
respective fields are nominally opposed or cancel each other at
netic and non-ferromagnetic particles passing through the
a point inside the tube at the center sensor coil. Signal
sensor. For a non-ferromagnetic particle, the surface area and
orientation of the particle and the conductivity of the material,
The sole source of supply of the apparatus known to the committee at this time
determine the magnitude of the signal.Also, for a given size of
is GasTOPS, Ltd., Polytek St., Ottawa, Ontario K1J 9J3, Canada. If you are aware
particle,theamountofdisturbancecausedtothemagneticfield
of alternative suppliers, please provide this information to ASTM International
by a ferromagnetic particle is considerably greater than that
Headquarters.Your comments will receive careful consideration at a meeting of the
responsible technical committee, which you may attend. caused by a non-ferromagnetic particle resulting in the sensor
D7685 − 11 (2016)
FIG. 4 Principle of Operation (12)
being able to detect smaller ferromagnetic than non- The particle used to represent typical bearing damage metallic
ferromagnetic particles. Note that the detection capability of wear debris was a ferromagnetic flake, rectangular in shape
the sensor is limited to distinguishing ferromagnetic materials with the thickness being considerably less than the length and
from non-ferromagnetic (conductive) materials.
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D7685 − 11 D7685 − 11 (Reapproved 2016)
Standard Practice for
In-Line, Full Flow, Inductive Sensor for Ferromagnetic and
Non-ferromagnetic Wear Debris Determination and
Diagnostics for Aero-Derivative and Aircraft Gas Turbine
Engine Bearings
This standard is issued under the fixed designation D7685; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
In-line wear debris sensors have been in operation since the early 1990s. There are now thousands
of these devices operating in a wide variety of machinery applications accruing millions of operational
hours. Wear debris sensors provide early warning for the abnormal conditions that lead to failure.
Improved machine reliability is possible due to the enhanced sensor data granularity, which provides
better diagnostics and prognostics of tribological problems from the initiating event through failure.
1. Scope
1.1 This practice covers the minimum requirements for an in-line, non-intrusive, through-flow oil debris monitoring system that
monitors ferromagnetic and non-ferromagnetic metallic wear debris from both industrial aero-derivative and aircraft gas turbine
engine bearings. Gas turbine engines are rotating machines fitted with high-speed ball and roller bearings that can be the cause of
failure modes with high secondary damage potential. (1)
1.2 Metallic wear debris considered in this practice range in size from 120 μm 120 μm (micron) and greater. Metallic wear
debris over 1000 μm 1000 μm are sized as over 1000 μm.1000 μm.
1.3 This practice is suitable for use with the following lubricants: polyol esters, phosphate esters, petroleum industrial gear oils
and petroleum crankcase oils.
1.4 This practice is for metallic wear debris detection, not cleanliness.
1.5 The values stated in SI units are to be regarded as standard. The values given in parentheses are provided for information
only.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
2. Terminology
2.1 Definitions of Terms Specific to This Standard:
2.1.1 condition monitoring, n—field of technical activity in which selected physical parameters associated with an operating
machine are periodically or continuously sensed, measured and recorded for the interim purpose of reducing, analyzing, comparing
and displaying the data and information so obtained and for the ultimate purpose of using interim result to support decisions related
to the operation and maintenance of the machine. (2)
2.1.2 control unit, n—electronic controller assembly, which processes the raw signal from the sensor and extracts information
about the size and type of the metallic debris detected.
This practice is under the jurisdiction of ASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcommittee
D02.96.07 on Integrated Testers, Instrumentation Techniques for In-Service Lubricants.
Current edition approved Jan. 1, 2011Oct. 1, 2016. Published March 2011November 2016. Originally approved in 2011. Last previous edition approved in 2011 as
D7685 – 11. DOI: 10.1520/D7685–11.10.1520/D7685-11R16.
The boldface numbers in parentheses refer to a list of references at the end of this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7685 − 11 (2016)
2.1.2.1 Discussion—
A computer(s), accessories, and data link equipment that an operator uses to control, communicate and receive data and
information.
2.1.3 full flow sensor, n—monitoring device that installs in-line with the lubrication system and is capable of allowing the full
flow of the lubrication fluid to travel through the sensor. Also referred to as a through-flow sensor.
2.1.4 inductive debris sensor, n—device that creates an electromagnetic field as a medium to permit the detection and
measurement of metallic wear debris via permeability for ferromagnetic debris and eddy current effects for non-ferromagnetic
debris.
2.1.4.1 Discussion—
A device that detects metallic wear debris that cause fluctuations of the magnetic field. A device that generates a signal proportional
to the size and presence of metallic wear debris with respect to time.
2.1.5 machinery health, n—qualitative expression of the operational status of a machine sub-component, component or entire
machine, used to communicate maintenance and operational recommendations or requirements in order to continue operation,
schedule maintenance or take immediate maintenance action.
2.1.6 metallic wear debris, n—in tribology, metallic particles that have become detached in a wear or erosion process.
2.1.7 sensor cable, n—specialized cable that connects the sensor output to the electronic control module.
2.1.8 trend analysis, n—monitoring of the level and rate of change over operating time of measured parameters.
3. Summary of Practice
3.1 A full flow sensor is fitted in the oil line to detect metallic wear debris. The system counts wear debris, sizes debris, and
calculates debris mass estimates as a function of time. This diagnostic information is then used to assess machine health relative
to cumulative debris count, or estimated cumulative debris mass warning and alarm limits, or a combination thereof. From this
information, estimates of remaining useful life of the machine can also be made.
4. Significance and Use
4.1 This practice is intended for the application of in-line, full-flow inductive wear debris sensors. According to (1), passing the
entire lubrication oil flow for aircraft and aero-derivative gas turbines through a debris-monitoring device is a preferred approach
to ensure sufficient detection efficiency.
4.2 Periodic sampling and analysis of lubricants have long been used as a means to determine overall machinery health (2). The
implementation of smaller oil filter pore sizes for machinery operating at higher rotational speeds and energies has reduced the
effectiveness of sampled oil analysis for determining abnormal wear prior to severe damage. In addition, sampled oil analysis for
equipment that is remote or otherwise difficult to monitor or access is not practical. For these machinery systems, in-line wear
debris sensors can be very useful to provide real-time and near-real-time condition monitoring data.
4.3 In-line full-flow inductive debris sensors have demonstrated the capability to detect and quantify both ferromagnetic and
non-ferromagnetic metallic wear debris. These sensors record metallic wear debris according to size, count, and type
(ferromagnetic or non-ferromagnetic). Sensors are available for a variety of oil pipe sizes. The sensors are designed specifically
for the protection of rolling element bearings and gears in critical machine applications. Bearings are key elements in machines
since their failure often leads to significant secondary damage that can adversely affect safety, operational availability, or
operational/maintenance costs, or a combination thereof.
4.4 The main advantage of the sensor is the ability to detect early bearing damage and to quantify the severity of damage and
rate of progression of failure towards some predefined bearing surface fatigue damage limiting wear scar. Sensor capabilities are
summarized as follows:
4.4.1 In-line full flow non-intrusive inductive metal detector with no moving parts.
4.4.2 Detects both ferromagnetic and non-ferromagnetic metallic wear debris.
4.4.3 Detects 95%95 % or more of metallic wear debris above some minimum particle size threshold.
4.4.4 Counts and sizes wear debris detected.
4.5 Fig. 1 presents a widely used diagram (2) to describe the progress of metallic wear debris release from normal to
catastrophic failure. It must be pointed out that this figure summarizes metallic wear debris observations from all the different wear
modes that can range from polishing, rubbing, abrasion, adhesion, grinding, scoring, pitting, spalling, etc. As mentioned in
numerous references (1-11), the predominant failure mode of rolling element bearings is spalling or macro pitting. When a bearing
spalls, the contact stresses increase and cause more fatigue cracks to form within the bearing subsurface material. The propagation
of existing subsurface cracks and creation of new subsurface cracks causes ongoing deterioration of the material that causes it to
D7685 − 11 (2016)
FIG. 1 Wear Debris Characterization
become a roughened contact surface as illustrated in Fig. 2. This deterioration process produces large numbers of metallic wear
debris with a typical size range from 100 to 1000 microns or greater. Thus, rotating machines, such as gas turbines and
transmissions, which contain rolling element bearings and gears made from hard steel tend to produce this kind of large metallic
wear debris that eventually leads to failure of the machines.
4.6 In-line wear debris monitoring provides a more reliable and timely indication of bearing distress for a number of reasons:
4.6.1 Firstly, bearing failures on rotating machines tend to occur as events often without sufficient warning and could be missed
by means of only periodic inspections or data sampling observations.
4.6.2 Secondly, since it is the larger wear metallic debris that are being detected, there is a lower probability of false indication
from the normal rubbing wear that will be associated with smaller particles.
4.6.3 Thirdly, build or residual debris from manufacturing or maintenance actions can be differentiated from actual damage
debris because the cumulative debris counts recorded due to the former tend to decrease while those due to the latter tend to
increase.
4.6.4 Fourthly, bearing failure tests have shown that wear debris size distribution is independent of bearing size. (2-5) and (11).
5. Interferences
5.1 Wear debris counts may be invalid due to excessive noise from environmental influences. See 7.4.
6. Apparatus
6.1 Sensor —A sensor system is identified that is a through-flow device that installs in-line with the lubrication oil system. The
subsections in this section provide examples for a certain type of inductive debris sensor system. The sensor has no moving
components. As seen in Fig. 3, the sensor incorporates a magnetic coil assembly and signal conditioning electronics that are
capable of detecting and categorizing metallic wear debris by size and type. The magnetic coil assembly consists of three coils that
surround a magnetically and electrically inert section of tubing. The two outside field coils are driven by a high frequency
alternating current source such that their respective fields are nominally opposed or cancel each other at a point inside the tube at
the center sensor coil. Signal conditioning electronics process the raw signal from the sensor and extract information about the size
and type of the metallic debris detected. The sensor electronics perform several functions including: data processing,
communication control, and Built-In-Test (BIT). Ferromagnetic and non-ferromagnetic wear debris counts are binned according
to size. Signal conditioning using a threshold algorithm is used to categorize the metallic wear debris that pass through the sensor
on the basis of size. Several size categories can be configured which allow the tracking of the distribution of debris.
6.2 Principle of Operation—The sensor operates by monitoring the disturbance to the alternating magnetic field caused by the
passage of a metallic wear debris particle through the magnetic coil assembly as shown in Fig. 4 (12). The particle couples with
the magnetic field to varying degrees as it traverses the sensing region, resulting in a characteristic output signature. The magnitude
of the disturbance measured as a voltage defines the size of the metallic wear debris and the phase shift of the signal defines
whether the wear debris is ferromagnetic or non-ferromagnetic. When a ferromagnetic particle passes by each field coil, it
strengthens the magnetic field of that coil due to the high magnetic permeability of the particle relative to the surrounding fluid
(oil). This disrupts the balance of the fields seen by the sense coil, resulting in a characteristic signal being generated as the particle
passes through the entire sensing region of the sensor. The signal looks much like one period of a sine wave where the amplitude
The sole source of supply of the apparatus known to the committee at this time is GasTOPS, Ltd., Polytek St., Ottawa, Ontario K1J 9J3, Canada. If you are aware of
alternative suppliers, please provide this information to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of the responsible
technical committee, which you may attend.
D7685 − 11 (2016)
FIG. 2 Typical Bearing Spall
FIG. 3 Sensor Major Components (3)
of the signal is proportional to the apparent size of the particle and the period of the signal is inversely proportional to the speed
at which the particle passes through the sensor. For a ferromagnetic particle, the size, shape, and orientation of the particle and the
magnetic susceptibility of the material determine the magnitude of the signal. When a non-ferromagnetic (conductive) particle
passes by each field coil, the principle is similar except that the presence of the particle in the magnetic field weakens the field
due to the eddy currents generated in the particle. This results in a difference in the signal phase allowing the processing electronics
to differentiate between ferromagnetic and non-ferromagnetic particles passing through the sensor. For a non-ferromagnetic
particle, the surface area and orientation of the particle and the conductivity of the material, determine the magnitude of the signal.
Also, for a given size of particle, the amount of disturbance caused to the magnetic field by a ferromagnetic particle is considerably
greater than that caused by a non-ferromagnetic particle resulting in the sensor being able to
...