Below is a few articles of beta ratio, efficiency, ratings that you might find interesting:
Filters are rated on their ability to remove particles of a specific size from a fluid, but the problem is that a variety of very different methods are applied to specify performance in this way.
Pore size ratings refer to the size of a specific particle or organism retained by the filter media to a specific degree of efficiency. A filter that is marked '10 micron' has some capability to capture particle as small as 10 micrometers. However you do not know exactly what this means unless you also have a description of the test methods and standards used to determine the filter rating.
The two most used reported media ratings are nominal and absolute micron rating.
Absolute rating
The absolute rating, of cut-off point, of a filter refers to the diameter of the largest spherical glass particle, normally expressed in micrometers (mm), which will pass through the filter under laboratory conditions.
It represents the pore opening size of the filter medium. Filter media with an exact and consistent pore size or opening thus, theoretically at least, have an exact absolute rating.
The absolute rating shouldn't be confused with the largest particle passed by a filter under operating conditions: the absolute rating simply determines the size of the largest glass bead which will pass through the filter under very low pressure differentials and nonpulsating conditions.
This does not usually apply in practice: pore size is modified by the form of the filter element and it is not necessarily consistent with the actual open areas. Furthermore the actual form of the contaminants are not spherical and the two linear dimension of the particle can be very much smaller than its nominal one, permitting it to pass through a very much smaller hole (i.e. cylindrical particles with a thickness less than the slot opening of the filter). The passage of oversize particles in this manner depends very largely on the size and shape of the opening and on the depth over which filtering is provided.
Most of filters generate a filter bed: contaminants collecting on the surface impart a blocking action decreasing the permeability of the element bad improving filter efficiency. When the blocking is so severe that the pressure drop is excessive, the flow rate through the system decrease seriously. This explains why the performance of a filter can often exceed its given rating based on the performance of a clean element and why test figures can differ widely with different test conditions on identical elements.
It may be argued that the term absolute rating is not a realistic description. Strictly speaking the term absolute indicates that no particle larger than that rating can pass through the filter, limiting the type of media to those of consistent pore size where they show 100% retention of particles.
Nominal rating
The nominal rating refers to a filter capable of cutting off a nominated minimum percentage by weight of solid particles of a specific contaminant (usually again glass beads) greater than a stated micron size, normally expressed in micrometers (mm). I.e. 90% of 10 micron.
It also represents a nominal efficiency figure, or more correctly, a degree of filtration.
Process conditions such as operating pressure, concentration of contaminant etc, have a significant effect on the retention of the filters. Many filter manufacturers use similar tests but, due to the lack of uniformity and reproducibility of the basic method, the use of nominal ratings has fallen into disfavor.
Mean filter rating
The mean filter rating refers to the measurement of the average pore size of a filter element. It establishes the particle size above which the filter starts to be effective. It is determined by the bubble point test and it is more meaningful than a nominal rating and, in casa of filter elements with varying pore size, more realistic than an absolute rating.
Source: 'Filters and Filtration Handbook', T Christopher Dickenson, Elsevier, January 1, 1997
Filter Element Beta Ratio Information
Filter Beta Ratios
The Beta Ratio equals the ratio of the number of particles of a minimum given size upstream of the filter to the number of particles of the same size and larger found downstream. Simply put, the higher the Beta Ratio the higher the Capture Efficiency of the filter.
Filtration Ratings Defined
Filter ratings are an often misunderstood area of contamination control. The most commonly used rating is the Beta Ratio, which is defined as the ratio of the number of particles upstream of the test filter versus the number downstream, greater than a given size. Using the Beta Ratio, a 5 micron filter with a Beta 1000 Rating, will have on average 1000 particles larger than 5 micron upstream of the filter for every one 5 micron or greater particle downstream.
The efficiency of the filter can be calculated directly from the Beta Ratio since the % efficiency is simply (beta-1)/beta x 100. A Beta 1000, 5-micron filter is thus said to be 99.99% efficient at removing 5 micron and larger particles.
Caution must be exercised when using Beta Ratios since they do not take into account field operating conditions such as pressure surges and changes in temperature, which can affect real life performance. A filter's Beta Ratio also does not give any indication of its dirt holding capacity, the total amount of material that can be trapped by the filter throughout its life, nor does it account for how the capture efficiency changes over time. Nevertheless, Beta Ratios are an effective way of gauging the expected performance of a filter.
The ISO standard for Multi-pass filter testing (ISO 16889) has changed to require filter manufacturers to determine the average particle sizes which yield Beta Ratios equal to 2, 10, 75, 100, 200, and 1000, again using the multi-pass test stand approach. The new standard gives a better interpretation of a filter's overall performance.
Of course, regular monitoring of fluid cleanliness using ISO particle counting should be used to determine the efficiency of the filter in actual field conditions.
The Micron Rating for Media in Fluid Filters
A micron rating for a fluid filter is a generalized way of indicating the ability of the
filter's media to remove contaminants by the size of particles it is exposed to. The
micron rating does not properly or fully describe either the efficiency or the
contaminant-holding capacity of the filter media. ENGINE AIR FILTER MEDIA IS
NOT RATED BY MICRON SIZE. (Refer to TSB 04-3, Air Filter Life and Efficiency
Ratings)
What does the word micron mean? The word micron is another term for
micrometer (1 millionth of a meter). A micrometer is a unit of linear measure in
the metric system used to measure distance from one point to another. It is used
like the inch, foot, centimeter and millimeter to measure length, width or diameter
of objects. Its scientific notation is ƒÊ. Some linear equivalents are 1 inch is 25,400
microns and 1 micron is .000039 inches. Some comparative sizes are:
Diameter of average human hair 70 microns
Lower limit of visibility (naked eye) 40 microns
White blood cells 25 microns
Talcum powder 10 microns
Red blood cells 8 microns
Bacteria 2 microns
Carbon black 0.6 microns
Tobacco smoke 0.5 microns
A filter that is marked or rated "10 micron" has some capability to capture
particles as small as 10 micrometers. However, when you see a filter marked "10
micron", you do not know exactly what this means unless you also have a
description of the test methods and standards used to determine the filter rating.
The results from the different test methods may not be comparable as their
methodology varies greatly.
The two most popular reported media ratings are a nominal micron rating (50%)
and an absolute micron rating (98.7%). A nominal rating usually means the filter's
media can capture a given percentage of particles of a stated size. For example,
a filter might be said to have a nominal rating of 50% for particles 10 micrometers
in size or larger. An absolute micron rating can be determined by single-pass or
multi-pass testing and is usually obtained by passing a test fluid containing
particles of a known size through a small, flat sheet of filter media. Any particles
that pass through the media are captured and measured. An absolute rating is
also expressed in the form of a percentage of the size of particles captured.
Until recently, there has not been one universally accepted test method to
measure or describe the media pore size or the size of particles a filter media
can capture and hold. Depending on which test method was used, the same filter
media could be rated with different micron ratings, thus leading to confusion
regarding how well the filter's media actually performs. Fortunately, there now
exists a test procedure called multi-pass testing or Beta ratio testing (ƒÀ) which is,
a universally accepted test method that yields readily comparable test results.
Multi-pass testing has been recognized by SAE (SAE J1858), ISO (ISO 4548-12,
lube oil and ISO16889, hydraulic or fuel), ANSI (American National Standards
Institute) and NFPA (National Fluid Power Association).
Multi-pass testing uses a specified contaminant, of known sizes, added regularly
in measured quantities to the fluid which is pumped continuously through the
filter. Measured samples of fluid are then taken at timed intervals from the
upstream and downstream sides of the filter. The contaminant in the samples is
measured for particle sizes and quantities of each size or range of sizes. From
these upstream and downstream measurements, a Beta ratio is formulated by
dividing the number of particles of a particular size in the upstream flow by the
number of particles of the same size in the downstream flow.
X(c) per ISO 16889
In this example, the equation provides the following information: regarding 10-
micrometer or micron size particles, the filter media tested has a Beta ratio of 2.
This information is helpful but not useful without knowing what the ratio actually
means. To translate the Beta ratio into meaningful information, subtract 1 from
the original ratio and divide that answer by the original ratio. This answer
represents the efficiency of the media at the specified particle size. For this
example, take the Beta ratio of 2, subtract 1 from it and divide that answer by the
original ratio of 2 or 2 - 1 = 1 € 2 = 50% efficient at removing 10-micrometer or
micron size particles. This formula is used to translate any Beta ratio into a
percent efficiency at removing the size of particle tested. Here are a few Beta
ratios and their corresponding efficiencies:
Beta ratio information can also be stated as ƒÀ 5/10/20 = 2/20/75. In this example,
the media tested removed 50% of 5-micrometer or micron size particles, 95% of
10-micrometer or micron size particles and 98.7% of 20-micrometer or micron
size particles presented to it. This same ratio information can also be stated as
ƒÀ 2/20/75 = 5/10/20. Both equations state the same information in two different
ways and are both accepted by the industry.
Multi-pass testing provides an accurate, universally accepted, comparable test
method to describe the efficiency of a media's ability to remove certain size
contaminants. It can also determine the total contaminant holding capacity of the
filter as well as some of its differential pressure capabilities. Its use eliminates the
inaccuracies and confusion caused by the use of "micron ratings". For further
information, see TSB 97-1R1, Hydraulic Filter Performance Criteria and
TSB 04-2R1, ISO Updates to Multi-pass Liquid Filter Test Procedures.
Filters are rated on their ability to remove particles of a specific size from a fluid, but the problem is that a variety of very different methods are applied to specify performance in this way.
Pore size ratings refer to the size of a specific particle or organism retained by the filter media to a specific degree of efficiency. A filter that is marked '10 micron' has some capability to capture particle as small as 10 micrometers. However you do not know exactly what this means unless you also have a description of the test methods and standards used to determine the filter rating.
The two most used reported media ratings are nominal and absolute micron rating.
Absolute rating
The absolute rating, of cut-off point, of a filter refers to the diameter of the largest spherical glass particle, normally expressed in micrometers (mm), which will pass through the filter under laboratory conditions.
It represents the pore opening size of the filter medium. Filter media with an exact and consistent pore size or opening thus, theoretically at least, have an exact absolute rating.
The absolute rating shouldn't be confused with the largest particle passed by a filter under operating conditions: the absolute rating simply determines the size of the largest glass bead which will pass through the filter under very low pressure differentials and nonpulsating conditions.
This does not usually apply in practice: pore size is modified by the form of the filter element and it is not necessarily consistent with the actual open areas. Furthermore the actual form of the contaminants are not spherical and the two linear dimension of the particle can be very much smaller than its nominal one, permitting it to pass through a very much smaller hole (i.e. cylindrical particles with a thickness less than the slot opening of the filter). The passage of oversize particles in this manner depends very largely on the size and shape of the opening and on the depth over which filtering is provided.
Most of filters generate a filter bed: contaminants collecting on the surface impart a blocking action decreasing the permeability of the element bad improving filter efficiency. When the blocking is so severe that the pressure drop is excessive, the flow rate through the system decrease seriously. This explains why the performance of a filter can often exceed its given rating based on the performance of a clean element and why test figures can differ widely with different test conditions on identical elements.
It may be argued that the term absolute rating is not a realistic description. Strictly speaking the term absolute indicates that no particle larger than that rating can pass through the filter, limiting the type of media to those of consistent pore size where they show 100% retention of particles.
Nominal rating
The nominal rating refers to a filter capable of cutting off a nominated minimum percentage by weight of solid particles of a specific contaminant (usually again glass beads) greater than a stated micron size, normally expressed in micrometers (mm). I.e. 90% of 10 micron.
It also represents a nominal efficiency figure, or more correctly, a degree of filtration.
Process conditions such as operating pressure, concentration of contaminant etc, have a significant effect on the retention of the filters. Many filter manufacturers use similar tests but, due to the lack of uniformity and reproducibility of the basic method, the use of nominal ratings has fallen into disfavor.
Mean filter rating
The mean filter rating refers to the measurement of the average pore size of a filter element. It establishes the particle size above which the filter starts to be effective. It is determined by the bubble point test and it is more meaningful than a nominal rating and, in casa of filter elements with varying pore size, more realistic than an absolute rating.
Source: 'Filters and Filtration Handbook', T Christopher Dickenson, Elsevier, January 1, 1997
Filter Element Beta Ratio Information
Filter Beta Ratios
The Beta Ratio equals the ratio of the number of particles of a minimum given size upstream of the filter to the number of particles of the same size and larger found downstream. Simply put, the higher the Beta Ratio the higher the Capture Efficiency of the filter.
Filtration Ratings Defined
Filter ratings are an often misunderstood area of contamination control. The most commonly used rating is the Beta Ratio, which is defined as the ratio of the number of particles upstream of the test filter versus the number downstream, greater than a given size. Using the Beta Ratio, a 5 micron filter with a Beta 1000 Rating, will have on average 1000 particles larger than 5 micron upstream of the filter for every one 5 micron or greater particle downstream.
The efficiency of the filter can be calculated directly from the Beta Ratio since the % efficiency is simply (beta-1)/beta x 100. A Beta 1000, 5-micron filter is thus said to be 99.99% efficient at removing 5 micron and larger particles.
Caution must be exercised when using Beta Ratios since they do not take into account field operating conditions such as pressure surges and changes in temperature, which can affect real life performance. A filter's Beta Ratio also does not give any indication of its dirt holding capacity, the total amount of material that can be trapped by the filter throughout its life, nor does it account for how the capture efficiency changes over time. Nevertheless, Beta Ratios are an effective way of gauging the expected performance of a filter.
The ISO standard for Multi-pass filter testing (ISO 16889) has changed to require filter manufacturers to determine the average particle sizes which yield Beta Ratios equal to 2, 10, 75, 100, 200, and 1000, again using the multi-pass test stand approach. The new standard gives a better interpretation of a filter's overall performance.
Of course, regular monitoring of fluid cleanliness using ISO particle counting should be used to determine the efficiency of the filter in actual field conditions.
The Micron Rating for Media in Fluid Filters
A micron rating for a fluid filter is a generalized way of indicating the ability of the
filter's media to remove contaminants by the size of particles it is exposed to. The
micron rating does not properly or fully describe either the efficiency or the
contaminant-holding capacity of the filter media. ENGINE AIR FILTER MEDIA IS
NOT RATED BY MICRON SIZE. (Refer to TSB 04-3, Air Filter Life and Efficiency
Ratings)
What does the word micron mean? The word micron is another term for
micrometer (1 millionth of a meter). A micrometer is a unit of linear measure in
the metric system used to measure distance from one point to another. It is used
like the inch, foot, centimeter and millimeter to measure length, width or diameter
of objects. Its scientific notation is ƒÊ. Some linear equivalents are 1 inch is 25,400
microns and 1 micron is .000039 inches. Some comparative sizes are:
Diameter of average human hair 70 microns
Lower limit of visibility (naked eye) 40 microns
White blood cells 25 microns
Talcum powder 10 microns
Red blood cells 8 microns
Bacteria 2 microns
Carbon black 0.6 microns
Tobacco smoke 0.5 microns
A filter that is marked or rated "10 micron" has some capability to capture
particles as small as 10 micrometers. However, when you see a filter marked "10
micron", you do not know exactly what this means unless you also have a
description of the test methods and standards used to determine the filter rating.
The results from the different test methods may not be comparable as their
methodology varies greatly.
The two most popular reported media ratings are a nominal micron rating (50%)
and an absolute micron rating (98.7%). A nominal rating usually means the filter's
media can capture a given percentage of particles of a stated size. For example,
a filter might be said to have a nominal rating of 50% for particles 10 micrometers
in size or larger. An absolute micron rating can be determined by single-pass or
multi-pass testing and is usually obtained by passing a test fluid containing
particles of a known size through a small, flat sheet of filter media. Any particles
that pass through the media are captured and measured. An absolute rating is
also expressed in the form of a percentage of the size of particles captured.
Until recently, there has not been one universally accepted test method to
measure or describe the media pore size or the size of particles a filter media
can capture and hold. Depending on which test method was used, the same filter
media could be rated with different micron ratings, thus leading to confusion
regarding how well the filter's media actually performs. Fortunately, there now
exists a test procedure called multi-pass testing or Beta ratio testing (ƒÀ) which is,
a universally accepted test method that yields readily comparable test results.
Multi-pass testing has been recognized by SAE (SAE J1858), ISO (ISO 4548-12,
lube oil and ISO16889, hydraulic or fuel), ANSI (American National Standards
Institute) and NFPA (National Fluid Power Association).
Multi-pass testing uses a specified contaminant, of known sizes, added regularly
in measured quantities to the fluid which is pumped continuously through the
filter. Measured samples of fluid are then taken at timed intervals from the
upstream and downstream sides of the filter. The contaminant in the samples is
measured for particle sizes and quantities of each size or range of sizes. From
these upstream and downstream measurements, a Beta ratio is formulated by
dividing the number of particles of a particular size in the upstream flow by the
number of particles of the same size in the downstream flow.
X(c) per ISO 16889
In this example, the equation provides the following information: regarding 10-
micrometer or micron size particles, the filter media tested has a Beta ratio of 2.
This information is helpful but not useful without knowing what the ratio actually
means. To translate the Beta ratio into meaningful information, subtract 1 from
the original ratio and divide that answer by the original ratio. This answer
represents the efficiency of the media at the specified particle size. For this
example, take the Beta ratio of 2, subtract 1 from it and divide that answer by the
original ratio of 2 or 2 - 1 = 1 € 2 = 50% efficient at removing 10-micrometer or
micron size particles. This formula is used to translate any Beta ratio into a
percent efficiency at removing the size of particle tested. Here are a few Beta
ratios and their corresponding efficiencies:
Beta ratio information can also be stated as ƒÀ 5/10/20 = 2/20/75. In this example,
the media tested removed 50% of 5-micrometer or micron size particles, 95% of
10-micrometer or micron size particles and 98.7% of 20-micrometer or micron
size particles presented to it. This same ratio information can also be stated as
ƒÀ 2/20/75 = 5/10/20. Both equations state the same information in two different
ways and are both accepted by the industry.
Multi-pass testing provides an accurate, universally accepted, comparable test
method to describe the efficiency of a media's ability to remove certain size
contaminants. It can also determine the total contaminant holding capacity of the
filter as well as some of its differential pressure capabilities. Its use eliminates the
inaccuracies and confusion caused by the use of "micron ratings". For further
information, see TSB 97-1R1, Hydraulic Filter Performance Criteria and
TSB 04-2R1, ISO Updates to Multi-pass Liquid Filter Test Procedures.
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