It is difficult to base a filter performance by any particular count on a filter's upstream and downstream side.
Also, various problems occur due to the description of particle size which is in microns
unit. Thereupon, we shall introduce here particle count methods that are typically
applied.
1. Automatic Particle Counter method
This is further divided into 3 kinds of measurement principles.
(1). Light Scattering method
(2). Light Block method
(3). Electrical Resistance method(Coulter method)
1) Light Scattering method
As the particles pass through the laser beam they scatter light. Some fraction
of this is collected by the optics and focused on a photodiode
The peak amplitude of each pulse is compared with preset voltage thresholds,
and a count is assigned to the bin number that corresponds
to the channel
numbers whose upper and lower thresholds bracket the pulse height value or
int his case, a particular particle
size.
2) Light Block method
When a particle passes through a parallel emitted light source, it blocks the
passage of light and creates a shadow.
A sensor notes the varying intensity of the light as it is blocked by the
different particles in the stream and transforms this into electrical signals.
This method measures then the particle counts for ranges of particle sizes.
3)Electrical Resistance method
The Coulter counter measures particle counts by an electrical resistance
law called the Coulter Principle.
The Coulter method of sizing and counting particles is based on measurable
changes in electrical impedance produced by non conductive
particles suspended
in an electrolyte. A small opening or aperture between electrodes is the
sensing zone each particle displaces its own
volume of electrolyte.
Volume displaced is measured as a voltage pulse; the height of each pulse
being proportional to the volume of the particle. The quantity of suspension
drawn through the aperture is precisely controlled to allow the system to count
and size particles for an exact reproducible volumeDSeveral thousand particles
per second are individually counted and sized with great accuracy. This method
is independent of particle shape, color, density, and electolyte
temperature.
2. Direct Examination method
This method involves actual examination of particles collected on a membrane filter
from filtering a sample fluid. The particles are counted visually through an optical microscope according to particle sizes(Sizes are determined and examined first through a Scanning Electron Microscope).
This measurement procedure is documented in JIS B9930(Small Particle Measurement in Hydraulic Oil).
3. Microorganism counting
A microorganism is used for measuring filtration efficiency through a method like bacteria challenge.
A cultured medium(bacteria) is usually used for this method.
| Test Name |
Test Description |
Direct Microscope Examination
Method(Nomura method) |
A 500 ml sample fluid is filtered through a 0.2 micron membrane filter, then
blow-dyed before measurement. |
| Bacteria Culture Method |
ASTM revised method
A 1,000 ml sample fluid is filtered through a 0.2 micron membrane filter
After filtering, the membrane filter is subjected to a M-TGE medium at 35 for 24
hours
ASTM method(For electrical industry water analysis)
10 - 500 ml of sample fluid is filtered through a 0.45 micron membrane filter.
After filtering, the membrane filter is subjected to a M-TGE medium at 35 for 24
hours"
Satellite Test method(drinking water test)
Innoculation of 1 ml of ordinary drinking water.
Innoculation at 35-37 for 22-26 hours.
JIS
Direct innoculation of JISK-0101 K-0102 bacterium test.
Innoculation at 35-37 for 24-28 hours.
General Asepsis Test(Bacteria Test)
Innoculation by general asepsis test medium, Thioglycollate
Innoculation at 31}1 for 7 days. |
| Real Bacteria Culture Method |
General Asepsis Test(Bacteria Test)
Innoculation by general asepsis test medium, Glucose Peptone Broth
Innoculation at 25}1 for 10 days.
ASTM methodiYeast and mold Countj
10 - 500 ml of sample fluid is filtered through a 0.45 micron membrane filter.
After filtering, the membrane filter is subjected to a yeast and mold medium at 30 for 72 hours.
JIS
Fungi test method in accordance to JISK-0101, wherein 25-35 ml of a specimen
sample is boiled and innoculated in a hemp substance at room temperature for several days.
Other fungi is innoculated in 1 ml of waxman japanese gelatin medium.
Innoculation at 35-37 for 24}2 hours.
Results are further subjected to a similar operation using another type of gelatin
medium.
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