Particle Size Measurement - Answer to Competitor Comments

7/31/2019 Particle Size Measurement - Answer to Competitor Comments

1/21

Laser Diffraction and TOT

Topics Covered:

Competitor version of TOT

Facts of TOT

Facts of Laser Diffraction

Laser DiffractionIs it a viabletechnique??


2/21

Competitor Comment!!

Time of TransitionA Laser, but not Laser Diffraction

The particles are scanned bya rotating laser beam.

Only particles in the focussedarea are measured


3/21

YES, They are right!!

It is not Laser Diffraction

It is a better technique than Laser

Diffraction

IT IS TIME OF TRANSITION!


4/21

YES, Particles are scanned by the

rotating laser beamThis would allow measurement in the time

domain


5/21

Time Of Transition

The diameter of the particle is directly correlated to theTime-Of-Transition.

A rotating laser beam scans single particles within its focus.

Time Domain Measurement:


6/21

Time Of Transition

The Time Of Transition (t) together with the knownrotation velocity of the laser beam (v) makes it

possible to calculate the particle diameter (D):

D = v . t

In relation to the high speed of the rotating laser, the

particles are stationary. So, particle movement does not

effect particle size measurement.

No requirement for pre-knowledge of:- Refractive index- Temperature- Viscosity variation- Electrical conductivity


7/21

Laser Diffraction

Resolution limited by Number of Detectors ! Higher the

number better the resolution

Failure of one detectorcost to be paid for all detectors!! Huge

Maintenance Costs !!!

Optics alignment is critical for proper measurement!


8/21

IS this possible in Laser

Diffraction?? Can Laser Diffraction systems analyse samples

without the knowledge of

Refractive Index of Sample

Refractive Index of Dispersant

Temperature (RI is dependant on Temperature)

Sample that is transparent (As the fundamentalassumption is particles are opaque)

High Concentration Samples (Which cause multiplediffraction)

Contd


9/21

IS this possible in Laser

Diffraction??.... Can Laser Diffraction systems analyse

samples

That are fibres, needle-like and irregular shapes

For Particles that are not spherical

For viscous samples

Samples that are mixtures (have samples ofdifferent RIs)


10/21

THE ANSWER IS

NO for Laser Diffraction

YES for TOT


11/21

NO by Laser Diffraction because

Fundamental Assumptions:

Particles are to be spherical

Particles are to be opaque

No Multiple Scattering Events

Total Diffraction = Sum of Individual

Random Particle Orientation

Spherical Equivalent Diameter Data

Volume (Weight) based Results

Limited resolutiondepends up on the number ofdetectors


12/21

Fact is

Not all particles are spherical

Not all particles are opaque

Not all particles diffract light with equal

efficiencies

Can Laser Diffraction take care of all this??


13/21

YES by TOT because

NO Fundamental Assumptions

Measurements are in time domain, HenceNo need of knowledge of RI, Temperature

All samples including fibers can be measured

Can take higher concentrationsMixtures can be analysed without any problem.

.contd


14/21

More from TOT

Results are not just volume based. You can

also get number based, area based, length

based etc

Laser light intensity and power fluctuations

dont affect measurements (as in Laser

Diffraction) since the measurements arebased on Time Domain.


15/21

Competitor Comment !!

Time of Transition

A Laser, but not Laser Diffraction

The particles are counted(number distribution)

However because the sameparticle can be counted many

times, it cannot be a trueabsolute particle counter


16/21

FACTS

It is not just number distribution that TOT

provides, but also volume, area, length etc When the sample is in circulation, all techniques

(including Laser Diffraction) measure the sameparticles several times. Whats a big difference in

Laser Diffraction!!

The sample can be made to not circulate henceavoid interaction with same particlethis is truewith Laser Diffraction also.

AN INVALID COMMENT FROMCOMPETITION


17/21

Competitors Comment !!

Time of Transition


Because only particles in thefocussed area are accepted,

up to 97% of data is rejected.

The sizing information is

therefore unrepresentativeand unreliable.


18/21

FACTS Is there any practical data for showing that 97% of

data is rejected ? Particles are measured in the focused area even in

Laser Diffraction. Does that also mean Laser

Diffraction provides data which is 3% and still

Laser Diffraction data is reliable??

What is important is the representative data and

concentration of particles measurable.

Beyond doubt, Laser diffraction can accept lowerconcentration (otherwise it will lead to multiple

diffraction) than TOT.


19/21

Competitors Comment ! !

Time of Transition


This technology satisfiesnone of the criteria laid down

in ISO13320 for a laserdiffraction particle sizer


20/21

ISO 13320

Yes, ISO 13320 mentions about LaserDiffraction

It also specifies that Minimum particle sizemeasurable is 40 * , where is the

wavelength of light source.

For a laser which is 532.8nm, minimumparticle size measurable is 25 microns.

This means Laser Diffraction is not suitablefor particle sizes less than 25 microns !!

This is a limitation besides other limitations

discussed in previous slides.


21/21

Want to learn more about Laser

Diffraction drawbacks !!! Refer to the presentation on False Assumptions:

Laser Diffraction PSA Systems Exposed by

Richard N KellyPrincipal ScientistJJPRD. Ifyou dont have one, request for the same.

Refer www.ankersmid.com

Contact Technical Trade Links Pvt. Ltd.,

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Particle Size Measurement - Answer to Competitor Comments