Browse Prior Art Database

Self-Calibrating Particle Counters for Fluids

IP.com Disclosure Number: IPCOM000104322D
Original Publication Date: 1993-Apr-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 2 page(s) / 89K

Publishing Venue

IBM

Related People

Batchelder, JS: AUTHOR [+2]

Abstract

Disclosed is a method for making or modifying particle counters for fluids so that the counters may be used to calibrate By calibration is meant determination of the fraction of the true concentration that the counters measure, as a function of particle size.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Self-Calibrating Particle Counters for Fluids

      Disclosed is a method for making or modifying particle counters
for fluids so that the counters may be used to calibrate By
calibration is meant determination of the fraction of the true
concentration that the counters measure, as a function of particle
size.

      Optical particle counters determine the number of particles in
a liquid or a gas (a fluid) by counting pulses of light scattered by
single particles when each particle is illuminated.  Determining the
detection efficiency, the fraction of particles successfully sensed,
is important, but difficult.  This invention allows detection
efficiency to be determined without disconnecting the sensor from the
process being inspected.

      The invention is a combination of valving and moving elements
that reduces the usual flow to a small fraction of its original value
(by partially closing a valve, for example), then superimposes on
this low flow a variable flow (such as a simple oscillatory flow).
Particles in the fluid will pass through the illuminating zone with a
velocity that is the superposition of the low flow and the variable
flow, and the electronic circuits analyzing the signal can be
adjusted to detect the characteristic signal from superposition,
greatly improving the signal-to-noise ratio.  For particles having
sizes within the  high-efficiency detection range of the
superposition flow condition, the concentration of the particles can
be detected accurately, for comparison against the concentration
determined by the usual flow conditions, from which ratio the
detection efficiency can be inferred.

      Consider  the  normal operation of an optical particle counter.
The flow path is into a sensor, past an illuminating and sensing
region, then to the exhaust.  The  normal flow  is v*.  The normal
time of passage through the beam is t*.  Nominal signals have widths
on the order of t* and heights that are determined by the particle's
size, trajectory, composition, shape, noise, and other effects.

      In contrast, consider the self-calibrating optical particle
counter.  The flow can be throttled down and a variable component
super-imposed  using  a  "squeezer".  The squeezer is controlled by a
signal generator which is also connected  to a lock-in amplifier.

      In  practice,  the  squeezer  could  be made by constricting
tubin...