Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02347740 2001-04-18
EVALUATION METHOD FOR A PARTICLE COUNTER AND DEVICE
FOR C'.ARRYING OUT SAID METHOD
The invention relates to an evaluation method for a particle counter, in which
a detector signal is
produced by means of a detector which reacts to the presence of particles in a
measuring zone in
which a liquid flow is being conveyed, the detector signal is treated by a
signal processing device
and, taking into account at least one calibration factor, is converted into a
display value
indicating the particle density of the liquid flow. The invention also relates
to a device for
carrying out the evaluation method.
From European Patent 0 427 908 is known a particle counter which works by the
opacity method
and includes a light enclosure of which the receiver produces detector signals
showing the
presence of opaque; particles in the measuring zone. An evaluation method of
the
aforementioned type is used in the evaluation of these detector signals,
carried out by the method
disclosed in DE 41 10 231 Al, and the degree of contamination of the liquid
flow flowing
through
CA 02347740 2001-04-18
the measuring zone is to be monitored, in which it has to do preferably with
hydraulic petroleum,
in so many words, l:he densities of charges of solid materials such as
metallic and nonmetallic
impurities or contaminants in said liquid are established, or even the
presence of air bubbles or
water droplets, which in the light enclosures likewise lead to the appearances
of opacities which
appear on the detector signal.
In the conventional evaluation method, particles which are present in a
certain volume to be
measured are countc;d in channels of different magnitudes, associated with
particles which are in
classes of different magnitudes and in turn are counted as pulses of the
detector signal. The
volume to be measured in turn is determined by volume flow measurement. The
particle count is
then corrected by multiplication with the relevant channel magnitudes of
corresponding
individual calibration factors. These corrected particle numbers are then
translated into classes
of contamination in order to correspond to the NAS 1638- or ISO 4406-Tables.
DE 1 294 051 B discloses a method and device for the measurement of the volume
or weight of a
volume of essentially nonuniform bodies being conveyed through a channel of
predetermined
diameter. In this case the detector signal is converted by means of a trigger
stage into pulses of
constant amplitude. These pulses arf; fed to an integrator, in which occurs a
time integration of
the discrete individual pulses. Following each pulse the output signal of the
integrator is
returned to start. Thf; method supplies an output signal which represents a
mean value of the
volume or weight of the bodies conveyed in a time lapse to be studied.
MODIFIED PAGE
la
CA 02347740 2001-04-18
GB 2 082 764 A discloses a device for measuring particles in liquids in which
the appearance of
particles is established as a phenomenon and the phenomena are summarized by
means of a
counter. When a predetermined number of phenomena has been exceeded a switch
is activated,
which can set off an alarm or react otherwise. For determination of the
particle density,
additional and indc;pendent measurements of the volume flow must be carried
out.
The object of the invention is to disclose a method of evaluation which, as
opposed to the
conventional method, is characterized in that the density of the particle
charge of the relevant
liquid flow can be evaluated at lower cost and with greater precision.
With an evaluation method of the aforementioned type, this object is attained
according to the
invention in that the treatment of the detector signal is carried out in such
a manner that the
individual residence times of the particles in the measuring zone are
determined within a
predetermined lapse of time, and that by summation of the residence times a
summation signal is
formed and this summation signal is used with taking into account at least one
calibration factor
for the representation of the display value.
Owing to the fact that the display value is no longer determined on the basis
of the counted
number of particles present in a certain liquid volume, but rather on the
basis of a summation of
the individual residence times of the particles within the zone of measurement
carried out within
a certain predetermined lapse of time, the measurement of the volume flow,
which is required in
the conventional method, as well as other measures which have been required in
cooperation
MODIFIED PAGE
2
CA 02347740 2001-04-18
with the conventional method, can be deleted. Thus the method according to the
invention is
characterized not only by simplified capacity of execution with decreased
outlay of apparatus,
but also by a comparably higher precision in the results, because, since no
knowledge concerning
the present volume flow is required, the evaluation is dependent neither on
any measurement or
limitation of the volume flow being considered nor of its condition otherwise.
Regarding a
higher level of precision, the circumstance is also to be considered that no
error of the volume
flow measurement need be taken into consideration for the calculations.
One method for ascertaining the distribution of the particle dimensions of the
particles dispersed
in liquids is already known from DE 32 09 510 C2 (= US 4,491,926), by
determining the
residence times of particles in the measuring zone. Differing from that, the
method according to
the invention carries out the treatment of the detector signal in such a
manner that residence
times of the particles in the measuring zone are determined on the basis of
the number of counted
pulses.
As in the conventional evaluation method, in the invention the evaluation can
be based on the
different classes according to particle size, as found in the so-called
magnitude-channels,
whereby a suitable calibration factor is used for each relevant channel
magnitude, for the
determination of the display value. Thus, the particle number per liquid
volume can be deduced
from the summation signal, for example the count per 100m1, so that then in
turn the correlation
to classes of contaminants relating to this particle number can be undertaken
corresponding to the
NAS 1638- or ISO 4406-Tables relating thereto.
MODIFIED PAGE
CA 02347740 2004-10-12
For evaluation of the pulse height in the detector signal for correlation to
the channel magnitudes,
the detector signal can be converted by means of a comparator circuit into a
comparator output
signal representing the residence times while taking into account a
predetermined threshold
value, which output signal is used for the summation of the residence times.
Said output signal
can be analog or digital. With the analog determination the comparator output
signal is
integrated within the predetermined lapse of time to a voltage value
representing a summation
signal. With the digital determination according to one preferred embodiment
it is corned out so
that the summation of the residence times is demonstrated in such a manner
that oscillator pulses
are counted, which have been released within the predetermined lapse of time
according to the
measure of the comparator output signal.
According to one other aspect of the invention, it is also intended to
disclose a device for
execution of the disclosed evaluation method. As described herein the device
of the invention
includes a signal processing device with a comparator circuit for generation
of a comparator
output signal representing the residence times of the particles in the
measuring zone while taking
into consideration a predetermined threshold value, with a pulse generator for
production of a
pulse signal defining the predetermined lapse of time, as well as with a
summation device.
According to a further aspect of the present invention there is provided a
method for
evaluating a particle counter, comprising the steps of producing a detector
signal by a
detector reacting to presence of particles in a measuring zone through which a
liquid flow
is conveyed, and treating the detector signal by a signal processing device
and converting
the detector signal into a display value, while taking into account at least
one calibration
factor, such that the display value indicates a particle density in the liquid
flow by
ascertaining the individual residence times of the particles in the liquid
flow in the
3a
CA 02347740 2004-10-12
measuring zone and within a predetermined lapse of time and by performing a
summation of the residence times to form a summation signal, while taking into
account
the at least one calibration factor, for representing the display value.
According to a further aspect of the present invention there is provided a
device for
evaluating a particle counter, comprising a detector for producing a signal
reacting to
presence of particles in a measuring zone through which a liquid flow is
conveyed, a
signal processing device, including a comparator circuit, for generating a
comparator
output signal representing residence times of the particles in the measuring
zone, taking
into account a predetermined threshold value, a pulse generator for producing
a pulse
signal defining a predetermined lapse of time, and a summation device for
forming a
summation of the comparator output signal, taking into account the at least
one
calibration factor, to represent a display value indicating particle density
in the liquid
flow.
Hereinafter the invention is to be explained in greater detail relative to the
drawings. In the
drawings are shown
Fig. 1 a diagrammatically simplified, partially cut out plan view of an
arrangement including particle counter and associated evaluation device,
represented with cover removed from the device,
Fig. 2 a greatly simplified block diagram of one embodiment of the signal
processing device for use with the modular unit of the device of Fig. 1;
Figs. 3 and 4 diagrams of the temporal cycle of signal pulses of the signal
processing
device of Fig. 2;
Fig. 5 a representation corresponding to that of Fig. 2 of a different
arrangement
of the signal processing device, and
Figs. 6 and 7 diagrams corresponding to Figs. 3 and 4 of the temporal cycle of
signal
pulses from the signal processing device of Fig. 5.
4
CA 02347740 2001-04-18
A modular unit shown in Fig. 1 has an aluminum housing 11 with the cover
removed, in which is
arranged a detector module 13 with a particle detector 15. The particle
detector is a conventional
type of detector, known from European Patent 0 427 908, which produces-
detector signals
according to the opacity principle lby means of a light enclosure arrangement,
which transmits
signals representing the presence. of particles in a measuring zone. For the
feed and the discharge
of the liquid flowing through the measuring zone, housing 11 has a liquid
inlet 17 and a liquid
outlet 19. Detector module 13 also incorporates a pressure valve 21 in order
to facilitate the
shutting off on a pressure-loaded conduit.
A signal processing device serving as evaluation circuit for the detector
signals of the particle
detector 15, which likewise is mounted in housing 11, is designated in Fig. 1
with reference 23.
The power supply or power source for particle detector 15 and for signal
processing device 23
comes through a cable 25, through which the output signal is also delivered,
which is
characterized by a ~1AS-contamination class and for example is published as
pulse duration-
modulated square-wave signal. t:)n.e example of a digital evaluation method
for the production of
such an output signal is explained in greater detail relative to Figs. 2 to 4.
In these drawings, (2) symbolizes a time signal defining a predetermined lapse
of time, and is fed
from the pulse generator of a controller unit, with (3) symbolizing the
detector signal of particle
detector 15, with (5) being a threshold value signal, with ( 1 ) symbolizing a
comparator output
signal produced by operation of the comparator out of (3) and (5), and with
(6) symbolizing
counter [or counted] signal pulses, which appear when oscillator pulses (4)
are being released by
the comparator output signal (1). Fig. 3 shows one example in which with a
given flow rate Q of
the flowing liquid during the predetermined lapse of time T = constant (for
example one minute),
the detector signal (3) signals the presence of two particles, which with the
selected threshold
CA 02347740 2001-04-18
value (S) as output signal of a comparator circuit indicated in Fig. 2 with K,
lead to a comparator
output signal (1), which indicates a residence time denoted by t for each
particle.
In the case of the present oscillator frequency which has been selected as
(4), its release leads
through the comparator output signal over each of the residence times t to six
counter pulses for
each one, which at the end of the lapse of time T lead to a summarized counter
state of I2, see
Fig. 3.
Fig. 4 shows the ratio with the identical liquid, in other words liquid having
the same particle
density as in Fig. 2, whereby however the flow rate of the liquid is 2 X Q, in
other words double
the rate shown in Fig. 3. This doubled flow rate of the liquid having the
identical particle density
leads to the appearance of a detector signal (3), which signals four particles
collected by the
detector, whereby however the individual residence time is only tl2 as a
result of the doubled
flow rate. With identical oscillator frequency with any individual residence
time of tl2 there
appear in turn three counter pulses (6), which in turn, within the time lapse
T including four
summarized residence times t/2, lead to the identical counter state 12 with
the flow rate 2 x Q.
The state of the counter following the running out of the time interval T in
other words is
independent of the .flow rate which is the identical rate. By customary
calculation with suitable
calibration factors therefore from the counter state the particle density or
the degree of
contamination can be deduced according to Iv~AS or ISO.
Figs. 5 to 7 show one possible arrangement for analog evaluation, whereby a
current source is
indicated with 1 in the diagrammatical representation of Fig. 5. In Figs. 6
and 7, corresponding
to Figs. 3 and 4, the ratios with flow rate Q or flow rate 2 X Q are
represented in turn. As
signaled previously, with the flow rate 2 X Q, the comparator output signal (
1 ), with given
6
CA 02347740 2001-04-18
threshold (5), delivers double the number of residence times as compared with
Fig. 6, whereby
the individual residence times as compared with t of Fig. 6 are decreased to
t/2 in Fig. 7. The
voltage integrated by means of an integrator in the circuit of Fig. 5
according to the measure of
the comparator output signal (1) rises in the example of Fig. 6 during each of
the individual
residence times t in terms of two voltage units, so that the integrated
voltage with the flow rate Q
is referenced according to the lapse of time T as four voltage units.
In the example of F ig. 7 the voltage (6) is modified on the basis of the
halved residence time t/2
in turn for one voltage unit only, which following running out of the time
lapse T with the
doubled flow rate ? X Q likewise leads to the integrated value of four voltage
units. The
evaluation result is likewise again :independent of the flow rate
7
