FORM 2
THE PATENT ACT 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See Section 10, and rule 13)
1. TITLE OF INVENTION
RADIOMETRIC MEASURING ARRANGEMENT AND METHOD FOR DETECTING A DEPOSIT FORMATION IN A RADIOMETRIC MEASURING ARRANGEMENT
2. APPLICANT(S)
a) Name : ENDRESS+HAUSER GMBH+CO. KG
b) Nationality : GERMAN Company
c) Address : HAUPTSTRASSE 1,
79689 MAULBURG,
GERMANY
3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention
and the manner in which it is to be performed:-
2
The invention relates to a method for detection of accretion formation in containers,
in which a radiometric measuring arrangement for measuring and/or monitoring a
measured variable, especially a fill level or a density of a substance located in a
container, is provided, as a well as to a radiometric measuring arrangement
comprising a measuring system, which during operation sends radioactive radiation
along a measuring path through the container. The measuring system includes a
detector, which measures radiation intensity emerging from the container along the
measuring path, and an evaluation unit, which, based on calibration data of the
measuring system and based on the measured radiation intensity ascertained in the
case of accretion free container, determines and outputs a measurement result
corresponding to the measured variable.
Radiometric measuring arrangements are applied in industrial measurements
technology, for example, for measuring a fill level of a fill substance in a container,
for monitoring exceeding or subceeding of a predetermined fill level of a fill
substance in a container, or for measuring a density of a fill substance.
Radiometric measuring arrangements are usually applied when conventional
measuring methods are not applicable due to especially rough conditions at the
measuring location. Very frequently present at the measuring location are extremely
high temperatures and pressures or chemically and/or mechanically very aggressive
environmental influences, which make use of other measuring methods impossible.
A fundamental principle of radioactive measurements technology is that one or more
radioactive radiators, such as e.g. Co60 or Cs137 preparations, are positioned at a
measuring location in such a manner that radiation emitted by them penetrates a
region to be registered metrologically, e.g. a part of a container filled with a fill
substance, and a radiation intensity emerging on a container side lying opposite the
radiator is measured with an appropriate detector, e.g. a scintillation detector. The
emerging radiation intensity depends on the geometric arrangement and the
absorption along the path traveled by the radiator to the detector. The latter is in the
case of fill level measurement dependent on the fill level of the fill substance located
in the measuring path in the container and in the case of density measurement on
the density of the fill substance located in the measuring path. As a result, the
3
emerging radiation intensity is a measure for the current fill level, respectively the
current density, of the fill substance in the container.
There are a large number of industrial applications, in the case of which, with time,
accretion can form on the inner walls of the container. The terminology, accretion,
refers here to deposits of material attached to the inner walls. Accretion arises, for
example, when the fill substance located in the container, or, in the case of tubular
containers, flowing through the container, clings to the inner wall, and thereby
establishes an accretion layer on the inner wall of the container. With time, other
deposits or attached material causes the layer to become increasingly thicker.
In such case, there is the problem that the measuring path through the container
leads through the layer of accreted material both in the case of its entry into the
container as well as also in the case of its exit from the container. Correspondingly,
both entrance side as well as also exit side, a part of the radiation sent through the
container is absorbed in the accretion layer. Since the accretion layer has a higher
density deviating, as a rule, from the medium, it absorbs radioactive radiation more
strongly than the fill substance. In this way, the radiation intensity emerging in
measurement operation is increasingly reduced, and, thus, the measurement result
becomes more and more corrupted. Due to the accretion related, lower measured
radiation intensity, a too high fill level, respectively a too high density, is measured.
If this measurement error is not recognized, such can have fatal effects, especially in
safety-relevant applications.
There is, consequently, a need to detect accretion formation in containers as early
as possible. Exactly in applications in which radiometric measuring systems are
applied, it is, as a rule, not, or not directly, possible to open the container, in order, in
given cases, to detect accretion formation early.
Moreover, container cleaning, in the case of which accretion is removed, is, as a
rule, especially complicated and expensive, particularly in these applications.
Described in US 3,594,575 A1 is a fill level measuring arrangement, in the case of
which, in given cases, accretion formation arisen in the container can be taken into
4
consideration by a new calibration of the measuring arrangement executed on-site.
In the new calibration, the dependence of the measured radiation intensities on the
fill level is determined anew in the case of a currently present container state. In
ongoing operation, it is, however, not possible to detect whether accretion has
formed. Insofar, there remains even here the possibility of an unrecognized
measuring result corruption due to accretion formation.
It is an object of the invention to provide a radiometric measuring arrangement and a
method executable therewith, in the case of either of which accretion formation in the
container of the measuring arrangement is detectable.
To this end, the invention resides in a method for accretion detection in a container,
wherein a radiometric measuring system is provided for measuring and/or monitoring
a measured variable, especially a fill level or a density of a fill substance located in
the container, which method comprises steps as follows:
- sending during operation radioactive radiation along a measuring path through
the container, measuring radiation intensity emerging from the container along
the measuring path, and, based on calibration data of the measuring system and
measured radiation intensity ascertained in the case of accretion free container,
determining a measurement result corresponding to the measured variable,
wherein,
- by means of a comparison measuring system, radioactive radiation is sent along
a comparison path through the container, a radiation intensity emerging from the
container along the comparison path is measured, and, based on calibration data
of the comparison measuring system and measured radiation intensity
ascertained in the case of accretion free container, a measurement result
corresponding to the measured variable is determined,
-- wherein the comparison path extends in such a manner through the container
that, in the case of presence of an accretion layer on the inner walls of the
container, a ratio of a sum of the two segments of the measuring path extending
through the accretion layer to the length of an additional segment of the
measuring path extending between these two segments is different from the ratio
formed in the same manner for the comparison path, and
5
- an occurrence of accretion formation is detected based on deviations ascertained
in ongoing operation between the measurement results of the measuring system
and the measurement results of the comparison measuring system.
In a preferred embodiment, the ratio of the sum of the two segments of the
measuring path extending through the accretion layer to the length of the additional
segment of the measuring path extending between these two segments is smaller
than the ratio formed in the same manner for the comparison path.
In an additional preferred embodiment, the exceeding of a predetermined threshold
value for the deviation between the two measurement results means that an
accretion formation in the container corrupting the radiometric measuring of the
measured variable has been detected.
Moreover, preferably a need dependent scheduling of container cleanings is
performed based on the deviations between the measurement results of the
measuring system and the measurement results of the comparison measuring
system.
Additionally, the invention resides in a further development of the method, wherein,
in the case of known density of the accretion, a thickness of the accretion layer in the
container is determined based on
- the radiation intensity measured with the measuring system and the radiation
intensity measured with the comparison measuring system, and
- a container geometry and positions of measuring and comparison paths in the
container.
A further development of the latter further development includes a method, in the
case of which, based on the radiation intensity measured with the measuring system,
the thickness and the density of the present accretion layer, a measurement result
corrected as regards an accretion related measurement error is determined.
Moreover, the invention resides in a radiometric measuring arrangement for
measuring and/or monitoring a measured variable, especially a fill level or a density,
of a fill substance located in a container, comprising
6
- a measuring system,
-- which during operation sends radioactive radiation along a measuring path
through the container,
-- which includes a detector, which measures a radiation intensity emerging from
the container along the measuring path, and
-- which includes an evaluation unit, which, based on calibration data of the
measuring system and the measured radiation intensity ascertained in the case
of accretion free container, determines and outputs a measurement result
corresponding to the measured variable, and
- a comparison measuring system,
-- which during operation sends radioactive radiation along a comparison path
through the container,
-- wherein the comparison path extends in such a manner through the container
that in the case of presence of an accretion layer on the inner walls of the
container a ratio of a sum of the two segments of the measuring path extending
through the accretion layer to the length of an additional segment of the
measuring path extending between these two segments is different from the ratio
formed in the same manner for the comparison path,
-- which includes a detector, which measures a radiation intensity emerging from
the container along the comparison path, and
-- which includes an evaluation unit, which, based on calibration data of the
comparison measuring system and the measured radiation intensity ascertained
in the case of accretion free container, determines a measurement result
corresponding to the measured variable and provides such for detection of
accretion formation in the container, wherein accretion is detected based on
deviations ascertained in ongoing operation between the measurement results of
the measuring system and the measurement results of the comparison
measuring system.
In a preferred embodiment, the radiometric measuring arrangement includes,
connected to the measuring system and to the comparison measuring system, an
evaluating unit, which during operation continuously determines deviations between
the measurement results of the measuring system and the measurement results of
the comparison measuring system.
7
A first variant of the invention includes a radiometric measuring arrangement, in the
case of which the measuring system and the comparison measuring system each
has a radioactive radiator arranged externally on the container, and in the case of
which the detectors of the measuring system and the comparison measuring system
are each arranged externally on the container on a side of the container lying
opposite the respective radiator along the measuring, respectively the comparison,
path.
In a preferred embodiment of the first variant, the container has a circular cross
sectional area, and the measuring path extends parallel to and offset from the
comparison path.
A second variant of the invention includes a radiometric measuring arrangement, in
the case of which
- there is provided arranged externally on the container only a single radioactive
radiator, which during operation transmits radiation along the measuring path and
along the comparison path,
- the measuring path and the comparison path extend at an angle to one another,
- the detector of the measuring system is arranged externally on the container on a
side of the container lying opposite the single radiator along the measuring path,
and
- the detector of the comparison measuring system is arranged externally on the
container on a side of the container lying opposite the single radiator along the
comparison path.
Additionally, the invention resides in a variant of a radiometric measuring
arrangement of the invention, in the case of which
- each of the measuring system and the comparison measuring system is a system
for detecting and/or monitoring an ex- or subceeding of a predetermined fill level
in the container,
- each of the measuring system and the comparison measuring system has an
output, via which it outputs a measurement result corresponding to radiation
intensity measured by it and based on calibration data ascertained in the case of
accretion free container, and
8
- the measuring system detects and/or monitors the ex- or subceeding of the
predetermined fill level based on the measured radiation intensity or based on the
measurement results.
The invention and other advantages will now be explained in greater detail based on
the figures of the drawing, in which three examples of embodiments are presented;
equal parts are provided in the figures with equal reference characters. The figures
of the drawing show as follows:
Fig. 1 a radiometric density measuring arrangement in cross section;
Fig. 2 a longitudinal section through the density measuring arrangement of Fig. 1
in the plane of the measuring system;
Fig. 3 an alternative embodiment of a density measuring arrangement of the
invention; and
Fig. 4 a longitudinal section through a fill level measuring arrangement in the plane
of the measuring system.
Fig. 1 shows, for measuring and/or monitoring a measured variable, especially a fill
level or a density �� of a fill substance 3 located in a container 1, a sketch of the
principles of a first example of an embodiment of a radiometric measuring
arrangement of the invention, with which the method of the invention for detection of
accretion formation in the container 1 of the measuring arrangement is performable.
The invention will, first of all, be described using the example of a measuring
arrangement for measuring the density �� of the fill substance.
Container 1 is shown here in cross section and is, for example, a pipe, through which
the fill substance 3 flows, or a standing, cylindrical tank, which contains the fill
substance 3.
The measuring arrangement includes a measuring system, with which the density ��
of the fill substance 3 is measured. The measuring system includes, arranged
9
externally on the container 1, a radioactive radiator 5, which during operation sends
radioactive radiation along a measuring path A through the container 1. For
achieving an as high as possible accuracy of measurement, the measuring path A
passes preferably through a midpoint of a cross sectional area of the container 1. In
this way, the part of the measuring path A relevant for the accuracy of measurement
in the container 1 has in the container 1 a maximum possible length, so that the
measurement effect is maximum.
Moreover, the measuring system includes a measuring unit 7, which measures a
radiation intensity emerging from the container 1 along the measuring path A, and,
based on calibration data of the measuring system and the measured radiation
intensity ascertained in the case of accretion free container 1, determines and
outputs a measurement result corresponding to the measured variable, here the
density ��. Fig. 2 shows, in this connection, a longitudinal section through the
radiometric measuring arrangement of Fig. 1 in the plane of the measuring system.
Measuring unit 7 includes, for this, a detector 9, which converts the radiation
intensity striking thereon into an electrical signal reflecting the measured radiation
intensity, and an evaluation unit 11 connected thereto, which, based on the electrical
signal and the calibration data, determines and outputs a measurement result
corresponding to the measured density ��.
The calibration data are determined in the simplest case by a two point alignment,
which, for example, in the context of a start-up of the measuring system, is executed
with an accretion free container 1. For this, for example, the radiation intensity is
measured, which impinges on the detector 9, when such is filled with a fill substance
3, which has a density ��min corresponding to a measuring range lower limit of the
measuring system, and the radiation intensity is measured, which impinges on the
detector 9, when such is filled with a fill substance 3, which has a density ��max
corresponding to a measuring range upper limit of the measuring system. From
these two measurement points giving the radiation intensity measured as a function
of the density, a scale can then be defined, based on which each radiation intensity
measured in measurement operation and lying between the two extreme values is
10
associated with a particular density ��. This is presented here, however, only as a
possible example. In radiometric measurements technology, as a rule, more
complex calibration methods are applied, which utilize, for example, more alignment
points, linearizing methods, as well as compensation methods for compensation of
dependencies of the measured radiation intensity on additional process variables,
such as, for example, temperature.
According to the invention, the measuring arrangement includes, moreover, a
comparison measuring system, with which the density �� of the fill substance 3 is
likewise measured. The latter can be embodied identically to the measuring system.
Also this includes in the illustrated example of an embodiment, arranged externally
on the container 1, a radioactive radiator 13, which during operation sends
radioactive radiation along a comparison path B through the container 1, and a
measuring unit 15, which measures by means of a detector 17 a radiation intensity
emerging from the container 1 along the comparison path B. Detector 17 is
connected with an evaluation unit 19, which, based on calibration data of the
comparison measuring system and the measured radiation intensity ascertained in
the case of accretion free container, determines a measurement result
corresponding to the density ��.
According to the invention, the comparison path B extends in such a manner through
the container 1 that in the case of presence of an accretion layer 21 on the inner
walls of the container 1, a ratio VA of the path lengths extending along the
measuring path A in the interior of the container 1 within and outside the accretion
layer 21 is different from the corresponding ratio VB along the comparison path B. In
such case, it is to be taken into consideration that the measuring path A and the
comparison path B each extend input side through the accretion layer 21, which
adheres internally on the container wall facing the respective radiator 5, 13, and
output side through the accretion layer 21, which adheres internally on the container
wall facing the respective detector 9, 17.
The ratios VA, VB are given, in each case, by the ratio of the sum of the lengths of
the segments A1, A3, respectively B1, B3 of the respective radiation path extending
11
input side and output side through the accretion layer 21 to the additional segment
A2, respectively B2, of the respective radiation path extending respectively between
these two segments. I.e. measuring path A and comparison path B are specified
according to the invention in such a manner that:
2
1 3
2
1 3
B
VB B B
A
VA A A
+
≠ =
+
=
This condition is directly fulfillable in any container 1, since the two paths are
positioned and oriented in such a manner that their sections leading through the
container interior have different lengths. Such is always possible for any container
cross-section. Thus, for example, the measuring path A can be led in a broadest
region of the container 1 through the container middle, while the comparison path B
traverses only an edge region of the container 1.
In the illustrated example of a container 1 with circularly shaped cross section, this is
implemented by leading measuring path A and comparison path B parallel to one
another and offset from one another through the container 1, wherein the measuring
path A passes through the broader container middle.
Since, from the above explanations regarding the accuracy of measurement
achievable with the measuring system, preferably the path with the greatest total
length extending in the container interior is used as measuring path A, the ratio VA is
preferably smaller than the ratio VB. Such offers the additional advantage that the
measurement result along the measuring path A, due to the smaller ratio VA, also
experiences a lesser degrading of the measurement result from accretion formation.
Due to the calibration of measuring system and comparison measuring system in the
case of accretion free container 1, the measurement results of the two systems
agree in the case of accretion free container 1, within the achievable accuracy of
measurement.
If the measuring arrangement in the case of accretion free container 1 is placed in
service, the measurement results thus, first of all, agree. If there forms in ongoing
12
operation an accretion layer 21 on the container inner walls growing with time in its
thickness, then the two measurement results change as a function of the density ��A
and the thickness of the accretion layer 21.
The reason for this is that measuring system and comparison measuring system
then no longer register exclusively the desired density �� of the fill substance 3, but,
instead, an average density present along the respective radiation path in the
container interior. Since the accretion layer 21 usually has a higher density ��A than
the fill substance 3, the two measurement results increase with increasing thickness
and with increasing density ��A of the accretion layer 21.
In such case, there holds for the average density ��meas measured by the measuring
system:
1 2 3
( 1 3) 2
A A A
A A A A
meas + +
+ +
=
ρ ρ
ρ
Correspondingly, there holds for the average density ��comp determined by the
comparison measuring system:
1 2 3
( 1 3) 2
B B B
B B A B
comp + +
+ +
=
ρ ρ
ρ
Due to the paths predetermined according to the invention, however, the density
��meas measured by the measuring system increases with increasing thickness and
density of the accretion layer 21 significantly slower than the density ��comp measured
with the comparison measuring system. This means that the measurement results of
measuring system and comparison measuring system deviate increasingly from one
another with increasing density ��A and increasing thickness of the accretion layer 21.
Correspondingly, accretion formation in the container 1 is detected according to the
invention based on deviations of the measurement results of measuring system and
comparison measuring system ascertained in ongoing operation. In such case, for
example, the ratio of the two measurement results can be calculated as a
13
quantitative measure of the deviation. Alternatively, also their difference can be
taken into consideration as a measure.
In such case, the size of the deviation is a measure for degradation of the accuracy
of measurement of the radiometric measuring arrangement. Correspondingly, a
threshold value can be predetermined for the deviation, the exceeding of which
threshold value means that an accretion formation in the container 1 corrupting the
radiometric measurement of the measured variable has been detected.
Measurement corrupting accretions can, thus, be detected early and correspondingly
taken into consideration.
Moreover, the deviations between the measurement results of the measuring system
and the measurement results of the comparison measuring system ascertained in
ongoing operation can be used for need dependent scheduling of container
cleanings. In such case, the time development of the deviations can be taken into
consideration, in order to make predictions concerning the point in time when the
deviation will exceed the threshold value, or some other, for example, user defined
criterion making a cleaning required.
If the density ��A of the accretion is known, then, based on
- the radiation intensity IA measured with the measuring system
- the radiation intensity IB measured with the comparison measuring system
- the container geometry,
- the position and the length of measuring and comparison paths A, B, and
- the density ��A of the accretion,
a thickness d of the accretion layer 21 adhering in the container 1 can be
approximately calculated.
The measured radiation intensities IA, IB required for this are determined in the case
of the measuring in any event, and can, thus, be directly used. Alternatively, they
can be determined by back calculating based on the measurement results of the
measuring system and the measurement results of the comparison measuring
system and the associated calibration data.
14
The thickness determination offers the advantage that the measurement result ��meas
of the measuring system can be corrected as regards the therein contained accretion
related measurement error based on thickness d and density ��A of the present
accretion layer 21.
Under the assumption that the thickness d of the accretion layer 21 on the container
inner walls is uniform, based on the container geometry and the positions of the
measuring and comparison paths A, B in the container 1, a ratio k of the sum D‘= B1
+ B3 of the lengths of the segments extending entrance side and exit side along the
comparison path B through the accretion layers 21 to the sum D= A1 + A3 of the
lengths of the segments extending entrance side and exit side along the measuring
path A through the accretion layers 21 can be determined. I.e.:
1 3
' 1 3
A A
B B
D
k D
+
+
= =
This ratio k is subsequently assumed as constant for simplifying understanding of the
thickness determination method and the correction method. Actually, however, the
ratio k is in most measuring arrangements dependent on the thickness d. In such
case, the method steps given below are basically analogously performable. The
individual equations presented below are in that case, however, no longer
analytically but, instead, only numerically solvable.
In the case of an accretion layer 21 of uniform thickness d, the radiation intensity IA
measured by the measuring system is:
D (XA D)
A A
A M I = I e−μρ e−μρ −
0 (1)
wherein XA = A1 + A2 + A3, and
wherein other parameters are defined as follows:
I0A a starting intensity dependent on the radiation intensity sent by the radiator 5,
the applied radiation source and the square of the distance between the
radiator 5 and the detector 9,
15
D the sum of the lengths of the segments extending input side and output side
through the accretion layer 21 (D = A1 +A3),
��M the density of the medium 3,
��A the density of the accretion layer 21,
XA the known total container 1 length of the
measuring path A, and
μ a proportionality constant assumed here as approximately equal in the medium
1 and in the accretion layer 21 for the fill substance 3 and the accretion to show
the exponential dependence of the radiation attenuation on the density of the
irradiated material. The proportionality constant μ is, as a rule, at least
approximately known, or can be determined by reference measurements.
Correspondingly, the radiation intensity IB measured by the comparison measuring
system is:
kD (XB kD)
B B
A M I = I e−μρ e−μρ −
0 (2)
wherein XB = B1 + B2 + B3, and
wherein other parameters are defined as follows:
I0B a starting intensity dependent on the radiation intensity sent by the radiator 13,
the applied radiation source and the square of the distance between the
radiator 13 and the detector 17,
XB the known total length of the comparison path B in the container 1, and
μ the above explained proportionality constant.
By dividing by I0A, taking the log and solving equation (1), one obtains an expression
for the density ��M of the medium 3 as follows:
( )
ln
0
XA D
I
D I
A
A A
M
−
⎟ ⎟
⎠
⎞
⎜ ⎜
⎝
⎛
⎟ ⎟⎠
⎞
⎜ ⎜⎝
⎛
+
= −
μ
μρ
ρ (3)
If one inserts this expression into an equation obtained by division by I0B and
subsequent taking the log of equation (2):
16
ln ( )
0
kD XB kD
I
I A M
B
B = + − ⎟
⎟⎠
⎞
⎜ ⎜⎝
⎛
− μρ μρ (4)
There results in the case of constant k a quadratic equation for D, from which D can
be determined.
Under the above made assumption of a uniform thickness d of the accretion layer
21, the thickness d can now be determined based on D, the geometry of the
container 1 and the position of the measuring path A in the container 1. In the
example of an embodiment illustrated in Fig. 1, the two segments A1 and A3
extending along the measuring path A through the accretion layer 21 are clearly
equally long, so that the thickness d of the accretion layer 21 is here determined by
d= ½ D.
Based on the radiation intensity IA measured with the measuring system, the
thickness d and the density ��A of the accretion layer 21, there can now be
determined according to equation (3) a measurement result for the density of the
medium corrected relative to the accretion related measurement error.
In this way, the influence of accretion formation on the achievable measurement
accuracy can clearly be reduced. Correspondingly, the time periods between
following container cleanings can be optimally adapted as a function of the
application dependent, required accuracy of measurement. Since cleaning occurs
now only in the case of need and no longer as a matter of precaution, a lengthening
of the time intervals between sequential cleanings is obtained.
In the simplest case, the accretion detection can be performed by the operator of the
measuring arrangement by comparing the output, respectively displayed,
measurement results of the measuring system and the comparison measuring
system.
Preferably, however, this procedure is automated by equipping the radiometric
measuring arrangement with an evaluation unit 23 connected with the measuring
17
system and the comparison measuring system for continuously determining during
operation the deviations between the measurement results of the measuring system
and the measurement results of the comparison measuring system. For this, the
evaluation unit 23 includes preferably an intelligent electronic unit, such as e.g. a
microprocessor, which performs, besides the pure deviation determination, other
software based functionalities, such as e.g.
- comparing the deviations with the threshold value,
- scheduling need dependent container cleaning,
- determining the thickness d of the accretion layer 21 in the case of known
density ��A of the accretion, as well as
- in the case of known density ��A of the accretion and therefrom ascertained
thickness d of the accretion layer 21, correcting the accretion related
measurement error of the measuring system.
.
In such case, the evaluating unit 23 must naturally also be fed the measured
variables and parameters required for performing the additional functionalities,
especially the measured radiation intensities IA, IB, the associated starting intensities
I0A, I0B, the ratio k of the sum D‘= B1 + B3 of the lengths of the segments extending
along the comparison path B through the accretion layers 21 to the sum D= A1 + A3
of the lengths of the segments extending along the measuring path A through the
accretion layers 21, and the proportionality constant μ.
The evaluating unit 23 is preferably equipped with an output system 25, via which it
selectively outputs, displays and/or provides for additional evaluation and/or
processing
- the deviations,
- the next cleaning date,
- the thickness d of the accretion layer 21, and/or
- the corrected measurement result of the measuring system.
Moreover, it can supplementally be equipped with an alarm, which is triggered, for
example, when the deviation achieves a threshold value predetermined for such.
Moreover, naturally other measurement results based, alarm initiating criteria can be
created.
18
Fig. 3 shows a variation of the radiometric measuring arrangement illustrated in Fig.
1. It differs from the form of embodiment illustrated in Fig. 1 only in that it has
externally arranged on the container 1 just a single radioactive radiator 27, which
during operation transmits radiation along the measuring path A and on a
comparison path C extending here at an angle α from the measuring path A. This is
effected, for example, by applying as the single radiator 27 a point shaped
radioactive source, which is placed in a radiation protection container, which has an
exit opening 29 with an aperture angle corresponding to the angle α. Also, in the
case of this variant, measuring path A and comparison path C are selected in such a
manner that the corresponding ratios VA and VC of the sum of the lengths of the
segments extending in the accretion layers A1, A3, respectively C1, C3, to the
lengths of the segments A2, C2 extending therebetween in the medium 3 is different
for the two paths, i.e.:
2
1 3
2
1 3
C
VC C C
A
VA A A
+
≠ =
+
=
Preferably, the measuring path A also extends here again through the region of the
container 1, in the case of which the total length extending within the container 1
along this measuring path A is maximum. In case required due to conditions on-site,
also an orientation can be selected, in the case of which the two paths each extend
at an angle to a diagonal through a container cross-section, i.e. to a diameter of the
here circularly shaped container cross-section. In that case, the angles of the two
paths from the diagonal must, however, be different, in order to assure the inequality
of the ratios VA and VC.
The measuring system and the comparison measuring system comprise also here,
again, respectively, detectors 9, 17 arranged externally on the container 1 and the
thereto connected evaluation units 11, 19. Also here, the detector 9 of the
measuring unit 7 of the measuring system is arranged externally on the container
1on a side of the container 1 lying opposite the radiator 27 along the measuring path
A, and the detector 17 of the measuring unit 15 of the comparison measuring system
is arranged externally on the container 1 on a side of the container 1 lying opposite
the single radiator 27 along the comparison path C.
19
The invention is also applicable in radiometric measuring arrangements for fill level
measurement. Applied here according to the invention is again a measuring system
for determining the fill level in the container 1 with corresponding measurement
results and a corresponding comparison measuring system, with which likewise the
fill level in the container 1 is measured. Fig. 4 shows a longitudinal section through
such a measuring arrangement in the plane of the measuring system.
In contrast to density measurement, for fill level measurement, applied preferably
externally arranged in the upper region of the container 1 are radioactive radiators 5‘,
13‘, whose radiation is transmitted collimated in the horizontal direction, however, in
the vertical direction, it is transmitted with an aperture angle β. This happens
regularly by placing a point shaped radiator in a radiation protection container, which
has a correspondingly formed exit opening. In this way, it is achieved that the
radiation in the vertical direction is sent into that region of the container 1 fixed by the
aperture angle β, over which the fill level should be registered. For measuring the
radiation intensity emerging in the vertical direction over this region along the
radiation path, a detector 9‘, 17‘ covering this region is used, e.g. a detector
equipped with a scintillation rod of appropriate length. These differences related to
the measured variable concern naturally both the measuring system as well as also
the comparison measuring system.
It should be pointed out that the accretion detection occurs in the same manner
already described above as regards the density measuring arrangement. Applied in
such case, due to the transmitted radiative power being greater in any event
resulting from the vertical aperture angle β, is preferably the, as regards
construction, variant corresponding to the form of embodiment illustrated in Fig. 1
with two radioactive radiators 5‘, 13‘. In such case, for fill level measurement, the
radiator 5‘ sends radiation along the measuring path A‘ collimated in the horizontal
direction and fanned out in the vertical direction over the aperture angle β, and the
radiator 13‘ sends radiation along the comparison path B‘ collimated in the horizontal
direction and fanned out in the vertical direction over the aperture angle β.
In the case of parallel measuring and comparison paths A‘, B‘ in a container 1 with
circularly shaped cross section, the picture in plan view for radiometric fill level
20
measurement is the same as that shown in Fig. 1 for density measurement. The
corresponding reference characters of the fill level measuring arrangement have
therefore been given in Fig. 1 alongside the reference characters of the density
measuring arrangement.
In applications, in which there are basically no concerns relative to increased
radiation exposure, naturally also a form of embodiment corresponding to the variant
illustrated in Fig. 3 for density measurement with only a single radiator could be
applied for transmitting radiation in the horizontal direction with the aperture angle α
and in the vertical direction with the aperture angle β.
Also in fill level measuring arrangements of this type, the thickness d of the accretion
layer 21 can be determined approximately based on the deviations of the
measurement results of measuring and comparison systems. In such case, because
of the fundamental physical principle being applied, the basic explanations set forth
above in conjunction with density measurement hold analogously. However, in the
case of fill level measurement, a radiation intensity integrated over the height of the
measuring range is measured, from which, based on calibration data determined in
the case of accretion free container 1, the fill level is derived. This is taken into
consideration in setting up the basic equations from the physical conditions for
determining the thickness d of the accretion layer 21 and, based on the thickness d,
the correction of the fill level, measurement results of the measuring system.
Additionally, the absorption characteristics of the fill substance 3 are taken into
consideration. Fill level measuring systems are regularly designed as regards the
sent radiative power in such a manner that their radioactive radiation is completely
absorbed in the fill substance 3. In that case, only the irradiated region of the
container 1 located above the surface of the fill substance contributes to the
deviation between the measurement results of measuring system and comparison
system. There are, however, also measuring systems, in the case of which higher
radiation powers are applied, so that some radiation passes through the fill
substance 3. In that case, the entire height of the measuring range and the
absorption in the fill substance 3 are taken into consideration. In such case, the
absorption in the fill substance 3 must be known or ascertained. It is determinable,
21
for example, based on the density ��M of the fill substance 3, which is usually
assumed as known in fill level measuring applications.
Fundamentally, the accretion detection of the invention is also applicable in
connection with radiometric measuring arrangements, which determine and/or
monitor an ex- or subceeding of a predetermined fill level. In such case, an ex- or
subceeding of this predetermined fill level is registered with a radiometric measuring
system arranged at the height of a predetermined fill level. These measuring
arrangements, frequently referred to as limit switches, differ from density measuring
systems essentially only by the further processing of the measured radiation
intensity. Also in the case of limit switches, using an accretion free container 1, a
two point calibration is performed at a fill level lying below and at a fill level lying
above the predetermined fill level to be monitored. Also here, the two radiation
intensities measured in the case of the two point calibration in the accretion free
container 1 define a scale, based on which measurement results can be derived
from intensities measured during operation.
The accretion detection can, thus, also be performed here based on these
measurement results in the manner already described above in connection with the
density measuring arrangement. In such case, the above details already explained
above in connection with the density measuring system hold equally for the
construction and positioning of the measuring system and the comparison measuring
system, as well as for the measuring path and the comparison path.
For detecting and/or monitoring the ex- or subceeding of the predetermined fill level,
it suffices to establish, based on the radiation intensities measured in the case of the
two point calibration, a threshold value for the measured radiation intensity or for the
measurement result derived therefrom based on the calibration data. Upon
exceeding this threshold value, a subceeding of the predetermined fill level is
displayed and, conversely. Accretion detection cannot, however, be performed
based on this detecting, respectively monitoring.
22
In order to be able to perform the accretion detection in the above described manner,
the measuring system embodied as a limit switch and the comparison measuring
system embodied as a limit switch must be connected with an output, via which the
above described measurement result of the respective system for accretion
detection is available as determined based on the calibration data in the case of
accretion free container.
23
1 container
3 fill substance
5 radiator
7 measuring unit
9 detector
11 evaluation unit
13 radiator
15 measuring unit
17 detector
19 evaluation unit
21 accretion layer
23 evaluation unit
25 output system
27 radiator
29 exit opening
24
WE CLAIM:
1. Method for accretion detection in a container (1), in which a radiometric
measuring system is provided for measuring and/or monitoring a measured
variable, especially a fill level or a density (��) of a fill substance (3) located in
the container (1), comprising steps as follows:
- sending during operation radioactive radiation along a measuring path (A,
A‘) through the container (1), measuring radiation intensity (IA) emerging
from the container (1) along the measuring path (A, A‘), and, based on
calibration data of the measuring system and measured radiation intensity
(IA) ascertained in the case of accretion free container (1), determining a
measurement result corresponding to the measured variable, wherein
- by means of a comparison measuring system, radioactive radiation is sent
along a comparison path (B, B‘, C) through the container (1), a radiation
intensity (IB) emerging from the container (1) along the comparison path
(B, B‘, C) is measured, and, based on calibration data of the comparison
measuring system and measured radiation intensity (IB) ascertained in the
case of accretion free container (1), a measurement result corresponding
to the measured variable is determined,
-- wherein the comparison path (B, B‘, C) extends in such a manner through
the container (1) that, in the case of presence of an accretion layer (21) on
the inner walls of the container (1), a ratio (VA) of a sum of the two
segments (A1, A3) of the measuring path (A) extending through the
accretion layer (21) to the length of an additional segment (A2) of the
measuring path (A, A‘) extending between these two segments (A1, A3) is
different from the ratio (VB, VC) formed in the same manner for the
comparison path (B, B‘,C), and
- an occurrence of accretion formation is detected based on deviations
ascertained in ongoing operation between the measurement results of the
measuring system and the measurement results of the comparison
measuring system.
25
2. Method as claimed in claim 1, wherein the ratio (VA) of the sum of the two
segments (A1, A3) of the measuring path (A, A‘) extending through the
accretion layer (21) to the length of the additional segment (A2) of the
measuring path (A,A‘) extending between these two segments (A1, A3) is
smaller than the ratio (VB, VC) formed in the same manner for the
comparison path (B, B‘, C).
3. Method as claimed in claim 1, wherein the exceeding of a predetermined
threshold value for the deviation between the two measurement results
means that an accretion formation in the container (1) corrupting the
radiometric measuring of the measured variable has been detected.
4. Method as claimed in claim 1, wherein a need dependent scheduling of
container cleanings is performed based on deviations between the
measurement results of the measuring system and the measurement results
of the comparison measuring system.
5. Method as claimed in claim 1, wherein, in the case of known density (��A) of
the accretion, a thickness (d) of the accretion layer (21) in the container (1) is
determined based on
- the radiation intensity measured with the measuring system (IA) and the
radiation intensity measured with the comparison measuring system (IB),
and
- a container geometry and positions of measuring and comparison paths
(A, A‘, B, B‘) in the container (1).
6. Method as claimed in claim 5, wherein, based on the radiation intensity (IA)
measured with the measuring system, the thickness (d) and the density (��A) of
the present accretion layer (21), a measurement result corrected as regards
an accretion related measurement error is determined.
26
7. Radiometric measuring arrangement for measuring and/or monitoring a
measured variable, especially a fill level or a density (��), of a fill substance (3)
located in a container (1), comprising
- a measuring system,
-- which during operation sends radioactive radiation along a measuring path
(A, A‘) through the container (1),
-- which includes a detector (9, 9‘), which measures a radiation intensity (IA)
emerging from the container (1) along the measuring path (A, A‘), and
-- which includes an evaluation unit (11, 11‘), which, based on calibration
data of the measuring system (7) and the measured radiation intensity (IA)
ascertained in the case of accretion free container (1), determines and
outputs a measurement result corresponding to the measured variable,
and
- a comparison measuring system,
-- which during operation sends radioactive radiation along a comparison
path (B, B‘, C) through the container (1),
-- wherein the comparison path (B, B‘, C) extends in such a manner through
the container (1) that in the case of presence of an accretion layer (21) on
the inner walls of the container (1) a ratio (VA) of a sum of the two
segments (A1, A3) of the measuring path (A, A‘) extending through the
accretion layer (21) to the length of an additional segment (A2) of the
measuring path (A, A‘) extending between these two segments (A1, A3) is
different from the ratio (VB, VC) formed in the same manner for the
comparison path (B, B‘, C),
-- which includes a detector (17, 17‘), which measures a radiation intensity
emerging from the container (1) along the comparison path (B, B‘, C), and
- which includes an evaluation unit (19, 19‘), which based calibration data of
the comparison measuring system (15) and the measured radiation
intensity (IB) ascertained in the case of accretion free container (1),
determines a measurement result corresponding to the measured variable,
and provides such for detection of accretion formation in the container (1),
wherein accretion is detected based on deviations ascertained in ongoing
operation between the measurement results of the measuring system and
the measurement results of the comparison measuring system.
27
8. Radiometric measuring arrangement as claimed in claim 7, further
comprising, connected to the measuring system and to the comparison
measuring system (23), an evaluating unit, which during operation
continuously determines deviations between the measurement results of the
measuring system and the measurement results of the comparison measuring
system.
9. Radiometric measuring arrangement as claimed in claim 7, wherein the
measuring system and the comparison measuring system each has a
radioactive radiator (5, 5‘, 13, 13‘) arranged externally on the container (1)
and the detectors (9, 9‘,17, 17‘) of the measuring system and the comparison
measuring system are each arranged externally on the container (1) on a side
of the container lying opposite (1) the respective radiator (5, 5‘, 13, 13‘) along
the measuring, respectively the comparison, path (A, A‘, B, B‘).
10. Radiometric measuring system as claimed in claim 9, wherein
- the container (1) has a circular cross sectional area, and
- the measuring path (A, A‘) extends parallel to and offset from the
comparison path (B, B‘).
11. Radiometric measuring arrangement as a claimed in claim 7, wherein
- there is provided arranged externally on the container (1) only a single
radioactive radiator (27), which during operation transmits radiation along
the measuring path (A) and along the comparison path (C),
- the measuring path (A) and the comparison path (C) extend at an angle
(α) to one another,
- the detector (9) of the measuring system is arranged externally on the
container (1) on a side of the container (1) lying opposite the single
radiator (27) along the measuring path (A, B), and
- the detector (17) of the comparison measuring system is arranged
externally on the container (1) on a side of the container (1) lying opposite
the single radiator (27) along the comparison path (C).
28
12. Radiometric measuring arrangement as claimed in claim 7, wherein
- each of the measuring system and the comparison measuring system is a
system for detecting and/or monitoring an ex- or subceeding of a
predetermined fill level in the container (1),
- each of the measuring system and the comparison measuring system has
an output, via which it outputs a measurement result corresponding to
radiation intensity measured by it and based on calibration data
ascertained in the case of accretion free container (1), and
- the measuring system detects and/or monitors the ex- or subceeding of
the predetermined fill level based on the measured radiation intensity or
based on the measurement results.