X-ray or gamma ray systems or devices – Specific application – Absorption
Reexamination Certificate
2002-02-08
2002-12-10
Church, Craig E. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Absorption
Reexamination Certificate
active
06493418
ABSTRACT:
FIELD OF THE INVENTION
The invention refers to a method for measuring mass material's weight especially refers to the use of nuclear radiation high precision measuring of mass material's weight with high precision nucleonic weigher (nucleon scale) to apply this method.
BACKGROUND OF THE INVENTION
Nucleonic weigher (nucleon scale) is manufactured on the research basis of material's absorption principle to gamma ray.
The existing nucleon scale's operation principle is shown in FIG.
1
. In this diagram, the nucleon scale includes a gamma radiation source (
1
), a gamma ray detector (
2
), a gamma ray radiation area (
3
), a speed measuring device (
4
), a Data Processing Unit (DPU) (
5
), a scale frame and protecting case (
6
), a conveyer belt and mass meterial (
7
). On the top of nucleon scale's frame there sets the gamma radiation source and underneath the frame there sets gamma ray detector. Conveyer belt with bulk mass material go through the frame. Gamma ray radiation source steadily emits gamma ray with constant intensity. When the belt carries no material the gamma ray received by the gamma ray detector is also a constant and at same time the gamma ray detector's output voltage is U
0
and when the belt carries material a part of gamma ray emitted by the radiation source is absorbed by mass material and the rest part penetrating mass material is received by the gamma ray detector and at same time the gamma ray detector's output voltage is U
i
. According to material's absorption law to gamma ray it is known that U
0
, U
i
and the mass material have the following relations:
U
i
=U
0
e
−&mgr;
&rgr;
&rgr;d
(1)
where &mgr;
&rgr;
—material's mass absorption coefficient to gamma ray
&rgr;—material's density
d—material's thickness
to move line and also to multiply S/S on the exponent so we get
U
i
U
0
=
ⅇ
-
μ
ρ
ρdS
/
S
(
2
)
W
=
ρ
ds
U
i
U
0
=
ⅇ
-
μ
ρ
W
/
S
where S—material's area on the belt to apply logarithm on both sides of formula (2) and let W/S=F, K=−1/&mgr;
&rgr;
so we get
F
=
K
×
Ln
U
i
U
0
(
3
)
where F—material's load;
K—material's rating coefficient;
The conveyer belt's speed V can be measured by the speed sensor so material flow P on the belt is: P=FV
The accumulative mass material W
h
moved in a period of time is:
W
h
=
∑
i
=
1
n
F
i
V
i
(
4
)
The existing scale takes K as a constant in formula (3) but actually K is not a constant and it varies with the change of belt load. The main cause is the existing nucleon scale makes 2 approximations while applying absorption law to gamma ray by material and they are:
1) to assume scattering factor=1 is to ignore the gamma ray scattering influence. In fact, the more density and thickness as mass material has, the bigger influence as scattering gets.
2) the absorption law of gamma ray by mass material requires gamma ray in parallel, but actually the existing nucleon scale is to use spot source which produces fan beamed gamma ray as shown in FIG.
2
. When material is on position A the absorbed gamma ray situates on plane a-b and when material is on position B the absorbed gamma ray situates on plane c-d. Obviously c-d is greater than a-b.
Therefore, change of material load, piling shape with difference of positions plus the influence of scattering factor is the main cause to restrict measuring precision of the existing nucleon scale.
At present nucleon scales available at home and abroad all adopt mass material total weight to rate coefficient K, such as Chinese Patent ZL95106808.3 (Announced Patent No.CN1039160C). Using this method to rate coefficient K the nucleon scale records only material's weight but not the change of material's load so the rated coefficient K is of no relation with belt's material load and does not meet the actual situation. Evidently the existing nucleon scale can not proceed instantaneous correction to coefficient K according to belt load variation so it has rather big measuring error with less precision.
SUMMARY OF THE INVENTION
An aim of this invention is to solve the above mentioned problem. It provides a dynamic high precision measuring method to reduce and eliminate influence to measuring accuracy in respect of change of material load, piling shape with difference of positions plus the influence of scattering factor and also to proceed dynamic correction. The high precision nucleon scale is manufactured to apply this method. In order to realize above mentioned aim the invention adopts following technique schemes:
A method for measuring mass material's weight with high precision is to include following steps:
(1) installing multiple gamma radiation sources with corresponding gamma ray detectors and in between them to install the mass material conveyer device;
(2) measuring the gamma ray detector's output voltages U
0
with no material and U
i
with material to input to DPU which is connected to gamma ray detector;
(3) using the speed sensor to measure moving speed V
i
of the conveyer device to input to DPU (PLC or industrial control machine) which is connected to speed sensor;
(4) the DPU calculates the accumulative weight W transmitted in a period of time according to formula:
W
=
∑
i
=
1
n
KLn
(
U
i
/
U
0
)
V
i
The material rated coefficient K in the formula is dynamically corrected to follow the change of mass material's load and influence of gamma ray scattering. The above mentioned material rated coefficient K to follow the change of material load is determined by object's rated method with following steps:
(1) to use a standard scale to read out material's weight W
aB
. The conveyer device steadily transmits mass material's load to nucleon scale for measurement;
(2) from instantaneously collected parameters of gamma ray detector's output voltage U
i
, speed sensor's moving speed V
i
, and transmission time t
i
to calculate formulae:
F
Ba
=
W
B
∑
i
=
1
n
V
i
t
i
(
L
n
u
i
u
0
)
aAVG
=
∑
i
=
1
n
L
n
U
i
U
0
n
Set up a coordinate system with F
B
as ordinate and LnU
i
/U
0
as abscissa. According to the calculated F
Ba
and (LnU
i
/U
0
)
aAvG
to determine point a in the coordinate system to get K which is the sloping rate of 0a;
(3) Corresponding to different material weights W
bB
, W
eB
, W
dB
. . . to adopt same method as above we can determine points b, c, d . . . in the coordinate system. Hence we get Kb, Kc, Kd . . . and functional relation of F
B
=f(LnU
i
/U
0
) as shown in FIG.
3
.
Using multi-section's linear relation of F=b
j
+k
j
Ln(U
i
/U
0
) to replace function F
B
=f(LnU
i
/U
0
) where j is linear section numbers we have following steps:
(1) to connect
0
a, ab, bc, cd . . . to get each linear section;
(2) to utilize
0
, a, b, c, d . . . each point's coords value to separately get each linear section's b and k ; or to use multi-items method to joint F
B
=f(LnU
I
/U
0
). For a, b, c, d . . . each point coordinates to use minimum 2 multiplication method to get coefficients a
0
, a
1
, a
2
. . . a
K
from multi-items formula: F=a
0
+a
1
(LnU
i
/U
0
)+a
2
(LnU
i
/U
0
)
2
+ . . . +a
k
(LnU
i
/U
0
)
k
where k=0, 1, 2, 3 . . . k.
It is another object of this invention to provide a nucleon scale with high measuring precision, wide application ,good stability, small maintenance and low cost.
A nucleon scale applying above mentioned method is to include:
1-N gamma radiation sources where N=2-10.
Gamma ray detector corresponds to gamma radiation source which transfers gamma ray intensity into voltage parameter. The mass material's conveyer device is installed between the detectors and radiation sources.
Speed sensor can measure moving speed of the mass material's conveyer device.
Micro-computer or
Church Craig E.
McDonnell & Boehnen Hulbert & Berghoff
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