CN117451149A - Calibration method of radar level gauge - Google Patents
Calibration method of radar level gauge Download PDFInfo
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- CN117451149A CN117451149A CN202311615479.5A CN202311615479A CN117451149A CN 117451149 A CN117451149 A CN 117451149A CN 202311615479 A CN202311615479 A CN 202311615479A CN 117451149 A CN117451149 A CN 117451149A
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- 238000000034 method Methods 0.000 title claims abstract description 28
- 238000005259 measurement Methods 0.000 claims abstract description 51
- 239000000463 material Substances 0.000 claims abstract description 19
- 230000015572 biosynthetic process Effects 0.000 claims abstract description 5
- 238000003786 synthesis reaction Methods 0.000 claims abstract description 5
- 229910000831 Steel Inorganic materials 0.000 claims description 12
- 239000010959 steel Substances 0.000 claims description 12
- 238000004364 calculation method Methods 0.000 claims description 8
- 239000000523 sample Substances 0.000 claims description 3
- 238000011156 evaluation Methods 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
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- 238000001514 detection method Methods 0.000 description 1
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- 239000000428 dust Substances 0.000 description 1
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- 239000002184 metal Substances 0.000 description 1
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F25/00—Testing or calibration of apparatus for measuring volume, volume flow or liquid level or for metering by volume
- G01F25/20—Testing or calibration of apparatus for measuring volume, volume flow or liquid level or for metering by volume of apparatus for measuring liquid level
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
- G01F23/22—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
- G01F23/28—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring the variations of parameters of electromagnetic or acoustic waves applied directly to the liquid or fluent solid material
- G01F23/284—Electromagnetic waves
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- Physics & Mathematics (AREA)
- Fluid Mechanics (AREA)
- General Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Thermal Sciences (AREA)
- Measurement Of Levels Of Liquids Or Fluent Solid Materials (AREA)
Abstract
The invention discloses a radar level gauge calibrating method, which comprises the following steps: s1, calculating an indication error: measuring the distance from the zero position of the radar level gauge to the reflecting surface as an actual value, selecting a plurality of measuring points, and respectively measuring each measuring point of the level gauge, wherein the difference between the display value of the level gauge and the actual value is the display value error of the point; s2, repeatedly measuring for a plurality of times, and calculating the measurement repeatability of the material level meter; s3, uncertainty assessment: evaluating the standard uncertainty of the arithmetic average input quantity of the indicating value of the level indicator and the standard uncertainty of the actual distance input quantity from the zero position of the level indicator to the reflecting surface; calculating the uncertainty of the synthesis standard; and S4, calculating the relative error rate of the level indicator, and obtaining a true value interval of the level indicator error according to the indication error, the synthetic standard uncertainty and the relative error rate. The radar level gauge calibrating method can improve the measuring precision of the level gauge.
Description
Technical Field
The invention relates to the technical field of calibration and measurement, in particular to a radar level gauge calibration method.
Background
Radar waves are a special form of electromagnetic waves, and radar level gauges use the special properties of electromagnetic waves for level detection. The physical properties of electromagnetic waves are similar to those of visible light, and the propagation speed corresponds to the speed of light. The frequency is 300MHz-3000GHz. Electromagnetic waves can penetrate through space steam, dust and other interference sources, obstacles are easy to reflect, and the better the conductivity or the larger the dielectric constant of a measured medium is, the better the reflection effect of echo signals is.
The basic principle of radar level gauge operation is transmission-reflection-reception. The antenna of the radar sensor emits radar signals in the form of a beam, the reflected signals are still received by the antenna, and the running time of the radar signals of the radar level gauge from emission to reception is proportional to the distance of the sensor from the medium surface and the level.
The radar level gauge needs to be checked before measuring the level height of the material to ensure the accuracy of measurement. At present, the radar level gauge is checked in an on-line checking mode, namely, the head of the radar level gauge extends into a container, a flange plate of the radar level gauge is fixed on the container, and checking is carried out in the production process, but when the radar level gauge is checked in an on-line mode, the radar level gauge is easily affected by various conditions such as a material body state and a production state, and the checking accuracy is difficult to guarantee.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the invention provides a radar level gauge calibrating method.
In order to solve the technical problems, the technical scheme provided by the invention is as follows:
a method of calibrating a radar level gauge, comprising the steps of:
step S1, calculating an indication error: measuring the distance from the zero position of the radar level gauge to the reflecting surface as an actual value, selecting a plurality of measuring points, and respectively measuring each measuring point of the level gauge, wherein the difference between the display value of the level gauge and the actual value is the display value error of the point;
step S2, repeatedly calibrating: selecting a measuring point with 75% of the maximum range, repeatedly measuring for a plurality of times, and calculating the measurement repeatability of the level gauge;
step S3, uncertainty assessment: arithmetic mean value input H for level indicator m Standard uncertainty, actual distance input quantity H from zero position of level indicator to reflecting surface b Evaluating the standard uncertainty; calculating the uncertainty of the synthesis standard;
and S4, calculating the relative error rate of the level indicator, and obtaining a true value interval of the level indicator error according to the indication error, the synthetic standard uncertainty and the relative error rate.
The technical scheme is further improved as follows:
further, in the step S1, the indication error is calculated, the measurement range is calculated by adopting a formula (1) within a range of 30m, and the measurement range exceeding 30m is calculated by adopting a formula (2);
i, calculating the indication error of the measurement point according to the formula (1) as
Δ i ＝x i -x i0 (1)
Wherein:
Δ i -an indication error of a measurement point;
x i -a level gauge display value at a measurement point;
x i0 -the actual value of a certain measurement point;
taking the maximum absolute value in the error values as the indicating value error of the level gauge;
II, calculating the indication error of the measurement point according to the following formula
Δ H ＝H d -H s (2)
Wherein:
Δ H -indication error of each calibration point;
H d -actual values of the calibration points of the level gauge;
H s -a standard value of a calibration point of the level gauge;
because the measuring range is larger, the sectional calculation is needed, and the error of each measuring point is the sectional indication error average value of the level gauge.
Further, in the step S2, the measurement repeatability of the level gauge is calculated:
wherein R is measurement repeatability; x is x i Displaying a value for a level gauge for a certain measurement;for measuring the average value of the display values of the level indicator for a plurality of times.
Further, in the step S3, the uncertainty propagation rate formula is as follows:
wherein:
wherein Deltah is the indication error of the level gauge, H m Is the arithmetic average value of the indication value of the level indicator, H b Is the actual distance from the zero position of the level gauge to the reflecting surface.
Further, the input quantity H m The standard uncertainty of (2) includes the following two parts:
c. standard uncertainty term u (H) introduced by level gauge indication repeatability m1 )；
d. Standard uncertainty term u (H) introduced by resolution of level gauge m2 )。
Further, the input quantity H b The standard uncertainty of (2) includes the following two parts:
a. standard uncertainty term u (H) introduced by laser rangefinder or steel tape b1 )；
b. Standard uncertainty term u (H) b2 )。
Further, in the step S4, when the measurement range exceeds 30m, the relative error rate Er (Δ H )：
Wherein k is 1 Is constant, B 1 For the repeated use of the error rate generated by the level meter, a 1 Is the maximum allowable measurement error of the level gauge.
Further, in the step S1, a site comparison method is adopted for calibrating the site undetachable level gauge:
(1) The material level meter measures the distance from the probe or reference point of the material level meter to the material reflecting surface, and the measuring axis is clung to the measuring axis of the material level meter and is parallel to the material level meter;
(2) The comparison of each point is measured on at least four points which are symmetrical around the level gauge, and the arithmetic average value is taken as a measurement result.
Compared with the prior art, the radar level gauge calibrating method provided by the invention has the following advantages:
at present, the domestic calibration radar level gauge is compared with reference to a mechanical industry standard JB/T13252-2017 microwave (radar) level gauge, national verification regulations JJG971-2019 liquid level gauge, and the metering standard is complex in selection and operation method; the calibration method is suitable for calibrating the radar level gauge for measuring the level of liquid, sauce and particle materials in various metal and nonmetal containers or pipelines. The standard devices such as the steel tape and the laser range finder adopted by the invention are common measuring devices, and are easy to find in the market; the method adopted has low requirements on experimental environment, can be used for laboratory calibration and field comparison, and has the advantages of simplicity, applicability and strong operability; the indication error calculation can be calculated by adopting two modes of relative error and absolute error, and is flexible and convenient.
Drawings
Fig. 1 is a schematic flow chart of risk identification and risk level evaluation according to the present invention.
Description of the reference numerals:
1. a level gauge; 2. an adjustable bracket; 3. and a reflecting plate bracket.
Detailed Description
The technical solutions of the embodiments of the present specification will be clearly and completely described below with reference to the drawings in the embodiments of the present specification, and it is apparent that the described embodiments are only some embodiments of the present specification, not all embodiments. All other embodiments, which can be made by one of ordinary skill in the art without undue burden from the present disclosure, are intended to be within the scope of the present invention based on the embodiments herein.
According to the radar level gauge calibrating method of the present invention, the measuring device includes an adjustable support 2 and a reflective plate support 3, the adjustable support 2 needs to have a support for fixing the radar level gauge 1, and has a lifting structure, the adjustable support 2 and the reflective plate support 3 generally translate on a running track, and the adjustable support 2 and the reflective plate support 3 have structures that are already used in the prior art and are not described herein. The main technical scheme of the invention is the calibration of the level gauge.
Step S1, calculating an indication error
S1-1, when measuring radar level gauge indication errors, the level gauge is horizontally placed, and radar antenna beams are perpendicular to the reflecting plate, namely parallel to the movable reference running track.
And measuring the distance from the zero position of the radar level gauge to the reflecting surface of the reflecting plate by using a laser range finder or a steel tape as an actual value. The selection of the measuring points should be uniformly distributed according to the measurement process, and the measurement is carried out by not less than 5 points.
S1-2, selecting a measuring point, and selecting according to a preset position.
S1-3, turning on a power supply of the material level indicator, and respectively measuring each measuring point of the material level indicator, wherein the difference value between the display value and the actual value of the material level indicator is the display value error of the point. The measuring range is calculated by adopting a formula (1) within the range of 30m, and the measuring range exceeding 30m is calculated by adopting a formula (2).
I, calculating the indication error of the measurement point according to the formula (1) as
Δ i ＝x i -x i0 (1)
Wherein:
Δ i -an indication error of a measurement point;
x i -a level gauge display value at a measurement point;
x i0 -the actual value of a certain measurement point.
The maximum absolute value of the error values is taken as the indicating value error of the level gauge.
II, calculating the indication error of the measurement point according to the following formula
Δ H ＝H d -H s (2)
Wherein:
Δ H -indication error of each calibration point;
H d -actual values of the calibration points of the level gauge;
H s -the standard value of a calibration point of the level gauge.
Because the measuring range is larger, the sectional calculation is needed, and the error of each measuring point is the sectional indication error average value of the level gauge.
Step S2, repeatability calibration
During repeatability calibration, a measurement point with 75% of the maximum range is generally selected, the measurement is repeated for a plurality of times, the measurement is generally carried out for 10 times (n=10), and the measurement repeatability of the level gauge is calculated according to a formula (3):
wherein:
r-measurement repeatability;
x i -a level gauge display value of a certain measurement;
-measuring the average of the level gauge display values a plurality of times.
Step S3, uncertainty evaluation
S3-1, indicating value error of radar level gauge
The indication error of the radar level gauge is expressed as:
Δh＝H m -H b
wherein:
Δh—indication error of radar level gauge;
H m -an arithmetic mean of the radar level gauge readings;
H b -the laser rangefinder or steel tape measure the actual distance (standard value) from the zero position of the level gauge to the reflecting surface of the reflecting plate.
S3-2, standard uncertainty assessment
Uncertainty propagation rate is formulated as follows:
wherein:
s3-2-1, input H m Standard uncertainty u (H) m ) Assessment of (2)
Input quantity H m The standard uncertainty of (2) is mainly composed of the following two parts:
e. standard uncertainty term u (H) introduced by level gauge indication repeatability m1 )；
f. Standard uncertainty term u (H) introduced by resolution of level gauge m2 )。
S3-2-1-1, level gaugeStandard uncertainty term u (H) m1 ) Is a rating of (2).
For example, by calibrating the level gauge with the device of the present invention, at reference point 25m, 10 measurements were repeated (n=10), the measured data are as follows (in m): 25.01, 25.01, 24.99, 25.01, 24.99, 24.99, 25.00, 25.01, 25.01, 25.01. The standard deviation is as follows
S3-2-1-2, the standard uncertainty term u (H) introduced by the resolution of the level gauge m2 ) Is a rating of (2).
For example, the resolution of the level gauge is 0.01m, the half width is 0.005m, it is considered to be subject to uniform distribution,uncertainty u (H) introduced by resolution m2 ) The method comprises the following steps:
the uncertainty of the repeatability-introduced standard and the uncertainty of the resolution-introduced standard take large values, so that:
u(H m )＝3mm
s3-2-2, input H b Standard uncertainty u (H) b ) Assessment of (2)
Input quantity H b The standard uncertainty of (2) is mainly composed of the following two parts:
a. standard uncertainty term u (H) introduced by laser rangefinder or steel tape b1 )；
b. Standard uncertainty term u (H) b2 )。
S3-2-2-1, standard uncertainty term u (H) introduced by a laser rangefinder or steel tape b1 ) Assessment of
The maximum allowable indication error of the grade II steel tape adopted in the embodiment is ± (0.3mm+2×10) -4 L) is a rounded integer number of meters, 1m when the length is less than 1, and the half width a is (0.3mm+2×10) -4 L), obeys a uniform distribution,then L is substituted by 25m to obtain uncertainty subentry u (H) introduced by a laser range finder or a steel tape b1 )：
S3-2-2-2, standard uncertainty subentry u (H) introduced by verticality of reflecting plate b2 ) Assessment of
For example, uncertainty u (H) b2 ) According to the requirement that the normal verticality is not more than 5mm, the product is considered to be subjected to normal distribution, and the factor k is 1.96
u(H b2 )＝5mm/1.96＝3mm
S3-3, uncertainty of synthesis standard
S3-3-1, wherein the main standard uncertainty in the embodiment comprises the repeatability of indication value of a level gauge, a laser range finder or a steel tape and the perpendicularity of a reflecting plate.
S3-3-2, calculation of uncertainty of synthetic Standard
Input quantity H m And H b Independent of each other, the synthesis criterion uncertainty can be calculated as equation (4):
step S4, level gauge calibration
In the calibration method of this embodiment, when the calibration method is implemented and the error of the radar level gauge is measured, the level gauge may be placed horizontally (as shown in fig. 1), and the radar antenna beam is perpendicular to the reflecting plate (parallel to the movable reference running track). The lower edge of the radar level gauge flange is used as a measuring zero position, and a steel tape (or other measuring equipment) is used for measuring the distance from the zero position of the radar level gauge to the reflecting surface of the reflecting plate as an actual value. The selection of the measurement points should be uniformly distributed according to the measurement, and generally, the measurement is performed by not less than 5 points, and can also be designated by a user.
And starting a power supply of the level indicator, and measuring three times at each measuring point of the level indicator respectively, wherein the difference value of the three average values of the display value and the actual value of the level indicator is the indication error of the point.
The indication error is calculated according to step S1, and then the relative error rate is calculated.
The calculation method of the relative error rate is described by taking the range exceeding 30m as an example.
The relative error rate Er (delta) of the level gauge is calculated according to the following formula H )：
Wherein k is 1 Is constant, usually 2 or 3, and is selected according to different measuring methods during calculation, B 1 For the repeated use of the error rate generated by the level meter, a 1 Is the maximum allowable measurement error of the level gauge.
Obtaining a true value interval of the level gauge error according to the indication error, the synthetic standard uncertainty and the relative error rate:
[Δ H -u c (Δh)-Er(Δ H ),Δ H +u c (Δh)+Er(Δ H )]。
when the measuring range is within 30m, the calculation method is the same.
In another embodiment, in step S1, the site alignment method is used for calibrating the site undetachable level gauge:
(1) The radar level gauge uses a laser range finder or a heavy hammer steel tape to measure the distance from a radar level gauge probe or a reference point to a material reflecting surface, and in order to ensure the accuracy of a measurement result, a measurement axis is closely attached to and parallel with the measurement axis of the radar level gauge.
(2) In order to eliminate the influence of the material stacking gradient on the measurement result, the ratio of each point is correspondingly measured on at least four points which are symmetrical around the radar level gauge, and an arithmetic average value is taken as the measurement result.
The above embodiments are merely preferred embodiments of the present invention, and are not intended to limit the present invention in any way. While the invention has been described with reference to preferred embodiments, it is not intended to be limiting. Therefore, any simple modification, equivalent variation and modification of the above embodiments according to the technical substance of the present invention shall fall within the scope of the technical solution of the present invention.
Claims (8)
1. The radar level gauge calibrating method is characterized by comprising the following steps of:
step S1, calculating an indication error: measuring the distance from the zero position of the radar level gauge to the reflecting surface as an actual value, selecting a plurality of measuring points, and respectively measuring each measuring point of the level gauge, wherein the difference between the display value of the level gauge and the actual value is the display value error of the point;
step S2, repeatedly calibrating: selecting a measuring point with 75% of the maximum range, repeatedly measuring for a plurality of times, and calculating the measurement repeatability of the level gauge;
step S3, uncertainty assessment: arithmetic mean value input H for level indicator m Standard uncertainty, actual distance input quantity H from zero position of level indicator to reflecting surface b Evaluating the standard uncertainty; calculating the uncertainty of the synthesis standard;
and S4, calculating the relative error rate of the level indicator, and obtaining a true value interval of the level indicator error according to the indication error, the synthetic standard uncertainty and the relative error rate.
2. The method according to claim 1, wherein in the step S1, the indication error is calculated, the range is calculated by using formula (1) within 30m, and the range is calculated by using formula (2) beyond 30 m;
i, calculating the indication error of the measurement point according to the formula (1) as
Δ i ＝x i -x i0 (1)
Wherein:
Δ i -an indication error of a measurement point;
x i -a level gauge display value at a measurement point;
x i0 -the actual value of a certain measurement point;
taking the maximum absolute value in the error values as the indicating value error of the level gauge;
II, calculating the indication error of the measurement point according to the following formula
Δ H ＝H d -H s (2)
Wherein:
Δ H -indication error of each calibration point;
H d -actual values of the calibration points of the level gauge;
H s -a standard value of a calibration point of the level gauge;
because the measuring range is larger, the sectional calculation is needed, and the error of each measuring point is the sectional indication error average value of the level gauge.
3. The method according to claim 2, wherein in the step S2, the repeatability of the measurement of the level gauge is calculated:
wherein R is measurement repeatability; x is x i Displaying a value for a level gauge for a certain measurement;for measuring the average value of the display values of the level indicator for a plurality of times.
4. A method of calibrating a radar level gauge according to claim 3, wherein in said step S3, the uncertainty propagation rate formula is as follows:
wherein:
wherein Deltah is the indication error of the level gauge, H m Is the arithmetic average value of the indication value of the level indicator, H b Is the actual distance from the zero position of the level gauge to the reflecting surface.
5. The method of calibrating a radar level gauge according to claim 4, wherein said H m The standard uncertainty of (2) includes the following two parts:
a. standard uncertainty term u (H) introduced by level gauge indication repeatability m1 )；
b. Standard uncertainty term u (H) introduced by resolution of level gauge m2 )。
6. The method of calibrating a radar level gauge according to claim 5, wherein said H b The standard uncertainty of (2) includes the following two parts:
a. standard uncertainty term u (H) introduced by laser rangefinder or steel tape b1 )；
b. Standard uncertainty term u (H) b2 )。
7. The method according to claim 2, wherein in the step S4, the relative error rate Er (Δ H )：
Wherein k is 1 Is constant, B 1 For the repeated use of the error rate generated by the level meter, a 1 Is the maximum allowable measurement error of the level gauge.
8. The method for calibrating a radar level gauge according to claim 1, wherein in said step S1, a field alignment method is used for calibrating a level gauge which cannot be detached in the field:
(1) The material level meter measures the distance from the probe or reference point of the material level meter to the material reflecting surface, and the measuring axis is clung to the measuring axis of the material level meter and is parallel to the material level meter;
(2) The comparison of each point is measured on at least four points which are symmetrical around the level gauge, and the arithmetic average value is taken as a measurement result.
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