NL2015441B1

NL2015441B1 - Fill Level Measurement Testing Facility.

Info

Publication number: NL2015441B1
Application number: NL2015441A
Authority: NL
Inventors: Iwamatsu Masaaki
Original assignee: Endress+Hauser Yamanashi Co Ltd
Priority date: 2014-09-29
Filing date: 2015-09-15
Publication date: 2017-04-05
Also published as: NL2015441A; DE102014114139A1

Abstract

The invention relates to a testing facility (1) for testing the accuracy of at least one fill level measurement device (4), wherein a computing unit is provided, which serves to compare a distance measurement of at least one fill level measuring device (4) to a reference measurement carried out by an indicating device (11), said distance measurement and said reference measurement being made in the testing facility with respect to a movable target surface (19) that serves to simulate a fill level, wherein the target object is the upper surface (19) of a material (18) in a container (9) in the testing facility (1), wherein a positioning mechanism (6) is provided which serves to position the container (9) containing the material (18), thereby simulating a fill level, and wherein the indicating device (11) is a laser tracker (11) which transmits and receives a laser distance measurement signal to and from a reflector (21).

Description

Fill Level Measurement Testing Facility

The invention relates to testing facility for testing the accuracy of at least one fill level measurement device, wherein a computing unit is provided, which serves to compare a distance measurement of at least one fill level measuring device to a reference measurement carried out by an indicating device, said distance measurement and said reference measurement being made in the testing facility with respect to a movable target surface that serves to simulate a fill level.

In the field of process automation the ability to accurately measure the fill level of a material in a container, such as water or oil for example, is in many cases of great importance. For example, in the pharmaceutical or food and beverage industries, accurate amounts of liquids need to be determined precisely for reaction processes. Accurate determinations of the amounts of material in containers are also required for custody transfers in the oil and gas industry, for example, where monetary transactions are based on the precise amount of material that is to change hands.

In order to assure that fill level measurement devices can perform accurate level measurements organizations such as OIML {ORGANISATIONINTERNATIONALEDE MÈTROLOGIE LÉGALE) for example, offer certificates for measuring devices that meet certain criteria. To obtain such a certificate it is often necessary to perform tests on the fill level measurement devices to prove their accuracy capabilities. Such testing is often carried out in so-called calibration rigs, which are large enclosed spaces, in a building for example, where a fill level of a material is simulated and subsequently measured using the fill level measuring devices.

Testing the accuracy of level measuring devices involves many challenging aspects. It is necessary, for example, to provide a means of making a reference measurement of the simulated fill level of the material, to which the measurements made by the fill level devices can be compared. There are also other considerations that have to be taken into account, such as temperature and vibration control of the testing environment, so that additional sources of disturbance, which could affect the reference measurement, can be controlled for. Another challenge that presents itself is the simulation of a fill level for large distance ranges, such as 0 to 40 meters, for example. The provision of a container of these dimensions that can be filled with and emptied of a material would be impractical in light of the amount of material required, the time required to fill and empty the container and the energy requirements for these operations, to name a few examples.

In the publication “SMARTLINE non-contact Radar Calibration procedure Description VI”, from Dec. 14, 2009, Honeywell Process Solutions, 512 Virginia Drive, Fort Washington, PA 19034 (4 pages) available for download at www.honeywellprocess.com, two calibration rigs for testing non-contact radar fill level measuring devices are described. A vertical rig for standard calibration and a horizontal rig for specific calibration are disclosed. The vertical rig has two fixed targets whose unmovable distances are determined with a magnetic ruler. The horizontal rig has a movable target whose distance is likewise read from a magnetic ruler. The magnetic ruler of the horizontal rig is calibrated against a laser interferometer. This publication describes setting a datum point, which is a reference point in relation to which distance measurements are made, at the non-contact radar measurement devices’ bottom flange.

The object of the invention is to provide a testing method and a test facility, in which the testing method can be used, for testing the accuracy of at least one fill level measurement device with a high degree of precision.

The object of the invention with regard to the testing facility is achieved with a testing facility for testing the accuracy of at least one fill level measurement device, wherein a computing unit is provided, which serves to compare a distance measurement of at least one fill level measuring device to a reference measurement carried out by an indicating device, said distance measurement and said reference measurement being made in the testing facility with respect to a movable target surface that serves to simulate a fill level, wherein the movable target surface is the upper surface of a material in a container in the testing facility, wherein a positioning mechanism is provided which serves to position the container containing the material, thereby simulating a fill level, and wherein the indicating device is a laser tracker which transmits and receives a laser distance measurement signal to and from a reflector situated on a float, said float provided on the upper surface of the material whose distance is to be measured by the at least one fill level measurement device, said reflector being positioned with a defined spatial relationship to the upper surface of the material.

The laser tracker can, for example, be a FARO Laser Tracker proffered by the company FARO Technologies in 2014. By using a laser tracker of this sort, reference measurements of the simulated fill level can be made to a high degree of accuracy, such as 0.015mm for example, or in some cases even up to 0.001mm. The container can have horizontal dimensions such as 0.5 meters by 2 meters, for example, with a depth of 0.5 meters, for example. When considering the cost of filling a tank that has a depth of 40 meters, for example, a container having such smaller dimensions is quite advantageous. The material used to fill the tank is in most cases a fluid such as oil or water. It would also be possible to fill the tank with a fine grain material so long as the float can maintain a defined position on the materials upper surface. This position can be influenced by the material properties of the material in the container and of the float, as well as the form of the float.

The at least one fill level measurement device can for example be a tank gauging system based on the principle of displacement measurement, wherein a small displacer is accurately positioned in the liquid medium using a servo motor. The displacer is suspended on a measuring wire which is wound onto a finely grooved drum housing within the measurement device. The drum is driven via coupling magnets which are completely separated by the drum housing. Outer magnets are connected to the wire drum whilst the inner magnets are connected to the drive motor. As the magnets turn, its magnetic attraction causes the outer magnets to turn as well, as a result turning the entire drum assembly. The weight of the displacer on the wire creates a torque on the outer magnets generating the change of magnetic flux. These changes generated between the drum assembly are detected by a unique electromagnetic transducer on the inner magnet. The drive motor is actuated to balance the voltage generated by the variations of magnetic flux to equal the reference voltage defined by the operating command. When the displacer is lowered and touches the liquid, the weight of the displacer is reduced because of the buoyant force of the liquid. As a result, the torque in the magnetic coupling is changed and this change is measured by sets of Hall sensor chips which can be temperature dependent. The signal, an indication of the position of the displacer, is sent to the motor control circuit. As the liquid level rises and falls, the position of the displacer is adjusted by the drive motor. The rotation of the wire drum is precisely evaluated to determine the level value which can be accurate to +/- 0.7 mm. The level value can then be output to the computing unit for comparison with a level value generated by the indicating device. The computing unit can store and/or manipulate data that is generated by the indicating device and/or at least one fill level measurement device. The result of the comparison can be output to a user interface and/or stored in a databank.

In an advantageous embodiment of the invention, the testing facility is constructed so that an outer wall of the testing facility at least partially encloses a space having a vertical height that is at least as large as a specified measurement range that is to be tested of said measurement device, and so that at least one half of the height of the testing facility is below ground level. By situating the testing facility at least partially underground, geothermal energy can be used to control the temperature of the testing facility. Furthermore, disruptive effects such as vibration for example, can be effectively damped by the earth’s crust so that a stable testing environment can be provided.

In an embodiment of the invention a first isolation wall is provided in the space enclosed by the outer wall, said first isolation wall serving to thermally isolate a first space within the enclosed space, said first space enclosing the elevator and the container. Control over the temperature in the space in which the fill level measuring device is tested is important for a number of reasons. The accuracy of the laser tracker is advantageously less dependent on changes in temperature than a magnetic ruler or a measuring tape for example, whose accuracy can be affected due to thermal expansion along their measuring lengths. However, certain electrical components of a laser tracker as well as the transmission properties of the transmission medium of the laser signal in the testing facility - which is typically air - can still be affected by temperature changes. In general, every component of the testing facility can be affected by thermal expansion effects, so that temperature control plays an important role for carrying out reliable accuracy tests. The first isolation wall serves to inhibit such temperature changes.

In an advantageous embodiment of the invention a second isolation wall is provided in the first space enclosed by the first isolation wall, said second isolation wall serving to thermally isolate a second space within the first space, said second space enclosing the elevator and the container. Thus, a third layer of thermal protection can be provided for the space in which accuracy testing is carried out, so that the temperature of this space remains stable.

In a further development of the advantageous embodiment of the invention a first air duct is provided for the first isolation wall, said first air duct extending from a region of the first isolation wall near the top of the testing facility to a region of the first isolation wall near the bottom of the testing facility, said first air duct serving to transport air between the top of the first space and the bottom of the first space. In particular for testing facilities having a vertical height of 40 meters or more, a temperature gradient along the measuring range can develop. In testing facilities that are largely underground, the geothermal temperature gradient can come into effect. In testing facilities that are at least partially above ground, the ambient temperature outside the testing facility, which is generally seasonally dependent, can be an influencing factor in the development of the temperature gradient inside the testing facility. In order to mitigate the effects of such temperature changes over the height of the measuring range, it is advantageous to provide at least one air duct, which can transport air either from the top to the bottom of the testing facility and/or from the bottom to the top of the testing facility.

In another further development of the advantageous embodiment of the invention a second air duct is provided for the second isolation wall, said second air duct extending from a region of the second isolation wall near the top of the testing facility to a region of the second isolation wall near the bottom of the testing facility, said second air duct serving to transport air between the top of the second space and the bottom of the second space. The temperatures and/or temperature gradients of the air inside the first but outside the second space and of the air inside the second space can differ from each other such that it is beneficial to provide two air circulation pathways, one for each of the first and second spaces. In this way, more control over the temperature of each of the spaces can be won.

In an advantageous embodiment at least one air conditioning unit is provided inside the first space and/or second space. Additional artificial temperature control in the form of an air conditioning unit provides an additional means to control the temperature of the space in which the accuracy testing of the fill level measurement device occurs. An air conditioning unit in the sense of the invention can be a device that heats and/or cools a predetermined volume of air.

In a further development of the invention, said first space and said first air duct serve to circulate air from the top to the bottom of the first space or from the bottom to the top of the first space. Due to the fact that the ambient temperature outside of the testing facility can depend on the weather and/or on seasonal changes, the direction in which air is transported can be advantageously adjusted. For example, in the summer time, when the ambient temperature outside the testing facility is higher than the temperature inside the testing facility due to geothermal energy underground, air at the top of the testing facility that takes on the ambient outside temperature can be transported downwards to the bottom of the testing facility. Or in winter, for example, when the geothermal energy causes temperatures inside the testing facility that are higher than the ambient temperature outside the testing facility, the air can be circulated so that the warmer air near the bottom of the testing facility is transported to the top.

In another further development of the invention, said second space and said second air duct serve to circulate air from the top to the bottom of the second space or from the bottom to the top of the second space. As with the first isolation wall and the first air duct, the second isolation wall and second air duct form an air circulation pathway in which air can be transported in either direction. Advantageously, the air circulation pathway formed with the first space and the air circulation pathway formed with the second space can be completely isolated from each other, so that the two circulation pathways circulate air in counteracting directions. For example, the first space could be used to circulate air from the top of the facility to the bottom of the facility while at the same time the second space could be used to transport air from the bottom of the facility to the top of the facility. This permits the testing facility to achieve a remarkably stable temperature along its entire vertical height.

The object of the invention with regard to the method is achieved with a method for testing the accuracy of a fill level measurement device through the use of one of the embodiments of the testing facility,

Characterised by the following step: setting a datum surface or a datum point and a datum axis for the reference measurements of the indicating device, wherein the datum surface or the datum point and datum axis are set when the reflector is at a distance far enough from the indicating device that the magnitude of any error in the reference measurement of the vertical distance of the datum point and/or datum surface, wherein said error is due to a horizontal variation in the position of the datum point and/or datum axis, is so small that it can have no influence on the indicating device’s ability to achieve a reference measurement accuracy with an error that is less than a target error. In the case where the indicating device is a laser tracker that determines the distance to a reflector, said reflector being positioned on a float on the surface of a material, an error can occur during the determination of the vertical distance of a datum point and/or surface due to horizontal variations in the position of the reflector on the float, or due to variations in the horizontal position of the float on the surface of the material. By setting the datum point and/or datum surface and axis when the float and reflector are in a region near the bottom of the testing facility, the influence of these horizontal variations in position on the determination of the vertical distance can be reduced. If, for example, the position of the float is known to vary by +/- 20mm in a horizontal direction on the surface of the material in the container, then the error introduced into the vertical determination of the distance, when the float is in reality vertically separated by a distance of 20mm from the indicating device can be as much as 8mm. However, when the datum point is set when the float is separated from the indicating device by 40 vertical meters, then the error introduced due to a horizontal variation in the position of the float is only 0.0050mm. When the target error of the indicating device is specified, at 0.1mm for example, then the error introduced by setting the datum point can be made inconsequential by setting the datum point at a vertical distance at which the error becomes negligible, such as at the bottom of the testing facility, for example.

The method is further characterized by the step of simulating a fill level to be measured by positioning the container containing a fill material through the use of the elevator.

The method is further characterized by the step of indicating the simulated fill level by performing a reference measurement. The reference measurement can be made by an indicating device, wherein a preferred means of performing a reference measurement is through the use of a laser tracker as an indicating device.

The method is further characterized by the step of circulating the air in the testing facility and/or conditioning the air in the testing facility in order to bring the temperature of the area in which the fill level measuring device is to be tested into a predetermined optimal working range of the testing facility and/or in particular of the laser tracker.

The method is further characterized by the step of measuring the simulated fill level with a fill level measuring device whose accuracy is to be proved.

The method is further characterized by the step of comparing the result of the fill level measurement of the fill level measuring device with the indicated fill level determined by the indicating device to determine the accuracy of the fill level measurement of the fill level measuring device. In order to compare these measurements an computing unit is provided, which can store and/or manipulate data that is generated by the indicating device and/or at least one fill level measurement device.

The invention will next be more closely described with reference to the following figures. The show:

Fig. 1: an exemplary schematic of a testing facility;

Fig. 2: a schematic with directional arrows indicating air circulation in a testing facility; and

Fig. 3a, b: two different possibilities for setting a datum surface and datum axis for an indicating device in a testing facility.

Fig. 1 shows an exemplary schematic of a testing facility 1. The testing facility 1 structure is partially above ground and partially below ground, wherein ground level 2 is indicated with a dotted line. As is shown, the testing facility encloses a space 3 in which the accuracy of at least one fill level measurement device 4 can be proved. In the center region 5 of the testing facility 1 an elevator 6 is represented by a spool 7 and a wire 8 attached to a container 9 positioned between the top 16 and the bottom 10 of the testing facility 1. The container 9 is preferably filled with a liquid material 18 of the sort whose fill level is commonly measured by the fill level measuring device 4 in a container in an industrial plant for example.

An indicating device 11 is shown, which is preferably a laser tracker 11. The laser tracker 11 sends a laser signal to a reflector 21 situated on a float 20, wherein the float is located on the surface 19 of the material 18 in the container 9. The reflected laser signal travels back to the laser tracker 11 and an indication of the distance to the surface 19 of the material 18 can be obtained with a degree of accuracy that is greater than the desired accuracy of the fill level measuring device 4.

Fig. 1 further shows a first isolation wall 12 which encloses a first space 13 inside the space 3 enclosed by the testing facility 1. Also shown is a second isolation wall 14, which encloses a second space 15 within the first space. The function of these walls 12, 14 and enclosed spaces 13,15 will hereafter be described in more detail with reference to Fig. 2.

Fig. 2 shows a schematic with directional arrows Al, A2, BI, B2 indicating air circulation in a testing facility 1. A first isolation wall 12 encloses a first space 13, and a second isolation wall 14 inside the first isolation wall 12 encloses a second space 15 inside the first space 13. In order to maintain a constant temperature over the height of the testing facility 1, air can be circulated according to the pathways indicted by arrows Al, A2. BI, B2. A first circulation pathway for the first isolation wall 12 is defined by a first set of solid arrows Al. Here the pathway includes some means, preferably an air duct, to transport air from the top 16 of the first space 13 enclosed in the testing facility 1 to the bottom 10 of the first space 13. Accordingly, the air in within the first space 13 moves in an upward direction so that a closed air flow circuit is formed. A first set of dashed line arrows B1 are provided which define an air flow circuit that circulates the air in the first space 13 in the opposite direction.

Advantageously, some means for setting the air in motion such as a fan can be employed to circulate the air in either direction as needed in order to maintain a constant temperature. A maximum permissible temperature variation within the first space 13 can be predetermined. For example, the requirements for some certificates specify a maximum temperature change of +/- 1.5 degrees Celsius along the height of the measuring range.

Fig. 2 further shows a second isolation wall 14, which encloses a second space 15 inside the first space 13. A second set of solid arrows A2 indicates a first air circulation pathway for the second isolation wall 14 and second space 15. A second set of dashed line arrows B2 indicate a second air circulation pathway through the second space 15 where the air flow is in the opposite direction. The air circulation pathways defined by the first and second sets of solid and dashed line arrows Al, A2, BI, B2 can be utilized according to some predetermined air circulation scheme and/or they can be utilized in an adaptable way, for example according to commands given by a facility operator, or in another example, in response to stimulus from sensors such as temperature or humidity sensors.

The isolation walls 12, 14 serve generally to inhibit heat flow into or out of the respective spaces 13, 15 that they enclose. The air circulation pathways generally serve to stir and mix the air in the testing facility 1 thereby inhibiting the development of a temperature gradient within the facility 1. Advantageously, air and/or thermal energy can be exchanged between the first space 13 and second space 15, for example by means of vents that can be opened or closed in a controlled way. The air circulation implemented in the testing facility 1 can also be determined on the basis of the prevailing temperatures outside of the testing facility 1.

Fig. 3a und Fig. 3b show two different ways of setting a datum surface D1 and datum axis D2 for an indicating device 11 in a testing facility 1. In Fig. 3a the datum surface D1 is set at a first distance dl from the indicating device 11. In Fig. 3b the datum surface Dl is set at a second distance d2 from the indicating device 11, wherein the first distance dl is less than the second distance d2. For the case where the indicating device 11 is a laser tracker 11, error can be introduced to the overall accuracy of the reference measurement of the indicating device 11 when there is a horizontal variation in the position of the reflector, which is located on a float on the surface a material in the container 9. The closer the datum surface Dl is to the indicating device 11, the more error can be introduced by these horizontal variations. This can be seen by comparing the two possibilities shown in Figs. 3a and 3b. The error here is the difference in length between the diagonally extending measurement lines 17 and the vertical measurement lines 18 that extend between the respective indicating devices 11 and datum surfaces Dl. Given a maximum possible horizontal variation in the position of the reflector, the maximum possible deviation between the lengths of the diagonal and vertical measurement lines will decrease with distance from the indicating device, therefore, a datum point for the laser tracker 11 that is set at the bottom 10 of the testing facility 1 will have the smallest possible error.

List of Reference Characters 1 testing facility 2 ground level 3 space enclosed by the testing facility 4 fill level measurement device 5 center region of the testing facility 6 positioning mechanism/ elevator 7 spool of the elevator 8 wire of the elevator 9 container 10 bottom of the testing facility 11 indicating device/laser tracker 12 first isolation wall 13 first space 14 second iso lation wall 15 second space 16 top of the testing facility 17 outer wall of testing facility 18 material 19 movable target surface /upper surface of material 20 float 21 reflector 22 first air duct 23 second air duct 24 computing unit A1/A2 first circulation pathway for the first/second isolation wall B1/B2 second circulation pathway for the first/second isolation wall D1 /D2 Datum surface/Datum Axis dl/d2 first/second distance

Claims

Testing device (1) for testing the accuracy of at least one filling level measuring device (4), wherein a calculation unit (24) is provided, which serves to compare a distance measurement of at least one filling level measuring device (4) with a reference measurement which is performed by an indication device (11), wherein the distance measurement and the reference measurement are performed in the test device with respect to a movable target surface (19) which serves to simulate a filling level, characterized in that the movable target surface (19) the upper surface (19) is of a material (18) in a holder (9) in the testing device (1), which is provided with a positioning mechanism (6) which serves to position the holder (9) that holds the material (18) includes, by means of which a fill level is simulated, and that the indicating device (11) is a laser tracking device (11) which transmits and receives a laser distance measurement signal to a ref detector (21) located on a float (20), the float (20) being provided on the upper surface (19) of the material (18) whose distance is to be measured by means of the at least one fill level measuring device (4) ), wherein the reflector (21) is positioned with a defined spatial relationship to the upper surface (19) of the material (18).

Test device (1) according to claim 1, characterized in that the test device (1) is constructed such that an outer wall (17) of the test device (1) at least partially encloses an enclosed space (3) which has a height that is at least as large as a specified measuring range of the measuring device (4) to be tested, and such that at least half the height of the testing device (1) is located underground (2).

Testing device (1) according to at least one of the preceding claims, characterized in that a first insulating wall (12) is provided in the space (3) enclosed by the outer wall, the first insulating wall (12) serving for thermally insulating a first space (13) within the enclosed space (3), the first space (13) enclosing the positioning mechanism (6) and the holder (9).

Testing device (1) according to at least one of the preceding claims, characterized in that a second insulating wall (14) is provided in the first space (13) enclosed by the first insulating wall (12), the second insulating wall (14) serves for thermally insulating a second space (15) within the first space (13), the second space (15) enclosing the positioning mechanism (6) and the holder (9).

Testing device (1), according to at least one of the preceding claims, characterized in that a first air duct (22) is provided for the first insulation wall (12), the first air duct (22) extending from an area of the first insulating wall (12) near the ceiling (16) of the testing device (1) to an area of the second insulating wall (12) near the bottom (10) of the testing device (1), the first air duct (22) serving conveying air between the ceiling of the first space (13) and the bottom of the first space (13).

Test device (1) according to at least one of the preceding claims, characterized in that a second air duct (23) is provided for the second insulating wall (14), the second air duct (23) extending from an area of the second insulation wall (14) near the ceiling (16) of the test device (1) to an area of the second insulation wall (14) near the bottom (10) of the test device (1), the second air duct (23) serving for conveying air between the ceiling of the second room (15) and the bottom of the second room (15).

Test device (1) according to at least one of the preceding claims, characterized in that at least one air treatment unit is provided for the first space (13) and / or the second space (15).

Test device (1) according to at least one of the preceding claims, characterized in that the first space (13) and the first air duct (22) serve to circulate air from the ceiling (16) to the bottom (10) from the first space (13) or from the bottom (10) to the ceiling (16) of the first space (13).

Test device (1) according to at least one of the preceding claims, characterized in that the second space (15) and the second air duct (23) serve to circulate air from the ceiling (16) to the bottom ( 10) from the second space (15) or from the bottom (10) to the ceiling (16) of the second space (15).

A method for testing the accuracy of a fill level measuring device (4) in the testing device (1) according to claim 1, characterized by the following step: - setting a given surface (D1) or a given point and a given axis ( D2) for the reference measurements of the indication device (11), wherein the given area (D1) or the given point and the given axis (D2) are set when the reflector is at a distance (d1, d2) so far from the indication device (11) that the magnitude of an error, if any, in the reference measurement of the height of the reflector (21), the error being the result of a horizontal variation of the position of the reflector (21), is so small that it cannot affect the ability of the indication device (11) to achieve an accuracy of the reference measurement with an error that is smaller than a predetermined error.

The method of claim 10, further comprising the steps of: - simulating a fill level to be measured; - providing an indication of the simulated filling level with the indication device (11); - circulating the air in the test device (1) and / or subjecting the air to the test device (1) to air treatment; - measuring the simulated filling level with a filling level measuring device (4); - comparing the result of the filling level measurement of the filling level measuring device (4) with the indicative filling level determined by the indicating device (11); and - determining the accuracy of the fill level measuring device based on the comparison.