Functional Diagnosis of an Electromechanical Fill State Measuring Device

Abstract

A method for the functional diagnosis of an electromechanical fill state measuring device in which a displacement element on a measuring wire is lowered into a filling material in a container such that in an equilibrium state, the weight of the displacement element minus a displacement element buoyancy, which depends upon at least one equilibrium volume, is determined to be equal to a resulting weight of the displacement element. The resulting weight is specified, and the specified resulting weight is kept constant by correspondingly changing the length of the measuring wire in the equilibrium state. The fill state of the filling material is ascertained using the length of the lowered measuring wire. In order to diagnose a function, the specified value of the equilibrium volume of the displacement element is changed, and the resulting change in the length of the measuring wire is ascertained on the basis of the constant equilibrium state of the resulting weight.

Claims

1-10. (canceled)

11. A method for the functional diagnosis of an electromechanical fill state measuring device comprising the steps of: lowering a displacement element on a measuring wire into a filling material in a container such that, in an equilibrium state, the weight of the displacement element minus a buoyancy of the displacement element, which buoyancy depends upon at least one equilibrium volume, is determined to be equal to a resulting weight of the displacement element; specifying the resulting weight, and the specified resulting weight is kept constant by correspondingly changing the length of the measuring wire in the equilibrium state; and ascertaining the fill state of the filling material using the length of the lowered measuring wire, wherein: for the functional diagnosis, the specified value of the equilibrium volume of the displacement element is varied using a defined equilibrium volume change; and the resulting change in the length of the measuring wire is ascertained based upon the equilibrium state, kept constant, of the resulting weight.

12. The method according to claim 11, wherein: the specified value of the equilibrium volume of the displacement element is changed via the defined equilibrium volume change by changing a parameter of the equilibrium volume in an evaluation algorithm of the electromechanical fill state measuring device.

13. The method according to claim 11, wherein: the corresponding change in the length of the measuring wire wound onto a measuring drum in one layer causes a change in the torque on the measuring drum, from which a change in the resulting weight is determined by the evaluation algorithm.

14. The method according to claim 11, wherein: the defined equilibrium volume change is performed in one step, whereby a correspondingly large change in the length of the measuring wire or a correspondingly large height change in the immersion depth of the displacement element in the filling material is caused which is greater than or equal to the smallest possible resolution of the measurement of the fill state of the electromechanical fill state measuring device; and the resulting large changes in the measured value of the fill state are appropriately compensated for by the evaluation algorithm.

15. The method according to claim 11, wherein: the equilibrium volume change is performed in very small, individual steps, whereby a correspondingly very small change in the length of the measuring wire or very slight height changes in the displacement element are caused, which are smaller than the smallest possible resolution of the measurement of the fill state of the electromechanical fill state measuring device; and the determinations of the fill state are thus not affected by the evaluation algorithm.

16. The method according to claim 15, wherein: the number of the small individual steps is calculated by the evaluation algorithm by determining the height change from the equilibrium volume change, knowing the cross-sectional area of the displacement element, and by determining the number of the small individual steps to be larger than the quotient of the height change divided by the smallest possible resolution of the measurement of the fill state.

17. The method according to claim 15, wherein: small individual steps for height changes are performed in an area of the displacement element between an upper limit and a lower limit of the equilibrium volume, in which the cross-sectional area of the displacement element is constant.

18. The method according to claim 15, wherein: the height changes are performed with different small individual steps with different step heights.

19. The method according to claim 15, wherein: the functional diagnosis is continuously performed by the evaluation algorithm during the measurement operation of the electromechanical fill state measuring device; and these do not affect each other, in that the displacement element is steadily lowered and raised by the height changes in small individual steps.

20. The method according to claim 11, wherein: the movement of the servomotor, the weight measurement of the displacement element, the movement of the measuring drum and of the displacement element, the parameters entered regarding the displacement element currently hanging on the measuring wire, and the sensor electronics unit, the main electronics unit, and the evaluation algorithm are checked and monitored by means of this functional diagnosis of the electromechanical fill state measuring device.

Description

[0021] Additional details, features, and advantages of the object of the invention result from the following description with the associated drawings, in which preferred exemplary embodiments of the invention are illustrated. In the exemplary embodiments of the invention shown in the figures, elements that correspond in their structures and/or in their functions are provided with the same reference symbol for the sake of clarity and simplicity. The figures show:

[0022] FIG. 1—an exemplary embodiment of a measuring device for determining the fill state according to the displacement measuring principle,

[0023] FIG. 2—a schematic block diagram of an electromechanical fill state measuring device,

[0024] FIG. 3—a schematic drawing regarding the displacement element buoyancy,

[0025] FIG. 4—a schematic drawing of the variation according to the invention in the equilibrium volume of the displacement element,

[0026] FIG. 5—a schematic drawing of the variation according to the invention in the equilibrium volume of the displacement element in small steps.

[0027] FIG. 1 shows a mechanical fill state measuring device 1, which is, for example, sold by the applicant under the name PROSERVO NMS 53x—tank measuring system and is based upon the principle of the displacement measurement of a displacement element 11. A small displacement element 11 is positioned precisely in the fluid 14 in the container 15 by means of a servomotor 3 on a measuring rope 19. As soon as the fill state L of the fluid 14 in the container 15 rises or falls, the displacement element 11 is repositioned by the servomotor 3 by rotating the measuring shaft 10 with the measuring drum 27, 12, 13. The rotation of the measuring drum 27, 12, 13 is evaluated, in order to determine the fill state 16. The determination of other measurands, such as separation layer measurement and density measurement, of the individual layers of the filling material 14 can also be performed using this measuring principle.

[0028] In modern industrial plants, field devices are generally connected via bus systems 24, such as Profibus® PA, Foundation Fieldbus®, or HART®, to at least one higher-level control unit, which is not explicitly shown here. The data communication controlled by the control unit on the bus system 24 can be both wired and wireless. Usually, the higher-level control unit is an SPS or a PLC (programmable logic controller), or a DCS (distributed control system). The higher-level control unit is used for process control, process visualization, process monitoring, as well as commissioning and operating the field devices.

[0029] FIG. 2 shows a block diagram of a fill state measuring device 1, which functions according to the displacement measuring principle of a displacement element or float 11. The displacement element or the float 11 is attached to one end of a measuring rope or measuring wire 19, and the other end of the measuring rope 19 is mostly wound onto an outer rope drum 12 or an outer measuring drum 27 in one layer.

[0030] A small displacement element 11 is positioned precisely in the fluid or in the liquid filling material 14 at a boundary of the equilibrium volume VB by means of a small servomotor 3. The displacement element 11 hangs on a measuring wire or measuring rope 19, which is wound with a constant winding diameter in one layer onto a measuring drum 27 or an outer rope drum 12 provided with fine grooves inside the measuring device 1. The outer rope drum 12 is, for example, coupled via coupling magnets with the inner rope drum 13, which are spatially separated completely and hermetically sealed from one another by the drum housing. The outer magnets are connected to the outer rope drum 12, and the inner magnets to the inner rope drum 13. While the magnets rotate, the magnetic pull causes the outer magnets to co-rotate so that the entire drum assembly consisting of the outer rope drum 12 and the inner rope drum 13 rotates on the measuring shaft 10.

[0031] While the magnets rotate with the inner rope drum 13, the magnetic pull causes the outer magnets to co-rotate on the outer rope drum 12 so that the entire drum assembly rotates. As a result of the weight of the displacement element 11 on the measuring wire 19, a torque acts on the outer magnet, whereby a change in the magnetic flux comes about. These magnetic field changes acting between the components of the measuring drum 12, 13 are detected by a special electromagnetic transducer 21, e.g., a Hall sensor, on the inner measuring drum 13. The transducer signal 8 is further processed by the sensor electronics unit 18 into a weight measurement signal 6. The weight measurement signal 6 of the sensor electronics unit 18 is conducted via sensor signal lines 22 along the measuring shaft 10 to a sliding contact and/or rotation transformer 4, and forwarded to the main electronics unit 17. This weight measurement signal 6 is evaluated with the position data signal 7 of an encoder or coder 20, which is located on a drive motor shaft, by a microprocessor 25 in the main electronics unit 17. A corresponding motor control signal 5 is transmitted by a motor control electronics unit to the drive motor 3. The drive motor 3 is controlled by the motor control signal 5 such that the voltage produced by the changes in the magnetic flux is adapted at the transducer 21 to the voltage specified by the operating command. When the displacement element 11 is lowered and placed on the surface of the fluid 14, the weight of the displacement element 11 is reduced by the buoyancy F.sub.B of the displacement element 11 in the fluid 14. The torque in the magnetic coupling between the outer rope drum 12 or measuring drum 27 and the inner rope drum 13 changes thereby. This change is, for example, measured by five temperature-compensated Hall detector chips as measuring element 21. The position data signal 7, which indicates the position of the displacement element 11, is transmitted to the motor control electronics unit 26 in the main electronics unit 17, such as a microprocessor 25. As soon as the level of the fluid 14 rises and falls, the displacement element 11 is repositioned by the drive motor 3 by means of gears 23 and the servomotor 3. The rotation of the measuring drum 27 is precisely evaluated from at least the position data signal 7 and the weight measurement signal 6, in order to determine the fill state value 16 up to a precision of +/−0.7 mm.

[0032] This design of an electromechanical fill state measuring device 1 with a sliding contact located on the measuring shaft 10 for transmitting an electrical transducer signal 8 of the electromagnetic transducer 21 in the inner rope drum 13 to the main electronics unit 17—in particular, the servomotor control electronics unit 26—has the disadvantage that this mechanical tapping of the transducer signal 8 via the sliding contacts does not take place without wear, and that a torque change can be generated by frictional resistances and measurement inaccuracies thus occur. For this reason, it is advantageous, for the transmission of the electrical transducer signal 8, to arrange the sensor electronics unit 18 on the inner rope drum 13 and to, for example, use an inductive rotation transformer 4. This rotation transformer 4 transmits a digital weight measurement signal 6 from the sensor electronics unit 18 to the main electronics unit 17—in particular, the microprocessor 25. As a result of the good transmission properties of the radial rotation transformer 4 of the weight measurement signal 6 and, in the opposite direction, the possibility of the reliable energy supply of the sensor electronics unit 18 by the main electronics unit 17, it is possible to design the sensor electronics unit 18 directly inside the inner rope drum 13 close to the measuring elements 21. A more precise evaluation of the measuring elements 21—in particular, the Hall sensors—and a preprocessing of the measured values of the measuring elements 21 is thereby made possible.

[0033] FIG. 3 shows a schematic drawing regarding the derivation of the buoyancy F.sub.B of the displacement element 11. If a displacement element 11 is immersed in a fluid 14, the resulting weight F.sub.res on the measuring wire 19 changes due to the buoyancy F.sub.B acting on the displacement element 11. The buoyancy F.sub.B can be derived using the following calculations:

F.sub.B=F.sub.res−F.sub.g=A*p.sub.2−A*p.sub.1=A(p.sub.2−p.sub.1)

[0034] The buoyancy F.sub.B is a resulting weight F.sub.res opposing the gravitational force F.sub.g on a displacement element 11 in fluids or gases 14.

p.sub.liq*g*h

[0035] The pressure p.sub.liq in the fluid 14 can be determined via the product of the density p.sub.liq of the fluid 14, the height h, and the gravitational acceleration g. From this, a formula, which is dependent upon the total immersion depth h.sub.2 and the submersion depth h.sub.1, for the buoyancy F.sub.B can be derived.

F.sub.B=A*p.sub.liq*g*(h.sub.2−h.sub.1)

[0036] The equilibrium volume V.sub.B of the displacement element 11 results from the difference of the total immersion depth h.sub.2 and the submersion depth h.sub.1 multiplied by the cross-sectional area A of the displacement element 11.

V.sub.B=A*(h.sub.2−h.sub.1)

[0037] This results in a formula for the buoyancy F.sub.B

F.sub.B=p.sub.liq*g*V.sub.B

[0038] The resulting mass m.sub.res of the displacement element 11, if it is immersed in the fluid 14 in a balanced manner, results from the following formulas:

F.sub.res=F.sub.Disp−F.sub.B

F.sub.res=m.sub.Disp*g−p.sub.liq*g*V.sub.B

m.sub.res=m.sub.disp−p.sub.liq*V.sub.B

[0039] For each displacement element 11, an equilibrium volume V.sub.B is specified as parameter, at which equilibrium volume the displacement element 11 is generally immersed halfway in the medium. If the parameters of the equilibrium volume V.sub.B and the density p.sub.liq of the fluid 14 are thus specified to the electromechanical fill state measuring device 1, the evaluation electronics unit can determine the resulting mass m.sub.res of the displacement element 11 by means of the evaluation algorithm and balance the displacement element according to the submersion depth h.sub.1.

[0040] FIG. 4 and FIG. 5 show schematic drawings of the variation according to the invention of the equilibrium volume V.sub.B of the displacement element 11. For the functional diagnosis of the electromechanical fill state measuring device, the movement of the servomotor 3, the resulting mass m.sub.res of the displacement element 11, the movement of the measuring drum 27 and of the displacement element 11, and the checking of entered parameters regarding the displacement element 11 currently hanging on the measuring wire 19 can, for example, be checked and monitored. In the functional diagnosis according to the invention, the parameter of the equilibrium volume V.sub.B is changed for this purpose on the electromechanical fill state measuring device 1 during the fill state measurement. If the equilibrium volume V.sub.B is, for example, increased in a single step or in small individual steps dn up to an upper limit of the equilibrium volume V.sub.BH, the resulting mass m.sub.res is reduced to a first resulting mass m.sub.res1 at the upper limit, whereby the displacement element 11 is lowered to a first height h.sub.B1, measured starting from the upper edge of the displacement element 11, until the measured resulting mass m.sub.res is equal to the first resulting mass m.sub.res1 at the upper limit. However, if the equilibrium volume V.sub.B is, for example, decreased in a single step or in small individual steps dn to a lower limit of the equilibrium volume V.sub.BL, the resulting mass m.sub.res is increased to a second resulting mass m.sub.res2 at the lower limit, whereby the displacement element 11 in turn is raised to a second height h.sub.B2, measured starting from the upper edge of the displacement element 11, until the measured resulting mass m.sub.res is equal to the second resulting mass m.sub.res2 at the lower limit.

[0041] In order for the jumps in the measurement signal of the resulting weight F.sub.res or the resulting mass m.sub.res to be small, the equilibrium volume change ΔV.sub.B is performed in very small individual steps dn, whereby correspondingly very small changes in the length of the measuring wire 19 or very small height changes Δh in the displacement element 11 are caused, which are smaller than the smallest possible resolution of the measurement of the fill state L of the electromechanical fill state measuring device, and the determinations of the fill state L and/or the resulting mass m.sub.res are thus not affected by the evaluation algorithm.

[0042] For this purpose, the equilibrium volume V.sub.B is changed in small individual steps dn, with, for example, a same step height dh or also with a different step height dh1, dh2 in the area of an upper limit of the equilibrium volume height h.sub.BH and a lower limit of the equilibrium volume height h.sub.BL.

[0043] The evaluation algorithm can calculate the number of small individual steps dn by determining the height change Δh from the equilibrium volume change ΔV.sub.B, knowing the cross-sectional area A of the displacement element 11. This height change Δh can, for example, be less than 10 millimeters. The number of the small individual steps dn is selected such that the quotient of the height change Δh divided by the smallest possible resolution of the evaluation algorithm of the electromechanical fill state measuring device 1 is smaller. As described previously, the smallest resolution of the evaluation algorithm of the electromechanical fill state measuring device 1 can, for example, be specified as less than 0.7 millimeters. The number of the small individual steps dn of the evaluation algorithm for the functional diagnosis must be greater than the number of steps that would be necessary for the height change Δh with the smallest possible resolution of the evaluation algorithm of the electromechanical fill state measuring device 1 as step size. According to the example values, with a height change Δh of 10 millimeters and with a smallest resolution of the evaluation algorithm of 0.7 millimeters, the number of small individual steps dn can be at least 15 steps. In this way, the evaluation algorithm of the functional diagnosis does not affect the evaluation algorithm of the measurement operation of the electromechanical fill state measuring device 1, since the displacement element 11 is always lowered and raised by the height changes Δh in small individual steps dn, and these changes are beyond the resolution capacity of the evaluation electronics unit or of the evaluation algorithm of the electromechanical fill state measuring device 1.

LIST OF REFERENCE NUMBERS

[0044] 1 Fill state measuring device

[0045] 2 Sensor housing

[0046] 3 Stepping motor, servomotor, drive motor

[0047] 4 Radial rotation transformer

[0048] 5 Motor drive signal, motor control signal

[0049] 6 Weight measurement signal

[0050] 7 Position data signal

[0051] 8 Transducer signal

[0052] 9 Drive shaft

[0053] 10 Measuring shaft

[0054] 11 Displacement element, float

[0055] 12 Outer rope drum

[0056] 13 Inner rope drum

[0057] 14 Filling material, medium, fluid, gases

[0058] 15 Container

[0059] 16 Measuring room

[0060] 17 Main electronics unit

[0061] 18 Sensor electronics unit

[0062] 19 Measuring rope, measuring wire

[0063] 20 Coder, encoder

[0064] 21 Measuring element, transducer

[0065] 22 Sensor signal lines

[0066] 23 Gears

[0067] 24 Field bus, two-wire line

[0068] 25 Microprocessor, evaluation and control unit

[0069] 26 Motor control electronics unit

[0070] 27 Measuring drum

[0071] V.sub.B Equilibrium volume

[0072] V.sub.BH Upper limit of the equilibrium volume

[0073] V.sub.BA Lower limit of the equilibrium volume

[0074] ΔV.sub.B Equilibrium volume change

[0075] Δh Height changes

[0076] h.sub.B Equilibrium volume height

[0077] h.sub.B1 First height, which is measured from the upper edge of the displacement element

[0078] h.sub.B2 Second height, which is measured from the upper edge of the displacement element

[0079] h.sub.BH Upper limit of the equilibrium volume height

[0080] h.sub.BL Lower limit of the equilibrium volume height

[0081] h.sub.1 Submersion depth

[0082] h.sub.2 Total immersion depth

[0083] dn Small individual steps

[0084] L Fill state

[0085] F.sub.res Resulting weight

[0086] F.sub.g Weight, gravitational force

[0087] F.sub.B Buoyancy