Method for determining a measurement uncertainty of a measured value of a field device

Abstract

The present disclosure relates to a computer-implemented method for determining at least one measurement uncertainty for at least one measured value of a field device, in which a set of calculation parameters is created that contains at least all standard parameters of a set of standard parameters in the form of a respectively corresponding calculation parameter, and the at least one measurement uncertainty and/or a measurement uncertainty budget is calculated and/or specified based upon at least one calculation parameter value of at least one calculation parameter. Each standard parameter of the set of standard parameters comprising at least one standard parameter represents an independent variable causing the measurement uncertainty. To each calculation parameter is assigned at least one calculation parameter value in the form of at least one standard parameter value, one device parameter value, and/or one application parameter value.

Claims

1. A computer-implemented method for determining at least one measurement uncertainty for at least one measured value of a field device, comprising: creating a set of calculation parameters that includes at least all standard parameters of a set of standard parameters in the form of a respectively corresponding calculation parameter, wherein each standard parameter of the set of standard parameters comprising at least one standard parameter represents an independent variable causing the at least one measurement uncertainty, wherein to each calculation parameter is assigned at least one calculation parameter value in the form of at least: one standard parameter value of a respectively corresponding standard parameter; one device parameter value of a respectively corresponding device parameter of a set of device parameters, which consists of a subset of the set of standard parameters, wherein each of the device parameters represents at least one independent variable, which is specific to the field device; and/or one application parameter value of a respectively corresponding application parameter of a set of application parameters, which consists of a subset of the set of standard parameters, wherein each of the application parameters represents at least one independent variable that is specific to an application of the field device; and calculating and/or specifying the at least one measurement uncertainty and/or a measurement uncertainty budget based upon at least one calculation parameter value of at least one calculation parameter; wherein, where the set of application parameters has a respectively corresponding application parameter, the respectively corresponding application parameter value of the corresponding application parameter is assigned to at least one calculation parameter value of at least one calculation parameter, wherein when the set of application parameters does not contain a corresponding application parameter and the set of device parameters includes a respectively corresponding device parameter, the respectively corresponding device parameter value of the corresponding device parameter is assigned to at least one calculation parameter value, and wherein in the case where neither the set of application parameters has a corresponding application parameter nor the set of device parameters has a corresponding device parameter, the respectively corresponding standard parameter value of the corresponding standard parameter is assigned to at least one calculation parameter value; wherein a processor performs a calculation of a measured value deviation using a standard parameter representing an independent variable; completing the at least one measured value of the field device based on the measurement uncertainty; and controlling an automation process using the completed measured value.

2. The method of claim 1, wherein the at least one independent variable is an environmental condition, a process condition, information from a calibration, qualification, and/or adjustment of the field device, or at least one secondary variable that is included in the determination of a measured value measured by means of the field device.

3. The method of claim 1, wherein to each standard parameter is assigned at least one standard parameter value, to each device parameter is assigned at least one device parameter value, to each application parameter is assigned at least one application parameter value, and/or to each calculation parameter is assigned at least one calculation parameter value.

4. The method of claim 1, wherein to at least one standard parameter value, device parameter value, application parameter value, and/or calculation parameter value is assigned at least one neutral placeholder.

5. The method of claim 1, wherein a mathematical, modular, expandable model for calculating and/or specifying the measurement uncertainty and/or the measurement uncertainty budget is created.

6. The method of claim 5, wherein a partial measurement uncertainty and/or a partial measurement uncertainty budget is/are determined based upon the model, based upon a subset of the set of calculation parameters.

7. The method of claim 1, wherein at least one sensitivity factor for at least one calculation parameter value of at least one calculation parameter is determined based upon the model.

8. The method of claim 7, wherein the at least one sensitivity factor is used to calculate and/or specify the at least one measurement uncertainty.

9. The method of claim 1, wherein a set of measuring point parameters with at least one measuring point parameter and with at least one measuring point parameter value assigned to the at least one measuring point parameter is provided, which set of measuring point parameters is a subset of the set of standard parameters, wherein each measuring point parameter describes an independent variable, which is specific to a measuring point at which the field device is used, and wherein at least one measuring point parameter value of at least one measuring point parameter is assigned to at least one calculation parameter value of at least one calculation parameter.

10. The method of claim 1, wherein a mathematical combination of at least one measuring point parameter value of at least one measuring point parameter, at least one application parameter value of at least one application parameter, at least one device parameter value of at least one device parameter, and/or at least one standard parameter value of at least one standard parameter is assigned to at least one calculation parameter value of at least one calculation parameter.

11. The method of claim 1, wherein each standard parameter, device parameter, application parameter, calculation parameter, and/or measuring point parameter is at least one physical or chemical variable, which describes at least one independent variable at least partially.

12. The method of claim 11, wherein the respectively at least one standard parameter value, device parameter value, application parameter value, calculation parameter value, and/or measuring point parameter value is a value or measured value for the physical or chemical variable or is a measurement uncertainty or a distribution function for a measurement uncertainty.

13. The method of claim 9, wherein at least one measuring point parameter value is at least one value determined at or in the measuring point, the at least one value determined based upon a specific process in which the field device is operated or based upon a statistical analysis of at least one physical or chemical variable relevant to the measuring point; an input entered by an operator at a site of the measuring point; and/or a value determined during the operation of the field device at or in the measuring point.

14. The method of claim 1, wherein: where no standard parameter value, device parameter value, and/or application parameter value is assigned to at least one standard parameter, device parameter, and/or application parameter assigned to at least one measuring point parameter, the measuring point parameter value of the respective at least one measuring point parameter is entered into the set of standard parameters, the set of device parameters, and/or the set of application parameters as standard parameter value, device parameter value, and/or application parameter value for the respective standard parameter, device parameter, and/or application parameter; and/or where a standard parameter value, device parameter value, and/or application parameter value is already assigned to at least one standard parameter, device parameter, and/or application parameter assigned to the at least one measuring point parameter, the respective standard parameter value, device parameter value, and/or application parameter value of the respective standard parameter, device parameter, and/or application parameter is replaced by the measuring point parameter value of the measuring point parameter, is replaced by a mathematical combination of the respective measuring point parameter value and of the respective standard parameter value, device parameter value, and/or application parameter value, or is changed based upon the respective measuring point parameter value.

15. The method of claim 1, wherein, where the measurement uncertainty is caused by at least two independent variables, the contribution of each of the independent variables is specified for the measurement uncertainty.

16. The method of claim 5, wherein the set of standard parameters, the set of device parameters, the set of application parameters, the set of measuring point parameters, and/or the model are stored on at least one storage medium.

17. A computer program for determining at least one measurement uncertainty for at least one measured value of a field device using computer-readable program code elements, which, when executed on a computer, perform operations comprising: creating a set of calculation parameters that includes at least all standard parameters of a set of standard parameters in the form of a respectively corresponding calculation parameter, wherein each standard parameter of the set of standard parameters comprising at least one standard parameter represents an independent variable causing the at least one measurement uncertainty, wherein to each calculation parameter is assigned at least one calculation parameter value in the form of at least: one standard parameter value of a respectively corresponding standard parameter; one device parameter value of a respectively corresponding device parameter of a set of device parameters, which consists of a subset of the set of standard parameters, wherein each of the device parameters represents at least one independent variable, which is specific to the field device; and/or one application parameter value of a respectively corresponding application parameter of a set of application parameters, which consists of a subset of the set of standard parameters, wherein each of the application parameters represents at least one independent variable that is specific to an application of the field device; and calculating and/or specifying the at least one measurement uncertainty and/or a measurement uncertainty budget based upon at least one calculation parameter value of at least one calculation parameter; wherein the set of application parameters has a respectively corresponding application parameter, the respectively corresponding application parameter value of the corresponding application parameter is assigned to at least one calculation parameter value of at least one calculation parameter, wherein the set of application parameters does not contain a corresponding application parameter and the set of device parameters includes a respectively corresponding device parameter, the respectively corresponding device parameter value of the corresponding device parameter is assigned to at least one calculation parameter value, and wherein in the case where neither the set of application parameters has a corresponding application parameter nor the set of device parameters has a corresponding device parameter, the respectively corresponding standard parameter value of the corresponding standard parameter is assigned to at least one calculation parameter value; wherein a processor performs a calculation of a measured value deviation using a standard parameter representing an independent variable; completing the at least one measured value of the field device based on the measurement uncertainty; and controlling an automation process using the completed measured value.

18. A computer program product comprising: at least one computer-readable medium; and a computer program for determining at least one measurement uncertainty for at least one measured value of a field device using computer-readable program code elements, which, when executed on a computer, perform operations comprising: creating a set of calculation parameters that includes at least all standard parameters of a set of standard parameters in the form of a respectively corresponding calculation parameter, wherein each standard parameter of the set of standard parameters comprising at least one standard parameter represents an independent variable causing the at least one measurement uncertainty, wherein to each calculation parameter is assigned at least one calculation parameter value in the form of at least: one standard parameter value of a respectively corresponding standard parameter; one device parameter value of a respectively corresponding device parameter of a set of device parameters, which consists of a subset of the set of standard parameters, wherein each of the device parameters represents at least one independent variable, which is specific to the field device; and/or one application parameter value of a respectively corresponding application parameter of a set of application parameters, which consists of a subset of the set of standard parameters, wherein each of the application parameters represents at least one independent variable that is specific to an application of the field device; and calculating and/or specifying the at least one measurement uncertainty and/or a measurement uncertainty budget based upon at least one calculation parameter value of at least one calculation parameter, wherein: where no standard parameter value, device parameter value, and/or application parameter value is assigned to at least one standard parameter, device parameter, and/or application parameter assigned to at least one measuring point parameter, the measuring point parameter value of the respective at least one measuring point parameter is entered into the set of standard parameters, the set of device parameters, and/or the set of application parameters as standard parameter value, device parameter value, and/or application parameter value for the respective standard parameter, device parameter, and/or application parameter; and/or where a standard parameter value, device parameter value, and/or application parameter value is already assigned to at least one standard parameter, device parameter, and/or application parameter assigned to the at least one measuring point parameter, the respective standard parameter value, device parameter value, and/or application parameter value of the respective standard parameter, device parameter, and/or application parameter is replaced by the measuring point parameter value of the measuring point parameter, is replaced by a mathematical combination of the respective measuring point parameter value and of the respective standard parameter value, device parameter value, and/or application parameter value, or is changed based upon the respective measuring point parameter value, and wherein at least the computer program, the set of standard parameters, the set of device parameters, the set of application parameters, the set of measuring point parameters, and/or the set of calculation parameters is/are at least partially stored on the at least one computer-readable medium; wherein the set of application parameters has a respectively corresponding application parameter, the respectively corresponding application parameter value of the corresponding application parameter is assigned to at least one calculation parameter value of at least one calculation parameter, wherein the set of application parameters does not contain a corresponding application parameter and the set of device parameters includes a respectively corresponding device parameter, the respectively corresponding device parameter value of the corresponding device parameter is assigned to at least one calculation parameter value, and wherein in the case where neither the set of application parameters has a corresponding application parameter nor the set of device parameters has a corresponding device parameter, the respectively corresponding standard parameter value of the corresponding standard parameter is assigned to at least one calculation parameter value; wherein a processor performs a calculation of a measured value deviation using a standard parameter representing an independent variable; completing the at least one measured value of the field device based on the measurement uncertainty; and controlling an automation process using the completed measured value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present disclosure is explained in more detail with reference to the following figures. These show:

(2) FIG. 1 shows a schematic illustration of the sequence of the method according to the present disclosure; and

(3) FIG. 2 shows a schematic illustration of an amperometric oxygen sensor.

DETAILED DESCRIPTION

(4) A value p, determined by means of a field device, for a process variable P is fundamentally afflicted by a measurement error, which is usually specified in the form of a measurement uncertainty ΔP for this measured value. The following applies:
P=p+/−ΔP
where the measurement uncertainty ΔP is caused by various independent variables E.sub.1-E.sub.n, which must be known as precisely as possible in order to determine the measurement uncertainty ΔP precisely.

(5) FIG. 1 shows a schematic illustration of the set of parameters relevant to the method according to the present disclosure and explains their interaction for carrying out the method, by way of example. The relevant independent variables E.sub.1-E.sub.N [not shown] are combined in a set of standard parameters S in the form of the standard parameters S.sub.1-S.sub.N. To each standard parameter S.sub.1-S.sub.N is respectively assigned at least one standard parameter value s.sub.1i-s.sub.Ni.

(6) The letter “i” represents the number of parameter values respectively assigned to a parameter (in the case of the other sets of parameters as well). For the sake of clarity, the same letter “i” has here, for all parameter values, been used to denote the number. It goes without saying, however, that the number of values assigned to a parameter can vary from parameter to parameter. In the case where no value or a neutral placeholder is assigned to a parameter, the symbol (#) was also used uniformly.

(7) In addition to the set of standard parameters S, a set of device parameters G, a set of application parameters A, and a set of measuring point parameters M also exist. It is pointed out that the set of measuring point parameters M is optional for the method according to the present disclosure.

(8) All three sets of parameters the set of device parameters G, the set of application parameters A, and the set of measuring point parameters M are subsets of the set of standard parameters S. This means that the device parameters in this case, G.sub.3 and G.sub.4, respectively correspond to the standard parameters in this case, S.sub.3, S.sub.4, i.e., represent the same independent variable. The application parameters A.sub.5, A.sub.6 likewise correspond to the respective standard parameters S.sub.5, S.sub.6, and the measuring point parameters M.sub.7 and M.sub.8 to the standard parameters S.sub.7 and S.sub.8. Respectively corresponding parameters, preferably, basically represent the same independent variable. These respectively are, then, in principle the same parameters in different sets of parameters with different assigned parameter values, where applicable.

(9) To each of the device parameters G.sub.3, G.sub.4, application parameters A.sub.5, A.sub.6, and measuring point parameters M.sub.7, M.sub.8 is respectively assigned at least one device parameter value g.sub.3i, g.sub.4i, at least one application parameter value a.sub.5i, a.sub.6i, and at least one measuring point parameter value m.sub.7i, m.sub.8i. With this, the device parameters G.sub.3, G.sub.4 respectively represent independent variables that are specific to the construction of the field device, whereas the application parameters A.sub.5, A.sub.6, on the other hand, represent independent variables that are specific to an application of the field device, and the measuring point parameters M.sub.7, M.sub.8 describe or represent independent variables that are specific to a measuring point at which the field device is used.

(10) The various sets of parameters can be stored at various locations, or centrally at a single location. They can, for example, be recorded and stored electronically in the form of databases or the like. The set of standard parameters S can, for example, be compiled in the course of the development of the field device, whereas the set of device parameters G is preferably created within the framework of the production of the field device. The set of application parameters A, on the other hand, can be created within the framework of planned operating sites or planned applications or the like. Finally, the set of measuring point parameters M is preferably created at the operating site in particular, at least partially during the operation of the field device in an operating process. This is motivated by some independent variables E.sub.1, . . . E.sub.N being dependent upon the specific operating site at a measuring point in an ongoing process. The set of measuring point parameters M can, for example, be created by a customer or by service personnel on location at the operating site. The set of measuring point parameters M is also stored there, where applicable. Alternatively, it is also possible to analyze in particular, statistically several measuring points in particular, during the continued operation of the measuring points and to store the results of the analyses in a sensor administration database. The later can, for example, be updated continuously.

(11) The recording of various parameters in different sets of parameters, which are, where applicable, created at different points in time and/or at different locations, advantageously allows for each of the relevant independent variables E.sub.1, . . . E.sub.N represented by a parameter to be determined as precisely as possible. The information and knowledge available during different stages, from the development to the use, of the field device are thus used optimally to determine the measurement uncertainty ΔP.

(12) It is pointed out that the individual sets of parameters S, G, A, M can be expanded continuously and that the set of standard parameters S can also be supplemented by the set of device parameters G, the set of application parameters A, and/or the set of measuring point parameters M, or be updated with respect to its standard parameter values s.sub.N. For the embodiment described here, an expansion of the set of device parameters G, the set of application parameters A, and/or the set of measuring point parameters M by a new parameter necessarily involves this parameter also being added to the set of standard parameters S. The parameter values g.sub.Ni, a.sub.Ni, m.sub.Ni of the set of device parameters G, of the set of application parameters A, and/or of the set of measuring point parameters M, on the other hand, do not necessarily have to be added to the set of standard parameters S.

(13) The set of calculation parameters B is created in order to calculate and/or specify the measurement uncertainty ΔP. Said set of calculation parameters includes all standard parameters S.sub.N respectively in the form of a corresponding calculation parameter B.sub.N. The calculation parameter values b.sub.Ni for each of the sets of calculation parameters B are composed in this case of the parameter values of the set of standard parameters S, of the set of device parameters G, of the set of application parameters A, and/or of the set of measuring point parameters M. For a certain calculation parameter value b.sub.Ni, either a respectively corresponding parameter value from one of the other sets of parameters S, G, A, M can be used or, alternatively, several corresponding parameter values of at least two sets of parameters can be suitably offset to one another.

(14) In the case where at least one parameter value g.sub.Ni, a.sub.Ni, m.sub.Ni is specified for a device parameter G.sub.Ni, application parameter A.sub.Ni, or measuring point parameter MM corresponding to a calculation parameter B.sub.Ni, this parameter value is preferably, but not necessarily, entered into the set of calculation parameters B. Such an assignment is illustrated in FIG. 1 by way of example.

(15) In order to calculate the measurement uncertainty and/or a measurement uncertainty budget, at least one calculation parameter value b.sub.Ni of at least one calculation parameter B.sub.Ni of the set of calculation parameters B is then used. The calculation of the measurement uncertainty ΔP and/or of the measurement uncertainty budget is preferably carried out based upon the in particular, modular mathematical model C, which can be expanded, preferably, continuously, just as with the individual sets of parameters. This model can be stored independently of the sets of parameters S, G, A, M or together with at least one of the sets of parameters preferably, with the set of standard parameters S.

(16) For example, the mathematical model maps a measurement of a value p for a process variable P, such that the following applies to the measured value p:
p=P(E.sub.1,E.sub.2, . . . ,E.sub.N),
where E.sub.1, . . . E.sub.N describe the respective independent variables, and the following applies to the measurement uncertainty ΔP assigned to the measured value p:

(17) $\Delta P\left(p\right)=\sqrt{{\left(\Delta E_1\frac{\partial p}{\partial E_1}\right)}^2+\mathrm{.Math.}+{\left(\Delta E_N\frac{\partial p}{\partial E_N}\right)}^2},$
where ΔE.sub.N represents the uncertainty caused by a certain independent variable E.sub.n and where the partial derivatives are respectively assigned to a sensitivity coefficient.

(18) It is outlined by way of example below how the measurement uncertainty ΔP for an amperometric oxygen sensor can be calculated based upon the present disclosure. For this purpose, FIG. 2 shows a schematic illustration of such a sensor 1 for determining the concentration c.sub.x of oxygen, O.sub.2. The electrochemical sensor 1 is designed in the form of a measuring probe 3 with an immersion section for immersing the measuring probe 3 in the respective measured medium 2, which is located in the container 2a. The basic structure of such a sensor 1 and its functional principle are, per se, known from the prior art.

(19) The measuring probe 3 has an electrolyte chamber 8a, which is filled with an electrolyte 8 and ends on the medium side with a sensor membrane 4. A glass body 6 with a first sensor electrode 5, which consists of platinum, for example, and serves as cathode, and a second electrode 7, which consists of silver, for example, and serves as anode, protrudes into the electrolyte chamber 8a. The electrodes are in particular, electrically connected within the measuring probe 3 via connecting lines 10a, 10b through the insulated feedthroughs 9a, 9b.

(20) The electrodes 5, 7 are brought into contact with the measured medium 2 via the sensor membrane 4. From the measured medium 2, oxygen O.sub.2 diffuses into the electrolyte chamber 8a filled with the electrolyte 8, so that the following reactions take place at the cathode 5 and the anode 7:

(21) At the cathode,
O.sub.2+2H.sub.2O+2e.sup.−.fwdarw.4OH.sup.−

(22) is converted, while at the anode, silver, for example, is oxidized:
Ag+Cl.sup.−.fwdarw.AgCl+e.sup.−

(23) In order to determine the oxygen concentration c.sub.x, a suitable voltage is applied via the connecting lines 10a, 10b to the electrodes 5, 7, and the flowing current I is measured, which is proportional to the oxygen concentration of the measured medium 2. The following applies
I.sub.mess=Ac.sub.x+B

(24) The necessity of knowing as accurately as possible all independent variables and their interactions is explained below on the basis of a few exemplary independent variables for the case of an amperometric oxygen sensor.

(25) A particularly relevant independent variable is, in this case, for example, the temperature T of the measured medium 2, since it influences the membrane permeability to the oxygen O.sub.2 present in the measured medium 2. The influence of the temperature T can, for example, be expressed by a factor, which can, in a temperature range specific to the respective field device 1, in turn be approximated by a polynomial. For the determination of the oxygen concentration c.sub.x, a temperature compensation function, e.g., in the form of a polynomial function, must accordingly always be taken into account.

(26) The individual coefficients of the polynomial are individual constants, which are taken into account for the determination of the measurement uncertainty in addition to the individual parameters representing the relevant independent variables. Other constants included in the determination of the measurement uncertainty ΔP are given by the pressure often for correction to the standard pressure p.sub.std=1013 millibar (mbar) in accordance with the standard conditions the saturation concentration of oxygen often specified for air-saturated water under standard conditions 8.5 mg/l and the oxygen partial pressure. This is thus a complex interaction of many different factors.

(27) Two additional important independent variables for the measurement accuracy of an amperometric oxygen sensor are given by the sensor slope, as well as by the sensor zero point of a sensor characteristic curve. The parameters representing these independent variables are thus preferably part of the set of device parameters G, wherein parameter values for these parameters are determined, for example, in the course of a factory calibration of the field device 1. Since the oxygen concentration in ambient air can be assumed to be a constant 20% (pO.sub.2=0.2), a calibration and/or adjustment of a sensor with respect to the sensor slope is possible by operating the sensor in air. To this end, a conversion from the current air pressure to standard pressure p.sub.std=1013 mbar must, however, take place. For a calibration/adjustment of the sensor zero point, on the other hand, it is advisable to operate the sensor in an oxygen-free medium.

(28) A set of standard parameters S for an amperometric oxygen sensor 1 thus comprises, for example, the sensor slope, the sensor zero point, and/or the temperature. In addition, independent variables given by the respectively implemented electronic measuring unit must be taken into account. These independent variables can, for example, be determined by specific measurements under known conditions. The environmental conditions and many other things also play a vital role.

(29) Some relevant independent variables can, for example, be determined within the framework of a factory calibration of the respective field device, or even several field devices. If such a calibration takes place in an open system, the respective environmental conditions, e.g., the air pressure respectively prevailing in the environment of the sensor, influence the respective result of the factory calibration. Such dependencies must then, for example, be taken into account in a further calibration taking place at the operating site of the respective sensor. Other relevant environmental conditions, depending upon the type of sensor 1, are given by, for example, the temperature, the pressure, or the salinity of a medium, provided that the factory calibration is, for example, carried out in a reference medium.

(30) Other independent variables can, for example, be estimated based upon operating the sensor 1 for a fictitious standard application and later be determined more precisely based upon the set of application parameters A and/or the set of measuring point parameters M.