DE102019127961A1 - Procedure for checking the functionality of measuring systems - Google Patents

Abstract

The invention relates to a method for checking the functionality of a measuring system for process automation, in particular a measuring system for determining the dielectric value. The measuring system must be designed to implement the method in order to measure at least two correlating measured variables. According to the method, a correlation coefficient between the at least two measured variables is calculated on the basis of a predefined correlation pattern and the measuring system is classified as inoperative if the correlation coefficient falls below a predefined first limit value. Depending on the implementation of the method, the functionality can be determined almost instantaneously during the ongoing measurement operation, which prevents potentially dangerous states within the corresponding process system.

Description

The invention relates to a method for checking the functionality of measuring systems in automation technology.

In automation technology, in particular in process automation technology, field devices are often used that are used to record and / or influence various measured variables. The measured variable to be determined can be, for example, a level, a flow rate, a pressure, the temperature, the pH value, the redox potential, the conductivity or the dielectric value of a medium. To acquire the corresponding measured values, the field devices each include suitable measured value pickup units or are based on suitable measurement principles. A large number of different types of field devices are manufactured and sold by the Endress + Hauser group of companies.

The determination of the dielectric value (also known as "dielectric constant" or "relative permittivity") of various media is of great interest in the case of solids as well as liquid media and gases such as fuels, sewage, gases or chemicals, because this value represents a reliable indicator of impurities, the moisture content or the composition of the substance. In the context of the invention, the term “container” also includes non-closed containers, such as, for example, basins, lakes or flowing waters.

Among other things, the TDR principle (TDR is an acronym for “Time Domain Reflectometry”) is used to measure the dielectric value. With this measuring principle, the transducer unit sends a pulse-shaped high-frequency signal with a frequency between 0.1 GHz and 150 GHz along a conductive measuring probe and measures the duration of the pulse until the reflected high-frequency signal is received. This makes use of the effect that the pulse transit time depends on the dielectric value of the substance that surrounds the measuring probe. The functional principle of TDR-based transducer units is described, for example, in the publication EP 0622 628 A2 . Corresponding field devices are sold in numerous embodiments, for example by IMKO Mikromodultechnik GmbH. Another advantage of TDR-based transducer units is that, in addition to the dielectric value, the dielectric loss factor or the electrical conductivity of the medium can potentially also be determined. The measured dielectric value and the measured conductivity correlate inversely proportional to one another in a functioning TDR-based measured value recorder.

In particular, high-frequency-based field devices, such as, for example, TDR-based dielectric value measurement, can be disturbed by environmental influences, such as electromagnetic radiation, so that the functionality of the field device is lost. The same also applies to the entire measuring system in process plants, which can comprise several field devices or measured value pickup units and thus record different measured variables. If a measured value pickup unit or corresponding parts of the measuring system are not functional, this can in turn lead to faulty control of the process plant and thus potentially also to dangerous situations. Accordingly, it is advantageous if the process control center can be informed about the current functionality of the field device or the measuring system.

The invention is therefore based on the object of providing a method with which the functionality of measuring systems in corresponding systems can be checked.

• - Aufnahme einer ersten Mehrzahl an Messwert-Paaren während einer Messbetriebs-Phase,
• - Berechnung eines Korrelations-Koeffizienten zwischen der ersten Mehrzahl an Messwert-Paaren auf Basis eines vordefinierten Korrelationsmusters, und
• - Einstufung des Mess-Systems als funktionsunfähig, sofern der Korrelations-Koeffizient einen vordefinierten ersten Grenzwert unterschreitet.

The invention solves this problem with a method for checking the functionality of a measuring system for process automation. To use this method, the measuring system must be designed to be able to measure at least two correlating measured variables, as in the case of the TDR measuring principle, the dielectric value and the conductivity. The procedure comprises the following procedural steps:

• - Recording of a first plurality of pairs of measured values during a measuring operation phase,
• Calculation of a correlation coefficient between the first plurality of pairs of measured values on the basis of a predefined correlation pattern, and
• - Classification of the measuring system as inoperable if the correlation coefficient falls below a predefined first limit value.

The invention is therefore based on checking the correlation of the individual measured variables with one another. If the method detects a strong correlation between the measured variables, this is assessed as evidence of the functionality of the measuring system. In the other case, a malfunction of the measuring system can be assumed, so that the measured values can be classified as incorrect or at least not trustworthy.

In the context of the invention, a pair of measured values corresponding to the number of measured variables is defined as at least two measured values, with these measured values consist of one measured value for each measured variable. The measured values of the respective measured value pair have a time-defined relationship to one another; in the simplest case, they are measured simultaneously.

In principle, the choice of the correlation pattern and the first number of pairs of measured values is not strictly prescribed within the scope of the invention, but rather is to be selected as a function of the specific measuring system. Relevant variables here are the number of correlating measured variables and the number of measured values that should or can be used to calculate the correlation value. If at least the last hundred pairs of measured values are used as the first number to calculate the correlation coefficient, the correlation can be determined by such a large number with a comparatively high degree of certainty.

If only two measured variables are to be checked for their correlation, a Pearson correlation, for example, can be used as the correlation pattern. In particular, if the number of measured values that are used to calculate the correlation value is selected to be small (e.g. a maximum of 10 measured values per measured variable), the function check can be performed very quickly on the basis of the Pearson correlation coefficient and thus during the ongoing Measurement operation phase. If there are more than two measured variables to be checked for correlation, a partial correlation can be used, for example. Depending on the choice of the correlation pattern, the correlation coefficient and the first limit value are calculated as a vector quantity, or they can be represented in vector form. For example, the correlation coefficient can be represented as an eigenvector.

The method according to the invention can be expanded to the effect that a variance is additionally calculated using the measured values of at least one of the measured variables from the first number of measured value pairs. In this case, the measuring system is only classified as functional if not only a minimum correlation is exceeded, but the variance also falls below a predefined second limit value. This further increases the reliability with which the functionality is determined.

• - Eine erste Messwertaufnehmer-Einheit, die ausgelegt ist, über mehrere Mess-Zyklen hinweg zumindest die erste Messgröße zu messen,
• - eine zweite Messwertaufnehmer-Einheit, die ausgelegt ist, die zweite Messgröße zu messen,
• - eine Steuer-Einheit, die ausgelegt ist, um
  • o zumindest anhand der Messwerte der ersten Messgröße und anhand der Messwerte der zweiten Messgröße eine entsprechende erste Anzahl an Messwert-Paaren von vergangenen Mess-Zyklen zu bilden,
  • o den Korrelations-Koeffizienten zwischen der ersten Mehrzahl an Messwert-Paaren auf Basis des vordefinierten Korrelationsmusters zu berechnen, und
  • o das Mess-Systems als nicht funktionsfähig einzustufen, sofern der Korrelations-Koeffizient den vordefinierten ersten Grenzwert unterschreitet.

A measuring system that is suitable for carrying out the method according to one of the design variants described above must accordingly include at least the following components:

• - A first transducer unit which is designed to measure at least the first measured variable over several measuring cycles,
• - a second transducer unit, which is designed to measure the second measured variable,
• - a control unit that is designed to
  • o to form a corresponding first number of pairs of measured values from previous measurement cycles at least on the basis of the measured values of the first measured variable and on the basis of the measured values of the second measured variable,
  • o calculate the correlation coefficient between the first plurality of pairs of measured values on the basis of the predefined correlation pattern, and
  • o classify the measuring system as non-functional if the correlation coefficient falls below the predefined first limit value.

Instead of a second measured value sensor, the method according to the invention can of course also be used when the first measured value sensor unit of the measuring system is designed to measure the second measured variable in addition to the first measured variable. The method can therefore also be used, for example, in the case of TDR-based dielectric value measurement, in which the first transducer unit is designed on the basis of the TDR measurement principle in such a way that the dielectric value and the conductivity of a medium are determined as measured variables.

In the context of the invention, the term “unit” in the context of the invention is in principle understood to mean any electronic circuit that is designed to be suitable for the intended use. Depending on the requirement, it can therefore be an analog circuit for generating or processing corresponding analog signals. However, it can also be a digital circuit such as an FPGA or a storage medium in conjunction with a program. The program is designed to carry out the corresponding process steps or to apply the necessary arithmetic operations of the respective unit. In this context, different electronic units of the level measuring device in the sense of the invention can potentially also access a common physical memory or be operated by means of the same physical digital circuit.

The invention is explained in more detail with the aid of the following figure. It shows: 1 : A TDR-based transducer unit for measuring the dielectric value and conductivity of a medium in a container.

For a general understanding of the method according to the invention is in 1 a measuring system 1 , 4th shown, which is used to determine the dielectric value and to determine the electrical conductivity of a medium 2 serves. This is where the medium is located 2 in a suitable container 3 , where it is the medium 2 liquids such as beverages, paints, cement or fuels such as liquefied gases or mineral oils. However, it is also conceivable to use the measuring system 1 , 4th in the case of media in the form of bulk goods 2 such as grain.

To determine the dielectric value and the conductivity of the medium 2 includes the measuring system 1 , 4th a transducer unit 1 on the side of a connector on the container 3 , for example. A flange connection is arranged. Here is the transducer unit 1 attached roughly form-fitting to the inner wall of the container. The in 1 shown transducer unit 1 on the TDR principle, for example in the publication EP 0622 628 A2 is described. It is thus possible to determine the measured values of the conductivity and the dielectric value at the same time during the regular measuring operation phase and to repeat this cyclically, for example at a maximum interval of 100 ms.

The transducer unit 1 is at the in 1 embodiment shown with a control unit 4th of the measuring / system, such as a process control system of the process plant. "PROFIBUS", "HART", "Wireless HART" or "Ethernet" can be implemented as the interface. The dielectric value and the conductivity value can be transmitted via this. However, other information about the general operating state of the transducer unit can also be provided 1 communicated.

The control unit is based on the dielectric value and the corresponding, i.e. the conductivity value measured at the same time 4th According to the invention, one pair of measured values per measurement cycle. Accordingly, the control unit 4th Calculate a correlation coefficient between the dielectric value and the conductivity based on the pairs of measured values measured in previous measuring cycles. Depending on how many pairs of measured values or how many previous measuring cycles (for example the 100 previous measuring cycles) are used for the calculation, the correlation coefficient can be determined with a statistically correspondingly high degree of certainty.

Since the 1 The embodiment shown, the correlation coefficient between only two measured variables, that is, the dielectric value and the conductivity is calculated, the control unit can 4th calculate the correlation coefficient on the basis of a Pearson correlation, for example. A Pearson correlation is in turn particularly advantageous if only 20 or fewer previous measurement cycles or their measurement value pairs are used to calculate the correlation value. In this case the control unit can 4th Calculate the correlation coefficient so quickly that the functionality of the measuring system can be determined almost without delay during the current measuring phase: If the correlation coefficient falls below a predefined first limit value, the measuring system is classified as no longer functional and can for example, a corresponding warning signal can be generated. Otherwise it can be assumed that the measuring system is functional.

The control unit 4th is shown as a separate, higher-level unit in the illustration shown. In the context of the invention, however, it is also conceivable to use the control unit 4th not as an external device, but as an integral component of the TDR-based transducer unit 1 to interpret. Of course, the method according to the invention can also be used instead of TDR-based measured value recorders in any other system by means of which two or more correlating measured variables are measured in a process plant.

List of reference symbols

1

Transducer unit

2

medium

3

container

4th

Control unit

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• EP 0622628 A2 [0004, 0018]

Claims (8)

A method for checking the functionality of a measuring system (1, 4) for process automation, the measuring system (1, 4) being designed to measure at least two correlating measured variables, comprising the following method steps: Recording a first plurality of pairs of measured values, a pair of measured values corresponding to the number of measured variables consisting of at least two measured values, each with one measured value per measured variable, and the at least two measured values of the respective measured value pair with a time-defined relationship to one another, in particular at the same time to be measured - Calculation of a correlation coefficient between the at least two measured variables on the basis of the first plurality of measured value pairs on the basis of a predefined correlation pattern, and - Classification of the measuring system (1, 4) as inoperable if the correlation coefficient falls below a predefined first limit value. Procedure according to Claim 1 , a Pearson correlation or a partial correlation being used as the correlation pattern. Method according to one of the preceding claims, wherein at least the last hundred pairs of measured values are used as the first number for calculating the correlation coefficient. Procedure according to Claim 1 to 3 , the last ten pairs of measured values being used as the first number to calculate the correlation coefficient, provided that a Pearson correlation is used as the correlation pattern. Method according to at least one of the preceding claims, wherein a variance is calculated based on the measured values of one of the at least two measured variables from the first number of measured value pairs, and the measuring system (1, 4) is classified as functional if the variance falls below a predefined second limit value. Method according to at least one of the preceding claims, wherein the correlation coefficient and the first limit value are calculated as a vector quantity. Measuring system for carrying out the method according to one of the preceding claims, comprising: - A first transducer unit (1) which is designed to measure at least the first measured variable, - A second transducer unit, which is designed to measure the second measured variable during the operating phase, or wherein the first transducer unit (1) is designed to measure the first measured variable and the second measured variable during the operating phase, - A control unit (4) which is designed to o to form a corresponding first number of pairs of measured values at least on the basis of the measured values of the first measured variable and on the basis of the measured values of the second measured variable, o using the first plurality of pairs of measured values on the basis of the predefined correlation pattern to calculate the correlation coefficient between the measured variables, and o classify the measuring system as inoperable if the correlation coefficient falls below the predefined first limit value. Measuring system according to Claim 7 , wherein the first transducer unit (1) is designed on the basis of the TDR measuring principle in order to measure the dielectric value and the conductivity of a medium (2) as measured variables.

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