DIAGNOSIS OF POSSIBLE CAUSES OF CHANGES TO AN ACTIVATION VALVE

Description

Field of the invention

[0001] The invention relates to a method for diagnosing possible causes of changes in at least one control valve with an actuator, in a system of which the control valve is a part, or in a process carried out in the system, as well as to a control valve with corresponding means.

[0002] Control valves, also called process valves, consist of a movable actuator or valve element and an opening in the valve housing. The valve element is capable of either partially or completely opening or closing this opening.

[0003] Optimization of the operation and maintenance of these valves, as well as the early detection of possible malfunctions or incorrect design of such valves, are very important in practice. State of the art

[0004] EP 315 391 B1 describes several scanning systems in which sampled values ​​are compared with reference values ​​to detect deviations in the operation of a valve. The disadvantage is that either additional force sensors or additional scanning devices are required to detect valve wear. The valve's operating point is not taken into account.

[0005] EP 2 884 358 B1 describes a control system for an entire plant that uses process data and relates it to standard values. Operating points or operating ranges of the individual valves involved are not evaluated; rather, it essentially involves a complex plant control system.

[0006] The document DE 197 23 650 A1 describes a method and a device for monitoring a control device with at least one actuator, a valve, a spindle and a position controller.

[0007] Publication WO 2013 / 184863 A1 discloses methods and devices for monitoring and / or controlling a pneumatic actuator of a valve. These methods, in particular, detect error states and, as a result, adjust a safety position of the valve, for example. Task

[0008] The object of the invention is to provide methods and devices for diagnosing possible causes of changes in at least one control valve, a system of which the control valve is a part, or a process, which do not require additional sensors or scanning devices. Solution

[0009] This problem is solved by the subject matter of the independent claims. Advantageous developments of the subject matter of the independent claims are characterized in the subclaims. The wording of all claims is hereby incorporated by reference into this description.

[0010] The use of the singular shall not exclude the plural, and this shall also apply in the reverse sense unless otherwise disclosed.

[0011] Individual procedural steps are described in more detail below. The steps do not necessarily have to be performed in the order given, and the procedure described may also include additional steps not mentioned.

[0012] To achieve this objective, a method is proposed for diagnosing possible causes of changes in at least one control valve having an actuator, in a system of which the control valve is a part, or in a process carried out in the system. The method comprises the following steps: When the actuator is not moving, i.e. in particular when no movement is intended and no control pulse is present, data relating to the position of the actuator is recorded at a plurality of points in time. This data can be, for example, the exact position of the actuator or the state of the associated controller as well as the associated point in time. This recording takes place at least in a first and a second time interval, typically at regular time intervals. Characteristics of the data relating to the position of the actuator are determined from the first time interval.This could be, for example, the operating point, a mean value, its variance, an operating range, or, if present, local maxima. When investigating the operating point or operating range, it is of particular interest whether a clustering of the data can be identified. The same characteristics are determined for the data concerning the position of the actuator from the second time interval. The further steps are only carried out if, for each time interval under consideration, one of the characteristics of the data from the time interval under consideration is that at least one local maximum can be assigned to the position of the actuator. Only then is it possible to determine the operating point or operating range without great uncertainty and / or great effort. If this is the case, the characteristics of the data concerning the position of the actuator from the two time intervals are compared in order to detect changes.This can particularly involve changes in the operating point, the valve cone, or the valve seat. Based on detected differences in the characteristics, possible causes for changes in at least one control valve, the system, or the process are diagnosed, and this diagnosis is output.

[0013] In this way, it is possible to easily detect whether the state of the process or the control valve is changing without the need for additional sensors or complicated monitoring systems, and in particular to derive a diagnosis from this change, which makes it possible to react early or in a proactive manner to emerging problems or undesirable developments.

[0014] Of course, it is useful to check the diagnosis on the system and / or the control valve in an additional step.

[0015] By examining the significance of any differences in the characteristics of the data from the two time intervals, it can be ensured that the diagnosis is based on real effects. False alarms and nonsensical diagnoses can thus be suppressed.

[0016] For a meaningful evaluation of the data, especially with regard to the operating point or operating range of the control valve, it is helpful to exclude the data relating to the position of the actuator and not record it if the corresponding position of the actuator corresponds to 0% or 100%. This corresponds to the closed and fully open valve positions, respectively, which naturally have nothing to do with the valve's operating point.

[0017] The diagnosis becomes particularly meaningful if an operating point and / or an operating range of the control valve is determined from the characteristics of the data for each time interval considered.

[0018] Incorrect control valve sizing can be diagnosed if the operating point does not correspond to a valve position between 50% and 70%. This is because control valves operate most effectively at a position of approximately 70%. For safety reasons, a certain degree of oversizing of the valves is often desirable.

[0019] A change in the process or a change in the fluid controlled by the valve can be diagnosed when differences in the characteristics of the data from two time intervals are detected, with the time intervals being separated by no more than two weeks, preferably one week, more preferably 96 hours, and most preferably 48 hours. Such changes are considered short-term and cannot be caused by wear phenomena.

[0020] Wear or a defect in the valve can be diagnosed if differences in the characteristics of the data from two time intervals are only detected if the time intervals are separated by more than 3 weeks, preferably more than 2 months, more preferably more than 6 months, and most preferably more than one year. Such changes are long-term in nature and therefore do not correspond to process changes.

[0021] Deposits on the valve seat or valve cone can be diagnosed when the operating point and / or operating range shifts toward a more open valve position. Such deposits reduce flow through the valve.

[0022] Wear or tear of the valve seat and / or valve cone can be diagnosed when the operating point and / or operating range shifts toward a more closed valve position. Such wear increases the flow through the valve.

[0023] If not only an operating point but also a working range with a width is determined, a decrease in the stability of the process can be diagnosed from an increase in the width of this working range, and / or an increase in the stability of the process can be diagnosed from a decrease in the width of the working range.

[0024] If a diagnosis of possible causes for changes in a system or process with multiple valves is planned, a pump defect can be diagnosed if the operating point and / or operating range of a plurality of valves interacting with the pump shifts toward a more open valve position. In this case, the combined flow of this plurality of valves is lower than expected, which argues against a single cause in any one of these valves.

[0025] A particularly advantageous method for determining the operating range of the control valve is achieved by performing the following steps in the time interval under consideration: A histogram is created from the data concerning the actuator position. The local maximum of the actuator position frequencies in this histogram is determined and assigned to the operating range. As long as the frequency assigned to the operating range is less than 50% of the total frequency, the actuator position with the highest frequency directly adjacent to the operating range in the histogram is added to the operating range. This results in the range around the local maximum in which at least 50% of all actuator position data lies.There is therefore not only a local maximum at a sharp position, but a contiguous area with a certain width that includes the positions in which the actuator of the control valve is most frequently located.

[0026] The object is also achieved by a control valve having means for acquiring data relating to the position of the actuator and the associated time, said means being configured such that they can acquire data relating to the position of the actuator and the respectively associated time when the actuator is not moving, i.e. in particular when no movement of the actuator (120) is provided and / or no control pulse is present. Furthermore, having means for determining time intervals, said means being able to determine at least a first and a second time interval, and data relating to the position of the actuator and the respectively associated time being acquired in at least the first and second time intervals.Furthermore, means are provided for determining characteristics of data from time intervals, wherein these means are configured to determine and compare the same characteristics of the data from the aforementioned first and second time intervals. The characteristics are selected from a group comprising at least the following members: the operating point, a mean value, its variance, a working range, and local maxima.The control valve also has means for determining whether, for each time interval under consideration, the characteristics of the data relating to the position of the actuator from the time interval under consideration include that at least one local maximum can be assigned to the position of the actuator, as well as means for comparing characteristics of data from time intervals, these means being configured to compare the same characteristics of the data from the aforementioned first and the aforementioned second time interval with each other, and further means for creating and outputting a diagnosis; these means being able to create and output a diagnosis if the aforementioned means for determining and comparing characteristics of data detect differences in the characteristics of the data from the first and second time intervals. The control valve is configured to carry out a method as already described.

[0027] The control valve is particularly simple and secure (e.g. with regard to network security) if a control module is present, whereby the means for acquiring data, determining time intervals, determining and comparing characteristics of data, and creating and outputting a diagnosis are provided by the control module.

[0028] Centralized monitoring and comparatively low effort for any complex calculations and / or data analyses that may be required are achieved if the control valve has a control module, wherein the means for acquiring data, determining time intervals, determining and comparing data characteristics, and creating and outputting a diagnosis are provided by at least one device connected to the control module via a network. The at least one device can be, for example, computers in a cloud.

[0029] Furthermore, the object is achieved by a computer program which contains executable instructions which, when executed on a computing unit, a microcontroller, DSP, FPGA or computer or on a plurality thereof in a network, carry out the method according to one of the preceding method claims.

[0030] Furthermore, the object is achieved by a computer program with program code means for carrying out the method according to the invention in one of its embodiments when the program is executed on a computing unit, a microcontroller, DSP, FPGA, or computer, or on a plurality thereof in a network. In particular, the program code means can be instructions stored on a computer-readable data carrier.

[0031] Furthermore, the object is achieved by a data carrier on which a data structure is stored which, after being loaded into a working and / or main memory of a computing unit, a microcontroller, DSPs, FPGAs or computers or a plurality thereof in a network, can execute the method according to the invention in one of its embodiments.

[0032] The object is also achieved by a computer program product with program code means stored on a machine-readable medium for carrying out the method according to the invention in one of its embodiments when the program is executed on a computing unit, a microcontroller, DSP, FPGA, or computer, or on a plurality of these in a network. A computer program product is understood to mean the program as a tradable product. It can, in principle, exist in any form, for example, on paper or a computer-readable data medium, and can, in particular, be distributed via a data transmission network.

[0033] Finally, the object is achieved by a modulated data signal which contains instructions executable by a computing unit, a microcontroller, DSP, FPGA or computer or by a plurality thereof in a network for carrying out the method according to the invention in one of its embodiments.

[0034] A computer system for executing the method can be a single computer or microcontroller, DSP, or FPGA, as well as a network of microcontrollers, DSPs, FPGAs, or computers, for example, an in-house, closed network, or even computers connected via the Internet. Furthermore, the computer system can be implemented in a client-server configuration, with parts of the invention running on the server and others on a client.

[0035] Furthermore, the object is achieved by a control module for a control valve, which provides means for carrying out the described method. With such a control module, existing control valves can be retrofitted in the manner according to the invention.

[0036] Further details and features will become apparent from the following description of preferred embodiments in conjunction with the subclaims. The respective features can be implemented individually or in combination with one another. The possibilities for solving the problem are not limited to the embodiments. For example, range specifications always include all intermediate values ​​(not mentioned) and all conceivable subintervals.

[0037] The exemplary embodiments are illustrated schematically in the figures. Identical reference numerals in the individual figures denote identical or functionally equivalent elements, or elements that correspond to one another in terms of their functions. In detail: Fig. 1A shows the typical structure of a control valve in the open position; Fig. 1B shows the typical structure of a control valve in the closed position; Fig. 2A shows a typical histogram of the valve position, where the control valve can be identified as oversized based on the operating range; Fig. 2B shows a histogram of the valve position, where the operating range is Fig. 2A is shifted towards the more open state.; Fig. 3A another typical histogram of a valve position; and Fig. 3B a histogram of the valve position in which the working range is shifted towards Fig. 3A is strongly shifted towards the more closed state.

[0038] Fig. 1A shows a typical design of a control valve 100 with a valve housing 105. Between the inflow side 110 and the outflow side 115 is a valve member 120, which can be pressed into the valve seat 125 to throttle the flow of a process fluid flowing from the inflow side 110 to the outflow side 115. The valve stem or actuator stem 130 serves this purpose. The passage of the valve stem 130 through the fluid-tight valve housing 105 is sealed by a seal or stuffing box 140.

[0039] At the upper end of the valve rod 130 is a fluidic actuator 145, where the drive fluid is typically gas. The actuator 145 has two chambers, a lower compressed air chamber 150 and an upper chamber 155, in which springs 160 act on the valve rod 130 via a plate 165. The two chambers 150 and 155 are separated from each other by a diaphragm 170, with the diaphragm 170 being impermeable to the drive fluid, typically compressed air. Such a configuration is referred to as a single-acting pneumatic actuator because compressed air is only introduced into one chamber, the compressed air chamber 150, and not into both. The passage of the valve rod 130 through the housing of the actuator 145 must be impermeable to the drive fluid. For this purpose, this passage is sealed by an actuator housing seal 175.

[0040] Typically, a signal receiver or position sensor 180 is located on the valve rod 130 for determining the position of the valve member 120.

[0041] In Fig. 1A There is sufficient compressed air in the compressed air chamber 150 so that the control valve 100 is open.

[0042] In Fig. 1B the compressed air chamber 150 is vented so that the springs 160 can close the control valve 160.

[0043] The determination of the operating point or operating range is preferably based on the evaluation of the histogram of the valve position. The histogram is analyzed for clusters. Typical histograms of this type are shown in the Figuren 2A , 2B , 3A and 3B For evaluation purposes, the marginal areas (i.e., those data corresponding to 0% or 100%, since the valve is then completely closed or open) are cut off.

[0044] To obtain the working range, the highest column of the histogram (except for 0% and 100%), i.e., the local maximum of the frequency, is preferably used as the starting point. Neighboring columns are then added if necessary until a certain percentage of the total frequency is reached, e.g., 50%. Then, the valve moves within this range for at least 50% of the time. In the typical procedure, the adjacent column of the histogram with the highest frequency is always added to the working range.

[0045] Of course, other approaches are also conceivable, for example, adding both adjacent columns until the desired frequency is reached. Or, the mean + / - one or more standard deviations can be defined as the working range.

[0046] The histograms can be used to identify various changes in the working area, which can lead to different diagnoses.

[0047] In Fig. 2A For example, it is clearly visible that the operating range is closer to 40% than the optimal range of 60-70%. This allows the conclusion that the control valve is oversized for the process taking place there, since it does not normally open as wide as would be reasonable to achieve maximum efficiency during valve operation.

[0048] In further analysis, it is useful to distinguish between short-term and long-term changes. Long-term changes can extend over several months, years, or even the entire service life of the system or valve. Short-term changes, on the other hand, can range from hours, a few days, to a maximum of weeks. Depending on whether the changes occur in the short or long term, it can be assumed that they are due to process changes, for example, changes in the composition of the fluid being controlled (short-term), or, for example, to wear on the valve (long-term).

[0049] When transitioning from Fig. 2A to Fig. 2B It can be seen that the work area in Fig. 2B shifted toward the more open position. If this is a long-term effect, deposits on the valve seat or valve cone, for example, would be a possible cause.

[0050] However, if the effect occurs in the short term, and possibly also in other valves downstream in the process, a possibly defective pump (which delivers less than intended) in the supply area of ​​the valve could be diagnosed.

[0051] When transitioning from Fig. 3A to Fig. 3B It can be seen that the operating range is significantly shifted toward the more closed state. If this is a long-term effect, wear of the valve seat or valve cone could be diagnosed.

[0052] However, given the magnitude of the shift, it can be assumed that process changes may also play a role. In the case of a short-term change of this kind, this would also be the diagnosis to be made.

[0053] Changes in the width of the working area are also relevant. As the working area widens, a decrease in process stability is observed. Conversely, as the working area narrows, the process appears to be more stable.

[0054] With these rules, simply knowing the control valve's resting positions makes it possible to diagnose problems that may arise and cause changes to the control valve. Based on these diagnoses, maintenance measures can be initiated, for example, before damage or failure occurs in the system. And these diagnoses do not require any additional sensors. glossary Workspace

[0055] This refers to a range or interval that contains the operating point. This is always useful when an operating point cannot be precisely determined, for example, because the position resolution of the available data is too low or the recorded state fluctuates too greatly. Such a working range can be defined, for example, by requiring that 50% of the values ​​be included. Operating point

[0056] The operating point, also called the operating point or operating state, is a specific point in the characteristic map or on the characteristic curve of a technical device that is assumed based on the system properties and external influences and parameters (according to https: / / de.wikipedia.org / wiki / Arbeitspunkt). For a control valve, this is the opening state intended for normal operation. Control valves are typically designed so that the operating point is at 70% opening at its optimum. Process valve, control valve

[0057] Process valves, also called control or regulating valves, are used to throttle or regulate fluid flows. For this purpose, a throttle body or valve element is moved by a drive in the flow opening of a valve seat. Reference symbol

[0058] 100Control or process valve 105Valve body 110Inflow side 115Downflow side 120Valve element 125Valve seat 130Valve stem or actuator stem 140Stuffing box or seal 145Fluidic actuator 150Compressed air chamber 155Upper chamber 160Spring 165Plate 170Diaphragm 175Actuator housing seal 180Signal pickup cited literature cited patent literature

[0059] EP 315 391 B1 EP 2 884 358 B1 DE 197 23 650 A1 WO 2013 / 184863 A1

Claims

1. A method for diagnosing possible causes of changes in at least one control valve (100) with a control element (120), in a plant of which the control valve (100) is a part, or in a process performed on the plant, comprising the following steps: 1.1 when no movement of the control element (120) is intended and / or there is no control impulse, data concerning the position of the control element (120) are recorded at a plurality of times 1.2 this occurs at least in a first and in a second time interval; 1.3 characteristics of the data relating to the position of the control element (120) from the first time interval are determined; 1.3.1 wherein the characteristics are chosen from a group comprising at least the following members: the operating point, a mean value, the variance thereof, an operating range, local maxima; 1.4 the same characteristics are determined for the data relating to the position of the control element (120) from the second time interval; 1.4.1 wherein the further steps are only performed if for each time interval considered the characteristics of the data relating to the position of the control element (120) from the time interval considered include that at least one local maximum can be assigned to the position of the control element; 1.5 the characteristics of the data relating to the position of the control element (120) from the two time intervals are compared; 1.6 possible causes for changes in the at least one control valve (100), in the plant or in the process are diagnosed from differences determined in the characteristics; 1.7 the diagnosis is output.

2. The method according to the preceding claim, characterized in that the data concerning the position of the control element (120) is rejected and not recorded if the corresponding position of the control element corresponds to 0% or 100%.

3. The method according to one of the preceding claims, characterized in that for each time interval considered, an operating point and / or an operating range of the control valve (100) is determined from the characteristics of the data.

4. The method according to the preceding claim, characterized in that an incorrect sizing of the control valve (100) size is diagnosed if the operating point does not correspond to a valve position between 50% and 70%.

5. The method according to one of the preceding claims, characterized in that a change in the process or a change in the fluid controlled by the valve (100) is diagnosed if differences in the characteristics of the data between two time intervals are determined, wherein the time intervals are not more than 2 weeks apart.

6. The method according to one of the preceding claims, characterized in that wear or a defect in the valve (100) is diagnosed if differences in the characteristics of the data of two time intervals are determined only if the time intervals are more than 3 weeks apart.

7. The method according to the preceding claim, characterized in that deposits on the valve seat (125) or valve cone (120) are diagnosed if a difference is determined in that the operating point and / or operating range is shifted towards a more open valve position.

8. The method according to one of the preceding claims, characterized in that that wear or abrasion of the valve seat (125) and / or valve cone (120) is diagnosed if a difference is determined in that the operating point and / or operating range is shifted towards a more closed valve position.

9. The method according to claim 3, wherein an operating range with a width is determined, characterized in that from an increase in the width of the operating range, a decrease in the stability of the process is diagnosed, and / or from a decrease in the width of the opreating range, an increase in the stability of the process is diagnosed.

10. The method according claim 3, providing a diagnosis of possible causes of changes in a plant or process having a plurality of valves, characterized in that a defect in a pump is diagnosed if a difference is determined in that, for a plurality of valves interacting with the pump, the operating point and / or operating range is shifted to a more open valve position.

11. The method according to claim 3, characterized in that the following steps are performed to determine the operating range of the control valve (100) in the considered time interval: 11.1 a histogram is formed from the data concerning the position of the control element (120); 11.2 the local maximum of the frequencies of the position of the control element (120) in this histogram is determined and assigned to the operating range; 11.3 as long as the frequency assigned to the operating range is less than 50% of the total frequency, the position of the control element (120) with the highest frequency directly adjacent to the operating range in the histogram is added to the operating range.

12. A control valve (100), having: 12.1 means for acquiring data on the position of the control element (120) and the associated time, said means being configured to acquire data on the position of the control element (120) and the associated time when no movement of the control element (120) is intended and / or there is no control impulse; 12.2 means for determining time intervals, said means being able to determine at least a first and a second time interval; 12.3 wherein data on the position of the control element (120) and the respective associated time are acquired in the at least first and second time intervals; and with 12.4 means for determining characteristics of data from time intervals, said means being configured to determine the same characteristics of data from said first and second time intervals; 12.4.1 wherein the characteristics are chosen from a group comprising at least the following members: the operating point, a mean value, the variance thereof, an operating range, local maxima; 12.5 means for determining for each time interval considered whether the characteristics of the data relating to the position of the control element (120) from that time interval include that at least one local maximum can be assigned to the position of the control element, 12.6 means for comparing characteristics of data from time intervals, said means being configured to compare the same characteristics of data from said first and second time intervals; and 12.7 means for establishing and issuing a diagnosis; said means being capable of establishing and issuing a diagnosis if said means for determining and comparing characteristics of data detect differences in the characteristics of the data from the first and second time intervals; 12.8 wherein the control valve (100) is configured to perform a method according to one of the preceding method claims.

13. A computer program, characterized in that the computer program contains executable instructions which, when executed on a computing unit, a microcontroller, DSP, FPGA or computer or on a plurality thereof in a network, performs the method according to one of the method claims14. A data carrier, whereon a data structure is stored which, after being loaded into a working and / or main memory of a computing unit, a microcontroller, DSP, FPGA or computer or a plurality thereof in a network, performs the method according to one of the method claims15. A control module for a control valve (100), characterized in that the control module provides means to perform the method according to one of the method claims.