Method, system and devices for detecting the cause of vibrations in a control loop of a control valve in a controlled process plant

Abstract

Method for detecting the cause of at least one vibration in a process plant comprising at least one inner control circuit (120) of a control valve (230) and at least one outer control loop, comprising the following steps: 1.1 the setpoint (w) and the actual value (x) of the inner control loop (120) of the control valve (230) are determined over time; 1.2 the setpoint value (w) determined over time and the actual value (x) determined over time are each checked to see whether they exhibit oscillation; 1.3 If at least one oscillation is detected, its amplitude and / or period are determined; 1.4.1 if an oscillation is detected only in the actual value (x) or only in the setpoint value (w), the period and / or the amplitude of this oscillation is compared with a predetermined characteristic value of the control valve (230); 1.4.2 If an oscillation is detected in both the actual value (x) and the setpoint value (w), a phase shift of the two oscillations relative to each other is determined and / or the respective amplitudes are compared with each other and / or at least one of the period durations is compared with a predetermined characteristic value of the control valve (230); and 1.5 From the comparisons carried out and / or the phase shift, a possible cause of at least one oscillation is identified.

Description

Field of the invention

[0001] The invention relates to a method for detecting the cause of vibrations in a control circuit of a control valve in a controlled process plant.

[0002] Control valves are used in technical systems to regulate a process variable, e.g. a flow, a pressure, a differential pressure, a temperature, a pH value, etc. For this purpose, the control valve is connected to the process and a controller assigned to the process in such a way that a cascade control is achieved (see Fig. 1). The controller assigned to the process ensures that a process variable or an associated actual process value is brought closer to the process setpoint. To do this, the controller assigned to the process calculates an output variable, which serves as a setpoint, e.g., as a position setpoint, for a valve element of the control valve in the cascade structure. The control loop of the control valve forms the inner control loop of the cascade (see Fig. 2) and generates an actual value depending on the setpoint of the control valve, e.g. for the position of the valve element, which in turn is an input variable for the physical process.

[0003] A key requirement for control loops is to ensure stable overall system behavior. For process control, this means that a process setpoint is regulated and should match the corresponding process variable, up to a tolerable deviation. Undesirable, unstable system behavior can manifest itself, for example, in the form of continuous oscillations of signals within the control loop. This can arise, for example, if the control signal for the control valve itself exhibits an oscillation caused by a change in one or more process variables, or if the control valve itself introduces an oscillation, for example, due to unstable position control or uneven friction.

[0004] In the event of instability in a cascaded control loop of a process plant, such continuous oscillations must be eliminated. Otherwise, for example, a product could be produced outside of specifications, resulting in the disposal or reprocessing of a production batch. To do this, maintenance personnel must search for the cause of the fault on-site within the plant. The cause may lie in one of the components of the cascade—the process controller, the valve controller, the physics of the valve or its actuator, or the process itself. State of the art

[0005] Various evaluation methods and devices for identifying oscillations in control loops are known, but in many cases they are not suitable for cascade structures.

[0006] For example, publication US 2016 / 0239015 A1 discloses a diagnostic device and a corresponding method for monitoring the operation of a control loop with a networked structure. This diagnostic device records data series of the control loop's target and actual values. Stochastic characteristics related to the dispersion of the actual and target values ​​are determined, so that the control quality can be evaluated from their quotients.

[0007] Publication US 2007 / 0150079 A1 describes a self-testing process control loop for a process plant. For diagnostic purposes, signal data from the normal operation of the process control loop components is measured, from which control loop parameters are determined, allowing conclusions to be drawn about the state of the process control loop.

[0008] In both cases, however, the possible causes of unstable behavior, poor control quality, or oscillations are not determined.

[0009] DE 602 20 438 T2 describes a method and apparatus for determining the presence and source of instabilities, such as limit cycles, within a process control loop. The goal is to determine whether instabilities are present and, if so, whether the source of an instability lies within a servo control loop or outside a servo control loop and is due to friction, external forces, or mechanical anomalies.

[0010] EP 1 528 447 B1 describes a diagnostic device and a diagnostic method for the quasi-permanent and automatic monitoring of a control loop with regard to its functionality and control quality. A first evaluation device determines stochastic characteristics of process variables, and a second evaluation device determines deterministic characteristics, and compares them with associated predetermined reference values. A selection device activates an evaluation device suitable for diagnosis depending on the operating state. Task

[0011] The object of the invention is to provide a method and devices which make it possible to determine or at least limit the cause of vibrations in the control circuit of a control valve within a process plant which is itself controlled. Solution

[0012] This problem is solved by the subject matter of the independent claim. Advantageous developments of the subject matter of the independent claim are characterized in the subclaims. The wording of all claims is hereby incorporated by reference into this description.

[0013] The use of the singular shall not exclude the plural, and this shall also apply in the reverse sense unless otherwise disclosed.

[0014] Individual method steps are described in more detail below. In a preferred variant of the invention, the steps are performed in the order specified. However, the steps do not necessarily have to be performed in the order specified, and the method to be described may also include additional, unmentioned steps.

[0015] To solve the problem, a method for detecting the cause of at least one vibration in a process plant comprising at least one inner control circuit of a control valve and at least one outer control loop is proposed, comprising the following steps: - The setpoint and actual value of the control valve's internal control loop are determined over time. This control loop controls the position of the valve element, meaning that the setpoint and actual values ​​relate to this position. - The setpoint value determined over time and the actual value determined over time are each checked to see whether they exhibit oscillation, ie in particular continuous oscillation. - If at least one oscillation is detected, its amplitude and / or period are determined. Alternatively to the period, the frequency can also be determined, as these two quantities are easily converted into one another. - If an oscillation is detected only in the actual value or only in the setpoint, the period and / or amplitude of this oscillation is compared with a predefined characteristic value of the control valve. Switching hysteresis may be provided if necessary to prevent excessively rapid and / or frequent changes between states. - If an oscillation is detected in both the actual value and the setpoint, a phase shift of the two oscillations relative to each other is determined and / or the respective amplitudes are compared with each other and / or at least one of the period durations is compared with a predetermined characteristic value of the control valve. - A possible cause of the oscillation is identified from the comparisons made and / or the phase shift.

[0016] Preferably, the identified possible cause of the vibration is output, e.g., as a diagnosis and / or message. Output can be made directly at the control valve or, e.g., via an interface to the control system of the process plant or another monitoring system. The identified possible cause of at least one vibration can also be saved on a data storage medium. This allows the information obtained to be used at a later time, e.g., during scheduled maintenance of the plant or control valve.

[0017] This method can be used to determine or at least isolate the cause of vibrations in a control valve's control loop, minimizing the effort required for on-site troubleshooting by maintenance personnel, as the cause of the problem can be targeted and located at the right location. If possible, the method identifies whether an instability or vibration originates from the process control or the valve control. This minimizes production downtime and avoids unnecessary costs.

[0018] The oscillation to be detected by the method preferably goes beyond individual oscillation processes in the signals. Preferably, the oscillation to be detected is essentially stable or recurring, in particular over a period of time in which the oscillation occurs, and in particular does not decay. Preferably, the number of oscillation processes of the oscillation to be detected is greater than 20, preferably greater than 30, and particularly preferably greater than 40. In particular, the oscillation to be detected is designed as an instability in a signal of the control loop(s). Preferably, the oscillation to be detected is a continuous oscillation. It is conceivable that the oscillation to be detected is composed of a plurality of oscillations, wherein in particular there may be multiple causes for the oscillations.

[0019] Preferably, the identified possible cause of the at least one oscillation is assigned to the inner control loop or the outer control loop. This advantageously enables easy diagnosis and / or elimination of the cause.

[0020] Apart from the setpoint and the actual value of the control valve's control loop, only those variables that can be measured at the control valve and preferably no other variables are measured and / or used to identify the cause of the at least one oscillation. Variables that can be measured at the control valve are typically the actuator pressure and supply air pressure (in the case of a control valve with a pneumatic actuator), structure-borne noise at the valve, the control signal (air pressure or current), and a corresponding time stamp. This enables the process to run smoothly on the control valve's positioner, for example, without the need for additional connections or the appropriate configuration of any other device. Furthermore, no additional sensors or similar are required.

[0021] Erroneous or uncertain diagnoses can be avoided by determining whether the setpoint and actual value of the control valve's control loop contain noise, and by only performing further steps if the noise is below a specified threshold. This prevents, for example, incorrect vibration characteristics from being determined due to noisy signals. Noise detection is therefore preferably performed immediately before checking whether continuous vibration is present.

[0022] Simplified operation and lower maintenance costs can be achieved if the method additionally provides for the detected possible cause of at least one oscillation to be automatically remedied by adjusting parameters in the valve position control. For example, if it is detected that the gain parameter k pof the proportional part of the position control of the control valve is too large, it could be reduced automatically, observing whether the continuous oscillation subsides.

[0023] The same applies to the gain parameter k i of the integral component of the position control. Once the continuous oscillation has subsided, the problem would be solved, and maintenance by a technician, for example, would no longer be necessary.

[0024] The method can be carried out with particularly low computing power and memory requirements if, to check whether the setpoint and / or actual value are oscillating, local extreme values ​​of the setpoint and / or actual value determined over time are counted and / or evaluated in a specified time interval. Determining local extreme values ​​requires only low computing capacity. For example, a period can be deduced from the distances between successive alternating local maxima and minima, while the amplitude can be obtained from the difference between two successive local maxima and minima. Whether a continuous oscillation is present can be recognized, for example, by whether the determined amplitude is constant from one specified time interval to the next within a specified tolerance, or at least does not decrease.

[0025] Preferably, a diagnosis and / or maintenance of the control valve is requested if a vibration is only detected in the setpoint. This is because the fact that the actual value does not follow a vibration of the setpoint could be due to a defect or maintenance requirement in the valve or its actuator. If the control valve has a positioner with an on-board diagnostic function, this can be used for this purpose and, for example, triggered automatically. Results of the diagnosis and / or maintenance can, if available, be used to improve the identification of the cause of the at least one vibration. The detected cause of the vibration can be compared with a diagnostic status of the valve, if such a diagnostic status exists.

[0026] In a preferred development of the method, a characteristic period or frequency of the control valve serves as the predetermined characteristic variable. A setting of the control of the control valve that is unfavorable for operation of the system is recognized as a possible cause of the at least one oscillation if an oscillation is only detected in the actual value and / or if the amplitude of the oscillation of the actual value is greater than the amplitude of the oscillation of the setpoint value and / or if the period or frequency of the at least one oscillation corresponds to the characteristic period or frequency of the control valve. As an alternative to the period, the frequency of the oscillation can of course also be considered. The characteristic period is preferably determined from the running time of the valve element when fully opening or closing, i.e. from the time that the control valve requires to fully open and close.This individual property of the respective valve is typically determined or ascertained during valve setup or commissioning. The characteristic period thus describes an oscillation occurring at the maximum possible speed at which the valve element can be moved. This is typically significantly higher than the speed of oscillations caused, for example, by faulty process control.

[0027] If the control valve's control has a proportional component (P component) and / or an integrating component (I component), a more precise diagnosis can be achieved as follows: It should be noted that the control valve's control may also have other components, such as a differential component. So-called PID controllers are often used, which incorporate all of the aforementioned control components. All possible combinations of these control components are possible.If, as already described, an unfavorable setting of the control of the control valve was recognized as a possible cause of at least one oscillation, a parameter of the proportional part of the control of the control valve that is unfavorable for the operation of the control valve is recognized as a possible, more precise cause of the oscillations if the period of the oscillation is shorter than the specified characteristic period and / or the frequency of the oscillation is greater than the specified characteristic frequency and / or the phase shift between the oscillations of the actual value and the setpoint value is below a specified threshold.A parameter of the integrating component of the control valve's control that is unfavorable to the operation of the control valve is identified as a possible, precise cause of the oscillations if the period of the oscillation is greater than the specified characteristic period and / or the frequency of the oscillation is less than the specified characteristic frequency and / or the phase shift between the oscillations of the actual and setpoint values ​​is above the specified threshold. "Greater" or "smaller" here and in the following always means taking a tolerance factor into account, i.e., one of the variables to be compared is multiplied by a specified factor that ensures that the respective comparison is fulfilled with sufficient margin.

[0028] In a preferred development of the method, a characteristic period or frequency of the control valve serves as the predetermined characteristic variable, as already explained above. A problem with the control of the process plant is identified as a possible cause of the oscillations if an oscillation is only detected in the setpoint and / or if the amplitude of the oscillation of the setpoint is greater than the amplitude of the oscillation of the actual value and / or if the period or frequency of the oscillation of the setpoint is greater than the characteristic period of the control valve or if the frequency of the oscillation of the setpoint is lower than the characteristic frequency of the control valve.

[0029] A hysteresis width of the control valve, in particular of the drive, the control system and / or the valve element of the control valve, can also serve as a predefined characteristic variable. This hysteresis is particularly pronounced in pneumatic drives. Preferably, if oscillation is only detected in the setpoint, the amplitude of the oscillation is compared with the predefined characteristic variable, with diagnosis and / or maintenance of the control valve only being requested if the amplitude of the oscillation exceeds the width of the combined hysteresis. This makes it possible to take into account the fact that the actual value of the oscillation may not follow the setpoint because the amplitude is too small, meaning that the valve drive cannot execute the corresponding movements. In this case, there is no indication of a malfunction and / or defect in the valve, so diagnosis and / or maintenance would be unnecessary.

[0030] Another possible cause of vibrations can be identified by providing an acceleration and / or structure-borne sound sensor. This detects or measures shocks and vibrations in the system. Signals from the acceleration and / or structure-borne sound sensor are checked for vibrations as described above. If vibrations are detected, their period and / or frequency are determined. If vibrations are detected in the actual value and in a signal from the acceleration and / or structure-borne sound sensor, but not in the setpoint, the period and / or frequency of these vibrations are compared.A vibration in the system is identified as a possible cause of at least one vibration if the period durations and / or frequencies of these vibrations in the actual value and in a signal from the acceleration and / or structure-borne sound sensor are the same within a specified tolerance.

[0031] Yet another possible cause of vibrations can be identified if an actual process value is provided. This is checked in the manner already described to determine whether it exhibits vibration. If vibration is detected, its period and / or frequency are determined. If vibration is detected in the actual value and the actual process value, but not in the setpoint, the period and / or frequency of these vibrations are compared. A pulsating fluid flow in the system is identified as a possible cause of at least one vibration if the period and / or frequency of these vibrations in the actual value and the actual process value are the same within a specified tolerance.

[0032] Desired vibrations that do not require maintenance can be detected if a process setpoint is also provided. This is then checked for any vibration. If vibration is detected, its period and / or frequency are determined. If vibration is detected in both the actual value, the setpoint, and the process setpoint, the period and / or frequency of these vibrations are compared. At least one vibration is identified as desired if the period and / or frequency of these vibrations in the actual value, the setpoint, and the process setpoint are the same within a specified tolerance.

[0033] The object is further achieved by a position controller for a control valve, wherein the position controller comprises a computing unit and means that are suitable and configured to carry out the steps of the method as described above (with the exception of those methods that require an acceleration and / or structure-borne sound sensor). These means comprise, for example, a position sensor for measuring the actual position of the valve element. The computing unit can be, for example, control electronics, a digital signal processor (DSP), a microcontroller, a computer or a plurality thereof in a network with corresponding programming. The programming can be implemented, for example, within the framework of a fixed circuit arrangement of the control electronics, the DSP and / or the microcontroller or with the aid of field-programmable gate arrays (FPGAs).

[0034] The problem is also solved by a diagnostic box for use with a control valve. The diagnostic box, just like the positioner just described, comprises a computing unit with means suitable and configured to carry out the steps of the method described above (with the exception of those methods requiring an acceleration and / or structure-borne sound sensor). Such a diagnostic box can be used directly by maintenance technicians when troubleshooting the process plant, possibly even on control valves that only have a positioner that does not adequately meet the requirements described above. Such a diagnostic box could also be retrofittable.

[0035] The task is also solved by a control valve with a positioner as described above.

[0036] Furthermore, the object is achieved by a computer program comprising commands which cause the position controller described above and / or the diagnostic box described above to carry out the method steps according to a method as described above (with the exception of those methods which require an acceleration and / or structure-borne sound sensor).

[0037] A computer-readable medium on which the computer program just described is stored also solves the problem.

[0038] Further details and features will become apparent from the following description of preferred embodiments in conjunction with the figures. 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.

[0039] The exemplary embodiments are illustrated schematically in the figures. Identical reference numerals in the individual figures denote identical or functionally identical elements, or elements that correspond to one another in terms of their functions. In detail: Fig. 1 a schematic representation of a cascade consisting of a process control loop and a control valve; Fig. 2 a schematic representation of the control circuit of the control valve from Fig. 1; Fig. 3A is a diagram of the time course of the actual and setpoint values ​​of the outer control loop for a simulated example in which no continuous oscillations occur; Fig. 3B is a diagram of the time course of the actual and setpoint values ​​of the inner control loop for a simulated example in which no continuous oscillations occur; Fig. 4A is a diagram of the time course of the actual and setpoint values ​​of the outer control loop for a simulated example in which the valve control causes a continuous oscillation; Fig. 4B is a diagram of the time course of the actual and setpoint values ​​of the inner control loop for a simulated example in which the valve control causes a continuous oscillation; Fig. 5A an enlarged section of the diagram Fig. 4A; Fig. 5B shows an enlarged section of the diagram Fig. 4B; Fig. 6A is a diagram of the time course of the actual and setpoint values ​​of the outer control loop for a simulated example in which the process control causes a continuous oscillation; Fig. 6B is a diagram of the time course of the actual and setpoint values ​​of the inner control loop for a simulated example in which the process control causes a continuous oscillation; Fig. 7A shows an enlarged section of the diagram Fig. 6A; Fig. 7B shows an enlarged section of the diagram Fig. 6B; Fig. 8 a flow chart for a possible case distinction when the actual and setpoint values ​​of the valve position control both oscillate; and Fig. 9 an overview of the entire procedure.

[0040] Fig. Figure 1 shows a schematic representation of the interconnection of a process control loop, which forms the outer control loop 100 of a cascade, with a process controller 110, which is supplied with a setpoint r for a process parameter to be controlled. The process controller 110 generates a setpoint w for the position of the control valve as a manipulated variable, which is controlled in the inner control loop 120 of the cascade. As a result of this cascaded control, the actual value x of the position of the control valve influences the process 130. The process parameter to be controlled changes as a result of what is measured and what is provided to the process controller 110 as the actual value p. The elements assigned to the outer control loop 100 of the cascade are highlighted by the dashed border.

[0041] The associated inner control loop 120, which is formed by the position control of the control valve 230, is in Fig. 2 by the dashed border. The input variable for the valve position controller 210 is the setpoint w for the position of the control valve specified by the process controller 110. The valve position controller 210 generates a manipulated variable y from this, which influences the drive 240 of the control valve 230, typically an electrical current or voltage or an air pressure, depending on the type of valve drive 240 present. The position of the valve element of the control valve 230 changes accordingly, which is provided to the valve position controller 210 as the actual value x.

[0042] The position controller of a control valve within such a process control system normally only has access to the setpoint w and the actual value x of the valve element's position. In addition, a diagnostic function may be available that can analyze the current state of the control valve and save the results of such a diagnosis in a log, e.g., possible causes of errors. Certain characteristic variables of the control valve may also be present, e.g., the valve runtime, which indicates how long the valve typically takes to open or close. Further data, e.g., the setpoint r and actual value p of the process control system, are generally not available to the position controller of the control valve. To nevertheless determine the cause of instability or continuous oscillation in a cascade control system, the following steps can be provided: - Assess signal noise - The signal noise of the setpoint w and the actual value x of the valve position is determined. If the signals examined are too noisy, no further analysis should be performed, as the vibration characteristics, in particular, cannot be determined accurately. Instead, a message is preferably output and / or stored indicating that the procedure cannot be performed due to excessive signal noise. - Carry out vibration analysis - Detect whether vibrations of the actual value x and the setpoint value w of the valve position are present and determine the characteristic vibration variables, ie preferably amplitude and period duration, if necessary also phase shift of the vibrations against each other. - Case differentiation of the detected system behavior: Case 1: No continuous vibrations detected - no need for action. Case 2: Only continuous oscillation of the actual value x - the cause is probably to be found in the valve control, therefore the characteristic oscillation variables are compared with characteristic variables of the control valve. Case 3: Only continuous oscillation of the setpoint w – the cause of the oscillation is likely to be found in the process control. Since there is no oscillation of the actual value, the valve is not following the oscillation, so there may be a blockage or something similar at the valve. Therefore, the diagnostic function may be called or a valve check may be requested. Case 4: Continuous oscillations of both the setpoint w and the actual value x - here a more detailed investigation is required, therefore a comparison of the characteristic oscillation variables of the setpoint and actual values ​​is carried out with each other and, if necessary, with characteristic variables of the control valve. - Generate a diagnostic message for the detected case, which is output and / or saved if necessary.

[0043] The vibration analysis can be carried out using Fourier analysis, for example. However, a procedure that requires significantly less computing power and memory is preferred. With the help of the evaluation of the number and / or distances between local extreme values ​​in the time series of the setpoint w and the actual value x in a specified time interval Δt, a flag, i.e. a Boolean parameter, is set, for example, which states whether the current signal exhibits a continuous oscillation or not. Whether the continuous oscillation continues in the next time interval Δt is recognized by whether the amplitude of the signal recognized as oscillating remains approximately the same. This must also be checked. In the case of a continuous oscillation, the amplitude and period of the identified oscillation are determined. If a continuous oscillation is detected for both the setpoint w and the actual value x, it may be possible tothe phase shift between the two oscillations can also be determined.

[0044] The most complex situation arises when both the setpoint w and the actual value x of the valve position exhibit continuous oscillations. In this case, an examination of the amplitudes of the two oscillations can provide information about their possible cause.

[0045] This can take advantage of the fact that both the control loop of the control valve and the process control as a whole have a low-pass characteristic, i.e. the amplitude of an oscillation of the actual value of the respective control loop is attenuated at higher frequencies compared to the amplitude of the setpoint.

[0046] In this way, two cases can be distinguished: - If the control valve couples the continuous oscillation into the overall control loop, the oscillation amplitude of the actual value x is damped by the strong low-pass behavior of the process control at frequencies near and above the cut-off frequency and is consequently fed back to the setpoint w with a lower amplitude. - If the process controller causes the continuous oscillation and couples it into the valve position control, the resulting oscillation amplitude of the setpoint w may be dampened by the low-pass behavior of the valve position control, resulting in a lower amplitude of the oscillation of the actual value x. However, it may also be the case that the frequency of the continuous oscillation in the process control loop is sufficiently below the cutoff frequency of the low-pass characteristic of the valve position control, allowing the actual value x to follow the setpoint w. In such a case, both would have the same amplitude.

[0047] In the Fig. Figures 3A to 7B show exemplary simulations of the behavior of the actual and setpoint values ​​of the process control loop and the position control loop of the control valve for various cases. This illustrates how the behavior of the actual value x and setpoint w of the valve position can be used to determine the overall vibration situation.

[0048] The Fig. 3A and Fig. 3B show the desired situation where neither the process control loop nor the position control loop of the control valve exhibits a continuous oscillation. In this example, the setpoint r of a process variable changes from 0% to 25%. Fig. In Figure 3A, this curve is represented by the dot-dash line. The step response of the actual value p of this process variable is represented by the solid line. It can be seen that the actual value approaches the setpoint, and an initial oscillation is strongly damped as the setpoint is approached. A continuous oscillation is not present.

[0049] In Fig. Figure 3B shows the corresponding curve of the setpoint w (dash-dotted line) and the actual value x (solid line) of the valve position. In this example, the valve position at which the process variable reaches the desired value of 25% is 50%, meaning the flow is halfway open. The entire cascade of the outer and inner control loops is stable.

[0050] Fig. 4A and Fig. 4B show the same basic situation, ie the setpoint r of the process variable jumps from 0% to 25%. However, in this case, the cascade of outer and inner control loops is unstable because the valve position controller causes a continuous oscillation, e.g. due to an excessive gain of its proportional component (P component). The representation otherwise corresponds to the representation of Fig. 3A and Fig. 3B.

[0051] An enlarged section of the range from 300 to 340 s from Fig. 4A and Fig. 4B is in Fig. 5A and Fig. 5B. In this range, any transients have already subsided, so that only the continuous oscillations are visible. It is clear from the comparison of Fig. 5A and Fig. 5B shows that the control valve, ie the inner control loop, oscillates, not the process control, ie the outer control loop. In Fig. 5B also shows that the actual value x oscillates with a greater amplitude than the setpoint w. According to the above explanations, the cause of this oscillation lies in the control valve or in the position control of the valve element. The process, ie the external control loop, remains almost unaffected by the oscillations in this example, as Fig. 5A.

[0052] In Fig. 6A, the setpoint r of the process variable also jumps from 0% to 25%. The representation of the Fig. 6A and Fig. 6B again corresponds to the representation of the Fig. 3A and Fig. 3B. How to Fig. 6A and Fig. As can be seen in Figure 6B, the cascade of the outer and inner control loops is unstable in this case. Since the setpoint w and actual value x follow the process controller's specifications with approximately the same amplitude, the cause of the continuous oscillation probably lies in the process controller. For example, the process controller could have an excessively high gain in its proportional control component.

[0053] Fig. 7A and Fig. 7B again show an enlarged section of the range from 300 to 340 s of the Fig. 6A and Fig. 6B. At this higher resolution, it is clearly visible that in this case, the amplitude of the oscillation of the setpoint w of the valve position is greater than the amplitude of the oscillation of the actual value x. This also indicates that the causes of the continuous oscillation lie in the process control loop.

[0054] If you compare Fig. 5B with Fig. 7B, it can be seen that the period duration of the observed oscillations can also be used as a distinguishing criterion. Fig. The oscillations shown in Figure 5B, which are caused by the - comparatively fast - control of the control valve, have a period of approximately 3 s in the present example, while the oscillations shown in Figure 5B Fig. The oscillations shown in Figure 7B, which were caused by the comparatively slow process control, have a period of approximately 15.5 s. Knowing the corresponding characteristic properties of the control loops, it is easy to define limits that allow these cases to be clearly distinguished.

[0055] Fig. Figure 8 shows in the form of a flow chart how different possible cases in which both the actual value x and the setpoint value w of the position control of the control valve exhibit a continuous oscillation (referred to above and below as case 4) can be distinguished from one another.

[0056] The amplitudes of the quantities x and w are denoted by capital letters X and W. They have the same units as the quantities x and w, and are therefore given in % in typical applications.

[0057] A possible test to determine whether it is a desired continuous oscillation (case 4d) would be Fig. 8.

[0058] First, Fig. 8 checks whether the amplitude X of the actual value x of the valve position is greater than the amplitude W of the setpoint w.

[0059] Preferably, all such comparisons are made using a factor f (f 1 , f 2 , f 3, f 4 ), which defines a suitable tolerance threshold. This ensures that these comparisons are robust and always deliver a clear result. Alternatively or in addition, switching hysteresis could be provided to prevent excessively rapid and / or frequent changes between states. These could also be used to specify the size of the tolerance factors.

[0060] If the amplitude X is now greater than f 1 * W, it can be assumed that the cause of the continuous oscillations lies in the position control of the control valve. In order to determine the cause of the oscillations more precisely, we will now further investigate whether the period T x the oscillation of the actual value x of the valve position is significantly greater than a characteristic period T assigned to the control valve c (T c depends on X and v max, which is explained below). If this is not the case - i.e. the control valve oscillates at approximately the maximum possible speed - it can be assumed that the oscillation is caused by an incorrect parameter in the proportional part of the position control. Typically, the gain parameter k p chosen too large (case 4a). This allocation of the error is due to the fact that the proportional component of a control always acts directly, without a time delay.

[0061] If the period T x the oscillation of the actual value x of the valve position is actually significantly larger than the characteristic period T cof the control valve, however, it is assumed that the cause of the oscillation lies in the integrating component of the position control when the parameter is incorrect (case 4b). This is because an integrating controller sums the control deviation, i.e., a memory size is increased or decreased. This behavior has a time delay compared to a proportional controller. Furthermore, the gain factor of the integrating component of a control is usually smaller than that of the proportional component, which also results in a comparatively slower behavior. If case 4b is detected, the cause of the error is often a dead band that is too small or a gain parameter k that is too large. i the integrating part of the position control.

[0062] Alternatively, the phase shift of the oscillations of the setpoint and actual values ​​can also be considered here. This is because the different behavior of proportional and integrating controllers ensures that a correspondingly small or large phase shift occurs between the oscillations due to the immediate (proportional) or time-delayed (integrating) control response. The phase shift is preferably determined when determining the oscillation properties (i.e., period duration and / or frequency as well as amplitude). The time stamps of the local maxima and / or minima of the actual and setpoint values ​​can be compared for this purpose. If they are different, an average of these differences could, for example, be assumed to be the phase shift.

[0063] If the first query determines that the amplitude X of the oscillation of the actual value x is not greater than the amplitude W of the oscillation of the setpoint w, a subsequent check is made to determine whether the opposite is the case. If so, it is also examined whether the period T x the oscillation of the actual value x of the valve position is significantly greater than a characteristic period T assigned to the control valve c Alternatively, instead of T x of course the corresponding value T w the oscillation of the setpoint – the period durations of these oscillations should be the same anyway. If this condition is met, i.e., the valve oscillates significantly slower than its maximum possible speed, it is assumed that the oscillations are caused by the higher-level process control (case 4c).

[0064] If, however, it is first established that X is not greater than W and then it turns out that W is not greater than X, or if it is established that - although W is greater than X - the oscillation is fast, then no statement about the cause of the oscillation is possible with the available means (case 4e).

[0065] The characteristic period T c The speed of the control valve can be determined for these considerations as follows: From the initialization of the control valve during commissioning, the times for a venting and aeration process of the valve are known. From this, the travel speed of the valve element can be determined for both directions. This value is averaged and used as the reaction speed v maxThe characteristic period can now be estimated, for example, based on a triangular or sinusoidal oscillation. For a triangular oscillation, the period for an amplitude X is T c = 4 * X / v max . For a sinusoidal oscillation x(t) = X * sin(ωt) we have v max = X * ω and ω = 2π / T c , thus T c = 2π * X / v max .

[0066] In Fig. Figure 9 shows an overview of one embodiment of the entire method. Activation by a user, e.g., by operating a switch or requesting a diagnosis or similar, can serve as a starting point. Only the actual value x and setpoint w of the position control of the control valve are required as measurement data. It is therefore particularly advantageous to execute the method on the position controller of the control valve, provided that this has the necessary computing power, e.g., by means of a digital signal processor. However, for some optional, additionally distinguishable sub-cases, further data, e.g., from sensors and / or the process control, is required.

[0067] The measurement signals of the actual value x and setpoint w are preferably first analyzed for noise, using known noise detection methods, depending on the type of noise expected in the process plant. If the signals are too noisy, the further procedure cannot be carried out effectively, as vibration detection would most likely produce false or unreliable results. Therefore, the procedure ends with a corresponding message 910. This indicates the high level of noise and the likely need for maintenance on the plant, without specifically narrowing it down, as the cause of the noise is not readily identifiable.

[0068] If the signals are not noisy, a vibration analysis is performed for each signal. This means that, as described above, it is determined whether a continuous vibration is present in x and / or w. If so, the characteristic vibration parameters, i.e., period duration and amplitude, are determined. The results of the vibration analysis serve as the basis for case differentiation 900. Depending on whether the setpoint w and / or actual value x are oscillating or not, the situation is assigned to one of four cases: Case 1: There are no continuous oscillations. In this case, the procedure ends with message 920, indicating that everything is OK. Case 2: Only the actual value x exhibits a continuous oscillation. Here, further subcases are distinguished, which may require different reactions. For this purpose, the period T x the oscillation with the characteristic period T c of the control valve as it is in Fig. 8 for Case 4 and described above. Case 2a: T x is not significantly larger than T c The cause of the continuous oscillation is probably an incorrect setting of the proportional component of the valve position control. The procedure ends with message 930, indicating that the control valve requires maintenance. This message may, of course, also contain more precise information in the specific case, e.g., that the gain parameter k p needs to be checked as it may be too big. Case 2b: T x is significantly larger than T c The cause of the continuous oscillation is probably an incorrect setting of the integrating component of the valve position control. The procedure ends with message 930 indicating that the control valve requires maintenance. In this case, too, the message may contain additional information. Case 2c: Vibrations in the system are superimposed on the valve actuator or the position measurement signal. However, this case can only be detected with optional additional sensors (e.g., an acceleration sensor or structure-borne sound sensor). It is present when the signal from this sensor exhibits an oscillation with a period or frequency that corresponds to the period or frequency of the oscillation of the actual value x of the valve control. This should preferably be checked before distinguishing between cases 2a and 2b. If this case occurs, the process ends with message 940 stating that the system requires maintenance and that the cause of the vibration is to be found outside the control valve. Case 2d: For example, a pulsating fluid flow transmits vibrations to the valve element, which in turn transmits these vibrations to the position measurement signal via the valve drive. To detect this, however, the actual process value p would also have to be available and examined for vibrations, which is not possible in every embodiment. This case occurs when the actual process value p and the actual valve position value x oscillate with approximately the same period or frequency, but the valve position setpoint w does not. This should also preferably be checked before distinguishing between cases 2a and 2b. If this case occurs, the process ends with a message 940 that the system requires maintenance and that the cause of the vibration is to be found outside the control valve. Case 2e: This covers all other situations in which only the actual value of the control valve position exhibits a continuous oscillation, but which cannot be assigned to one of the other cases 2a-2d. For example, if, in addition to the actual value x, both the process setpoint p and the signal from an acceleration sensor exhibit oscillations of a similar period. This case does not have to be realized in every embodiment - in the particularly preferred embodiment without additional sensors and without knowledge of the actual process value p, a distinction is only made between subcases 2a and 2b, which, with a reasonable choice of tolerances, always delivers a clear result. If this case occurs, the method ends with a non-specific message 910 indicating that maintenance is required. Case 3: Only the setpoint w exhibits a continuous oscillation. Further subcases are distinguished here, which may require different responses. Case 3a: If the positioner has diagnostic functions for the control valve, these are executed. The fact that the actual value x does not follow the continuous oscillation of the setpoint w could be due to a defect in the control valve (e.g., no compressed air supply to the actuator, mechanical jamming, I / P converter defect, etc.). The procedure ends with message 930, indicating that the control valve requires maintenance. Case 3b: If the setpoint signal w has an amplitude that is too small, the position control of the valve generates a control signal that is too small and is not sufficient to cause the valve actuator to overcome the hysteresis of the control valve, preferably consisting of a hysteresis of the - typically pneumatic - actuator, the I / P converter, the control and / or the valve element of the control valve, as well as the mechanical friction on the valve. Therefore, the valve element does not move. This is preferably checked first, i.e., before case 3a is considered. In this case, the method ends with a message 940 that maintenance is required on the system and that the cause of the vibration is to be sought outside the control valve. This message can also contain the information that the strength of the setpoint signal w to the control valve must be checked. Case 3c: This covers all other situations in which only the setpoint w of the control valve position exhibits a continuous oscillation, but which cannot be assigned to Case 3a or 3b, e.g., if the amplitude of the oscillation of w is sufficiently large, but the control valve inspection (e.g., using a partial stroke test) confirms its functionality. In this case, the procedure ends with a non-specific message 910 indicating that maintenance is required. Case 4: Both the actual value x and the setpoint w of the control valve position exhibit continuous oscillations. In this case, a more detailed investigation is required, which can be carried out as in Fig. 8 and described above. Case 4a: In this case, the gain parameter k is incorrectly set pof the P component of the control valve's position control. The procedure ends with a corresponding message 930 indicating that the control valve requires maintenance. Case 4b: In this case, the I component of the control valve's position control is incorrectly set. The procedure ends with a corresponding message 930 indicating that the control valve requires maintenance. Case 4c: In this case, it is assumed that the process controller is the cause of the continuous oscillation. The procedure ends with a corresponding message 940 indicating that the system requires maintenance and that the cause of the oscillation is outside the control valve. Case 4d: In certain operating scenarios, an oscillating process setpoint may be required. To detect this case, however, the process setpoint r would have to be available and examined for oscillations, which is not possible in every implementation. This case occurs when the process setpoint r, the valve position setpoint w, and the actual value x oscillate with approximately the same period or frequency. The verification of this case is described in Fig. 8 and should be performed before the other tests described there. If this occurs, the procedure ends with a message 920 indicating that everything is OK. Case 4e: This covers all other situations in which both the actual value and the setpoint of the control valve position exhibit continuous oscillation, but which cannot be assigned to one of the other cases 4a-4d. In this case, the procedure ends with a non-specific message 910 indicating that maintenance is required.

[0069] In some of the cases mentioned, it may also be provided that the present method already automatically provides a remedy. This applies in particular to cases 2a, 2b, 4a and 4b. If it is detected that the gain parameter k p If the proportional component of the position control of the control valve is too large, it could be automatically reduced, observing whether the continuous oscillation subsides. The same applies to a reduction of the gain parameter k iand / or an increase in the dead zone of the integral part of the position control is conceivable. In case 4c, parameters of the position control could also be adjusted to achieve process stabilization. For example, the gain parameter k p The proportional part of the control could be reduced, or a differential part of the control could be increased, if present. Since the cause of the vibration was located outside the control valve, maintenance of the system is nevertheless preferable in this case.

[0070] The described method allows for statements about whether occurring continuous vibrations are caused by the control valve or other devices or components of the process plant. This is already very important for elimination or compensation - regardless of a more precise determination of the origin of the vibrations. It is conceivable that a user may only be informed of the type of the detected case according to or similar to Fig. 9 is communicated, or that, depending on the nature of the case, additional diagnostic steps and / or additional devices or sensors are activated and / or added in order to further narrow down the origin of the continuous vibrations if necessary. GlossaryAppendix

[0071] A plant represents a planned assembly of technical components. These components can include machines, devices, apparatus, storage facilities, lines or transport routes, and / or control or regulating elements. They can be interconnected, wired, or linked to one another for functional, control, and / or safety reasons. Plants are operated in many different areas for a variety of purposes. These include, for example, process engineering plants, which in many cases are part of the chemical industry. The term "plant" also includes refineries, district heating systems, geothermal or solar thermal plants, food production plants, fresh water supply or wastewater disposal plants, biogas plants, etc. Cutoff frequency of a low-pass filter

[0072] The cutoff frequency of a low-pass filter is typically defined as the frequency at which the output signal A is attenuated by 3 dB compared to the sinusoidal input signal E. This corresponds to A = 0.707 * E. control circuit, control loop

[0073] A control loop consists of a controller, a controlled system, and a feedback loop. The controlled system acts on a controlled variable. A setpoint w is specified for this variable. The actual value of the controlled variable x is measured. From the actual value x and the setpoint w, the controller determines a manipulated variable y according to the desired dynamics of the control loop. This manipulated variable y acts on the controlled variable via the controlled system with the goal of bringing the actual value x closer to the setpoint w. Control with integrating component

[0074] Integrating controllers (also abbreviated as I-controllers) are used to completely compensate for control deviations at every operating point. The control difference or control deviation e is understood to be the difference between the setpoint w and the actual value x: e = w - x. As long as the control deviation is not equal to zero, the magnitude of the manipulated variable y changes. The control system only reaches steady state when the reference and controlled variables, i.e., the setpoint w and the actual value x, are equal, but at the latest when the manipulated variable reaches its system-dependent limit (e.g., maximum voltage). The mathematical formulation of this integral behavior is: The value of the manipulated variable y is proportional to the time integral of the control difference e: y=ki∫e dt

[0075] The gain parameter k i usually defined as the inverse of the integration time. A dead zone, e.g., in the form of a characteristic curve, is often placed upstream of the integrating component of a controller. Control with proportional share

[0076] In a proportional controller (also abbreviated to P-controller), the manipulated variable y is always proportional to the detected control deviation e (the difference between the setpoint and actual value). This means that a P-controller reacts to a control deviation without delay and generates a manipulated variable y when such a deviation occurs. The amplitude of the manipulated variable depends on the control deviation e and the magnitude of the proportional coefficient k. p , which is also called reinforcement: y=kp*e

[0077] A controller compensates for the effect of disturbances by generating a correspondingly opposite manipulated variable. However, a P-controller can only generate this manipulated variable if a control deviation is present. Therefore, persistent disturbances can never be completely compensated with a P-controller; a permanent control deviation always remains. A large k pleads to smaller control deviations due to a stronger control intervention. Too large k p However, values ​​increase the tendency of the control loop to oscillate. control valve

[0078] Control valves, also called process or control valves, are used to throttle or regulate fluid flows. For this purpose, a valve element is moved by an actuator in a flow opening of a valve seat. This allows the flow opening to be opened or closed, thereby changing the flow rate, up to and including the complete opening or closing of the flow opening. Typically, a pneumatic or electric actuator is used for this purpose. Positioner

[0079] A positioner is the element of a control valve that operates the actuator of the valve member to open or close the valve. Each positioner includes a control loop to regulate the position of the valve member based on a specified input, such as a signal from a control room. The actuator of the valve member—often an electric or fluidic actuator, the latter of which can be operated either hydraulically or with compressed air—is part of the control loop and is thus clearly assigned to the positioner, even if the actuator is located outside the actual positioner. Reference symbol 100 outer control loop 110 process controllers 120 inner control loop 130 Process 210 valve position controller 230 control valve 240 Control valve drive 900 Case distinction 910 Maintenance requirement (unspecific) 920 no need for action 930 Maintenance requirement control valve 940 Maintenance requirement process control p Actual value of the process control r Setpoint of the process control w Setpoint of the valve position control x Actual value of the valve position control y Control variable of the valve position control W Amplitude of the continuous oscillation of w X Amplitude of the continuous oscillation of x T x Period of oscillation of x T c characteristic period assigned to the control valve v max maximum travel speed of the valve element cited literature

[0080] cited patent literature DE 602 20 438 T2 EP 1 528 447 B1 US 2007 / 0150079 A1 US 2016 / 0239015 A1

Claims

[1] Method for detecting the cause of at least one vibration in a process plant comprising at least one inner control circuit (120) of a control valve (230) and at least one outer control loop, comprising the following steps: 1.1 the setpoint (w) and the actual value (x) of the inner control loop (120) of the control valve (230) are determined over time; 1.2 the setpoint value (w) determined over time and the actual value (x) determined over time are each checked to see whether they exhibit oscillation; 1.3 If at least one oscillation is detected, its amplitude and / or period are determined; 1.4.1 if an oscillation is detected only in the actual value (x) or only in the setpoint value (w), the period and / or the amplitude of this oscillation is compared with a predetermined characteristic value of the control valve (230); 1.4.2 If an oscillation is detected in both the actual value (x) and the setpoint value (w), a phase shift of the two oscillations relative to each other is determined and / or the respective amplitudes are compared with each other and / or at least one of the period durations is compared with a predetermined characteristic value of the control valve (230); and 1.5 From the comparisons carried out and / or the phase shift, a possible cause of at least one oscillation is identified. [2] Method according to the preceding claim, characterized by that the detected possible cause of the at least one oscillation is assigned to the inner control loop (120) or the outer control loop. [3] Method according to one of the preceding claims, characterized bythat in order to detect the cause of the at least one oscillation, in addition to the setpoint value (w) and the actual value (x) of the control circuit (120) of the control valve (230), only further variables that can be detected at the control valve are measured and / or used. [4] Method according to one of the preceding claims, characterized by , 4.1 determining whether the setpoint (w) and the actual value (x) of the control loop (120) of the control valve (230) contain noise; and 4.2 that further steps are only carried out if the noise is below a predetermined threshold. [5] Method according to one of the preceding claims, characterized by the additional step that the detected possible cause of at least one vibration is automatically remedied by adjusting parameters in the valve position control. [6] Method according to one of the preceding claims, characterized bythat in order to check whether the setpoint (w) and / or actual value (x) exhibit an oscillation, local extreme values ​​of the setpoint (w) and / or actual value (x) determined over time are counted and / or evaluated in a predetermined time interval. [7] Method according to one of the preceding claims, characterized by that a diagnosis and / or maintenance of the control valve (230) is requested if an oscillation is detected only in the setpoint (w). [8] Method according to one of the preceding claims, characterized by , 8.1 that a characteristic period or frequency of the control valve (230) serves as the predetermined characteristic variable; and 8.2 that a setting of the control (210) of the control valve (230) which is unfavourable for the operation of the system is recognised as a possible cause of the at least one oscillation if an oscillation is only detected in the actual value (x) and / or if the amplitude of the oscillation of the actual value (x) is greater than the amplitude of the oscillation of the setpoint value (w) and / or if the period or frequency of the at least one oscillation corresponds to the characteristic period or frequency of the control valve (230). [9] Method according to claim 8, 9.1 wherein the control (210) of the control valve (230) has a proportional component and / or an integrating component, characterized by , 9.2 that a parameter of the proportional part of the control (210) of the control valve (230) that is unfavorable for the operation of the control valve is recognized as a possible cause of the at least one oscillation if the period of the oscillation, taking into account a tolerance factor, is shorter than the predetermined characteristic period and / or the frequency of the oscillation, taking into account a tolerance factor, is greater than the predetermined characteristic frequency and / or the phase shift between the oscillations of the actual value and the setpoint value is below a predetermined threshold; and 9.3 that a parameter of the integrating part of the control (210) of the control valve (230) which is unfavorable for the operation of the control valve is recognized as a possible cause of the at least one oscillation if the period of the oscillation, taking into account a tolerance factor, is greater than the predetermined characteristic period and / or the frequency of the oscillation, taking into account a tolerance factor, is smaller than the predetermined characteristic frequency and / or the phase shift between the oscillations of the actual value and the setpoint value is above the predetermined threshold. [10] Method according to one of the preceding claims, characterized by , 10.1 that a characteristic period or frequency of the control valve (230) serves as the predetermined characteristic variable; and 10.2 that a problem with the control (110) of the process plant is identified as a possible cause of the oscillation if an oscillation is only detected in the setpoint (w) and / or if the amplitude of the oscillation of the setpoint (w) is greater than the amplitude of the oscillation of the actual value (x) and / or if the period of the oscillation is greater than the characteristic period of the control valve (230) or if the frequency of the oscillation is lower than the characteristic frequency of the control valve (230). [11] Method according to one of the preceding claims, characterized by , 11.1 that a width of a hysteresis of the control valve (230), in particular of the drive, the control, and / or the valve element of the control valve, serves as the predetermined characteristic variable; and 11.2 that if a vibration is detected only at the nominal value (w), the amplitude of the vibration is compared with the specified characteristic value; 11.3 wherein diagnosis and / or maintenance of the control valve (230) is only requested if the amplitude of the oscillation exceeds the width of the combined hysteresis of the control valve. [12] Method according to claim 1, characterized by , 12.1 that an acceleration and / or structure-borne sound sensor is provided; 12.1.1 whereby signals from the acceleration and / or structure-borne sound sensor are checked to determine whether they exhibit vibration; 12.1.2 if an oscillation is detected, its period and / or frequency is determined; and 12.2 that if a vibration is detected in the actual value (x) and in a signal from the acceleration and / or structure-borne sound sensor, but not in the setpoint value (w), the periods and / or frequencies of these vibrations are compared; 12.3 wherein a vibration in the system is identified as a possible cause of the at least one vibration if the period durations and / or frequencies of these vibrations in the actual value (x) and in a signal of the acceleration and / or structure-borne sound sensor are the same within a specified tolerance. [13] Method according to claim 1, characterized by , 13.1 that an actual process value (p) is provided; 13.1.1 wherein the actual process value (p) is checked to see whether it exhibits an oscillation; 13.1.2 if an oscillation is detected, its period and / or frequency is determined; and 13.2 that if an oscillation is detected in the actual value (x) and in the process actual value (p), but not in the setpoint (w), the periods and / or frequencies of these oscillations are compared; 13.3 wherein a pulsating fluid flow in the system is identified as a possible cause of the at least one oscillation if the period durations and / or frequencies of these oscillations in the actual value (x) and in the process actual value (p) are the same within a specified tolerance. [14] Method according to claim 1, characterized by , 14.1 that a process setpoint (r) is provided; 14.1.1 wherein the process setpoint (r) is checked to see whether it exhibits an oscillation; 14.1.2 if an oscillation is detected, its period and / or frequency is determined; and 14.2 that if an oscillation is detected in the actual value (x), the setpoint (w) and the process setpoint (r), the periods and / or frequencies of these oscillations are compared; 14.3 wherein the at least one oscillation is recognized as desired if the period durations and / or frequencies of these oscillations in the actual value (x), the setpoint value (w) and the process setpoint value (r) are the same within a predetermined tolerance. [15] Position controller (210) for a control valve (230), wherein the position controller (210) comprises a computing unit and means which are suitable and arranged to carry out the steps of the method according to one of the preceding method claims 1 to 11, 13 or 14. [16] Diagnostic box for use with a control valve (230), the diagnostic box comprising a computing unit with means suitable and arranged to carry out the steps according to any one of the preceding method claims 1 to 11, 13 or 14. [17] Control valve (230) with a position controller (210) according to claim 15. [18] Computer program comprising instructions which cause the position controller (210) according to claim 15 and / or the diagnostic box according to claim 16 to carry out the method steps according to one of the preceding method claims 1 to 11, 13 or 14. [19] A computer-readable medium on which the computer program according to the immediately preceding claim is stored.

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