Position controller for a process plant with valve control device and corresponding diagnostic procedure

Description

[0001] The disclosure relates to a valve actuator for a process plant, such as a chemical plant, for example, a petrochemical plant, a power plant, for example, a nuclear power plant, a food processing plant, for example, a brewery, or the like. The disclosure may relate, among other things, to a process plant having a valve actuator. Furthermore, the disclosure relates to the use of a valve actuator for performing a diagnostic method with respect to a process plant.

[0002] Valve actuators are often used in process engineering systems within a cascaded process control system, such as in Fig. 0is shown schematically. In cascaded process control, or cascade control, several controllers are cascaded, and the associated control loops are nested within each other. At least one other process controller (120) is superordinate to a control device (1). The output variable (pg ) of the process controller (120) serves as the reference variable for the valve control device.

[0003] Typical process control applications use valve actuators with control valves to influence a downstream process toward a specified steady-state or dynamic target by changing the volumetric or mass flow rates. Process controllers used for process control do not directly control the mechanical position of the control valve. This is done in a subordinate, i.e., cascaded, control loop using the valve actuator's control electronics.

[0004] In the Figure 0In the controller cascade shown as an example, the process control difference (pd) formed as the difference between a process target signal (pg) and a process actual signal (pi) is fed to the process controller (120) as an input signal in the higher-level, pictorially outer control loop. The process control method of the process controller (120) can be set up to compensate for disturbances acting on the process. Using a control method implemented in the process controller (120), an output variable is generated from the process control difference (pe), which can be referred to as the process control signal (pg) and describes the target position of the control valve (35). This process control signal (pg) is fed to the control device (1). In addition, the valve control device (1) detects a signal (i) representing the actual position of the control valve.From this, the position controller (31) of the valve actuator (1) determines a control signal (g) for controlling an actuator (33), which can be, for example, a pneumatic or electric actuator of a control valve. The control method of the position controller (31) can be configured to compensate for the valve disturbances acting within the valve actuator.

[0005] EP 1 451 649 B1 concerns the detection and differentiation of instabilities in a control device. In a valve control device installed in a process environment, comprising a positioner, actuator, and control valve, the aim is to detect whether an undesirable oscillation is due to a mechanical fault in the connection between the actuator and the control valve or due to a faulty configuration of a positioner. To this end, EP 1 451 649 B1 proposes capturing signals within the valve control device and using an assessment unit to determine the presence and source of instabilities. To detect the presence of instability, the assessment unit is to perform statistical analyses. To identify the cause of the detected instability, the assessment unit is to check whether a limit cycle exists in the control loop of the valve control device based on the phase angles of causally correlated signals.If necessary, the time offset between the control pressure and the valve position should be determined to locate the cause of the fault in the actuator. The diagnostic routines described in EP 1 451 649 B1 are typically aimed at fault causes located within the actuator.

[0006] Disturbances resulting from the interaction between the valve actuator and the higher-level process controller can often only be taken into account incompletely. This complicates the diagnosis of problem causes in situations where multiple control loops in a controller cascade exhibit undesirable behavior. Furthermore, the diagnosis of a fault supposedly located in the valve actuator may be an artifact of an operating behavior imposed on the valve actuator via the process controller. In such cases, it can be useful to provide additional process signals to the diagnostics performed in a valve actuator, allowing for a more accurate identification of the actual cause of the fault.

[0007] US 7,085,610 B2 relates to an industrial process diagnostic device for identifying a source or root cause of an anomaly in an industrial process. A diagnosis of the process control loops in a process plant is to be determined based on a plurality of process signals in a process plant (including process variables, control signals, and diagnostic signals) using a root cause calculation device. The root cause calculation device is to perform an analysis to determine the root cause of an anomaly, which analysis can, for example, be rule-based or carried out using regressive learning, fuzzy logic, or a neural network. The root cause calculation device is to be implemented in any process device of a process plant, for example in a transmitter, a controller, a mobile communication device, or a computer in a central control room.In practice, it has been shown that process signals required to perform diagnostics to determine the root cause of errors in the interaction of cascaded control loops are only available to the higher-level process controllers at best. Process signals from higher-level control loops or other valve control devices are generally not communicated to lower-level valve control devices. Often, no communication interfaces are available to transmit a wide variety of process signals. Even if all necessary interfaces were available, many process signals cannot practically be made available to individual valve control devices, especially not in real time, due to the limited bandwidth available in typical communication networks in process plants. Samson Aktiengesellschaft

[0008] EP 1 599 712 A0 discloses a method for performing online valve diagnostics for a valve operating in a process, comprising obtaining valve information while the valve is operating in response to a control signal controlling the process, the valve operating through a series of step-wise movements, the valve information comprising at least two of setpoint data, position data and pressure data, and deriving at least one of step response, friction and spring length for the valve based on the valve information.

[0009] WO 2020 / 049214 A1 discloses the use of an embedded digital twin of a physical part of a valve assembly in a microprocessor system of a valve position controller for fault diagnosis. The digital twin comprises a plurality of simulation model parameters, including at least one fault-related simulation model parameter. The digital twin receives a control signal representing a real control of at least one part of the valve assembly and generates simulated measurements related to the result of the simulated control.

[0010] WO 2015 / 012832 A1 discloses a cooling tower simulation system that can receive a measurement from a cooling tower sensor and generate a predicted performance of a cooling tower system based on a model of the cooling tower system. The simulation system can generate an estimated output using an extended Kalman filter with the measurement and the predicted output as inputs, wherein the estimated output represents a property of the cooling tower system.

[0011] It can therefore be seen as an object to overcome the problems of the prior art, in particular to provide a valve actuator and / or a diagnostic method which, on the basis of the limited number of process signals available locally in the valve actuator, enables a statement to be made about the causes of errors both inside and outside the valve actuator.

[0012] The problem is solved by the subject matter of independent claims 1 and 6.

[0013] Accordingly, a position controller is provided for a valve actuator of a process plant. The position controller comprises a first signal input for a command signal, in particular a process control signal from a process controller of the process plant. The command signal can in particular be discretely or continuously time-varying. The command signal can be defined as a time series, wherein in particular the time series comprises discrete, time-dependent command values. The position controller is configured to generate a manipulated variable for the actuator based on the command signal, in particular the process control signal, and an actual position signal. The manipulated variable can in particular be discretely or continuously time-varying.In particular, the valve actuator comprises a position sensor, such as a travel sensor or a position sensor, which generates an actual position signal depending on the actual position of the control valve, in particular a valve element or a control rod of the control valve, and provides it to the position controller.

[0014] The position controller can comprise position controller electronics and, if appropriate, a computer-implemented position controller module. The position controller has a first input for a particularly electrical command signal, in particular a process control signal. The position controller can have a second input for a particularly electrical actual position signal. In particular, the position controller can have a second signal input for an actual position signal relating to a control valve, such as a second signal input for receiving a sensor value relating to an absolute or relative position of the control valve. The position controller has an output for outputting the, in particular electrical or pneumatic, manipulated variable for the actuator. The output of the position controller can have a digital-to-analog converter or an electropneumatic converter.The actuator can be configured to convert a received electrical or pneumatic control variable into a force or torque with which the actuator acts on the control valve. The position controller can be configured to generate a control variable, in particular a pneumatic one, for an actuator for actuating the control valve based on the command signal and the actual position signal and can comprise a control output, in particular a pneumatic one, for the control variable.

[0015] According to the invention, the position controller is configured to calculate an approximation signal based on the reference signal by means of a configurable controller model related to a specific controller, in particular the process controller. The controller model is configured such that a signal generated by the specific controller based on the approximation signal corresponds to the reference signal. In particular, the hypothetical signal and the reference signal can approximately correspond to one another. The controller model is, in particular, deterministic. A deterministic controller model can define a unique, in particular reversible, correlation between the reference signal and the approximation signal.

[0016] According to the invention, the position controller is further configured to determine an approximation signal based on the reference signal, in particular the process control signal, and a control inversion related to the process controller. Furthermore, the position controller is configured to perform at least one diagnostic routine taking the approximation signal into account. An approximation signal can, in particular, be discretely or continuously time-varying. The approximation signal can be defined as a time series. The approximation signal can be referred to as a virtual input variable time series, wherein the input variable time series, in particular, comprises discrete, time-dependent input variable values.

[0017] The position controller can comprise a computer-implemented inverter module. The position controller, in particular its inverter module, is configured to approximately calculate the behavior of the process controller superordinate to the valve actuator, taking into account only the actuator signals available in the actuator. The inverter module can be configured to calculate an approximation signal corresponding to an actual signal of the process controller that is not transmitted to the valve actuator by the process controller. For example, the position controller can determine an approximation signal corresponding to a process controller input signal of the process controller, such as an actual process controller signal.

[0018] The position controller electronics and the inverter module can be implemented in functional union by a particularly configurable electronic computing and data storage device of the valve actuator, for example, a microcontroller or the like. The position controller can comprise the diagnostic electronics and / or the control electronics. The valve actuator, in particular its inverter module, can be designed in particular to perform an approximate calculation of a process target signal or a process control difference based on the command signal received from the valve actuator, in particular the process control signal, in order to determine the approximation signal.

[0019] The positioner, in particular a diagnostic electronics unit or a diagnostic module of the valve actuator, can then execute a diagnostic routine that takes the previously calculated approximation signal into account, for example, to check whether an error occurs with a certain probability, preferably with certainty, within the valve actuator or has its origin in a controller cascade higher upstream of the valve actuator, in particular the process controller. For example, the valve actuator can be configured to check whether the approximation signal lies within an unremarkable or conspicuous value range, with the latter indicating the higher-level process controller as the source of the error.A diagnostic module, a position controller module and / or an inverting module can be implemented by various at least partially different hardware components, for example different microcontrollers of a single valve actuator or alternatively by the same hardware, for example a single microcontroller, of the valve actuator.

[0020] According to one embodiment, the position controller comprises a memory occupied with process context data. The position controller can be configured to determine the approximation signal taking into account the process context data. Additionally or alternatively, the position controller can be configured to perform the at least one diagnostic routine taking into account the process context data.

[0021] According to one embodiment of a position controller, process context data can characterize a particularly constant process target signal. According to a first embodiment, process context data can characterize a temporal signal profile of the process target signal and, in particular, a temporally constant process target signal. According to a further development, process context data can define a particularly constant process target signal with respect to a specific time period. According to a second embodiment, process context data can define a defined set of specific points in time or time periods and associated constant process target signals. According to an alternative embodiment, it is conceivable for the process context data to define characteristic variables of a process target signal.A characteristic quantity can, in particular, be a value that is constant with respect to the signal curve of the process target signal, the first derivative of the signal curve, or the second derivative of the signal curve. Under certain circumstances, the approximation of a process signal by a sinusoidal time curve can be appropriate. With regard to a process target signal with a known or assumed sinusoidal curve, characteristic quantities such as amplitude, frequency, offset of the process target signal in the time dimension and / or amplitude dimension, in particular relative to an actual process signal, can be defined as process context data. With regard to a process target signal with a known or assumed step-like curve, characteristic quantities such as step amplitude and / or step time can be defined as process context data.Process context data can computationally define a process controller controller structure for a controller model, for example, a specific PID controller structure, such as a P, I, PI, PD, or PID controller structure; or alternatively, another controller structure, such as a two-point controller structure.

[0022] The position controller, in particular the inversion module, can be configured to determine the approximation signal taking into account the process context data. For example, the position controller can be configured to perform an approximate calculation of a process controller control difference or an actual process signal based on the command signal received from the process controller, in particular the process control signal, and on the basis of a description of the controller structure of the process controller contained in the process context data. Alternatively or additionally, the position controller, in particular the diagnostic module, can consider process context data in addition to the approximation signal in order to determine whether the approximated behavior of the controller indicates normal operation or faulty operation of the controller.

[0023] According to another development, which can be combined with the previous one, the position controller is further configured to perform the at least one diagnostic routine taking into account at least one actuator signal from the list comprising the manipulated variable, the actual position signal, and the reference signal, in particular the process control signal. In particular, an actuator signal can be selected from the list consisting of the manipulated variable, the actual position signal, and the reference signal. For example, the diagnostic routine can include a test in which at least one actuator signal available in the position controller is used to perform a known actuator diagnosis. Diagnostic routines are known, for example, from DE 10 2017 124 293 A1, DE 10 2010 015 647 B4, DE 10 2006 003 750 B4, DE 10 2005 024 674 B4, DE 10 2005 024 686 B4 and DE 197 23 650 B9.

[0024] According to a further alternative or additional embodiment, the position controller, in particular the inversion module, can be configured to determine an approximation signal corresponding to a process signal, such as a process control difference signal and / or actual process signal, of the process controller that is not available to the valve actuator. The valve actuator can be configured to determine an approximation signal corresponding to a process signal of the process controller that is not directly transmitted from the process controller to the valve actuator. In this way, the valve actuator is enabled to approximately map a process signal of a higher-level control loop.The approximately mapped process signal can be used to diagnose possible errors whose root cause lies not in the cascade stage of the valve actuator but in the cascade stage of the process controller upstream of the valve actuator.

[0025] The disclosure also relates to a valve control device for a process plant, comprising a control valve for adjusting the process fluid flow, an actuator for actuating the control valve, and a position controller configured as described above for generating a manipulated variable for the actuator. The actuator may be a pneumatic actuator, such as a pneumatic actuator, or an electric actuator, such as an electric actuator.

[0026] The disclosure also relates to a process plant, for example, a food processing plant, such as a brewery, a power plant, such as a nuclear power plant, a chemical plant, such as a petrochemical plant, or the like. The process plant comprises a valve actuator for adjusting a process fluid flow. The process plant may comprise multiple valve actuators for adjusting one or more process fluid flows. One or more valve actuators of the process plant may be configured as described above.

[0027] Furthermore, the process plant comprises at least one process fluid user that receives the process fluid flow set, in particular upstream, by the valve actuator, or delivers the process fluid flow set, in particular downstream, by the valve actuator. A process fluid user can be, for example, a reactor, a heat exchanger, a cooling tower, or the like. A process fluid user can generally be a component of a process plant that generates, uses, or consumes process fluid.

[0028] The process engineering system also comprises a process sensor that detects an actual process signal related to the process fluid user and / or the process fluid. An actual process signal related to the process fluid can, for example, describe its temperature, pressure, volume flow, flow velocity, or the like. An actual process signal related to a process fluid user can, in particular, describe a measured value related to the process fluid user, such as a mixing ratio, a proportion of one of several materials to be processed in the process, an ambient temperature, a pressure, a pressure difference, or a pressure gradient in the process fluid user, or the like.

[0029] In addition, the process engineering system comprises a process controller that provides a process control signal as a command signal for the valve actuator, which is dependent on a process target signal and the process actual signal. The process controller can be designed to compare the process actual signal with the process target signal and, based on the comparison, provide a process control signal for the valve actuator. For example, the process controller can calculate a process control difference between the process target signal and the process actual signal and, using a process control routine, determine a process control signal based on the process control difference and provide it to the valve actuator. The process controller can optionally be implemented in a PID controller structure. In particular, the process engineering system is designed such that the process controller provides the valve actuator exclusively with the process control signal, in particular directly.In particular, the process plant is designed such that the process controller transmits neither the process target signal nor the process actual signal nor the process control difference to the valve actuator, in particular directly.The disclosure also relates to a diagnostic method for a valve actuator used in a process plant comprising a valve actuator and a process controller. During the use of the valve actuator in the plant, a process control signal is provided to the valve actuator by the process controller. The process control signal can be determined by the process controller based on one or more process signals. The valve actuator can in particular be designed as described above. The process plant can in particular be designed as described above.

[0030] In the diagnostic method, an approximation signal, which corresponds in particular to a process signal, is determined by the valve actuator, in particular based on the process control signal and a controller model related to a specific controller, in particular the process controller, in particular a control inversion. The valve actuator executes at least one diagnostic routine taking this approximation signal into account. In this way, a diagnostic method of the valve actuator can be carried out not merely limited to the manipulated variables directly available in the actuator. The diagnostic routine can be executed to determine a diagnostic result and to generate a diagnostic code representing the diagnostic result.It has proven advantageous that the diagnostic procedure can also, at least approximately, take into account process signals that are present in a higher-level controller, in particular a higher-level process controller, or a higher-level process control cascade, but are not directly fed to the valve actuator. In this way, a diagnostic routine implemented in a valve actuator can identify error causes outside the sphere or cascade stage of the positioner.

[0031] The disclosure may also relate to a method for operating a valve actuator in a process plant having a process controller, wherein a process control signal is provided to the valve actuator by the process controller. The process control signal is processed, if appropriate, in combination with an actual position signal from the valve actuator to determine a control signal. The control signal, in particular an electrical or pneumatic control signal, is used to control an actuator of the valve actuator so that the actuator actuates a control valve to adjust a process fluid flow. In the operating method, the control signal may be a pneumatic or electrical control signal generated by control electronics of the valve actuator and provided to an actuator of the valve actuator.As part of the operating method for generating the manipulated variable, the valve actuator can take into account a position control difference between the process control signal and the actual position signal. The operating method includes the valve actuator performing at least one diagnostic method as described above. The diagnostic method can take into account the process control signal, the actual position signal, and / or the manipulated variable.

[0032] According to a further development of the diagnostic method, the controller model, in particular the control inversion, i.e., the determination of the approximation signal, and / or the diagnostic routine are carried out based on process context data that characterize the process target signal. The process context data can, in particular, characterize a constant process target signal. For example, the diagnostic method can first perform a control inversion that is related to a known controller structure of the process controller. Process context values ​​can define one or more boundary conditions of a mathematical equation or system of equations that represents the process controller.The diagnostic routine can calculate a difference between a process approximation signal corresponding to an actual process signal and an approximated, in particular constant, process target signal in the form of the process context data in order to determine a further approximation signal corresponding to a process control deviation. The diagnostic routine can compare an approximation signal corresponding to a process control deviation with a permissible value range and, in the event of a deviation from the permissible value range, output faulty behavior of the process controller as a diagnostic result.

[0033] In a further development of the diagnostic method, a time interval can be determined to which the process context data refers. The diagnostic routine can be performed relative to a predetermined time interval to which the process context data also refers. For example, process context data can be defined relative to one or more time-stationary sections in which the process context data characterize a constant process target signal, whereby different, particularly consecutive, time intervals can be assigned to different process target signals.

[0034] According to an alternative embodiment, the process context data can include a delay line and / or a signal shape definition of the process target signal. With such an embodiment of the diagnostic method, it can be advantageous if a process target signal is provided to the valve actuator. The diagnostic method can be carried out using the process context data and at least one predetermined process target signal, taking into account a previously known delay line and / or taking into account a known signal shape definition. By determining a time interval to which the process context data refers, the diagnostic method can be based on a temporal correlation between process context data and valve actuator variables detected in the valve actuator, such as the process control signal, actual position signal, position error of the control inversion, and / or the diagnostic routine.For example, the diagnostic method can include a delay line to account for a time offset, particularly due to a control cycle time, between the receipt of a process setpoint signal by the process controller and the output of a process control signal by the process controller, so that the diagnostic method, particularly the control inversion and / or the diagnostic routine, can causally analyze closely related signals. The diagnostic method can, for example, consider a signal shape definition of the process setpoint signal as process context data, from which it can be seen, for example, that the process setpoint signal has a ramp-like curve, a sinusoidal curve, or a step-like curve.If the signal shape of the process setpoint signal is known at least approximately, this allows the valve actuator to perform a more precise diagnostic procedure, even if the process setpoint signal cannot be characterized as a constant value.

[0035] According to one embodiment of a diagnostic method, the process control signal is stored. In particular, the temporal profile of the process control signal is stored. It can be advantageous if the diagnostic method stores the process control signal or its temporal profile, for example, as a series of discrete values, in particular with reference to a time interval, so that the diagnostic method can use the process control signal or its temporal profile as the basis for control inversion and / or the diagnostic routine. With the aid of a stored process control signal or the stored temporal profile of the process control signal, the behavior of a higher-level process controller can be precisely mapped, in particular in combination with process context data that relates to a time interval.

[0036] According to a preferred embodiment, the control inversion of the diagnostic method is determined based on a predetermined continuous-time, in particular real and / or parallel, controller structure. A predetermined continuous-time controller structure can correspond to an analog process controller control routine. According to an alternative embodiment, the control inversion of the diagnostic method can be determined based on a predetermined discrete-time, in particular real and / or parallel, controller structure. In particular, the control inversion can be performed based on a PID controller structure. The predetermined discrete-time controller structure can correspond to a digital control of the process controller.

[0037] The control inversion or an inversion module can be set up to use an inverted transfer function G of a process PID controller to calculate the inverse in the Z domain over the variable z by G − 1 z = 1 K P a 2 ⋅ z 2 − a 1 ⋅ z + a 0 b 2 ⋅ z 2 + b 1 ⋅ z + b 0

[0038] For the assumption that is applicable in many cases: τ = TC / 2, the transfer function can be simplified to: G − 1 z = z 2 − z a ⋅ z 2 + b ⋅ z + c to calculate. The parameters a0, a1, a2, as well as b0, b1 and b2 or a, b and c can be transmitted in the same way as the process context data that characterizes the process controller. In a suitable embodiment, the parameters can comprise constant predetermined parameters (a, b and / or c) for calculating an inverted process control function. The stored parameters can be used as the basis for the control inversion to determine a process approximation signal ap. It has been shown that sufficiently accurate results can be provided with a simplified calculation if c=0 is assumed, so that the simplified equation G ab − 1 z = z − 1 a ⋅ z + b The parameters a, b and / or c can be specified to the valve actuator via manual user input.

[0039] It is conceivable that process context data can be determined at least partially automatically by the valve actuator using an initialization routine. Based on reference systems or empirical values, process context data can be stored in a memory of the valve actuator, in particular the positioner.

[0040] According to one embodiment, the diagnostic method can comprise calculating an approximated actual process signal. The approximated actual process signal can be calculated using a particularly linear function based on the process control signal. For example, in a particularly simple approach, the actual process signal can be equated to the manipulated variable.

[0041] In a preferred embodiment of the diagnostic method, a comparison of the diagnostic result with a predetermined target behavior of the actuator is performed. If a deviation between the diagnostic result and a predetermined target behavior is detected, a diagnostic code can be generated. If no deviation between the diagnostic result and the predetermined target behavior is detected, a diagnostic code can be suppressed and / or deleted.By first performing a control inversion related to the process controller higher up the valve actuator in order to generate an approximation signal, the diagnostic procedure can then use this process approximation signal, which maps the behavior of the process controller higher up the valve actuator, in the further diagnostic procedure to check whether the actual behavior of the valve actuator, taking into account the approximated behavior of the process controller, corresponds to a desired or at least tolerated valve actuator target behavior.If the valve actuator exhibits abnormal behavior, but at the same time, based on the approximation signal determined using the diagnostic procedure, it can be determined that the abnormal behavior corresponds to a behavior imposed by the process controller, a diagnostic code that would otherwise have been generated and possibly output as a result of the abnormal behavior of the valve actuator can be suppressed and / or deleted. This can prevent the output of false-positive diagnostic codes. Alternatively or additionally, a diagnostic code can be generated that indicates abnormal behavior of the process controller higher up the valve actuator if the diagnostic result reveals a discrepancy with a predetermined target behavior.In particular, a diagnostic code can be output if the comparison shows that the actual behavior of the valve actuator deviates from a predetermined target behavior, while no unusual behavior of the valve actuator is indicated based on the approximated behavior of the process controller mapped by means of an approximation signal.

[0042] Further properties, advantages and features will become clear from the following description of preferred embodiments based on the accompanying drawings, in which: Figure 1 shows a schematic representation of a process plant with a valve actuator; Figure 2 shows a schematic block diagram of a digital position controller; Figure 3 shows a schematic representation of a first operating method of the process plant with the valve actuator; and Figure 4 shows a schematic representation of a second operating method of the process plant with the valve actuator.

[0043] In the following description of preferred embodiments, identical or similar components are provided with the same or similar reference numerals to simplify readability.

[0044] The explanations can in particular illustrate how a position controller in a control device can obtain additional information for the diagnosis of the control device by the approximate reconstruction of the reference or controlled variable of the higher-level controller and how the approximate reconstruction can be understood mathematically in some cases as an inversion of the transfer function of a sufficiently accurate model of the higher-level controller.

[0045] Figure 1 shows a schematic representation of a process plant 100 that includes one or more cascaded control loops. For the sake of simplicity, in the schematic representation according to Figure 1only a single control cascade is shown. The control cascade comprises a higher-level process controller 120 and a lower-level valve actuator 1. Exactly one field device, two, three, or more field devices, in particular actuators, can be subordinate to the higher-level process controller 120, which is not shown in detail here.

[0046] The higher-level process controller 120 can be configured to control a plant process 111. For this purpose, the process controller 120 can receive as an input signal an actual process signal pi or multiple actual process signals, for example from a process sensor 105 of a process fluid user 110. With regard to a desired process behavior, a desired process signal p W is specified to the process controller 120. The desired process signal p W can be specified to the process controller 120, for example, via a user interface, such as a control computer 101 in a control room of a process plant. The process controller 120 is configured to compare the desired process signal p W and the actual process signal pi, on the basis of which a process control difference pe is determined. Based on the process control difference pe, a process control routine is implemented by the process controller 120.As a result of the process control routine, the process controller 120 outputs a process control signal pg, which is fed to a subordinate valve actuator 1 so that the valve actuator 1 acts on a process fluid in a desired manner with the aim of adjusting the actual process signal pi to the desired process signal p W.

[0047] The valve actuator 1 comprises a positioner 31, an actuator 33, and a control valve 35. The control valve 35 acts on the process fluid provided to the process fluid user 110. Alternatively, control valves can also act on the outflow of a process fluid from a process fluid user 110 (not shown). The control valve 35 can influence a process fluid pressure, a flow velocity, or the like. It is clear that a process fluid user 110 can comprise multiple process fluid inlets and / or multiple process fluid outlets, wherein valve actuators can be assigned to one or more of the process fluid inlets and / or outlets of the process fluid user 110.

[0048] The valve actuator 1 comprises a positioner 31 with an analog or digital positioner electronics 400, as shown below in the Figure 2In detail, it can be implemented at least partially as a computer-implemented control module 401. The position controller electronics 400 has a first signal input 420 for a process control signal pg and a second signal input 436 for an actual position value i. Depending on the actual position value i and the process control signal pg, a comparison is carried out using a control routine in order to calculate a position controller control difference and to determine a control signal g. The position controller electronics 400 outputs the control signal g for actuating the actuator 33 at an output 433.

[0049] The position controller electronics 400 further comprises an inversion module 405, which is supplied with the process control signal pg as a signal input and which can receive process context data k from a memory 404, which describes the behavior of the higher-level process controller 120. The inversion module 405 is configured to determine, based on the process control signal pg, an approximation signal a P describing the higher-level process controller 120 by means of a control inversion. The approximation signal a P can, for example, correspond to a process controller actual value or to a process controller control difference pe . An actual process signal generally depends on the temporal progression of a process controller actual value, for example a series of discrete process controller actual values ​​or a continuous-time development of the process controller actual value. Suitable embodiments and functions of the inversion module 405 are explained in detail below.The valve actuator 1 can further comprise a diagnostic module 407, for example, diagnostic electronics, which can perform diagnostic routines related to the valve actuator 1. The diagnostic module 407 can be configured to perform known diagnostic routines for valve actuators. The diagnostic module 407 can be configured to generate at least one diagnostic code 408 depending on at least one diagnostic routine. The diagnostic code can be shown to a user on a visual display of the valve actuator 1. The diagnostic code 408 can be transmitted for processing to the process control room, the process controller 120, or to a portable computer, for example, a tablet PC. The diagnostic module 407 can be configured to perform at least one diagnostic routine based on the approximation signal a P.During the diagnostic routine based on the approximation signal, the diagnostic module 407 can take into account further signals available in the valve actuator 1, in particular its position controller electronics 31. For example, when performing the diagnostic routine based on the approximation signal a P, the diagnostic module 407 can take into account the process control signal pg, the control signal g, an actual position signal i, a position controller control difference, or the like. Possible embodiments of the position controller 400, a configurable electronic computing and data storage device with a computer-implemented diagnostic module 407, are described below. Figure 2shows a block diagram of a digital position controller 31 formed with a configurable electronic computing and data storage device 400. The schematic block diagram illustrates a digitized position controller electronics 400 with a configurable electronic computing and data storage device. However, the functions disclosed herein in this regard could be implemented partially or entirely using analog position controller electronics components.

[0050] The digital position controller electronics 400 comprises a processor 403, for example in the form of a microprocessor, which is configured to perform various calculations. The processor 403 of the digital position controller electronics 400 is linked to a memory 404. Various data and / or routines for use by the processor 403 can be stored in the memory 404. A first calculation module 401 for a control routine of the valve actuator 1 can be stored in the memory 404. The first calculation module 401 can be described as a control module. A digital position control can be implemented with the control module. The control module 401 can be implemented with the processor 403 in order to provide a control signal g for actuating the actuator 35 at the output 433 of the digital position controller electronics 400.The processor 403 can be configured, with the aid of the control module 401, to calculate a control routine based on an actual position signal i provided by a position sensor 36 and a process control signal pg provided by the higher-level process controller 120. The control routine of the first calculation module 401 can be, for example, a digital PID control routine.

[0051] The position controller electronics 400 can have two or more signal inputs 420, 436 for signals to be processed in the processor 403 according to a routine. The digital position controller electronics 400 includes a first signal input 420 for receiving a process control signal pg . In some embodiments, this first signal input 420 can include an analog-to-digital converter to generate a digital signal for use in the digital position controller electronics 400, for example, based on simple analog signals, such as an analog 4..20 mA process control signal. The digital position controller electronics 400 further includes a second signal input 436 for receiving an actual position signal i. The digital position controller electronics 400 further includes a control signal output 433.The processor 403 can be configured to execute the control module 401 with the control routine in order to perform a position control based on the signals i, pg received at the inputs 420, 436 and, as a result, to provide a control signal g for actuating an actuator 33 at the control signal output 433. In embodiments, the control signal output 433 can have a digital-to-analog converter or an electropneumatic converter in order to provide a control signal g adapted to the actuator 33. The digital position controller electronics 400 can have additional signal inputs or outputs (not shown in detail). Furthermore, the position controller can have an interface for manual data input.

[0052] The actuator 33 may be equipped with a signal amplifier to amplify a control signal g using electrical and / or pneumatic auxiliary energy from an auxiliary energy source.

[0053] The memory 404 of the digital position controller electronics 400 can be assigned one or more diagnostic routines to implement a diagnostic module 407. The diagnostic routines are configured to be executed by the processor 403. The processor 403 can execute a diagnostic routine, for example, based on the actuating signal g and the actual position signal. For example, a diagnostic routine can initiate the execution of a partial stroke test and evaluate its results.

[0054] The memory 404 can be occupied with input data 402, wherein the input data 402 stored in the memory 404 is expediently assigned to a specific point in time or time interval. In one embodiment, input data 402 are exclusively actuator signals. The processor 403 can be configured to perform a diagnostic routine using the input data 402, which is related to a predetermined time interval, for example, to compare current input data 402 of a current time interval with historical input data 402 of another time interval or a specific reference interval. A deviation from historical diagnostic results from a reference interval can, for example, indicate wear on the control valve 35. The diagnostic routine can be designed to determine whether an unusual signal curve, such as a run, is present.

[0055] As explained above, the valve actuator 1 can comprise a position controller 31 configured to perform a diagnostic routine by equipping the position controller 31 with digital position controller electronics 400, which includes a memory 404 with a diagnostic routine 407 stored thereon and a processor 403 for performing the diagnostic routine 407. The position controller 31 can generate a manipulated variable g for an actuator 33 using the digital position controller electronics 400.

[0056] Within the scope of the present disclosure, the position controller is further configured to perform a control inversion related to a higher-level process controller 120. Using the control inversion, an approximation signal a P can be determined based on the process control signal pg. The approximation signal a P can form the basis of a diagnostic routine 407. For this purpose, the memory 404 of the configurable electronic computing and data storage device 400 can be equipped with a second calculation module 405, which can be referred to as a modeling module or inversion module.

[0057] The second calculation module includes configuration data 406 for defining a control model for a specific controller. The configuration data 406 for adapting the model are used to adapt the control model to a specific controller, for example the process controller that is superior to the valve positioning device. Optionally, process context data 409 can additionally be stored on the memory 404, which characterize the behavior of the process controller 120 that is superior to the valve positioning device 1. The processor 403 can be configured to execute the second calculation module 405 and / or at least one diagnostic routine 407 taking into account the process context data 409. A schematic illustration of the position control taking place in the position controller 31, as well as the control inversion taking place in parallel thereto and optionally the diagnosis, is in a first embodiment in Figure 3 and in a second embodiment in Figure 4 shown.

[0058] Referring to Figure 1 It should be understood that, within the scope of the process control performed with the process controller 120, an actual process signal pi and a desired process signal p W are assumed as known process variables, on the basis of which a process control signal pg is determined as an unknown process variable to be calculated by means of the predetermined process control routine. This process control routine can be represented by a model controller. The process control signal pg is transmitted to the subordinate position controller 1. The desired process signal p W , the actual process signal pi , and other process signals are generally unknown to the valve position controller 1.

[0059] Figure 3shows an embodiment of an operating method in which a closed-loop control and, in parallel, a diagnostic method including a closed-loop control inversion and, if applicable, a diagnostic routine are carried out. The second calculation module 405 can include configuration data 406 for adapting the model. The second calculation module or inversion module 405 can, in particular, be configured to map the inverse of a model controller with which the process control routine of the process controller 120 superordinate to the valve actuator 1 is approximated. The second calculation module 405 is configured to invert a transfer function related to the superordinate process controller 120 in a spectral range, for example, a Laplace or Z space.The implementation of the control inversion performed with the second calculation module 405 in the processor 403 of the digital position controller electronics 400 serves to approximately reconstruct the input data (pi, pW) of the process controller 120 on the basis of the process manipulated variable pg output by the process controller 120, which is received by the actuator 1. The second calculation module 405 is designed so that the processor 403, starting from the process control signal pg as a known variable, with the aid of process context data k, performs a calculation in order to calculate an approximation signal aP regarded as an unknown variable. The approximation signal aP corresponds to a process signal, in particular the process control difference pe or the actual process signal pi.

[0060] The process context data k or 409 can be related to the process target signal. Based on the process context data k, an at least temporarily constant process target signal pw can be assumed during control modeling, in particular inversion, with the second calculation module 405. The control inversion can be based on several different, in particular constant, process target signals pW, which are assigned to various different time intervals, using the process context data k. Alternatively or additionally, the second calculation module 405 can use process context data k that maps a temporal profile of a non-constant process target signal pW. According to a further alternative option, the process context data k can provide the second calculation module 405 with information about signal profile characteristics of the process target signal pW.For example, process context data k can provide the second calculation module 405 with information about, for example, a linear, ramp-like profile of the process target signal pw . The process context data k can provide the second calculation module with information regarding a sinusoidal profile of the process target signal, for example, its frequency, amplitude, offset in the amplitude direction, or offset in the temporal dimension. Alternatively or additionally, the second calculation module can consider process context data that describe a step-like behavior of the process target signal, for example, its amplitude, frequency, step time, or the like.

[0061] The Figure 3 The illustrated operating procedure refers to a position controller 31, which exclusively processes the process control signal pg from the higher-level process controller 120. The position controller 31 according to the Figure 3The embodiment shown does not process any signals received directly from the higher-level controller cascade other than the process control signal pg . In particular, the position controller 31 does not receive any signals from the higher-level process control cascade other than the process control signal pg . Figure 3 In the method illustrated, predetermined process context data k(t) are provided to the positioner, particularly related to time intervals t 2 -t 1 . For example, process context data k can be entered manually as empirical values ​​via a user interface. Alternatively or additionally, process context data k can be stored in a factory setting in the memory 404 of the positioner electronics 400 before the valve actuator 1 is put into operation for the first time.

[0062] Figure 4shows an alternative embodiment of an operating procedure in which a control and, in parallel, a diagnostic procedure including a control inversion and, if necessary, a diagnostic routine are carried out. Figure 4 The schematically illustrated operating procedure differs from the procedure according to Figure 3 essentially only by providing or receiving process context data k. The valve actuator 3 has, when executed according to Figure 4a further input in order to receive at least one process target signal p W from the process plant 100. The process target signal p W can be received, for example, as a series of digital process target signals. For example, an analog or digital signal input of the valve actuator 1 can receive the process target signal p W as a further input value, which is then fed to the process controller 120 for process control in the process plant 100. Alternatively, it is conceivable that the process controller 120 is configured and connected to the valve actuator 1 for signal transmission in order to additionally transmit the process target signal p w to the further input of the valve actuator 1. The process target signal p g can be received by the valve actuator 1, for example, in digital form as several process target signals p W to be processed in sequential order.The time series q of process setpoint signals can be stored retrievably by the digital position controller electronics 31 in the memory 404 as process context data k(q). According to an advantageous embodiment, a specific point in time or time interval t would be assigned to each of the received process setpoint data of the time series q of process context data. Process setpoint signals pW received as time series q can be stored as process context data 409, correlated to a delay line or a time offset. With the aid of a time offset or delay line 411, a correlation can be established between upstream process setpoint signals pW and downstream process control signals pg, which are to be linked to one another in the, in particular, inverted control routine, which can be adapted with configuration data 406, according to the second calculation module 405.For example, the control inversion can be based on a process control signal pg in combination with the process setpoint signal p W shifted by one cycle time of the digital position controller electronics 400.

[0063] In digital process control or digital actuator control, there is usually a time delay between the receipt of a (process) setpoint and the output of the (process) control signal assigned to this (process) setpoint by the (process) control routine, in particular by exactly one (process) controller cycle time. So that the control inversion can determine a more precise approximation of an actual process value or a process control value based on the process control value, it can be helpful to include a process control value and in particular a process setpoint that is exactly one process controller cycle time older than the process setpoint for the control inversion. Alternatively, particularly for sluggish processes with a slowly, in particular continuously, changing process setpoint signal, a sufficiently accurate approximation can be carried out by means of control inversion without a delay path.

[0064] The second calculation module 405 can preferably map the inverse of a process controller 120 as a model controller configured according to a PID controller structure. For example, the second calculation module 405 can implement a control inversion, in particular with regard to a process controller 120 modeled as a PID controller. In particular, the inversion module 405 can perform the control inversion on a process controller 120 modeled as a P controller, I controller, PD controller, PI controller, or PID controller. A process controller 120 modeled in a PID controller structure can be described by a mathematical function G PID , which determines a process control signal pg based on the known variables process setpoint signal p W , process actual signal pi , and / or process control deviation pe as an unknown variable and output value.In the modeling module or inversion module 405, the previously known mathematical control function can be used as the basis for a calculation in an inverted manner such that the process control signal pg is taken into account as a known variable together with a process setpoint signal pW, which is regarded as an at least approximately known variable, in order to determine an approximation signal aP, which corresponds in particular to a process actual value pi or a process control deviation pe. The process control routine of a process controller 120 in a, for example, in . Figure 0 The PID controller structure outlined can be represented mathematically in Laplace space L using the equations: X s = W s − G PID − 1 s ⋅ Y V s x t = L − 1 X s where W(s) is the Laplace transform of the real-valued function describing the temporal course of the process setpoint p W pw ( t ): ℝ → ℝ ; X is a process actual value of the discrete or time-continuous process actual signal pi ; YV is a process control value of the discrete or time-continuous process control signal pg ; and G PID describes the transfer function of the PID process controller and represents its dependence on the Laplace variable.

[0065] The transfer function of a continuous-time PID controller in parallel structure with real D-component time constant τ in the Laplace domain with the proportional gain KP , the reset time TN and the derivative time TV is: G PID s = K P ⋅ 1 + 1 T N ⋅ 1 s + T V ⋅ s τ ∗ s + 1

[0066] For a valve position controller, it may be advantageous to convert equation (5) into a difference equation and insert it into the following equation (6) and consider it with respect to a discrete sampling step k: x k = w k − e k = w k − Z − 1 Y V z G PID − 1 z

[0067] For a discrete-time controller, the transfer function can be determined using the Tustin transformation according to equation (7), where TC is chosen according to a cycle time of the process controller: s = 2 T C ⋅ z − 1 z + 1

[0068] This results in G PID − 1 = 1 K P ⋅ a 2 z 2 + a 1 z + a 0 b 2 z 2 + b 1 z + b 0

[0069] Where a 2 = 2 T N T C + 2 τ a 1 = − 8 τT N a 0 = − 2 T N T C − 2 τ b 2 = 2 T N T C + 2 τ + T C T C + 2 τ + 4 T N T V b 1 = − 8 τT N + 2 T C 2 − 8 T N T V b 0 = − 2 T N T C − 2 τ + T C T C − 2 τ + 4 T N T V

[0070] Using the position controller electronics 400, the modeling or inverting module 405 can approximately calculate an approximation signal a P starting from the process control signal pg, which correlates to the process control difference pe or to the process actual signal pi.

[0071] Alternatively, for some controller structures, another calculation can be performed directly in the time interval without using a Laplace space. For example, an approximation signal corresponding to a signal response of a PI controller can be determined. The inversion of a time(t)-dependent transfer function G PI (t) of a PI process controller is known. The controller model can be configured with a proportional back calculation factor with regard to the P factor of the transfer function G PI (t) and with a differentiation plus a proportional differentiation factor with regard to the I factor (not shown in detail). With such an inverted transfer function of a continuous-time PI controller G PI (t), an approximation signal a P can be determined based on a reference signal provided by the process controller.

[0072] Diagnostic routine 409 can be configured to analyze one or more approximation signals a P representing process control differences, for example, a set of approximated control differences pe determined in a time sequence q. Diagnostic routine 407 can use this information to determine a diagnostic code 408 relating to the steady-state accuracy, overshoot, stability, etc. of the higher-level process control. For example, the stability of the overall control loop, including process and position control, can be assessed.

[0073] For example, the number of overshoots can be taken into account for diagnosis. Based on the number and amplitude of overshoots, a diagnostic code 408 relating to the quality of process control and position control can be determined by diagnostic routine 407. For example, a diagnostic routine 407 can determine as a diagnostic result that efficient process control and position control are present if there are few overshoots. If the number of overshoots exceeds a threshold value, diagnostic routine 407 can determine that an improvement in process control and position control is recommended by adjusting the control parameters of positioner 1 and / or process controller 120.

[0074] The features disclosed in the above description, the figures and claims may be important both individually and in any combination for the realization of the invention in the various embodiments. List of reference symbols

[0075] 1 Control device 31 Positioner 33 Actuator 35 Control valve 100 Process plant 105 Process sensor 110 Process fluid user 111 Plant process 120 Process controller 400 Positioner electronics 401 Control module 402 Input data 403 Processor 404 Memory 405 Calculation module 406 Configuration data 407 Diagnostic module 408 Diagnostic code 409 Process context data 411 Delay line 420 First signal input 433 Output 436 Second signal input a P approximation signal g control signal i actual position value k process context data pd process control difference pe process control difference pg process setpoint signal pi process actual signal p W process setpoint signal q time series

Claims

1. A positioner (31) for a valve control device (1) of a process plant (100), comprising: a first signal input for a command signal, such as a process control signal (pg) from a process controller (120) of the process plant (100), a second signal input for an actual position signal (i) regarding a control valve (35), wherein the positioner (31) is configured to generate a control variable (g) for an actuator (33) to actuate the control valve based on the command signal and the actual position signal (i) and comprises a control output for the control variable (g), characterized in that the positioner (31) is configured to calculate an approximation signal (ap) using a configurable controller model related to a specific controller based on the command signal and a control inversion related to the process controller (120), wherein the controller model is configured such that a signal generated by the specific controller based on the approximation signal (ap) corresponds to the command signal, and that the positioner (31) is further configured to perform at least one diagnostic routine taking into account the approximation signal (ap).

2. The positioner (31) according to claim 1, further comprising a memory (9) loaded with process context data (k), and wherein the positioner (31) is configured to determine the approximation signal (ap) taking into account the process context data (k) and / or is configured to perform the at least one diagnostic routine taking into account the process context data (k).

3. The positioner (31) according to any of the preceding claims, wherein the positioner (31) is further configured to perform the at least one diagnostic routine taking into account at least one actuator device signal from the list comprising control variable (g), actual position signal (i), and process control signal (pg).

4. The positioner (31) according to any of the preceding claims, wherein the positioner (31) is configured to determine the approximation signal (ap) such that it corresponds to a process control difference signal (pe) and / or actual process signal (pi) of the process controller (120) that is not available to the valve control device (1).

5. A valve control device (1) for a process plant (100), comprising a control valve (35) for adjusting a process fluid flow, an actuator (33) for actuating the control valve (35), and a positioner (31) according to any of claims 1 to 4.

6. A diagnostic method for a valve control device (1) in a process plant (100) with a control valve for adjusting a process fluid flow, an actuator for actuating the control valve, a positioner (31) for generating a control variable for the actuator, and a process controller (120) controlling the valve control device (1), wherein the positioner comprises a first signal input for a command signal, such as a process control signal (pg), from a process controller (120) of the process plant (100) and a second signal input for an actual position signal (i) regarding a control valve (35), wherein the positioner (31) is configured to generate a control variable (g) for the actuator (33) to actuate the control valve based on the command signal and the actual position signal (i) and comprises a control output for the control variable (g), wherein the positioner (31) is provided with a process control signal (pg) by the process controller (120), and wherein a controller model related to a specific controller is configured, characterized in that the positioner (31) determines an approximation signal (ap) based on the process control signal (pg) and the controller model related to the controller as well as a control inversion related to the process controller (120), wherein the controller model is configured such that a signal generated by the specific controller based on the approximation signal (ap) corresponds to the command signal, and wherein the positioner (31) performs at least one diagnostic routine taking into account the approximation signal (ap).

7. The diagnostic method according to claim 6, wherein the determination of the approximation signal (ap) and / or the diagnostic routine is further performed based on process context data (k) characterizing the process setpoint signal (pw).

8. The diagnostic method according to claim 7, wherein a time interval is determined to which the process context data (k) relate and / or wherein the process context data (k) comprise a delay line and / or a signal form definition of the process setpoint signal (pw).

9. The diagnostic method according to any of claims 6 to 8, wherein the process control signal (pg) is stored.

10. The diagnostic method according to any of claims 6 to 9, wherein the controller model is determined based on a predetermined time-continuous or time-discrete controller structure.

11. The diagnostic method according to claim 10, wherein the control inversion is configured to calculate an inverse in the Z-domain over the variable z using an inverted transfer function G of a process PID controller by G approx − 1 z : = z 2 − z a ⋅ z 2 + b ⋅ z + c .

12. The diagnostic method according to any of claims 7 to 11, wherein a comparison of the diagnostic result with a predetermined setpoint behavior of the valve control device (1) is performed.

13. The diagnostic method according to claim 12, wherein a diagnostic code is generated if a deviation between the diagnostic result and the predetermined setpoint behavior is detected during the comparison, and / or wherein a diagnostic code is suppressed and / or deleted if no deviation between the diagnostic result and the predetermined setpoint behavior is detected during the comparison.