Control and procedures for controlling a process and process control system

Abstract

Control (11) for a process, wherein a process signal specifies a process variable of the process and wherein the control comprises the following: a processor (23); and a control module (84) that is set up for periodic execution by the processor and configured to receive non-periodic measurement updates of the process variables and to respond to the process variable to generate a control signal for the process; wherein an iteration of the periodic execution of the control module includes the implementation of a routine (32, 34) configured to generate a reproduction of a process response to the control signal, wherein the reproduction of the process response is calculated on the basis of the last control signal and the time elapsed since the receipt of the last non-periodic measurement update, wherein the routine is further configured to maintain the reproduction over several iterations (40-54) of the periodic execution of the control module and until a new non-periodic measurement update of the process variables is available, wherein the playback of the process response includes a playback of the response of the process variables and wherein the routine is further configured to update the playback of the response of the process variables when the non-periodic measurement update of the process variables is available, wherein the routine is further trained to determine the expected response of the process based on a recent update of the process variables, the control signal, and the time elapsed since the last non-periodic measurement update of the process variables, and the routine is configured to determine an updated reset percentage based on the expected process response to the last update and the time elapsed since the last non-periodic measurement update.

Description

TECHNICAL AREA

[0001] This invention generally relates to process control systems and in particular to the transmission and processing of wireless and / or non-periodic control communications in process control systems. DESCRIPTION OF THE STATE OF THE ART

[0002] Process control systems, such as distributed or scalable process control systems used in chemical, petroleum refining, and other processes, typically comprise one or more process controllers communicating with each other via analog, digital, or combined analog-digital buses, with at least one host or operator workstation, and with one or more field devices. The field devices, which may include valves, valve positioners, switches, and transmitters (e.g., temperature, pressure, and flow rate sensors), perform functions within the process, such as opening or closing valves and measuring process parameters.The process controller receives signals indicating measurements taken by the field devices and / or other information relating to the field devices. It uses this information to implement a control routine that generates control signals sent via buses to the field devices to control process operation. Information from the field devices and the controller is typically made available to one or more applications running from the operator workstation, enabling the operator to perform any desired functions related to the process, such as viewing the current process state, modifying process operations, and so on.

[0003] Some process control systems, such as the DeltaV® system distributed by Fisher Rosemount Systems, Inc., located in Austin, Texas, USA, use function blocks, or groups of function blocks called modules, arranged in the controller or in different field devices to perform control operations. In these cases, the controller or other device can include and execute one or more function blocks or modules, each receiving inputs from other function blocks and / or providing outputs to other function blocks (either in the same device or in different devices) and performing specific process operations, such as measuring or detecting a process parameter, controlling a device, or executing a control operation, such as implementing proportional-integral-derivative (PID) control.The different functional blocks and modules within a process control system are generally configured to communicate with each other (e.g. via a bus) in order to form one or more process control loops.

[0004] Process controllers are typically programmed to execute a different algorithm, subroutine, or control loop (each of which is a control routine) for each loop of a number of loops defined for or contained within a process, such as flow control loops, temperature control loops, and so on. Generally speaking, each of these control loops can include one or more input blocks, such as an analog input (AI) function block, a single-input control block, such as a proportional-integral-derivative (PID) control block or a fuzzy logic control function block, and an output block, such as an analog output (AO) function block. Control routines and the function blocks that implement these routines are configured according to a number of control techniques, such as PID control, fuzzy logic control, and model-oriented techniques.the Smith predictor or the model predictive control (MPC) control.

[0005] To support the execution of routines, a typical industrial or process plant has a central control room that communicates with one or more process controllers and process I / O subsystems, which in turn are connected to one or more field devices. Traditionally, analog field devices were connected to the controller via two- or four-wire current loops for both signal transmission and power supply. An analog field device transmitting a signal to the control room (e.g., a sensor or transmitter) modulates the current flowing through the current loop so that the current is proportional to the process variable being queried. Conversely, analog field devices executing an operation controlled by the control room are controlled by the current in the loop.

[0006] More recently, field devices have been overlaying the current loop used to transmit analog signals with digital data. For example, the Highway Addressable Remote Transducer (HART) protocol uses the loop current to send and receive analog signals, but also overlays the current loop signal with a digital carrier signal to enable two-way field communication with intelligent field devices. Another protocol, generally referred to as the Fieldbus protocol, defines two subprotocols: one that supports data transmission at speeds up to 31.25 kilobits per second while simultaneously powering field devices connected to the network, and the other that supports data transmission at speeds up to 2.5 megabits per second without providing power to field devices.Using communication protocols of this type, field devices, which are normally entirely digital, support a number of maintenance modes and advanced functions not provided by older control systems.

[0007] With the increased volume of data transmission, a particularly important aspect of a process control system concerns how field devices are communicatively connected to each other, to controllers, and to other systems or equipment within a process control system or process plant. Generally, the various communication channels, connections, and paths that enable the operation of field devices in the process control system are collectively referred to as the input / output (I / O) communication network.

[0008] The topology of the communication network and the physical connections or paths used to implement an I / O communication network can significantly impact the robustness or integrity of field device communication, especially when the network is exposed to adverse environmental factors or harsh conditions. These factors and conditions can compromise the integrity of communications between one or more field devices, controllers, and so on. Communications between controllers and field devices are particularly vulnerable to such disturbances because the controller routines typically require periodic updates of process variables for each iteration of the routine.Impaired communication processes could therefore lead to reduced efficiency and / or profitability of the process control system, as well as excessive wear and tear or damage to the equipment and any number of potentially dangerous errors.

[0009] To ensure robust communication, I / O communication networks used in process control systems have traditionally been hardwired. Unfortunately, hardwired networks introduce a number of complexities, challenges, and limitations. For example, the quality of hardwired networks can degrade over time. Furthermore, hardwired I / O communication networks are typically expensive to install, especially when the network serves a large industrial plant or facility spread over a wide area, such as an oil refinery or a chemical plant covering several hectares.The long cabling runs required typically entail significant labor, material, and cost expenditure, and can introduce signal degradation due to cable impedance and electromagnetic interference. For these and other reasons, hardwired I / O communication networks are generally difficult to reconfigure, modify, or upgrade.

[0010] The use of wireless I / O communication networks has been proposed to circumvent some of the difficulties associated with hardwired I / O networks. For example, US Patent Publication No. 2003 / 0043052, entitled "Apparatus for Providing Redundant Wireless Access to Field Devices in a Distributed Control System," the entirety of which is expressly incorporated herein, discloses a system using wireless communication between controllers and field devices to enhance or supplement hardwired communication.

[0011] Generally speaking, the use of wireless communication for control-related transmissions has been limited, partly due to reliability concerns. As described above, modern process control relies on reliable data communication between the controller and field devices to achieve optimized control levels. Furthermore, typical controllers execute control algorithms at high speeds to quickly correct undesirable process deviations. Unfortunately, environmental factors or other conditions can create intermittent interference that hinders or prevents the rapid communication required to support the execution of these control algorithms.

[0012] Power consumption is a further complicating factor in wireless communication operations in process control. When disconnected from the I / O network, field devices may need to provide their own power sources. Accordingly, field devices can be powered by batteries, solar energy, or by utilizing environmental energy such as vibration, heat, pressure, etc. For these devices, the energy consumed for data transmission can represent a significant portion of the total energy consumption. For example, more power may be consumed while attempting to establish and maintain a wireless connection than during other critical operations performed by the field device, such as the steps involved in querying or detecting measured process variables.

[0013] Relevant state of the art is represented by DE 103 04 902 A1 and the scientific-technical publication MONTESTRUQUE, Luis A.; ANTSAKLIS, Panos: Stability of model-based networked control systems with timevarying transmission times. In: IEEE Transactions and Automatic Control, Vol. 49, 2004, No. 9, pp. 1562-1572. - ISSN 0018-9286.

[0014] These each disclose a controller and a control procedure for controlling a process, wherein a process signal specifies a process variable of the process, and wherein the controller comprises: a processor; and a control module set up for periodic execution by the processor and configured to respond to the process variable in order to generate a control signal for the process; wherein an iteration of the periodic execution of the control module includes the implementation of a routine configured to generate a playback of a process response to the control signal, and wherein the routine is further configured to maintain the playback through several iterations of the periodic execution of the control module and until an update of the process variable is available. They further disclose a corresponding process control procedure and system. SUMMARY OF THE REVELATION

[0015] The present invention is defined as a control system with the features of claim 1, a process control system with the features of claim 8, and a method for controlling a process with the features of claims 15 and 18. Advantageous embodiments of the invention are the subject of the respective dependent claims.

[0016] According to one aspect of the disclosure, a controller is useful for a process in which a process signal represents a process variable. The controller comprises a processor and a control module, which is set up for periodic execution by the processor and configured to respond to the process variable in order to generate a control signal for the process. One iteration of the periodic execution of the control module includes and involves the implementation of a routine configured to generate a representation of the process's response to the control signal. The routine is further configured to maintain the representation across multiple iterations of the periodic execution of the control module and until an update of the process variable is available.

[0017] In some cases, the process variable update is made available via wireless transmission of the process signal.

[0018] The control module can include a closed-loop control scheme that uses the process response to determine the control signal. Alternatively or additionally, the routine includes a positive feedback network to determine the process response based on past values ​​of the control signal. Alternatively or additionally, the routine implements a filter algorithm to determine the process response.

[0019] In some cases, the routine is further configured to implement based on non-periodic updates of the process variables. Alternatively or additionally, the process response replay may include a replay of the response of a process variable, and the routine may further be configured to update the replay of the process variable's response when the process variable update is available. The routine can then determine the expected process response based on the last process variable update, the control signal, and the time elapsed since the last process variable update. The routine can also determine an updated reset portion based on the expected process response to the last update and the time elapsed since the last update.The expected response of the process may include a model that incorporates a process or measurement delay.

[0020] According to another aspect of the disclosure, a process control system comprises a field device for transmitting a process signal representing a process variable, and a controller communicating with the field device to receive an update of the process variable via the process signal and to generate a control signal for the process. The controller has a processor and a control module configured for periodic execution by the processor. The field device wirelessly transmits the process signal non-periodically, depending on whether the process variable has changed by more than a predetermined threshold.

[0021] In some embodiments, the field device transmits the process signal if a refresh time has elapsed since the last transmission.

[0022] The routine can be further configured to maintain a replay of the process response, which may be generated by a routine implemented via the periodic execution of the control module, across multiple iterations of the periodic execution of the control module and until the process signal is transmitted by the field device. The control module may include a closed-loop control scheme that uses the replay of the process response to determine the control signal. Alternatively or additionally, the routine may include a positive feedback network to determine the replay of the process response based on past values ​​of the control signal. Alternatively or additionally, the routine may implement a filter algorithm to determine the replay of the process response.Alternatively or additionally, the routine can be further configured to implement the response based on non-periodic updates of the process variables. The process response replay can include a replay of the process variable response, with the routine further configured to update the replay of the process variable response when the process variable update is available. The routine can then determine the expected process response based on the last process variable update, the control signal, and the time elapsed since the last process variable update.

[0023] According to yet another aspect of the disclosure, a method for controlling a process includes the implementation of a process control routine for generating a control signal for the process based on a process variable and detecting whether an update of the process variable is available. The implementation of the process control routine includes or relates to generating a representation of the process's response to the control signal and maintaining the representation of the process's response through several iterations of the implementation step until the update of the process variable has been detected.

[0024] In some cases, the procedure also includes or involves receiving a wireless transmission of a process signal that reflects the updating of the process variables.

[0025] The implementation of the process routine further includes or relates to the execution of a closed-loop control scheme that uses the reproduction of the process response to determine the control signal.

[0026] In some cases, the process response representation includes a representation of the process variable response, so the process control routine implementation further includes or involves updating the representation of the process variable response when the process variable update is available. The control routine implementation may then include or involve determining the expected process response based on the most recent process variable update, the control signal, and the time elapsed since the last process variable update. The control routine implementation may further include or involve determining an updated reset component based on the expected process response to the most recent update and the time elapsed since the last update.

[0027] According to another aspect of the disclosure, a method for controlling a process with a process variable is advantageous. The method includes or relates to the wireless reception of a process signal to obtain an update of the process variable, as well as the periodic implementation of a process control routine to generate the control signal for the process based on the process signal. The reception step is non-periodic, so the process control routine is configured to use non-periodic updates of the process variable, which are received when the process variable changes by more than a predetermined threshold or when a period of time has elapsed since a previous update of the process variable.

[0028] In some cases, the implementation step includes or involves the execution of a routine configured to generate a playback of the process's response to the control signal and to maintain this playback across multiple iterations of the implementation step until the process variable update is available. The process control routine may include a closed-loop control scheme that uses the playback of the process response to determine the control signal. The playback of the process response may include a playback of the process variable's response, so the implementation step further includes or involves updating the playback of the process variable's response when the process variable update is available.The implementation step may further include or involve determining the expected response of the process based on the most recent update of the process variables, the control signal, and the time elapsed since the last update of the process variables. The implementation step may further include or involve determining an updated reset component based on the expected response of the process to the most recent update and the time elapsed since the last update. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] For a more comprehensive understanding of the revelation, reference is made to the following detailed description and the accompanying drawings, where identical numbers denote identical elements in the figures. They show: Fig.Figure 1 is a schematic representation of a process control system comprising a controller configured according to one aspect of the disclosure to implement one or more control routines using non-periodic or less frequent control communication operations transmitted via hard-wired connections between the controller and a number of field devices. Fig. Figure 2 is a schematic representation of the implementation of a control routine by the in Fig. 1. Control represented via a graphic showing a process response to a process input and exemplary instances of measurement transfers and iterations of control execution. Fig.Figure 3 is a schematic representation of a process control system with a controller configured according to one aspect of the disclosure to implement one or more control routines using non-periodic or less frequent control communication operations transmitted via wireless links between the controller and a number of field devices. Fig. 4 is a schematic representation of the in Fig. 1 or in Fig. 3. Control system as described in one embodiment, wherein the control system generates a process input signal to control a process despite wireless, non-periodic or other transmission of measurements at a lower frequency than the execution rate of the control system. Fig.Figure 5 is a schematic representation of a control system according to an alternative embodiment, configured to control a process with a process and / or measurement delay.

[0030] Although the disclosed system and method exist in various embodiments, specific embodiments of the invention are shown in the drawing (and in the following description), whereby the disclosure is intended for illustrative purposes and is not intended to limit the invention to the specific embodiments described and shown here. DESCRIPTION OF PREFERRED EXECUTION FORMS

[0031] A process control system and a method are described that implement communication and control techniques to support the transmission of process control data between a controller and field devices such as transmitters and other equipment. According to a further aspect of the disclosure, the disclosed techniques enable the controller to use process measurements and other information acquired by the field devices when implementing one or more process control routines.

[0032] Up to now, such measurements have been received and transmitted by the controller on a regularly spaced or periodic basis to ensure that the updated data was available for each iteration of the periodic execution of the process control routines. In contrast, the disclosed techniques enable the transmission of such data non-periodically and / or at intervals longer than the controller's execution period. Consequently, the disclosed techniques may be well suited to supporting process control measurements that can be provided less frequently or irregularly. Irregular or less frequent transmissions may be advantageous for a number of reasons, and they may arise from any number of factors, conditions, or aspects of the process control system or its environment.

[0033] According to some embodiments, the disclosed techniques are used in conjunction with communication schemes, such as wireless communications, that involve the transmission of process control data based on exception reporting. Exception reporting of process control data in the context of wireless communication can offer several advantages. For example, the amount of power consumed by transmitters and other field devices can be reduced, thereby saving battery power or other limited power sources.

[0034] Unlike previous exception reporting methods, the disclosed techniques support the transmission of data used in a periodically executed process control routine. And despite past discouraging experiences with executing process control routines using data triggered by events, the use of these disclosed techniques integrates the periodic execution of process control routines without significant performance degradation.

[0035] Although the disclosed techniques are well suited for wireless communication schemes and are occasionally described here in this context, they are not limited to any particular communication scheme, context, or protocol, nor to any process control network, architecture, controller, or system. Rather, the disclosed techniques can be applied in any number of contexts where process control data is transmitted less frequently with respect to the frequency of the execution period and for any desired reason. Accordingly, the following description is given with the understanding that the use of the disclosed techniques is not limited to the low-energy wireless communication context described below.

[0036] With reference to Fig.1 comprises a process control system 10, a process controller 11, which is connected to a data historian 12 and one or more host workstations or computers 13 (which can be any type of personal computer, workstation, etc.), each of which has a display screen 14. The controller 11 is also connected to field devices 15-22 via input / output (I / O) cards 26 and 28. The data historian 12 can be any desired type of data acquisition unit with any desired storage type and with any desired or already known software, hardware, or firmware for storing data. The data historian 12 can (as shown in the illustration in Fig.1) may be located separately from the workstations 13, or it may be part of one of the workstations. The controller 11, which may be, for example, the DeltaV Controller distributed by Fisher-Rosemount Systems, Inc., is communicatively connected to the host computers 13 and to the data historian 12 via an Ethernet connection or any other desired communication network. The controller 11 is also communicatively connected to the field devices 15-22 using a hardwired or wireless communication scheme, as described below. In each case, any desired hardware, software, and firmware may be used to implement the schemes, which may be associated, for example, with standard 4-20 mA devices (in the case of hardwiring) and / or any intelligent communication protocol, such as the FOUNDATION fieldbus protocol, the HART protocol, etc. In the Fig.In the exemplary embodiment shown in 1, however, the communication processes between the controller 11 and the field devices 15-22 use hard-wired connections.

[0037] In general, field devices 15-22 can be any type of field device, such as sensors, valves, transmitters, positioners, etc., while I / O cards 26 and 28 can be any type of I / O device that meets the requirements of any desired communication operations or communication protocols. In the Fig.In the embodiment shown in Figure 1, the field devices 15-18 are standard 4-20 mA devices that communicate with the I / O card 26 via analog lines, while the field devices 19-22 are intelligent devices such as fieldbus devices that communicate with the I / O card 28 via a digital bus using fieldbus protocol communication operations. Of course, the field devices 15-22 can conform to any other desired standards or protocols, including any standards or protocols that may be developed in the future.

[0038] The controller 11 comprises a processor 23 that implements or monitors one or more process control routines stored in a memory 24 (or any modules, blocks, or subroutines thereof). The process control routines stored in memory 24 may contain or be associated with control loops stored therein. In general terms, the controller 11 communicates with the devices 15-22, the host computers 13, and the data historian 12 to control a process in any desired manner. It should be noted that parts of any control routines or modules described herein can be implemented or executed by different controllers or other devices as needed. Accordingly, the control routines or modules described herein can be implemented in any form, including software, firmware, hardware, etc., for use in the process control system 10.For the purposes of this disclosure, a control module can be any part or section of a process control system stored on any computer-readable medium, including, for example, a routine, a block, or any element thereof. Control routines, which can be modules or any part of a control procedure, such as a subroutine, parts of a subroutine (like lines of code), etc., can be implemented in any desired software format, such as using object-oriented programming, ladder logic, sequential function chart (SFC) state diagrams, function block diagrams, or any other software programming languages ​​or design paradigms. Accordingly, the control routines can be hard-coded, for example, in one or more EPROMs, EEPROMs, application-specific integrated circuits (ASICs), or any other hardware or firmware elements.Furthermore, the control routines can be designed using any design tools, including graphical design tools and software / hardware / firmware programming or design tools of any other type. Thus, the controller 11 can be configured in any desired way to implement a control strategy or control routine.

[0039] In some embodiments, the controller 11 implements a control strategy or control scheme using components generally referred to as function blocks, each function block being an object or other part (e.g., a subroutine) of an overall control routine that operates (via communication operations referred to as links) in conjunction with other function blocks to implement the process control loops in the process control system 10. Function blocks typically perform an input function, such as the input function associated with a transmitter, sensor, or other measuring device for process parameters; or they perform a control function, such as the control function associated with a control routine that performs PID, fuzzy logic control, etc.; or they perform an output function that controls the operation of certain devices, such as...the operation of a valve to perform certain physical functions in the process control system 10. Of course, hybrid and other types of function blocks exist that can be used for this purpose. The function blocks can be stored and executed by the controller 11, which is usually the case when the function blocks are used for or associated with standard 4-20 mA devices and some types of intelligent field devices, such as HART devices. Alternatively or additionally, the function blocks can be stored and implemented by the field devices themselves, as may be the case with fieldbus devices. While the description of the control system 10 is provided here using a function-block-based control strategy, the disclosed techniques and the system can also be implemented or designed using other conventions, such as...from ladder logic, state diagrams in sequential function chart (SFC) etc., or using any other desired programming languages ​​or paradigms.

[0040] According to the presentation by the in Fig.Block 30, shown as an exploded view, can comprise a series of single-loop control routines, represented as routines 32 and 34, and, if required, it can implement one or more extended control loops, shown as control loop 36. Each of these loops is commonly referred to as a control module. Single-loop control routines 32 and 34 are shown to perform single-loop control using a single-input, single-output fuzzy logic control block and a single-input, single-output PID control block, each connected to associated analog input (AI) and analog output (AO) function blocks that can be associated with process control devices such as valves, measuring devices such as temperature and pressure transmitters, or any other devices in the process control system 10.The extended control loop 36 is depicted as comprising an extended control block 38, the inputs of which are communicatively connected to one or more AI function blocks and the outputs of which are communicatively connected to one or more AO function blocks, although the inputs and outputs of the extended control block 38 may be connected to any other desired function blocks or control elements to receive other types of inputs and to provide other types of control outputs. The extended control block 38 can implement any type of multi-input, multi-output control scheme, and it may form or comprise a model predictive control (MPC) function block, a neural network modeling or control block, a multi-variable fuzzy logic function block, a real-time optimizer block, and so on. It is evident that the in . Fig.The functional blocks shown in 1, including the extended control block 38, can be executed by the controller 11 or alternatively arranged in and executed by any other processing units, including one of the workstations 13 or one of the field devices 19-22.

[0041] With reference to Fig.2 is the implementation of each of the control loops 32, 34, and 36 generally set up for periodic execution over several iterations 40 of the control routine. In a conventional case, each iteration 40 is supported by an updated process measurement 42, provided, for example, by a transmitter or other field device. To avoid the limitations of synchronizing the measured value with the control, many controllers (or control loops) have previously been designed to oversample the measurement by a factor of 2 to 10. This oversampling was helpful in ensuring that the process measurement was current for use in the control scheme. To minimize control variation, conventional concepts also stipulated that the feedback control should be executed 4 to 10 times faster than the process response time, which is specified in Fig.2 is represented as a time constant of the process plus a process delay after a step change 44 in the process input. More generally, the process response is indicated by a change in a process output or variable 46 over time. To comply with these requirements of conventional concepts, the measured value was determined according to the representation in Fig. 2 is therefore often sampled much faster than the process reacts.

[0042] In general terms, the disclosed techniques address the task of transmitting measured values ​​at such high rates. As described above, for example, the sampling functionality associated with the measurement may not consume much of the energy supplied to the sensor or transmitter, but transmitting the measured value over a wireless communication link can represent a significant energy drain over time. Even when, as in Foundation Fieldbus control schemes, the measurement and control execution are synchronized, the conventional approach of control scheduling, which is 4-10 times faster than the process response, can still lead to excessive power consumption during data transmission. To reduce energy consumption by the transmitter, the disclosed techniques therefore generally support minimizing the frequency with which a measured value is communicated.

[0043] To this end, and in accordance with one aspect of the disclosure, the disclosed techniques generally configure the process control system 10, the controller 11, the transmission, and other related field devices to transmit a new measurement value on a non-periodic basis when certain conditions are met. In one embodiment, a new measurement value is transmitted depending on whether the process variable has changed by more than a predetermined threshold (e.g., an amount recognized as significant). In particular, if the magnitude of the difference between the new measurement value and the last communicated measurement value is greater than a predetermined resolution, a trigger can be generated so that the measurement is updated.

[0044] In other cases, a new measurement is transmitted when the difference exceeds the specified resolution (as in the example above), as well as when the time since the last communication exceeds a predetermined refresh time. In other words, both a change in the process variables (e.g., the process response between iterations 48 and 50 of the control execution) and the elapse of a predetermined time (e.g., the time elapsed between iterations 52 and 54) can trigger a measurement transmission. The refresh time or the predetermined time for measurement transmission can differ between control loops, insofar as more or less frequent updates may be appropriate depending on whether the process reacts slowly or quickly (for example, according to the process's time constant).In some cases, a determination based on the time constant can be made during the control loop setup and subsequently adjusted if necessary. In any case, the predefined or refresh time acts as an integrity check or override process after periods without a measurement update. Such checks can be useful, for example, to enable the final targeting of the process variables.

[0045] In the meantime, the transmitter, sensor, or other field device responsible for receiving the measured values ​​can continue to periodically query the measurement at any desired frequency, such as 4-10 times faster than the process response time. The disclosed techniques then determine whether the queried values ​​are transmitted to the controller 11.

[0046] Fig.Figure 3 provides an exemplary case in which the disclosed techniques can be used to reduce energy consumption during the wireless communication of process control data to support the operation of the controller and, in particular, the in Fig. 1 to reduce the process control system 10 shown in the image. However, it should be noted in principle that the in Fig. 1 and Fig.The hardwired connections shown in section 3 can also utilize and benefit from the application of the disclosed techniques. For example, one or more of the hardwired devices can also be based on a limited power supply or otherwise benefit from the reduced data transmission. In an exemplary case, system 10 can include a sampled analyzer or other sampling system designed to provide measurement data at rates slower than the execution rate of the controller.

[0047] It should also be noted that, for the sake of clarity, a number of field devices have been added to the process control system 10, with the field devices 15-22 remaining hardwired to the controller 11 via the I / O devices 26 and 28. In alternative embodiments, one or more field devices 15-22 can additionally or alternatively communicate wirelessly with the controller 11 according to the disclosed techniques.

[0048] At the in Fig.However, in the exemplary case described in Figure 3, the disclosed techniques relate to the wireless transmission of data measured or sampled by transmitters 60-64. The wireless communication processes can be implemented using any desired equipment, including existing or future hardware, software, firmware, or a combination thereof. The exemplary equipment of this embodiment is represented by an antenna 65 connected to and associated with transmitter 60, and by a wireless router or other module 66 with an antenna 67 for jointly managing communication processes of transmitters 61-64.In some cases, the transmitters 60-64 may represent the only link between the process sensors and the control room and, as such, rely on transmitting accurate signals to the control network to ensure that product quality and throughput are not compromised. Thus, the transmitters 60-64, often referred to as process variable transmitters (PVTs), can play a significant role in the process control system 10.

[0049] On the receiving end of the wireless communication links, the controller 11 can have one or more I / O devices 68 and 70 with associated antennas 72 and 74. More generally, the use of the disclosed techniques is not limited to a configuration of transmitters and wireless devices.

[0050] Each of the transmitters 60-64 or each of the other field devices transmits a process signal to the controller 11 for use in one or more control loops or routines. This process signal specifies an associated process variable (e.g., flow, pressure, temperature, or level). In general terms, the controller 11 can comprise a number of elements designed to support wireless communication and, in particular, to receive the process signals. These elements can include, for example, software routines stored in memory 24 or hardware or firmware located elsewhere in the controller 11. In any case, the way in which the wireless communication processes are received (e.g., demodulated, decoded, etc.) can take any desired form and is only discussed here in general terms.In one example, the controller 11 can include a communication stack 80 for processing the incoming signals and a module or routine 82 for detecting when an incoming signal has provided a measurement update. The detection routine 82 can then generate a flag or other signal to indicate that data provided via the communication stack 80 contains a new measurement or measurement update. The new data and update flag can then be provided to one or more control modules 84 to perform the following actions as described above in conjunction with the general functions described in [reference to relevant document]. Fig. The routines shown in section 1 and described in more detail below will be implemented.

[0051] In some cases, the communication stack 80 and the detection module 82 are used for updates by one or more I / O devices 26, 28, 68 and 70 ( Fig.1 and Fig. 3) implemented. Furthermore, the way in which the detection module 82 determines updates can involve hardware, software, firmware, or any combination thereof, and it can include any suitable routines for comparing the values ​​of the process variables.

[0052] The communication techniques described above for wireless (or other) transmitters generally result in non-periodic, irregular, or otherwise less frequent data transmissions. However, the communication of measured values ​​from the control devices 11 is traditionally structured for periodic reporting in order to support the periodic execution of the control routine(s). In other words, the control routines are generally designed for, and based on, periodic updates of the measured values.

[0053] To accommodate non-periodic measurement updates, another aspect of the disclosure generally focuses on modifying or restructuring the control routine(s). In this way, the process control system 10 can be based on non-periodic or other updates that occur less frequently than the control execution period. Consequently, despite the periodic execution of the process control routines, the disclosed techniques generally support a form of exception reporting for the measurements of the process variables.

[0054] The underlying assumption in the control concept (e.g., Z-transformation, differential equations) and the digital implementation of control routines such as proportional-integral-derivative (PID) control is that the algorithm executes on a periodic basis. If the measurement is not updated, steps such as the integral (or reset) section or portion of the routine may be incorrect. For example, if the control algorithm continues to execute using the last, outdated measurement, the output will continue to fluctuate based on the reset setting and the error between the last measurement and the setpoint. Conversely, if the control routine only executes when a new measurement is communicated, the control response to setpoint changes and feedback processes during measured disturbances could be delayed.Control routines can also include calculations based on the time elapsed since the last iteration. However, for non-periodic and / or less frequent transfers, calculating the reset component based on the control execution period (i.e., the time since the last iteration) can lead to increased process variability.

[0055] In light of the aforementioned challenges and to provide accurate and responsive control when measured values ​​are not updated periodically, control techniques are disclosed here that generally modify the process control routine depending on whether an update of the process variables is available. In some cases, the control routine can be restructured according to the disclosed techniques based on the expected process response since the last measurement update.

[0056] In Fig.Figure 4 shows an exemplary embodiment of a control scheme configured according to one aspect of the disclosed techniques, the process being specified generally and schematically at Figure 100. The exemplary control scheme can correspond to a component 102 (or, if necessary, a group of components) of the control 11, which is configured according to the representation and description in connection with Figure 102. Fig. 3 are configured to provide the functionality of the communication stack 80, the detection module 82 for updates, and the control module 84. In general terms, the controller 11 receives a setpoint, for example, from one of the workstations 13 ( Fig.1) or from another source in or communicating with the process control system 10 to generate one or more process inputs or other control signals for controlling the process 100, which may be subject to measured or unmeasured disturbances as schematically represented in 104. According to the foregoing description, the process input signal(s) can control an actuator associated with a valve or any other field device to produce a response during process operation. The process response to changes in the process input signal is measured or queried by a transmitter, sensor, or other field device 106, such as any of the... Fig.This can correspond to the transmitters 60-64 shown in Figure 3. Accordingly, the communication link between transmitter 106 and controller 11 (shown with dashed lines) can include a wireless connection. Alternatively or additionally, the communication processes can, if necessary, include a hard-wired connection that can utilize the disclosed techniques because, for example, it is intermittently available or operational.

[0057] In this exemplary case, the controller 11 implements a control routine with a single control loop, such as the PI control routine. Accordingly, the control loop has several standard elements of the PI control scheme, including a summing point 108 for comparing the setpoint with the data of the process variables, as well as a proportional gain element 112, another summing point 112 for combining, for example, the proportional and integral contributions, and a high-low limiter 114. In addition to the standard elements of the control scheme, this embodiment of the disclosed control technology uses a modified filter 116 to provide an indication of the expected process response for the control signal.In this exemplary case, the expected process response is classified as primary and is implemented by the modified filter contained in the positive feedback loop, which determines the integral part of the PI control scheme. More generally, the expected process response used in the control implementation can be provided by any process model and is not limited to integration into a positive feedback loop, a filter, or an integral or reset part. For example, using a model to provide the expected process response, the control can include a differential part, so the control routine implements a PID control scheme.

[0058] The modified filter 116 differs from a traditional reset or integral component in several ways. As background information, traditional PI control can be implemented using a positive feedback network to determine the reset component. It can be mathematically shown that the transfer function for the traditional implementation is equivalent to the standard formula for unrestricted control, i.e., unlimited output: O(s)E(s)=KP(1+1sTReset) with Kp=proportional gain TReset = Reset, seconds

[0059] One advantage of the positive feedback network is that the increase in the reset component is automatically prevented if the control output is limited upwards or downwards, such as by limiter 114.

[0060] According to one aspect of the disclosure, the control technique implemented by the disclosed system and method includes the use of a non-periodic measurement update of the process variables. The positive feedback network of the reset component (or another filter or routine) is modified to accommodate such updates. In particular, filter 116 (or the other routine) is configured to retain the last calculated filter output until a new measurement is communicated (e.g., received). When a new measurement is received, filter 116 calculates the new filter output based on the last control output (i.e., the control signal) and the time elapsed since the communication of a new measurement. An exemplary case of this control technique is given below: FN=FN−1+(ON−1−FN−1)∗(1−eT−ΔTReset) with F N = new filter output FN-1 = Filter output on last run = Filter output after last new measurement O N-1 = Control output on last execution ΔT = elapsed time since the communication of a new value

[0061] In this way, the control routine takes into account the expected process response to the last measurement transmission, based on the new measurement, when calculating the control input. As a result, the transmitter can implement any communication technique, such as those described above, where an update is not provided for every iteration of the control execution. For wireless communication techniques, this allows wireless transmitters and other equipment to minimize the amount of energy consumed as a result of data transmission for process control.

[0062] It should be noted that the reset component of a control routine with a closed-loop system, such as the one described above, can provide an accurate representation of the process response in several ways, as if the process were exhibiting, for example, continuous-state behavior. Other processes, such as dead-time dominant processes, may involve the inclusion of additional components in the routine that models the expected process response, as described below. However, with respect to processes represented by a first-order model, the process time constant can be used to determine the reset time for the PI (or PID) control. In particular, if the reset time is set equal to the process time constant, the reset component cancels out the proportional component, so that the routine reflects the expected process response over time. This approach is described in the Fig.The exemplary embodiment shown in Figure 4 illustrates this, wherein the reset component is introduced by a positive feedback network that has a filter with the same time constant as the time constant of the process. Although other models can be used, the network, filter, or positive feedback model provides a convenient mechanism for determining the expected response of a process with a known or approximately estimated time constant.

[0063] For example, the number of communication operations during a test was reduced by more than 96% using the disclosed techniques when the rules for wireless communication were followed. The impact of non-periodic updates on control performance was also minimized by using the modified PI algorithm described above. In particular, the difference in control performance is shown in Table 1 below, which compares the integral absolute error (IAE) for periodic measurement updates versus non-periodic updates. TABLE 1 - DIFFERENCE IN CONTROL PERFORMANCE Communication processes / control Number of communication processes IAE Periodic / Standard PI Control: Revealed Techniques 692 123 (Non-periodic communication with modified PI control) 25 159

[0064] For processes requiring PID control, the rate component for the PID output can only be recalculated and updated when a new measurement is received. In such cases, the differential calculation can similarly utilize the time elapsed since the last new measurement.

[0065] According to the representation in Fig. 4. The communication stack 80 and, in some embodiments, the detection module 82 process updates ( Fig. 3) The data received from transmitter 106 is used to generate a new value flag for the modified filter 116. This new value flag is provided to the modified filter 116 to determine when the new filter output should be calculated.

[0066] With reference to Fig. 5 is an alternative control system 120 configured according to the disclosed control techniques from many perspectives of the in Fig.The control 11 shown in Figure 4 is similar. Accordingly, elements common to both control systems are designated with the same identifiers. However, control 120 extends the routine by an additional element that determines the expected process response between measurement transfers. In this case, the process can be characterized by having a considerable amount of dead time, and therefore the model includes a unit or block 122 for compensating the dead time. The inclusion of the dead time unit 122 is generally helpful for obtaining a more accurate representation of the process response. In particular, the dead time unit 122 can be implemented in any desired way, and it can include or use methods common in Smith predictor controls or other known control routines.

[0067] As illustrated by the embodiments described above, the feedback, filtering, or other routines that determine the expected process response to the control signal can include any type of model, network, or other arrangement of process control elements that are useful in removing offset or other errors from the rest of the process control routine. In this way, the disclosed techniques are well suited for a wide variety of processes and are not limited to those exhibiting first-order behavior. Conversely, the disclosed techniques are applicable in contexts where different models, filters, or blocks are involved in determining the expected process response and need not be limited to situations where the process model is highly accurate.

[0068] As described above, the disclosed techniques support a process control configuration that avoids the need for oversampling process variables, thereby enabling the use of wireless communication and other transmitter scenarios, where measured values ​​may not be available regularly or as frequently as the control execution period. In short, the disclosed techniques circumvent the requirement to constantly transmit measurement data for the execution of the process control routine. As a result of the disclosed modifications to the transmitter (or other field device) concept and the modified control, measured values ​​are generally transmitted only to communicate significant changes (of the last communicated value) or changes after a refresh period.Consequently, both the frequency of transmitter communication processes and the amount of energy consumed for data transmission are significantly lower.

[0069] The use of the disclosed methods, systems, and techniques is not limited to any particular wireless architecture or communication protocol. Suitable exemplary architectures and schemes for communication support are described in US 2005 / 0 276 233 A1. Thus, the disclosed modifications to the control routines are well suited for any context in which the control routine is implemented periodically but without measurement updates of the process variables for each iteration of the control. Other exemplary contexts include the case where a sampled value is provided irregularly or less frequently, for example, by an analytical facility or via laboratory samples.

[0070] The application of the disclosed technique is not limited to PI or PID control routines with a single input and a single output, but the technique can be applied to a range of different control schemes with multiple inputs and / or multiple outputs and to cascaded control schemes. More generally, the disclosed technique can also be applied in the context of any model-based control routines with a control loop that involve one or more process variables, one or more inputs, or other control signals, such as in a model predictive control (MPC) system.

[0071] The term "field device" is used here in a broad sense and encompasses a range of devices or combinations of devices (i.e., devices that provide multiple functions, such as hybrid transmitters / actuators) as well as any other devices that perform a function in a control system. In any case, field devices can include, for example, input devices (e.g., devices such as sensors and instruments that provide status, measurement, or other signals indicating process control parameters such as temperature, pressure, flow rate, etc.) as well as control operators or actuators that perform operations in response to commands received from controllers and / or other field devices.

[0072] If any software described herein is implemented, it may be stored in any computer-readable memory, such as on a magnetic disk, a laser disk, or any other storage medium, in the RAM or ROM of a computer or processor, etc. Accordingly, the software may be made available to a user, process plant, or operator workstation by any known or desired method of delivery, such as on a computer-readable data carrier or other portable computer storage mechanism, or via a communication channel such as a telephone line, the Internet, the World Wide Web, any other local area network (LAN), or wide area network (WAN) (which shall be considered equivalent or interchangeable with respect to the provision of such software via a portable storage medium).Furthermore, this software can be provided directly without modulation or encryption, or it can be modulated and / or encrypted before transmission over a communication channel using any suitable modulation carrier wave and / or encryption technique.

Claims

[1] Control (11) for a process, wherein a process signal specifies a process variable of the process and wherein the control comprises: a processor (23); and a control module (84) that is set up for periodic execution by the processor and configured to receive non-periodic measurement updates of the process variables and to respond to the process variable to generate a control signal for the process; wherein an iteration of the periodic execution of the control module includes the implementation of a routine (32, 34) configured to generate a reproduction of a process response to the control signal, wherein the reproduction of the process response is calculated on the basis of the last control signal and the time elapsed since the receipt of the last non-periodic measurement update, wherein the routine is further configured to maintain the reproduction over several iterations (40-54) of the periodic execution of the control module and until a new non-periodic measurement update of the process variables is available, wherein the playback of the process response includes a playback of the response of the process variables and wherein the routine is further configured to update the playback of the response of the process variables when the non-periodic measurement update of the process variables is available, wherein the routine is further trained to determine the expected response of the process based on a recent update of the process variables, the control signal, and a time elapsed since the last non-periodic measurement update of the process variables, and the routine is configured to determine an updated reset percentage based on the expected process response to the last update and the time elapsed since the last non-periodic measurement update. [2] Control (11) according to claim 1, wherein the measurement update of the process variables is provided via a wireless transmission of the process signal. [3] Control (11) according to claim 1, wherein the control module (84) comprises a control scheme with a control loop (36) or control circuit which uses the reproduction of the process reaction to determine the control signal. [4] Control (11) according to claim 1, wherein the routine (32, 34) comprises a positive feedback network (36) to determine the reproduction of the process response based on previous values ​​of the control signal. [5] Control (11) according to claim 1, wherein the routine (32, 34) implements a filter algorithm to determine the reproduction of the process reaction. [6] Control (11) according to claim 1, wherein the routine (32, 34) is further configured for implementation based on non-periodic updates of the process variables. [7] Control (11) according to claim 1, wherein the expected process response comprises a model that includes a process or measurement delay. [8] Process control system (40) for a process with a process variable, comprising the following: a field device (15-22) for transmitting a process signal that specifies the process variable of the process; and a controller (11) in communication with the field device for receiving a non-periodic measurement update of the process variables via the process signal and for generating a control signal for the process, wherein the controller has a processor (23) and a control module (84) which is set up for periodic execution by the processor; wherein the field device wirelessly transmits the process signal non-periodically depending on whether the process variable has changed by more than a predetermined threshold value, and wherein the periodic execution of the control module generates a reproduction of a process response to the control signal, such that the reproduction of the process response includes a reproduction of the response of the process variables, wherein the reproduction of the process response is calculated on the basis of the last control signal and a last update of the process variables as well as the time elapsed since the receipt of the last non-periodic measurement update, where the routine (32, 34) is further configured to update the display of the response of the process variables when the non-periodic measurement update of the process variables is available, wherein the routine is further trained to determine the expected response of the process based on a recent update of the process variables, the control signal, and a time elapsed since the last non-periodic measurement update of the process variables, and the routine is configured to perform an updated reset portion or The reset percentage is determined based on the expected process response to the last update and the time elapsed since the last non-periodic measurement update. [9] Process control system (10) according to claim 8, wherein the field device (15-22) transmits the process signal when a refresh time has been exceeded since a last transmission. [10] Process control system (10) according to claim 8, wherein the periodic execution of the control module implements a routine (32, 34) configured to generate a reproduction of a process response to the control signal. [11] Process control system (10) according to claim 10, wherein the routine (32, 34) is further configured to maintain the reproduction of the process response over several iterations of the periodic execution of the control module and until the process signal is transmitted by the field device. [12] Process control system (10) according to claim 10, wherein the control module (84) comprises a control scheme with a control loop (36) which uses the reproduction of the process reaction to determine the control signal. [13] Process control system (10) according to claim 10, wherein the routine (32, 34) comprises a positive feedback network (36) to determine the reproduction of the process response based on previous values ​​of the control signal. [14] Process control system (10) according to claim 10, wherein the routine (32, 34) implements a filter algorithm to determine the reproduction of the process response. [15] Method for controlling a process with a process variable, wherein the method comprises the following steps: Implementation of a process control routine to generate a control signal for the process depending on the process variable; and Detection of whether a non-periodic measurement update of the process variables is available; wherein the implementation of the process control routine includes the step of generating a reproduction of a process response to the control signal, such that the reproduction of the process response includes a reproduction of the response of the process variables, wherein the reproduction of the process response is calculated on the basis of the last control signal and a last update of the process variables as well as the time elapsed since the receipt of the last non-periodic measurement update, and Maintaining the representation of the process response across multiple iterations of the implementation step until a new non-periodic measurement update of the process variables is detected, wherein the reproduction of the process response includes a reproduction of the response of the process variables and wherein the implementation step further includes the step of updating the reproduction of the response of the process variables if the non-periodic measurement update of the process variables is available, wherein the implementation step further includes the step of determining the expected response of the process based on a last non-periodic measurement update of the process variables, the control signal and a time elapsed since the last non-periodic measurement update of the process variables, and where the implementation step finally includes the step of determining an updated reset fraction based on the expected response of the process to the last non-periodic measurement update and the time elapsed since the last non-periodic measurement update. [16] Method according to claim 15, further comprising the step of receiving a wireless transmission of a process signal indicating the non-periodic measurement update of the process variables. [17] Method according to claim 15, wherein the implementation step further comprises the step of executing a control scheme with a control loop which uses the reproduction of the process response to determine the control signal. [18] Method for controlling a process with a process variable, wherein the method comprises the following steps: Wireless reception of a process signal to obtain an update of the process variables; and Periodic execution of a process control routine to generate a control signal for the process based on the process signal; wherein the receive step is non-periodic, so that the process control routine is configured to use non-periodic updates of the process variables that are received because of the change of the process variables by more than a predetermined threshold or because of a time elapsed since a previous update of the process variables, wherein the implementation step (a) includes generating a reproduction of a process response to the control signal, such that the reproduction of the process response includes a reproduction of the response of the process variables, the reproduction of the process response being calculated on the basis of the last control signal and a last update of the process variables and the time elapsed since the last non-periodic measurement update was received, (b) includes the step of maintaining the representation of the process response through several iterations of the implementation step and until an update of the process variables is available, (c) the step of determining the expected response of the process includes, based on a recent update of the process variables, the control signal and the time elapsed since the last update of the process variables, (d) the step of determining an updated reset fraction based on the expected response of the process to the last update and the time elapsed since the last update, and (e) includes the step of updating the display of the response of the process variables, if the process variable update is available. [19] Method according to claim 18, wherein the process control routine comprises a control scheme with a control loop which uses the reproduction of the process response to determine the control signal.

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