Modulating control valve

Transcription

1 Modulating control valve

2 Automatic modulating valve Automatic modulating valve Diaphragm Pneumatic Actuator Positioner Pneumatic Actuator Positioner Air filter regulator gauge = AIRSET BALL VALVE GLOBE TYPE CONTROL VALVE

3 Principle of modulating control Pressure application Temperature application Level application Flow application

4 Principle of modulating control Pressure transmitter Temperature transmitter Level transmitter Flow transmitter Modulating controller PLC Programmable Logic Controller DCS Distributed Control System

5 Principle of modulating control Pressure application Temperature application Level application Flow application

6 Why do we need positioner? At factory, the control valve is set without any fluid flowing through the control valve, we call this bench setting. The co-relationship between air supply pressure & the % of valve opening is represented with BLUE line in the above chart When the fluid is introduced into the control valve, a normally closed control valve s co-relationship between air supply pressure & the % of valve opening will be shifted as shown in the above chart with RED line

7 Why do we need positioner? At factory, the control valve is set without any fluid flowing through the control valve, we call this bench setting. The co-relationship between air supply pressure & the % of valve opening is represented with BLUE line in the above chart When the fluid is introduced into the control valve, a normally open control valve s co-relationship between air supply pressure & the % of valve opening will be shifted as shown in the above chart with RED line

8 Why do we need positioner? For many applications, the 0.2 to 1 bar pressure in the diaphragm chamber may not be enough to cope with friction and high differential pressures. A higher control pressure and stronger springs could be used, but the practical solution is to use a Positioner. Positioner is an additional item (see Figure ), which is usually fitted to the yoke or pillars of the actuator, and it is linked to the spindle of the actuator by a feedback arm in order to monitor the valve position. It requires its own higher-pressure air supply, which it uses to position the valve. A valve positioner relates the input signal and the valve position, and will provide any output pressure to the actuator to satisfy this relationship, according to the requirements of the valve, and within the limitations of the maximum supply pressure.

9 Why do we need positioner? A positioner translates the input signal received from a controller to a required valve s position & supplies the valve s actuator with the required air pressure to move the valve into the correct position A positioner ensures that there is a linear relationship between the signal input pressure from the control system and the position of the control valve. This means, that for a given input signal, the valve will always attempt to maintain the same position regardless of changes in valve differential pressure, stem friction, diaphragm hysteresis and so on. A valve positioner relates the input signal and the valve position, and will provide any output pressure to the actuator to satisfy this relationship, according to the requirements of the valve, and within the limitations of the maximum supply pressure

10 Smart valve positioner

11 Output signal The output signals from most control systems are low power 4-20 ma analogue signals but there is a growing use of digital systems such as HART, Foundation Fieldbus ' DeviceNet or 'Profibus '. An analogue system provides a continuous but modulating signal Whereas a digital system provides a stream of binary numeric values represented by a change between two specific voltage levels or frequencies.

12 Problem with analog signal Noise & Grounding In transmitting 4-20 ma analog signals across a process plant or factory floor, one of the most critical requirements is the protection of data integrity. However, when a data acquisition system is transmitting low level analog signals over wires, some signal degradation is unavoidable and will occur due to noise and electrical interference. Noise and signal degradation are two basic problems in analog signal transmission. Noise is defined as any unwanted electrical or magnetic phenomena that corrupt a message signal. Noise can be categorized into two broad categories based on the source-internal noise and external noise. While internal noise is generated by components associated with the signal itself, external noise results when natural or man-made electrical or magnetic phenomena influence the signal as it is being transmitted. Noise limits the ability to correctly identify the sent message and therefore limits information transfer. Some of the sources of internal and external noise include: Electromagnetic interference (EMI); Radio-frequency interference (RFI); Leakage paths at the input terminals; Turbulent signals from other instruments; Electrical charge pickup from power sources; Switching of high-current loads in nearby wiring; Self-heating due to resistance changes; Arcs; Lightning bolts; Electrical motors; High-frequency transients and pulses passing into the equipment; Improper wiring and installation; Signal conversion error; and Uncontrollable process disturbances etc.

13 Analog signal Imagine two people, person A and person B, each on opposite hilltops and each with a flag and a flag-pole. The aim is for person A to communicate to person B by raising his flag to a certain height. Person A raises his flag half way up his pole. Person B sees this and also raises his flag halfway. As person A moves his flag up or down so does person B to match. This would be similar to an analogue system.

14 Digital signal Now assume that person A does not have a pole but instead has two boards, one with the figure '0' and the other with the figure '1', and again wants person B to raise his flag half way, that is to a height of 50% of his flag-pole. The binary number for 50 is , so he displays his boards, two at a time, in the corresponding order. Person B reads these boards, translates them to mean 50 and raises his flag exactly half way. This would be similar to a digital system. It can be seen that the digital system is more precise as the information is either a '1' or a '0' and the position can be accurately defined. The analogue example is not so precise because person B cannot determine if person A's flag is at exactly 50%. It could be at 49% or 51%. It is for this reason, together with higher integration of microprocessor circuitry that digital signals are becoming more widely used.

15 Binary

16 Binary Explanation of Binary code

17 HART HART is probably the most widely used digital communication protocol in the process industries, and is supported by all of the major suppliers of process field instruments. Preserves existing control strategies by allowing 4-20 ma signals to co-exist with digital communication on existing 2-wire loops. It Is compatible with analogue devices. Easy to set (can be set by a slave handheld communicator) Provides important information for installation and maintenance, such as Tag- IDs, measured values, range and span data, product information and diagnostics. Can support cabling savings through use of multidrop networks (maximum 15 devices) Reduces operating costs via improved management and utilisation of smart instrument networks.

18 Profibus PROFIBUS is an open fieldbus standard for a wide range of applications in manufacturing and process automation independent of manufacturers. Manufacture independence and transparency are ensured by the international standards EN 50170, EN and IEC It allows communication between devices of different manufacturers without any special interface adjustment. PROFIBUS can be used for both high-speed time critical applications and complex communication tasks. PROFIBUS offers functionally graduated communication protocols DP and FMS. Depending on the application, the transmission technologies RS-485, IEC or fibre optics can be used. It defines the technical characteristics of a serial Fieldbus system with which distributed digital programmable controllers can be networked, from field level to cell level. PROFIBUS is a multi-master system and thus allows the joint operation of several automation, engineering or visualization systems with their distributed peripherals on one bus. At sensor/actuator level, signals of the binary sensors and actuators are transmitted via a sensor/actuator bus. Data are transmitted purely cyclically. At field level, the distributed peripherals, such as I/O tutorials, measuring transducers, drive units, valves and operator terminals communicate with the automation systems via an efficient, real-time communication system. As with data, alarms, parameters and diagnostic data can also be transmitted cyclically if necessary. At cell level, programmable controllers such as PLC and IPC can communicate with each other. The information flow requires large data packets and a large number of powerful communication functions, such as smooth integration into company-wide communication systems, such as Intranet and Internet via TCP/IP and Ethernet

19 Foundation Fieldbus (FF) Foundation Fieldbus is an all-digital, serial, two-way communications system that serves as a Local Area Network (LAN) for factory/plant instrumentation and control devices. The Fieldbus environment is the base level group of the digital networks in the hierarchy of plant networks. Foundation Fieldbus is used in both process and manufacturing automation applications and has a built-in capability to distribute the control application across the network. Unlike proprietary network protocols, Foundation Fieldbus is neither owned by any individual company, nor regulated by a single nation or standards body. The Foundation Fieldbus, a not-for-profit organization consisting of more than 100 of the world's leading controls and instrumentation suppliers and end users, controls the technology. While Foundation Fieldbus retains many of the desirable features of the 4-20 ma analogue system, such as a standardized physical interface to the wire, buspowered devices on a single wire, and intrinsic safety options, it also offers many other benefits.

20 PLC (programmable logic controller)

21 P L C A programmable logic controller (PLC), or programmable controller is an industrial digital computer which has been ruggedized and adapted for the control of manufacturing processes, such as assembly lines, or robotic devices, or any activity that requires high reliability control and ease of programming and processing PLCs are robust and can survive harsh conditions including severe heat, cold, dust, and extreme moisture. Their programming language is easily understood, so they can be programmed without much difficulty. Boolean Algebra

22 P L C PLCs are modular so they can be plugged into various setups. Conventional relays switching under load can cause undesired arcing between contacts. Arcing generates high temperatures that weld contacts shut and cause degradation of the contacts in the relays, resulting in device failure. Replacing relays with PLCs helps prevent overheating of contacts.

23 P L C PLCs work with inputs, outputs, a power supply, and external programming devices

24 Conventional simple control system A timer is controlling the timing for a batch production The 1 st move is for the water to fill in the tank There is a level switch to control the opening & closing of the water solenoid valve The 2 nd move is the steam coming into the heating coil to heat the water inside the tank, to become hot water with a certain temperature setting There is a temperature switch to control the opening & closing of the steam solenoid valve The 3 rd move is the draining of the hot water When the timer is OFF, the drain solenoid valve will open to drain the hot water from the tank it is the end of the batch production

25 Conventional simple control system We have to install the timer & relays inside a simple control box We have to connect/wire the input level switch & temperature switch to the timer & relays inside the control box We have to connect/wire the output solenoid valves to the relays inside the control box It takes time to do the above sequences

26 P L C OUTPUT INPUT PLC has already the relays & timer integral inside it We Just connect/wire the level switch & temperature switch to the INPUT terminal of the PLC We just connect/wire the solenoid valves to the OUTPUT terminal of the PLC Then we can program the control sequence It saves a lot of times in doing it compare with the conventional system!

27 PLC

28 P L C

29 HMI (human machine interface)

30 HMI Human Machine Interface also known as an HMI is a software application that presents information to an operator or user about the state of a process, and to accept and implement the operators control instructions. Equipment HMI is a software interface between the machine or plant with the operator and bystanders. Usually bigger HMI consists of a computer centre and a few separate computers and is used to monitor and control the machine. Features used by HMI are a plant information, presentation methods and equipment. Whereas the components used are media communications, computer hardware and software HMI. Typically information is displayed in a graphic format (Graphical User Interface or GUI).

31 HMI The main HMI terminal is typically a desktop PC complete with a Microsoft Windows operating system and a standard HMI graphics application package. Example of the software platform are as follows: WonderWare Cimplicity FactoryTalk View

32 HMI

33 HMI Advantages include many advanced features now available through Microsoft Windows such as networking, data sharing between applications and multitasking. The system flexibility allows the terminal to be applied as any of the following: Primary Operator Interface Historian Engineering Workstation

34 HMI A Human Machine Interface (HMI) is exactly what the name implies; a graphical interface that allows humans and machines to interact. Human machine interfaces vary widely, from control panels for nuclear power plants, to the screen on an iphone. However, for this discussion we are referring to an HMI control panel for manufacturing-type processes. An HMI is the centralized control unit for manufacturing lines, equipped with Data Recipes, event logging, video feed, and event triggering, so that one may access the system at any moment for any purpose. For a manufacturing line to be integrated with an HMI, it must first be working with a Programmable Logic Controller (PLC). It is the PLC that takes the information from the sensors, and transforms it to Boolean algebra, so the HMI can decipher and make decisions

35 There are three basic types of HMIs: The pushbutton replacer The data handler The overseer. HMI Before the HMI came into existence, a control might consist of hundreds of pushbuttons and LEDs performing different operations. The pushbutton replacer HMI has streamlined manufacturing processes, centralizing all the functions of each button into one location. The data handler is perfect for applications requiring constant feedback from the system, or printouts of the production reports. With the data handler, you must ensure the HMI screen is big enough for such things as graphs, visual representations and production summaries. The data handler includes such functions as recipes, data trending, data logging and alarm handling/logging. Finally, anytime an application involves SCADA or MES, an overseer HMI is extremely beneficial. The overseer HMI will most likely need to run Windows, and have several Ethernet ports.

36 HMI

37 RTU (remote terminal units)

38 RTU RTU is connected into sensors at site/process and it will converting the sensor signal into digital data to be sent to the supervisory system such as Scada An RTU is sophisticated and intelligent enough to control multiple processes without requiring user intervention or input from a more intelligent controller or master controller. Because of this capability, the purpose of the RTU is to interface with distributed control systems (DCS) and supervisory control and data acquisition (SCADA) systems by sending telemetry data to these systems. But in most cases, even intelligent RTUs are connected to a more sophisticated control system such as an actual computer, which makes their reprogramming, monitoring and control of the entire system easier for a user.

39 RTU An RTU can monitor a field's analog and digital parameters through sensors and data received from connected devices and systems it then sends these data to the central monitoring station, as is the case in many industrial facilities like power, oil and water distribution facilities. An RTU includes a setup software that connects input and data output streams; the software can define protocols and even troubleshoot installation problems. RTU

40 RTU Depending on the manufacturer, purpose and model, an RTU may be expandable and custom fitted with different circuit cards including communication interfaces, additional storage, backup power and various analog and digital I/O interfaces for different systems. Because of their widely varying applications, RTUs come in vastly different hardware and software configurations and may not even be remotely compatible with each other. For example, RTUs used in telecommunication automation may not be usable at all for oil and gas applications as the processes and hardware systems used would be completely different.

41 RTU SCADA (Supervisory control and data acquisition) systems help to maintain efficiency, process data for smarter decisions, and communicate system issues to help mitigate downtime. The basic SCADA architecture begins with programmable logic controllers (PLCs) or remote terminal units (RTUs) which are microcomputers that communicate with an array of objects such as factory machines, HMIs, sensors, and end devices, and then route the information from those objects to computers with SCADA software.

42 SCADA

43 SCADA Supervisory control and data acquisition (SCADA) is a system of software and hardware elements that allows industrial organizations to: Monitor, gather, and process real-time data Directly interact with devices such as sensors, valves, pumps, motors, and more through human-machine interface (HMI) software Record events into a log file Control industrial processes locally or at remote locations

44 SCADA SCADA systems are crucial for industrial organizations since they help to maintain efficiency, process data for smarter decisions, and communicate system issues to help mitigate downtime. The basic SCADA architecture begins with programmable logic controllers (PLCs) or remote terminal units (RTUs). PLCs and RTUs are microcomputers that communicate with an array of objects such as factory machines, HMIs, sensors, and end devices, and then route the information from those objects to computers with SCADA software. The SCADA software processes, distributes, and displays the data, helping operators and other employees analyse the data and make important decisions. For example, the SCADA system quickly notifies an operator that a batch of product is showing a high incidence of errors. The operator pauses the operation and views the SCADA system data via an HMI to determine the cause of the issue. The operator reviews the data and discovers that Machine 4 was malfunctioning. The SCADA system s ability to notify the operator of an issue helps him to resolve it and prevent further loss of product.

45 SCADA

46 SCADA

47 SCADA Data acquisition begins at the RTU or PLC level and includes meter readings and equipment status reports that are communicated to SCADA as required. Data is then compiled and formatted in such a way that a control room operator using the HMI can make supervisory decisions to adjust or override normal RTU (PLC) controls. Data may also be fed to a Historian, often built on a commodity Database Management System, to allow trending and other analytical auditing. SCADA systems typically implement a distributed database, commonly referred to as a tag database, which contains data elements called tags or points. A point represents a single input or output value monitored or controlled by the system. Points can be either "hard" or "soft". A hard point represents an actual input or output within the system, while a soft point results from logic and math operations applied to other points. (Most implementations conceptually remove the distinction by making every property a "soft" point expression, which may, in the simplest case, equal a single hard point.) Points are normally stored as value-timestamp pairs: a value, and the time-stamp when it was recorded or calculated. A series of value-timestamp pairs gives the history of that point. It's also common to store additional metadata with tags, such as the path to a field device or PLC register, design time comments, and alarm information.

48 DCS Distributed control system

49 D C S PLC- Programming Logic Controller is used for controlling and monitoring high speed process parameters in a factory automation structure but they cannot use complex structures because of the restriction of the number of input devices. But then Distributed Control System (DCS) is mostly suitable for complex systems where more than one input devices is used for example batch process control. Hence DCS is recommended for complicated management programs with more variety of I/O s with devoted remotes. These are used in production procedures where developing of several products are in several procedures such as group procedure management.

50 D C S As the name suggests distributed control system is a control system in which the control is distributed throughout the system. Instead of having a central control mechanism by using a central controllers: A DCS divides the controlling tasks among multiple distributed system. This provides the system to have more redundancy then a centrally controlled system (such as PLC). In case any single part of the system fails, the plant still keeps on operating. More so a DCS is very similar to SCADA with difference only lying in DCS is more process oriented then SCADA.

51 D C S

52 D C S The lowest level is process control and measurement on the plant floor. At this level, microprocessor- based controllers such as programmable controllers execute loop control, perform logic functions, collect and analyse process data, and communicate with other devices and to other levels in the system. The process data collected at level 1 is transferred to level 2. At this level, process operators and engineers use operator consoles that have a keyboard, mouse, and video display to view and adjust the various processes being controlled and monitored by the system. Also, at level 3, process and control engineers implement advanced control functions and strategies, and members of the operations management team perform advanced data collection and analysis on process information. The various plant management systems such as inventory management and control, billing and invoicing, and statistical quality control exist at level 3. The highest level (level 4) is used in large industrial plants to provide corporate management with extensive process and operations information

53 D C S DCSs are by definition hierarchical systems, although not all systems share an identical hierarchy. The image below shows a typical DCS. Individual controllers, supervised by master controllers, make up the lowest "field" or "plant" level of the hierarchy. The master controllers connect to individual computers and servers, which are further connected to video output devices and a human machine interface (HMI), which is the actual point of user control. DCSs are usually networked using standard protocols such as PROFIBUS and Ethernet, the latter of which is used in this particular system.