Home - Product & Technology Descriptions

5/21/2009

AC Drives

AC drives control speed, torque, acceleration, deceleration, and rotation direction of AC motors. AC drives save energy by tailoring the power delivered to meet the actual load requirements.

AC drives replace mechanical gearboxes, belts, hydraulic couplings, DC drives, servo-drives, or eddy current drives in many situations. Advantages of AC drives include providing an accurate and wide range of smooth and step-less control of motor speed and torque in a highly efficient, low maintenance, compact size package with versatile built-in functions, complex control and networking capabilities, and freedom from mechanical inertia and resonance. In low power AC drives, the use of Pulse Width Modulated (PWM) technology has emerged as the industry standard.

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HVAC System

A typical HVAC system consists of functionally and/or geographically distributed controllers capable of controlling various processes throughout a building or group of buildings from a central host computer or over the internet from a unit that combines the functions of host computer and web server. Today's controllers have extensive computational capabilities and can generally control processes such as off-normal alarms, event initiated programs, time-based programs, and energy management programs. Through a communication protocol, the controllers share data with each other and the host computer. Many of today's controllers also have the intelligence to operate as stand-alone control systems in the absence of a host computer. HVAC equipment is becoming increasingly available with embedded controllers, and the I/O can be integral with the controller or located remotely.

Depending on the system, configuration may be accomplished at a workstation, an off-line personal computer, an HMI terminal, or, increasingly, with web-enabled devices, including laptops and PDAs. Local communication is typically handled by the control network with transmission over shielded twisted pair copper cable, direct dial telephone lines, and fiber optic cable, although wireless connections are becoming more commonplace.

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5/17/2009

On-line Optimization

On-line optimization is designed to continuously monitor the state of the process and, through model reference, predict an optimum operation path. On-line optimization software typically employs technology for solving simultaneous equations. The model is part of an application package that presents the best direction for the process operation to go in order to meet the objective function. Presentation of the output of the optimization software may simply be in an advisory fashion to the operator, or may directly set a new target to a lower-level control strategy. Improved economics of the operation are the driving force for using these applications. Optimization software packages may contain:

Model building application from first-principles or empirical methods.
Simultaneous equation-solving technology.
Methods to find optimum for non-linear process.
Support software for "what if" and other analysis.
On-line data reconciliation methods.
Links to raw material, intermediate product, and finished product cost information.

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Advanced Process Control

Advanced process control includes model-based software that is used to direct the process operation. The most popular technology in this area is commonly referred to as multivariable predictive control (MPC). These applications require that the process model created accurately represents the process dynamics. Improved economics of the operation or production improvements are typical driving forces for using these applications. Advanced process control software may include:

Off-line model building, model verification and data analysis tools.
Driver software to collect historical data from control systems or online process historian systems.
Operator guidance to advise where the APC is taking the process.
Prediction of controlled variables based on future planned moves of manipulated variables.
Run-time MBC tuning to adjust for changes in process dynamics without having to rebuild the model.
Controller monitoring and performance analysis software.

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5/15/2009

Operator Training Simulator

Simulation software used for training is always dynamic. These simulators may connect directly to an actual control system or to an emulated control system, and act as the process. Therefore, at a minimum, the resulting model must reflect real-time responses of the simulated process. Because the emphasis is on running in real-time, these software systems may not be as rigorous as the engineering design products are. The following are also typical functions that are found in these types of simulation systems:

Initialize simulator from preset operating conditions.
Faster than real-time process dynamics.
Run, freeze and restart operations from instructor's console.
Playback operator actions for reviewing.
Abnormal situation simulation.
Training session reports.

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Distributed Control Systems

A typical DCS consists of functionally and/or geographically distributed digital controllers capable of executing from 1 to 256 or more regulatory control loops in one control box. The I/O can be integral with the controller or located remotely via a field network. Controllers currently available have extensive computational capabilities and, in addition to PID control, can generally perform logic and sequential control.

DCSs may employ one or several workstations and can be configured at the workstation or by an off-line personal computer. Local communication is handled by a control network with transmission over twisted pair, coaxial, or fiber optic cable. A server and/or applications processor may be included in the system for extra computational, data collection, and reporting capability.

Hardware

With the increasingly amorphous nature of evolving DCS architecture, as well as the ever expanding business model of DCS suppliers, ARC has made an effort to focus its definition of DCS from including all elements of plant automation. Other related plant automation elements are typically covered in separate studies from ARC.

At the hardware level, DCS begins at the I/O and reaches all the way up through controllers, application processors, workstations, PCs, and networking equipment within the DCS control domain. PLCs sold as part of an independent PLC product business, such as Rockwell ControlLogix and Siemens S7 PLCs, are not included in this report. PLCs and PLC-type controllers that are sold as part of an integrated system offering, such as the Siemens Simatic PCS 7 and Rockwell Logix Integrated Architecture system, are included. DCS controllers that replace PLCs in the integrated system are also included.

	Small	Medium	Large
Workstations	1-2	3-8	>8
Controllers	1-2	3-8	>8
Analog I/O Points	0-599	600-1499	1,500+
Digital I/O Points	0-299	300-799	800+

ARC DCS Size Definitions

Excluded from the DCS hardware definition are field instruments, control valves, analytical devices, all specialty measurement equipment, such as paper machine gauges and condition monitoring devices, and any other devices that exist outside the I/O level of the system. Also excluded are supervisory workstations that execute advanced control, production management, optimization, simulation, or plant asset management applications.

ARC's primary segmentation of the DCS marketplace is by DCS size. We have segmented DCSs into small, medium, and large systems based on hardware content. Hardware specifically includes all controllers, application processors, I/O, workstations and communications networks. PCs used for system configuration and real time control are included in DCS prices, as are computers used for supervisory control, if they are sold as part of the system. PLCs sold by DCS suppliers integrated with DCSs are also included.

Software

DCS software includes basic embedded controller software as well as some, but not all, software that is sold bundled with a system. DCS software includes control, HMI, plant information management (PIM) software, such as embedded data historians, engineering and configuration software.

Aside from performing HMI functions, DCS HMI software can also perform other functions, such as I/O communication. HMI software typically resides in the DCS workstation or PC. Control software typically resides in controllers and performs basic control functions. Programming software accounts for a small part of the total DCS software business and is used to program and configure the various functions of the control system at startup.

Supervisory software that performs production management (MES) and advanced control functions typically resides in the application processor or supervisory computer and is excluded from the DCS definition. Supervisory software includes categories, such as advanced process control, multivariable control, real time process optimization (RPO), process simulation and optimization (PSO), and plant asset management (PAM) applications. These applications are covered in other ARC reports.

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Control Valves

A control valve regulates the rate of fluid flow as the position of the valve plug or disk is changed by an actuator. Control valves are used to maintain a process variable as close as possible to the desired set point.

A control valve installation consists of a valve body, actuator, positioner and accessories. The body includes a bonnet assembly and trim-parts. Its design withstands fluid pressure, allows fluid flow, provides pipe-connecting ends, and supports seating surfaces and a valve closure member. Actuators are pneumatic, hydraulic, or electrically powered devices that provide the force to open and close the valve. Positioners monitor and control true actuator movement to maintain a desired set-point. Accessories include electro-pneumatic transducers, pressure regulators, hand wheels and limit switches.

Classification by Hardware, Software, and Services

ARC segments the CVAP market by the nature of supply in terms of hardware, software, and services. Hardware revenues include the CVAP assembly as a whole; most notably valve bodies, valve actuators, valve positioners, and accessories. Hardware revenues also include valve actuators or positioners shipped separately. Software refers to sizing, control, programming, supervisory software, and custom software related to control valve sales.

Suppliers provide project and maintenance services to manufacturers. This facilitates manufacturers to focus on core competencies and look to suppliers to assume single point accountability to suit their needs and provide supplier-initiated maintenance and upgrade programs to preserve their investment. Project services include project engineering, application engineering, application software development, and project management. Maintenance services include installation, startup, and commissioning. Maintenance services also include non-contract maintenance and operations services. Non-contract maintenance services include engineering, programming, training, and network management. Operations services include performance enhancement services.

Classification by Actuator Type

ARC has divided actuators into three main types: pneumatic, electric, and other actuators. Pneumatic actuators are diaphragm or piston-based. Diaphragm-based actuators use air supply from controller or positioner, and include various styles, such as direct acting, reverse acting, and reversible. Piston-based actuators use high-pressure plant air, and are double acting, to give maximum force in both directions. Electric actuators use an electric motor and some form of gear reduction to move the valve. Other types of actuators include hydraulic and electro hydraulic actuators.

Actuator Type	Power Source	Major Variants
Pneumatic	Compressed Air/Gas	Piston, Diaphragm, Vane
Electric	Motors or Solenoids	Single Phase, Three Phase
Remainder:
Hydraulic	Compressed Liquids	Cylinder, Rack & Pinion
Mechanical	Varies	Levers, etc
Manual	Man Power	Hand wheels

Control Valve Actuators by Type

Classification by Positioner Type

ARC has segmented valve positioners into three main types: pneumatic, electro pneumatic, and digital. Pneumatic positioners receive a pneumatic signal and supply the valve actuator with the air pressure required to move the valve to the desired position. Electro pneumatic positioners accept 4-20 mA as input signal and translate it to the required air pressure. Digital positioners have microprocessors that provide expanded functionality. Digital positioners feature two-way digital communication that provides feedback to a control or monitoring system on issues such as stem wear and other diagnostic tasks. They can also have advanced capabilities such as embedded PID control.

Digital Positioners by Communication Protocol

Digital positioners use HART, Foundation Fieldbus, Profibus, Proprietary digital, and "other" communication protocols. HART superimposes a serial digital signal over a 4-20mA control signal to communicate with the microprocessor embedded in the digital positioner. Bidirectional communication is available using HART, without affecting the analog signal. HART can be used in multi drop applications as long as an analog signal is not used.

The general term "Fieldbus" refers to all standard, multi-drop, multi-layered digital communication protocols currently vying for industry recognition. This category includes open digital communications, such as Profibus and Foundation Fieldbus.

The Remainder category predominantly consists of closed proprietary digital protocols, such as Honeywell DE, Foxboro FoxComm, and Yokogawa Brain. It also consists of protocols, such as ASI, Devicenet, Ethernet/IP, Interbus, Modbus, Lonworks, and other such protocols mostly used in the discrete industries.

Posted at 12:00 AM by Dick Hill | Permalink | Email this Post | Comments (0)

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