process control

Process control is an engineering discipline that deals with architectures, mechanisms, and algorithms for controlling the output of a specific process. See also control theory.For example, heating up the temperature in a room is a process that has the specific, desired outcome to reach and maintain a defined temperature (e.g. 20°C), kept constant over time. Here, the temperature is the ''controlled variable''. At the same time, it is the ''input variable'' since it is measured by a thermometer and used to decide whether to heat or not to heat. The desired temperature (20°C) is the ''setpoint''. The state of the heater (e.g. the setting of the valve allowing hot water to flow through it) is called the ''manipulated variable'' since it is subject to control actions.A commonly used control device called a ‘’’programmable logic controller’’, or a PLC, is used to read a set of digital and analog inputs, apply a set of logic statements, and generate a set of analog and digital outputs. Using the example in the previous paragraph, the room temperature would be an input to the PLC. The logical statements would compare the setpoint to the input temperature and determine whether more or less heating was necessary to keep the temperature constant. A PLC output would then either open or close the hot water valve, an incremental amount, depending on whether more or less hot water was needed.In practice, process control systems can be characterized as one or more of the following forms:

Discrete – Found in many manufacturing, motion and packaging applications. Robotic assembly, such as that found in automotive production, can be characterized as discrete process control. Most discrete manufacturing involves the production of discrete pieces of product, such as metal stamping.

Batch – Some applications require that specific quantities of raw materials be combined in specific ways for particular durations to produce an intermediate or end result. One example is the production of adhesives and glues, which normally require the mixing of raw materials in a heated vessel for a period of time to form a quantity of end product. Other important examples are the production of food, beverages and medicine. Batch processes are generally used to produce a relatively low to intermediate quantity of product per year(a few pounds to millions of pounds).

Continuous – Often, a physical system is represented though variables that are smooth and uninterrupted in time. The control of the water temperature in a heating jacket, for example, is an example of continuous process control. Some important continuous processes are the production of fuels, chemicals and plastics. Continuous processes, in manufacturing, are used to produce very large quantities of product per year(millions to billions of pounds). Applications having elements of discrete, batch and continuous process control are often called ''hybrid'' applications.

Examples - A thermostat is a simple example for a closed control loop: It constantly measures the current temperature and controls the heater's valve setting to increase or decrease the room temperature according the user-defined setting. A simple method switches the heater either completely on, or completely off, and an overshoot and undershoot of the controlled temperature must be expected. A more expensive method varies the amount of heat provided by the heater depending on the difference between the required temperature (the "setpoint") and the actual temperature. This minimizes over/undershoot.An anti-lock braking system (ABS) is a more complex example.

See also -

Actuator

Automation

Automatic control

CALS

Closed-loop controller

Control engineering

Control panel

Control system

Control theory

Controllability

Controller (control theory)

Cruise control

Current loop

Digital control

Distributed control system

Feedback

Feed-forward

Fieldbus

Flow control valve

Fuzzy control system

Laplace transform

Measurement instruments

Negative feedback

Non-linear control

Open-loop controller

PID controller

Positive feedback

Regulator (automatic control)

Setpoint

Sliding mode control

Temperature control

Transducer

Valve

Watt governor

External links - onesmartclick.com - covers many subtopicsCategory:Chemical engineeringCategory:Production and manufacturing

www.CombustionSoftware.com
Combustion Expert™ v4 - New Software saves Fuel In order to make real improvement to the fuel economy of your process, you need to know the efficiency. This software calculates the fuel efficiency as well as the furnace efficiency and the over-all-process heat efficiency. This software shows you how to adjust fuel and airflow for changes in temperature, barometric pressure and humidity so that the heat dissipated in the furnace remains the same. Using OPC or DDE communication with a PLC you can see the furnace efficiency in real time, while you receive set points for temperature, mass flow rates or volumetric flow rates based on measured flows, temperatures, gauge pressures, barometric pressure and relative humidity. This new version in addition to calculations of compressibility, chemical equilibrium, revamping of older furnaces, change of fuel, conversion to all-oxygen-fuel system adds heating of boxed shaped objects with radiative heat transfer, calculation of heat transfer coefficients, viewing factors, radiosity , gas emissivity and temperature distribution in bars or slabs. The software gives you a real time picture of your process and its emissions. A report generator gives five different reports for heating values, mass balances, furnace losses, heat losses and process summaries.
http://www.combustionsoftware.com/

Analytical balances and scales
US manufacturer of laboratory balances, scales, micro balances, and laser power meters
http://www.scientech-inc.com/

Machine Intelligence & Machine Vision
Advanced integration of optics and customized computer processing of data to provide meaningfull feedback and automation in manufacturing and security applications.
http://www.hpmwoodsolutions.com/

Dick Caro's Business Website - CMC Associates
CMC Associates is dedicated to helping process control and industrial automation suppliers plan products needed by automation engineers. We are dedicated to the process of bringing new innovative products to market. Our past succeses have been with secure industrial data communications such as Foundation Fieldbus.
http://cmc.us/

Protomation - In control by simulation.
Protomation develops software instruments and renders technical services for the oil, gas and chemical industry and production facilities. Our background includes over 20 years of ndustrial engineering experience in software development, electronics, system analyses, process control and chemical processes.
http://www.protomation.com

Process Studio - In control by simulation
Process Studio is an integral PC-based program that offers insight into process runs, thereby making them easier to control. This training program makes it possible to simulate specific process situations, or even crisis situations. With Process Studio, operators have an opportunity to understand and control highly complex processes. The program is suitable for both beginners and experienced employees. This leads to improved reliability of operation, less malfunctions and thus higher returns.
http://www.process-studio.com

Solvent Extraction and Electrowinning Pilot Plants
SX Kinetics designs and manufactures solvent extraction and electrowinning pilot plants for the recovery of metals
http://www.sxkinetics.com/

Process Control/ SCADA
Promation, Inc. is an innovative systems integrator dedicated to providing clients with advanced types of process control automation. Typically, industries include: chemicals, xray diagnostics, steel, coatings, inks, petroleum, foods, beverages, pharmaceuticals, paint, public address, measurement, etc.
http://www.promationinc.com/

Precision Controls and Automation Ltd
Incremental and absolute Encoders and measuring electronic devices for automation
http://www.pcaltd.net/

Software Expert
A group of loosely associates ready to tackle you software project.
http://www.bbnj.us/

MRAM-Info
MRAM (Magnetic RAM) information, news, articles, forums and more
http://www.mram-info.com/

PENSA
Specializing in computer system validation projects for pharmaceutical, medical device and biotechnology manufacturers, PENSA can guide your Life Sciences company toward meeting worldwide regulatory compliance. PENSA's validation products and services include 21 CFR Part 11 assessments, quality audits, creating/managing compliance documentation and validation training which follow cGMPs as put forth by the FDA.
http://www.gmps.com/

ScienceDirect
Research papers published on the net , subscription required for some sections.
http://www.sciencedirect.com

OPC Specification
The specifications of the OPC standard architecture.
http://www.opcfoundation.org/

Institute for Process Control and Robotics at the University of Karlsruhe
Sensor research.
http://wwwipr.ira.uka.de/

WWW Virtual Library - Process Modelling
Software and other information resources relevant to chemical and process engineering.
http://www.che.ufl.edu//WWW-CHE/topics/modeling.html