Intro4u2u

Instruments and sensors used to test, measure, analyze, control, calibrate, display and record data in laboratory and other testing situations.

Analytical Instruments (4906 companies)
A wide classification of instruments that are used to analyze material samples, or their components, and record data specific to the application.

Calibration Instruments, Standards and Reference Sources (1541 companies)
Calibration instruments, standards and references consist of an accurate meter or provide a precision source value.

Chromatography Instruments (257 companies)
Instruments used to separate chemical mixtures, carried by liquids or gases, into components as a result of differential distribution of the solutes as they flow around or over a stationary liquid or solid phase.

Dimensional Measurement (1446 companies)
Equipment for metrology, inspection and quality control of dimensional features.

Electronic Test and Interconnect Accesories (4718 companies)
Connectors, cables, and accessories for electrical and electronic testing.

Electrical Testing Equipment (844 companies)
Electrical testing instruments for current leakage and insulation resistance measurements.

Environmental Instruments (3279 companies)
A wide variety of instruments for measurement and testing of changes in environmental conditions, including radiation (both wavelength and as a hazardous emission), temperature, moisture, dew point, smoke, dust, opacity, light, weather, and water quality.

Environmental Test Equipment (898 companies)
Environmental test equipment includes environmental test chambers and other specialized equipment that provides a temperature, humidity, or atmosphere controlled environment for testing for testing or evaluating products or materials.

Fiber Optic Test Equipment (222 companies)
Equipment (fiber identifiers, spectrum analyzers, reflectometers, etc.) used for monitoring and testing fiber optic equipment

Lab and Test Equipment (3653 companies)
Instruments used to test, analyze, control, calibrate, display and record data in laboratory and other testing situations.

Machine Vision Equipment (908 companies)
Systems using optical, video and computer hardware for automated inspection and measurement in production environments.

Meters, Readouts and Indicators (1646 companies)
Any type of equipment used to display information in various formats including, digital readouts, indicator lights or panel meters.

Multimeters and Electrical Test Meters (994 companies)
Devices, including voltmeters, ammeters and multimeters, used to detect and measure electrical signals.

Non-destructive Testing Equipment (2484 companies)
Instruments and other devices used in testing methods that examine an object, material, or system without impairing its future usefulness. NDT measurements include flaws, thickness, material condition, corrosion, bulk conductivity and others.

Process Controllers (1730 companies)
Instruments for monitoring and automatically revising process parameters such as temperature, pressure, force, humidity, level and flow.

Product and Material Testing (1604 companies)
Instruments and equipment that evaluate mechanical, thermal or other material properties, or simulate field conditions.

Recorders and Loggers (1385 companies)
Devices that are used to acquire and retain data (digital or analog) from sensors or other sources.

Sample Preparation and Wet Chemical Analysis (802 companies)
Processes and instruments used to prepare and analyze wet chemical samples in a laboratory.

Separation Techniques (453 companies)
Products using various methods, including electrophoresis, chromatography and titration, to separate the components of a mixture.

Sensing and Measurement Instruments (4503 companies)
Instruments for the detection and measurement of physical variables such as flow, pressure, temperature, humidity, velocity, acceleration, and vibration.

Spectrometers and Analytical Photometers (648 companies)
Any instrument used for measuring wavelengths of light spectra, optical or atomic emissions for the analysis of samples.

Vibration Testing (615 companies)
Instruments, sensors and equipment for testing, producing, controlling or measuring oscillatory or vibratory motion.

Water Quality Instruments (644 companies)
Instruments and sensors designed to test water for a variety of chemical and biological agents as well as clarity, rate of movement, etc.

Analog and Mixed Signals (366 companies)
Analog and mixed signal ICs are integrated circuits in which many discrete logic and/or analog components are fabricated on a single chip of semiconductive material and packaged in a single case to form a functional unit.

Audio, Video IC (119 companies)
Audio and Video ICs are integrated circuit components that are designed for audio, video and multimedia applications.

Communication IC (868 companies)
Communication ICs are integrated circuits used in general telecommunication electronic modules that enable the transmission, reception and analysis of data and signals.

Discrete (672 companies)
Discrete ICs are integrated circuits that contain only one type of electronic component (i.e., transistors or diodes).

IC Circuit Protection Devices (53 companies)
IC circuit protection devices are used to protect electronic components from unwanted transients such as current and voltage surges, electrostatic discharge (ESD), lightning, spikes and other signals that can imperil the operation or damage the component.

IC Interface Devices (234 companies)
IC interface devices or gate drivers provide the required current and voltage necessary to switch or power an electronic component based on the output signals from a logic device.

IC Optoelectronics (987 companies)
IC optoelectronics are integrated circuits that combine optical components (i.e. laser optocoupler, LEDs, etc.) with electronic devices or circuits (i.e. transistors, diodes, etc.).

Logic (150 companies)
Logic devices are integrated circuits that perform logic operations using Boolean logic.
JTAG Products (14 companies)
Joint Test Action Group (JTAG) products are semiconductor devices that allow access to the inner workings of an IC for testing, controlling, and programming purposes. Learn more about JTAG Products

Memory Chips (397 companies)
Memory chips are integrated circuits that temporarily store data and code for processing.

Microprocessors and Microcontrollers (543 companies)
Microprocessors and microcontrollers are IC chips that perform arithmetic and logic operations.

Passive (873 companies)
Passive IC components do not amplify signals and do not require any power (bias) to operate. Examples of these devices include resistors, inductors, potentiometers, and capacitors.

Power and Power Management IC (488 companies)
Power and power management ICs are used to monitor, control, apply, and distribute power to systems such as microprocessors.

Programmable Logic Devices (253 companies)
Programmable logic devices have configurable logic and flip-flops linked together by programmable interconnects. Memory cells control and define the functions that the logic performs, and how the various logic functions are interconnected.

Sensor IC (99 companies)
Sensor ICs are integrated circuits or dies incorporating semiconductor circuit elements that are used to detect and/or respond to changes in some physical parameter and convert it to an electrical signal.

Timing Circuits (551 companies)
IC timing devices are integrated circuits that generate, control, keep, and apply time and frequency to electronic systems.

Bar Code Software (135 companies)
Bar code software identifies or decodes bar code symbology, generates output strings corresponding to barcode values, creates bar code fonts, prints bar codes, and/or performs tracking, etc. Learn more about Bar Code Software

BPM Software (Business Process Management) (105 companies)
Business process management (BPM) software enables companies to map, model and improve business processes across the organization. Companies use BPM software to define business rules, model current processes, and identify areas for improvement. Learn more about BPM Software (Business Process Management)

Business Transaction and Personal Business Software (1641 companies)
Business transaction, financial and personal business software is used to facilitate any aspect of business transactions. Learn more about Business Transaction and Personal Business Software

CAD / CAM Software (565 companies)
Computer-aided design (CAD), computer-aided manufacturing (CAM), and computer aided engineering (CAE) software is used for mechanical, electrical or electronic design; simulation, drafting, and engineering; and analysis and manufacturing. Learn more about CAD / CAM Software

Calibration Management Software (53 companies)
Calibration management software is used to generate documentation of calibration results, calibration certificates and reports. It also provides lookups of calibration procedures and database functions. Learn more about Calibration Management Software

Civil Engineering and Architectural Software (55 companies)
Civil engineering and architectural software is the set of tools used to design, simulate and analyze civil engineering structures such as bridges, roads and buildings. Learn more about Civil Engineering and Architectural Software

Cluster Software / Tools (12 companies)
Cluster software and tools are used to create, analyze, optimize, expand and manage high performance applications on clusters. Learn more about Cluster Software / Tools

CMMS / EAM Software (128 companies)
Computerized maintenance management systems / enterprise asset management (CMMS/EAM) software is used to manage maintenance operations on capital equipment and other assets and properties. Learn more about CMMS / EAM Software

Code Analyzer Software / Tools (11 companies)
Code analyzer software and tools enable programmers and quality assurance (QA) managers to check source code for compliance with established standards. These products are also useful for improving source code. Learn more about Code Analyzer Software / Tools

Communications Software (909 companies)
Communications and network software is used for the setup and management of digital communication networks such as LAN and WAN computer networks, electronic mail, audio and video networks, wireless communication systems, etc. Learn more about Communications Software

Computational Fluid Dynamics Software (CFD) (36 companies)
Computational fluid dynamics software (CFD) is used for the calculation of flow parameters in fluids, and for the design and simulation of the behavior of fluidic systems. Learn more about Computational Fluid Dynamics Software (CFD)

CRM Software (416 companies)
Customer relationship management (CRM) software is used to support business processes and to find and retain customers. Typically, CRM software consists of modules such as sales force automation, call management, self-service, etc. Learn more about CRM Software

Data Acquisition and Analysis Software (573 companies)
Data acquisition, SCADA and analysis software is designed to collect, record, store, present and analyze data collected from sensors and other digital devices. Learn more about Data Acquisition and Analysis Software

Data Storage Management Software (424 companies)
Data storage management software is designed for database management, data backup and recovery, and other data management functions. Learn more about Data Storage Management Software

Document Management Software and ECM (237 companies)
Document management software and enterprise content management software are used to manage file documents. Functions performed by this type of software system include: produce, dispose, organize, monitor, use, retrieve, archive and interchange. Learn more about Document Management Software and ECM

EDA Software (65 companies)
Electronic design automation (EDA) software and electronic computer-aided design (ECAD) software are tools used to design and develop electronic systems and integrated circuits. Technology Computer-Aided Design (TCAD) designs and simulate processes. Learn more about EDA Software

Educational and Training Software (256 companies)
Educational and training software is used in applications such as distance learning, online training, and more specific programs such as equipment training and support. Learn more about Educational and Training Software

Engineering Analysis Software (722 companies)
Engineering analysis and modeling software is designed to model, analyze, and predict responses and interactions for applications such as materials, structures, chemical and biological processes, electronic system performance, etc. Learn more about Engineering Analysis Software

ERP Software (553 companies)
Enterprise resource planning (ERP) software supports the entire business process. Typically, ERP consists of modules such as marketing and sales, field service, production, inventory control, procurement, distribution, human resources (HR), etc. Learn more about ERP Software

Finite Element Analysis Software (41 companies)
Finite element analysis (FEA) software uses a numerical technique to model and analyze complex structures by solving boundary-value problems. The structure to be analyzed is divided into points (elements) that make a grid called a mesh. Learn more about Finite Element Analysis Software

Fleet Management Software (103 companies)
Fleet management software and Transportation Management System Software (TMS Software) are used to supervise, manage, locate, schedule and maintain vehicle fleets. Learn more about Fleet Management Software

Graphics Software (98 companies)
Graphics software is used to produce video graphics and to edit and convert graphic files of different formats. These types of software include raster graphics, vector graphics, raster to vector conversion (R2V), and others. Learn more about Graphics Software

Graphing and Visualization Software (97 companies)
Graphing and visualization software visually present abstract scientific data. The programs take numerical data and create (render) images for analysis. Learn more about Graphing and Visualization Software

HMI Software (25 companies)
Human machine interface (HMI) software enables operators to manage industrial and process control machinery via a computer-based graphical user interface (GUI). The computer on which HMI software is installed is called a human machine interface or HMI. Learn more about HMI Software

Image Analysis Software (177 companies)
Image analysis software is used to enhance, identify or quantify features in an image by breaking down or applying digital image filters. Learn more about Image Analysis Software

Laboratory Information Management Systems (LIMS) (24 companies)
Laboratory information management systems (LIMS) software is used to manage information and data in scientific and commercial laboratories. Learn more about Laboratory Information Management Systems (LIMS)

Language Translation Software (8 companies)
Language translation software is used to translate documents from one human language to another. Learn more about Language Translation Software

Machine Control Software (248 companies)
Machine control software is designed for personal computers (PCs) or stand-alone controllers. It allows personnel to configure, program, and calibrate computerized machinery. Learn more about Machine Control Software
Manufacturing Execution System (MES) Software (32 companies)
Manufacturing execution system (MES) software is used to manage and monitor work-in-process on the factory floor. MES software supports activities such as finite scheduling, workflow monitoring, and materials management. Learn more about Manufacturing Execution System (MES) Software

Manufacturing Support Software (400 companies)
Manufacturing support software is used in shop floor, process, tool and maintenance management. Learn more about Manufacturing Support Software

Math Calculation Software (12 companies)
Math calculation software is used to perform mathematical calculations. These programs provide general core calculations as well as graphical analysis that can be used in science, engineering and technology. Learn more about Math Calculation Software

MCAD Software (28 companies)
Mechanical computer aided-design (MCAD) software packages are tools used by mechanical engineers and designers to design and develop mechanical systems. Learn more about MCAD Software

Media and Presentation Software (122 companies)
Media and presentation software include tools and applications for the creation of multimedia presentations for broadcast or advertising and marketing use. It often uses media such as CDs and DVDs. Learn more about Media and Presentation Software

Medical Software (329 companies)
Medical and healthcare software is used in hospitals, clinics, and related facilities. This category includes software used to control and monitor medical devices, and software used for medical practice management and patient billing. Learn more about Medical Software

Microprocessor Compilers and Debuggers (67 companies)
Microprocessor compilers are programs that translate high-level language codes into assembly (machine) code. Debuggers are programs that track and correct errors (bugs) in program code. Learn more about Microprocessor Compilers and Debuggers

Middleware (8 companies)
Middleware is software that allows otherwise separate software components or applications to share data. Learn more about Middleware

Mobile / Wireless Software (44 companies)
Mobile and wireless software is used to program and manage mobile and wireless devices such as cell phones, personal digital assistants (PDA), and global positioning systems (GPS). Learn more about Mobile / Wireless Software

Motion Control Software (96 companies)
Motion control software uses advanced algorithms for programming, monitoring, and optimizing digital motion control products. Learn more about Motion Control Software

Network Monitoring Software (176 companies)
Network monitoring software is used to monitor network traffic for user-defined parameters. Learn more about Network Monitoring Software

PDM / PLM Software (101 companies)
Product data management (PDM) software is used to manage the operation, development and maintenance of products. Product lifecycle management (PLM) tools are used to manage the entire lifecycle of a product. Learn more about PDM / PLM Software

Programming Languages and Database Tools Software (375 companies)
Programming languages and database tools software are development suites for computer languages that provide the commands, grammar and syntax for instructing digital devices (computers) to perform specific tasks. Learn more about Programming Languages and Database Tools Software

Protocol Stack Software (23 companies)
Protocol stack software is a set of hierarchical network protocols that manage the flow of data in communication systems. Each protocol in the stack or suite supports the protocol above it and uses the one below it. TCP/IP is an example of a stack. Learn more about Protocol Stack Software

Quality Assurance, Inspection, and Compliance Software (241 companies)
Quality assurance, inspection, and compliance software is used for the verification and inspection of products and processes. It is used in compliance monitoring and may be involved in product or system certification. Learn more about Quality Assurance, Inspection, and Compliance Software

RFID Software (79 companies)
RFID software is used to process data sent to and received from radio frequency identification (RFID) devices such as RFID readers, writers, and printers. Learn more about RFID Software

Scanning / OCR / Imaging Software (364 companies)
Scanning, OCR and imaging software is used in optical and document scanners, specialized imaging equipment, and optical character recognition (OCR) systems. Products are used to digitize, create, edit or evaluate images. Learn more about Scanning / OCR / Imaging Software

Scheduling and Productivity Software (1857 companies)
Scheduling and productivity software is designed for monitoring and improving scheduling, efficiency, productivity and project management. Learn more about Scheduling and Productivity Software

Security Software (298 companies)
Security software programs are used to restrict access to data, files and users on a computer or server. Learn more about Security Software

Server & Operating System Software (452 companies)
Server and operating system software includes platforms for operating, managing, and monitoring industrial networks and computers. Learn more about Server & Operating System Software

Shipping, Mailing, and Logistics Software (142 companies)
Shipping, mailing and logistics software is used in the management and scheduling of mailing, shipping, and tracking of letters, packages, equipment, etc. Learn more about Shipping, Mailing, and Logistics Software

Simulation Software (211 companies)
Simulation software is used to mimic a process or a system (e.g., electrical, optical, or mechanical) for the purposes of testing or calibration. Learn more about Simulation Software

Software Drivers (109 companies)
Software drivers are programs that provide the interface between general use software (such as an operating system) and specific hardware or software modules. With personal computers (PCs), drivers are often packaged as dynamic link library (DLL) files. Learn more about Software Drivers

Specialty Software (2032 companies)
Specialty or proprietary software includes firmware, gaming software, and digital imaging and automation software. Learn more about Specialty Software

Statistical Analysis Software (24 companies)
Statistical analysis software analyzes data to make predictions using statistical methods. It can be used to solve manufacturing problems, develop efficient industrial processes, or to make breakthrough discoveries. Learn more about Statistical Analysis Software

Supply Chain Management Software (SCM) (167 companies)
Supply chain management software (SCM) is used to track and monitor products and services. Learn more about Supply Chain Management Software (SCM)

Voice Recognition Software (75 companies)
Voice recognition software is designed to recognize spoken words and convert them into digital data, computer commands, or text. Learn more about Voice Recognition Software

Warehouse Management Systems (WMS) (98 companies)
Warehouse management systems (WMS) are used to manage the movement and storage of materials in a warehouse. Learn more about Warehouse Management Systems (WMS)

Analog I/O (101 companies)
Analog I/O devices process analog signals (e.g., output of transducers) and output the results in analog format. Learn more about Analog I/O

Analog-to-Digital Converter Chips (ADC) (73 companies)
Analog-to-digital converter chips (ADC) transform information from analog form into digital form.
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Analog-to-Digital Converters (213 companies)
Analog-to-digital converters (ADC) sample an analog signal and convert it to a series of digital values to represent the signal to a computer processor.
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Bridge Conditioners (96 companies)
Bridge conditioners are instruments that provide excitation and support for strain gages, Wheatstone bridges, load cells, and sensors. They also include circuitry for signal conditioning, amplification, and processing.
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Charge and Capacitive Signal Conditioning (14 companies)
Charge and capacitive signal conditioning modules or systems amplify, attenuate, filter and/or convert a charge signal from an accelerometer, load cell, pressure transducer, displacement transducer or other type of capacitive sensor. Learn more about Charge and Capacitive Signal Conditioning

Charge Amplifiers and Charge Converters (29 companies)
Charge converters and charge amplifiers convert the charge output from a piezoelectric, capacitive or other charge-producing sensor to a signal such as analog voltage or current.
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Chart Recorders and Strip Charts (214 companies)
Chart recorders and strip charts are data acquisition tools used to generate a plot, graph or other visualization of data versus time.
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Chart Recording Paper and Consumables (26 companies)
Paper recording charts and consumables consist of circular charts, strip charts, markers, fanfolds, sheets, pens, and pen arms used in chart and strip recording instruments. Learn more about Chart Recording Paper and Consumables

Computer Boards, Data Acquisition (163 companies)
Data acquisition computer boards are self-contained printed circuit boards that typically plug into the backplane, motherboard, or otherwise interface directly with the computer bus.
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Counter and Timer Boards (67 companies)
Counter and timer boards are computer cards that perform digital counting and/or timing functions.
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Current Loop Converters (73 companies)
Current loop converters convert an analog or digital signal to a current loop output such as 4-20 mA or 0-20 mA.
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Current-to-Voltage Converters (49 companies)
Current-to-voltage converters scale and convert current signal input to the desired output voltage range.
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Data Acquisition (1372 companies)
Data acquisition is the digitizing and processing of multiple sensor or signal inputs for the purpose of monitoring, analyzing and/or controlling systems and processes. Signal conditioning includes the amplification, filtering, converting, and other processes required to make sensor output suitable for rereading by computer boards.
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Data Acquisition Input Modules (183 companies)
Data acquisition input modules accept sensor and other signal output for data acquisition systems. They may include signal conditioning prior to the analog-to-digital conversion stage.
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Data Acquisition Systems and Instruments (444 companies)
Data acquisition systems and instruments collect, digitize and process multiple sensor or signal inputs for the purpose of monitoring, analyzing and/or controlling systems and processes.
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Data Acquisition Output Modules (127 companies)
Data acquisition output modules or cards transfer amplified, conditioned, or digitized signals.
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Data Collection Terminals (107 companies)
Data collection terminals are portable or handheld devices that are used to input, read, and/or log data. They often have barcode and wireless data transmission capability. Learn more about Data Collection Terminals

Data Input Devices (889 companies)
Devices such as a keyboard or mouse, used to interact with other devices or computers for the purpose of inputting data.

Data Loggers and Data Recorders (668 companies)
Data loggers and data recorders acquire digital data from sensors and other signals. They are primarily used to store data for subsequent downloads to a host PC, but may also include real-time features such as monitors and alarms.
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Digital I/O (126 companies)
Digital I/O devices process digital signals (e.g., outputs from a controller) and output the results in digital format. Learn more about Digital I/O

Digital-to-Analog Converter Chips (DAC) (70 companies)
Digital-to-analog converter chips (DAC) convert digital signals that represent binary numbers into proportional analog voltages.
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Digital-to-Analog Converters (129 companies)
Digital-to-analog converters (DAC) transform a digital number into a corresponding analog voltage or current.
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Encoder and Resolver Signal Conditioners (94 companies)
Encoder and resolver signal conditioners accept encoder and resolver measurements and convert or condition these signals into digital data or suitable levels.
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Frequency / Pulse Signal Conditioners (13 companies)
Frequency / pulse signal conditioners accept the output of devices that are specifically designed for frequency measurement and convert or condition these signals to digital data or suitable levels for digitization. Learn more about Frequency / Pulse Signal Conditioners
Frequency Converters and Translators (46 companies)
Frequency converters and translators scale and/or filter frequency inputs to produce outputs signals with frequencies that are a function of the inputs.
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Frequency-to-Current Converters (11 companies)
Frequency-to-current converters accept a frequency (an AC signal) and produce an output current whose value is a function of the input frequency. Learn more about Frequency-to-Current Converters

Frequency-to-Voltage Converters (67 companies)
Frequency-to-voltage converters accept a signal and convert its frequency to a corresponding analog voltage level.
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I/O Modules, Data Acquisition (266 companies)
Data acquisition I/O modules or cards have both input and output functionality. Digital or discrete I/O modules include on-off signals used in communication, user interface, or control.
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Instrumentation Amplifiers (117 companies)
Instrumentation amplifiers are differential amplifiers that have been optimized for use with DC signals. They are characterized by high gain, high common mode rejection ratio (CMRR), and high input impedance.
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Isolation Amplifiers (15 companies)
Isolation amplifiers electrically isolate input and output signals, often by inductive couplings. Learn more about Isolation Amplifiers

LVDT and RVDT Signal Conditioners (53 companies)
Linear variable differential transformer (LVDT) and rotary variable differential transformer (RVDT) signal conditioners are devices that translate the linear or rotary movement of a ferromagnetic armature into an AC voltage that is proportional to the armature position.
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Optical Character Recognition (OCR) Products (16 companies)
Optical character recognition (OCR) products are used to read text from paper and translate it into data that can be manipulated by computers. Learn more about Optical Character Recognition (OCR) Products

Sensor Multiplexers (51 companies)
Sensor multiplexers allow the signal delivered to an instrument to be scanned or switched between multiple sensors. The multi-channel testing of multiple sensors/samples increases sample throughput and the productivity of costly instrumentation. Learn more about Sensor Multiplexers

Sensor Transmitters (770 companies)
Standardized measurement packages consisting of a transducer, its power supply, and a signal conditioner / retransmitter that converts the transducer signal into a standardized output.

Signal Amplifiers (225 companies)
Signal amplifiers accept signals from sensors and other devices and amplify them to levels suitable for further processing or digitization by computer elements.
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Signal Conditioning (549 companies)
Signal conditioning includes the amplification, filtering, converting, and other processes required to make sensor output suitable for reading by computer boards.
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Signal Converters (461 companies)
Signal converters contain inputs for one type of signal and outputs of another. Features can also include filtering and amplification or attenuation.
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Signal Filters (121 companies)
Signal filters block or decrease (attenuate) unwanted frequencies or signal wave characteristics.
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Signal Isolators (41 companies)
Signal isolators must be used when connecting grounded signal sources to grounded signal followers. If the speed control input of an adjustable frequency drive is grounded, any input signal must be ungrounded. Learn more about Signal Isolators

Signals Intelligence Systems (9 companies)
Signals intelligence (SIGNT) systems intercept technical and other intelligence-rated information from foreign electronic emissions. Learn more about Signals Intelligence Systems

Spectrum Analyzers and Signal Analyzers (153 companies)
Spectrum analyzers and signal analyzers display raw, unprocessed signal information such as voltage, power, period, wave shape, sidebands, and frequency. They can provide the user with a clear and precise window into the frequency spectrum.
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Telemetry Receivers and Telemetry Transmitters (270 companies)
Telemetry receivers and telemetry transmitters are data acquisition components used to gather information from remote locations via wireless communication.
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Temperature Signal Conditioning (195 companies)
Temperature signal conditioning devices accept outputs from temperature measurement devices such as resistance temperature detectors (RTDs), thermocouples, and thermistors. They then filter, amplify, and/or convert these outputs to digital signals, or to levels suitable for digitization.
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Voltage and Current Signal Conditioners (20 companies)
Voltage and current signal conditioners amplify or modulate AC or DC current or voltage and process signals to improve transmission. Learn more about Voltage and Current Signal Conditioners

Voltage Converters and Voltage Inverters (101 companies)
Voltage converters and voltage inverters accept voltage input and provide a scaled voltage output. Conversion types include scaling up a low-level signal, voltage doubling, and inversion (converting a positive voltage to negative and vice versa).
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Voltage-to-Frequency Converter Chips (6 companies)
Voltage-to-frequency converter chips provide a signal frequency output as a function of an analog input voltage. Learn more about Voltage-to-Frequency Converter Chips

Voltage-to-Frequency Converters (30 companies)
Voltage-to-frequency converters accept a voltage signal and convert its analog level to a signal with a corresponding frequency.
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Abrasives, Grinding and Finishing (2082 companies)
Equipment and products used for abrading , smoothing, or polishing.

Air Quality (1555 companies)
Instrumentation and equipment used to control the properties and degree of purity of air. These types of equipment include dust collectors, oxidizers, scrubbers and adsorption equipment.

Building and Construction Equipment (160 companies)
Building and construction equipment is used in a wide variety of construction projects. Product types include earth-moving equipment, cement mixers, elevators, and tower cranes. Learn more about Building and Construction Equipment

Ceramics and Glass Materials (1036 companies)
Any man-made solid produced by the fusion or sintering of mineral substances in a kiln or hard, heat resistant substances such as fire clay, bricks or blocks.

Cutting Tools (2180 companies)
Wide variety of tools for cutting, shaping, and finishing metals and other materials in the manufacturing process.

Electronics and Microelectronics Manufacturing (1324 companies)
Microelectronics and thin film manufacturing equipment including vacuum systems and components, gas delivery systems, deposition systems, photolithography units, etching equipment, annealing furnaces and other accessories.

Environmental Instruments and Equipment (1994 companies)
Instruments and equipment involved in testing, monitoring, and remediation of environmental factors. Specific aspects covered include water and wastewater treatment, air and groundwater quality analysis, waste processing, and pollution control.

Gas Handling Equipment (563 companies)
Any piece of equipment used to monitor, distribute, generate, compress and store process and industrial gases.

Filtration and Separation Products (2675 companies)
Processing equipment such as centrifuges, clarifiers, and several filter technologies used to filter or separate media of different materials or sizes.

Heating and Cooling Equipment (3786 companies)
Ovens, furnaces, induction heaters, welding equipment, heat exchangers, fans, blowers, refrigerators, baths and other equipment for heating or cooling materials.

Industrial Assembly (2277 companies)
Tools, equipment, and supplies for industrial fabrication, assembly, and prototyping.

Industrial Cleaning and Surface Preparation (2002 companies)
Equipment and supplies used to refine or roughen a surface to meet surface finish requirements or to clean, strengthen or prepare the surface for additional processing.

Industrial Heaters and Heating Elements (1140 companies)
Electrical resistance heaters or their internal elements; designed to provide an integrated thermal source for products or systems.

Industrial Machine Safeguarding (805 companies)
Components or systems that protect industrial machinery, operators or moving parts from injury or damage from electrical, mechanical or other potential hazards.

Inspection Tools and Instruments (1799 companies)
Equipment for metrology, inspection and quality control of dimensional features, internal flaw levels, surface characteristics and other industry specialized parameters.

Machine Tools (2679 companies)
Machine tools are power driven machines used to cut, form, or shape metal and other materials.

Machine Tool Accessories (3709 companies)
Tooling components and accessories for manufacturing equipment.

Materials Processing Equipment (3569 companies)
Extruding, casting, forging, compacting, heat treating, molding, rolling or other processing machines and components used for metals, polymers or other materials.

Pipe, Tubing, Hose, Fittings and Accessories (5110 companies)
Fluid transfer components, including all size hose, pipe, and tubing, with various general use and application-specific fittings.

Personal Protective Equipment (1482 companies)
Personal protective equipment is used to protect individuals from personal injury.

Process Controllers (1734 companies)
Instruments for monitoring and automatically revising process parameters such as temperature, pressure, force, humidity, level and flow.

Pumps (3077 companies)
Machines and devices used for the raising, compression or transference of a variety of materials.

Safety Sensors and Switches (224 companies)
Safety sensors and switches are used in machines and other industrial aplications to safeguard equipment and prevent personal injury.

Solids Processing and Bulk Material Handling (6952 companies)
Solids processing and bulk material handling equipment, including milling, classifying, compacting, granulating, feeding, flow-controlling or drying machines and components used to process powders or other bulk materials.

Specialty Manufacturing Products (1105 companies)
Equipment and components used for specialized applications. Some examples include wire straightening, lubrication, and the creation of extrusions, pultrusions, castings, and molded shapes.

Stock Fabricated Materials and Components (6460 companies)
Stock materials such as wire rope, fabrics, stock extrusions, strip, bar or sheet materials.

Surface Coating and Protection (3034 companies)
Products to coat and protect surfaces from contamination and corrosion.

Tanks and Vessels (1291 companies)
Equipment used to contain or store materials prior to, during, and after their processing.

Vacuum Equipment (1571 companies)
Vacuum equipment is used for degassing, welding, and the manufacturing of thin films, semiconductors, optics and specialty materials.

Web Handling and Processing Equipment (835 companies)
Equipment for handling, processing and converting continuous webs of textiles, paper, plastic films, metal sheet or other materials.

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Single component diaphragm valves are designed to provide a precise fluid supply depending on the application. The dispensed output can be a bead, dot or fill. Material pressure upon the valve forces the diaphragm to allow material through the fluid body and out the dispensing tip. Applying air pressure to the top of the diaphragm forms a seal, thus, closing off the valve. Diaphragm valves generally have a low number of moving parts and are often used to dispense low viscosity fluids including cyanoacrylates (superglue).

Diaphragm valves are related to pinch valves, but use an elastomeric diaphragm, instead of an elastomeric liner in the valve body, to separate the flow stream from the closure element.  Instead of pinching the liner closed to provide shut-off, the diaphragm is pushed into contact with the bottom of the valve body to provide shut-off.  Diaphragm valves are excellent for controlling the flow of fluids containing suspended solids and offer the flexibility of being installed in any position.  These types of valves have found widespread use in the pharmaceutical, food processing, and water treatment industries.

Manual diaphragm valves are ideal for flow control by offering a variable and precise opening for controlling pressure drop through the valve.  Actuated varieties can offer features as adjustable opening, positioners for precise flow control, and electric relay of valve position.

The advantages provided by diaphragm valves are many.  They are extremely clean, and can form a nearly leak-proof seal for tight shut-off.  The diaphragm design provides for easy maintenance and repair as it can be replaced without disturbing the piping line.  However, they are limited to moderate temperatures (-60 to 450°F) and pressure service (approximately 300 psi) by the mechanical properties of most common diaphragm materials. They cannot be used in multi-turn operations.

Diaphragm valves are available in two basic forms: weir type and straight through types.

The weir design is best for general use applications or for tough corrosive and abrasive services.  The straight through type can be used in situations where the flow direction changes within the system.  They are excellent for use with sludge, slurries and other viscous fluids.  Both styles provide a streamlined path for fluid flow that yields minimal pressure drop across the valve.

Single component diaphragm valves offer a number of specific advantages when working with viscous fluids.  First, their single part construction lacks specific weak points that multiple part devices have.  Therefore, they can accommodate the greater pressures and stresses that accompany high viscosity products.  Additionally, these diaphragm valves have fewer seam locations that could allow external air ingress that would cause aerobically curable products to harden. The result of this would be product backing up in the system and eventual seizure, leading to production downtime and extensive cleaning.

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What are the factors to consider for selecting & sizing damper actuator? The application is to control air stream from a blower. 

One way of approaching this is to try to make up a model number for an actuator and see what you have to specify, things like:

proportional or on-off?

1) How much torque is needed to move the damper and maintain position in the flow stream. Is it going to ice up in the winter?

2) response time from open to closed. Actuators can be slow or fast. What do you need?

3) power to drive the actuator: DC? AC? air?

4) Signal to the actuator? digital (which)? electronic (what kind)? pneumatic?

5) feedback signal: do you need to know the position?

6) auxiliary switches: do you have to prove the damper’s position?

7) enviromeental rating: indoors, outdoors, chemical spills on it?

Introduction

IEEE 1394 emerged as a serial bus standard in 1995, after being initially defined as “Firewire” by Apple. Rapidly it became the bus of choice for the Digital Consumer Electronic manufacturers owing to its extremely high data transfer rates (up to 800Mbps) and support for real time data streams. The dream of being able to Internet work all Consumer Devices in a home became a possibility with 1394 as Peer-Peer communication became a reality. The guaranteed delivery of data coupled with other above-mentioned advantages made 1394 a boon for Multimedia applications. IEEE 1394 is now suitably positioned to move into the orbit of Industrial Automation Systems and to radically change the approach to automation control design by challenging conventional bus technologies.

Traditional Automation Control Architecture

Current solutions in industrial automation and instrumentation can be characterised as centralised and backplane oriented. Backplane based controllers were considered to be natural choices for the designers of yesterday, as it was assumed that they could provide high communication speeds needed for industrial processes like synchronising motion, synchronising images and data acquisition. The rack mounted back plane, which is the standard implementation for most Industrial and Laboratory Automation controllers, uses bus solutions like VME, VXI, and PXI apart from proprietary buses like Modbus. In recent times, PCI buses have gained popularity in this market segment owing to the penetration of Windows based PCs. In the conventional architecture, all sensors, motors, digital inputs and outputs and analog signals are cabled from the point of use to converge at the centralised controllers with individual backplane cards designed to handle each specialised function. All signals are brought to the physical location of the system controller using multi-wire cable bundles. Figure 1 is a schematic of a Typical Automation Machine System with 6 axes of motion control, machine vision and process control.

These types of Machine Systems typically use several specialised backplanes to implement different control functions. Bus to bus communication between various subsystems is often through traditional RS-232/422/485 serial communication channels or through bus converters. This centralised approach limits reliability and configurability as hundreds of conductors are required to route signals to the central control chassis.
Overall this traditional approach is cumbersome, physically larger and is expensive with prices in the is cumbersome, physically larger and is expensive with prices in the range of $10,000 to $30,000 depending upon performance specifics. Another big problem is the software used for controllers. Due to the lack of standard interfaces, different vendors follow different software approaches to develop various subsystems and to integrate them proves to be expensive and time consuming.
Distributed Control Systems

To avoid the use of a centralised back plane based system, it is important to localise control of devices performing similar functions. This Distributed Control System (DCS) architecture uses some form of serial or parallel cable to link the already digitised information from point of use. In DCS, analog signals are quickly digitised, and functions that do not need to be centrally supervised are localised.
The advantages of using DCS are as follows:

* Greater signal integrity (S/N) by reducing the distance that an analog signals must travel before they are digitised, is important in applications where signal to noise ratio maximisation is demanded.
* Cabling can be simplified and functional sub systems can be modularised. These subsystems can be then plugged into bigger and more complex networks hence simplifying system configuration.
* Remote monitoring of signals or control functions over a corporate or public network is simpler with a DCS architecture as it is naturally packet driven

A distributed control system (DCS) refers to a control system usually of a manufacturing system or process or any kind of dynamic system, in which the controller elements are not central in location (like the brain) but are distributed throughout the system with each component sub-system under the control of one or more controllers. The entire system may be networked for communication and monitoring.

Distributed control systems (DCSs) are used in industrial, electrical, computer and civil engineering applications to monitor and control distributed equipment with or without remote human intervention; the nomenclature for the former ‘manual control’ and the latter ‘automated control’.

A DCS typically uses computers (usually custom designed processers) as controllers and use both proprietary interconnections and protocols for communication. Input & output modules form component parts of the DCS. The processor (which is a part of the controller) receives information from input modules and sends information to output modules. The input modules receive information from input instruments in the process (aka field) and output modules transmit to the output instruments in the field. Computer buses or electrical buses connect the processor and modules through multiplexers/demultiplexers. They also connect the distributed controllers with the central controller and finally to the Human-Machine Interface (HMI) or control consoles. See PAS.

DCS is a very broad term that describes solutions across a large variety of industries, including:

* Electrical power grids and electrical generation plants
* Environmental control systems
* Traffic signals
* Water management systems
* Refining and chemical plants
* Pharmaceutical manufacturing
* Sensor Networks

The broad architecture of a solution involves either a direct connection to physical equipment such as switches, pumps and valves or connection via a secondary system such as a SCADA system.

A DCS solution does not require operator intervention for its normal operation, but with the line between SCADA and DCS merging, systems claiming to offer DCS may actually permit operator interaction via a SCADA system.

Distributed Control Systems (DCSs) are dedicated systems used to control manufacturing processes that are continuous or batch-oriented, such as oil refining, petrochemicals, central station power generation, pharmaceuticals, food & beverage manufacturing, cement production, steelmaking, and papermaking. DCSs are connected to sensors and actuators and use setpoint control to control the flow of material through the plant. The most common example is a setpoint control loop consisting of a pressure sensor, controller, and control valve. Pressure or flow measurements are transmitted to the controller, usually through the aid of a signal conditioning Input/Output (I/O) device. When the measured variable reaches a certain point, the controller instructs a valve or actuation device to open or close until the fluidic flow process reaches the desired setpoint. Large oil refineries have many thousands of I/O points and employ very large DCSs. Processes are not limited to fluidic flow through pipes, however, and can also include things like paper machines and their associated variable speed drives and motor control centers, cement kilns, mining operations and ore processing facilities, and many others.

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 input/output devices (I/O) can be integral with the controller or located remotely via a field network. Today’s controllers have extensive computational capabilities and, in addition to proportional, integral, and derivative (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.

[edit] History

The DCS was introduced in 1975. Both Honeywell and Japanese electrical engineering firm Yokogawa introduced their own independently produced DCSs at roughly the same time, with the TDC 2000 and CENTUM systems, respectively. US-based Bristol also introduced their UCS 3000 universal controller in 1975. In 1980, Bailey (now part of ABB) introduced the NETWORK 90 system.

The DCS largely came about due to the increased availability of microcomputers and the proliferation of microprocessors in the world of process control. Computers had already been applied to process automation for some time in the form of Set Point Control, where process computers supervised clusters of analog controllers. The proliferation of microprocessors allowed suppliers to take this mode to the next step by deploying minicomputers in a supervisory role, controlling several digital loop controllers. A CRT-based workstation provided visibility into the process using text and crude character graphics. Availability of a fully functional graphical user interface was a long way away.

Central to the DCS model was the inclusion of control function blocks, which were introduced by the Foxboro company. One of the first embodiments of object-oriented software, function blocks were self contained “blocks” of code that emulated analog hardware control components and performed tasks that were essential to process control, such as execution of PID algorithms. Function blocks continue to endure as the predominant method of control for DCS suppliers, and are supported by key technologies such as Foundation Fieldbus [1] today.

Digital communication between controllers and supervisory computers was one of the primary advantages of the DCS, and attention was duly focused on the networks, which provided the all-important lines of communication that, for process applications, had to incorporate specific functions such as determinism and redundancy. As a result, many suppliers embraced the IEEE 802.4 networking standard. This decision set the stage for the wave of migrations necessary when information technology moved into process automation and IEEE 802.3 rather than IEEE 802.4 prevailed as the control LAN.

The Network Centric Era of the 1980s

The DCS brought distributed intelligence to the plant and established the presence of computers and microprocessors in process control, but it still did not provide the reach and openness necessary to unify plant resource requirements. In many cases, the DCS was merely a digital replacement of the same functionality provided by analog controllers and a panelboard display. This was embodied in The Perdue Reference Model (PRM) that was developed to define Manufacturing Operations Management relationships. PRM later formed the basis for ISA95 standards activities today.

In the 1980s, users began to look at DCSs as more than just basic process control. It was believed that if openness could be achieved and greater amounts of data could be shared throughout the enterprise that good things could be achieved, although few were sure what these benefits would be. The first attempts to increase the openness of DCSs resulted in the adoption of the predominant operating system of the day — UNIX. UNIX and its companion networking technology TCP-IP were developed by the Department of Defense for openness, which was precisely the issue the process industries were looking to resolve.

As a result suppliers also began to adopt Ethernet-based networks with their own proprietary protocol layers. The full TCP/IP standard was not implemented, but the use of Ethernet made it possible to implement the first instances of object management and global data access technology. The 1980s also witnessed the first PLCs integrated into the DCS infrastructure. Plant-wide historians also emerged to capitalize on the extended reach of automation systems. The first DCS supplier to adopt UNIX and Ethernet networking technologies was Foxboro, who introduced the I/A Series system in 1987.

The Application Centric Era of the 1990s

The drive toward openness in the 1980s gained momentum through the 1990s with the increased adoption of Commercial-Off-The-Shelf (COTS) components and IT standards. Probably the biggest transition undertaken during this time was the move from the UNIX operating system to the Windows environment. While the realm of the real time operating system (RTOS) for control applications remains dominated by real time commercial variants of UNIX or proprietary operating systems, everything above real-time control has made the transition to Windows.

The invasion of Microsoft at the desktop and server layers resulted in the development of technologies such as OLE for Process Control (OPC), which is now a de facto industry connectivity standard. Internet technology also began to make its mark in automation and the DCS world, with most DCS HMI supporting Internet connectivity. The ’90s were also known for the “Fieldbus Wars”, where rival organizations competed to define what would become the IEC fieldbus standard for digital communication with field instrumentation instead of 4-20 milliamp analog communications. The first fieldbus installations occurred in the 1990s. Towards the end of the decade, the technology began to develop significant momentum, with the market consolidated around Foundation Fieldbus and Profibus PA for process automation applications. Some suppliers built new systems from the ground up to maximize functionality with fieldbus, such as Emerson with the DeltaV control system.

The impact of COTS, however, was most pronounced at the hardware layer. For years, the primary business of DCS suppliers had been the supply of large amounts of hardware, particularly I/O and controllers. The initial proliferation of DCSs required the installation of prodigious amounts of this hardware, most of it manufactured from the bottom up by DCS suppliers. Standard computer components from manufacturers such as Intel and Motorola, however, made it cost prohibitive for DCS suppliers to continue making their own components, workstations, and networking hardware.

As the suppliers made the transition to COTS components, they also discovered that the hardware market was shrinking fast. COTS not only resulted in lower manufacturing costs for the supplier, but also steadily decreasing prices for the end users, who were also becoming increasingly vocal over what they perceived to be unduly high hardware costs. Some suppliers that were previously stronger in the PLC business, such as Rockwell Automation and Siemens, were able to leverage their expertise in manufacturing control hardware to enter the DCS marketplace with cost effective offerings.

To compound the issue, suppliers were also realizing that the hardware market was becoming saturated. The lifecycle of hardware components such as I/O and wiring is also typically in the range of 15 to over 20 years, making for a challenging replacement market. Many of the older systems that were installed in the 1970s and 1980s are still in use today, and there is a considerable installed base of systems in the market that are approaching the end of their useful life. Developed industrial economies in North America, Europe, and Japan already had many thousands of DCSs installed, and with few if any new plants being built, the market for new hardware was shifting rapidly to smaller, albeit faster growing regions such as China, Latin America, and Eastern Europe.

Because of the shrinking hardware business, suppliers began to make the challenging transition from a hardware-based business model to one based on software and value-added services. It is a transition that is still being made today. The applications portfolio offered by suppliers expanded considerably in the ’90s to include areas such as production management, model-based control, real-time optimization, Plant Asset Management (PAM), Real Time Performance Management (RPM) tools, alarm management, and many others. To obtain the true value from these applications, however, often requires a considerable service content, which the suppliers also provide. DCS supplier services have also expanded in scope to the point where many suppliers can act as Main Automation Contractors (MACs), providing a single point of responsibility for all automation-related facets of a project

A valve-proving system confirms the effective closure of both main safety valves in fuel-fired equipment. Should you add it to your gas control scheme?

Simply put, a valve-proving system is a safety control used on gas fuel-fired equipment that verifies the effective closure of two safety shutoff valves in series by detecting gas leakage.

TIP 1: Understand Valve-Proving Systems’ Beginnings

Figure 1
Figure 1. Rather than proving both safety valves at the same time, the passive valve-proving system proves each safety valve separately.

In the 1950s and ’60s, as the gasification of Europe began, the European code bodies adopted the U.S. safety standards and practices for gas combustion. Europe simply had little experience with natural gas at that time, and the U.S. safety practices, which applied redundant safety controls, were adopted. As a result, Europe adopted the “double block and vent” and “proof-of-closure” concepts as a means to validate the prepurge cycle.

As Europeans gained experience with fuel-fired equipment, incidences occurred that illustrated the shortcomings of proof-of-closure switches and vent valves, which could allow the system to operate under unsafe conditions. This provided the impetus for European manufacturers to look for other solutions, and the concept of a valve-proving system (VPS) was introduced in Germany in the early 1970s.

TIP 2: A Valve-Proving System Confirms the Effective Closure of Both Safety Valves

Figure 2
Figure 2. The active valve-proving system confirms the effective closure of both safety valves by opening an internal safety valve, starting an internal pump and internal timer, and monitoring positive differential pressure between the two safety valves within the specified time.

Currently, two basic types of valve-proving systems are available: the active, or pressure, system and the passive, or static, system.

The active valve-proving system detects gas leakage by verifying flow through an orifice of known diameter and proves both safety valves simultaneously (figure 1). The active valve-proving system confirms the effective closure of both safety valves by:

* Opening an internal safety valve, which typically is a 1 to 2 mm port diameter auxiliary safety valve that bypasses the first main safety valve.

* Starting an internal pump and simultaneously starting an internal timer. The pump pressurizes the volume between the two main safety valves using gas pressure from upstream of the first main safety valve.

* Monitoring positive differential pressure between the two safety valves within the specified time.

If the differential pressure between the safety valves reaches approximately 0.5 psi over the inlet pressure within the specified time, both safety valves are proven closed. If the pressure between the safety valves fails to reach the overpressure level within the specified time, the valve-proving system detects a leak and locks out the system.

Rather than proving both safety valves at the same time, the passive valve-proving system proves each safety valve separately (figure 2). When proving the No. 1 main safety valve, the passive valve-proving system detects gas leakage by monitoring for pressure rise between both safety valves; and subsequently when proving the No. 2 main safety valve, it monitors for pressure decay between both safety valves. The passive valve-proving system may have its own auxiliary safety valves that bypass main safety valves, or it may simply cycle the main safety valves during valve proving. However, to illustrate the valve proving sequence, it is easiest to show auxiliary safety valves. During valve proving, the passive valve-proving system proves the effective closure of the No. 2 main safety valve by:

* Opening the No. 1 auxiliary safety valve and allowing upstream gas pressure to fill the volume between both main safety valves.

* Closing the No. 1 auxiliary safety valve, and simultaneously starting an internal timer.

* Using the No. 1 pressure sensor to monitor the pressure between the two safety valves.

If the No. 1 pressure sensor does not detect pressure decay within the specified time, the second main safety valve is proven closed.

Essentially, the same process is repeated for proving the No. 1 main safety valve, but this time, the No. 2 auxiliary safety valve vents the volume between the main safety valves and the No. 2 pressure sensor monitors the manifold for pressure rise. If the No. 2 pressure sensor does not detect pressure rise within the specified time, the first main safety valve is proven closed.

If either pressure sensor detects a leak due to pressure decay or pressure rise, the valve-proving system locks out the system.

TIP 3: Valve-Proving Systems Are Included in Standards

Figure 3
Figure 3. In the United States, a valve-proving system can be used as an alternative to a vent valve in several standards.

A valve-proving system currently is used on gas-fuel-fired equipment in Europe, Australia, China, Russia and in South and North America (figure 3). The following codes and standards that apply the use of valve-proving systems can be used as reference:

* European Standard EN 746-2 for industrial thermoprocessing equipment.

* European Standard EN 676 for automatic forced draft burners for gaseous fuels.

* Australian AG 501 code for industrial and commercial gas-fired appliances.

In the United States, a valve-proving system can be used as an alternative to a vent valve in the following standards:

* NFPA 85 (when venting of gas is prohibited).

* NFPA 160, Standard for Flame Effects Before an Audience.

* Fuel-fired equipment insured by Factory Mutual (FM).

* Fuel-fired equipment insured by GE Global Asset Protection (GAP) Services (formerly IRI).

* Ford Motor Co. specification.

* General Motors specification.

Also in the United States, a valve-proving can be used as an alternative to proof-of-closure in the following standards:

* Fuel-fired equipment insured by FM.

* Fuel-fired equipment insured by GE GAP Services.

NFPA 86 currently is under revision, and the revision has provisions for either a valve-proving system or a proof-of-closure switch.

TIP 4: Understand Why Equipment Standards Require a Proof-of-Closure Switch, Normally Open Vent Valve, and/or a Prepurge

One major hazard with fuel-fired equipment is having an explosive mixture of fuel in an enclosed, or semi-enclosed, area that cannot safely relieve the expansion forces of the gas when ignited. Historically, the number of boiler and furnace explosions were reduced by requiring certain safety practices and incorporating certain safety controls into the fuel-fired equipment. This was done to provide an acceptable level of risk to the public.

For fuel-fired equipment, a high risk of incident occurs during burner lightoff. One important practice to reduce the risk of explosions is to prepurge the combustion chamber. The intent of prepurge is to remove all combustible gases from the combustion chamber before introducing an ignition source; the common four air-change prepurge is based on a worst-case scenario of having a burner chamber completely filled with fuel gas.

If both safety valves did not leak gas, there would actually be no reason to prepurge. However, loss experience has shown that safety valves can fail to close and can leak gas into the combustion chamber; therefore, the chamber is prepurged to provide redundant safety in the system in case both safety valves leak gas into the combustion chamber. The addition of proof-of-closure switches and/or a vent valve provides an additional level of safety to simply validate prepurge.

TIP 5: Proof-of-Closure Switches Are One Way to Validate Prepurge

Figure 4
Figure 4. A proof-of-closure switch does not detect problems with a valve seat but only verifies the position of the valve stem. In this example, a 0.25 mm dia. wire inserted below the valve seat of an energized (open) valve. The valve then is de-energized (closed), and the valve stem fully closes while at the same time the valve seat does not.

Before introducing an ignition source, prepurge should be validated. Validate does not imply guarantee but rather implies a high degree of confidence that the risk to introduce an ignition source in the combustion chamber is considered negligible. For example, a prepurge is not valid if the safety valves were wide open during prepurge.

To validate the prepurge, a combustion air switch verifies adequate airflow. In addition, there should be some means to verify that gas is not flowing into the combustion chamber at a rate such that prepurge is not able to remove enough gas from the chamber to remain far below the lower explosive limit (LEL) during ignition. A proof-of-closure switch on a safety valve provides a degree of confidence in the “validity” of the prepurge by verifying that the valve is in its fully closed position. A proof-of-closure switch on each safety valve provides even a higher degree of confidence.

A normally open vent valve mounted in between both safety valves also provides a degree of confidence in the “validity” of the prepurge. This valve prevents the buildup of pressure between the safety valves and thus minimizes gas leakage to the burner if both the No. 1 valve leaks and the No. 2 valve leaks in the closed position.

TIP 6: A Valve-Proving System Is an Alternative to a Normally Open Vent Valve

In the case that No. 1 valve and the No. 2 valve leak in the closed position, the vent valve mounted in between two safety valves provides a degree of validity to the prepurge. The vent valve minimizes the potential for leakage into the furnace by diverting any leaking gas to a safer location. Unlike a vent valve, the valve-proving system does not allow for ignition if either valve is detected as leaking, thereby validating the prepurge cycle. Furthermore, a vent valve will not interrupt the limit circuits; thus, ignition is still allowed. By contrast, a valve-proving system locks out the ignition sequence when a problem is detected.

Unlike a valve-proving system, a vent valve allows ignition under conditions when far more gas can leak to the burner. Instances when a vent valve would allow ignition include:

* Both valves, which have severely damaged valve seats, leak in the closed position.

* The No. 1 valve fails to close and the No. 2 valve leaks.

* The No. 1 valve leaks in the closed position and the No. 2 valve fails to close.

* Both valves fail to close.

TIP 7: A Valve-Proving System Is an Alternative to Proof-of-Closure Switches

A proof-of-closure switch validates prepurge by proving that the valve stem is in the minimum (closed) position. The valve stem position is related to the valve seat position. If a switch indicates that the valve stem is closed, there is a high degree of certainty that the valve seat is not leaking gas into the burner.

Similarly, a valve-proving system provides a high degree of certainty by directly verifying the position of both valve stems. If a valve stem does not close all of the way, the valve seat is not in contact with the valve disc, and the valve-proving system detects an open valve due to gas leakage. The valve-proving system also verifies the valve seats. If the valve stem closes 100 percent but the valve seats are damaged, a valve-proving system will detect a problem and prevent ignition.

A proof-of-closure switch does not detect problems with a valve seat but only verifies the position of the valve stem. Figure 4 shows a relationship between valve seat closure and valve stem closure. Illustrated is a 0.25 mm dia. wire inserted below the valve seat of an energized (open) valve. The valve then is de-energized (closed), and the valve stem fully closes while at the same time the valve seat does not. The amount of gas leakage due to the 0.25 mm dia. wire is detected by a valve-proving system but not a proof-of-closure switch.

TIP 8: Don’t Consider a Valve-Proving System an Alternative to the Annual Valve Seat Bubble Test

The valve seat “bubble” test is an annual maintenance requirement for installed safety valves in most fuel-fired equipment standards and generally a requirement or recommendation of safety valve manufacturers. The allowable valve seat leakage rates on installed safety valves are determined by the safety valve manufacturer, who typically applies the same requirements as specified in the safety valve standard ANSI Z21.21/CGA 6.5. This standard is applied to new safety valves leaving the factory. The allowable rates for installed valves typically are not more stringent than ANSI Z21.21/CGA 6.5 requirements.

A valve-proving system is not designed to detect leakage rates less than or equal to the ANSI Z21.21/CGA 6.5 standard; it is designed to detect leakages above the ANSI Z21.21/CGA 6.5 standard. Therefore, a valve-proving system, which is intended to prove the effective closure of both safety valves by detecting leakage, is not currently an alternative to the annual valve seat bubble test.

TIP 9: Don’t Confuse the Valve-Proving System’s Detection Limit with the Valve Bubble Test Standard

Generally speaking, a valve-proving system’s detection limit is the maximum amount of gas leakage at which a prepurge can still be validated. A valve-proving system should take into account application-specific variables such as operating pressure, fuel gas type and the manifold volume. To simplify this, the European standard EN 1643, “Valve Proving Systems,” adopts a maximum rate of 1.76 ft3/hr (50 l/hr) or 0.10 percent of burner capacity. In combination with a prepurge, this maximum rate still provides a high degree of certainty to allow burner ignition.

A common error in thinking is that a valve-proving system should detect leakage rates to the ANSI Z21.21/CGA 6.5 safety valve standard. This might be applicable if a valve-proving system were used as an alternative to the annual valve seat bubble test. However, no equipment standard requires a valve seat bubble test at every burner startup or shutdown.

TIP 10: Take Advantage of a Valve-Proving System’s Safety Features

A valve-proving system provides several safety benefits. It actively checks the integrity of both safety valves on every startup or shutdown. It detects safety shutoff valve problems that other safety controls ignore. It is equally safe with heavier-than-air fuels as with lighter-than-air fuels. Also, it gives the user at least some idea of the condition of the safety valve seat leakage rate.

When a valve-proving system is used as an alternative to a vent valve, no gas is released to the atmosphere. As a result, it is environmentally friendly. Furthermore, unlike a proof-of-closure switch, a valve-proving system is a “self-checking” safety control, which means that the system faults and does not allow ignition if its internal proof-of-closure signal fails to change state.