Glossary of Terms
A
ActiveX
Microsoft's toolkit for Web developers, using OLE and incorporating Sun's Java language. ActiveX helps in building software to integrate with Microsoft's Internet Explorer, or any ActiveX container such as programs written with Microsoft's Visual Studio.
Actuator
In a closed-loop control system, that part of the final control element that translates the control signal into action by the control device.
AS-I (Actuator-Sensor Interface)
A low-cost electromechanical connection system designed to operate over a two-2ire cable carrying data and power over a distance of up to 100m, or more if repeaters are used. Visit www.as-interface.com for more information.
Analog Input Module
An I/O module that contains circuits that convert analog dc input signals to digital values that can be manipulated by the processor. By implication, these analog inputs are usually direct (i.e., a data table value directly reflects the analog signal value).
Analog Output Module
An I/O module that contains circuits that output an analog dc signal proportional to a digital value transferred to the module from the processor. By implication, these analog outputs are usually direct (i.e., a data table value directly controls the analog signal value).
B
Bar Code
A series of horizontal stripes or bars of varying width which represent a string of characters that can be read by a bar code reader (scanner).
Bill of Materials (BOM)
A list of components, ingredients, or materials needed to manufacture a product; the hierarchy of materials or components making up a product or subassembly including the proper ratios of quantities of each item.
Brushless Servomotor
A class of servomotors which operates using electronic commutation of phase currents rather than electromechanical (brushes) commutation. Commutation is a function of rotor position. These motors typically have a permanent magnet rotor and wound stator.
C
CAD (Computer Aided Design)
Programs used to design architectural, mechanical and electrical engineering drawings.
CAM (Computer Aided Manufacturing)
Programs used to control manufacturing equipment.
Computer Integrated Manufacturing (CIM)
A term used for describing a high level of automation in a manufacturing enterprise.
CMOS (Complimentary Metal-Oxide-Semiconductor)
Family of logic devices that uses p-type and n-type channel devices on the same IC. It has the advantage of offering medium speed and very low power requirements.
CNC (Computer Numerical Control)
Allows the control of motion in an accurate and programmable manner through use of a dedicated computer within a numerical control unit, with a capability of local data input such that machine tools are freed from the need for "hard-wired" controllers.
ControlNet
A real-time, control-layer network providing high-speed transport of both time-critical IO data and messaging data, including upload/download of programming and configuration data and peer-to-peer messaging, on a single physical media link.
Conveyor
A horizontal, inclined or vertical device for moving or transporting bulk materials, packages, or objects in a path predetermined by the design of the device and having points of loading and discharge fixed, or selective.
Crossdocking
In warehouse management, sending parts from receiving directly to shipping to be placed in outgoing orders. Crossdocking allows orders to be filled quickly and precludes parts from staying in a warehouse long enough to be counted as inventory.
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D
DAC (Digital-to-Analog Converter)
An electronic device, often an integrated circuit, that converts a digital number into a corresponding analog voltage or current.
Data Acquisition
A term commonly used for equipment or software that gathers data from devices through a communications channel.
Data Highway
The proprietary data network used by Allen Bradley PLCs to communicate information to and from other PLCs on the network or to and from host computers attached to the network.
Device Driver
A software component that permits a computer system to communicate with a device.
DeviceNet
A low-cost communication link that connects industrial devices to a network.It is based on broadcast-oriented communication protocol - the Controller Area Network (CAN).
Distribution Center
Intermediate warehouse where products from different sources are assembled for shipment and distribution to specific customer locations.
Downtime
Periods where computers, equipment, or manufacturing systems are not available to perform work.
DLL (Dynamic Link Library)
A software module loaded into memory at execution time in order to access functions of that module.
DSP (Digital Signal Processor)
An integrated circuit designed for high-speed data manipulations. Used in audio, communications, image manipulation, and other data-acquisition and data-control applications.
E
ECP (Extended Capabilities Port)
An asynchronous, 8-bit-wide parallel channel defined by IEEE 1284-1944 that provides PC-to-peripheral and peripheral-to-PC data transfers.
EEPROM (Electrically Erasable Programmable Read-Only Memory)
ROM that can be erased with an electrical signal and reprogrammed.
Embedded System
A combination of computer hardware and software, and perhaps additional mechanical or other parts, designed to perform a dedicated function. In some cases, embedded systems are part of a larger system or product, as is the case of an anti-lock braking system in a car. Contrast with general-purpose computer.
Defined by Michael Barr, President, Netrino Consultants Network.
Encoder
A feedback device which converts mechanical motion into electronic signals. Usually an encoder is a rotary device that outputs digital pulses which correspond to incremental angular motion. The encoder consists of a glass or metal wheel with alternating clear and opaque stripes that are detected by optical sensors to produce the digital outputs.
EPROM (Erasable Programmable Read Only Memory)
This sounds like a contradiction in terms as ROMs are Read only Memory that by definition cannot be erased by switching off the current. However, EPROM acts as ROM unless special action is taken. An EPROM contains charge in a transistor gate that holds it for up to 10 years. Applying ultraviolet light to the chip's surface dissipates the charge, erasing the memory content and allowing the reprogramming of the chip through the transistor gate using a higher voltage than is normally present on a PC board.
Ethernet
The standard for local communications networks developed jointly by Digital Equipment Corp., Xerox, and Intel. Ethernet baseband coaxial cable transmits data at speeds up to 10 megabits per second. Ethernet is used as the underlying transport vehicle by several upper-level protocols, including TCP/IP.
F
Fault Tolerant
Able to withstand a considerable degree of error without crashing. This may involve copying data or mirroring data and having extra capacity. It is often achieved by using several separate processors, each monitoring the others and operating a voting system, so that if one fails, the others shut it down, call for human help and carry on operations.
Fiber Optics
A data transmission medium using light conducted through glass or plastic fibers. A fiber-optic cable has cores capable of conducting modulated light signals by internal reflection.
Fieldbus
Fieldbus is a generic term used to describe a common communications protocol for control systems and/or field instruments. Although some standard forms have been agreed for instruments, the DCS industry as a whole has so far no agreed fieldbus. Often, the Foundation Fieldbus is referred to simply as the Fieldbus.
Firmware
A computer program or software stored permanently in PROM or ROM.
Flash Memory
A RAM-ROM hybrid that can be erased and rewritten under software control. Such devices are divided into blocks, called sectors that are individually erasable. Flash memory is common in systems that require nonvolatile data storage at very low cost. In some cases, a large flash memory may even be used instead of a disk drive.
Foundation FieldBus
A digital, two-way communication link among intelligent field-level and control devices that will replace the 4-20 mA standard.
Frequency
Defines number of events during a time period. Hertz (Hz) is a measurement of frequency.
G
Gain
A term used in a PID loop calculation. It is the "P" in PID, since gain is the inverse of proportional band. Gain acts directly on the change in error since the last scan.
GMP (Good Manufacturing Practices)
A methodology of specification for a manufacturing process that ensures quality, safety, and engineering tolerances are met.
Grounding
The intentional connection of sections of an electrical circuit to a common reference conductor called the ground. The ground is almost always at a potential of zero volts and serves as the reference for the other voltages in the circuit.
GUI (Graphical User Interface)
A type of display format that enables the user to choose commands, start programs, and see lists of files and other options by pointing to pictorial representations (icons) and lists of menu items on the screen. Choices can generally be activated either with the keyboard or with a mouse.
H
Hertz (Hz.)
A unit of measurement that measures how often a periodic event, such as a waveform, occurs. One hertz equals one cycle per second. Frequency is often measured in kilohertz (KHz, 1000Hz), megahertz (MHz, 1000 KHz), gigahertz (GHz, 1000MHz), or terahertz (THz, 1000 GHz).
Hot Swap
Exchange of components during operation.
I
I/O port
A channel through which data is transferred between an input or output device and the microprocessor. The port appears to the CPU as one or more memory addresses that it can use to send or receive data.
ISA (Industry Standard Architecture)
An unofficial designation for the bus design of the IBM PC/XT, which allows various adapters to be added to the system by means of inserting plug-in cards into expansion slots.
IEEE (Institute of Electrical and Electronics Engineers)
An organization of engineering and electronics professionals notable for developing the IEEE 802 standards for the physical and data-link layers of local area networks following the ISO Open Systems Interconnection model.
Integrated Circuit
A collection of electronic devices working together.
J
K
Kanban
Kanban is often seen as a central element of lean manufacturing and is probably the most widely used type of ‘Pull’ signaling system. Kanban was derived from the Japanese language and means “card-signal.”
There are two fundamentally different approaches to controlling how downstream activities signal their needs to upstream activities. In Pull Production, authorizations to produce more (or replenish inventories of purchased materials) are based on the consumption of the material from controlled inventory locations. “Use one, make one” is the simplest form of this method. In Push Production, however, the authorizations to produce more or purchase more of an item are based on the anticipation of its use. A Push system attempts to predict when the item or material will be needed and launch authorizations in anticipation of this need.
Kanban systems are commonly used within the automotive industry where there is a stable demand and flow. Other such stable manufacturing environments will also likely benefit from a Kanban system.
The manufacturing operations of some companies does not experience stable demand within any particular product. In fact, the opposite is quite often the case—high product variety and low volumes. In these circumstances a Kanban system may not be suitable for the entire production process but there are probably sub areas where a Kanban system of one form or another will aid production planning and material control.
Once the proper manufacturing environment has been identified, there are number of critical rules that apply to all Kanban systems, including:
•Customer processes order goods in the precise amounts specified on the Kanban.
•Supplier processes produce goods in the precise amounts and sequence specified by the Kanban.
•No items are made or moved without a Kanban.
•All parts and materials always have a Kanban attached.
•Defective parts and incorrect amounts are never sent to the next process.
•The number of Kanbans is reduced carefully to lower inventories and reveal problems.
L
Latency
The delay time between the end of one communication and the start of another. During this time, the processes associated with the communication are hung up and cannot continue. Software engineers work to reduce latency to a minimum.
Legacy Systems
Computer systems or application programs which are outdated and incompatible with other systems, but are too costly to replace or redesign. They are often large, intimidating, and difficult to modify.
M
Material Handling
The movement, storage, control, and protection of materials and products throughout the process of their manufacture, distribution, consumption and disposal.
ModBus
Protocol originally developed by Modicon, now part of Schneider Automation.
N
O
OOA (Object Oriented Analysis)
Developing software engineering requirements and specifications that expressed as a system's object model ( which is composed of a population of interacting objects), as opposed to the traditional data of functional views of systems.
OOD (Object Oriented Design)
Developing of Object Oriented model of a software system to implement the identified requirements.
Open Systems
Those systems that can be supplied by hardware components from multiple vendors, and whose software can be operated from different platforms. They are opposite to closed or proprietary systems.
Oscilloscope
A Hardware debugging tool that allows you to view the voltage on one or more electrical lines. For example, you might use an oscilloscope to determine if a particular interrupt is currently asserted.
P
Pamux
A high-speed, high-density distributed I/O system that accommodates both digital and analog I/O modules. Pamux supports up to 32 stations containing up to 512 I/O points. Contact OPTO22 for more information.
PCI (Peripheral Component Interconnect)
A high-performance expansion bus architecture originally developed by Intel to replace ISA and EISA. It is achieving widespread acceptance as a standard for PCs and workstations; it offers a theoretical maximum transfer rate of 132 Mbytes/s.
PCM (Pulse Coded Modulation)
A method of encoding information in a signal by varying the amplitude of pulses. The most common method of encoding an analog signal into a digital bit stream, usually 16 bits per sample.
PID Loop
An I/O element used to drive an analog input toward a particular value (called the setpoint) and to keep the input very close to that value. PID loops include a gain term (abbreviated P for proportional, which is the inverse of gain), an integral term (I), and a derivative term (D). Temperature control is a typical application for a PID.
PLC (Programmable Logic Controller)
A class of industrially hardened devices that provides hardware interface for input sensors and output actuators. PLCs can be programmed using relay ladder logic to control the outputs based on input conditions and / or algorithms contained in the memory of the PLC.
Priority Inversion
An unwanted software situation in which a high-priority task is delayed while waiting for access to a shared resource that is not even being used at the time. For all practical purposes, the priority of this task has been lowered during the delay period.
Profibus
Vendor-independent open fieldbus standard for use in manufacturing and building automation as well as process control. Utilizes a non-powered two-wire (RS485) network. PROFIBUS is standardized under the European Fieldbus Standard EN 50 170. Includes 3 versions - FMS, DP and PA. Visit www.profibus.com for more information.
PROM (Programmable Read-Only Memory)
A type of ROM that can be written (programmed) with a device programmer. These memory devices can be programmed only once, so they are sometimes referred to as write-once or one-time programmable devices.
PWM (Pulse Width Modulation)
A switch-mode control method used in amplifiers and drivers to control motor voltage and current to obtain higher efficiency than linear control. PWM refers to variable on/off times (or width) of the voltage pulses applied to the transistors.
Q
Quadrature
A technique that separates signal channels by 90ø (electrical) in feedback devices. It is used with encoders and resolvers to detect direction of motion.
R
Redundancy
The capacity to switch from primary equipment to standby equipment automatically without affecting the process under control.
Relay Ladder Logic
This programming language expresses a program as a series of "coils" and "contacts", simulating the operation of electromechanical relays. The resultant program is the equivalent of a boolean equation, which is executed continuously in a combinatorial manner. The advantage of this language is the familiarity many electricians have with the simple operation of relays. Disadvantages include the complexity of large, cross-connected programs, and the difficulty of expressing such non-binary functions as motion control and analog I/O.
Remote Access
Access to a network in another location.
Ribbon Cable
A flat cable in which the conductors are arranged side-by-side. Also called flat-ribbon cable.
RS232
A standard for serial transmission of data between two devices. This defines the pin and plug in terms of size, shape and number of pins. An interface based on the RS232 standard.
RS422
A standard for serial transmission of data between two devices. This defines the pin and plug in terms of size, shape and number of pins. An interface based on the RS422 standard. Allows longer distances between devices than RS232.
RS485
A standard for serial transmission of data between multiple devices. This defines the pin and plug in terms of size, shape and number of pins. An interface based on the RS485 standard.
RTOS (Real-Time Operating System)
An operating system designed specifically for use in real-time systems that respond to external events within a short and predictable time frame.
RTX
Real time extension for Windows NT developed by VenturCom .
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S
Sampling Rate
The frequency with which samples of a physical variable, such as sound are taken. The higher the sampling rate, the more closely the digitized result resembles the original.
Scan Time
The time to completely execute a PLC program once, including I/O update.
SCADA (Supervisory Control and Data Acquisition)
The level of applications that monitor and control devices such as programmable controllers. These systems are usually PC or workstation based.
SDS (Smart Distributed System)
An advanced bus system for intelligent sensors and actuators developed by Honeywell Inc., Micro Switch Division. The SDS specification covers physical layer and application layer. Smart Distributed System devices have advanced device-level functions, system and device diagnostics.
SERCOS (SErial Real-time COmmunications System)
The standard (IEC-61491) for interfacing between controllers, digital servo drives, and I/O devices. The SERCOS interface is implemented with fiber optic cable that increases the reliability and noise-immunity of a multi-axis control system.
Serial Interface
Relating to the electrical interconnection between the computer and peripheral units (for instance, a printer) in which data is transmitted 1 bit at a time over a single wire.
Serial Port
A computer interface for connecting to external drives where data is transferred serially.
Servo Motor
A power-driven mechanism that supplements a primary control operated by a comparatively feeble force (as in a servo mechanism).
Sorter
A conveyor that receives mixed unit loads and discharges them to segregated spaces or conveyors in response to an automatic dispatch control.
System Integration
The process of connecting systems, devices, and programs together in a common architecture so as to share and exchange data.
T
TTL (Transistor-Transistor Logic)
One of the more common logic families in use today. Other logic families include CMOS (complementary metal oxide semiconductor) and ECL (emitter-coupled logic). Different logic families are distinguished by such electrical characteristics as logic levels, input current, speed, power consumption, and the supply voltage required.
Turnkey
A type of outsourcing method that turns over to the subcontractor all aspects of manufacturing including material acquisition, assembly and testing. Its opposite is consignment, where the outsourcing company provides all materials required for the products and the subcontractor provides only assembly equipment and labor.
Twinaxial Cable
A transmission line made up of a twisted pair of insulated conductors centered inside and insulated from a conductive shield.
U
UART (Universal Asynchronous Receiver/Transmitter)
A module composed of a circuit that contains both the receiving and transmitting circuits required for asynchronous serial communication.
UPS (Uninterruptible Power Supply)
A series of batteries through which the main supply is passed. Should the main supply fail, the batteries ensure continuity of power to the computer for a short time, allowing the computer to shut down in an organized way and avoiding corrupted or incomplete data files.
V
Velocity loop
A feedback control loop in which the controlled parameter is motor velocity. Usually uses a tachometer for a feedback device.
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W
WMS (Warehouse Management System)
Software that integrates activities performed mechanically and by humans with an information system to effectively manage warehouse business processes and direct warehouse activities.
Watchdog
A fail-safe mechanism that can be used to set I/O points to a "safe" state if communications with the controller is lost.
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X
X10 Protocol
A powerline carrier protocol that allows compatible devices throughout the home to communicate with each other via the existing 220V or 110V wiring in the house. Visit www.x10.org for more information.
Y
Z
ZIF connector (Zero-Insertion-Force connector)
A connector for which male and female contacts do not initially touch each other while the connector halves are being engaged. Instead, the halves are physically positioned together, and then a turn of an actuating cam arrangement mates all the contacts at once.