0. Logical 0. Used to indicate an open ("OFF") Digital Input circuit. Used to indicate a de-energized ("OFF") Digital Output signal.

1. Logical 1. Used to indicate an closed ("ON") Digital Input circuit. Used to indicate a energized ("ON") Digital Output signal.

ALU. An Arithmetic Logic Unit is designed to handle all logical and basic arithmetic functions. It is usually in control of a microcomputer or is imbedded in a Microcomputer chip.

Asynchronous. The transmission of computerized information by individual frames having start and stop signals. Data is transmitted in irregular spurts, where the time interval varies between successive transmitted frames.

A/D. Analog to Digital Conversion is the process of converting an analog value into a digital value that could be used by a computer. Analog signals, from field instruments, are either unipolar or bipolar, and are further classified as a voltage or current type signal.

Baud. Baud rate is the number of signal changes per second on a communication line. Baud rate is frequently, and incorrectly, used as being synonymous to bits per second. Note: A single signal change can represent more than one bit of information.

Buss. A method of transferring information between various devices. All busses contain "wires" to transmit and receive data, control, and in some cases arbitration.

Control Output. Relay control either non-secure or secure. See digital output.

CPU. A Central Processor Unit is the "heart" of all processor, MPU, microcomputers, and micro-processors. It makes up the logic that fetches and decodes instructions, maintains pointers, counters, arithmetic-logic functions, and handles interrupts. In a more general use the word could refer to the complete Computer device such as a IBM PC excluding the I/O devices. See Microcomputer.

Data Terminal Equipment. Term given to distinguish the computing instrument apart from any device used to perform the analog transmission and reception of data. Examples of DTE devices include computers, video display terminals, RTUs, and PLCs.

Data Communications Equipment. The communications device that adapts digital signals from a connected "DTE" device, to the physical communications media implemented in a system. Examples of DCE devices include modems and radios.

Digital to Analog Conversion. "D/A" is the process of converting a digital value generated by a computer into a corresponding analog output (eg, volts or milliamps) for output to an analog control device. See analog output, setpoint control.

Digital to Analog Converter. A "DAC" is a device which receives digital input from some processor device and converts the digital value to a corresponding analog output to drive an analog control device.

EPROM. Erasable Programmable Read Only Memory is a nonvolatile memory component which can be read but not written by a computer but can be erased and reprogrammed by a "PROM" programmer device.

EEPROM. Electrical Erasable Programmable Read Only Memory is a nonvolatile memory component which can be read and written to by a computer device. Typically used to store unit configuration data, which is modifiable by the end-user.

Firmware. Computer instructions that are embedded in the hardware, stored in PROM, EPROM or EEPROM devices, and is generally not modifiable by the end-user.

Frame. Pertaining to a communication device, a frame is the total sum of all the signal changes that make up one "character" that can be passed to the computer device, to include timing required to achieve synchronization. For example, during asynchronous communication, a frame is all the signal changes between the start bit and stop bit.

Hertz. A unit of frequency equal to 1 cycle per second.

Integrated Circuit. A tiny complex of electronic components and their connection produced on a slice of material such as silicon.

Indication input. Input from some field device that is either in an ON (1) or OFF (0) state. Also known as Status Input or Field Status.

Industrial Automation. General term used in applying electronic or computer-based systems towards automatically controlling a manufacturing process.

Input/Output is a process of passing data from an external device to a computer or of passing data from a computer to an external device.

IOC. Input/Output Controller. An electronic device used to control and monitor Input/Output points, within a overall system, and to communicate the derived data to a master station or other "host" unit.

LED. Light Emitting Diode. A diode that emits light when current passes through it.

Master. The "head-end" computer in a SCADA system.

Microcomputer. A computer based on a particular microprocessor. The architecture is best suited to a real-time environment because of its interrupt structure. This device is given an assorted number of names; MPU, CPU and Microprocessor to name a few.

Microprocessor. Subsystem circuit of a microcomputer that performs the sequential manipulation of data. See Microcomputer.

Modem. A MOdulator/DEModulator is a communications device providing an interface point to a communication line. It converts digital data to analog for transmission and analog data to digital for reception.

MPU. MicroProcessor Unit. See microcomputer.

Preventive Maintenance. "PM" is the scheduled downtime for equipment during which equipment that is in marginal working condition is identified and remedied. PM includes routine mechanical maintenance and adjustments.

Process. The collective external function performed by the control equipment, involving process variables and setpoint controls.

Process variable. A system parameter (ie, an analog signal) that is monitored and controlled (eg by an associated setpoint control signal, generated by the control unit) by a controller.

PROM. Programmable Read Only Memory is a memory component which can be read by, but not written by, a computer. The memory contents of this device can be set only once by using special programming device.

Protocol. Set of rules governing message exchange between two communications processes.

RAM. Random Access (Read/Write) Memory is a volatile memory component which can be both written and read by a computer. A computer's main memory is RAM.

Refresh. In the computer memory, dynamic RAM, in order to maintain the stored information, must have each of its memory locations addressed periodically. This process is called memory refresh.

Remote. A computer, typically with I/O, located in a remote site away from the Master (Control Center).

Restart. When a unit or device initializes itself due to power failure, error conditions, or commanded by a computer. There are generally two types of Restarts, 1) Cold Start and 2) Warm Start. Warm start occurs when conditions are such that only resetting some of the unit's parameters and logic is necessary, where Cold start occurs when everything must be "restarted" in order to maintain operating order.

ROM. Read Only Memory is a memory component which can be read, not written, by a computer. The memory contents are set by the manufacturer.

RS-232. RS-232 interface specification defines the number of wires that are used to connect a modem ("DCE") to a computer or terminal ("DTE"), the electrical signals that are sent along these wires, and the signal levels that are used. Frequently, the RS-232 interface is used to connect a terminal to a computer without intervening modem equipment. RS-485 and RS-422 are similar interfaces for interconnecting DTE devices.

RTD. Resistance Temperature Detector. An small assembly of special metals and alloys used for deriving process temperatures. The electrical resistance of the device changes over a temperature range, and generally in a non-linear manner. See Thermocouple.

RTU. Remote Terminal Unit. An electronic device used to control and monitor Input/Output points, within a overall system, and to communicate the derived data to a master station or other "host" unit.

Rx. Receive. Usually in reference to some communication interface.

Scan. The process of requesting information and receiving it. When applied to RTU communications, it is the whole process of requesting input signal data (eg status, analogs, and accumulators) from a RTU and receiving a reply.

Setpoint. The desired value for a given process variable. Sometimes refers to analog outputs from an IOC or RTU.

Synchronous. Fixed-rate transmission of bits of data, synchronized by a common clock signal, for both the sender and the receiver.

Thermocouple. A sensor, similar in functionality to a RTD, used for obtaining process temperatures.

Trigger. A trigger is either a hardware or software qualification set to monitors a condition that when it occurs, some action is either started or stopped.

Tx. Transmit. Usually in reference to some communication interface.

UART. Universal Asynchronous Receiver/Transmitter is an integrated circuit that performs peripheral interfacing functions with serial devices. The functions typically include:

UCS. Universal Configuration System is a DOS executable program used to configure and operate various IOC/RTU units provided by the Company. End-users use this software to configure and calibrate station-level units for proper operation with an overall control system.

USART. Universal Synchronous/Asynchronous Receiver/Transmitter is an integrated circuit that performs peripheral interfacing functions with serial devices. The functions are the same as a UART but also include:

SCADA is an acronym for:

Supervisory Control And Data Acquisition

SCADA is used by utilities and other process-oriented operations to collect data from machinery, which may be located over a very large geographic area. A basic SCADA system consists of two types of computers 1) "Master" and 2) "Remote." The Master (or host) resides at a centrally-manned location (eg a control center) while the Remotes are generally placed at un-manned locations.

An example is an electric utility, where the master is located at the control center (where system operators monitor and control the entire system) and remotes are substations where distribution power lines are interconnected. Remote computers, usually a Remote Terminal Unit "RTU" or a Programmable Logic Controller "PLC" will respond to inquiries from the Master (ie status of equipment) and will accept commands from the Master (open circuit breaker B3) for controlling equipment.

Communications between a Master and a number of remotes can be via telephone-like circuits, radio channels, or via fiber-optic communications media.

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