A

abandoned

Many components in the Logix Designer programming environment are composed of several pieces. For instance, a tag is composed of the tag object you see, plus an underlying data target. This target can be either a data table object, or a Message, Axis, or Motion Group object. Under certain fault conditions (for example, a loss of communications while creating or deleting one of these composite objects), the pieces can get separated. For instance, the tag may get deleted, but the underlying target object may not. In this case, the lone target object is considered an abandoned component in the system. In other cases, the tag may be created, but the underlying object may not. This leaves a tag that you can see, but that is not all there. This is considered an abandoned tag.

These abandoned pieces can exist in the Controller, in the project file, or both. Uploading from a controller that contains abandoned components saves them to the project file. These components are undesirable, and can cause problems, particularly tag, Message, Axis, and Motion Group components. For this reason, a project that contains these abandoned components will not download.

On Download, a message in the Results window will indicate the presence of abandoned components, and direct you to use the Compact command from the

File

menu, or to use export and import to purge these abandoned components from the project. Once removed from the project, downloading to the controller will eliminate them from the controller.

Abandoned data table objects are much more benign, and much more difficult to detect. The current release does not detect data table abandoned objects on download, and the Compact command will not remove them; Export and import, however, will.

absolute move

A move to a specified absolute position relative to a fixed zero position.

absolute position

A position referenced to a fixed zero position.

acceleration

The rate of change in velocity. Negative acceleration is usually described as deceleration.

accumulated value (ACC)

The number of elapsed time intervals or counted events.

.ACD

The file extension used for project files created by the Logix Designer application.

An ASCII control character is used to acknowledge the reception and acceptance of a transmission block.

active sequence

An active sequence is downloaded into the controller and has received a START command to make it execute.

actual position

The position as it is currently registering on the feedback element.

actual velocity

The velocity as it is currently registering on the feedback element.

actuator (output device)

A device that converts an electrical signal into mechanical motion. In the most general sense, an actuator is any machine/process load device (for example, a transducer) of a controller output circuit.

adapter module

A module in an I/O chassis that provides a communication interface between a scanner and the I/O modules in that chassis. This adapter reads input data from input circuits and transmits it to the scanner. It also receives output data from the scanner and writes it to output circuits.

Add-On Instruction

An instruction that is defined as an add-on to the Logix defined instruction set. Once defined, an Add-On Instruction can be used like any system-defined instruction and can be used across various projects. An Add-On Instruction is composed of parameters, local tags, logic routine, and optional scan mode routines.

address

A PLC-5/SLC term. File, element, and bit addresses (for example, N:7/0) no longer exist in ControlLogix. Instead, memory is allocated and named using tags.

alias tag

A tag that references memory defined by another tag. An alias tag may refer to another alias tag or a base tag. An alias tag may also refer to memory within another tag by referencing a member of a structure tag, or a bit within an integer tag or member.

amplifier

A device that draws power from a source other than its input signal to produce an output that is a magnified reproduction of the input signal.

ANSI

American National Standards Institute. An organization that develops and publishes voluntary industry standards in the United States.

ASCII

American Standards Code for Information Interchange. This is a 7-bit code with an optional parity bit used to represent alphanumerics, punctuation marks, and control-code characters.

atomic

The basic definition of a data type used to allocate bits, bytes, or words of memory and to define their numeric interpretation. This includes BOOL, SINT, INT, DINT, and REAL data types.

attribute

A characteristic that has a measure or a value and can be specified or manipulated.

Audit Value

The Audit Value is a unique value that is generated when a project is downloaded to the controller or loaded from removable storage. This value is updated when an event occurs. Some events will always cause an Audit Value change, while others are selectable based on the settings of the Detection Specification.

availability

The ability of a device to carry out its assigned functions based on its probability of failure. Mean Time Between Failure (MTBF) is a measure of availability.

average velocity

The average of the last N samples of velocity as it was registered on the feedback element.

AXIS

A structure data type that contains status and control information for an axis of motion.