F

FALSE
The status of an instruction that does not provide a continuous logical path on a ladder rung.
fault
A problem or error detected by the control system hardware or software. A fault is identified by an error code or an error bit.
fault action
Indicates the action to be taken when one of several error conditions is detected. The fault actions are:
  • Shutdown
  • Disable Drive
  • Stop Command
  • Status Only
Fault mode
The controller mode entered when a major fault occurs and is not handled by a fault routine or controller fault handler program. Most operations act as if the controller were in Program mode, but it is impossible to switch back to Run mode without clearing the fault condition.
fault routine
A routine that is configured to execute when a program fault occurs.
feedback
The signal(s) returned from a controlled machine or process to denote its response to the command signal.
feedback control loop
A closed signal path in which feedback is compared with the commanded value to obtain a corrective error signal.
feedback element
Pertains to a control system. An element (transducer) that converts motion, position, pressure, flow, or temperature to an electrical signal for comparison to the command signal.
feedback resolution
The smallest increment of change that the feedback element can distinguish and reproduce as an electrical output.
feedback signal
The measurement signal indicating the value of a directly controlled variable, which is compared to the commanded value to obtain the corrective error signal.
feedforward
The gain that is multiplied by a derivative of the command and is fed forward and summed with the standard loop outputs.
feedforward control action
The control action in which information, concerning upstream conditions, is converted into corrective commands to minimize the deviations of the controlled variable.
field
A single data definition within a structure consisting of an atomic data type, a structure, or a single dimensioned array.
FIFO
First-In-First-Out. The order in which data is entered into and retrieved from a file.
file
A collection of information organized into one group.
filter
A device that controls the bandwidth of the signal that is being transmitted. It is generally used to eliminate high frequency oscillations or spikes from input or output signals. By removing the high frequency noise, the application may be able to accurately operate on the true variation of the input or output.
Tip:
Use caution when applying filtering since, by definition, it makes the system more sluggish and less responsive.
flag
A marker used in processing or interpreting information; a signal indicating the existence or status of a particular condition.
Flags can be:
  • a code, embedded in data, that identifies a condition, such as the beginning or end of a word or message.
  • one or more bits set internally by hardware or software to indicate an event, such as an error or the result of a comparison of values.
flag bit
A processor memory bit, controlled through firmware or a user program, used to signify a certain condition (for example, low battery).
FLEX I/O assembly
An Allen-Bradley compact modular system comprised of I/O modules, terminal bases, and an adapter/power supply.
float
The real values displayed and entered in floating point format. The number of digits to the left of the decimal point varies according to the magnitude of the number.
following error
The difference between the command position and the actual position.
force
A feature that allows you to:
  • set the value of one or more bits of an input or output tag, regardless of the actual state of the input or output
  • set the numeric value of an input or output tag member, regardless of the state of the input or output
    Tip:
    Logix Designer
     always displays the value of the tag as seen from your program logic (that is, inputs are displayed with forces applied and outputs are displayed without forces applied).
force disabled
A controller sub-state that indicates any force values installed in the controller, if there are any, are disabled (i.e., inactive). This state is independent of the Force Installed (that is, you can remove or add forces and doing so will not enable/disable all forces).
Tip:
This behavior is different from RSLogix 5 and RSLogix 500 behavior. In those packages, removing the last force transitions the Force Enabled state to the Force Disabled state.
force enable indicator
A solid red triangle icon (force enable indicator), shown to the left of a tag whose value has been forced and forces are enabled. This indicator enables you to see exactly which tags are forced.
Force Enabled
A controller sub-state that indicates that any force values installed in the controller, if there are any, are enabled (that is, active). This state is independent of the Force Installed state.
Force Installed
A controller sub-state that indicates there is at least one force value existing in the controller.
force mask
A mask that indicates what bits within a value are forced. In
Logix Designer
:
  • "1" indicates that a bit is forced on
  • "0" indicates that a bit is forced off
  • "." indicates that no force is present
forward kinematics
The solution of source positions given the target positions. In practice, this would be computing the Cartesian positions given the Joint positions.
forward transform
The solution of source positions given target positions.
frequency
The number of periodic cycles per unit of time.
full-duplex
A bidirectional mode of communication where data may be transmitted and received simultaneously.
function block routine
A function block routine consists of a series of sheets. You can navigate to any sheet in the routine, and you can add and remove sheets as you choose.
The function block routine always consists of at least one sheet, and the Function Block Editor displays a single sheet at a time.
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