fail safe - a design concept where system failure will bring the system to an idle or safe state.

Faraday's electromagnetic induction law - if a conductor moves through a magnetic field a current will be induced. The angle between the motion and the magnetic field needs to be 90 deg for maximum current.

Farenheit - a temperature system that has 180 degrees between the freezing and boiling point of water.

fatal error - an error so significant that a software/hardware cannot continue to operate in a reliable manner.

fault - a small error that may be recoverable, or may result in a fatal error.

FAX (facsimile) - an image is scanned and transmitted over phone lines and reconstructed at the other end.

FCS (Frame Check Sequence) - data check flag for communications.

FDDI (Fibre Distributed Data Interface) - a fibre optic token ring network scheme in which the control tokens are counter rotating.

FDX (Full Duplex) - all characters that are transmitted are reflected back to the sender.

FEA (Finite Element Analysis) - is a numerical technique in which the analysis of a complex part is subdivided into the analysis of small simple subdivisions.

feedback - a common engineering term for a system that examines the output of a system and uses is to tune the system. Common forms are negative feedback to make systems stable, and positive feedback to make systems unstable (e.g. oscillators).

fiberoptics - data can be transmitted by switching light on/off, and transmitting the signal through an optical fiber. This is becoming the method of choice for most long distance data lines because of the low losses and immunity to EMI.

FIFO (First In First Out) - items are pushed on a stack. The items can then be pulled back off last first.

file - a concept of a serial sequence of bytes that the computer can store information in, normally on the disk. This is a ubiquitous concept, but file is also used by Allen Bradley to describe an array of data.

filter - a device that will selectively pass matter or energy.

flag - a single binary bit that indicates that an event has/has not happened.

flag - a single bit variable that is true or not. The concept is that if a flag is set, then some event has happened, or completed, and the flag should trigger some other event.

flame - an email, or netnews item that is overtly critical of another user, or an opinion. These are common because of the ad-hoc nature of the networks.

floating point - uses integer math to represent real numbers.

flow chart - a schematic diagram for representing program flow. This can be used during design of software, or afterwards to explain its operation.

flow meter - a device for measuring the flow rate of fluid.

flow rate - the volume of fluid moving through an area in a fixed unit of time.

fluorescence - incoming UV light or X-ray strike a material and cause the emission of a different frequency light.

FM (Frequency Modulation) - transmits a signal using a carrier of constant magnitude but changing frequency. The frequency shift is proportional to the signal strength.

force - a PLC output or input value can be set on artificially to test programs or hardware. This method is not suggested.

format - 1. a physical and/or data structure that makes data rereadable, 2. the process of putting a structure on a disk or other media.

forward chaining - an expert system approach to examine a set of facts and reason about the probable outcome.

fragmentation - the splitting of an network data packet into smaller fragments to ease transmission.

frame buffers - store the raster image in memory locations for each pixel. The number of colors or shades of gray for each pixel is determined by the number of bits of information for each pixel in the frame buffer.

free field - a sound field where none of the sound energy is reflected. Generally there aren't any nearby walls, or they are covered with sound absorbing materials.

frequency - the number of cycles per second for a sinusoidally oscillating vibration/sound.

friction - the force resulting from the mechanical contact between two masses.

FSK (Frequency Shift Keying) - uses two different frequencies, shifting back and forth to transmit bits serially.

FTP (File Transfer Protocol) - a popular internet protocol for moving files between computers.

fudge factor - a number that is used to multiply or add to other values to make the experimental and theoretical values agree.

full duplex - a two way serial communication channel can carry information both ways, and each character that is sent is reflected back to the sender for verification.

fuse - a device that will destruct when excessive current flows. It is used to protect the electrical device, humans, and other devices when abnormally high currents are drawn. Note: fuses are essential devices and should never be bypassed, or replaced with fuses having higher current rating.

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