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- Fahrenheit
- The temperature scale that sets the freezing point of
water at 32ºF and its boiling point at 212ºF at standard
atmospheric pressure. The formula for conversion to Celsius
is: ºC = 5/9 (ºF - 32ºF).
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- Failsafe Output
- Output value where device goes to protect against effects of failure of the
equipment, such as fuel shutoff in the event of loss of flame in a furnace or a
sensor break.
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- Fall Time
- Measure of the time required for the output voltage of a circuit to change
from a high voltage level to a low voltage level, once a level change has
started (90% to 10%).
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- False Pulse
- Improper change of state of the output, usually associated with Turn-Off or
Turn-On.
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- False Pulse Protection
- Circuitry designed to clamp output Off until the power supply has time to
reach proper voltage level. Typically 200-500 msec.
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- Farad
- Unit of capacitance.
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- Fast Fourier Transfer (FFT)
- An analysis algorithm - given a finite set of data points, FFT expresses the
data in terms of its component frequencies.
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- Feedback Control
- Error-driven control system where control signal to actuators is
proportional to difference between a command signal and a feedback signal from
the process variable being controlled.
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- Feedforward Control
- Method of control that compensates for disturbance before its effect in
output. Based on a model that relates output to input where disturbance occurs.
In distillation, the disturbances are usually feed rate and feed compositions.
Steady-state feedforward models usually combine with dynamic compensation
functions to set manipulative variables and combined with feedback adjustment
(trim) to correct for control model accuracy constraints.
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- Fiber Optics
- Transparent fibers of glass or plastic used for conducting and guiding light
energy. Fiber optics are used in photoelectrics as light pipes, consisting of a
bundle of small optical fibers (glass) or single strand (plastic) housed inside
a flexible sheathing.
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- FIFO buffer
- First in, first out storage method. The first value placed in the buffer
(queue) is the first value subsequently read.
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- Filter - Digital Filter (dF)
- A filter that slows the response of a system when inputs
change unrealistically or too fast. Equivalent to a standard
resistor-capacitor (RC) filter.
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- Filtering
- Attenuating components of a signal that are undesired. Reduce noise errors
in a signal.
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- First-Order Lag
- Term describing signal-delaying and signal-size-changing effects of a pad of
control loop. Name comes from the form of the equation that represents the
relation between output and input. Effects evaluated by a time constant.
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- Fixed Sensing Distance
- Capacitive sensors with a fixed sensing distance do not
have a potentiometer for sensitivity adjustment.
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- Flow
- The motion of liquids or gases in response to a force.
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- Flush Mounting
- See Shielded
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- FM Approved
- An instrument that meets a set of specifications
established by the Factory Mutual Research Corporation.
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- Force Differential
- Difference between the operating force and the release force.
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- Force, Contact
- The force holding closed contacts together.
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- Foreground Suppression
- The ability of a special set of photo electric sensors
to detect targets irrespective of color and surface
properties provided the background is defined. Sensors with
foreground capabilities exhibit no blind range.
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- Fork and Angle Sensors
- Emitter and receiver are integrated in a fork or angle
housing facing each other. These one-piece units require
none of the difficult alignment and wiring tasks of their
two-piece counterparts.
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- Form A
- A single-pole, single-throw relay that uses only the
normally open (NO) and common contacts. These contacts close
when the relay coil is energized. They open when power is
removed from the coil.
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- Form A or C
- An electromechanical relay capable of Form A or C
function, selected by a jumper wire.
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- Form B
- A single-pole, single-throw relay that uses only the
normally closed (NC) and common contacts. These contacts
open when the relay coil is energized. They close when power
is removed from the coil.
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- Form C
- A single-pole, double-throw relay that uses the normally
open (NO), Form A or Form B contact.
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- Frequency
- The number of cycles over a specified period of time,
usually measured in cycles per second. Also referred to as
Hertz (Hz). The reciprocal is called the period.
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- Frequency, Natural
- The frequency of free (not forced) oscillations of the sensing element of a
fully assembled sensor.
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- Frequency Counter
- Counts digital pulses over a defined gate time. A typical gate time is
between 0.1 and 10 seconds.
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- Frequency Output
- An output in the form of frequency, which varies as a function of the
applied pressure.
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- Frequency Response
- Response of a component, instrument, or control system to input signals at
varying frequencies.
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- Front Panel
- The front surface of a unit, generally containing switches and indicator
lights.
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- Full Overtravel Force
- Force required to depress the plunger of a switch to the full overtravel
point.
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- Full Overtravel Point
- The position of the plunger beyond which further overtravel would cause
damage to the switch or actuator.
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- Full Scale Output (Span)
- (1) Algebraic difference between output curve end points (outputs at
specified upper and lower output limits). (2) The difference between the minimum
output (normally zero) of a data acquisition device and the rated capacity.
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