. 29
( 42)


Relative plier that does not require a power supply, but
freq.,kHz operates only from the input signal energy. Usually
consists of one or more semiconductor diodes,
sometimes in conjunction with inductors and/or
capacitors. The output signals appear at integral
20 multiples of the input frequency.

’6 +2
’4 +6
’2 +4





passive infrared sensor A device that detects in-
passband ripple
frared directly, such as that given off by humans
because of their body heat. It does not generate
passivation The process of growing a thin oxide energy of any kind. It is used in some intrusion
film on the surface of a planar semiconductor de- detection systems.
vice to protect the exposed junction(s) from con- passive mixer A signal mixer using only passive
tamination and short circuits. See, for example, components (diodes, nonlinear resistors, and
PLANAR EPITAXIAL PASSIVATED TRANSISTOR nonlinear reactances) (i.e., one without active
and PLANAR TRANSISTOR. components, such as transistors). Passive mix-
passive absorber A substance that reflects mini- ers introduce some loss. Compare ACTIVE
mal sound energy. Examples include acoustical MIXER.
ceiling tile and thick carpeting. passive modulator A modulator using only pas-
passive circuit A circuit consisting entirely of non- sive components (diodes, nonlinear resistors, and
amplifying components, such as capacitors, re- nonlinear reactances) (i.e., one without active
sistors, inductors, and diodes. components, such as transistors). Passive modu-
passive communications satellite A communica- lators introduce some loss. Compare ACTIVE
tions satellite that reflects electromagnetic waves, MODULATOR.
but does not contain a transponder; that is, it passive network A network composed entirely of
does not receive and retransmit the signals. Also passive components (i.e., one containing no gen-
called passive comsat. Compare ACTIVE COM- erators and providing no amplification).
passive component A device that is basically passive reflector A metal surface used to reflect
static in operation (i.e., it is ordinarily incapable electromagnetic energy at ultra-high and mi-
of amplification or oscillation and usually crowave frequencies.
518 passive transponder • Pb

(RC) filter for treble boost, and a variable shunt
RC filter for bass boost. The input signal is ap-
plied in parallel to both filters. The outputs are
combined in an audio mixer.
patching The interconnection of two or more signal
media or lines.
patch panel A panel on which the terminals of a
X in
system are accessible for interconnection, tests,
etc. It is used especially in high-fidelity audio
recording systems. It was once commonly used in
manual telephone-switching applications.
patch up 1. To replace faulty or damaged parts in
an electronic system with roughly appropriate
surrogates to restore operation quickly (usually
Y in under emergency conditions). Also see DOCTOR.
2. To wire a circuit quickly using patch cords for
preliminary test and evaluation.
patent 1. A document awarded by a government
body, giving to an inventor the exclusive right to
exploit an invention for a specified number of
years. Formally called letters patent. 2. The
monopoly granted by a document, as defined
passive mixer in 1.
path 1. The route over which current flows. 2. In
passive transponder A device that allows a ma- radio and navigation, the imaginary line extend-
chine, such as a computer or robot, to identify an ing directly between transmitter and receiver (or
object. A bar-code reader is a common example. target). 3. In a computer program, the logical or-
Magnetic labels, such as those on credit cards der of instructions.
and bank cash cards, are another example. It is pathometer A form of lie detector that indicates
so named because it does not transmit data; it re- changes in the electrical resistance of the human
quires a sensor for data detection. body.
password As a security device in computer opera- pattern 1. An established sequence of steps in a
tions, a group of characters upon whose presen- process. 2. An arrangement of terms in a matrix.
tation to the system via a terminal the user is 3. The graphical representation of a varying
allowed access to memory or control of informa- quantity (e.g., an alternating-current wave pat-
tion. tern). 4. The image on the screen of an oscillo-
password retry limitation A security feature that scope, or the record traced by an oscillograph.
prevents hackers from making repeated guesses 5. The graphic polar representation of the radiation
at passwords in an attempt to break into a com- field of an antenna. 6. The arrangement of bits in
puter, network, or database. If more than three a word or field.
unsuccessful entries are made in succession, for pattern recognition In machine-vision systems, a
example, the system will not accept further ac- method of identifying an object or decoding data
cess attempts for a certain preprogrammed according to geometric shape. Optical character
length of time, say 1 hour. recognition (OCR) is an example. The machine
paste In “dry” batteries and electrolytic capacitors, recognizes combinations of shapes, and deduces
a gelatinous electrolyte. their meanings via a computer program.
patch 1. A temporary signal path, as between a ra- pause editing In the editing of audio tape record-
dio receiver and a telephone or, conversely, be- ings, the use of a “pause” switch to temporarily
tween a telephone line and a radio transmitter. stop the tape when necessary.
2. To make quick, usually temporary connections, PAV Abbreviation of PHASE-ANGLE VOLTMETER.
as with a patch cord. 3. Instructions entered by pawl In a mechanical stepping device, as in a non-
an unconditional branch to a computer program electric clock, a device made to engage the sloping
for the purpose of correction. sprockets on a wheel to ensure shaft rotation in
patch bay 1. See PATCH PANEL. 2. A set of patch one direction only.
panels. PAX Abbreviation of PRIVATE AUTOMATIC EX-
patch cord A flexible line of one or more conduc- CHANGE.
tors with a jack or connector at each end, used to pay-per-view Abbreviation, PPV. Television service
interconnect (patch) circuit points exposed for the in which each subscriber pays only for individu-
purpose on a panel or breadboard. ally selected programs.
Patchett tone control A dual tone-control circuit pay TV See SUBSCRIPTION TV.
using a variable series resistance-capacitance Pb Symbol for LEAD.
P band • peak envelope power

P band A radio-frequency band extending from 225 PDM Abbreviation of PULSE-DURATION MODULA-
to 390 MHz. TION.
PBX Abbreviation of PRIVATE BRANCH EX- PDM-FM Pertaining to a carrier that is frequency
CHANGE. modulated by one or more subcarriers that are
PC 1. Abbreviation of PERSONAL COMPUTER. frequency modulated by pulses that are pulse-
2. Abbreviation of PRINTED CIRCUIT. 3. Abbrevia- duration modulated. Also see FREQUENCY
COLUMN. 5. Abbreviation of POINT-CONTACT. TION.
6. Abbreviation of PERCENT (also, pct.). 7. Ab- PDM-FM-FM Pertaining to a carrier that is fre-
breviation of PROGRAM COUNTER. quency modulated by one or more subcarriers
pc 1. Abbreviation of PICOCOULOMB. Also, pC that are frequency modulated by pulses that are
(preferred). 2. Abbreviation of PICOCURIE. Also, pulse-duration modulated. Also see FREQUENCY
pCi (preferred). 3. Abbreviation of PARSEC. MODULATION and PULSE-DURATION MODULA-
pC Abbreviation for PICOCOULOMB. TION.
PCB Abbreviation of PRINTED-CIRCUIT BOARD. PDM-PM Pertaining to a carrier that is phase mod-
PC board See PRINTED-CIRCUIT BOARD. ulated by pulse-duration-modulated information.
p-channel junction field-effect transistor Abbre- PDVM Abbreviation of PRINTING DIGITAL VOLT-
viation, PFET. A junction-type FET in which METER.
the gate junction has been formed on a bar or PE 1. Abbreviation of POTENTIAL ENERGY. 2. Ab-
die of p-type semiconductor material. Compare breviation of PROFESSIONAL ENGINEER. 3. Ab-
SISTOR. peak 1. The maximum value of a quantity. 2. In an
p-channel MOSFET A metal-oxide semiconductor alternating-current cycle, the maximum positive
field-effect transistor in which the channel is or negative current or voltage point. 3. The fre-
composed of p-type silicon. Also see DEPLETION- quency at which the transmission by a bandpass
TYPE MOSFET, DEPLETION-ENHANCEMENT- circuit or device is maximum (attenuation is
TYPE MOSFET, and ENHANCEMENT-TYPE minimum), evidenced by a maximum in the
MOSFET. frequency-response curve.
pCi Symbol for PICOCURIE. peak amplitude 1. The maximum positive or neg-
PCL Abbreviation of PRINTED-CIRCUIT LAMP. ative current or voltage of a wave. 2. The maxi-
PCM Abbreviation of PULSE-CODE MODULATION. mum instantaneous power of a signal.
PCM-FM Pertaining to a carrier that is frequency peak anode (plate) current The maximum instan-
modulated by information that is pulse-code taneous current flowing in the anode (plate) cir-
modulated. Also see FREQUENCY MODULATION cuit of a vacuum tube.
and PULSE-CODE MODULATION. peak anode (plate) voltage The maximum instan-
PCM-FM-FM Pertaining to a carrier that is fre- taneous voltage applied to the anode (plate) of a
quency modulated by one or more subcarriers vacuum tube.
that are frequency modulated by information that peak chopper See PEAK CLIPPER.
is pulse-code modulated. Also see FREQUENCY peak current Abbreviation, Ip. The highest value
MODULATION and PULSE-CODE MODULATION. reached by an alternating-current half-cycle or a
PCM level In a pulse-code-modulated signal, one current pulse. Also called MAXIMUM CURRENT.
of several different possible signal conditions. peak detector See PEAK PROBE.
PCM-PM Pulse-code modulation that is accom- peak distortion 1. The maximum instantaneous
plished by varying the phase of the carrier wave. distortion in a signal, generally expressed as a
PC relay See PRINTED-CIRCUIT RELAY. percentage. 2. Distortion of a modulated signal at
PCS Abbreviation for PERSONAL COMMUNICA- envelope peaks.
TION SERVICE. peaked sawtooth A wave composed of a sawtooth
PC transistor See POINT-CONTACT TRANSISTOR. and peaking-pulse components. The deflection
PD 1. Abbreviation of PLATE DISSIPATION. 2. Ab- voltage of a magnetic-deflection cathode-ray tube
breviation of PULSE DURATION. 3. Abbreviation requires this waveform to produce a current saw-
of PROXIMITY DETECTOR. 4. Abbreviation of tooth in the deflecting coils.
POTENTIAL DIFFERENCE. peaked waveform An alternating-current wave-
Pd Symbol for PALLADIUM. form having nearly pointed positive and negative
PDA Abbreviation for personal digital assistant. See half-cycles. Such a wave contains appreciable
HANDHELD COMPUTER. third-harmonic energy.
PDAS Abbreviation of programmable data acquisi- peak envelope power Abbreviation, PEP. For a lin-
tion system. ear radio-frequency (RF) power amplifier han-
P display See PLAN POSITION INDICATOR. dling a modulated signal, the average RF output
520 peak envelope power • peak-to-peak voltage

Limiting level

peaked sawtooth

power during a single RF cycle at the highest
peak of the modulation envelope.
Limiting level
peaker 1. See PEAK FILTER. 2. See PEAKING
peaker-notcher See NOTCHER-PEAKER.
peak limiting
peak factor For an alternating-current wave, the
ratio Em/Erms or Im/Irms, where Em is the maximum
voltage, Erms is the effective (root-mean-square) peak point The highest current point in the cur-
voltage, Im is the maximum current, and Irms is the rent-voltage response curve of a tunnel diode.
effective current. Immediately beyond this point, the current
peak filter A frequency-selective circuit, such as a decreases as the applied voltage is increased,
bandpass filter, for producing a peak response indicating a negative-resistance region. Compare
peak inductor current In a switching regulator, peak power 1. Symbol, Pp. Unit, watt. Alternating-
the maximum instantaneous current through the current power that is the product of the peak volt-
inductor when the device is switching at its fully age (Ep) and the peak current (Ip). For Ep in volts
rated duty cycle. and Ip in amperes, the peak power in watts is
peaking The adjustment of a control or device for given by Pp = Ep Ip. 2. The highest output power
maximum indication on a meter or other display. that an amplifier or device can produce without
peaking coil A small inductor used to compensate excessive distortion. 3. The maximum instanta-
the frequency response of a circuit, such as a neous power that a speaker can handle without
video amplifier or video detector. Both series and risk of damage.
shunt peaking coils are used. peak probe A voltmeter test probe containing a
peaking transformer A transformer whose output diode circuit whose direct-current output voltage
waveform is sharply peaked (of short duration, is close to the peak value of the applied alternat-
with respect to a cycle). The effect is obtained by ing-current test voltage.
means of a special core that, because it contains peak recurrent forward current For a semicon-
little iron, saturates easily. ductor diode, the maximum repetitive instanta-
peak inverse voltage Abbreviation, PIV. Often neous forward current as measured under
used interchangeably with the term PEAK RE- specified conditions of operation.
VERSE VOLTAGE. 1. The peak value of the volt- peak reverse voltage Abbreviation, PRV. In semi-
age applied to a rectifier diode in the reverse conductor operations, the peak value of the volt-
direction. 2. The maximum value of reverse volt- age applied in reverse polarity across the
age that a rectifier diode will tolerate according to junction. It is often used interchangeably with the
its specifications. term PEAK INVERSE VOLTAGE.
peak level lamp In audio recording and reproduc- peak signal level The maximum instantaneous
tion, a bulb or light-emitting diode (LED) that signal power or voltage specified for particular op-
illuminates when sound peaks exceed a erating conditions.
predetermined amplitude. peak-to-peak Abbreviations, p-p or pk-pk. For an
peak limiting 1. A method of limiting the maxi- alternating-current waveform, pertaining to the
mum amplitude of a signal. When the instanta- arithmetic difference between the positive peak
neous peak amplitude, either positive or negative, and negative peak values of current or voltage.
exceeds a certain value, the output is clipped at peak-to-peak probe A voltmeter test probe con-
that value. 2. In pulse-code modulation, the ef- taining a diode circuit whose direct-current out-
fect resulting from the application of an input sig- put voltage is close to the peak-to-peak value of
nal in excess of the virtual decision value. the applied alternating-current test voltage.
peak modulated power In an amplitude- peak-to-peak voltage The arithmetic sum of posi-
modulated wave, the maximum instantaneous tive and negative peak voltages in an alternating-
signal power (including the carrier and current (ac) wave. Thus, a symmetrical sine-wave
sidebands). In 100-percent sinusoidal modulation, ac voltage of 115.0 V rms has a peak value of
the peak modulated power is four times the un- 162.63 V and a peak-to-peak value of 325.3 V.
modulated carrier power. Also see PEAK VOLTAGE.
peak torque • PEP transistor

+ pencil 1. A beam of electrons or other particles or
rays that either converges to, or diverges from, a
specific point. 2. A pair of geometric entities shar-

ing a property (e.g., lines intersecting at a single
pendulum switch A device that closes a circuit
when subjected to physical shock. One type con-
sists of a dangling element resembling a pendu-
’ lum, with one or more nearby contacts.
penetrating frequency For a particular layer of
the ionosphere, the lowest high frequency at
+ which a vertically propagated wave penetrates the
layer (i.e., it is not reflected back to earth). Also

penetrating radiation Ionizing radiation that
passes through otherwise opaque materials. A
relative term; low-energy X rays are less penetrat-
ing than high-energy X rays, which, in turn, are
less penetrating than gamma rays.
penetrating rays See COSMIC RAYS.

penetration depth See DEPTH OF PENETRATION.
pent Abbreviation of PENTODE.
+ pentavalent element An element whose atoms
have five valence electrons (e.g., antimony or ar-

pk-pk pentode A five-electrode vacuum tube in which the
electrodes are an anode, cathode, control grid,
screen grid, and suppressor grid.
pentode field-effect transistor A field-effect tran-
sistor with three separate gates.
’ pentode transistor A bipolar transistor with three
peak-to-peak voltage

peak torque Symbol, Tp. For a torque motor, the
maximum useful torque at maximum recom-
mended input current.
peak voltage Abbreviation, Ep. The highest value
reached by an alternating-current voltage half cy-
cle, or by a voltage pulse. Also called MAXIMUM
peak voltmeter 1. An alternating-current (ac) volt- E1 E3
meter that responds to the peak value of the ap-
plied voltage. 2. An ac voltmeter that responds to
pentode transistor
the average value of the applied voltage”even
though its scale reads in peak volts.
pea lamp A miniature incandescent bulb, some-
times used as a control-panel or meter light. penumbra 1. That part of a shadow in which the
PEC Abbreviation of PHOTOELECTRIC CELL. light source is not fully obscured by the eclipsing
pedestal See BLANKING PEDESTAL. object. 2. In a sunspot, the outer part of the spot;
pedestal level See BLANKING LEVEL. it is less dark than the inner portion.
pel See PIXEL. PEP 1. Abbreviation of PLANAR EPITAXIAL PASSI-
Peltier effect A drop below ambient temperature VATED. 2. Abbreviation of PEAK ENVELOPE
at the junction between two dissimilar metals POWER.
when an electric current is passed through the PEP diode See PLANAR EPITAXIAL PASSIVATED
junction. DIODE.
PEM Abbreviation of photoelectromagnetic. PEP reading wattmeter A wattmeter that shows
pen-and-ink recorder A graphic recorder in which the peak envelope power output of a transmitter.
a fountain-pen-type stylus inscribes an ink line PEP transistor See PLANAR EXPITAXIAL PASSI-
on a paper chart. Also called pen recorder. VATED TRANSISTOR.
522 perceived level • peripheral electron

perceived level The level of a disturbance, partic- travels faster than at any other point in the orbit.
ularly sound, as sensed by a person. It is gener- 2. The altitude, measured from the earth™s sur-
ally expressed in decibels, with respect to a face or the earth™s center, of an earth-orbiting
certain threshold value. The threshold is as- satellite at its closest approach.
signed an intensity of 0 dB. perihelion 1. The point at which a solar-orbiting
percent An expression of a fraction, in terms of satellite attains its lowest altitude. It occurs once
hundredths. A quantity of x percent indicates a for every complete orbit. At this point, the satel-
fraction of x/100. Percent is usually abbreviated lite travels faster than at any other point in the
by the symbol %. orbit. 2. The altitude, measured from the sun™s
percentage error The amount by which a mea- surface or the sun™s center, of a solar-orbiting
sured value differs from the true value, expressed satellite at its closest approach.
as a percentage (the number of parts per 100 that perimeter protection The use of a security system
the measurement is in error). to restrict or prevent access to a designated area,
percentage-modulation meter An instrument using sensors and/or barriers around the bound-
that provides direct readings of the modulation aries of the area.
percentage of an amplitude-modulated signal. period Symbol, T. Unit, second. The duration of a
The meter scale or dial is graduated in incre- complete alternating-current cycle or of any
ments from 0 to somewhat more than 100 per- cyclic event; T = 1/f, where f is the frequency
cent. in Hertz. Also see CYCLE, FREQUENCY, and
percentage uncertainty The maximum possible HERTZ.
error in a measurement, expressed as a percent- periodic and random deviation Abbreviation,
age of the measured value. Also see UNCER- PARD. In the direct-current output of a rectifier,
percent distortion Symbol, %D. In the determina- ripple, noise, hum, and transient spikes.
tion of harmonic distortion, the total harmonic periodic curve A curve that repeats its shape in
voltage expressed as a percentage of the funda- each period (e.g., a sine curve).
mental voltage, plus total harmonic voltage; %D = periodic deviation Repetitive deviation of a quan-
100Eh/Et, where Eh is the total voltage of the har- tity from its normal value (e.g., ripple in the
monic components, and Et is the total signal volt- direct-current output of a rectifier).
age (fundamental plus harmonics). periodic function A mathematical function that is
percent modulation See MODULATION PER- represented by a periodic curve (e.g., the sine
CENTAGE. function y = sin x).
percent modulation meter See PERCENTAGE- periodicity In a transmission line, the tendency
MODULATION METER. for power to be reflected at a point or points
percent ripple The amount of ripple voltage in the where the diameter of the line changes.
direct-current (dc) output of a rectifier or genera- periodic law The observation that when the chem-
tor, expressed as a percentage of the nominal dc ical elements (see ELEMENT, 3) are arranged in
output voltage. increasing order of atomic number, their physical
perfect crystal A crystal without defects or impu- and chemical properties recur periodically. Also
rities. The atoms are arranged in a regular pat- see PERIODIC TABLE.
tern with no faults. periodic table A table in which the chemical ele-
perforated board A plastic panel provided with a ments (see ELEMENT, 3) are arranged according
number of small holes in orderly columns and to the periodic law. The vertical columns in the
rows for the insertion of the pigtails of compo- table, labeled groups, contain elements possess-
nents, or of push-in terminals to facilitate quick ing related properties (e.g., silicon and germa-
assembly of prototype circuits. Also called perf- nium in group IV). The rows, labeled periods,
board. depict the periodic shift in the properties of the el-
performance curve A curve depicting the behavior ements.
of a component or circuit under specified condi- peripheral 1. Pertaining to equipment accessory to
tions of operation. Such a curve, for example, a central system (e.g., peripheral input/output
might display the variation of output power with devices online or offline to computers, data
input power, the variation of frequency with volt- recorders, and indicators). Also see ANCILLARY
age, etc. Compare CHARACTERISTIC CURVE. EQUIPMENT. 2. Peripheral equipment in a com-
performance test A test made primarily to ascer- puter system (e.g., printers, modems, external
tain how a system behaves. The test is concerned disk drives, tape drives, etc.).
with normal operation, whereas a diagnostic test peripheral buffer As part of a peripheral in a com-
is a troubleshooting procedure. Compare TROU- puter system, a storage unit in which data
BLESHOOTING TEST. temporarily resides on its way to or from the
perigee 1. The point at which an earth-orbiting central processing unit. Also called INPUT/
satellite attains its lowest altitude. It occurs once OUTPUT BUFFER.
for every complete orbit. At this point, the satellite peripheral electron See VALENCE ELECTRON.
peripheral equipment • persistor

peripheral equipment See PERIPHERAL, 1, 2. Coil
peripheral interface adapter Abbreviation, PIA.
An integrated circuit that acts as an input/out-
put port to interface a microprocessor with pe-
ripheral devices.
peripheral transfer In a computer system, the
transfer of a unit of data between peripherals, or
between a peripheral and the central processing
Permalloy A high-permeability alloy of iron and
permamagnetic speaker See PERMANENT- permeability tuning
permanent magnet A body that is always magne-
tized (i.e., without the application of electricity within the inductor. This type of tuning is used in
and without requiring the presence of another amplifiers, oscillators, filters, and wavetraps.
magnet). Compare TEMPORARY MAGNET. permeameter An instrument for measuring per-
permanent-magnet erase Erasure of magnetic meability.
tape by the field of a permanent magnet. Typi- permeance Unit, Wb/A. In a magnetic circuit, the
cally, it is a two-step process: a magnet erases ease with which a magnetic field is established.
what it can of the signal, leaving any residual The reciprocal of RELUCTANCE.
magnetization for erasure by a second magnet. Permendur A high-permeability magnetic alloy
permanent-magnet focusing In a cathode-ray containing equal parts of iron and cobalt. At sat-
tube, the focusing of the electron beam by means uration, the flux density of this material can be 2
of permanent magnets. teslas (20,000 gauss).
permanent-magnet generator An electromechan- Perminvar A high-permeability magnetic alloy of
ical generator in which the field (either stationary cobalt, iron, and nickel. At saturation, the flux
or rotating) is provided by a multipole permanent density of this material can approach 1.2 teslas
magnet. Also called magneto. (12,000 gauss).
permanent-magnet loudspeaker See PERMA- permittivity See DIELECTRIC CONSTANT.
NENT-MAGNET SPEAKER. permutation A selection of several factors or ob-
permanent-magnet magnetizer A magnetizer us- jects from a group, in a specific ordered sequence.
ing a permanent magnet as the magnetic-field For example, one of the permutations of the ele-
source. ments of the set (1, 2, 3, 4, and 5) is the ordered
permanent-magnet meter An indicating meter in sequence 4, 1, 3, 5, 2.
which a movable coil rotates between the poles of permutation modulation A method of modulation
a permanent magnet. Compare ELECTRODY- accomplished by varying the sequence of digital
permanent-magnet motor A motor having a per- peroxide of lead In a lead-acid cell or battery, a
manent-magnet field. compound of lead and oxygen that composes the
permanent-magnet relay A polarized relay using positive electrode or electrodes.
a permanent magnet. persistence 1. The effect whereby the retina of the
permanent-magnet speaker An acoustic loud- eye continues to register a projected scene for ap-
speaker in which the core is a strong permanent proximately 0.05 second after the scene disap-
magnet (as opposed to a direct-current electro- pears. This allows perception of a sequence of
magnet). Also see MAGNETIC SPEAKER. video frames as a continuous moving image.
permanent storage See NONVOLATILE MEMORY. 2. The tendency of certain phosphors to glow after
permeability Unit, H/m. A quantitative indicator the excitation has been removed. Thus, after the
of the extent to which a material concentrates electron beam in a cathode-ray tube has passed
magnetic flux: for a given constant magnetic-field over the screen, the phosphor might continue to
intensity, the ratio of magnetic flux density in the glow for a certain time along the path traced by
material to the magnetic flux density in air. the beam. Some phosphors, such as those used
permeability curve See B-H CURVE. in high-speed oscilloscopes, have virtually no
permeability-tuned oscillator A radio-frequency persistence, whereas others have long persis-
oscillator in which the frequency is varied or ad- tence.
justed by moving a ferromagnetic core in and out persistent oscillations Successive oscillations of
of the coil of an inductance-capacitance (LC) constant amplitude. Also called CONTINUOUS
tuned circuit. WAVE.
permeability tuning Variation of the resonant fre- persistor A device used at low temperatures for
quency of an inductance-capacitance LC circuit temporary memory storage that operates between
by changing the position of a magnetic core superconducting and normal conditions.
524 personal communications service • phase coincidence

personal communications service Abbreviation, within the tuning range of a receiver, the phan-
PCS. Also called digital cellular. An enhanced tom can be tuned in as a separate signal. But
wireless network using digital modulation, when the phantom corresponds to the intermedi-
cellular repeaters, and facilitating telephone and ate frequency (IF) of the receiver, it will ride into
Internet connections. Emphasis is on maximizing the IF amplifier and be present as an untunable
user mobility and portability, and minimizing interferential signal.
blind zones. Compare CELLULAR COMMUNICA- phantom channel In a properly phased high-
TIONS. fidelity stereo sound system, the apparent sound
personal computer A small computer equipped source centered between the left- and right-chan-
with a keyboard, display, hard disk, diskette nel loudspeakers.
drive(s), a modem or fax/modem, one or more se- phantom circuit In wire telephony, a third circuit
rial data ports, and one or more parallel data that has no wires; it results from a method (using
ports. They are used extensively by individuals repeating coils) of making two other circuits do
and businesses for record keeping, data process- the work of (this third) one.
ing, communications, word processing, graphics, phantom signal Also called bogey. In a radar sys-
etc.; they are also used in schools as an educa- tem, a signal that does not correspond to an ac-
tional aid. tual target. The origin of the phantom signal or
personal digital assistant Abbreviation, PDA. See echo cannot be readily determined.
personal equation The value of systematic error phase angle Unit, degree or radian. In an alternat-
for a person observing specific phenomena or ing-current (ac) circuit, the lag or lead between
making measurements. the instant that one alternating quantity reaches
personality Characteristics that make an intelli- its maximum value and the instant that another
gent computer or robot human-like. In general, alternating quantity reaches its maximum value.
the more powerful the computer, the more per- It is usually given in degrees (a complete cycle be-
sonality it can have, depending on the installed ing 360 degrees) along the horizontal axis of the
software. In some cases, certain malfunctions in time-versus-magnitude graph of the ac quantity.
a computer can produce personality quirks. phase-angle voltmeter An instrument that indi-
personal robot A usually autonomous robot in- cates both the magnitude and phase of a voltage.
tended for use by individuals. The most common phase coincidence For signals having the same
examples are robot toys, programmable with a frequency, the condition of their coinciding in
PERSONAL COMPUTER, intended for the educa- terms of instantaneous amplitudes, so positive
tion and entertainment of children. More sophis- peaks of the first signal correspond to positive
ticated devices can perform domestic tasks, such peaks of the second signal, and negative peaks of
as cleaning floors and mowing lawns. the first signal correspond to negative peaks of
peta- Abbreviation, P. A prefix meaning 1015. the second signal. For periodic waves that do not
petagram Abbreviation, Pg. A large unit of mass or change their characteristics with time, this is the
force, equal to 1015 grams or 1012 kilograms. same thing as being shifted by an integral multi-
petameter Abbreviation, Pm. A large unit of (astro- ple of 360 degrees in phase. Compare PHASE
nomical) distance, equal to 1015 meters or 1012 OPPOSITION.
pF Abbreviation of PICOFARAD.
pf Symbol for POWER FACTOR.
PG Abbreviation of POWER GAIN.
Pg Abbreviation of PETAGRAM.
pH 1. Symbol for hydrogen-ion concentration. Nu-
merically, pH is the negative logarithm of the ef-
fective hydrogen-ion concentration in gram
equivalents per liter. The scale runs from zero to
14, on which 7 denotes neutrality relative to acid-
ity vs. alkalinity; values between zero and 7 de-
note acidity, and values between 7 and 14 denote
alkalinity. 2. Abbreviation of PICOHENRY.
phantom Radio interference in the form of a beat
note (heterodyne), resulting from interference be-
tween two strong carriers, often from local radio
stations. When the phantom frequency lies
phase compensation • phase opposition

phase compensation In an operational amplifier, Signal
compensation for excessive phase shift in the input
(from IF)
phase compressor A push-pull phase-inverter cir-
cuit in which a capacitor is connected between
each collector or drain and the opposite output
terminal to attenuate in-phase components, such Phase
Filter Amplifier Output
as even-numbered harmonics. comparator
phase constant A figure providing the rate (in de-
grees of phase per unit length) at which the phase
lag of the current or voltage field component in a
traveling wave increases linearly in the propaga- Voltage-
tion direction. controlled
phase corrector A circuit that returns a signal to a oscillator
certain phase after the signal has passed through
a circuit or medium that has caused phase dis-
tortion. phase-locked loop
phased antenna See PHASED ARRAY.
phased array Also called phased antenna. An an-
tenna system having two or more driven elements divides the frequency by a specific integral value
fed with a certain relative phase, and spaced at a n chosen by the operator. The output frequency
certain distance, resulting in a directivity pattern of the divider is locked, by means of a phase com-
that exhibits gain in some directions and little or parator, to the signal from a crystal-controlled
no radiation/response in other directions. Such reference oscillator. As long as the output from
an array can have two elements, producing a uni- the divider is exactly at the reference-oscillator
directional cardioid or bidirectional figure-eight frequency, the two signals are in phase, and the
pattern. More complex arrays have several ele- output of the phase comparator is zero volts dc. If
ments, usually vertical antennas, strategically the VCO frequency changes, the phase also
positioned and fed with signals of specified phase changes, and the phase comparator produces a
to produce a highly tailored pattern. The most so- dc error voltage. The error voltage is applied to the
phisticated systems have rotatable or steerable VCO, causing the VCO frequency to correct itself.
radiation/response patterns. This maintains the VCO frequency at precisely n
phase-delay equalizer See DELAY EQUALIZER. times the reference-oscillator frequency.
phase detector See PHASE-SENSITIVE DETEC- phase-locked oscillator An oscillator in which the
TOR. inductance or the capacitance is varied periodi-
phase diagram A graphical representation of cally at half the driving frequency.
waves having equal frequency, but differing in phase margin In an integrated-circuit amplifier,
phase. The phase difference for two identical the extent to which the device shifts the phase of
waveforms is greater than or equal to zero de- a signal more or less than one-half cycle (180 de-
grees, but less than 360 degrees. grees) for a certain signal voltage.
phase difference 1. The difference (in time, angle, phase modulation Abbreviation, PM. A method of
or fractional cycle) between the instants at which modulation in which the phase of the carrier cur-
two alternating quantities reach a given value. rent is varied in accordance with the instanta-
2. For a dielectric, the complement of PHASE AN- neous modulating-signal voltage. The result is
GLE; that is, 90 degrees minus the phase angle in similar to FREQUENCY MODULATION.
degrees. phase modulator A circuit or stage that produces
TER-SEELEY DISCRIMINATOR, RATIO DETEC- phase multiplier A circuit used for the purpose of
TOR, and TRAVIS DISCRIMINATOR. phase comparison between signals. The fre-
phase distortion Distortion characterized by in- quency of the measured signal is multiplied, re-
put/output phase shift between various compo- sulting in multiplication of the phase difference.
nents of a signal passed by a circuit or device. This improves the sensitivity of the measuring
phase inverter A resistance-capacitance-coupled apparatus.
amplifier with a single-ended input and a push- phase opposition For signals having the same fre-
pull output. This circuit enables a push-pull am- quency, the condition of their being inverted rela-
plifier to be driven without an input transformer. tive to each other in terms of instantaneous
phase-locked loop Abbreviation, PLL. An oscillator amplitudes, so positive peaks of the first signal
that combines the flexibility of a conventional correspond to negative peaks of the second sig-
variable-frequency oscillator (VFO) with the sta- nal, and negative peaks of the first signal corre-
bility of a crystal oscillator. The oscillator output spond to positive peaks of the second signal. This
is passed through a programmable divider that is not the same thing as being shifted by an odd
526 phase opposition • phase windings



phase shift

change, as defined in 1, measured in fractions of
a wavelength or in electrical degrees.
phase-shift bridge A four-arm-bridge circuit for

shifting the phase of an alternating-current sig-
nal. Such a circuit is often used (with one arm

variable) to shift the phase of the firing voltage for
a thyratron.
phase-shift discriminator See FOSTER-SEELEY
phase shifter A circuit, such as an inductance-
integral multiple of 180 degrees in phase, capacitance (LC) or resistance-capacitance (RC)
although in practice, with sine waves and square network, or a device, such as a Helmholtz coil or
waves, the effect is the same. Compare PHASE phase-shifting capacitor, that introduces a phase
COINCIDENCE. shift between input and output signals.

phase resonance See VELOCITY RESONANCE. phase-shifting capacitor A special four-stator,
phase reversal 1. The inversion of an alternating- one-rotor variable capacitor that, with a trans-
current (ac) signal. The instantaneous ampli- former-coupled resistance-capacitance (RC) cir-
tude (current or voltage) is multiplied by a cuit, provides 360 degrees of continuously
negative constant. Thus, the positive half-cycles variable phase shift for one rotation of the rotor.
become negative, and the negative half-cycles The rotor plate turns like a cam under the stators
become positive. 2. A phase shift of ±180 because of the off-center insertion of the rotor
degrees (±1„2 cycle) in an ac signal. shaft.
phase-rotation relay See PHASE-SEQUENCE RE- phase-shift oscillator A single-stage oscillator in
LAY. which the required 180-degree phase shift in the
phase-rotation system A system for producing signal (fed back from output to input) is obtained
single-sideband signals without using selective by passing the output through a phase-shifting
filters. In one such system, two balanced modula- network.
tors are used. One of these receives carrier and phase-shift-type distortion meter A distortion
modulating voltages that are 90 degrees out of meter in which the output signal of a device un-
phase with voltages that are fed to the other bal- der test is compared with a distortion-free input
anced modulator. test signal. The output signal phase is shifted 180
phase-sensitive detector Abbreviation, PSD. A degrees, with respect to the input, and the two
detector for frequency modulation (FM) and amplitudes are made equal. If there is no distor-
phase modulation (PM). It delivers a direct- tion, the signals cancel each other, and the result
current output voltage whose value is proportional is zero. Any remaining signal is proportional to
to the difference in phase between a reference the total harmonic distortion (THD).
signal and the signal from a local oscillator. phase-splitting circuit A circuit that produces,
phase-sequence relay In a polyphase system, a re- from a single input signal, two output signals dif-
lay or relay circuit that is actuated by voltages fering in phase.
reaching maximum positive amplitude in a pre- phase-splitting driver A PHASE INVERTER used
determined phase sequence. Also called PHASE- as the driver of a push-pull amplifier.
ROTATION RELAY. phase velocity The velocity of a wave, provided by
phase shift 1. A change in the displacement, as a the product of the frequency and the wavelength.
function of time, of a periodic disturbance having phase windings In an alternating-current generator,
constant frequency. 2. The magnitude of a windings that deliver voltages that differ in phase.

phasing capacitor • phonetic alphabet

phasing capacitor In a crystal filter, a small vari- phone jack The female mating device for a PHONE
able capacitor that constitutes one arm of a PLUG.
four-arm bridge in which the crystal is another
arm. Adjustment of this capacitor balances the
bridge, thus preventing the undesirable passage
of a signal through the capacitance of the crystal
phenol-formaldehyde plastics A family of plastic
insulating materials made with phenolic resin,
and occasionally used as dielectrics and air-core
coil forms. Some of the trade names for these ma-
terials include Bakelite, Catalin, Durez, Durite,
Formica, and Micarta.
phenolic insulants See PHENOL-FORMALDE-
phenolic resin A synthetic resin made by con-
densing phenol (carbolic acid) with formaldehyde.
phenomenon An event or circumstance that can
be verified by the senses, as opposed to one sub-
ject to theory or speculation (e.g., the phe-
nomenon of magnetic attraction).
Phillips gate A device that allows measurement of
the gas pressure in a confined chamber. A cur- phone monitor A simple device for listening to
rent is passed through the gas. The magnitude of amplitude-modulated radio transmissions to
the current, for a given gas, is a function of the test their quality. In its most rudimentary form,
gas pressure and temperature. it consists of a pickup antenna, semiconduc-
Phillips screw A screw with a pair of slots in its tor-diode detector, and high-resistance head-
head. The slots are arranged like an x. Phillips phones.
screws are available in many different sizes, as are phone patch A device for establishing a connec-
ordinary screws. The x-shaped pair of slots re- tion (patch) between radio and wire-telephone fa-
duces the tendency for the screwdriver to slip out cilities. Also see PATCH.
of the screw head as the screw is rotated. phone plug A type of plug originally designed for
Phi phenomenon The illusion of motion resulting patching telephone circuits, now widely used in
from the rapid presentation to the eye of pictures electronics and instrumentation. In its conven-
showing objects in a succession of different posi- tional form, it has a rod-shaped neck that
tions. Television and motion pictures exploit this serves as one contact, and a ball on the tip of
illusion. Also see PERSISTENCE. the neck, but insulated from it, that serves as
the other contact. Typical diameters are 1„8 inch
pH meter An instrument used to measure the
and 1„4 inch.
acidity or alkalinity of solutions. Also see PH, 1.
phon A unit of apparent change in loudness dis-
cerned by a listener. Unlike the decibel, the phon
includes compensation for the ear™s nonlinear re-
sponse to attendant frequency changes. At a fre-
quency of 1 kHz, a change in loudness of 1 phon
is the equivalent of 1 decibel.
phone 1. Telephone (wire or radio). 2. To establish
communication via telephone. 3. Colloquialism
for voice communication (radiotelephone), partic-
ularly via amateur-radio single sideband on the
high-frequency bands (160 through 10 meters).
4. A minimal, unique speech sound. Also called
phoneme An individual sound or syllable in the phone test set An instrument for checking the
human voice, with a characteristic amplitude-vs. performance of a radiotelephone transmitter. The
frequency spectral pattern. It is important in set combines the functions of field-strength me-
speech recognition and speech synthesis. Com- ter, modulation indicator, and aural monitor.
puters can be programmed to identify and tran- Sometimes it includes a volt-ohm-milliammeter
scribe these sounds; computers can also be for troubleshooting the transmitter.
programmed to generate the sounds from text phonetic alphabet Words whose initial letters are
data. used to identify the letters of the alphabet for
528 phonetic alphabet • phosphor copper

which they stand. These words are spoken in ra- ties cause vibration in a PHONO CARTRIDGE as
diotelephony to identify letters that, if spoken by the turntable rotates.
themselves, might not be clearly heard. phonograph oscillator See PHONO OSCILLATOR.
phono jack Also called RCA jack. A jack similar to
Phonetic alphabet a PHONE JACK, designed especially for the quick
connection and disconnection of coaxial cables
used with audio and low-frequency devices.
(Capitals indicate
phonon A unit of energy resulting from vibration,
Letter emphasis)
as of a piezoelectric crystal.
A AL-fa
phono oscillator A small radio-frequency (RF) os-
cillator modulated by the audio-frequency (AF)
C CHAR-lie
voltage from a phonograph. The modulated RF
D DEL-ta
signal is picked up by a remote radio receiver
(usually in the same room), and the sound is re-
F FOX-trot
produced through a loudspeaker connected to
the receiver.
H ho-TEL
phono plug Also called RCA plug. A plug similar to
I IN-dia
a PHONE PLUG, designed especially for the quick
J Ju-li-ETTE
connection and disconnection of coaxial cables
K KEE-low
used with audio and low-frequency devices.
L LEE-ma
M Mike
N No-VEM-ber
O OS-car
P pa-PA
R ROW-me-oh
S see-AIR-ah
phono plug
U YOU-ni-form
V VIC-tor
W WHIS-key
phonoreception The hearing of high-frequency
X X-ray
Y YANK-key
phonorecord A PHONOGRAPH disc.
Z ZOO-loo
phonoselectroscope A special type of stethoscope,
phonetic alphabet code word In radio and wire in which the main heartbeat is attenuated. This
telephony, a word chosen for its easy recognition makes abnormal sounds more audible. The de-
by ear to identify the letter of the alphabet with vice can be adjusted in various ways to listen for
which it begins. For example: Golf for G, Juliet for abnormalities characteristic of various heart dis-
J, X-ray for X. eases.
phonics See ACOUSTICS, 1. phosphor A substance that glows when an elec-
phonocardiogram The record made by a PHONO- tron beam strikes it. Such a substance is used as
CARDIOGRAPH. a coating on the screens of cathode-ray tubes.
phonocardiograph An instrument that makes a See also BEAT ZINC SILICATE; CADMIUM
graphic record of heart sounds. BORATE, SILICATE, and TUNGSTATE; CAL-
phono cartridge The vibration-to-electricity trans- CIUM PHOSPHATE, SILICATE, and TUNG-
ducer (pickup) of a phonograph; it is actuated by STATE; MAGNESIUM FLUORIDE, SILICATE, and
the stylus (needle). Common types are ceramic, TUNGSTATE; ZINC ALUMINATE; ZINC BERYL-
variable-inductance, and variable-reluctance. See LIUM SILICATE; ZINC BERYLLIUM ZIRCONIUM
phonocatheter A microphone that can be inserted FIDE; ZINC GERMANATE; ZINC MAGNESIUM
into the body for the purpose of listening to the FLUORIDE; ZINC ORTHOSILICATE; ZINC OX-
functions of internal organs. IDE; ZINC SILICATE; and ZINC SULFIDE.
phonograph A device for reproducing sound phosphor bronze A form of bronze whose elastic-
recorded on disc. It consists of a turntable, an ity, hardness, and toughness have been greatly
amplifier, and one or more speakers. improved by the addition of phosphorus. The
phonograph cartridge See PHONO CARTRIDGE. metal is used for brushes, springs, switch blades,
phonograph disc A thin, lightweight disc, usually and contacts.
made of vinyl or similar plastic, on which audio- phosphor copper An alloy of copper and phospho-
frequency signals are recorded as irregularities in rus used in the manufacture of PHOSPHOR
a spiral groove. In reproduction, these irregulari- BRONZE.
phosphorescence • photoelectric efficiency

phosphorescence The property of some materials photoconductor 1. See PHOTOCONDUCTIVE MA-
that ordinarily fluoresce to continue to glow after TERIAL. 2. See PHOTOCONDUCTIVE CELL.
the stimulus (light or an electron beam) has been photocurrent See PHOTOELECTRIC CURRENT.
removed. Compare FLUORESCENCE. photo-Darlington Also, photodarlington. 1. A pho-
phosphorescent screen A viewing screen coated totransistor fabricated as a Darlington amplifier
with a phosphor (e.g., oscilloscope screen). for high output current. 2. A combination of pho-
phosphorous Exhibiting the properties of phos- todiode (see LIGHT-SENSITIVE DIODE) and Dar-
phor (e.g., glowing after stimulation with light). lington amplifier.
Not to be confused with PHOSPHORUS. photodecomposition Chemical breakdown by the
phosphorus Symbol, P. A nonmetallic element of action of radiant energy. Also called photolysis.
the nitrogen family. Atomic number, 15. Atomic photodetachment The removal of an electron from
weight, 30.974. It is used as a dopant in semi- an atom or ion, resulting from the impact of a
conductor processing. PHOTON.
phot The cgs unit of illumination: The direct illu- photodetector 1. An illumination meter that uses
mination produced upon a one-centimeter- a PHOTOCELL. 2. See OPTOELECTRONIC COU-
distant surface by a uniform point source of one PLER.
international foot-candle. Equivalent to one lu- photodielectric effect The tendency for the dielec-
men per square centimeter. tric constant of a substance to change when
photocathode 1. The photomosaic of a video cam- infrared radiation, visible light, or ultraviolet
era tube. 2. The light-sensitive cathode in a pho- radiation strikes it. Different substances exhibit
totube. different degrees of this effect.
PhotoCD Trade name for an image-recording sys- photodiffusion effect See DEMBER EFFECT.
tem developed by Kodak, in which photographs photodiode See LIGHT-SENSITIVE DIODE.
can be stored on compact discs. Viewing is ac- photodisintegration In the nucleus of an atom,
complished using personal computers. disintegration resulting from PHOTON bombard-
photocell See PHOTOELECTRIC CELL. ment.
photocell amplifier An amplifier used to boost the photoelasticity The tendency for the light-
output of a photocell. With respect to the nature transmission characteristics of a substance to
of the input signal, it can be an alternating- change with externally applied forces.
current (ac) or direct-current (dc) amplifier, depend- photoelectric alarm An alarm actuated when a
ing on whether the output of the photocell is light beam impinging on a photocell is inter-
modulated dc or pure dc. rupted.
photochemical effect The phenomenon whereby photoelectric amplifier 1. An amplifier for boost-
certain substances undergo chemical change when ing the output of a photosensitive device. 2. An
exposed to light or other radiant energy. An exam- OPTOELECTRONIC COUPLER possessing gain.
ple of such a substance is the silver bromide, silver photoelectric cell A device that converts infrared,
chloride, or silver iodide on photographic film. visible-light, or ultraviolet energy into electricity
photoconductive cell A photoelectric cell, such as or electrical effects. It can function by producing
the cadmium-sulfide type, whose resistance is a voltage (see PHOTOVOLTAIC CELL, SELENIUM
proportional to the intensity of light impinging CELL, SILICON CELL, SOLAR CELL, and SUN
upon it. The photoconductive cell acts as a light- BATTERY) or by acting as a light-sensitive resis-
sensitive variable resistor in a current path. Also tor (see LIGHT-SENSITIVE DIODE, PHOTOCON-
photoconductive effect The tendency for the elec- photoelectric constant The quantity h/e, where h
trical resistance of a substance to change when is Planck™s constant and e is the unit electron
infrared radiation, visible light, or ultraviolet ra- charge.
diation strikes it. Different substances exhibit dif- photoelectric counter A counting device (elec-
ferent degrees of this effect. tromechanical or fully electronic) that counts ob-
photoconductive material A substance that ex- jects as they interrupt a light beam impinging
hibits decreased electrical resistance when ex- upon a photocell.
posed to infrared rays, visible light, or ultraviolet. photoelectric disintegration See PHOTODISIN-
Some photoconductive substances are cadmium TEGRATION.
selenide, cadmium sulfide, germanium, lead sul- photoelectric effect The phenomenon whereby
fide, selenium, silicon, and thallous sulfide. Also temporary changes occur in the atoms of certain
see ACTINOELECTRIC EFFECT. substances under the influence of infrared, visi-
photoconductivity The phenomenon whereby the ble light, or ultraviolet radiation. Some of these
electrical resistance of certain materials (such as materials undergo a change in their electrical re-
cadmium sulfide, cadmium selenide, germanium, sistance, whereas others generate electric current
selenium, and silicon) is lowered upon exposure (see, for comparison, PHOTOCONDUCTIVE MA-
to infrared rays, visible light, or ultraviolet. Also TERIAL and PHOTOVOLTAIC MATERIAL).
see PHOTOCONDUCTIVE MATERIAL. photoelectric efficiency See QUANTUM YIELD.
530 photoelectric field-effect transistor • photographic sound recording

photoelectric field-effect transistor See
photoelectricity Electricity produced by the ac-
tion of light on certain materials, such as cesium,
selenium, and silicon. Also see PHOTOEMISSION
photoelectric material See PHOTOCONDUCTIVE
photoelectric multiplier A device that internally photoelectric wattmeter
amplifies the current resulting from bombard-
ment by infrared, visible light, or ultraviolet radi-
ation. A PHOTOMULTIPLIER TUBE is an example sured is applied to the lamp, which glows propor-
of such a device. tionately. The light excites the cell, causing it to
photoelectric photometer An instrument that deliver a direct current proportional to the power.
uses a photoelectric device for the purpose of This current deflects a milliammeter or microam-
measuring the intensity of infrared radiation, vis- meter. The meter can be calibrated to read di-
ible light, or ultraviolet radiation. rectly in watts.
photoelectric proximity sensor A device that photoelectromotive force The electromotive force
uses a light-beam generator, a photodetector, an (voltage) produced by a photovoltaic cell.
amplifier, and a microprocessor to detect the photoelectron An electron displaced within, or
presence of nearby objects. It is useful in robot ejected from, an atom, as the result of infrared,
guidance systems. visible light, or ultraviolet radiation striking the
photoelectric pyrometer An optical pyrometer in atom.
which a photocell and appropriate filters act in- photo-emf See PHOTOELECTROMOTIVE FORCE.
stead of the human eye. photoemission The ejection of electrons from cer-
photoelectric relay A relay actuated directly by a tain materials, such as cesium, when these mate-
photocell or a photocell and amplifier. This type of rials are exposed to infrared, visible light, or
relay is the basis of some PHOTOELECTRIC ultraviolet radiation. Also see PHOTOEMISSIVE
photoelectric sensor 1. See ELECTRIC EYE. photoemissive material A substance that emits
2. See PHOTOELECTRIC PROXIMITY SENSOR. electrons when exposed to infrared, visible light, or
3. See PHOTOELECTRIC CELL. ultraviolet radiation. A typical use of such a mate-
photoelectric smoke alarm An alarm that is rial is in the coating of the light-sensitive cathode
tripped by a PHOTOELECTRIC SMOKE DETEC- of a phototube. The metals cesium, potassium, ru-
TOR when the density of smoke exceeds a safe bidium, and sodium are photoemissive.
level. photofabrication 1. A method of circuit-board
photoelectric smoke control A system for making manufacturing. The etching pattern is placed
automatic adjustments to a burning process over the circuit-board material, the board is
when the smoke density exceeds a prescribed placed in a special solution, then the assembly is
level. The initial element in the system is a PHO- exposed to visible light. The light interacts with
TOELECTRIC SMOKE DETECTOR. the solution to dissolve the metal in areas ex-
photoelectric smoke detector A smoke detector posed to the light, but not in areas covered by the
in which a photocell, photodiode, phototransis- etching pattern. 2. The technique in 1, applied to
tor, or phototube is excited by a light beam pass- the manufacture of integrated circuits.
ing through the air. The cell output current photoFET A FIELD-EFFECT TRANSISTOR that ex-
decreases when smoke fills the air. This current hibits properties similar to those of a bipolar
change trips an alarm or deflects an indicating PHOTOTRANSISTOR.
meter when the density of the smoke exceeds a photoflash See ELECTRONIC FLASH, 1.
prescribed level. photoglow tube See DISCHARGE LAMP.
photoelectric tape reader A punched-tape reader photogram The permanent shadow produced by
using a photocell, photodiode, phototransistor, or an object placed between a light source and pho-
phototube to sense light passing through the tographic paper.
holes. photographic exposure meter See EXPOSURE
photoelectric transducer A photocell, photodiode, METER, 1.
phototransistor, or phototube used as a sensor. photographic recorder A graphic recorder that
photoelectric tube See PHOTOTUBE. uses a light beam, deflected by galvanometer
photoelectric wattmeter A power-measuring in- movement, that moves across photographic film
strument useful for the approximate measure- or paper to produce a trace representing a vary-
ment of radio-frequency power. It consists of an ing quantity.
incandescent lamp sharing an opaque enclosure photographic sound recording See OPTICAL
with a photovoltaic cell. The power to be mea- SOUND RECORDING.
photograph reception • photon

photograph reception 1. The use of FACSIMILE to
print photographs transmitted in analog form via

Relative perceived brightness for
wire or radio. 2. The use of a computer, equipped

light source of constant intensity


with a modem and graphics software, to display
and/or store photographs transmitted in digital
form via wire or radio.
photograph transmission 1. The use of FACSIM-

ILE to scan and send photographs in analog form

via wire or radio. 2. The use of a computer,
equipped with a modem and video camera or op-
tical scanner, to digitize and send photographs
via wire or radio.


photoionization The ejection of electrons from
atoms or molecules by the action of infrared, vis-
ible light, or ultraviolet radiation.
photojunction cell A photocell consisting of a semi- 200 300 400 500 600 700 800
conductor pn junction. The cell is useful mainly
Wavelength (nm)
for its photoconductivity, although infrared, visible
light, or ultraviolet energy striking the junction
produces a small amount of photovoltaic action.
photokinesis Light-induced motion, as in a RA-
photolithographic process A method of producing
integrated circuits and printed circuits by pho-
tographing (often at considerable reduction) an
enlarged pattern of the circuit on a suitable light-
sensitized surface of metal or semiconductor, and Focusing
chemically etching away unwanted portions of
the surface.
photomagnetic effect Light-sensitive magnetic
susceptibility in some materials.
photomap A photo taken of terrain from a high al-
titude and usually overlaid with a reference grid.
photomask In PHOTOFABRICATION, the trans-
parent film or template on which the etching pat-
tern is drawn. Returned, modulated
photometer An instrument used to compare the electron beam
luminous intensity of two light sources. beam
photometric measurement of power See PHOTO-
photometry The science of visible-light measure-
ment. The response of the human eye is used as
the basis for preferred sensors (those used with
photometric instruments, which have spectral
Electron gun
sensitivity curves resembling those of the eye).
photomosaic In a television camera tube, the flat
photocathode screen on which the image is pro-
jected by the lens system and scanning electron
beam. The surface of the screen is covered with
tiny light-sensitive droplets. Also see DISSECTOR are reflected to a second plate, where they dis-
TUBE, ICONOSCOPE, and ORTHICON. lodge still more electrons. This process continues
photomultiplier tube A type of PHOTOTUBE that from deflection plate to deflection plate through
delivers high output current for a given light in- the tube. The final plate deflects the accumulated
tensity by utilizing the secondary emission of elec- electrons to the anode (collector electrode).
trons. The initial light-sensitive cathode emits photon A quantum of radiant energy whose energy
electrons; these strike a specially placed metal constant W (in joules) is equal to hf, where h is
plate with a force that dislodges more electrons. the PLANCK CONSTANT and f is the frequency in
These electrons, together with the initial emission, Hertz.
532 photoneutron • pickoff

photoneutron A neutron released by PHOTODIS- Metal
photophone 1. A telephone-type communication
system using a modulated light beam transmitted +
between stations. 2. A process for recording
sound on motion-picture film (see OPTICAL Glass
photoresistive cell See PHOTOCONDUCTIVE
CELL. Metal base

photoresistive material See PHOTOCONDUC-
photoresistivity See PHOTOCONDUCTIVITY.
8 Saturation current
photoresistor See PHOTOCONDUCTOR, 1, 2.

Relative current
photosensitive device A light-sensitive electronic
device. See, for example, PHOTOCONDUCTIVE
photosphere The luminous layer at the surface of
a star.
photoswitch A light-activated switch. Some photo-
0 2 4 6 8 10
switches contain an electromechanical relay; oth- Relative light intensity
ers, such as the light-activated silicon-controlled
switch, have no moving parts.
photovoltaic cell
phototimer An electronic timer for timing photo-
graphic processes.
phototransistor A transistor in which current photran A light-sensitive, four-layer semiconduc-
carriers emitted as a result of illumination con- tor device, used for switching purposes.
stitute an input-signal current. This current is physical properties The distinguishing character-
amplified by the transistor. The output signal istics of matter, apart from its chemical proper-
delivered by the transistor, accordingly, is ties. Included are boiling point, density, ductility,
larger than the output of an equivalent photodi- elasticity, electrical conductivity, hardness, heat
ode. conductivity, index of refraction, malleability, melt-
phototube An electron tube that converts light en- ing point, specific heat, and state (solid, liquid,
ergy into electrical energy by acting as a light- gaseous, or plasma).
sensitive resistor. Characteristically, the tube physical quantity A quantity expressing the ac-
contains an illuminated cathode coated with a tual number of physical units under considera-
photoemissive material, and an anode wire situ- tion, as compared with a dimensionless number.
ated nearby. Light energy causes electrons to be Examples: 50 volts, 39 kilometers, and 30 pico-
emitted from the cathode in amounts propor- farads. Compare DIMENSIONLESS QUANTITY.
tional to light intensity; the electrons are at- physics The science of energy and matter and their
tracted by the anode, which is connected interactions. Physics is subdivided into several
externally to a positive direct-current voltage. fields, including mechanics, thermodynamics,
photovoltaic cell Also called solar cell. A semi- acoustics, optics, and electricity/magnetism.
conductor diode, usually made from silicon, that Many subdivisions are within the traditional
converts visible light, infrared, and/or ultraviolet fields.
directly into electric current. The device consists Pi Symbol for INPUT POWER.
of a flat P-N junction; the assembly is transparent picket fencing An effect often observed at very-
so that radiant energy can fall directly on the P- high frequencies (VHF) and ultra-high frequen-
type silicon. Metal ribbing, forming the positive cies (UHF), in which movement of the trans-
electrode, is interconnected with tiny wires. The mitting station antenna, the receiving station
negative electrode is a metal backing, placed in antenna, or both antennas causes rapid fading.
contact with the N-type material. The component The fading is the result of phase effects between
produces about 0.5 to 0.6 volts in direct sunlight the direct wave and indirect wave(s). These effects
under no-load conditions. are most pronounced with vertically polarized
photovoltaic material A substance that generates antennas.
a voltage when exposed to light. The principal PIA Abbreviation of PERIPHERAL INTERFACE
substances exhibiting this effect are silicon, sele- ADAPTER.
nium, and germanium. Also see ACTINOELEC- pickoff 1. To monitor a voltage, current, or other
TRIC EFFECT. characteristic in an active circuit, without dis-
pickoff • Pierce oscillator

turbing the operation of the circuit. 2. A device for picture element See PIXEL.
electronically monitoring linear or angular dis- picture information In a television signal, the
placement. variable-amplitude component (i.e., the one car-
pickup 1. A device that serves as a sensor of a sig- rying energy corresponding to the picture ele-
nal or quantity. This covers a wide variety of ments) that fills the space between blanking
items, including temperature sensors, vibration pulses.
detectors, microphones, phonograph pickups, etc. picture-in-picture Abbreviation, PIP. In some tele-
2. Collectively, energy or information that is re- vision receivers, a feature that allows simultane-
ceived (e.g., sound pickup). ous viewing of two programs. One program
pickup arm The pivoted arm that holds the car- occupies the full screen, and another program
tridge and stylus of a phonograph. appears in a small portion of the screen.
pickup cartridge See PHONO CARTRIDGE. picture reception 1. See PHOTOGRAPH RECEP-
pickup current 1. The current required to close a TION. 2. The reception of television signals.
relay. 2. Current flowing through, or generated picture transmission 1. See PHOTOGRAPH
by, a pickup. TRANSMISSION. 2. The transmission or broad-
pickup pattern The directional pattern of a micro- casting of television signals.
phone or other transducer that converts acoustic picture tube The cathode-ray tube used in a tele-
energy into electrical signals. vision receiver to display the image. Also called
pickup voltage 1. The voltage required to close a KINESCOPE.
relay or circuit breaker. 2. The voltage delivered
by a pickup.
pico- 1. Abbreviation, p. A prefix meaning 10“12. ’ + Grids
2. A prefix meaning extremely small.
picoammeter A usually direct-reading instrument
used to measure current in the picoampere Phosphor
range. Also see CURRENT METER. screen
picoampere Abbreviation, pA. A small unit of cur-
rent equal to 10“12 ampere. Electron
picocoulomb Abbreviation, pC. A small unit of
electrical quantity equal to 10“12 coulomb.
picocurie Abbreviation, pCi. A small unit of ra-
dioactivity equal to 10“12 curie. Signal Deflecting
picofarad Abbreviation, pF. A small unit of capaci- plates
tance equal to 10“12 farad. or
picohenry Abbreviation, pH. A small unit of induc-
tance equal to 10“12 henry.
picture tube
picosecond Abbreviation, ps or psec. A small unit
of time equal to 10“12 second.
pi coupler See COLLINS COUPLER.
pie chart See CIRCLE GRAPH.
picovolt Abbreviation, pV. A small unit of voltage
Pierce oscillator A simple crystal oscillator in
equal to 10“12 volt.
which the crystal is connected directly between
picovoltmeter A usually direct-reading electronic
the input and output terminals of the active de-
instrument used to measure electromotive force
vice (usually a bipolar or field-effect transistor). A
in the picovolt range.
tuned inductance-capacitance (LC) circuit might
picowatt Abbreviation, pW. A small unit of power
be included, but is not required.
equal to 10“12 watt.
pictorial diagram See PICTORIAL WIRING DIA- Y1
pictorial wiring diagram A wiring diagram in the
form of a drawing or photograph of the compo-
nents, as opposed to one of circuit symbols. The
components are shown in their positions in the
finished equipment, and the wiring as lines run-
ning between them. B+
picture black In facsimile or television, the signal
condition resulting from the scanning of a black B’
portion of the image.
picture detector See VIDEO DETECTOR.
picture diagram See PICTORIAL WIRING DIA-
Pierce oscillator
534 pie winding • pinch roller

pie winding A method of coil winding in which two
or more separate, multilayer coils are connected
in series and placed along a common axis. It is Input Output
sometimes used in radio-frequency chokes to
minimize capacitance among the windings.
piezo- A prefix meaning pressure (see PRESSURE,
piezodielectric A substance that, when stretched
Input Output
or compressed, exhibits a change in dielectric
piezoelectric accelerometer An accelerometer
using a piezoelectric crystal, whose voltage out-
pi filters
put is proportional to acceleration.
piezoelectric ceramic A ceramic material that de-
livers a voltage when deformed, or that changes
in shape when a voltage is applied to it. 2. Descriptive of a device containing a long lead
piezoelectric crystal A crystal (such as quartz, or leads, and usually mounted by such leads.
Rochelle salt, tourmaline, or various synthetics) pile 1. See VOLTAIC PILE. 2. See NUCLEAR REAC-
that delivers a voltage when mechanical force is TOR. 3. A battery of electrochemical cells. 4. Any
applied between its faces, or that changes its packed group of particles or granules.
shape when a voltage is applied between its faces. pillow speaker A small, flat loudspeaker intended
piezoelectric earphone See CRYSTAL EAR- for use under a pillow.
PHONE. PILOT Acronym for programmed inquiry learning or
piezoelectric filter See CRYSTAL FILTER and teaching. A straightforward high-level computer
CRYSTAL RESONATOR. programming language, used in computer-
piezoelectricity Electricity produced by deforming assisted instruction (CAI).
(squeezing, stretching, bending, or twisting) cer- pilot lamp See PILOT LIGHT.
tain crystals, such as those of quartz, Rochelle pilot light A usually small, incandescent or neon
salt, or tourmaline. lamp. When glowing, it serves as a signal that a
piezoelectric loudspeaker See CRYSTAL LOUD- piece of equipment is in operation.
SPEAKER. pilot model A preliminary model of a circuit or de-
piezoelectric microphone See CERAMIC MICRO- vice constructed primarily to test the efficacy of a
PHONE and CRYSTAL MICROPHONE. production process. The pilot model usually fol-
piezoelectric oscillator See CRYSTAL OSCILLA- lows the PROTOTYPE.
TOR. pilot production The often small-scale production
piezoelectric pickup See CRYSTAL PICKUP. of a device in a special assembly line apart from
piezoelectric resonator See CRYSTAL FILTER the main line in a factory.
and CRYSTAL RESONATOR. pilot regulator A variable-gain circuit that main-
piezoelectric sensor See CRYSTAL TRANS- tains a constant output”even if the input ampli-
DUCER. tude changes.
piezoelectric transducer See CRYSTAL TRANS- PIM Abbreviation of PULSE-INTERVAL MODULA-
piezoid A complete piezoelectric crystal device. pi mode In a vane-anode magnetron, the mode of
piezoresistance In certain substances, the ten- operation in which adjacent vanes have radio-
dency of the resistance to change with stretching frequency voltages of opposite polarity.
or compression. pin 1. A semiconductor junction consisting of a
piezo tweeter A tweeter of the piezoelectric type layer of instrinsic semiconductor material situ-
(see CRYSTAL LOUDSPEAKER). ated between n and p layers. 2. A slender,
pi filter An unbalanced filter section having one straight, stiff prong used as a terminal or locking
series arm and two shunt arms; its schematic device (see, for example, BASE PIN and BAYONET
representation has the general shape of the up- BASE).
percase Greek letter pi. pinchoff In a junction field-effect transistor, the
piggyback component See OUTBOARD COMPO- condition in which the gate voltage causes the
NENT. two depletion regions to meet and close the chan-
piggyback control See CASCADE CONTROL. nel to obstruct drain-current flow.
piggyback tuner A separate ultra-high-frequency pinchoff voltage In a junction field-effect transis-
(UHF) television tuner operated in conjunction tor, the lowest value of gate voltage that will pro-
with the very-high-frequency (VHF) tuner of the duce pinchoff.
receiver. pinch roller In a tape recorder, a rubber-tired, ro-
pigtail 1. A usually long and sometimes flexible tating cylinder that helps to pull the tape past the
lead, such as the pigtail of a fixed capacitor. recording and/or playback heads.
pincushion • pitch

pincushion A type of television picture distortion
in which each side of the raster sags toward cen-
ter screen. Also see ANTIPINCUSHIONING MAG-
Input Output
pincushion-correction generator A circuit for
generating a deflection signal to correct pincush-
ion distortion (see PINCUSHION). One form con-
sists of a parabola generator and op-amp-type
differentiator. pi pad
pin diode A silicon junction diode having a lightly
doped intrinsic layer serving as a dielectric bar-
rier between p and n layers. system. The bridge is balanced before evacuation
pi network See COLLINS COUPLER. starts. As evacuation progresses, the heat re-
ping An acoustic pulse; it can be audible sound or moved from the filament becomes proportional to
ultrasound. the pressure in the system, and the resistance of
pinhole 1. A tiny hole present as a defect in a film the filament changes accordingly. The bridge is
of dielectric, semiconductor, or metal. 2. A tiny then rebalanced, and the difference between ini-
aperture that acts as a universal lens by permit- tial and subsequent null conditions indicate the
ting the passage of a very small bundle of light extent of the vacuum when the bridge has been
rays. The smaller the aperture, the greater the appropriately calibrated.
depth of field. pi section An unbalanced filter or tuner section
pinhole detector An electronic device for finding whose schematic representation has the general
pinholes in materials. Also see PINHOLE, 1. shape of the uppercase Greek letter pi.
pin jack A jack into which a pin plug is inserted for pi-section coupling Use of a PI SECTION for cou-
quick connection. pling a radio transmitter to an antenna. Also see
pink noise Acoustical noise whose amplitude is COLLINS COUPLER and PI-SECTION TANK.
inversely proportional to the frequency within a pi-section filter A pi section used as either a low-
limited frequency spectrum. In the extreme, it pass or high-pass filter, depending on the posi-
creates a hissing sound. Compare WHITE tion of the capacitors in the circuit.
NOISE. pi-section tank A pi section used as the collector,
pinout A diagram of an integrated circuit depicting drain, or plate tank circuit of a radio-frequency
the locations of the pins for various functions. It power amplifier, and also serving as an antenna
generally takes the form of a rectangle for the cir- coupler.
cuit itself, and short lines for the pins with desig- piston 1. The movable element (cone) of a loud-
nators printed next to the lines. speaker. 2. The movable, solid plunger of a trim-
pin plug A plug consisting of a slender metal pin mer capacitor that consists of a plug within a
inserted between the blades of a PIN JACK for a cylinder.
quick connection. The plug usually has a small piston directivity Directivity of sound emitted by
insulated back for convenient handling. the piston of a loudspeaker (see PISTON, 1). As
pin straightener A device for straightening the the frequency of the audio signal increases, radi-
pins of a transistor, integrated circuit, or other ation from a loudspeaker tends to be concen-
electronic component. trated along the axis of the piston.
pin switch A switch that changes state when a pit 1. A microscopic depression in a compact disc;
small pin is pushed or pulled. scatters and/or absorbs light from the laser,
pin-usage factor For an integrated circuit, the rather than reflecting it. Compare LAND, 1. 2. In
number of gate equivalents per package pin. Also a printed-circuit board, a pockmark in a compo-
see GATE EQUIVALENT. nent or foil run. 3. A pockmark in a metallic sub-
PIO Abbreviation of parallel input/output. stance, resulting from corrosion.
pion A subatomic particle consisting of one quark pitch 1. The frequency of a sound, either in gen-
and one antiquark. eral terms (e.g., low, midrange, and high) or as a
PIP Abbreviation of PICTURE-IN-PICTURE. specific quantity (e.g., 2450 Hz). 2. The distance
pip See BLIP. between the peaks of adjacent grooves on a
pi pad A resistance-type attenuator having a series phonograph disc. 3. The distance between adja-
arm, a shunt input arm, and shunt output arm; cent threads of a screw. 4. The distance between
its name is derived from its resemblance to the centers of turns in a coil (see PITCH OF WIND-
Greek letter pi. Also see PAD. ING) 5. The number of teeth or threads per unit
pipe radiator A waveguide having an open end length. 6. The distance along its axis a propeller
from which microwave energy is radiated. moves in a revolution. 7. Up-and-down motion of
Pirani gauge A type of vacuum gauge in which a a robot end effector or other electromechanical
heated filament, composing one arm of a four- device. 8. The extent or range of movement, as
arm resistance bridge, is sealed into the vacuum defined in 7.
536 pitch of winding • plasma diode

pitch of winding In a coil, the distance from the Base
center of one turn to the center of the adjacent
turn in a single layer of winding.
pivot The sometimes jeweled, stationary member
of the bearing in an analog meter movement.
pi-wound choke A choke coil consisting of several n
series-connected sections, mounted on a single
core and separated to reduce internal capaci-
tance. n
pix Abbreviation of PICTURE.
pixel Contraction of picture element. The smallest
planar transistor
bit of data in a video image. Also called pel. The
smaller the size of the pixels in an image, the
greater the resolution for a given image area.
pixel aspect ratio In a video image, the ratio of plane of polarization The plane containing the di-
PIXEL height to pixel width. rection of propagation and the electric field vector
pix tube See PICTURE TUBE. of a plane-polarized wave (see POLARIZATION, 3


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