Appendix I Glossary - Cont'd -141200441

SHIELD-- A nonconducting coating, paint, or sheet

THERMAL-MAGNETIC TRIP ELEMENT-- A

that is used to beneficially change the current on a

single circuit breaker trip element that combines the

cathode or anode; normally used with impressed

action of a thermal and a magnetic trip element.

current or other high-potential cathodic protection

THERMOCOUPLE METER MOVEMENT-- A

systems to distribute the current beyond the

meter movement that uses the current induced in a

immediate vicinity of the electrode.

thermocouple by the heating of a resistive element

to measure the current in a circuit; used to measure

SILICON CONTROLLED RECTIFIER PACK-

AGE-- A device that furnishes controlled dc power

ac or dc.

to a device.

THETA

The greek letter used to represent phase

SINE WAVE-- The curve traced by the projection on a

angle.

uniform time scale of the end of a rotating arm, or

THRESHOLD-- The least value of current or voltage

vector. Also known as a sinusoidal wave.

that produces the minimum detectable response.

SOLENOID-- An electromagnetic device that changes

TIME CONSTANT-- (1) The time required to charge

electrical energy into mechanical motion; based

a capacitor to 63.2 percent of maximum voltage or

upon the attraction of a movable iron plunger to the

discharge to 36.8 percent of its final voltage. (2) The

core of an electromagnet.

time required for the current in an inductor to

SOLID STATE-- A class of electronics components,

increase to 63.2 percent of maximum current of

such as transistors, diodes, integrated circuits,

decay to 36.8 percent of its final current.

silicon controlled rectifiers, and so forth.

TOLERANCE-- (1) The maximum error or variation

SPAN-- The distance between two points.

from the standard permissible in a measuring

instrument. (2) A maximum electrical or

SPECIAL FUNCTION-- A unique service performed

mechanical variation from specifications that can

by a system; usually above and beyond the direct

be tolerated without impairing the operation of a

design intent of the system.

device.

STANDARD PRINT-- A standard drawing,

TRACKING-- One object or device moving with or

schematic, or blueprint produced in the applicable

following another object or device.

technical manual or other official technical

publication.

T R A N S D U C E R -- A device that converts a

mechanical input signal into an electrical output

STATUS LOG-- A record of the instantaneous values

signal.

of important conditions having analog values.

TRANSFORMER-- A device composed of two or

STRAY-CURRENT CORROSION-- Corrosion

more coils, linked by magnetic lines of force, used

caused by current flow from a source (usually dc)

to transfer energy from one circuit to another.

through paths other than the intended circuit or by

extraneous currents in the electrolytic solution.

TRANSFORMER, STEP-DOWN-- A transformer

so constructed that the number of turns in the

SYSTEM-- The major functional section of an

secondary winding is less than the number of turns

installation.

in the primary winding. This construction will

SYSTEM INTERRELATION-- Specific individual

provide less voltage in the secondary circuit than in

operations in one system affecting the operation in

the primary circuit.

another system.

TRANSFORMER, STEP-UP-- A transformer so

TACHOMETER GENERATOR-- A device for

constructed that the number of turns in the

converting rotational speed into an electrical

secondary winding is more than the number of turns

quantity or signal,

in the primary winding. This construction will

provide more voltage in the secondary circuit than

TESLA-- The tesla is a measurement of magnetic flux,

in the primary circuit.

equivalent to 1 weber per square meter. One tesla is

equal to 10,000 gauss.

TRIP ELEMENT-- The part of a circuit breaker that

TEST POINT-- A position in a circuit where

senses any overload condition and causes the circuit

instruments can be inserted for test purposes.

breaker to open the circuit.

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