Electronic Engineering Dictionary

Thermionic Emission. Emission of electrons from a solid body as a result of elevated temperature.

Thermistor. A semiconductor device whose resistance varies with temperature. A type of bolometer characterized by a decrease in resistance as the dissipated power increases. A resistor with a negative or positive non-linear temperature coefficient of resistance. Refer to the related list of Thermistor Manufacturers or the section covering the Resistor Thermistor Definition.

Thermocouple. A junction of two dissimilar metals that produces a voltage when heated. [Thermocouple Wire Manufacturers]

Thermocouple Meter Movement. A meter movement that uses the current induced in a thermocouple by the heating of a resistive element to measure the current in a circuit; used to measure ac or dc.

Thermopile. A component that contains more than one thermocouple, and used to convert thermal energy into electrical energy.

Thermoplastic. A synthetic mixture of rosins that is flexible and used as an insulting material. Generally used as an insulator for low- and medium-range voltages. [ABS Plastic]

Thermostatic Switch. A type of switch designed to operate as a function of temperature. More detail on Thermostatic Switches.

THETA. The Greek letter used to represent phase angle.

Thick Film Component. Passive circuit components (resistors and capacitors) having a film thickness of 0.001 centimeter or greater.

Thin Film Component. Passive circuit elements (resistors and capacitors) deposited on a substrate to a thickness of 0.0001 centimeter.

Three Later Diode. Another term for a Diac, but may also refer to a PIN diode.

Three Phase. Power transmission using three different phases of ac which differ in phase by one third of a cycle or 120 degrees.

Three Phase Four-Wire System. An AC system that uses three conductors as in a 3-phase systems and adds a four wire used as a neutral line, which than may be grounded.

Three Phase Three-Wire System. An AC system that uses three conductors as in a 3-phase systems with each conductor carring an AC voltage which differ in phase by one third of a cycle or 120 degrees.

Three Quarter Rectifier. A four diode bridge rectifier that has one of the diodes replaced by a resistor.

Three State. [3-State] See Tri-State.

Three-Way Speaker System. A speaker cabinet [for example] that holds [at least] three individual speakers each designed to reproduce a specific range of audio frequencies; commonly divided into low [woofer], mid-range [Midrange] and high frequency [tweeter]. The audio signals are separated by frequency and sent to the individual speakers by a Cross-Over Network.

Three-Wire System. [3-Wire] Also called a 3-wire, single-phase, mid-point neutral system, or split-phase system. Two conductors carry power at 180 degrees out of phase, with a third or neutral wire that carries half the voltage of the other wires. In a standard american configuration; connection between a live conductor and the neutral produces 120 volts, while a connection between the two live conductors produces 240 volts.

Threshold. The minimum value of a signal that can be detected by the system or sensor under consideration. The voltage point at which a digital logic gate recognizes a signal. Read more on TTL Voltage Thresholds.

Throughput. The number of bits, characters, or blocks passing through a data communication system, or portion of that system. A measure of the efficiency of a system which accounts for the data received or transmitted in a particular amount of time. Throughput measures data over time, so signalling bits, or control bits [over-head] reduces the system through-put, while increasing clock rates may increase system through-put.

Throw. In a switch, the number of different circuits each pole can control; for example, single throw and double throw.

Thru-hole Component. A part that uses terminals that pass-through a printed wiring board.

Thumbwheel Switch. A rotating switch that is moved by using the thumb to advance the switch to a different position, and normally indicates the position of the switch by a number [printed on the wheel] which is also advanced.

Thumbwheel

Thyratron Tube. A gas-filled triode in which a sufficiently large positive pulse applied to the control grid ionizes the gas and causes the tube to conduct, after which the control grid has no effect in conduction. A gas tube used as a modulator switching device. A 2D21 thyratron is shown in the side-bar to the lower right. Also refer to Vacuum Tube Classifications.

Thyristor. A bi-stable semiconductor device that comprises three or more junctions and can be switched from the off-state [non-conducting] or on-state [conducting] to the opposite state. Use this link to read about the Different Types of Thyristor Devices. Manufacturers that produce Thyristors.

Tickler Coil. A small coil connected in series with the collector or plate circuit of a transistor or tube and inductively coupled to the base or grid-circuit coil to establish feedback (regeneration). An example of tickler coil used in an Armstrong Oscillator.

Time Base. An oscillator found inside an electronic instrument that serves as a reference for all of the time and frequency functions performed by that instrument.

Time Code. A code (usually digital) that contains enough information to synchronize a clock to the correct time-of-day. See IRIG Standards]. A code used for the transmission and identification of time signals.

Time Constant. Time required for an exponential quantity to change by an amount equal to 63.2 percent of the total change that can occur. The interval required for a system or circuit to change a specified fraction from one state or condition to another.

Time Delay Relay. A relay in which its contacts are delayed from opening or closing after the relay has been energized or de-energized. Also see Relay Manufacturers.

Time-Division Multiple Access. [TDMA] A communications technique that uses a common channel (multipoint or broadcast) for communications among multiple users by allocating unique time slots to different users.

Time-Division Multiplexing. Digital multiplexing in which two or more apparently simultaneous channels are derived from a given frequency spectrum, i.e., bit stream, by interleaving pulses representing bits from different channels [TDM]. The process that periodically samples the full 360 degrees of each sine wave. The sample can be of a received signal or of a signal to be transmitted.

Time Domain. The measurement domain where voltage and power are measured as functions of time.

Time-Domain Reflectometer. [TDR] An electronic instrument used to characterize and locate faults in metallic cables (e.g., twisted pair, coax). A listing of TDR Manufacturers.

Time Jitter. Short-term variation or instability in the duration of a specified time interval. Read more on Logic Jitter.

Time Interval. The elapsed time between two events.

Time Lag. The delay in a servosystem between the application of the input signal and the actual movement of the load.

Timer. A circuit used to track the passage of time. A 555 IC is a common integrated circuit used as a timer via the charging rate of an RC circuit [as shown in the right side-bar]. Also refer to following 555 circuit descriptions; 555 Monostable Circuit, 555 Astable Circuit, and 555 50% Duty Cycle Circuit. See Synchronizer. Companies producing IC Clocks and Timers. Also see Watchdog Timer.

Time-Sharing. The interleaving of two or more independent processes on one functional unit.

Timing Skew. The difference in time between a pulse edge and a reference pulse or its expected transition. See Skew.

Tin Whisker. Tin whiskers are electrically conductive, crystalline structures of tin that sometimes grow from surfaces where tin (especially electroplated tin) is used as a final finish."NASA". [Tin Whisker Growth].

Tinning. The coating of a surface with a uniform layer of solder. Read more on Tinning

TNC Connector. A style of threaded coaxial connector. An example SMA to TNC adapter is shown to the right, using a jamnut interface. Refer to the TNC Connector Definition.

T-Network. A network with three branches which form a 'T' shape. One end of each branch to a common point, while the other ends become an input, an output and a common node between the input and output. Also check the resistor only T-Attenuator Network topic.

T-Network

Toggle. A T Flip Flop, T FF. A change of states between high and low or low to high.

Toggle Frequency. The maximum frequency a flip flop can be clocked. The number of times a flip flop changes state.

Toggle Rate. How fast a flip flop changes state.

Toggle Switch. A mechanical switch that uses a toggle action to actuate the switch. A toggle throw may be maintained or momentary, vertical and right angle mounting, and use a through hole or surface mount package. Toggle switches may also be locking, to hold its position when having a multi-position movement [more than two]. Also see Companies making Toggle Switches.

Toggle

Token. In certain local-area-network protocols, a group of bits that serves as a symbol of authority, is passed among data stations, and is used to indicate the station that is temporarily in control of the transmission defined. Also see Definitions of Network Protocols.

Token Passing. A network access procedure in which a token passes from station to station and the only station allowed to transmit information is the station with the token.

Token-Ring Network. A bus network in which a token passing procedure is used. For more detail see the Token-Bus Network description.

Tolerance. The maximum permissible error or variation from the standard in a measuring instrument. A maximum electrical or mechanical variation of specifications that can be tolerated without impairing the operation of a device. A documented range over which a specified value may vary. Resistor Tolerance. The permissible range of variation of some characteristic from its nominal value.

Tone Control. An audio circuit that combines both the Base Control and Treble Control functions. Also refer to the page covering an Audio Tone Control Circuit.

Topologies. The layout of a network. The method that devices are connected together Network Topologies.