Glossary T
Telecommunication:   The transmission of information from one point to another.

Temperature Error: The maximum change in output, at any measurand value within the specified range, when the temperature is changed from room temperature to specified temperature extremes.

Temperature Range, Compensated: The range of ambient temperatures within which all tolerances specified for Thermal Zero Shift and Thermal Sensitivity Shift are applicable (temperature error).

Temperature Range, Operable: The range of ambient temperatures, given by their extremes, within which the instrumentmay be operated. Exceeding compensated range may require recalibration.

Terminal: An input/output device used to enter data into a computer and record the output.

T Flip Flop: Toggle flip flop.

Thermal Coefficient of Resistance: The change in resistance of a semiconductor per unit change in temperature over a specific range of temperature.

Thermal Conductivity: The property of a material to conduct heat in the form of thermal energy.

Thermistor: A temperature-sensing element composed of sintered semiconductor material which exhibits a large change in resistance proportional to a small change in temperature. Thermistors usually have negative temperature coefficients.

Thermocouple: The junction of two dissimilar metals which has a voltage output proportional to the difference in temperature between the hot junction and the lead wires (cold junction) (refer to Seebeck emf).

Thermopile: An arrangement of thermocouples in series such that alternate junctions are at the measuring temperature and the reference temperature. This arrangement amplifies the thermoelectric voltage. Thermopiles are usually used as infrared detectors in radiation pyrometry.

Thermowell: A closed-end tube designed to protect temperature sensors from harsh environments, high pressure, and flows. They can be installed into a system by pipe thread or welded flange and are usually made of corrosion-resistant metal or ceramic material depending upon the application.

Thomson Effect: When current flows through a conductor within a thermal gradient, a reversible absorption or evolution of heat will occur in the conductor at the gradient boundaries.

Thyristor: A component rather like a diode but will not conduct until a voltage is applied to its third terminal known as the gate.

Time Base: Oscilloscope circuitry that controls the timing of the sweep. The time base is set by the seconds/division control.

Tolerance: The allowable percentage variation of any component from that stated on its body. For instance: red=2%, gold=5% and silver=10%.

Trace: The visible shapes drawn on a CRT by the movement of the electron beam.

Transducer: A device that receives energy in one form and supplies an ouput in another form or we can say a device that converts a specific physical quantity such as sound, pressure, strain, or light intensity into an electrical signal.

Transistor: A three leaded device (Collector, Base, Emitter) used for amplifying or switching. Also called a bi-polar transistor to distinguish it from Field Effect Transistor etc.

Transient: A signal measured by an oscilloscope that only occurs once (also called a single-shot event).

Triac: A solid state switching device used to switch alternating current wave forms.

Trigger: The circuit that commences a horizontal sweep on an oscilloscope and determines the beginning point of the waveform.

Trigger Holdoff: A control that inhibits the trigger circuit from looking for a trigger level for some specified time after the end of the waveform.

Trigger Level: The voltage level that a trigger source signal must reach before the trigger circuit initiates a sweep.

Trimmer: Trimmer Capacitor. A small variable capacitor used in paralled across a larger capacitor to adjust the total capacitance a small amount.

True RMS: The true root-mean-square value of an AC or AC-plus-DC signal, often used to determine power of a signal. For a perfect sine wave, the RMS value is 1.11072 times the rectified average value, which is utilized for low-cost metering. For significantly non-sinusoidal signals, a true RMS converter is required.

Truth Table: A tabular representation of a logic gate showing all the possible combinations.

TTL Unit Load: A load with TTL voltage levels, which will draw 40 µA for a logic 1 and -1.6 mA for a logic 0.

TTL-Compatible: For digital input circuits, a logic 1 is obtained for inputs of 2.0 to 5.5 V which can source 40 µA, and a logic 0 is obtained for inputs of 0 to 0.8 V which can sink 1.6 mA. For digital output signals, a logic 1 is represented by 2.4 to 5.5 V with a current source capability of at least 400 µA; and a logic 0 is represented by 0 to 0.6 V with a current sink capability of at least 16 mA.

TTL: Transistor-to-transistor logic. A form of solid state logic which uses only transistors to form the logic gates.

Typical: Error is within plus or minus one standard deviation (±1%) of the nominal specified value, as computed from the total population.