Resistor Terms:

Resistor Definitions
'A', 'B', 'C', 'D/E', 'F-L', 'M', 'N', 'O', 'P', 'R', 'S', 'T', 'V-Z'

T-Pad. A style of attenuator, with a configuration in the shape of the letter which is shown to the right. Also refer to Resistor Attenuator schematics for more detail and attenuator variations.

Fixed T Attenuator Network Schematic
Fixed T Attenuator

Tab Mounted Resistor. A mounting method used by some high power resistors. The resistor uses tabs as opposed to leads or metal pads.

Tab-terminal Power Resistor, mechanical drawing
Tab Mounting Resistor

Tap: A fixed terminal on a trimmer or potentiometer providing a fixed resistance value. A tap is placed between the two fixed ends of a variable resistor. Potentiometer Manufacturers.

Taper: References how a potentiometer changes value as the wiper is moved across its resistive element. There is two general types of taper used with potentiometers; a linear taper and an audio taper. The linear taper changes resistance in a linear manner as the wiper moves across the contract. An audio taper changes resistance in a logarithmic fashion, so the value changes in more in line with how the ear processes changes in sound.

Tapped Resistor: A wire-wound, fixed resistor having one or more additional terminals along its length, generally for voltage-divider applications. See the graphic in the side-bar.

TCR: Temperature Coefficient of Resistance. TCR causes the value of the resistance to vary with change in temperature.

Temperature Coefficient: The magnitude of change in resistance due to temperature, usually expressed in percent per degree Celsius or parts per million per degree Celsius (ppm/C).

Equation for Temperature Coefficient of Resistance

Termination Resistor: The resistor used to terminate [or match] a load to the incoming line impedance.
MIL-PRF-83401/9 Resistor Network, Fixed, Film, 10 Pin SIP
R1/R2 Resistor values are shown in the tables, below right.
How to calculate a termination resistor value.

Schematic of a parallel resistor termination network
Parallel Termination Resistor Schematic, MIL-PRF-83401/9

Also refer to the page covering Styles of Resistor Networks for a 16-pin DIP resistor network.

Terminal: The leads of a through-hole resistor, or the end caps of an SMD resistor.

Thermal Noise: [Johnson Noise] The noise caused by the increase of current carries in a resistor due a thermal increase in the device.

Thermal Shock: A sudden change in temperature. Thermal Shock test; The resistors shall then be mounted on a rack of low-heat conducting material, and rated power shall be applied until thermal stability has been reached. The power shall then be removed and within 8 seconds to 12 seconds, the resistors shall be subjected to an air temperature of -55OC +0OC, -5OC for a period of not less than 15 minutes. Measurement of resistance shall be made not less than 2 hours after final exposure.

Thermistor: A resistor whose resistance varies with temperature in a defined manner. A device which produces a large change in resistance due to a change in body temperature. There are two types of Thermistors: PTC and NTC. Companies that Manufacture Thermistors, Thermistor Derating Graph.

Resistor Thermistor Package Drawing
Thermistor Package

Thick Film Resistor: A resistor with an element having a thickness of 0.001 centimeter. --- MIL-PRF-55342.

Thin Film Resistor: A resistor with an element having a thickness of 0.0001 centimeter. --- MIL-PRF-55342.

Through-Hole Resistor: A resistor that uses leads that penetrate the printed wiring board for mounting. For example the RNC90 resistor shown in the side-bar.

Time Constant: The Time constant is the time it would take for the potential difference across the capacitor [in an RC circuit] to increase to the same level as the applied voltage. The capacitance voltage rises at an exponential rate. The voltage over the capacitor also falls at the same rate. One Time constant [TC] equals R x C. Two TC's equals 2 x[RC], and so on. Read more on calculating RC TC.

Graph of RC Time Constant
RC Time Constant

Tolerance: A permissible deviation from a specified value. A maximum electrical or mechanical variation of specifications that can be tolerated without impairing the operation of a device. Definition of Resistor Tolerance.

Trimmer: A variable resistor. Designed for less then frequent changes [occasional]~ a trim pot on a PCB to finalize a circuit resistance. A variable resistor used to trim resistance in a circuit, normally just once, or more to correct for component value drift. A Trimmer may be Single Turn or Multi-turn.

Resistor Trimmer Case Drawing
Trimmer, Trim Pot

Also refer to through-hole Trimmer Package Styles, or SMD Trimmer Package Styles.

Trimmer Potentiometer: [Trim Pot] A variable resistor. A potentiometer used as a trimmer for occasional and small resistance adjustments. A Potentiometer is a variable resistor, while a Trimmer is a variable resistor used for small circuit changes; so a Trimmer Potentiometer is a variable resistor used to make small changes in resistance.

However; in many cases a Trimmer is also considered to be a variable resistor which was designed to only be used for occasional changes [before the wiper wears out]. So in this case a Trimmer Potentiometer is a long life variable resistor being used only for small changes in circuit resistance.

A Trimmer Potentiometer may be either a variable mechanical resistor or Semiconductor Potentiometer, both of which may be found on the Manufacturers of Variable Resistor page. An example of a digital Trimmer Potentiometer is the DS1804 [Maxim].

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