US PATENT SUBCLASS 338 / 20
.~ Current and/or voltage (e.g., ballast resistor)

Current as of: June, 1999
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338 /   HD   ELECTRICAL RESISTORS

13  DF  RESISTANCE VALUE RESPONSIVE TO A CONDITION {10}
20.~ Current and/or voltage (e.g., ballast resistor) {3}
21  DF  .~.~> Voltage surge-responsive or lightning arrester type
22 R  DF  .~.~> Thermistor type {2}
24  DF  .~.~> Indirectly heated

DEFINITION

Classification: 338/20

(under subclass 13) Subject matter wherein the resistor is chemically constituted or otherwise formed to change its resistance value in response to an electric current passing through or a voltage impressed across the resistor, or wherein the resistor includes structure or composition which enables the resistor to change its resistance value in response to a current or voltage applied to a circuit other than to the resistor itself; as to an electric heater with a heat conducting path to the resistor.

(1) Note. Usually the current increases the temperature of

the resistor either directly or indirectly, and the resistor has an appreciable resistor temperature coefficient to cause the resistance value to change. In the case of the so-called voltage responsive resistors, a voltage change often produces a current change which in turn changes the resistance value as through the heating effect of the current. However, some resistors here classified do change value directly with the voltage gradient existing therein.

SEE OR SEARCH THIS CLASS, SUBCLASS:

25+, for resistors whose resistance value changes with ambient temperature.

103+, and 116, for mechanically adjustable or variable resistors with an electromagnetic operator, such as an electric motor.

SEE OR SEARCH CLASS 313, Electric Lamp and Discharge Devices,

341+, for electric lamp and discharge device filaments.

323, Electricity: Power Supply or Regulation Systems,

293+, for impedance systems automatically responsive to voltage and/or current.