(Electronics) A resistor inserted into a circuit to compensate for changes (such as those arising from temperature fluctuations); a thermal cymoscope.
Synonyms:ballast resistor. Note: The original form consisted of an extremely fine platinum wire loop attached to terminals and inclosed in a small glass or silver bulb. It operates by increased resistance when subjected to the influence of an electric current. In a later variety, called the liquid barretter, wire is replace by a column of liquid in a very fine capillary tube. A recent version has a resistor composed of an iron wire in a glass bulb containing hydrogen, with the temperature variation of resistance such that the current passing through it remains constant over a wide range of applied voltages.