An iron–hydrogen resistor consists of a

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...

-filled glass bulb (similar to a light bulb), in which an

iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...

wire is located. This resistor has a

positive temperature coefficient A temperature coefficient describes the relative change of a physical property that is associated with a given change in temperature. For a property ''R'' that changes when the temperature changes by ''dT'', the temperature coefficient α is def ...

of resistance. This characteristic made it useful for stabilizing circuits against fluctuations in power-supply voltages.Power Supply Stages
This device is often called a "barretter" because of its similarity to the barretter used for detection of radio signals. The modern successor to the iron–hydrogen resistor is the

current source A current source is an electronic circuit that delivers or absorbs an electric current which is independent of the voltage across it. A current source is the dual of a voltage source. The term ''current sink'' is sometimes used for sources fed ...

Operation

When the current increases, the temperature will increase. The higher temperature leads to a higher

electrical resistance The electrical resistance of an object is a measure of its opposition to the flow of electric current. Its reciprocal quantity is , measuring the ease with which an electric current passes. Electrical resistance shares some conceptual paralle ...

, opposing the increase in current. The hydrogen gas protects the iron against

oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...

and also enhances the effect, since the solubility of hydrogen in iron increases as temperature increases, resulting in higher resistance.

Uses

Iron–hydrogen resistors were used in the early

vacuum tube A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied. The type known as ...

systems in series with the tube heaters, to stabilize the heater circuit current against fluctuating supply voltage. In 1930s Europe it was popular to combine them in the same glass envelope with an NTC-type

thermistor A thermistor is a type of resistor whose resistance is strongly dependent on temperature, more so than in standard resistors. The word thermistor is a portmanteau of ''thermal'' and ''resistor''. Thermistors are divided based on their conduction ...

made of UO₂ until 1936, known as ''Urdox resistor'' and acting as an

inrush current limiter An inrush current limiter is a component used to limit inrush current to avoid gradual damage to components and avoid blowing fuses or tripping circuit breakers. Negative temperature coefficient (NTC) thermistors and fixed resistors are often us ...

for the series heater strings of domestic AC/DC tube radios.

References

External links

Praktikum der Physik von Wilhelm Walcher
Page 241
Regulator, Type 4A1, Museum of Victoria exhibit No: ST 029230
*Paleoelectronics RDH
Ch 33Ch 35
{{DEFAULTSORT:Iron-Hydrogen Resistor Resistive components Hydrogen technologies

Operation

Uses

See also

References

External links