Iron-hydrogen resistance

Iron-hydrogen resistance for 2 to 6 volts / 0.1 amps

Large iron-hydrogen resistor from Narva for 90 to 270 V / 1.1 A. 36 cm total length and E27 socket

An iron-hydrogen resistor is a PTC thermistor and consists of a glass bulb filled with hydrogen, similar to an incandescent lamp , with an iron wire inside. Iron-hydrogen resistors were used to provide a defined current in spite of (within limits) varying voltage ( constant current source ), but are no longer of any importance, since constant current sources are nowadays implemented as electronic circuits.

function

Close-up, in the middle the coiled iron wire in a vertical position

Iron-hydrogen resistors are PTC thermistors and constant current sources. If the resistance wire is loaded so that its temperature is around 700 ° C, the temperature dependence of the electrical resistance of the iron comes into play. When the voltage rises and the temperature increases as a result, the value of the resistance increases by leaps and bounds and a dark red glowing zone forms in the wire. As the voltage increases, this zone becomes longer and longer at the expense of the non-glowing section. The hydrogen filling not only protects the iron from oxidation , but also has the effect that the solubility of the hydrogen in the iron increases by leaps and bounds around 700 ° C, and with it the electrical resistance.

application

Iron-hydrogen resistors were developed as series resistors for operating the Nernst lamp .

In the meantime they had a somewhat greater importance in broadcast technology. In all-current devices , they were connected in series to the filaments of the electron tubes and stabilized the flow of current in the heating circuit when the mains voltage fluctuated. In addition, there was a so-called URDOX resistor ( NTC thermistor , which was made of uranium dioxide until 1936 ) in the heating circuit to limit the inrush current . This was partly housed in the same glass flask with the iron wire.

They were also used in de-excitation devices for synchronous machines and large chokes .

literature

• Wilhelm Walcher: Physics internship. Vieweg + Teubner Verlag, 2006, ISBN 978-3-835-10046-6 , p. 241 ( limited preview in the Google book search).

Individual evidence

1. ↑ solubility in iron vs. Temperature (PDF, 3.1 MB), see page 6.
2. ↑ The Nernst lamp. In: nernst.de. Retrieved February 15, 2017 .