The Franck-Hertz tube is a highly evacuated electron tube with mercury filling and plane-parallel electrode system consisting of indirectly heated oxide cathode with pinhole, reticulated anode and a collecting electrode. To obtain a high impact probability, the distance between cathode and anode is chosen to be large (8 mm) compared to the mean free path length in the Hg atmosphere (at approx. 180° C). In contrast, the distance between the anode and the collecting electrode is kept small.
In order to achieve the required mercury vapor pressure for a sufficient collision probability of the electrons with the mercury atoms, the electron tube must be heated in the furnace. The Franck-Hertz tube is positioned so that the entire tube, including the connecting wires, comes to a constant, homogeneous temperature. This is necessary because the vapor density of the mercury always follows the coldest part of the tube. The electric heating furnace with continuous temperature control is equipped with a digital temperature display of set and actual temperature. Temperature measurement and control is performed by an integrated microcontroller and Pt100 sensor.
The tube and heater are housed in a painted metal enclosure with two viewing windows. The housing is provided with an opening with clamp spring holder for thermometer and a thermally insulated carrying handle.
Heating: 4 to 12 V AC/DC
Grid voltage: 0 to 70 V
Counter voltage: approx. 1,5 V
Operating temperature: approx. 200° C
Dimensions: approx.. 130 mm x 26 mm Ø
Mass: approx. 380 g
Heater / Housing
Mains supply voltage: 230 V (50/60 Hz)
Opening of the front side: ca. 230 mm x 160 mm
Heating power: 400 W
Maximum temperature: 300°C
Temperature constancy: approx. ±1°C
Dimensions: approx. 335 mm x 180 mm x 165 mm
Mass: approx. 5,6 kg