US2044591A - Gas-filled electric discharge tube - Google Patents

Description

June 16, 1936. F. M. PENNING 2,044,591

GAS FILLED ELECTRIC DISCHARGE TUBE Filed Nov. 28, 1932 Patented June 16 1936 UNITED STATES PATENT OFFICE GAS-FILLED ELECTRIC DISCHARGE TUBE Frans Michel Penning, Eindhoven, Netherlands, assignor to Radio Corporation of America a corporation of Delaware 3 Claims.

This invention relates to. a new negative resistance device formed by a helium-filled electric discharge tube in which the electrode spacing and the pressure of gas are such that with cold electrodes the break-down voltage has more than one value.

For a detailed description of the present invention reference is made to the following specification taken in connection with the accompanying drawing in which Figs. 1 and 2 are curves serving to explain the operation of applicants device, Fig. 3 is a gas-filled discharge tube in accordance with the present invention, Fig. 4 represents curves graphically illustrating the characteristics of the tube shown in Fig. 3, and Fig. 5 shows the use of applicants invention in a suitable circuit arrangement.

If the break-down voltage of a gas-filled discharge tube provided with two parallel cold electrodes is determined as a function of the product of the electrode spacing and the pressure of gas, this function is found to have a minimum. This function, graphically illustrated, has generally the shape of the curve shown in Figure 1 in which the break-down voltage V is shown as a function of the pressure p (with constant electrode spacing) or of the electrode spacing d (with constant pressure).

By very accurate measuring operations it has now been found by the applicant, that with a helium-filled tube the part of the curve situated on the left of the minimum has not the variation that this curve was assumed hitherto to have and which is shown in Figure 1. It is surprising to find that this branch of the curve has the shape outlined in Fig. 2. The curve is measured on the discharge tube which is illustrated diagrammatically in Fig. 3. This tube contains a uni laterally closed metal cylinder 1 which is carried by a ferrochrome ring 2 into which the cylinder I fits exactly. This ring 2 is sealed to the glass wall part 3 and also to a glass tube 4. The wall part 3 is furnished with a stem 5 through which a. flexible leading-in wire 6 is taken. The glass tube 4 has in turn sealed to it a ferrochrome cylinder 1 which surrounds the cylinder l at a small distance for part of its length. The cylinder 1 contains a bottom 8 which separates the interior of the discharge tube from the open air and is furnished with a leading-in wire 9. This member 8 and the bottom ll! of the cylinder l constitute the two electrodes of the discharge tube which is filled with a supply of helium at a pressure of 0.84 ms. ,By displacing the cylinder 1 it is possible to vary the spacing between the electrodes and thus the product of the electrode spacing and the pressure of gas. Now, by determining at various values of this product the break-down voltage 1) the curve shown in Figure 2 was obtained, in which the break-down voltage is plotted as the ordinate and the electrode spacing (at a constant pressure of gas) as the abscissa. At the values of this spacing comprised between A and B, three values of the break-down voltage are found to exist.

When determining at a value of p d; (i. e. the product of pressure of gas and electrode spacing) comprised between A and B the voltage between the electrodes as a function of the current intensity, the curves shown in Figure 4 are obtained. The voltages are plotted as the ordinates and the currents as the abscissa. The curves I! and I2 indicate the results obtained with a helium pressure of 0.84 mms. and an electrode spacing of 2.65 cms. It is established by these curves that if at a suitable value of the current limiting resistance the voltage between the electrodes is increased from zero, current starts flowing through the discharge tube at a voltage C. At an increasing voltage the current intensity increases until the voltage has reached the value D. When the voltage keeps increasing the current intensity decreases until the voltage attains the value E. The part of the curve between K and F is unstable. The point F is determined by starting from a voltage lying beyond the value E and by decreasing it until the current starts flowing. When the Voltage increases beyond the value E, no current flows through the tube at first. Not until the value G is reached a passage of current occurs again. The discharge has then a strongly pronounced negative character so that the curve I2 can be determined only when a high resistance is connected in series with the discharge tube.

The curve I3 indicates the results obtained when the electrode spacing is 2.33 cms. and the helium pressure is again 0.84 mm.

The second branch of the curve corresponds essentially to the branch 82 but lies higher than the latter and is not shown in the figure.

The part of the curve II which is comprised between the points H and K represents, similarly to the part of the curve I3 that is comprised between the points L and M, a negative resistance, as the voltage increases at a decreasing current. Tests revealed that the discharge at a suificiently low current limiting resistance is nevertheless stable in these parts. This current limiting resistance may even be dispensed with entirely.

The discharge lends itself therefore with advantage to use as a negative resistance, for example for amplifying electric oscillations.

Figure 5 shows, for example, a suitable circuit arangement comprising a discharge tube M of the construction above described, a battery l5 of say 750 volts and an inductance l6 of say 250 henries. The discharge tube M has a negative resistance and the circuit illustrated has occurring in it electric oscillations that may be ob tained between the cnds of the inductance. At the indicated values of the elements of the circuit electric oscillations having a frequency of 200 per second, a voltage with a maximum value of 520 volts and a current intensity up to 30 m. amp. were ascertained.

What I claim is:

1. An electric discharge tube comprising a sealed envelope and a plurality of electrodes mounted therein, one of said electrodes being frictionally supported from a metallic member which forms a part of the sealed envelope.

2. An electric discharge tube comprising a sealed envelope and a pair of cold electrodes mounted therein, said envelope having an intermediate portion formed of metal, one of said electrodes being frictionally supported from said intermediate metallic portion, and the other electrode being positioned close to the first electrode and closing one end of the envelope.

3. An electric discharge tube comprising a, sealed cylindrical envelope, an intermediate annular portion thereof being formed of metal, a cylindrical electrode having one end closed and frictionally supported from said metal portion, and a second cylindrical electrode also closed at one end sealed to one end of said envelope and closing that end, the closed ends of said electrodes being disposed in spaced parallel relation.

FRANS MICHEL PENNING.

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