US2742594A - Variable high resistor - Google Patents

Description

April 17, 1956 W. L. MElER VARIABLE HIGH RESISTOR Filed Nov. 22, 1952 +I I I I I I I I I I I CURRENT I 50v. lOOv. l50v.

VOLTAGE v.

WILBER L. MEIER INVENTOR.

ATTORNEY United States Patent VARIABLE HIGH RESISTOR Wilber L. Meier, Chatham, N. J., assignor to Gera Corporation, New York, N. Y., a corporation of New Jersey A Application November 22, 1952, Serial No. 321,999

3 Claims. (Cl. 315-337) This invention relates to circuit components which can be adjusted to a desired value of resistance. It has particular reference to a gas discharge-device having a relatively constant source of ionization, thereby permitting small current values to be passed through the device while subjected to a Wide range of voltages.

In certain types of electronic circuits it is desirable to employ resistance elements which have values of 100 megohms to megohms. This is particularly true in circuits which are used with photoelectric cells and detectors of charged particles such as ion chambers. In the past such components have been made of composition material or of a sputtered film deposit in a vacuum container. These resistors are costly to make and are not reliable, changing their resistance values with time and temperature changes.

The present invention not only is reliable but is also adjustable within a wide range of resistance values and retains this value for long periods of time. It can be manufactured at a fraction of'the cost of prior art resistors.

One of the objects of this invention is to provide an improved variable resistor of high resistance value which avoids one or more of the disadvantages and limitations of prior art arrangements.

Another object of the invention is to reduce the cost of high resistance units.

Another object of the invention is to provide a resistance unit which is adjustable within a wide range of values.

Another object of the invention is to simplify and improve the construction of resistors having values greater than 100 megohms.

The invention comprises a closed envelope of glass having three electrodes within the envelope. One of the electrodes consists'of a sheetof conductive material having a small quantity of radioactive material on its surface or imbedded in the sheet. A second electrode consists of a wire positioned parallel to the sheet. Lead-in conductors to these two electrodes form the terminals of the resistance unit. A third electrode consists of a wire positioned parallel to the second electrode. This electrode is used as the control means to alter the resistance between the other two electrodes.

For a better understanding of the present invention, together with other and further objects thereof, reference is made to the following description taken in connection with the accompanying drawings.

Fig. 1 is a cross sectional view of the resistor unit.

Fig. 2 is a cross sectional view of the resistor unit taken along line 2-2 of Fig. 1.

Fig. 3 is a schematic diagram of connections to illustrate the method of deriving characteristic curves which illustrate the operation of the device.

Fig. 4 is a chart showing a series of curves plotted between ,voltage and current values and indicating the extent of the control circuit.

' in a generally symmetrical arrangement.

Fig. 5 is 'a diagram of connections showing one application of the resistor to a measuring circuit.

Referring now to Figs. 1 and 2, an envelope 10, generallyof glass, is employed to house the electrodes. A cylindrical electrode 11 having a lead-in conductor 12 is mounted within the envelope and contains a small quantity of radioactive material, such as radium, imbedded in its inside surface. Radium has been found to be a suitable radioactive material because it gives off alpha particles which cause strong gas ionization. Other radioactive materials may be used instead of radium as long as their emissions cause sufficient gas ionization to carry the current between electrodes.

' A pair of wires 13 and 14, having lead-in conductors i5 and 16, are mounted in the central part of the envelope One of these electrodes is used in conjunction with the cylindrical electrode to form the the resistor and the other wire electrode is used as a control element. The envelope may be filled with an inert gas, such as nitrogen or argon, at a pressure which may be as high as atmospheric pressure or much higher.

Fig. 3 shows a circuit which can be used to determin the characteristics of the discharge device. T

The circuit uses two sources of potential 17 and 18, each connected to a voltage divider 20, 21 for obtaining desired values of voltage which canbe applied to selected electrodes in the resistor element. Ammeters 22 and 23 are connected in series with the two wirexelectrode lead-in conductors 15 and 16 to measure the currents. The lead-in conductor 12 connected to the cylindrical electrode is connected to a common terminal which is also connected to the negative terminals of the batteries.

The results of the circuit shown in Fig. 3 are plotted in a chart, Fig. 4. When both Wires are connected together and the voltage varied by changing the setting of voltage divider 20, the curve A results showing a rapid rise in current at voltages less than 15 volts and showing an almost fiat horizontal characteristic above 15 volts. These values can be altered by changing the spacing, the pressure, or the amount of radioactivity in the envelope, the present values applying to a sample made at atmospheric pressure and having an envelope about 4 inch in diameter and about inch long. The flat portion of the curve is caused by the constant amount of ionization delivered by the radioactive surface. At 15' volts all of the ions and electrons generated by the alpha particles are drawn to the electrodes and at higher voltages no more can be attracted to the electrodes because no more exist in the envelope.

If, now, the voltage of one of the electrodes V2 be set at 50 volts and another set of current values observed while the applied voltage V1 is varied, the curve B results. At the point where V2=V1=50 volts the current will divide equally between the two wire electrodes and the current to each electrode has a value just one-half of curve A. AsV is increased the current to the associated wire electrode 13 increases but never quite reaches the value of curve A, since the voltage on electrode 14 always attracts some electrons and therefore draws a small current.

If the voltage of electrode 14 be kept constant at volts, a similar curve will result, each Wire electrode carrying half the current when their applied voltages are equal (curve C) and tapering off at other voltage values in a manner similar to that shown in curve B.

Curve D is similar to the other two curves B and C, except that voltage Va is kept constant at volts. It will be obvious, from a study of the above described curves, that a change of voltage applied to one wire electrode will alter the resistance value between the other two. Assuming that the current value of the flat part of curve A to be 10- amperes, the value of resistance of point 25 on curve B is approximately 10 ohms, the resistance of point 26 on curve C is approximately 2X10 ohms, the resistance of point 27 on curve D is approximately 3 1O ohms.

Fig.5 shows a circuit in which a high resistor is generally used. An ion chamber 30 is indicated, havinga collector plate 31 and guardrings 32. The'collector plate is connected directly to a control electrode in an amplifier tube 33. Between the control electrode and the cathode circuit (ground) a high resistance unit'35 (10 ohms) is connected and the voltage drop across this resistor is applied to the control electrode to'control the anode current and produce a change of reading in'a meter 34. A current of one micro-microampere through this resistor unit 35 from collector 31 to ground will produce one volt change of potential on the control'electrode and a corresponding change of current in meter 34; Voltagedivider 36 and battery 37 can be used to change the-sensitivity of the device as described above.

In the above description of the operation it has been assumed that the Wireelectrodes were positive with respect to the cylindrical electrode as indicated in the drawing. It should be pointed out herethat reversed polarity can be applied with about the same results since an ionized gas will conduct equally Well in either direction.

While there have been described and illustrated specific embodiments of the invention, it will be obvious that variouschanges and modifications can be made therein without departing from the field of the invention which should be limited onlyby the scope of the appended claims.

I claim:

1. A variable high resistor comprising, an envelope containing ionizable gas, three electrodes within the envelope, each electrode having a lead-in conductor for external connection, a quantity of radioactive material within the envelope which produces gas ionization, and means for applying a variable voltage across a first and second of said three electrodes to deionize a portion of the ionized gas, said variable voltage controlling the resistance between the first and third of said three electrodes and also controlling the range of the linear resistance characteristic between said first and third electrodes.

2. A variable high resistor in accordance with claim 1 wherein said variable voltage has a maximum value which is less than the ionizing potential of the gas.

3. A variable high resistor in accordance with claim 2 wherein the second and third of said electrodes are symmetrically positioned with respect to the first electrode.

References Cited in the file of this patent UNITED STATES PATENTS 2,457,973 Blau Jan. 4, 1949 2,497,213 Downing Feb. 14, 1950 2,616,986 Coleman Nov. 4, 1952 2,629,837 Benade et al Feb. 24, 1953 2,657,316 Friedman Oct. 27, 1953 FOREIGN PATENTS 776,272 France Oct. 31, 1934

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