US1815566A - Control device - Google Patents

Description

July 21, 1931.

R. C. HITCHCOCK CONTROL DEVICE Filed Jurie 22, 1927 ATTORNEY Patented July 21, 1931 RICHARD C. HITCHCOCK, OF WILKINSBURG, PENNSYLVANIA, ASSIGNOR- T0 WESTING- HOUSE ELECTRIC & MANUFACTURING OOBEPANY, A

VANIA CORPORATION OF PENNSYL- C'ONTROL DEVICE Application filed June 22,

My invention relates to control devices, and it has particular relation to devices intended to control the frequency of an oscillation generator comprising a thermionic tube.

One object of my invention is to provide a frequency-control device that shall be capable of controlling more power than similar devices known to the prior art.

Another object of my invention is to vide a frequency-control device of the piezoelectric-crystal type that may be accurately maintained at a predetermined temperature, irrespective of the amount of power being controlled thereby.

Another object of my invention is to provide a piezo-electric-crystal-holding device that may be entirely submerged in a cooling liquid, if desirable.

Another and more specific object of my invention is to provide a piezo electriocrystalholding device that shall be rugged in con struction, and one in which the spacing of the electrodes shall be relatively permanent, irrespective of the position in which the device is mounted, or the vibration to which it is subjected while in use.

When piezo-electric crystals are utilized to control the frequency of oscillations generated by a thermionic tube, in the manner now well known to those skilled in the art, it has been found that numerous factors combine to prevent the maintenance of a constant, unvarying frequency. As the amount of power controlled increases, the voltage fed back through the controlled tube also increases, thus causing the crystal to physically vibrate with greater amplitude and to accordingly generate a greater amount of heat. The heat generated, both by reason of the physical vibration of the crystal, and by the dielectric hysteresis losses therein causes the actual vibration frequency to change to a very marked degree unless it is dissipated by efficient cooling devices.

The effect of temperature upon crystal fre quency was appreciated by earlier workers in the art, as evidenced by Patent No. 1,609,7 i4l, issued to A. M. Trogner on Dec. 7, 1926, and by an application in the name of D. G. Little, Serial No. 78,115, filed December 29, 1925, and

pro-

1927. Serial No. 200,722.

assigned to lVestinghouse Electric & Manufacturing Company.

In the latter application, it is shown that the temperature of a control-crystal must be maintained reasonably constant, a chamber provided with a heating coil and a thermostat being disclosed for this purpose.

My present invention is in the nature of an improvement over the invention disclosed in the application of D. G. Little, being directed toward instrumentalities for more efiiciently conducting away the heat generated by a piezo-electric crystal, in order that the oscillation frequency thereof may be maintained accurately fixed.

To accomplish the purpose of my invention, 1 preferably mount the crystal-section in an evacuated container, or in a container filled with an inert gas at a very low pressure. The crystal is held in contact with a wall-portion of the container that is both electrically and heat-conducting, and the said wall portion, or the entire container, may be submerged in a body of insulating cooling liquid.

In some instances, when extremely accurate temperature control is desirable, or when, in order to influence the oscillation frequency, it is desired to maintain the crystal at a temperature higher than that which it would naturally assume in operation, the insulating liquid may be provided with a heating coil controlled by a thermostat.

Among the novel features of my invention are those particularly set forth in the appended claims. The invention in its generic aspect, however, as well as further objects and advantages thereof, will best be understood by reference to the following descrip tion taken in connection with the accompanying drawing, the single figure of which is a view of a preferred modification.

Referring to the drawing, the preferred modification of my invention comprises a container 1, preferably made of a translucent or transparent insulating material, such as glass, to one end of which is sealed a metallic cup 2, preferably made of copper, or other material which has good thermal conductivity. The end of the container opposite the metallic cup is provided with a re-entrant portion 8, through which extends a leadingin conductor t.

A relatively thick metallic electrode-device 5 rests upon the bottom of the metallic cup 2, being maintained in thermal and electrical contact therewith by brazing or soldering.

A second electrode device 6 is supported from the first electrode device 5, at a plurality of points around the circumference thereof', by means of insulating spaced elements 7 which encircle a plurality of studs 8 threadedly connected to the electrode 5. Theupper ends of the studs 8, at the points where they extend through openings in the upper electrode, are surrounded by insulating sleeves 10. 'l he electrode assembly rigidly held together by a plurality of lock nuts ll threaded on the upper ends of the studs, each of these nuts transmitting pressure to the insulating sleeves associated w'th the respective studs by means of spri g washers 12, or the like. I have found it preferable to use only three assembly study, since, b" using a three-point support for the upper -rode, inequalities in the height of the collars 7 will not introduce warping strains.

A connecting element 13 is atlixed to, and supported by, the upper electrode 6 and is connected, by a flexible conductor 14-, to the leading-in wire a.

A flexible conductor 15 is soldered or otherwise affixed to the metallic cup 2, in order that the cup may be electrically connected to the appropriate element of a thermionic tube when the device is utilized to control the frequency of oscillations generated thereby.

The space between the electrodes 5 and 6 is determined by the thickness of the insulating collars 7, and varies according to the thickness of a crystal-section 1.6 which is maintained intermediate the said electrodes, and is prevented from dropping out by the said collars. This space is so chosen that the upper electrode is not in electrical contact with the crystal in is a very slight distance above it, the said distance preferably being a non-integral multiple of the wave length, in air, of the crystal-frequency.

In order that sparking, if it occurs, shall not cause corrosion of the metallic portions of the device, it is preferable, after exhausting the container, to admit thereto a small amount of inert gas, such as neon or argon, at a pressure of about 5 to 15 millimeters of mercury.

hen employing a device constructed according to my invention for frequency control, the entire container may be, if desirable, immersed in a body of insulating liquid. It is also feasible to merely insert the lower metallic portion of the device into an inert body of cooling liquid, or a suitable receptacle may be provided through which the cooling liquid may be circulated in contact with the said metal portion. in certain instances, I have found it desirable to provide the liquid with a heating coil and to maintain the temperature constant by utilizing a thermostat to control the potential applied to the coil.

I have found that, when using a device constructed according to my invention for the control of the frequency of high-powdered oscillator-tubes, there is very little likelihood of the temperature rising sutliciently high to cause crystal breakage. 15y reason of the fact that the crystal is in intimate contact with the metallic cup, and the said cup being capable of being etliciently cooled, I am enabled to maintain the crystal temperature substantially constant, irrespective of the amount of power l eing controlled thereby.

/Vhen oscillating properly, the crystal is surrounded by a visible glow which results from ionization of that portion of the gas in the immediate vicinity thereof. By reason of the fact that the upper portion of the container is either translucent or transparent, the attendant can, at all times, satisfy himself by inspecting the glow that the crystalv properly oscillating, and that the out put frequency of the thermionic device as sociated' therewith is that frequency to which the crystal naturally oscillates.

The device may be subjected: to a reason able amount of rough treatment short of causing actual breakage thereof, with the full assurance that the initial spacing be tween the electrodes will. not change. This a decided advantage, inasmuch asthe device will often be carelessly handled by the attendant in charge of the radio transmitting station in which it is being used.

Although I have illustrated and described a specific embodiment of my invention, 1 am fully aware of the fact that many modifications thereof are possible. My invention, herefore, is not to be limited eXcept in so far as necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. As an article of manufacture, a piezoelectric-crystal-holding device comprising an evacuated container having a transparent insulating portion, a conductor extending through a wall of said transparent portion, a metallic base portion, an elecrodc, means independent of the crystal for insulatingly supporting said electrode from said base portion, and a connection between said electrode and said conductor.

2. In combination, an evacuated container having an electrically-conducting and heatconducting portion, a massive electrode sup ported in contact with said portion, an electrode insulatingly supported from said first electrode, a conductor aflixed to said second electrode and extending to the exterior of said container and a piezo-electric crystal intermediate said electrodes.

3. In combination, an evacuated container having an electrically-conducting and heat conducting portion, a translucent insulating portion, an electrode in said container in coir tact with said heat-conducting portion, a second electrode in said container, means for supporting said second electrode in a fixed position relative to said first electrode and for insulating it therefrom, a conductor atfixed to said second electrode and extending through said insulating portion and a piezoelectric crystal intermediate said electrodes.

4. In combination, an evacuated container having an electrically-conducting and heatconducting portion, a massive electrode in said container in contact with said portion, a second electrode and means for insulatingly supporting said second electrode from the massive electrode in fixed relation thereto.

5. A piezo-electric crystal holder comprising an evacuated container having an upper transparent portion, a lower heat-conducting and electrically-conducting portion supporting said first-named portion and adapted to be cooled by external agencies, and an electrode insulatingly supported from said lowor portion interiorly of said container to define a space wherein a piezoelectric crystal may be disposed.

6. A pieZo-electric crystal holder comprising an evacuated container having an upper transparent portion, a lower heat-conducting and electrically conducting portion supporting said first-named portion, an electrode in contact with said lower portion interiorly of said container, a second electrode disposed in parallel relation to said first-mentioned electrode, and a plurality of insulating devices for supporting said second electrode from said first electrode.

7. A piezo-electric crystal holder comprising an evacuated container having an electrically-conducting and heat-conducting portion, an electrode in said container in contact with said heat-conducting portion, a second electrode in said container, means for supporting said second electrode in substantial- 1y parallel relation to said first electrode and.

for insulating it therefrom, and resilient means tending to urge said electrodes toward each other.

8. A piezo-electric crystal holder comprising an evacuated container having an electrically-conducting and heat-conducting portion, an electrode in said container in contact with said heat-conducting portion, a second electrode in said container, and three insulating supporting elements for retaining said second electrode in substantially parallel relation to said first electrode to define a crystalreceiving space, the said supporting elements being disposed at the apices of a triangle.

9. A piezo-electric crystal holder comprising a container having an electrically-conducting and heat-conducting portion and a transparent insulating portion, a massive electrode in said container in contact with said heat-conducting portion, a second electrode in said container, means for supporting said second electrode in substantially parallel relation to said first electrode and for insulating it therefrom, a conductor affixed to said second electrode and extending through said transparent portion to the exterior of said container, and rarefied gas in said container that is inert with respect to said electrodes and the heat-conducting portion of the container.

In testimony whereof, I have. hereunto subscribed my name this 13th day of June,

RICHARD C. HITGHCOOK.

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