US1994228A - Temperature control of piezo-electric crystal apparatus - Google Patents

Description

March 12, 1935. M. osNos TEMPERATURE CONTROL OF PIEZO ELECTRIC CRYSTAL APPARATUS Filed Feb. 16, 1932 INVENTOR MENDEL OSNOS ATTORNEY Patented Mar. 12, 1935 TEMPERATURE CONTROL OF PIEZO-ELEC- TRIO CRYSTAL APPARATUS Mendel Osnos, Berlin, Germany, assignor to Telefunken Gesellschaft fiir Drahtlose Telegraphie m. b. H-., Berlin, Germany, a corporation of Germany Application February 16, 1932, Serial No. 593,253 In Germany February 19, 1931 7 Claims.

In radio work in general and in short wave WOI'kjlIl particular it is extremely important to stabilize the natural frequency of certain circuits so. as, to insure the greatest possible constancy. What. is. used for this purpose are piezoelectric crystals. However, it has been observed that the natural period thereof varies with the temperature in that it decreases with increase in temperature. According to the present invention the, harmful influence of temperature variations upon the natural period of circuits containing piezo-electric crystals is compensated wholly or partly by that in series or in parallel relation to. the crystals there. is connected a condenser whose capacity decreases with increase of temperature. As a result automatic compensation in whole or in part of the change in natural period of the crystal is assured.

This invention will be more clearly understood by referring to the accompanying drawing in which,

Fig. l is a; sectional view of a short wave piezoelectric crystal holder,

Fig. 2 is a circuit diagram wherein the capacity of a separate condenser is automatically varied with a temperature change in the piezo-electric crystal apparatus, 7

Fig. 3 is a sectional view of a crystal holder similar to the holder shown in Fig. 1 except that the upper electrode serves as one electrode or plate of a variable condenser, and there is also included in this figure the arrangement of a variable condenser plate or electrode positioned above the combined crystal electrode and the condenser fixed plate. Also a partial circuit diagram is shown connected to the crystal holder which is similar to the circuit shown in Fig. 2.

Referring now to the drawing, Figure 1 illustrates one specific embodiment of this invention wherein the capacity of the apparatus varies with change in temperature, and Figure 2 is a circuit diagram embodying another embodiment of the present invention wherein the capacity of a condenser separate and apart from the crystal is automatically varied with change in temperature of the apparatus.

Referring now in detail to Figure 1 of the drawing, 1 and 2 are metallic electrodes of dissimilar polarity which are spaced apart from each other by a cylindrical spacer means 3 possessing a suitable heat expansion coefficient such as rubber, hard rubber (ebonit) or the like. Inasmuch as the heat expansion of the drum 3 is much higher than that of the inner cylinder 2 it will be seen that the distance between the two capacitive surfaces of the electrodes grows with the temperature. In other words, the capacity decreases incidentally, and this is adapted to alter wholly or in major part the harmful influence of the changes in natural frequency of the crystal occasioned by temperature fluctuations by a convenient choice of the different parts of the con- 7 denser.

It will be understood that the construction of the variable condenser as hereinbefore disclosed is not the only possible form. Also a rotary condenser could be employed whose angular displacement is controlled by the intermediary of a suitable gearing by a body influenceable in its dimensions by action of the temperature.

One scheme of using the arrangement here disclosed for the purpose of insuring automatic regulation of a thermionic tube is shown in Figure 2. Referring to the same, 5 is a cathode tube (thermionic valve) whose grid circuit, as known in the prior art, contains a piezo-electric crystal stabilizer 6. '7 denotes a variable condenser according to the present invention connected in series with the crystal in any manner known to the art and whose capacity changes automatically with the temperature. 8 is an adjustable inductance coil which, in the presence of a definite temperature, servesto wholly or partly compensate the capacitive reactance of the condenser I.

Figure 3 shows an embodiment of the crystal holder and a variable condenser whose capacity decreases with rise in the temperature. The plates or electrodes of the condenser are 1 and 14. 14 is adjustable by spindle 4 which has a screw thread. Spacer 13 to which 14 is secured consists of a drum of hard rubber. The bottom condenser plate 1 also serves as the top electrode of crystal 6. 6 bears upon the lower electrode 2 of the crystal holder, which is built together with electrode 1 by a suitable insulation cylinder 8. 9 is cement for 8 and electrodes 1 and 2. 10, 11 and 12 are terminals. is electrically connected with spindle 4. If 10 and 12 are united with the external circuit then 6 is in series with the condenser. If 10 and 12 conjointly are associated with one binding post of the outer circuit, and terminal 11 with the other one, as shown in the drawing, then at least one of the electrodes for the crystal 6 and the condenser variable plate are connected in parallel.

I claim:

1. A piezo-electric crystal holder comprising two electrodes spaced apart from each other by insulation material, a piezo-electric crystal interposed between the two electrodes, a condenser plate spaced by insulation material and located above one of said electrodes and arranged for automatic temperature compensation wherein the space between said condenser plate and at least one of the electrodes which also serves as the other plate of a condenser, is varied to change the capacity between said electrode and said condenser plate corresponding with a given change of temperature surrounding the crystal holder.

2. A piezo-electric crystal holder comprising two electrodes spaced apart from each other by insulation material, a piezo-electric crystal interposed betwen the two electrodes, a condenser plate spaced by insulation material and located above one of said electrodes and arranged for automatic temperature compensation wherein the space between said condenser plate and at least one of the electrodes which also serves as the other plate of a condenser is varied to decrease the capacity between said electrode and said condenser plate when the temperature surrounding the crystal within the electrodes increases.

3. A piezo-electric crystal holder comprising two electrodes spaced apart from each other, a piezo-electric crystal interposed between the said electrodes, an insulating member spacing said electrodes, a condenser plate adjustably located directly above one of said electrodes, an insulating member supporting the condenserplate which is arranged for automatic temperature compensation by providing a variable space between said condenser plate and the crystal electrode.

4. A piezo-electric crystal holder comprising a lower electrode having a central cylindrical upright extending portion, an insulating casing slightly inside the periphery of the lower electrode,.

an upper electrode located directly above said insulating casing, a piezo-electric crystal interposed between the lower and upper electrodes, an insulating member located above said upper electrode, a metallic cover having a threaded aperture located on top of said insulating member, a threaded spindle passing through said threaded aperture, a condenser plate secured to the end of said spindle and arranged for automatic temperature compensation by providing a space which may be varied between said condenser plate and the upper crystal electrode.

5. A piezo-electric crystal holder comprising a lower electrode having a central cylindrical upright extending portion, a piezo-electric crystal located on the top of the upright extending portion, an upper electrode located above said crystal and spaced from said lower electrode by an insulating casing having alength substantially equal to the combined length of the upright extending portion of the lower electrode and the thickness of the piezo-electric crystal, an insulating member located on top of said upper electrode and a metallic cover having an aperture for securing a spindle which supports one plate of a condenser, the other plate of which is formed by one of said electrodes, said spindle insuring automatic temperature compensation in which the space between said condenser plate and the electrode serving as a condenser plate is varied due to the different coeflicient of expansion of the supports for said condenser plate and said electrode.

6. A piezo-electric crystal holder comprising three electrodes spaced apart from each other by insulating material, a piezo-electric crystal interposed between two of said electrodes, the third electrode being supported adjustably with respect to one of the other electrodes which is located in a position which is intermediate one of the other electrodes to form the plate of a variable condenser, the'intermediate positioned electrode also serving as the fixed plate of a variable condenser.

'7. A piezc-electric crystal holder comprising three electrodes spaced apart from each other by insulating material, a piezo-electric crystal interposed between two of said electrodes, the third electrode connected in parallel relationship with at least one of the electrodes adjacent said crystal, said third electrode being supported adjustably with respect to one of the other electrodes which is located in a position which is intermediate one of the other electrodes to form the plate of a variable condenser, the intermediate positioned electrode also serving as the fixed plate of a variable condenser.

MENDEL OSNOS.

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