DE574456C - Arrangement for keeping the natural frequency constant of piezo-electric crystals in a more or less perfect vacuum - Google Patents

Description

Arrangement for keeping the natural frequency constant from in one more or less perfect vacuum piezo-electric crystals Die The purpose of the invention is to determine the natural frequency of a used in a crystal holder piezo-electric crystal to make it independent of the temperature.

This is achieved: r. by such a construction of the crystal holder, that the distance crystal electrode increases with temperature and z. as a result of that the crystal in a manner known per se in as little air or gas as possible Space is located.

The effect of the arrangement can be explained as follows: As is well known, takes the natural frequency of a crystal decreases with increasing temperature, with decreasing Temperature against it. Assume now the temperature of the crystal environment and thus that of the crystal itself has increased, then its natural frequency increases as a result away. However, due to the same increase in temperature, it rises in accordance with the condition given above i the distance between electrode and crystal, which is known to increase the The natural frequency of the crystal. By suitable choice of material and the dimensions of the individual parts of the crystal holder, it is in principle possible both effects of the temperature increase cancel each other out.

With ordinary crystal holders, with those between the electrode and Crystal if there is air or gas, the construction is automatically changeable Electrode spacing practically completely unusable, because with these crystal holders because of the air damping the performance of the crystal depends very much on the distance between Crystal and electrode depends (see e.g. Telefunken-Zeitung, issue q., VIII. Article by Dr. K. Hegener “About measurements on piezo-electric crystals”, page 6o ff.), So that the distance between crystal and electrode for sufficient performance must have a very specific value; in other words: with the usual crystal holders with crystals in an air environment, the one chosen favorably may be allowed The distance between the crystal and the electrode cannot be changed. So it can with the usual crystal holders an arrangement in which the one specified at the beginning Condition i is fulfilled, not used at all. However, this arrangement will very effective and beneficial when looking at or around the area around the crystal mostly evacuated because at evacuated crystal holders falls the air influencing away, and one can thus adjust the distance between crystal and Change the electrode within relatively wide limits without extinguishing the performance.

An exemplary embodiment is shown in the drawing. Here mean: x a metal flange, z a metal electrode serving as a base for the crystal, 3, an electrode made of a conductive material from a very low coefficient of thermal expansion, e.g. made of nickel steel alloy, q. a quartz crystal, 5 a glass body, 6 a pump attachment, a cement compound.

If, as a result of an increase in temperature, the distance between the upper electrode and the crystal is increased by the expansion of the glass cylinder 5, the distance is reduced by the expansion of the nickel steel cylinder, since both expansions counteract each other, as can be seen from the drawing. Now the coefficients of thermal expansion of the respective type of glass or of the nickel steel alloy used may be 10-6-8.97 or xo-s. o.88 (see »German Calendar for Electrical Engineers«, x922, page 92). Since the lengths of the bodies 3 and 5 are approximately the same according to the drawing, it can be said that the increase d "of the distance between the electrode and the crystal per x ° C increase in temperature is given by the expression: d 1-la (xo- s. 8,97-xo-s # 0.88) @ .xo-s # 8, x h, where lt means the length of body 5. By an appropriate choice of the distance between crystal and electrode at the starting temperature and the length h can be easily achieved that the increase in frequency due to the change in distance is equal to the frequency decrease as by the temperature increase.

In order to avoid any high frequency losses through the nickel steel cylinder 3 it can be avoided with a thin copper coating. As a material for this cylinder comes with any alloy with the lowest possible coefficient of thermal expansion into consideration. So this is z. B. the nickel steel alloy known as "Invar" well usable, the thermal expansion of which is practically zero. In certain circumstances it can be recommended to enlarge the expansion of the body 5, this z. B. to make of brass, then the flange i must consist of an insulator. Man could also make the cylinder 5 partly from brass, partly from glass.

Of course, one could use the embodiment of the crystal holder described above change in various ways. When used in the opposite position as shown, the electrode 3 would serve as a base for the crystal and 2 as the top electrode. The electrode 2 could also have a cylindrical design in a manner similar to the electrode 3 will.

Claims (5)

PATENTAN $ PRÜCH-r: i. Arrangement for keeping the natural frequency constant of piezo-electric ones in a more or less perfect vacuum Crystals, characterized by such a construction of the crystal holder, that the distance between the crystal and the electrode not in contact with it the temperature increases. 2. Arrangement according to claim x, characterized by a such a choice of the material and the dimensions of the crystal holder that the frequency changes as a result of crystal heating and as a result of changes in the distance between Crystal and the electrode not touching it cancel each other out. 3. Arrangement according to Claim x or 2, characterized in that one or both electrodes are turned in and are designed, for example, as cylindrical hollow bodies, their thermal expansion is smaller than the thermal expansion of the (possibly likewise cylindrical) housing outer wall (5). q .. Arrangement according to claim x, characterized in that the outer wall (5) is made of glass. 5. Arrangement according to claim x or following, characterized in that the protruding into the crystal holder Electrode made of nickel steel alloy or a similar alloy as small as possible There is thermal expansion.