Разработка ионно-плазменной технологической установки для нанесения функционального покрытия на крышки масляных фильтров, страница 10

During deposition of covering critical parameter is deposition speed of covering. As the gauge fixing a course of process of dispersion, it is possible to use quartz weights-sensitive resonator [10]. Gauges with crystal resonators for measurement of dispersion speed have rather simple design. At the sensitivity approximately equal to sensitivity of microweights, they practically are not afraid of mechanical impacts and vibrations. For this reason crystal resonators widely use now for the control of thin films deposition. In the gauge with the crystal resonator use piezoelectric properties of quartz. The resonator represents a thin plate of quartz to which both surfaces electric contacts are brought. Such resonator joins in the electronic scheme of the generator. The appendix of the variable electric field leads to occurrence of fluctuations of a quartz plate on thickness. Resonant frequency of these fluctuations inversely proportional to thickness of the plate :

,                                                      (2.4)

where  - elastic waves  distribution speed in the direction of plate thickness.

At manufacturing quartz plates it is necessary to consider temperature dependence of resonant frequency. It is known, that the temperature factor of frequency (TFF) quartz is connected with elastic constants of the last. Negative and positive members which sizes depend on orientation of fluctuations concerning the cores of crystallographic axes of the monocrystal enter into expression for TFF. As the change of frequency connected with fluctuations of temperature, influences accuracy of definition of weight, quartz a plate cut out from a monocrystal in such orientation that various members in expression for TFF compensated each other. This requirement is answered with a cut which plane makes a corner approximately 35^о with a planexz, as shown in figure 3.3. Orientation of such cut is designated as the АТ-cut and this orientation used in all speed gauges.

Figure 2.3. Crystal of quartz with the plate which has been cut out under a corner of the АТ-cut.

Dependence of resonant frequency of shift fluctuations of the plate which have been cut out under a corner of the АТ-cut, on thickness of a plate looks like:

,                                                       (2.5)

where  h·mm.

Resonant frequency of a plate is influenced only with weight of the besieged substance, and parameters of substance, such as density and elastic constants, render insignificant influence. Dependence of frequency of fluctuations on quantity of the besieged substance can be derived from the equation (3.5) if its both parts differentiate on  and size of an increment of thickness of quartz  to express through weight of the besieged substance  and thickness of a film . Speed of dispersion of a material is directly proportional to an increment of thickness of a plate of quartz.

During technological process it is necessary to supervise also temperature of processable details, temperature of the cathode-target. As is known, to measurement of temperature apply thermoelement converters, i.e. gauges of temperature.

Thermoelements are intended for development of the signal in the form of convenient for recognition the observer, automatic processing, transfer and use in automatic control systems.

Thermoelements are classified on a number of attributes.

1. On the physical phenomenon put in a basis of a principle of action, distinguish:

- Thermometers of expansion,

- Thermometers of resistance,

- Thermoelectric thermometers,

- Pyrometers, etc.

2. On connection with object of measurement thermoelements can be contact and contactless.

3. On a class of accuracy thermoelements are defined by limits of admissible basic and additional errors, and also others influencing on accuracy of measurement by properties which values are established by special standards.