JPH01311241A - Crystal heat conduction type vacuum gauge - Google Patents

Abstract

PURPOSE:To realize a high-sensitivity and high-stability pressure sensing crystal sensor by reading variation in air pressure as variation in the frequency of a crystal oscillation circuit. CONSTITUTION:A crystal temperature sensor 1 which varies in frequency with the ambient temperature and a heat source 3 are paired and installed in a vacuum chamber. Here, when the pressure in the vacuum chamber is reduced, the gas density decreases, heating value from the heat source 3 to the sensor 1 is reduced, and the sensor 1 drops in temperature and increases in frequency. Further, when the air pressure in the vacuum chamber rises, the air density increases, the heating value increases, and the sensor 1 rises in temperature and decreases in frequency. For the purpose, the output signal of the oscillation circuit 2 is measured by a counter 5 to obtain a digital signal, which is displayed on a display device 8, thereby accurately measuring the air pressure in the vacuum chamber as the frequency variation of the sensor 1.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention utilizes a crystal resonator (hereinafter referred to as a crystal temperature sensor) and applies the property that the thermal conductivity of gas changes depending on its pressure. This relates to a thermal conduction type vacuum gauge (gas pressure gauge) that measures the pressure (degree of vacuum).

[Summary of the Invention] The present invention is a so-called thermal conduction vacuum gauge that utilizes the fact that air density is proportional to heat conduction, and uses a crystal oscillator as a sensor for heat supplied from a pair of heat sources. This device reads frequency changes as digital signals, and by providing a thermal insulation section between the heat sensing section of this sensor and the support section of the vibrator, the sensing accuracy is increased and a vacuum gauge with stable operation is obtained. .

[Prior art] A thermal conduction vacuum gauge, such as the Villa 2 vacuum gauge, is generally used to measure pressure in the medium and low pressure range (1'0-'' to 1 torr).Figure 3 shows a conventional digital display. A block diagram shows an example of the configuration of a thermal conduction vacuum gauge.The element 11 constituting the bridge circuit is a filament installed in a vacuum chamber and functioning as a pressure sensor.lla,
llb and 11c are bridge resistors installed outside the vacuum chamber, and the bridge is connected to a bridge DC power source 1.
2 applies a constant DC voltage. The balanced voltage of the bridge is amplified by a DC amplifier 13, and the A/D converter 14 converts the DC voltage into a digital signal. A counter 15 counts the output signal of the A/D converter,
This becomes an address signal for the ROM16. The ROM provides a display signal (i.e., pressure value signal) corresponding to the output signal (i.e., pressure information) of the counter to a decoder 17, and the decoder decodes the display signal and displays the display 18 (e.g., pressure value signal). The pressure value is displayed by a 7-digit LED display. A logic clock signal from the A/D converter to the decoder is supplied by a clock generator 19 whose source is a crystal oscillator 20.

For example, if the pressure inside the vacuum chamber decreases,
Since the amount of heat lost from the filament 11 is small, the temperature of the filament increases, resulting in a higher resistance of the filament and an increase in the equilibrium potential of the bridge. Since it is a function of pressure, the pressure inside the vacuum chamber can be determined by measuring the equilibrium potential.

Conventional thermal conductivity type vacuum gauges are widely used because they can easily measure gas pressure in medium and low pressure regions, but they have the following shortcomings:

■The drift of the DC amplifier 13 immediately causes a measurement error, so
A highly stable (and expensive) amplifier is required.

(2) Digital display requires an expensive A/D converter 14.

(2) Since the filament 11 serves as both a heat source and a pressure sensor, it deteriorates significantly as a sensor.

[Problem to be Solved by the Invention 1] As mentioned above, thermal conduction vacuum gauges according to the prior art require high-grade DC amplifiers and, in the case of digital display, expensive A/D converters. This method has disadvantages in that the device is expensive and the sensor is subject to significant deterioration.

[Means for Solving the Problems] In order to improve the above-mentioned drawbacks of the conventional thermal conduction type vacuum gauge, the present invention provides a crystal thermal vacuum gauge using a temperature-sensitive crystal resonator whose frequency changes sensitively depending on temperature. The present invention provides means for realizing a highly sensitive and highly stable pressure-sensitive crystal sensor used in a conduction type vacuum gauge and the crystal heat conduction type vacuum gauge.

[Example 1] Hereinafter, the present invention will be explained with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. 1 is a crystal temperature sensor whose frequency changes as shown in FIG. 4 depending on the ambient temperature. 2 maintains the vibration of the crystal temperature sensor (self-excited type)
The oscillation circuit is usually a simple unadjusted oscillation circuit such as a Colpitts circuit using a CMOS inverter. 3 is a means for heating the crystal temperature sensor, that is, a P8 source (for example, a filament), which is installed at an appropriate distance from the crystal temperature sensor. 4 is a heating power source that supplies power to the heat source 3; Here, the crystal temperature sensor 1
and the heat source 3 are installed in a vacuum chamber as a pair. When the pressure inside the vacuum chamber is reduced, the density of the gas decreases, the amount of heat transmitted from the heat source 3 to the crystal temperature sensor 1 decreases, the temperature of the crystal temperature sensor 1 decreases, and its frequency increases.

Conversely, when the pressure of the gas in the vacuum chamber increases,
As the density of the gas increases, the amount of heat transferred increases, and the temperature of the crystal temperature sensor 1 rises, so its frequency decreases as shown in FIG. 4.

In this manner, by accurately controlling the temperature of the heat source 3, the dimensions of the crystal temperature sensor 1, and their relative positions, the gas pressure within the vacuum chamber can be accurately measured as a frequency change of the crystal temperature sensor 1.

In this embodiment, as the crystal 13 degree sensor 1, the 33KHz
A tuning fork crystal resonator was used. The operating principle of the logic system is the same as the conventional technology.In the embodiment shown in FIG. 1, the period of the output signal of the oscillation circuit is measured by the counter 5,
The output signal of the counter 5 specifies the address of the ROM 6. The output signal of the ROM 6 is a binary signal representing a specific pressure value, and the decoder 7 applies the binary pressure signal to a display 8 consisting of 7 digital elements to display the specific pressure value. . 9 is the counter 5, the ROM 6,
It is a clock generator for supplying a clock signal to the decoder 7, and 10 is the crystal oscillator for the clock generator, and a 4.19 MHz AT crystal oscillator was used in this embodiment.

In this way, by utilizing changes in the oscillation frequency of the crystal oscillator as means for detecting temperature changes, a digital signal relating to pressure values can be obtained with an extremely simple configuration. Therefore, the present invention does not require an expensive DC amplifier or A/D converter unlike the conventional thermal conductive vacuum gauge, and realizes a thermal conductive vacuum gauge that is completely equivalent to the conventional technique at an extremely low cost. can do.

FIG. 2 is a plan view showing an embodiment of the crystal temperature sensor of the present invention. It has a tuning fork shape and its frequency is approximately 33KHz
It is. 1a and 1b are vibrating parts, and 1c and 1d are electrodes for forming an electric field for driving the vibrating part, which are arranged on the plane and side surfaces of the vibrating part as shown. The principle of performing bending vibration from the vibrating section using this type of electrode arrangement is well known, so a description thereof will be omitted. The electrodes 1c and 1d are connected to electrode leads 1j and 1k via electrode pads lh and 11 arranged on the support part II2. The crystal temperature sensor is spatially supported by the electrode leads lj, 1k. Reference numeral 1e denotes a base of the crystal temperature sensor in the shape of a tuning fork, and in a normal tuning fork-shaped crystal resonator, the electrode pads 1h and li are arranged on the base.1 The crystal temperature sensor 1 according to the present invention has a thin It is characterized in that the base portion 1e and the support portion lρ are mechanically coupled via the leg portions 1f and 1g. The legs If and Ig are formed by etching. 3 is a heat source, specifically a filament. The heat source is fixed at a constant distance from the crystal temperature sensor by supports 3a and 3b,
Heat is applied to the crystal temperature sensor.

Here, the amount of heat given by the heat source to the crystal temperature sensor is Q in (P) (ceP: gas pressure),
If the amount of heat flowing out from the electrode lead is Qout, the amount of heat ΔQ accumulated in the crystal temperature sensor 1 is ΔQ=Qin
(P) -Qout (1) Let the specific heat of the crystal temperature sensor 1 be C1 mass m, and the amount of temperature change of the crystal temperature sensor l due to the accumulated heat amount △Q is △T
Then, △T=△Q/ (mc) (
2). The frequency change due to △T of the crystal temperature sensor is as follows, where α is the temperature coefficient of the crystal temperature sensor, △f a= −(2△Tcc−a△Q/ (mc)
In order to increase the sensitivity (3), that is, to increase Δf, in equation (3), α and C have unique values in crystal, so Δα is increased and m is decreased. (to make it smaller). In order to increase ΔQ, according to equation (1), either increase Qin or decrease Qout. Qin is the amount of heat flowing from the filament 3 due to heat conduction of the gas, and the pressure of the gas It decreases as the value decreases. On the other hand, Qout is the amount of heat flowing out of the system through the crystal temperature sensor l and the electrode leads lj and 1k, and has no relation to the pressure of the surrounding gas. Therefore, in order to increase the pressure sensitivity of the crystal temperature sensor l in the low pressure region, the outflow heat amount Qout must be made as small as possible. That is, the legs 1f and 1g of the crystal temperature sensor l of the present invention must be , the heat source 3
As much as possible, the heat flowing into the electrode lead lj, 1
This is provided to prevent conduction to K. The amount of heat transmitted through the legs is proportional to the cross-sectional area of the path and inversely proportional to the length. can be made as small as possible, the pressure sensitivity in the low pressure region can be made high, and the leg portions 1f, 1
By providing g, pressure measurement in the 1XIO-'' Torr region can be easily performed.

[Effects of the present invention 1] As described above, according to the present invention, digital signals related to pressure values can be obtained with a very simple configuration.
An extremely inexpensive digital display thermal conduction vacuum gauge can be realized.

Furthermore, in the present invention, by providing as thin and long legs as possible between the vibrating part of the crystal temperature sensor and the supporting part, the amount of heat transmitted from the vibrating part to the supporting part is significantly reduced. By using the gas pressure detection means in combination with the heat source, it is possible to easily realize a gas pressure detection means having high sensitivity in a low pressure region. Furthermore, since the recording legs are formed simultaneously with the shape forming of the crystal temperature sensor using photoetching technology, they can be easily realized without additional steps.

Additionally, the frequency of a crystal oscillator generally changes only slightly over time, and even if there is a small amount of deposits on the oscillator, the relationship between pressure and frequency changes will not change significantly, making stable pressure detection possible. The present invention has the following effects, such as the ability to obtain an excellent vacuum gauge.

In this embodiment, only the digital display type is mentioned, but it is clear that the gas pressure detection means using the crystal temperature sensor according to the present invention has the same effect even in the analog display type.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a plan view showing an embodiment of a pressure-sensitive crystal resonator of the invention, and Fig. 3 is a digital display thermal conduction vacuum gauge according to the prior art. FIG. 4 is a diagram showing the relationship between the oscillation frequency and temperature of the pressure-sensitive crystal resonator according to the present invention. 1......Crystal temperature sensor 2...
...Oscillator circuit 3.11...Filament 4...Heating power supply 5.15...Counter 6, l6...・ ・ROM7
．． 17...Decoder 8.18...Display 9.19...Clock generator 1O120...Crystal oscillator 11a, 11b, 11c. Bridge resistor 12...
......DC power supply for bridge 1a, lb...
- Vibrating parts 1c, 1d... Electrodes 1f, 1g... Legs 1h, lk... Electrode pads 1j, 1k... Electrode leads and above Applicant Seiko Electronic Components Co., Ltd.

Claims (2)

[Claims] (1) A crystal resonator whose oscillation frequency changes depending on temperature, a means for heating the crystal resonator, and an oscillation circuit that maintains the vibration of the crystal resonator, in which the crystal resonator and the heating are provided. A crystal thermal conduction type vacuum gauge, characterized in that the means changes in response to the pressure of the gas, and the change is read as a change in the oscillation frequency of the oscillation circuit. (2) Item (1) above, wherein the crystal resonator is characterized in that the base and support portion of the resonator are mechanically coupled by one or more integrally formed legs. The crystal thermal conduction vacuum gauge described.