JPS62130325A - Crystal type gas manometer - Google Patents

Abstract

PURPOSE:To make the full-scale adjustment of a meter at the atmospheric pressure by holding the output voltage value of a rectifying circuit at the atmospheric pressure in a meter driving circuit and adding an adder in the driving circuit. CONSTITUTION:The output VDC of the rectifying circuit 7 is applied to the negative input terminal of an operational amplifier 8a. The negative input terminal and output terminal of the operational amplifier 8a are connected mutually by a variable resistor 8e, whose resistance value is varied to vary the opposite-phase amplification factor of the operational amplifier 8a. A switch 8g is connected across the variable resistor 8e. Further, the output voltage VF of an operational amplifier 8b is applied to the negative input terminal of the operational amplifier 8a through a resistance 8d. Then, the output voltage of the operational amplifier 8a drives the meter 9 through a resistance 9a. Consequently, a pressure measurement based upon the atmospheric pressure is taken once the meter is adjusted, so very reliable pressure data is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a gas pressure measuring device that uses a crystal oscillator to measure the pressure of gas around it.

[Conventional technology]

It has recently become clear that the resonance resistance of crystal vibration (especially bending mode) varies over a wide range with respect to the pressure of the surrounding gas, and if this is utilized, it can be used to
It has become clear that it is possible to realize a gas pressure gauge that can continuously measure up to 100 meters with a single sensor. For example, the monthly magazine "Keiso", 1984, Vol. 27. NO, 7
``Development of ultra-compact vacuum sensor using quartz crystal resonator''.

Next, the operating principle of a gas pressure gauge that utilizes the pressure dependence of the resonance resistance of a crystal resonator will be explained with reference to the drawings.

Figure 1 shows the gas C, Nt) pressure and the resonance resistance and resonance current of the crystal resonator in the bending mode of about 32 KHz.

FIG. 3 is a diagram showing the relationship between resonance frequencies. The resonant frequency begins to change when the pressure exceeds 10 Torr, but the frequency pressure sensitivity is almost zero below this pressure. On the other hand, the resonant resistance of a quartz crystal has an effective sensitivity to pressures from atmospheric pressure to about 10-3). If this crystal resonator is driven at a constant voltage, a resonance current-gas pressure curve shown at 10 in the figure is obtained. It has a pressure sensitivity from atmospheric pressure to about 10-3) as well as a resonant resistance. In terms of ease of measurement, it is better to measure the resonance current and use this to indicate the gas pressure.

FIG. 2 is an electronic circuit block diagram of a crystal gas pressure gauge (hereinafter referred to as a crystal gas pressure gauge) that utilizes the pressure dependence of the resonance resistance of a crystal resonator.

It is composed of a PLL circuit section, a modification conversion section, and a display circuit section. The PLL circuit section includes a variable frequency oscillator 1. controlled by voltage or current. crystal oscillator 5
An amplifier that amplifies the resonant current of 2 as a voltage. a phase comparator 3 that compares the phase difference between the output signal of the amplifier 2 and the output signal of the variable frequency oscillator 1 and outputs a signal proportional to the phase difference; and a phase comparator 3 that outputs a signal proportional to the phase difference; The low-pass filter 4 generates a DC voltage, and the output voltage of the low-pass filter 4 controls the oscillation frequency of the variable frequency oscillator l. The crystal resonator 5, which is a pressure sensor, is driven by the output voltage of the variable frequency oscillator l.

Since the operating principle of the PLL circuit is already widely known, it will not be described here. The oscillation frequency of the variable frequency oscillator 1 is controlled so that the phase difference with the current flowing through the crystal resonator 5 becomes zero. That is, the crystal resonator 5 is always driven at its own resonant frequency. This allows sufficient tracking even if the resonant frequency of the crystal resonator changes due to the pressure of the surrounding gas.

Next, the display conversion circuit unit is a circuit that converts a signal obtained by converting the resonant current of the crystal oscillator 5 into a voltage (hereinafter referred to as a resonant voltage) into an electric signal capable of displaying pressure. It consists of the following circuit. When the display section is composed of an ammeter, a main amplifier 6. 7. A rectifier circuit that converts the output signal of the main amplifier 6 into direct current. In the case of this example, which is a meter drive circuit 8 that converts the output voltage of the rectifier circuit 7 into a meter drive voltage, the display section is an ammeter (meter) 9, and the gas pressure is determined by the deflection angle of the needle of the meter 9. Know.

As shown in FIG. 3, when the gas pressure decreases, the output voltage VDC of the rectifier circuit 7 increases to the resonance current i in FIG.

(the maximum value of Voc is VI,
.

Let the minimum value be vL). If the meter 9 is driven in this state, the pressure will decrease and the deflection angle of the meter 9 will increase, resulting in an indication that goes against the common sense of a -m pressure gauge. In addition, if this continues, the zero point/full scale adjustment of the pointer of Make 9 cannot be performed, and the meter drive voltage will eventually become curve 3 in FIG. 3.

You have to make sure that it becomes.

[Problem that the invention seeks to solve]

The greatest feature of the crystal gas pressure gauge is that it can measure a wide range of pressures, but for practical purposes, it is necessary to realize the following points.

(1) When the pressure of the gas decreases, the angle of deflection of the pointer of the meter 9 also decreases.This is because the pressure display by the meter is in line with common wisdom, and although it is commonplace, it is important for practical use. It is an item.

(2) Full scale adjustment of the meter 9 is possible at atmospheric pressure, zero adjustment of the meter 9 is possible at high vacuum (pressure <lXl0-'Torr), and scraping is easy; Approximately 760 torr) is a kind of pressure standard value (reference value)
It's something like. Therefore, the ability to easily perform full scale adjustment of the meter 9 at atmospheric pressure means that the quartz crystal gas pressure gauge can always be calibrated at standard pressure. This is extremely important in practice.

[Means for solving problems]

The present invention has been made in view of the above-mentioned circumstances, and includes the following features: retaining the output voltage value of the rectifier circuit 7 at atmospheric pressure inside the meter drive circuit 8;
By providing an adder inside the item,
This realizes (1) and (2).

〔Example〕

Hereinafter, the present invention will be explained with reference to the drawings. FIG. 4 is a diagram showing an embodiment of the present invention, and FIG. 5 is a diagram explaining its principle.

The output of the rectifier circuit 7 (the value is VIIC) is connected to a resistor 8.
c (resistance value is R1) to the negative input terminal of the operational amplifier 8a. The negative input terminal and output terminal of the operational amplifier 8a are connected by a variable resistor 8e (resistance value is R2), and by changing the resistance value of the variable resistor 8e, the negative phase amplification degree A of the operational amplifier 8a can be adjusted. (=Rr/R1) can be changed. A switch 8g is connected to both ends of the resistor 8e. A resistor 8d (with a resistance value of R) is connected to the negative input terminal of the operational amplifier 8a.
The output voltage (value is assumed to be ■) of the operational amplifier 8b (used as a voltage follower) is applied through the operational amplifier 8b (used as a voltage follower). The output voltage of the operational amplifier 8a (value is assumed to be ■) drives the meter 9 via the resistor 9a. Further, a certain voltage (usually a power supply voltage terminal 2) is applied to the meter 9 via a variable resistor 9d, a resistor 9c, and the resistor 9b. Further, since a negative variable voltage is applied to the positive input terminal of the operational amplifier 8b by a variable resistor 8'' connected in series with a resistor 8h, the voltage V is specifically set to -1.5V from O to -1.5V. <You can change even leprosy.

Next, the operation will be explained with reference to FIG.

vNo" -R, (-!-c--■) R+ Rt Here, R+ = R* "If R, then VM6= "' (VDCVF) (1)
It is.

First, full scale adjustment of the meter 9 at atmospheric pressure will be explained.

When the switch 8g is closed, the operational amplifier 8a
Assume that the output voltage of is v and ll1=0. Then, the variable resistor 9d is adjusted so that the pointer of the meter 9 points to the full scale. At this time, a positive bias current corresponding to the full scale current is constantly flowing through the meter 9. Note that the voltage at the connection point of the resistors 9a, 9b, and 9c will be referred to as v7, and will be referred to as the meter drive voltage.

Next, after turning the switch 8g to "open" and setting the variable resistor 8e to the maximum value (Rr,...), the variable resistor 8f is adjusted so that the pointer of the meter points to full scale. . At this time, V, = VL (value of ■ at atmospheric pressure)
It should be +ΔV (about several mV). This Δ
V is an unavoidable error during matching. Output voltage V of the operational amplifier 8a. This is the curve (1) in FIG.

Next, as the pressure is lowered, the output voltage VaC of the rectifier circuit 7 increases, and the output voltage VM1 of the operational amplifier 8a increases.
1 changes like the song W(1) in FIG. Since a positive bias voltage is added to the curve (1), the meter drive voltage vH becomes as shown in the curve (2) in FIG. 5.
When the pressure falls below 104 Torr, the output voltage of the rectifier circuit 7 no longer increases and reaches the saturation value vu. At this time, the meter drive voltage vM does not become zero but becomes VH2 (<O).

Therefore, the variable resistor 8e is adjusted so that VMZ=O. At this time, the meter drive voltage v1. I is the fifth
The output voltage V of the operational amplifier 8a becomes curve (4). becomes curve (3) in the same figure, that is, curve (4
) is the curve (3) translated by +vH0, and V, = Vi. +v0.

Here, the final value Δ■゛ of the above-mentioned unavoidable fitting error is A<A. Since 1lIl, ΔV' = A・Δ■
/ AIIIX 〈ΔV, which is virtually negligible.

Since curve (3) is expressed by the following equation, it can be seen that pressure measurement based on atmospheric pressure is possible.

VND= A (VDCVL) (
4) However, when pressure = atmospheric pressure ■. . -Vso=0 at VL
So, when pressure <10-' Torr, VDC = VII, and v0
=-A (VU VL).

FIG. 6 shows the output voltage V of the operational amplifier 8 in another embodiment of the present invention. are operational amplifier 10a and operational amplifier 10b
is input to an adder circuit configured by resistance 10
Make the values of c, l Od, and 10 a all equal,
When the variable resistor 10f is adjusted to make the output voltage of the operational amplifier 10b equal to VMO, the output voltage of the operational amplifier 10a (also the meter driving voltage) 4 becomes VW = (VM(++VM11)), so the meter 9 The same result as the embodiment of FIG. 4 can be obtained by connecting the polarities of the circuits so that they are opposite to those of the embodiment of FIG. 4.

〔Effect of the invention〕

As described above, in the present invention, a bias voltage is applied to the meter so that the pointer of the meter for displaying gas pressure points to full scale in advance, and then, at atmospheric pressure,
At that time, the output voltage vL of the rectifier circuit is held in the circuit with one variable resistor, and at the same time, - adders are used to add negative values to the output voltage of the rectifier circuit, and the resulting voltage is In addition to the bias voltage of the meter, full scale adjustment is performed and under high vacuum, the gain of the adder is adjusted by another variable resistor so that the absolute value of its output is equal to the bias voltage, Zero point adjustment is performed by similarly adding the output voltage of the adder to the bias voltage.

According to the present invention, the quartz crystal gas pressure gauge, prior to use,
As common sense, the full scale adjustment of the meter is performed at atmospheric pressure, where the pressure value is relatively clear, and then the zero point is adjusted at high vacuum, where the pressure level disappears, so once the meter adjustment is completed, Since pressure can be measured with respect to the atmosphere, highly reliable pressure data can be obtained. In addition, since a normal exhaust system generally increases the pressure to atmospheric pressure and then reduces the pressure, the meter adjustment method according to the present invention is convenient because it follows those procedures. In addition, the present invention can be implemented with a small number of parts, such as two operational amplifiers, multiple resistors, and two variable resistors, so manufacturing costs do not increase and reliability can be easily ensured. It has advantages.

Although not mentioned in the embodiment, it is clear that the meter drive voltages v and l can be converted into digital signals by an A/D converter, and the pressure value can be digitally displayed.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the relationship between the resonant resistance, resonant current, and resonant frequency of the crystal resonator and the gas (N2) pressure, Fig. 2 is a block diagram of the electronic circuit of the crystal gas pressure gauge, and Fig. 3 is the electronic circuit block diagram of the crystal gas pressure gauge. A diagram showing the relationship between the rectifier circuit output voltage and the meter drive voltage in the circuit and the gas pressure, FIG. 4 is a diagram showing an embodiment of the present invention,
FIG. 5 is a diagram explaining the present invention in detail, and FIG. 6 is a diagram showing another embodiment of the present invention. 1. -.-.Variable frequency oscillator 2.--Amplifier 3.--.Phase comparator 4.--Low pass filter 5.--.Crystal oscillator 6-..-. Main amplifier 7 --- Rectifier circuit 8 --- Meter drive circuit 9 --- Meter 8 a, 8 b, l Oa, 10 b --
--- Operational amplifier 8c, 8d, 8h, 9a, 9b, 9c
, 10c. 10d, 10e, 10g, tQh-
- Mr. 8e, 8f, 9d, 10
r-・-1 Variable resistor 8g--...F force (N's F force (Tarr) above the switch) Figure 1 Figure 3 PLLrEJ external Figure 5 Figure 5 Recess

Claims (1)

[Claims] A phase-locked loop (PL) consisting of at least a variable frequency oscillator, a phase comparator, a low-pass filter, and an amplifier.
L) a circuit section, a crystal resonator inserted between the output terminal of the variable frequency oscillator and the input terminal of the amplifier, and the PL
a display section connected to an L circuit section, and measures the pressure of a gas surrounding the crystal oscillator from a resonance resistance value, a resonance current value, or a resonance voltage value of the crystal oscillator. , a circuit that holds a DC voltage value corresponding to the resonant current of the crystal resonator under atmospheric pressure, and a DC voltage corresponding to the resonant current of the crystal resonator under arbitrary gas pressure and the aforementioned holding voltage are added together. and an anti-phase amplifier, the anti-phase amplifier has means for changing the gain, and means for directly or indirectly applying a bias voltage to the display section, and the output of the anti-phase amplifier drives the display section. A crystal gas pressure gauge that is characterized by: