JPH042894B2 - - Google Patents

Description

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

[Summary of the invention]

This invention relates to a gas pressure measuring device using a crystal resonator, and even if the buffer bias amount is adjusted so that the meter needle points to full scale at atmospheric pressure (760 torr), it will not work in vacuum (≪10 ^-3 torr). The meter needle does not always point to zero, and conversely, even if you adjust it to zero in a vacuum, the needle will not always point to full scale at atmospheric pressure, so the needle will not always point to full scale at atmospheric pressure and zero at vacuum. It can be easily adjusted according to the instructions.

By holding the value of the output voltage of the rectifier circuit in the display conversion circuit section, the zero point and full scale of the meter can be adjusted independently and easily.

[Conventional technology]

It has recently become clear that the resonant resistance of a crystal resonator varies over a wide range with respect to the pressure of the surrounding gas ^.
It has become clear that it is possible to realize a gas pressure gauge that can continuously measure up to Torr with one sensor. For example, the monthly magazine "Insou", 1984, Vol.
27, No. 7 “Development of ultra-compact vacuum sensor using crystal oscillator”.

Next, the operating principle of a gas pressure gauge that utilizes the pressure dependence of the resonance resistance of a crystal oscillator will be explained with reference to the drawings. FIG. 2 is a diagram showing the relationship between gas pressure and characteristic values of a crystal resonator (resonant resistance value, resonant current, and resonant frequency). The resonant frequency begins to change when the gas pressure exceeds 10 Torr, but the sensitivity to gas pressure is almost zero when the gas pressure is less than 10 Torr. On the other hand, the resonant resistance of a crystal resonator is sensitive to gas pressure from atmospheric pressure to 10 ^-3 Torr. If this crystal vibration is driven at a constant voltage, a resonant current-gas pressure curve as shown by i ₀ in the figure can be obtained. It has a sensitivity to gas pressure from atmospheric pressure to 10 ³ Torr as well as the resonant resistance. Therefore, in terms of ease of measurement, it is better to measure the resonant current (or resonant voltage) than to measure the resonant resistance value.

FIG. 3 is a block diagram of an electronic circuit of a crystal gas pressure gauge that utilizes the pressure dependence of the resonant resistance of a crystal resonator. Broadly speaking, it is composed of a PLL circuit section, a display conversion circuit section, and a display section. Said PLL
The circuit section includes a variable frequency oscillator 1 controlled by voltage or current, an amplifier 2 that amplifies the resonant current of the crystal oscillator 5 as a voltage, and an output signal between the output signal of the amplifier 2 and the output signal of the variable frequency oscillator 1. It consists of a phase comparator 3 that compares phases and outputs a signal proportional to the phase difference, and a low frequency converter 4 that converts the pulsed output signal of the phase comparator 3 into a DC voltage.
The output voltage of the low frequency generator 4 controls the oscillation frequency of the variable frequency oscillator 1. The crystal oscillator 5, which is a pressure sensor, is connected to the variable frequency oscillator 1.
is connected to the output terminal of the amplifier 2 and the input terminal of the amplifier 2. .

Since the operating principle of the PLL circuit is already widely known, it is omitted here, but the oscillation frequency of the variable frequency oscillator 1 is determined by the output signal of the variable frequency oscillator 1, that is, the driving voltage of the crystal resonator 5, and the driving voltage of the crystal resonator 5. Control is always performed so that the phase difference with the output signal of the amplifier 2, ie, the current flowing through the crystal resonator 5, is zero. That is, the crystal resonator 5 is always driven at its own resonant frequency, which has an important meaning in implementing a crystal gas pressure gauge. This is because, as shown in FIG. 2, the resonant frequency of the crystal oscillator changes depending on the gas pressure. Next, the display conversion circuit section includes a main amplifier 6 that further amplifies the signal of the amplifier 2, a rectifier 7 that converts the output signal of the main amplifier 6 into DC, an inverter 8 that inverts the polarity of the output voltage of the rectifier 7, and and a buffer 9 for biasing the output voltage of the inverter 8. The amount of bias can be arbitrarily changed using the variable resistor 9a. The display section is a section that displays the gas pressure digitally or analogously, and in this example, it is constituted by a meter 10, and the gas pressure is read from the deflection angle of the meter 10.

As shown in Figure 2, the pressure characteristics of the resonant current of the crystal resonator are as follows: As the pressure of the surrounding gas decreases, the resonant current increases, so it is amplified as a voltage, converted to direct current, and directly drives the meter. Then, as shown by the curve V _DC in Figure 4, as the pressure decreases, the deflection angle of the follower meter increases, resulting in a display contrary to common sense. Therefore, by inverting the polarity of the DC voltage using the inverter 8 and applying a bias voltage using the buffer 9, a meter drive voltage as shown by the curve V _M in FIG. 4 can be obtained. . In the example of FIG. 4, the bias amount is adjusted so that the meter drive voltage is 10V at atmospheric pressure. In this way, a normal pressure display can be obtained in which the meter needle swings completely at atmospheric pressure and the swing angle of the meter needle decreases as the pressure decreases.

[Problems to be solved by the present invention]

However, the conventionally configured quartz crystal gas pressure gauge that utilizes the pressure dependence of the resonance resistance of a quartz crystal oscillator has the following problems. That is, as shown by curve a in FIG. 5, even if the bias amount of the buffer 9 is adjusted so that the needle of the meter 10 points to the full scale at atmospheric pressure, the vacuum (gas ^pressure The needle of the meter 10 does not always point to zero. Conversely, even if the bias amount of the buffer 9 is adjusted so that the needle of the meter 10 points to zero in vacuum as shown by curve c in FIG. 5, the needle of the meter 10 will not reach full scale at atmospheric pressure. It doesn't necessarily mean pointing. Therefore, curve b in FIG.
As shown, the needle of the meter 10 points to zero in vacuum and full scale at atmospheric pressure,
It must be possible to easily adjust the meter needle indication. This can be said to be an extremely important problem in the practical use of quartz crystal gas pressure gauges, considering the change in resonance resistance of the quartz crystal oscillator over time and the replacement of the quartz oscillator for some reason.

[Means for solving problems]

The present invention has been made in view of the above circumstances, and
By holding the value of the output voltage of the rectifier circuit 7 in vacuum in the display conversion circuit section, the zero point and full scale of the meter 10 can be adjusted independently and easily. It provides the means.

〔Example〕

Hereinafter, the present invention will be explained with reference to the drawings. FIG. 1 is a diagram showing an embodiment of the present invention. A variable resistor 2 is connected in series between the crystal resonator 5 and the amplifier 2.
a is connected. The variable resistor 2a is configured to control changes in resonance resistance of the crystal resonator 5 in vacuum over time, changes in resonance resistance due to changes in ambient temperature, etc.
The variable resistor 2a is provided to absorb relatively small changes in resonance resistance, and the maximum amount of change in the variable resistor 2a is about 1KΩ. In a normal state, the variable resistor 2a is set at a neutral position (ie, its resistance value is 1/2 of the maximum resistance value, in this case 0.5KΩ). The output of the rectifier circuit 7 is applied to the negative input of an operational amplifier 8' via a resistor 8a. The negative input terminal and output terminal of the operational amplifier 8' are connected through a variable resistor 8b, forming a variable gain anti-phase amplifier 8''.
The output of the negative phase amplifier 8'' drives a meter 10 via a resistor 8c (this is called a meter drive voltage). The output voltage of the operational amplifier 11 (constituting the portage and follower) is applied to the output voltage of the operational amplifier 11, which is connected to the positive input terminal of the variable resistor 1.
1b and the resistor 11 connected in series with it.
a and 11c, it is basically possible to change approximately ±3V around -10V.
Here, the values of the resistor 8a and the resistor 11d are made equal (R ₃ a=R ₁₁ d=R ₁ =10KΩ). Further, an arbitrary resistance value of the variable resistor 8b is assumed to be R ₂ (maximum value is 20KΩ).

The output voltage of the rectifier circuit 7 in vacuum when the variable resistor 2a is kept in the neutral position is V _U ,
Let the meter drive voltage be _VMU , the output voltage of the rectifier circuit 7 at atmospheric pressure _{be VL} , and the meter drive voltage be _VML . Further, the output voltage of the operational amplifier 11 is assumed to be V ₀ . At this time, V _MU and V _ML are expressed by the following equations.

V _MU = −R ₂ /R ₁ (V _U +V ₀ ) (1) V _ML = −R ₂ /R ₁ (V _L +V ₀ ) (2) Here, set R ₂ to the maximum (R ₂ =
R ₂ max), after evacuating the tank to a sufficient vacuum,
The variable resistor 11b is adjusted so that V ₀ =-V _U and its value is fixed. Then −R ₂ max/R ₁ . △V _MU =Amax△V _MU ≒0 (3). The reason why we set V _MU ≒ 0 here is that it is impossible to completely set V ₀ = −V _U through human manipulation, so
This is because the error ΔV _MU remains, although it is small. However, this completes the zero point adjustment of the meter 10 in actual use.

Next, with the gas pressure at atmospheric pressure, change the value of R ₂ and adjust the variable resistor 8 so that V _ML in equation (2) is exactly equal to the full scale needle of the meter 10.
Adjust b and fix its value (R ₂ =R ₂ ). That is,
This completes the full scale adjustment of the meter 10. The meter drive voltage V _ML at this time is V _ML =
R ₂ /R ₁ (V _U − V _L ) = A (V _U − V _L ) (4). Since the variable resistor 8b was adjusted during the full scale adjustment, the meter drive voltage V _M ′ _U when the vacuum is restored is V _M ′ _U =A. △V _MU , but
Since A < Amax, V _M ′ _U < V _MU , and it is virtually impossible for the zero point to go out of order.

Above, in principle, the zero point of the meter 10,
Full scale adjustment ends. In the circuit according to the invention, the voltage V _U that determines the zero point of the meter 10 is
The voltage _VML , which is held in the display conversion circuit as the value of the variable resistor 11b and provides the full scale of the meter 10, is obtained by adjusting the separate variable resistor 8b. Scale adjustments can be made independently without mutual interference.

The resonant resistance of a crystal resonator is stable, so it does not change much on a daily basis. However, zero point fluctuations caused by slight changes in the resonance resistance due to long-term use, adsorption of water vapor, changes in ambient temperature, etc. can be completely absorbed by adjusting the variable resistor 2a. For example, the maximum resistance value of the resistor 2a is
For 1KΩ, ±3% of meter full scale
It is possible to bring the meter needle to the zero point by adjusting the zero point fluctuation of ±5%. However, at atmospheric pressure, the resonant resistance value of the crystal resonator is 300
~400KΩ, so even if the resonance resistance changes by about 1KΩ by adjusting the variable resistor 2a,
The change in V _ML is virtually negligible, and the full scale of the meter needle hardly changes.

Conversely, when the full scale goes out of order for some reason at atmospheric pressure, even if the variable resistor 8b is readjusted in order to readjust the full scale, the meter drive voltage V _MU at the zero point The change in the zero point of the meter needle due to the change in _VMU can be made zero by adjusting the variable resistor 2a.

That is, once the adjustment of the zero point by the variable resistor 11b and the full scale by the resistor 8b has been completed, even if the zero point or full scale changes slightly for some reason, the adjustment of the variable resistor The readjustment of the zero point by the resistor 2a and the full scale by the variable resistor 8b can be done completely independently and easily.

〔Effect of the invention〕

As described above, according to the present invention, if the zero adjustment of the meter is performed in vacuum and the full scale adjustment of the meter is performed at atmospheric pressure using two variable resistors, in normal use, The zero point of the meter,
Since the full scale adjustment can be performed completely independently and easily, this has the effect of greatly facilitating the use of a crystal gas pressure gauge that utilizes the pressure dependence of the resonant resistance of a crystal resonator.

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing the relationship between the characteristic values of the crystal resonator (resonant resistance, resonant current, resonant frequency) and ambient gas pressure, and FIG. FIGS. 4 and 5, which are electronic circuit block diagrams of a conventional quartz crystal gas pressure gauge that utilizes the pressure dependence of the resonant resistance of a quartz crystal resonator, are diagrams showing the relationship between meter drive voltage and gas pressure. DESCRIPTION OF SYMBOLS 1... Frequency variable oscillator, 2... Amplifier, 3... Phase comparator, 4... Low frequency device, 5... Crystal resonator, 6...
Main amplifier, 7... Rectifier, 8... Inverter, 9... Buffer, 10... Meter, 11, 8'... Operational amplifier,
8a, 8c, 11a, 11c, 11d...Resistor,
2a, 8b, 11b...variable resistor.

Claims (1)

[Claims] 1. A phase filter consisting of at least a variable frequency oscillator, a phase comparator, a low-pass filter, and an amplifier.
a locked loop circuit (PLL circuit) section, a crystal resonator connected to the variable frequency oscillator, and a display conversion circuit section connected to the PLL circuit section;
and a display section connected to the display conversion circuit section, and measures the pressure of the gas surrounding the crystal oscillator from the resonance resistance value, resonance current value, or resonance voltage value of the crystal oscillator. A gas pressure gauge includes a circuit that generates a voltage by setting it with a variable resistor to offset the DC voltage corresponding to the resonance current value of the crystal oscillator at a certain gas pressure, and a variable resistor in the feedback circuit. and an anti-phase amplifier that adds the canceling voltage value to a DC voltage value corresponding to a resonance current value of the crystal resonator at a given gas pressure and then amplifies the result, and a combination of the amplifier and the crystal resonator in the PLL circuit section. A variable resistor provided between the crystal oscillator and a variable resistor for correcting a resonance resistance value of a crystal oscillator. A crystal gas pressure gauge characterized in that the output of the amplifier drives the display section.