JPH0380253B2 - - 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]

The present invention is a gas pressure measuring device that uses a crystal oscillator to measure the gas pressure around the crystal oscillator. Therefore, it provides a means for solving the drawbacks of the prior art described below.

[Conventional technology]

There is a strong industrial need to continuously measure gas pressure from atmospheric pressure to 10 ^-3 Torr with a single sensor.

Quartz crystal gas pressure gauges, which utilize the phenomenon that the resonant frequency of a crystal oscillator increases as the pressure of the surrounding gas decreases, meet the above industrial requirements to some extent, but the lower measurement limit is around 10 Torr. It has the major drawback of being. In addition, thermal conduction type vacuum gauges, such as Pirani vacuum gauges, have a lower measurement limit of 10 ^-4 to ^{10 -3} Torr, but an upper measurement limit of about 10 Torr, which also has the same drawbacks as the crystal gas pressure gauge. have.

On the other hand, it has recently become clear that the resonant resistance of a crystal resonator depends on the pressure of the surrounding gas over a wide range ^.
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,
It is disclosed in 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. 1 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 pressures up to 10 ^-3 Torr. If this crystal vibration is driven at a constant voltage, a resonance current-gas pressure curve as shown by io 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. 2 is a block diagram of an electronic circuit of a quartz crystal gas pressure gauge, which is the object of the present invention. Mainly PLL
It is composed of a circuit section, a display conversion circuit section, and a display section. The PLL circuit unit includes a variable frequency oscillator 1 controlled by voltage or current, an amplifier 2 that amplifies the resonant current of the crystal resonator 5 as a voltage, and an output signal of the amplifier 2 and the variable frequency oscillator 1.
The phase comparator 3 compares the phase with the output signal of the phase comparator 3 and outputs a signal proportional to the phase difference, and the low-pass filter 4 converts the pulsed output signal of the phase comparator 3 into a DC voltage. The output voltage of the low-pass filter 4 controls the oscillation frequency of the variable frequency oscillator 1. The crystal oscillator 5, which is a pressure sensor, connects the output terminal of the variable frequency oscillator 1 and the amplifier 2.
connected to the input terminal of

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 putting the crystal gas pressure gauge into practical use. This is because, as shown in FIG. 1, the resonant frequency of the crystal resonator 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 display section, in which the bias amount can be arbitrarily changed by the variable resistor 9a, digitally displays the gas pressure.
Alternatively, it is a part that is displayed in an analog manner, and in this example is constituted by a meter 10, and the meter 10
The gas pressure is read from the deflection angle.

As shown in FIG. 1, the pressure characteristics of the resonance current of the crystal oscillator are such that the resonance current increases as the pressure of the surrounding gas decreases, so it is amplified as a voltage.
If you switch back to direct current and drive the meter as it is, the swing angle of the meter will increase as the pressure decreases, resulting in a display that goes against common sense. Therefore, the inverter 8
Accordingly, by reversing the polarity of the DC voltage and further applying a bias voltage by the buffer 9, a meter driving voltage as shown in FIG. 3 can be obtained. In the example of FIG. 3, 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 decreases as the pressure decreases.

FIG. 4 is a diagram showing the characteristics of the drive voltage versus resonance resistance value of the crystal resonator 5 (ambient gas pressure is 1×10 ⁻⁴ Torr or less). When the voltage driving the crystal oscillator 5 exceeds 0.5 volts (effective value), the crystal oscillator becomes over-excited.

[Problems to be solved by the present invention]

However, in the above-described conventional crystal gas pressure gauge that utilizes the pressure dependence of the resonant resistance of the crystal oscillator, the voltage for driving the crystal oscillator 5 is constant, and the crystal oscillator 5 is at atmospheric pressure. If the value of the voltage for driving the crystal oscillator 5 is fixed so that the PLL circuit section operates normally even when the crystal oscillator 5 is under pressure of
When the crystal oscillator 5 is under very low pressure,
Since the resonant resistance of the crystal resonator 5 becomes small,
The disadvantage was that the driving voltage became relatively strong, leading to overexcitation. That is, the crystal resonator 5
When the crystal resonator 5 enters an overexcited state, vibration leakage of the crystal resonator 5 becomes large, and the value of the resonant current becomes unstable, reducing measurement accuracy. Also, of course, if the crystal resonator 5 is in an overexcited state, its reliability will decrease,
In severe cases, it may even be damaged, creating problems that cannot be overlooked in practical terms.

[Means to solve the problem]

The present invention has been made in view of the above circumstances, and solves the drawbacks of the prior art described above by automatically reducing the voltage that drives the crystal oscillator 5 according to the pressure of the surrounding gas. It provides a means to do so.

〔Example〕

Hereinafter, the present invention will be explained with reference to the drawings. FIG. 5 is a diagram showing an embodiment of the present invention. The output voltage of the variable frequency oscillator 1 is applied to the positive phase amplifier 11 after the DC component is removed by a capacitor 11a and a resistor 11b. The gain of the positive phase amplifier 11 is 1 when the switch 14a is open, and 1+ when the switch 14a is closed, where r ₁ is the resistance value of the resistor 11c and r ₂ is the resistance value of the resistor 11d.
It becomes r ₁ / r ₂ . That is, the voltage for driving the crystal oscillator 5, which is a gas pressure sensor, can be changed by opening and closing the switch 14a. Next, the current flowing through the crystal oscillator 5 is converted into voltage by a resistor 2a and amplified by a positive phase amplifier 2. resistance 2
b and resistor 2c determine the gain of the positive phase amplifier 2. A part of the output of the positive phase amplifier 2 is applied to the phase comparator 3 to complete the PLL circuit section.
The DC component of the other part of the output of the positive phase amplifier 2 is removed by a capacitor 6'a, and then applied to the negative phase amplifier 6'. The value of resistor 6'b is r ₃ and the value of resistor 6'c is
r ₄ and the value of the resistor 6'd is r ₅ , the gain of the anti-phase amplifier 6' is (r ₄ + r ₅ )/r ₃ when the switch 14b is open, and when the switch 14b is closed When , it becomes r ₅ / r ₃ . That is, the switch 14
b can change the gain of the anti-phase amplifier 6 by opening and closing. Here, the switch 14a and the switch 14b are linked by a relay 14, and when the switch 14a is open, the switch 14b is also opened, and when the switch 14a is closed, the switch 14b is also closed. It is.

Specifically, r ₁ = r ₂ = r ₃ = 10 kilohms, r ₄ =
r ₅ = 100 kilohms. The switch 14a
and 14b are open, the gain of the positive phase amplifier is 1, the voltage driving the crystal is 250 millivolts, and the gain of the negative phase amplifier 6 is 20. This corresponds to when the pressure of the gas surrounding the crystal resonator 5 is low.

Next, when the switches 14a and 14b are closed, the gain of the positive phase amplifier 11 is 2, the voltage driving the crystal oscillator 5 is 500 millivolts, and the gain of the negative phase amplifier 6' is 10. Become. This corresponds to when the pressure of the gas surrounding the crystal resonator 5 is high. That is, when the ambient gas pressure is low, the voltage driving the crystal oscillator 5 is halved compared to when the pressure is high, but on the other hand, the gain of the anti-phase amplifier 6' is doubled, so that the meter 10 is It is possible to prevent the crystal resonator from being overexcited without changing the indicated value at all. still,
A resistor 10a limits the current flowing through the meter 10.

A part of the output voltage of the buffer 9 in the display conversion circuit section is applied to the comparator 12. The output voltage of the comparator 12 activates the transistor 13 via the resistor 13a, and the relay 1
4 to close the switches 14a and 14b. That is, the voltage for driving the crystal resonator 5 is changed by the comparator 12. Note that the diode 14c absorbs the back electromotive voltage of the relay 14 and protects the transistor 13. Further, the resistor 13b is used to adjust the current flowing through the relay 14 to an appropriate value.

The reference voltage of the comparator 12 is specifically selected to be approximately 5.5 volts. At this time, the pressure of the gas surrounding the crystal resonator 5 is 1 Torr. That is, when the pressure of the surrounding gas is higher than 1 Torr, the output voltage of the comparator 12 becomes "positive",
The switches 14a and 14b are closed, and the crystal oscillator 5 is driven at 500 millivolts.
Next, when the pressure of the surrounding gas drops below 1 Torr, the output voltage of the comparator 12 becomes "negative",
The switches 14a, 14b are opened and the crystal 5 is driven at 250 millivolts. Here, since the gain of the negative phase amplifier 6' is twice that when the ambient gas pressure is 1 Torr or more, even if the driving voltage of the crystal resonator is halved, the reading on the meter 10 is It does not change,
It does not interfere with measurement in any way.

〔Effect of the invention〕

As described above, according to the present invention, when the gas pressure falls below a certain value, the voltage that drives the crystal oscillator that is the gas pressure sensor is automatically reduced without changing the gas pressure display value. This makes it possible to prevent overexcitation, which is the most important thing to avoid when using a crystal resonator, improve gas pressure measurement accuracy, and extend the life of the crystal resonator. Further, the present invention is useful even when measuring pressures higher than atmospheric pressure because the driving voltage of the crystal resonator can be freely selected.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between the characteristic values of a crystal resonator (resonant resistance, resonant current, resonant frequency) and ambient gas pressure, and Figure 2 is an electronic circuit block of a crystal gas pressure gauge, which is the subject of the present invention. 3 shows the relationship between the meter driving voltage and the ambient gas pressure, FIG. 4 shows the relationship between the voltage driving the crystal resonator and its resonance resistance, and FIG. 5 shows the relationship between the meter driving voltage and the ambient gas pressure. It is a figure showing an example. 1... variable frequency oscillator, 2... amplifier, 3...
... Phase comparator, 4 ... Reducing filter, 5 ... Crystal oscillator, 6 ... Main amplifier, 7 ... Rectifier, 8 ... Inverter, 9 ... Buffer, 10 ... Meter, 1
1... Positive phase amplifier, 12... Comparator, 13
...Transistor, 14...Relay, 14a, 1
4b...Switch, 6'...Negative phase amplifier.

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. The gas pressure gauge includes a comparator that compares the voltage applied to the display section with a reference voltage determined corresponding to a certain gas pressure value, a switch driven by the output voltage of the comparator, and the switch. The gain is switched by the quartz crystal oscillator, and the two quartz crystal oscillators are installed so that the gain product does not change before and after switching. A crystal gas pressure gauge characterized by comprising: an amplifier;