JPS61161432A - Crystal type gas pressure gauge - Google Patents

Abstract

PURPOSE:To prevent a crystal oscillator from excessive excitation, to improve the measuring accuracy of gas pressure and to prolong the life of the crystal oscillator by reducing a voltage for driving the crystal oscillator which is a gas pressure sensor automatically when the gas pressure is dropped less than a certain value. CONSTITUTION:The pressure gauge is provided with a PLL circuit part consisting of a frequency variable oscillator 1, a phase comparator 3, a low pass filter 4, amplifiers 11, 2, etc., the crystal oscillator 5 connected to the oscillator 1, a display conversion circuit part connected to the PLL circuit part, and a display part connected to the display conversion circuit part to measure the pressure of peripheral gas on the basis of a resonance resistance value, a resonance current value or a resonance voltage value of the oscillator 5. A comparator for comparing a voltage impressed upon the display part with a reference voltage, an amplifier 11 for changing its gain by a switch 14a driven by the output voltage of the comparator and driving the oscillator 5 and an amplifier 2 for amplifying the resonance current of the oscillator 5 are connected to reduce the driving voltage of the oscillator 5 automatically in accordance with the pressure of peripheral gas and to suppress excessive excitation.

Description

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

[Summary of the invention]

The present invention utilizes a crystal oscillator to
In the gas pressure measurement @ dog that measures body pressure, the above-mentioned drawbacks of the conventional technology are solved by automatically reducing the voltage driving the crystal oscillator 5t according to the pressure of the surrounding gas. It provides all the means to do so.

[Conventional technology]

There is a deep-rooted industrial demand for continuous and precise measurement of gas pressure from atmospheric pressure to 10 Torr with a single sensor.

The phenomenon in which the resonant frequency of a quartz crystal oscillator increases as the pressure of the surrounding gas decreases, and the gold-based quartz crystal gas pressure dynamometer is, to some extent, an answer to the above-mentioned industrial need. However, it suffers from the major drawback that the lower limit of measurement is about 10 torr. For example, the Virani vacuum gauge has a lower measurement limit of 10 to 10 Torr, but an upper measurement limit of about 10 Torr, and this also has the same drawbacks as the crystal gas pressure gauge. are doing.

On the other hand, it has recently become clear that the resonant resistance of a crystal resonator is dependent on the pressure of the surrounding gas over a wide range, and if this fact is utilized, one sensor can continuously It has become clear that it is possible to realize a gas pressure gauge that is easy to measure.

For example, the monthly magazine "Keiso J", 1984.

Vol. 27/2007, 7. Development of an ultra-compact vacuum sensor using a crystal oscillator.

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

The eleventh threshold is a diagram showing the relationship between the characteristic values (resonance resistance value, resonance current, and resonance frequency) of the gas upper blade and the crystal camera element. The resonance frequency begins to change when the gas pressure exceeds 10 Torr, but when the gas pressure is less than 10 Torr, the sensitivity to gas pressure is almost zero. On the other hand, the resonant resistance of a crystal resonator is sensitive to gas pressure from atmospheric pressure to 10 Torr. If this crystal vibration is driven at a constant pressure of 1, a resonant current-gas pressure self-destruction as shown by 1.) in the same figure will be observed. It is sensitive to gas pressure from atmospheric pressure to 10 Torr +3 degrees ti, similar to the resonant resistance value. Therefore, from the viewpoint of ease of measurement, it is better to measure the resonance '(current (or resonance voltage) t-#) than to measure the resonance resistance value.

Fig. 2 Co., Ltd., of the crystal gas pressure gauge which is the object of the present invention.
FIG. 2 is a block diagram of a box circuit. The main part is the PLL circuit section,
It is composed of a display conversion circuit section and a display section. Said FL
U, 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 sensor 5 as a voltage, and an output signal of the amplifier 2 and the frequency variable oscillator 1; The phase is compared with the output signal of the oscillator 1, and a proportional filter 4 is applied to detect the phase difference. The low frequency 4 wave generator 4"
The output '; pressure controls the oscillation frequency of the variable frequency oscillator 1. The crystal oscillator 5, which is a pressure sensor, is connected to the output terminal of the variable frequency oscillator 1 and the input terminal of the amplifier 20.

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 drive voltage of the crystal resonator 5, and the Control is always performed so that the phase difference between the output signal of the amplifier #A1 and the current '1 flowing through the crystal oscillator 5 becomes zero. That is, the crystal camera element 5
is always driven at the same wave number as its own resonance, which is extremely important for the practical use of crystal gas pressure gauges. This is due to the process shown in Figure 1 (ζ, resonance of the crystal camera)! This is because the d wave number changes depending on the gas pressure. Next, the display conversion circuit unit includes a main amplifier 6 that further amplifies the signal transmitted from the amplifier 2, an inverter 8 that inverts the polarity of the output voltage of the main extension device, and a device that biases the output voltage of the inverter 8. It consists of a buffer 9. The bias amount can be changed arbitrarily using the variable resistor 9aK.The display unit can display the gas pressure digitally or
This part is displayed in an analog manner, and in this example is constituted by a meter 10, and the gas power is read from the deflection angle of the meter 10.

As shown in Figure 1, 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 if it is amplified as a voltage, converted to direct current, and the meter is turned off as it is, As the pressure decreases, the deflection angle of the meter increases, resulting in an unconventional reading. Therefore, by inverting the polarity of the DC voltage using the impark 8 and applying a bias voltage using the buffer 9, a meter driving pressure as shown in FIG. 3 can be obtained. In the example of the ggs diagram, the meter needle is adjusted so that the meter drive voltage is 10 VK at atmospheric pressure Qζ - in this way, the meter needle swings completely at atmospheric pressure, resulting in a low pressure. Accordingly, the torsion angle of the meter decreases and the normal pressure display can be returned to t.

FIG. 4 is a diagram showing the characteristics of the drive voltage versus resonance resistance value of the crystal sensor 5 (Fa surrounding gas pressure is 1×10 Torr or less). The crystal oscillator 5 is moved @1 pressure is C
When L5 volts (effective value) ft is exceeded, the crystal sensor becomes over-excited.

[Problems to be solved by the present invention]

However, in the above-mentioned conventional crystal gas pressure gauge that utilizes the pressure dependence of the resonant resistance of the crystal resonator, the voltage for driving the crystal resonator 5 is constant and the crystal sensor 5 is large. The crystal oscillator 5t is driven so that the PLL 1g circuit operates normally even when the pressure is at atmospheric pressure or higher (if the pressure value t is fixed, the crystal oscillator 5 is driven under a very low pressure). , the resonant resistance of the crystal oscillator 5 becomes small, so the flat pressure acting on the quartz oscillator 5 becomes relatively strong, resulting in an overexcited imaging state. That is, when the crystal oscillator 5 becomes over-excited, the vibration leakage of the crystal oscillator 5 increases, the value of the resonant current becomes unstable, and the measurement accuracy decreases. If the crystal oscillator 5 falls into an unexcited state, its reliability will decrease, and in extreme cases it may even be damaged, which can occur for a period of time that cannot be overlooked in practice.

[Elaborate means to solve the gap'fIi]

The present invention was conceived in view of the above circumstances, and is a means of solving the drawbacks of the prior art described above by automatically reducing the voltage for driving the crystal oscillator 5 in accordance with the pressure of the surrounding gas. It provides:

〔Example〕

Hereinafter, the present invention will be explained with reference to the drawings. @Figure 5 is a diagram showing an embodiment of the present invention. The output voltage of the variable frequency oscillation 61 is applied to the positive phase amplifier 11 after the DC component is removed by the capacitor j1a and the resistor 11bK. The positive phase 1vII':'The gain of the oT device 11 is determined by the switch 14
When & is in the open state, it is 1, and when the switch 14a is in the closed state, the resistance value 'krt of the resistor 11c and the resistance value of the resistor 11d are r2, then 1+rl/rz. 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 14&. Next, the current flowing through the crystal oscillator 5't is converted into voltage by the resistor 2aK and amplified by the positive phase amplifier 2.

The resistor 2b and the 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. Is the other part of the output of the positive phase amplifier 2 normal? 6'a K&'
) The DC component is removed and applied to the anti-phase amplifier 6'. Assuming that the value of the resistor 6'b is r3, the value of the resistor 6'c is t''r4, and the value of the resistor 6'(l is 'jc r s), the gain of the anti-phase amplifier 6' is when the switch 14b is in the open state. is (r
4+rs)/rs, and when the switch 14b is closed, it becomes r5/rl. That is,
The switch 14b can change the gain of the negative phase amplifier B by opening and closing. Here, the switch 14a and the switch 14b are interlocked by a relay 14,
When the switch 14a is 1, the switch 14b is also open, and when the switch 14a is closed, the switch 14b is also closed.

Specifically, r I = r @ = r 3 = 10 kilohms, r4 == r6 = 100 kilohms. Said switch 14. When a and 14t+ are open, the gain of the positive phase amplifier is 1, the voltage driving the crystal oscillator is 250 m9 volts, 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, and the crystal oscillator 5t
-ffi operating voltage is 50 Q and 17 volts,
The gain of the anti-phase amplifier 6' is 10.

This is the r! of the crystal camera 5. This corresponds to when the pressure of the surrounding gas 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 The above crystal without changing the indicated value! It is possible to prevent the M oscillator from being overexcited. Note that the resistor 10a limits the current flowing to 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 is applied to the transistor 15 via the resistor 13a.
1, the relay 14Kt flow is made to flow, and the switches 14a and 14b are closed, 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 15b is used to adjust the current flowing through the relay 14 to an appropriate value.

Specifically, the reference voltage of the comparator 12 is about 55
Selected by Bolt. At this time, the pressure of the gas surrounding the crystal camera 5 is 1 Torr. That is, the pressure of the surrounding gas is 1
If the output of the comparator 12 is higher than
The voltage becomes "positive", the switches 14a and 14b are closed, and the crystal resonator 5 is driven at 500 mm and 17 volts. Then, when the pressure of the ambient gas falls 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 mm and 17 volts. here,
Since the gain of the anti-phase amplifier 6' is twice that when the ambient gas pressure is 1 Torr or more, even if the driving voltage of the crystal oscillator is halved, the reading on the meter 10 remains the same. In some cases, it does not change and does not interfere with measurement.

〔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 sensor, which is the gas pressure sensor, is automatically adjusted without changing the gas pressure display value. It is possible to prevent overexcitation, which is the most important thing to avoid when using a crystal resonator, to improve the measurement accuracy of gas pressure, and to extend the life of the crystal resonator. Further, the present invention is useful because the drive voltage of the crystal resonator can be freely selected even when measuring all pressures higher than atmospheric pressure.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the relationship between the characteristic values of the crystal resonator (resonant resistance, resonant current, resonant frequency) and the ambient gas pressure; Fig. 2 is a block diagram of the electronic circuit of the crystal gas pressure gauge of the present invention; 3
The figure shows the relationship between meter drive voltage and ambient gas pressure.
FIG. 4 is a diagram showing the relationship between the voltage for driving the crystal resonator and its resonance resistance, and FIG. 5 is a diagram showing an embodiment of the present invention. 1... Frequency variable oscillator 2... Amplifier 3... Phase comparator 4... Low pass filter 5... Crystal oscillator 6'... Main amplifier 7... Rectifier
8...Inverter 9...Buffer 1G
...Meter 11...Positive phase amplifier 12...Comparator 13...Transistor 14...Relay 14a, 14b...Switch 6'...Negative phase amplifier Fig. 1 Breast body pressure k Coloring O101001000 M Rage Level J Shishi (mVr rott figure 4

Claims (1)

[Claims] At least a phase-locked loop circuit (PLL circuit) section consisting of a variable frequency oscillator, a phase comparator, a low-pass filter, and an amplifier, a crystal resonator connected to the variable frequency oscillator, and the PLL circuit section. It has a display conversion circuit unit connected to the display conversion circuit unit and a display unit connected to the display conversion circuit unit, and the display unit has a display unit connected to the display conversion circuit unit. A crystal gas pressure gauge that measures the pressure of surrounding gas includes a comparator that compares the voltage applied to the display with a certain reference voltage, a switch driven by the output voltage of the comparator, and a gain that changes with the switch. and two amplifiers, one of which drives the crystal oscillator and the other amplifies the resonant current of the crystal oscillator. .