JPS62130326A - Crystal type gas manometer - Google Patents

Abstract

PURPOSE:To lock a PLL circuit by sweeping the oscillation frequency of a variable frequency oscillator with a start switch ON and tuning it to the resonance frequency of a crystal resonator. CONSTITUTION:When a power switch is turned on, the oscillation frequency fosc of the variable frequency oscillator 1 decreases gradually and becomes equal to the resonance frequency fo of the crystal resonator eventually. When the varying speed of this frequency almost matches with the response time of the crystal resonator 5, a resonance current is conducted through the crystal resonator 5 and is amplified by an amplifier 2 to lock the variable frequency oscillator 1 through a phase comparator 3 and a low-pass filter 4. The subsequent oscillation frequency fosc of the variable frequency oscillator 1 is equal to fo. Thus, the PLL circuit is locked at the resonance frequency of the crystal resonator 5.

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 been revealed that the resonant resistance of crystal vibration (especially in the bending mode) changes over a wide range with respect to the pressure of the surrounding gas, and if this is utilized, it is possible to continuously generate vibrations from atmospheric pressure to about 10-' Torr with one sensor. It became clear that a gas pressure gauge capable of measuring gas pressure could be realized. For example, the monthly magazine "Keiso", 1984, Vo I, 27, 7th
It is disclosed in the section ``Development of an ultra-small vacuum sensor using a crystal oscillator''.

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.

FIG. 1 is a diagram showing the relationship between the gas (N2) pressure and the resonant resistance, resonant current, and resonant frequency of a crystal resonator in a bending mode of about 32 kHz. The resonant frequency begins to change when the pressure exceeds 10 Torr, but the frequency pressure devil is almost zero in the region where the pressure is lower than that. On the other hand, the resonant resistance of a quartz crystal has an effective sensitivity to pressures from atmospheric pressure to about 10@-3 Torr. 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 pressure sensitivity from atmospheric pressure to about 101 Torr, 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 display conversion circuit section, and a display circuit section. The PLL circuit section includes a variable frequency oscillator 1 controlled by voltage or current, and a crystal oscillator 5.
an amplifier 2 that amplifies the resonant current of 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; A low-pass filter 4 generates a DC voltage proportional to the output signal of the phase comparator 3, and the output voltage of the low-pass filter 4 controls the oscillation frequency of the variable frequency oscillator 1. The crystal resonator 5, which is a pressure sensor, is driven by the output voltage of the variable frequency oscillator 1.

The operating principle of the PLL circuit is already widely known, so
Although omitted here, the phase difference between the output signal of the variable frequency oscillator 1 (i.e., the drive voltage of the crystal resonator 5) and the output signal of the amplifier 2 (i.e., the current flowing through the crystal resonator 5) is The oscillation frequency of the variable frequency oscillator 1 is controlled so that the frequency 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 voltage) into an electric signal capable of displaying pressure. Basically, it consists of the following circuit. When the display section is composed of an ammeter, these include a main amplifier 6 that further amplifies the output signal of the amplifier 2, a rectifier circuit 7 that converts the output signal of the main amplifier 6 into direct current, and the rectifier circuit 7. This is a meter drive circuit 8 that converts the output voltage of the meter into a meter drive voltage.

In this example, the display section is an ammeter (meter) 9, and the pressure of the gas is determined by the deflection angle of the needle of the meter 9.

As shown in FIG. 3, the output voltage VOC of the rectifier circuit 7 increases as the gas pressure decreases, matching the tendency of the resonant current io shown in FIG.
). If the meter 9 is driven in this state, the pressure will decrease and the deflection angle of the make 9 will increase, giving an indication that is contrary to common sense for a pressure gauge. Therefore,
The meter drive circuit receives the output voltage vIl of the rectifier circuit 7.
c is reversed as shown by curve v8 in Fig. 3, and the deflection angle of the pointer of the meter 9 is made full scale at atmospheric pressure, and the deflection angle of the pointer of the meter 9 is made zero at high vacuum. .

[Problem that the invention seeks to solve]

In a conventional gas pressure gauge using a self-help oscillator, a crystal resonator is used in the feedback loop of the self-help oscillator circuit, so an output voltage corresponding to the resonance resistance of the crystal resonator can be obtained.
The output voltage is strongly influenced by the loop gain of the automatic oscillator in addition to the resonance resistance value. Furthermore, since the resonant resistance of the crystal resonator changes by more than three orders of magnitude (30 to 0 Ω in high vacuum, 300 to 0 at atmospheric pressure) depending on the pressure, attempts were made to prevent the output voltage of the oscillator from saturating in high vacuum. Then, the level of the driving voltage of the crystal resonator must be lowered, which makes automatic oscillation near normal pressure difficult. In other words, in the self-oscillation method, the output voltage for measuring pressure is generally strongly influenced by factors other than the resonant resistance of the crystal oscillator that is the pressure sensor, and the pressure measurement range of the measuring device is The performance of the crystal oscillator as a pressure sensor cannot be fully utilized because the pressure range becomes narrower than the pressure range in which the oscillator can maintain its effective temperature. Also, in order to maintain stable oscillation, it is usually necessary to place the crystal resonator and the oscillation circuit as close as possible (the longer the sensor cable becomes, the more unstable the oscillation becomes due to stray capacitance). This is a major limitation.

On the other hand, in the crystal gas pressure gauge according to the present invention, since the output voltage of the variable frequency oscillator 1 is constant regardless of the resonance resistance value of the crystal oscillator 5, the crystal oscillator 5 is always in a resonant state and has a constant state. It is driven by a voltage of amplitude. For this reason,
As shown in FIGS. 1 and 3, the output voltage of the rectifier circuit is . , is the resonant current 10 of the crystal resonator, and the deflection angle of the output voltage v, l of the meter drive circuit (1 of the meter 9) is ■. ) corresponds to the resonance resistance R8 of the crystal resonator 5, respectively. That is, since the meter drive voltage (19) is determined only by the resonance resistance Ro of the crystal oscillator, such a gas pressure gauge can fully utilize the performance of the crystal oscillator as a pressure sensor. Furthermore, if the drive source impedance of the crystal oscillator and the input impedance of the amplifier that amplifies the synocular current of the crystal oscillator are sufficiently low, the cable connecting the sensor (crystal oscillator) and the gas pressure gauge body can be Make the length very long (e.g. 3
0 to 50m) without any problem. These are great practical advantages. However, this method also has the following problems. In other words, once the variable frequency oscillator of the PLL is locked at the resonant frequency of the crystal oscillator, its operation is extremely stable, and even if the pressure is suddenly returned from high vacuum to normal pressure (at this time, the crystal oscillator (The resonant frequency of the child changes by several Hz) The lock will not be lost, but
In order to achieve a locked state, the resonant frequency of the crystal oscillator, which varies by several H2, must be adjusted with very high precision (the Q of the crystal oscillator is approximately 100,000, so the precision is small (accuracy of lXl0-')). It is necessary to adjust the oscillation frequency of the variable frequency oscillator.

The present invention has been made in view of the above circumstances, and when a power switch or some kind of starting switch is turned on, the oscillation frequency of the variable frequency oscillator is swept and tuned to the resonant frequency of the crystal resonator. This locks the PLL circuit.

〔Example〕

Next, the present invention will be explained with reference to figures. FIG. 4 shows a process in which the variable frequency oscillator of the PLL is locked at the resonant frequency of the crystal resonator according to the embodiment of the present invention. Turn on the power switch (not shown) (time 1=0>,
The oscillation frequency of the variable frequency 1 fosc gradually decreases and eventually becomes equal to the resonant frequency f0 of the crystal resonator. If the rate of change in frequency is compatible with the response time of the crystal resonator 5, a resonant current flows through the crystal resonator, the amplifier 2 amplifies this, and the phase comparator 3 and the The variable frequency oscillator 1 is locked by a low pass filter 4. Therefore, the oscillation frequency of the variable frequency oscillator 1 thereafter is fosc=fo.

FIG. 5 is a block diagram of an embodiment of the invention.

Reference numeral 10 denotes a control voltage generator that generates a voltage whose peak value changes over time when a switch 10d connected to the power source is turned on, and the output voltage of the control voltage generator 10 passes through the switch circuit 1) to the variable frequency The switch circuit 1), which is connected to the oscillator l and has the function of sweeping its oscillation frequency, is normally in the "closed" state when the control voltage generator 1
An output voltage of 0 is applied to the variable frequency oscillator 1, but when the crystal oscillator 5 resonates (that is, the PLL locks), the output voltage of the rectifier circuit 7 appears, and the output voltage of the rectifier circuit 7 causes The output voltage of the control voltage generator 10 no longer sweeps the oscillation frequency of the variable frequency oscillator 1 (see FIG. 4), and the PLL circuit section is stabilized in its own state. It becomes like this. The switch circuit 1) is basically constituted by a three-terminal switching element such as a field effect transistor.

FIG. 6 is a diagram showing an example of the configuration of the control voltage generator 10. 10a is mono multi, 10b is integrator, 10c
is an attenuator. FIG. 7 is a diagram showing waveforms of output voltages of each component of the control voltage generator 10. When the switch 10d (which may be used as a power switch for the entire system) is closed, the monomulti 10a operates, and specifically generates a pulse with a width of about 8 seconds (see Fig. 7(a)). )
).

This pulse is applied to an integrator Job, and specifically, a triangular wave (FIG. 7(b)) with a peak value of about 15V is generated. This triangular wave is applied to the attenuator 10c, and specifically, an output voltage (control voltage V, waveform shown in FIG. 7(C)) with a peak value of about 8V is obtained. The magnitude of the control voltage VC is determined by the characteristics of the variable frequency oscillator 1.

The control voltage vc is applied to the variable frequency oscillator 1, so that the oscillation frequency of the variable frequency oscillator 1 is the seventh
It changes as shown in the figure +dl.

FIG. 8 shows another example of the configuration of the control voltage generator lO,
FIG. 8 (Al is composed of a charging circuit including a resistor 10e and a capacitor 10f, and a buffer 10g, and the crest in FIG. 8) is simply composed of the resistor 10e and the capacitor 10f. If the frequency control voltage input impedance of the variable frequency oscillator 10 is sufficiently high, the buffer 10g is not necessarily required. Figure 9 +a+ is the 8th
The waveform of the control voltage vc of the configuration example shown in the figure is shown in FIG.
bl indicates a change in the oscillation frequency of the variable frequency oscillator 1. Although the configuration example shown in FIG. 8 is very similar in configuration to an hour wheel, it has the following drawbacks. That is, in Figure 9 To), if the oscillation frequency of the variable frequency oscillator 1 at time t=0 is relatively high (fl), the time for the PLL to lock becomes very long (1 +) or how long does it take? will no longer lock. On the other hand, if the oscillation frequency of the variable frequency oscillator 1 is relatively low (r,), the rate of frequency change when crossing the resonance frequency r0 of the crystal oscillator 5 is too large, and the crystal oscillator 5 becomes unable to respond. , resulting in P
LL no longer locks. The disadvantage of the configuration example shown in FIG. 8 is that the frequency range in which the PLL locks becomes narrow in this way, and this is because the temporal change in the control voltage vc is a charging (discharging) curve. On the other hand, in the configuration example shown in FIG. 6, the temporal change in the control voltage Ve is linear (the seventh
(C)), it is clear that the configuration example shown in FIG. 8 does not have the drawbacks.

FIG. 1θ shows an example of a configuration in which the oscillation frequency of the variable frequency oscillator 1 is changed by applying the control voltage to the low-pass filter 4.

Low-pass filters can generally pass direct current, so the first
The configuration shown in Figure 0 is possible. Furthermore, since the input impedance of the low-pass filter is generally high, the configuration example shown in FIG. 10 has the advantage that the output impedance of the control voltage generator need not be taken into consideration much.

(Effects of the Invention) As described above, the present invention provides a crystal gas pressure gauge in which a crystal oscillator is driven by a PLL circuit, in which a frequency variable oscillator in the PLL circuit section or the oscillation frequency of the oscillator is controlled. By applying a voltage whose peak value changes over time to a low-pass filter, the oscillation frequency of the variable frequency oscillator is swept, and the resonant frequency of the crystal resonator, which is a pressure sensor, is within the frequency sweep width. By doing so, the PLL circuit is locked at the resonant frequency of the crystal resonator.

In a crystal gas pressure gauge that utilizes the gas pressure dependence of the resonance resistance of a crystal oscillator, it is essentially important to drive the crystal oscillator with a constant voltage, and a PLL circuit is excellent for driving the crystal oscillator at a constant voltage. As mentioned above, In order to lock the PLL circuit at the resonant frequency of the crystal resonator, it is essentially necessary to first bring the crystal resonator into a resonant state. According to the present invention, it is possible to first bring the crystal resonator into a resonant state; the present invention has a simple configuration of the circuit because the variable frequency oscillator itself built in the PLL circuit is used; The frequency variable oscillator can be used within a capture range (the frequency of the reference signal; in the present invention, the range of frequencies that can be pulled into lock when the frequency of the variable frequency oscillator is changed with respect to the resonant frequency of the crystal resonator). It is possible to tolerate fluctuations caused by aging of the oscillation frequency of the oscillation frequency, variations in component constants, etc. (In an example with a permissible frequency fluctuation range, it was 4 kHz or more. This means that if the resonant frequency of the crystal resonator is approximately 32 kHz, (equivalent to about 13%), which has a large practical effect.

Although not specified in the embodiments of the present invention, the PL
After the L circuit section locks at the resonant frequency of the crystal oscillator 5, instead of turning off the control voltage in the switch circuit 1), a means for maintaining the control voltage at a certain constant value is introduced. It is obvious that the switch circuit 1) can be eliminated by using the above method, and it goes without saying that such means are also included in the scope of the present invention.

Further, in the embodiment of the present invention, the meter is used as an element constituting the display section, but the effect is the same even if a digital display device using a digital circuit is used instead of the meter.

[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 above-mentioned A diagram showing the relationship between the rectifier circuit output voltage in the electronic circuit and the gas pressure of the meter drive voltage. Figure 4 is a diagram showing the process in which the variable frequency oscillator of the PLL locks at the resonant frequency of the crystal oscillator. Figure 5 is a block diagram of an embodiment of the present invention, FIG. 6 is a block diagram showing the configuration of a control voltage generator in an embodiment of the present invention, and FIG. 7 is a diagram showing waveforms of each component of the control voltage generator. FIG. 8 is a diagram showing another embodiment of the present invention, FIG.
This figure is a diagram showing waveforms of each component of the embodiment shown in FIG. 8, and FIG. 10 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 10...Control voltage generator 1)...Switch circuit 10a...Monomulti 10b...Integrator 10'C...Attenuator 10d...Switch 10e...Resistor 10f...・Capacitor 10g...Buffer or more yoke (Nri's tE force Cb) Figure 3

Claims (4)

[Claims] (1) A phase-locked loop (PLL) circuit section consisting of at least a variable frequency oscillator, a phase comparator, a low-pass filter, and an amplifier, and a crystal resonator connected between the variable frequency oscillator and the amplifier. and a display section connected to the PLL 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 quartz crystal gas pressure gauge comprising a control voltage generator whose output voltage changes over time, the control voltage generator being connected to the variable frequency oscillator or the low-pass filter. (2) A switch circuit activated by a voltage of a portion constituting the display section is connected between the control voltage generator and the variable frequency oscillator or the low-pass filter. crystal gas pressure gauge. (3) The control voltage generator is at least a mono-multi,
The crystal gas pressure gauge according to item (1), comprising an integrator. (4) The crystal gas pressure gauge according to item (1), wherein the control voltage generator is comprised of at least a resistor and a capacitor.