JPH049451B2 - - 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 oscillator to measure the pressure of gas around it.

[Conventional technology]

It has recently been revealed that the resonant resistance of crystal vibration (particularly 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 operate from atmospheric pressure to approximately 10 ^-3 Torr with a single sensor. It has become clear that it is possible to realize a gas pressure gauge that can measure This is, for example, the monthly magazine "Instrument", 1984
It is disclosed in the section ``Development of ultra-small vacuum sensor using crystal oscillator'', Vol. 27, No. 7, 2013.

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 functions of gas (N ₂ ) pressure and resonant resistance, resonant current, and resonant frequency of a crystal resonator in a bending mode of about 32 kHz. The resonance 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 crystal resonator has effective sensitivity to pressure from atmospheric pressure to about 10 ^-3 Torr. Here, if this crystal resonator is driven at a constant voltage, a resonant current-gas pressure curve indicated by _i0 in the figure is obtained. It is similar to the resonant resistance and is approximately
Pressure sensitive up to 10 ^-3 Torr. 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 is
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 a comparison of the phase difference between the output signal of the amplifier 2 and the output signal of the variable frequency oscillator 1. and a phase comparator 3 that outputs a signal proportional to the phase difference, and a low-pass filter 4 that generates a DC voltage proportional to the output signal of the phase comparator 3. The output voltage of the generator 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.

Since the operating principle of the PLL circuit is already widely known, it is omitted here, but the output signal of the frequency variable oscillator 1 (i.e., the crystal resonator 5
The oscillation frequency of the variable frequency oscillator 1 is controlled so that the phase difference between the drive voltage (driving voltage) and the output signal of the amplifier 2 (that is, 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. 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
The pressure of the gas is determined by the deflection angle of the needle of the meter 9.

As shown in FIG. 3, when the gas pressure decreases, the output voltage V _DC of the rectifier circuit 7 changes to the resonance current i ₀ in FIG.
Consistent with the trend of increasing (the maximum value of V _DC
V _U and the minimum value is V _L ). If the meter 9 is driven in this state, the pressure will decrease and the deflection angle of the meter 9 will increase, giving an indication that is contrary to common sense for a pressure gauge. Therefore, the meter drive circuit reverses the output voltage V _DC of the rectifier circuit 7 as shown by the curve V _M in FIG. At times, the deflection angle of the pointer of the meter 9 is made zero.

[Problem that the invention seeks to solve]

In a conventional gas pressure gauge using an automatic oscillator, a crystal resonator is used in the feedback loop of the self-excited oscillation circuit, so an output voltage corresponding to the resonant resistance of the crystal resonator is obtained. In addition to the resonance resistance value, it is strongly influenced by the loop gain of the self-excited oscillator. In addition, the resonance resistance of the crystal resonator is 3 digits (30kΩ in high vacuum, 300kΩ at atmospheric pressure).
Strong) and above also change depending on the pressure, so in order to prevent the output voltage of the oscillator from saturating in high vacuum, the driving voltage level of the crystal oscillator must be lowered, which makes it possible to reduce the voltage near normal pressure. self-sustained oscillation becomes difficult. In other words, in the self-oscillation method,
In general, the output voltage for reading pressure is strongly influenced by factors other than the resonance resistance of the crystal oscillator that is the pressure sensor, and the pressure measurement range as a measuring device is the pressure range within which the crystal oscillator can maintain effective sensitivity. As a result, the performance of the crystal resonator as a pressure sensor cannot be fully utilized. Also, to maintain stable oscillation,
Normally, the crystal resonator and oscillation circuit must be placed as close as possible (the longer the sensor cable, the more unstable the oscillation will be due to stray capacitance).
This is a major practical 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. Therefore, as shown in FIGS. 1 and 3, the output voltage V _DC of the rectifier circuit is equal to the resonance current i _O of the crystal resonator, and the output voltage V _M of the meter drive circuit ( The deflection angle of the needle is V _M
) is the resonant resistance of the crystal resonator 5
Match R _O respectively. That is, since the meter drive voltage V _M is determined only by the resonance resistance R _O of the crystal resonator, such a gas pressure gauge can fully utilize the performance of the crystal resonator as a pressure sensor. Furthermore, if the drive source impedance of the crystal oscillator and the input impedance of the amplifier that amplifies the resonant current of the crystal oscillator are sufficiently low, the length of the cable connecting the sensor (crystal oscillator) and the main body of the gas pressure gauge can be reduced. for a very long time (e.g. from 30
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, that lock 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 crystal oscillator changes by several Hz), but in order to maintain the lock state, the resonant frequency of the crystal oscillator, which changes by several Hz, must be adjusted to a very high precision (the resonant frequency of the crystal oscillator changes by several Hz). Since Q is approximately 100,000, it is necessary to adjust the oscillation frequency of the variable frequency oscillator with an accuracy of at least 1×10 ⁻⁵ .

The present invention was made in view of the above circumstances, and when a power switch or some kind of start 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. Figure 4 shows
3 illustrates the process in which the variable frequency oscillator of the PLL is locked at the resonant frequency of the crystal resonator according to the implementation of the present invention. Turn on the power switch (not shown)
When turned ON (time t=0), the variable frequency 1
The oscillation frequency of fosc gradually decreases and eventually becomes equal to the resonant frequency _fO 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= _fosc .

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. 1 and has the function of sweeping the oscillation frequency. The switch circuit 11 is normally in the "closed" state and applies the output voltage of the control voltage generator 10 to the variable frequency oscillator 1, but when the crystal oscillator 5 resonates (that is, the PLL is locked)
Then, the output voltage of the rectifier circuit 7 appears, and the output voltage of the rectifier circuit 7 becomes an "open" state. (see FIG. 4), and the PLL circuit becomes stable in its own state. The switch circuit 11 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 a monomulti, 10b is an integrator, and 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. 7a). ).

This pulse is applied to the integrator 10b, and specifically, a triangular wave (FIG. 7b) with a peak value of about 15V is obtained. This triangular wave is applied to the attenuator 10c, and specifically, the output voltage (control voltage
At V _C , the waveform shown in Figure 7c) is obtained. The magnitude of the control voltage V _C is determined by the characteristics of the variable frequency oscillator 1. The control voltage V _C is applied to the variable frequency oscillator 1, so that the oscillation frequency of the variable frequency oscillator 1 changes as shown in FIG. 7d.

FIG. 8 shows another example of the configuration of the control voltage generator 10, and FIG. 8a shows a resistor 10e and a capacitor 10.
The charging circuit shown in FIG. 8B is composed of only the resistor 10e and the capacitor 10f. If the frequency control voltage input impedance of the variable frequency oscillator 1 is sufficiently high, the buffer 10g is not necessarily required. 9a shows the waveform of the control voltage V _C in the configuration example shown in FIG. 8, and FIG. 9b shows the change in the oscillation frequency of the variable frequency oscillator 1. In FIG. Although the configuration example shown in FIG. 8 has a very simple configuration, it has the following drawbacks. That is, the ninth
In figure b, the time t of the variable frequency oscillator 1
If the oscillation frequency at = 0 is relatively high (f ₁ ), the PLL
The time it takes to lock becomes very long (t ₁ ) or it never locks. On the other hand, if the oscillation frequency of the variable frequency oscillator 1 is relatively low (f ₃ ), the rate of frequency change when crossing the resonant frequency f _O of the crystal oscillator 5 is too large, and the crystal oscillator 5 cannot respond. As a result, the PLL will no longer lock. The disadvantage of the configuration example shown in FIG. 8 is that the frequency range in which the PLL locks becomes narrow as described above, and this is because the temporal change in the control voltage V _C is a charging (discharging) curve. On the other hand, in the configuration example shown in FIG. 6, since the temporal change in the control voltage V _C is linear (FIG. 7c), it is clear that the configuration example shown in FIG. 8 does not have the drawbacks. .

FIG. 10 shows how the control voltage is applied to the low pass filter 4.
An example of a configuration is shown in which the oscillation frequency of the variable frequency oscillator 1 is changed by applying .

Since a low-pass filter can generally pass direct current, the configuration shown in FIG. 10 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.

〔Effect of the invention〕

As described above, in a crystal gas pressure gauge in which a crystal resonator is driven by a PLL circuit, the present invention provides a variable frequency oscillator in the PLL circuit, or a low frequency By applying a voltage whose peak value changes over time to the filter, the oscillation frequency of the variable frequency oscillator is swept, so that the resonant frequency of the crystal oscillator, which is the pressure sensor, is within the frequency sweep amplification. 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 uses the variable frequency oscillator itself built into the PLL circuit, so the circuit configuration is simple; The frequency can be varied within the capture range of the circuit (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 varied with respect to the resonant frequency of the crystal resonator). It must be able to tolerate fluctuations caused by aging of the oscillation frequency of the oscillator, variations in component constants, etc. (In the 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, 13%
This has great practical effects, such as:

Although not specified in the embodiments of the present invention,
After the PLL circuit unit is locked at the resonant frequency of the crystal oscillator 5, instead of turning off the control voltage using the switch circuit 11, a means for maintaining the control voltage at a certain constant value is introduced. It is obvious that the switch circuit 11 can be removed by using the above method, and it goes without saying that such means are also included in the spirit 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]

Figure 1 shows the resonant resistance, resonant current, and
A diagram showing the relationship between resonance frequency and gas (N ₂ ) pressure,
Figure 2 is an electronic circuit block diagram of a crystal gas pressure gauge, Figure 3 is a diagram showing the relationship between the output voltage of the rectifier circuit in the electronic circuit and the gas pressure of the meter drive voltage, and Figure 4 is the frequency of the PLL. A diagram showing the process in which the variable oscillator locks at the resonant frequency of the crystal resonator, FIG. 5 is a block diagram of an embodiment of the present invention, and FIG. 6 is a block diagram showing the configuration of the control voltage generator in the embodiment of the present invention. , 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, and FIG. 9 is a diagram showing each configuration of the embodiment shown in FIG. 8. FIG. 10 is a diagram showing a partial waveform, and 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, 11...switch circuit, 10a...monomulti, 10b...integrator, 10c...attenuator, 10d...switch, 10e...resistance , 10
f...Capacitor, 10g...Batsuhua.

Claims (1)

[Claims] 1. A phase locked loop (PLL) circuit section comprising at least a variable frequency oscillator, a phase comparator, a reduction filter, and an amplifier, and a phase locked loop (PLL) circuit section connected between the variable frequency oscillator and the amplifier. It has a crystal oscillator and a display section connected to the PLL 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 crystal gas pressure gauge includes a control voltage generator whose output voltage changes over time, and the control voltage generator is connected to a frequency control terminal of the variable frequency oscillator so as to sweep the oscillation frequency of the variable frequency oscillator. Or a crystal gas pressure gauge, characterized in that it is connected to the reduction filter. 2. The device according to item 1, characterized in that 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 reduction filter. crystal gas pressure gauge. 3. The crystal gas pressure gauge according to item 1, wherein the control voltage generator is composed of at least a monomultiplier and an integrator. 4. The control voltage generator is comprised of at least a resistor and a capacitor.
Crystal gas pressure gauge as described in section.