JPH01148932A - Gas pressure gauge - Google Patents

Abstract

PURPOSE:To enhance measuring accuracy, by employing circuit constitution based on a specific formula to exclude the effect of the variation component of inherent impedance. CONSTITUTION:Circuit constitution satisfying a condition of predetermined formula (wherein Vc is the amplitude of pulse voltage, Vo is constant voltage, k is an adjustable coefficient and Ic is a resonance current) is employed. An analogue switch 11 switches the DC constant voltage from an adder circuit 4 corresponding to the output signal of a polarity discrimination circuit 12 not only to obtain predetermined voltage Vc but also to apply the same to a quartz vibrator 2. A phase shifting circuit 13 is connected to the circuit 12 and discriminates the polarity of the AC signal V2 supplied from the circuit 13 to apply the same to the switch 11. A current/voltage converter circuit 14 for converting the current Ic flowing to the vibrator 2 voltage is connected to the output side of the vibrator 2. The vibrator 2 receives the voltage Vc from the switch 11 to permit a current Ic to flow. By this method, the apparent inherent impedance of the vibrator 2 can be made constant without being affected by the vibration component.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a gas pressure gauge using a crystal resonator, particularly a self-oscillation type gas pressure gauge.

[Background technology and its problems]

It is known that there is a certain correlation between the pressure of a specific type of gas and the impedance of a crystal resonator placed in the gas in a series resonance state.

Therefore, if the relationship between the pressure value of the gas and the impedance value of the crystal oscillator is determined in advance, the pressure of a gas whose composition is known can be determined from the impedance value of the crystal oscillator.
A self-oscillation type gas pressure gauge based on this principle has also been put into practical use.

By the way, the series resonance impedance Z of a crystal resonator in gas is vacuum (for example, 10-'T).

From the characteristic impedance Zo in (below rr) and the impedance change ΔZ depending on the gas pressure, Z = ΔZ + Z
o...Represented by (1).

It is known as a size effect that the impedance change ΔZ shows a high correlation with the gas pressure when the crystal resonators have the same structure and the same lot, and this correlation is determined by the shape of the crystal resonator. On the other hand, even if the crystal resonators have the same structure and the same lot, the specific impedance Zo will vary depending on the individual crystal resonators due to differences in the amount of internal friction, differences in the amount of vibration energy leaking into the crystal resonator fixing base, etc. Variations are observed between the vibrators. In addition, the characteristic impedance Zo varies to some extent due to changes in the amount of leakage of vibration energy described above, or due to contamination of the crystal resonator itself with oil mist in the gas. Therefore, the actual specific impedance Zo at this time is calculated from the design impedance Zop and the fluctuation component δZo, as follows: Zo=Zop+δZ o −...(2)
It is expressed as

Therefore, when a gas pressure gauge is constructed using an actual crystal resonator 2 in which the characteristic impedance Zo varies, the following problem occurs.

That is, the series resonant impedance Z of the crystal resonator 2 is as follows: Ic=Ve/Z-(3) where the equivalent excitation voltage applied to the crystal resonator 2 is Ve1, and the resonant current is Ic.
Alternatively, from the above equation (1), Ic=Ve ΔZ+Zo) (4).

Now, if Ve is a constant value and Zo matches the design impedance ZOp, that is, δZo=O, then equation (4) is expressed as Ic=V
ΔZ + Z op) - (5), which depends only on the impedance change ΔZ. Therefore, by converting the current Ic into pressure using an appropriate conversion means, one pressure value can be determined for a specific impedance change ΔZ.

However, in reality, the characteristic impedance Zo in equation (4) includes δZo as shown in equation (2), and also varies from crystal unit to crystal unit, so δZo≠0, and the resonant current Ic
The relationship between the specific impedance Zo and the specific impedance Zo differs depending on the crystal oscillator. In other words, the equation (5) does not match, and an error occurs in the relationship between the resonance current Ic and the gas pressure.

Therefore, in order to prevent such errors from occurring, it is possible to measure the intrinsic impedance Zo of the crystal resonator and select and use only those that are close to the design impedance Zop, but this would significantly reduce yield and be impractical. .

Another solution is to set the design impedance Zop high in advance and connect a variable correction resistor in series with the crystal oscillator to match the design impedance Zop. Since the circuit includes a variable resistor, there is a problem that the circuit becomes unstable.

Another solution is to calculate the series resonant impedance Z from the resonant current rc and subtract the characteristic impedance Zo including the fluctuation component δZo to obtain the impedance change ΔZ due to only the pressure. , or a microcomputer including an analog-to-digital converter is required, resulting in a problem that the circuit becomes complicated and expensive.

Note that symbols Ic representing voltage values and current values used in the explanation,
In order to simplify the expression, Ve, etc. represent the effective values of the respective voltage values and current values unless otherwise specified. The same applies to Vo, V, , 6, and 3, which will be described later.

[Means for solving problems]

The present invention aims to provide a gas pressure gauge that solves the problems existing in the above-mentioned background art, and is achieved by a gas pressure gauge 1 shown below.

That is, the gas pressure gauge 1 according to the present invention applies a predetermined pulse voltage Vc (voltage amplitude value) to the crystal oscillator 2 in the gas, and based on the resonance current Ic (current value) of the crystal oscillator 2, In a gas pressure gauge that measures the pressure of gas, in particular, the pulse voltage Vc changes from Vc=Vo+ to -Ic(
It is characterized by adopting a circuit configuration that satisfies the following conditional expressions: Vo (constant voltage) and k (variably adjustable coefficient). Therefore, in the present invention, the correction voltage k・corresponding to the resonant current Ic
It includes at least a coefficient circuit 3 that obtains Ic, and an adder circuit 4 that adds -Ic and a constant voltage Vo from a constant voltage power supply to this correction voltage.

Here, Vc is the amplitude value of the pulse voltage applied to the crystal resonator 2, and the waveform of the pulse voltage has a duty ratio of 50%.
When it is a rectangular wave, it has a constant relationship with the equivalent excitation voltage Ve that is effective for excitation of the crystal resonator 2, and is expressed as follows: Ve=vc-fr/yr
-(6) is known.

Therefore, the relationship between Ve and Vc is simply expressed as Ve=k
, -Vc -(7).

[For production]

Next, the operation of the present invention will be explained.

First, from each equation (3), (4), and (2) above, Ic
= Ve ΔZ + Zop + δZ o) −(8
).

Now, the applied pulse voltage Vc is calculated by the coefficient circuit 3 and the adder circuit 4 as follows: Vc=Vo+Ck ・I c) ・
・If the conditions in (9) are set to hold, (7),
From equations (8) and (9), I c−k + (Vo+ k I c) pΔZ+Zop
+δZO) - (10) If we further organize Ic, E c= k t ・Vo/(ΔZ+Zop+δZ O
k Ik )” (11).

As a result, if k, - is adjusted to = δZO, Ic = kI
・■o bar ΔZ + Z op) =-(12
), and this equation matches equation (5) by replacing ・Vo with Ve. In other words, the impedance change Δ
Once Z is specified, the resonant current Ic can be specified without being influenced by δZo, and the error can be eliminated.

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. Fig. 1 is a block circuit diagram of a gas pressure gauge according to the present invention, Fig. 2 is a time chart of signals in the inner portion of Fig. 1, and Fig. 3 is an electric circuit showing a specific circuit example of the gas pressure gauge. FIG. 4 is a gas pressure versus resonance current characteristic diagram.

First, the block configuration and functions of the gas pressure gauge 1 will be explained with reference to FIGS. 1 and 2.

2 is a crystal oscillator serving as a pressure measuring element. The output side of an adder circuit 4 is connected to this crystal resonator 2 via an analog switch 11. This analog switch 11 switches the DC constant voltage from the adder circuit 4 in response to the output signal of the polarity discrimination circuit 12 to obtain a predetermined pulse voltage Vc shown in FIG. Apply.

On the other hand, a phase shift circuit 13 is connected to the polarity discrimination circuit 12, and the AC signal V shown in FIG. 2(c) is supplied from the circuit 13.
, and applies it to the analog switch 11.

The output signal v3 of the polarity discrimination circuit 12 is shown in FIG. 2(d).
The pulse signal will be as shown in .

On the other hand, a current-voltage conversion circuit 14 is connected to the output side of the crystal oscillator 2, which converts the sinusoidal resonant current Ic shown in FIG. 2(a) flowing through the crystal oscillator 2 into a voltage. Note that the crystal resonator 2 is placed in a gas atmosphere when measuring gas pressure, and the pulse voltage V is applied from the analog switch 11.
When c is applied, a resonant current IC shown in the characteristic curve of FIG. 4 flows. The output signal V of the current-voltage conversion circuit 14 is shown in FIG. 2(b). Further, the phase shift circuit 13 is connected to the output side of the circuit 14. This phase shift circuit 13 has a function of shifting the phase of the output signal V1 of the current-voltage conversion circuit 14 by a predetermined amount. like this,
With the self-excited oscillation loop and phase shift circuit 13 shown in FIG.
The crystal resonator 2 can be fired near the electrical series resonance frequency, and optimal phase conditions and gain conditions can be set for the crystal resonator 2.

Furthermore, a display 16 is further connected to the output side of the current-voltage conversion circuit 14 via a detection circuit 15.

The output signal (2) of the current-voltage conversion circuit 14 is a sinusoidal AC output having an amplitude corresponding to the impedance value of the crystal resonator 2, that is, the magnitude of the gas pressure (inversely proportional to the impedance value). Therefore, the detection circuit 15 detects the signal V.
This can be converted into a DC voltage Vs as shown in FIG. 2(f), and the gas pressure can be displayed on a display 16 such as a meter having a corresponding display scale. Note that the output of the detection circuit 15 may also be used as a control signal for a printer or other actuator.

On the other hand, the DC voltage Vs, which is the output of the detection circuit 15, is input to the coefficient circuit 3. The coefficient circuit 3 calculates the coefficient k of the linear function so that the output voltage has a predetermined magnification with respect to the input voltage.
o is set so as to obtain a DC correction voltage having a magnitude of ko-vs. If the coefficient determined by the detection circuit 15 and the current-voltage conversion circuit 14 is m, then vs-m-Ic, so the output voltage ko-vs of the coefficient circuit 3 is k-Ic (k=
m-ko). Further, the coefficient ko is configured to be arbitrarily adjustable, thereby variably setting the magnitude of the coefficient for the resonance current Ic.

Furthermore, the output voltage of the coefficient circuit 3, that is, the correction voltage corresponding to -Ic, and the constant voltage V of FIG. 2(g) supplied from the constant voltage DC power supply 17.

is input to the adder circuit 4, and the output obtained by adding the pressures of both types, that is, Vo+ k ・I c=Vc −=(1
3) is applied to the analog switch 11 (FIG. 2(h)). Therefore, equation (13) is a conditional equation based on the present invention, and it is possible to have a circuit configuration that is not affected by the fluctuation component δZo, and it is possible to make the apparent characteristic impedance of the crystal resonator 2 constant.

FIG. 3 shows an electric circuit diagram that further embodies the gas pressure gauge 1 according to the present invention. In addition, in FIGS. 2 and 3, the same parts as in FIG. 1 are given the same reference numerals to clarify the structure. However, in the circuit shown in Fig. 3, (f) in Fig. 2
, (h) should be read with the polarity reversed.

First, the polarity determination circuit 12 uses a comparator 31 with one input set to zero level, and applies this output to the analog switch 11. In addition, the operational amplifier 32 and the resistor 33,
Further, the current-voltage conversion circuit 14 is configured by a capacitor 34 connected as necessary. Furthermore, capacitor 35
A CR circuit using a resistor 36 constitutes a phase shift circuit 13, and an operational amplifier 37.38 and a diode 39.40
, resistor 41, 42.43.44.45, capacitor 46
The detection circuit 15 is configured by: On the other hand, 50 is the coefficient circuit 3 using a variable resistor 51 and an operational amplifier 52.
The coefficient ko can be variably adjusted by a variable resistor (potentiometer) 51. That is, by adjusting the variable resistor 51, the apparent characteristic impedance of each crystal resonator can be made constant. Note that 53 and 54 indicate fixed resistances.

Although the embodiments have been described in detail above, the present invention is not limited to these embodiments.

For example, each block in a block circuit can be replaced by another electrical circuit with the same function. Further, a configuration may be adopted in which other optional accessory circuits (means) such as a temperature correction circuit are added. Other changes may be made in the configuration, arrangement, etc. of the net portions without departing from the spirit of the present invention.

〔Effect of the invention〕

As described above, the gas pressure gauge according to the present invention employs a circuit configuration based on a certain conditional expression to eliminate the influence of the fluctuation component of the characteristic impedance, and thus obtains the following significant effects.

■ It is possible to improve measurement accuracy and quality by eliminating variations. In particular, even if the fluctuation component of the crystal resonator's characteristic impedance changes due to drift, it can be readjusted, and high precision can be maintained over a long period of time. Measurement ability can be maintained.

■ Not only can all crystal units be used effectively, but there is no need to connect a variable resistor to the crystal unit as in the past, resulting in high stability.Furthermore, the circuit configuration is extremely simple, so It can contribute to cost reduction and miniaturization.

■ The apparent intrinsic impedance of the crystal resonator can be freely selected. Therefore, if the impedance is selected relatively small (large), the resonant current will change greatly even if the impedance change is small, and the sensitivity to low (high) pressure can be increased, greatly increasing the degree of freedom in sensitivity design. You can improve.

[Brief explanation of the drawing]

Figure 1: 2: Block circuit diagram of the gas pressure gauge according to the present invention; Figure 2: Figure 1: Time chart of signals in the inner container; Figure 3: Electrical circuit showing a specific circuit example of the gas pressure gauge. Figure 4: Gas pressure vs. crystal resonator current characteristic diagram. In the drawing, l: gas pressure gauge 2 = crystal oscillator 3: coefficient circuit
4: Adder circuit patent applicant: Patent attorney representing Nagano Keiki Seisakusho Co., Ltd.
Lower 1) Shigeru Figure 1

Claims (1)

[Scope of Claims] A gas pressure gauge that applies a predetermined pulse voltage to a crystal oscillator in gas and measures the pressure of the gas based on the resonance current flowing through the crystal oscillator, has a circuit configuration that satisfies the following conditional expression: A gas pressure gauge characterized by comprising: Vc=Vo+k・Ic where Vc: Pulse voltage amplitude Vo: Constant voltage k: Variable adjustable coefficient Ic: Resonant current (effective value)