JPS5838739B2 - pressure gauge - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pressure gauge configured to directly or indirectly apply a pressure to be measured (including differential pressure) to a vibrator and obtain the pressure to be measured from the natural frequency at that time. It is something.

In conventional pressure gauges of this type, the output signal varies greatly depending on the fluid density around the vibrator.

For this reason, the types of fluids to be measured are limited to those with the same density.

Furthermore, since the fluid density varies greatly depending on the temperature, there is also the problem that it can only be used in a measurement atmosphere at a constant temperature.

The purpose of the present invention is to solve the above problems, namely:
The objective is to realize a pressure gauge that can measure fluids of any density.

The present invention will be described in detail below using the drawings.

FIG. 1 is a cross-sectional view showing an embodiment of the pressure receiving portion of a pressure gauge according to the present invention, and FIG. 2 is a cross-sectional view taken along line XX in FIG.

In FIGS. 1 and 2, reference numeral 1 denotes a vibrator made of a stepped container having a stepped portion 11. In FIG.

In this vibrator 1, a thin cylindrical portion 13 and a thick inner cylindrical portion 14 continuous thereto are formed by a hole 12 drilled along the central axis.

In addition, the thick cylindrical portion 14 near the stepped portion 11 of the vibrator 1 has three counterbore holes 15 to 1 extending from the outer peripheral surface to near the inner wall.
7 are formed spaced apart by a constant angle (900).

2 and 3 are vibration detection piezoelectric elements attached to the bottoms of the counterbore holes 15 and 16, and 4 is a drive piezoelectric element attached to the bottom of the counterbore holes 17.

6 is a body, 7 is an OIJ song 8 that seals between the vibrator 1 and the body 6, and a bolt that connects the vibrator 1 and the body 6.

The body 6 is provided with a pressure introduction port 61 that communicates with the inside of the vibrator 1.

FIG. 3 is a diagram showing typical vibration frequency-gain characteristics of a cylindrical vibrator such as vibrator 1.

This characteristic is achieved by using a single piezoelectric element to drive the vibrator and detect vibration, and the piezoelectric element for vibration detection (which is always placed at a position where the maximum amplitude can be obtained) in response to the voltage applied to the driving piezoelectric element. The ratio is expressed in decibels and is defined as the gain.

In the following description, it is assumed that the vibrator 1 shown in FIGS. 1 and 2 has this third characteristic.

A, B, C, D, and E in Figure 3 are the gains when the in-plane vibration mode is 3rd, 4th, 2nd, 5th, and 6th, and the axial vibration mode is 1st, respectively. It shows.

FIG. 4 is a diagram showing an embodiment of the overall configuration of the device of the present invention shown in FIGS. 1 and 2 (the same parts as in FIGS. ).

In the figure, 60.70 is a charge amplifier that receives the output signals of the piezoelectric elements 2 and 3, 80.90 is a coefficient circuit that applies a constant value to the output signal of the charge amplifier 70, and 10
0 is an adder circuit that adds the output signals of the charge amplifier 60 and the coefficient circuit 80, and 110 is a 9 arithmetic circuit that subtracts the output signal of the coefficient circuit 90 from the output signal of the charge amplifier 60.

Further, 120 and 130 are low-pass filters that pass signals having a frequency of about 6 kHz or less, and 140 and 150 are amplifiers that receive the output signals of the low-pass filters 120 and 130, respectively, and output a voltage with a constant amplitude.

160 is a switch that selects either the output voltage of the amplifiers 140, 150 and applies it to the piezoelectric element 4; 170, 180;
are conversion circuits that receive the output signals of the amplifiers 140 and 150, respectively, and output voltages corresponding to the frequencies of the signals.

This conversion circuit 170.degree. 180 also has a hold function.

190 is an arithmetic circuit that receives the output signals of the conversion circuits 170 and 180 and outputs a signal corresponding to the pressure to be measured.

A control circuit 200 alternately switches the switch 160 at regular intervals and holds the values of the conversion circuits 170 and 180 immediately before switching the switch 160.

When the switch 160 is connected to the amplifier 140 side, the piezoelectric elements 2 to 4, the charge amplifiers 60 and 70, the coefficient circuit 80, the addition circuit 100, the low-pass filter 120, and the amplifier 140 act as a drive unit that vibrates the vibrator 1. Intimidate A.

In addition, when the switch 160 is connected to the amplifier 150 side, the piezoelectric elements 2 to 4, the charge amplifiers 60 and 70,
Coefficient circuit 90, subtraction circuit 110, low pass filter 13
0 and the amplifier 150 drive the drive section B that vibrates the vibrator 1.

Between the signal output from one point on the closed loop consisting of the drive unit A and the vibrator 1, and the signal returned after completing one cycle, there is almost no signal for the fourth-order vibration mode. It is constructed so that there is no phase shift.

Furthermore, there is a huge gap between the signal output from one point on the closed loop consisting of the drive unit B and the vibrator 1 and the signal returned after completing one cycle of the signal for the second-order vibration mode. It is constructed so that there is no phase shift.

Signals that can pass through the low-pass filters 120 and 130 include 3rd and 5th vibration modes as well as 2nd and 4th vibration modes; In the case of the next and fifth vibration modes, the piezoelectric element 2 is
output has reverse polarity.

Therefore, almost no signal components in the third and fifth vibration modes are positively fed back to the piezoelectric element 4.

Therefore, in a steady operating state (here, a steady operating state in which the switch 160 is connected to the amplifier 140 side will be described), the following signal VatVb is output from the charge amplifier 60.70.

The specific configuration of the coefficient circuit 80 is as follows:
The output signal of is multiplied by a value of rn2/rn□ (since m2 and m6 are signals of the same mode, this ratio can be said to be constant).

Therefore, the output signal of the adder circuit 100 is ■.

becomes as follows. However: Coefficient value of coefficient circuit 80 (m2/m'2) (2)
■c shown in the formula is a signal corresponding only to the fourth-order vibration mode.

And this ■. A signal Ve corresponding to is applied from the amplifier 140 to the piezoelectric element 4.

Therefore, in this state, the vibrator 1 reliably vibrates in the fourth vibration mode (this means that r in equation (1)
(meaning that n2 + rn'2 is approximately equal to zero)
.

Next, a state in which the switch 160 is connected to the amplifier 150 side will be explained.

At this time, the output signal Vat of the charge amplifier 60.70
Vb is determined by equation (1) and the specific configuration of the coefficient circuit 90, which gives the output signal of the charge amplifier 70 a value of m4olm4o' (
Since m4o and rn40' are signal valves in the same mode, this ratio can be said to be constant.

Therefore, the output signal Vd of the subtraction circuit 110 is as follows.

However, k': coefficient value of coefficient circuit 90 (m40 / m4ol)
Vd shown by this equation (4) is a signal corresponding only to the second-order vibration mode.

Then, the voltage is applied to the piezoelectric element 4 from the amplifier 150 of f corresponding to this Vd.

Therefore, in this state, the vibrator 1 reliably vibrates in the second-order vibration mode (this means m4 in equation (3)
(meaning that o2m4o' is approximately equal to zero).

Therefore, by switching the switch 160, the vibrator 1
is vibrating alternately in the second-order or fourth-order vibration mode.

The natural frequencies of the second and fourth vibration modes of the vibrator 1 in this state are f2. If f4 is set, the following formula holds true.

By eliminating ρX from equation (5) and rearranging for P, the following equation can be obtained.

Here, αI, α2', C2', β2' l C4'
, β4 are constant, so if A, B, C, D, and E are constants, equation (6) becomes as follows.

Five different pressures (reference pressure) P are applied and the vibration frequency at that time is f4. f2 (output signal Ve of amplifiers 140, 150,
Corresponding to the frequency of Vf), it is easy to obtain A,
The values of B, C, D, and E can be determined.

Therefore, A, B by this method. If C, D, and E are determined in advance, the frequency f2. when the pressure to be measured is applied.
From f4, the magnitude of the pressure to be measured can be measured based on equation (7).

The arithmetic circuit 190 performs this calculation (conversion circuit 1
The output signal of 70.180 is f4. (The value corresponds to f2).

A pressure gauge with this configuration is not affected by fluid density (7)
The pressure to be measured P is determined based on the formula.

Therefore, in principle, errors due to changes in the fluid density ρX do not occur.

In addition, in the above explanation, an example was shown in which a piezoelectric element installed in a counterbore hole was used to apply force to a vibrator and detect its strain. It is not necessarily necessary to attach the piezoelectric element to the piezoelectric element, and it is also possible to use something other than a piezoelectric element.

In addition, multiple piezoelectric elements are used for vibration detection, and an adding circuit,
We have shown an example in which mode rejection is performed using an arithmetic circuit and a filter, but depending on the characteristics of the vibrator, it is possible to simply pass the output signal of one piezoelectric element through two types of filters.
In some cases, a signal of a specific mode can be obtained.

Naturally, the same effect can be obtained even if the vibration mode is selected to be other than secondary and quartic.

Also, the frequency f2. Since equation (5) regarding f4 is also an approximate equation, in order to obtain a higher precision, f2. An approximate expression regarding f4 may be used.

As described above, according to the present invention, it is possible to realize a pressure gauge that is not affected by fluid density, that is, a pressure gauge that can measure fluids of any density.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the pressure receiving part of the pressure gauge according to the present invention, FIG. 2 is a sectional view taken along XX' in FIG. 1, and FIG. 3 is a typical characteristic diagram of a cylindrical vibrator. FIG. 4 is a diagram showing an embodiment of the overall configuration of the device of the present invention. 1... Vibrator, 2, 3... Piezoelectric element for vibration detection, 4
... Drive piezoelectric element, 6... Body, 7... O-ring, 8... Volt, 60.70... Charge amplifier, 80°90... Coefficient circuit, 100 addition circuit, 11
0... Subtraction circuit, 120, 130... Filter, 1
40,150...Amplifier, 160...Switch, 1
70, 180... Conversion circuit, 190... Arithmetic circuit,
200...control circuit.

Claims (1)

[Claims] 1. A cylindrical vibrator to which a pressure to be measured is applied, a driving means for vibrating this cylindrical vibrator, a vibration detecting means for detecting the vibration of the cylindrical vibrator, and a signal from the vibration detecting means is input. a first circuit means for vibrating the cylindrical vibrator at a constant vibration -E-) via the drive means; a second circuit means for vibrating in a vibration mode; a control circuit for alternately operating the first circuit means and the second circuit means; and a signal corresponding to the natural frequency in the certain vibration mode. and a calculation circuit that inputs a signal corresponding to the natural frequency in the vibration mode, performs a predetermined calculation, and outputs a signal related to the pressure to be measured.