JPS5945931B2 - Vibrating pressure gauge - Google Patents

Description

Detailed Description of the Invention (Technical Field of the Invention) The present invention provides a method for applying measured pressure (including differential pressure) to a vibrator directly or indirectly, and calculating the measured pressure from the natural frequency of the vibrator at that time. This relates to a vibrating pressure gauge that determines the

(Prior Art) Pressure gauges have been known that apply pressure or a force corresponding to pressure to a vibrator and determine the pressure from the natural frequency of the vibrator.

However, this type of pressure gauge has the disadvantage that its output signal is affected by the fluid density and temperature around the vibrator.

For this reason, the type of fluid to be measured has the same density and can only be used at a constant temperature.

(Objective of the present invention) The object of the present invention is to eliminate such drawbacks of conventional devices, and to realize a vibrating pressure gauge that can measure fluids of any density and is not subject to limitations on operating temperature. It's about doing.

(Practical Figure 1 is a configuration diagram showing an example of a vibrator of a pressure gauge according to the present invention, in which a is a vertical cross-sectional view and b is a cross-sectional view taken along line bb in figure a.

This vibrator uses a thin cylindrical shape with a closed tip, and the measurement pressure T)1)DO is applied to the inside and outside of the cylindrical vibrator 1.
is designed to measure the differential pressure of the introduced girth wall pressure.

This cylindrical vibrator 1 has a thick flange portion 10, and four counterbore holes 11, 12, 13, and 14 are formed in this flange portion 10 at 90 degrees apart, reaching from the outer peripheral surface to near the inner wall. ing.

Piezoelectric elements 21 and 22 for driving the cylindrical vibrator 1 are attached to the bottoms of the counterbore holes 11 and 12, and piezoelectric elements 21 and 22 for driving the cylindrical vibrator 1 are attached to the bottoms of the counterbore holes 13 and 14 and to the tip of the cylindrical vibrator 1. Piezoelectric elements 23, 24, and 25 are attached to detect vibrations of this cylindrical vibrator 1.

30 is the body, 40 is the flange part of the vibrator 1 and the body 3
This is an O-ring that seals between the

FIG. 2 is an electrical circuit diagram of the device according to the invention.

In the figure, 3 is the signal elj from the piezoelectric element 23.25.
4 is a subtraction circuit that receives the signal else2 from the pressure element 23, 25 and calculates the difference signal between both signals; 5 is a subtraction circuit that receives the signal from the addition circuit 3; 6 is a second low-pass filter and amplifier that receives the signal from the subtraction circuit 4; 7 receives the output signal els89 of the first and second amplifiers 5 and 6; An adder circuit 8 applies a signal obtained by adding both signals to the piezoelectric element 21, and 8 inputs frequency signals ωi and ωj corresponding to the natural frequencies obtained from the first and second amplifiers, and performs predetermined calculations. signal e corresponding to the pressure to be measured.

This is an arithmetic circuit that outputs . Here, the piezoelectric elements 23, 2
5. The loop composed of the adder circuit 3, the first low-pass filter and amplifier 5, the adder circuit 7, and the piezoelectric element 21 vibrates in an annular direction when the vibrator 1 is cut in a plane perpendicular to its axis l. is a fourth-order vibration mode, and an oscillation circuit is formed in which vibration in the axial direction of the vibrator is a first-order vibration mode.

In addition, the loop composed of the piezoelectric element 23, 25, the pull g circuit 4, the second low-pass filter* and amplifier 6, the adder circuit 7, and the piezoelectric element 21 has an annular vibration in a fourth-order vibration mode. An oscillation circuit is formed in which vibration in the axial direction becomes a secondary vibration mode.

In this way, the vibrator 1 is driven by two oscillation loops, and as a result, the vibrator 1 vibrates in the fourth-order vibration mode in the annular direction as shown in Figure 3a. However, in the axial direction, it vibrates in a plurality of vibration modes including a primary vibration mode and a secondary vibration mode, as shown in FIG.

When a cylindrical vibrator with a closed tip vibrates in two different vibration modes in its axial direction, when pressure is applied inside the cylindrical vibrator 1, the tension in the cylindrical direction changes. The resonant frequency in each vibration mode changes.

Now, the natural frequency of each vibration mode is ωi
, ωj, these can be expressed by equations (1) and (2), respectively.

EOl+β(t to)
(□)ω”””ao2(' v2) ” po+Mi
/ho G (i-ho /ao-10/a□s A
p) Eo l+β(t to) ωJ2−” ” G(jt ho/
a□s 10/aot Δp) (2)a
o2 (t-siri ρ.

+Mj/h. However, 1s j is the axial vibration mode order of the cylindrical vibrator,
It is an integer (i\j) greater than or equal to 1.

Eo: temperature t.

Elastic modulus β: thermoelastic coefficient t: temperature ao: inner radius of vibrator 1 (t=to) C: Poissonization ρ.

: Density of oscillator 1 (2t.) ho = Thickness of oscillator 1 (
t=to) Equivalent surface density Δp of two M fluids: Pressure difference lo: Length G of vibrator 1 (1) h□/ &6@l□/ ao, Δp
)) G(j)ho/ao, lo/ao, Δp) is
Indicates that it is a function in parentheses.

In addition, assuming that the circular mode order n1, the axial mode order m1, the pressure sensitivity to the pressure difference Δp, Spnm1i, the density sensitivity to the body density ρX, Sdnm, the natural frequency of the cylinder is f.
is expressed in the functional form of equation (3) with respect to the natural frequency 9 m fn, rno in vacuum.

'n, m='n, mO(1+Sd -px)
(1+spΔp)(1+βt)
...(3) Also, pressure sensitivity Spnm1 density sensitivity S d
nm If Δnm is a constant depending on the shape of the vibrator, then Equations (4) and (5) are obtained.

(l-n2)2 ao 1-shi2 Spnm2□・-豐□...(4) 1+n2 h Eo・Δnm EO 8dnm= −(= −n+x) '=(5)
ρX a□ Now, the natural frequency ωi expressed by equations (1) and (2)
.

By calculating the frequency ratio γ of ωj, equation (6) is obtained.

7=(bib・=ρ・+Mj/h・.

ωJ ρo+Mi/h□ G (1) ho/a□t 10/aotΔp)G (
js ho/a□s 10/aOsΔp); (1+-(
Mj-Mi)) hOρOG (1s h□/ao* i'o/aosΔp) /
G(j, ho/ao, to/ao, Δp) ・(6
) In equation (6), the isometric surface density (equivalent mass) M of the fluid
has been analyzed by M, K Young, and r
Free V 1bration of F
1uid coupled C□axialCylin
drical 5heiles of Diff
erentLengthTransactions
of ASME Journal of App
Lied Mechanics* 480/ 48
4 (1976) J, it depends on the vibration mode order n in the annular direction (in FIG. 3a, the fourth vibration mode is n-4), and can be expressed by equation (7).

ρG-ao b9'n-n-1-a 2n□・□ ・・・・・・(7) n b□ aQ however ρ0: Density of measurement medium vinegar.

=Outer radius of the vibrator 1 (t to) In the device according to the present invention, there are multiple vibration modes in the axial direction of the vibrator 1, and in this embodiment, there are two vibration modes, primary and secondary. On the other hand, the vibration mode in the annular direction is equal and single (fourth-order vibration mode in this example), so in equation (6), the term (M j −M i ) is It can be made zero.

Therefore, equation (6) becomes as shown in equation (8).

~G(i, ho/ao, lo/ao, Δp)γ=□・・
...(8) G (J s ho/a os lo/a □ s
Δp) Therefore, as shown in equation (9), the differential pressure Δp corresponds to the frequency ratio γ, and the thermoelastic coefficient β and the density ρ of the measurement medium.

Don't be influenced by such things as L. Δp ”F (It J s
hO/aot lO/'aO) γ) "" (9) That is, in order to simplify the natural frequencies of the two modes in the axial direction, the pressure sensitivities of fo and f2 are set to 81. s2
If the density sensitivity is sdl and sd2 and high-order nonlinear terms are ignored, the differential pressure Δp1 is the fluid density ρ.

The following equation holds true for . f to f1o(1+S1Δp
+Sd1ρ.

)...(b) f22 f2o (1+S2Δp+5d2p
G) ・Fluid density ρ from (1m)αO) formula and α■ formula.

By eliminating , we obtain equation 12).

Δp=A ((ft/fto') (f2/f20
1)=B)...(2) However, A and B are calibration constants, f□.

) f20 are fl and f2 in vacuum, respectively.

As is clear from equation (12), if the rate of change from the reference state (flOjf2o) of the natural frequencies of two modes with different pressure sensitivities is measured, the fluid/body density ρ can be determined from equation (2).

The differential pressure Δp can be determined without being influenced by the above factors.

The arithmetic circuit 8 in FIG.
, and calculate the image frequency ratio γ, that is, (
By performing calculations such as 12X, an output signal e corresponding to the differential pressure Δp is obtained.

I am getting .

FIG. 4 is a longitudinal sectional view showing another example of the structure of the vibrator used in the present invention.

This vibrator is provided with thick-walled flange portions 10.20 at both ends of a cylindrical vibrator 10, and each of these flange portions 10.20 is provided with a counterbore hole reaching from the outer peripheral surface to the vicinity of the inner wall, and a neck counterbore hole is formed in each of these flange portions 10.20. A drive piezoelectric element 21.25 and a vibration detection piezoelectric element 23.26 are attached.

The pressure to be measured is introduced into the inside and outside of a cylindrical shape with one end open.

In each of the above-described embodiments, an example was shown in which a piezoelectric element was used to drive the vibrator and detect vibrations, but something other than a piezoelectric element may be used, and the mounting position may be other than the piezoelectric element.

Further, although the vibration of the vibrator is set to be a fourth-order vibration mode in the annular direction and a first-order and second-order vibration mode in the axial direction, other vibration modes may be used.

(Effects of the present invention) As explained above, according to the present invention, there is no influence of the density, temperature, etc. of the medium to be measured (therefore, fluids of any density can be measured. It is possible to realize a vibrating pressure gauge that is not subject to restrictions on operating temperature.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an example of a vibrator of a device according to the present invention, in which a is a vertical cross-sectional view, b is a cross-sectional view taken along line b in FIG. a, and FIG. 2 is an electric circuit diagram of a device according to the present invention. , FIG. 3 is an explanatory diagram of the operation of the vibrator, and FIG. 4 is a vertical sectional view showing another example of the vibrator used in the present invention. 1... Vibrator, 11-14... Counterbore, 21-2
5... Piezoelectric element, 30... Body, 3... Addition circuit, 4... Subtraction circuit, 5... 10th-pass filter and amplifier, 6... 20th-pass filter and Amplifier, 7... adder circuit, 8... arithmetic circuit.

Claims (1)

[Claims] 1. A cylindrical vibrator having one end closed and the other end open and having a thick flange on the other open end side, a driving means and vibration detecting means for the cylindrical vibrator attached near the flange, A vibration detecting means attached to one closed end of the cylindrical vibrator receives signals from each of the vibration detecting means and drives the cylindrical vibrator in a plurality of vibration modes in its axial direction. a circuit means for outputting a drive signal for driving the cylindrical vibrator so as to drive the cylindrical resonator; and an arithmetic circuit that outputs a signal related to the pressure difference applied between the inside and outside of the cylindrical vibrator.