JPS5834764B2 - Flow velocity flow measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a flow rate measuring device that detects a flow rate as an electrical signal corresponding thereto.

An object of the present invention is to realize a device of this type that has a simple structure and is inexpensive to manufacture.

FIG. 1 is a sectional view of the structure of an embodiment of the present invention, and FIG. 2 is a perspective view, partially shown in cross section.

In both figures, 1 is a conduit through which a fluid to be measured flows, and 2 is an orifice disposed within this conduit 1, which constitutes an obstacle wall to the flow.

This orifice 2 has a thickness d in the fluid flow direction larger than that of a known orifice, and is configured so that the entire orifice 2 does not flexibly deform.

Reference numeral 21 denotes a mounting flange for the orifice 2, which is fixed to the conduit 1 by means such as welding.

Reference numeral 3 denotes a stress detection section provided inside the orifice 2 so as to be integrated with the orifice.

FIG. 3 is an enlarged view of the vicinity of the stress detection section 3.

In this embodiment, a recess 31 is formed from the flange 21 to the orifice 2, and two piezoelectric elements 4 made of a single piezoelectric material 40 are placed in the recess 31, with their centers facing the flow of the orifice 2. The orifice 2 and the piezoelectric element 4 are integrated by pouring a sealing body 32 made of an insulating material such as glass into this recess and fixing it. I try to have a structure.

FIG. 4 is a configuration diagram showing an example of the piezoelectric element 4 used in the present invention.

Reference numeral 40 denotes a piezoelectric element material formed into a disk shape, for example, lithium niobate (LiNbO2) is used.

Reference numerals 41, 42, and 43.44 each represent semicircular electrodes, which are provided with the piezoelectric element material 40 sandwiched from both sides.

FIG. 5 shows an electrical circuit of the piezoelectric element configured as shown in FIG. 4, in which an amount of charge corresponding to the force applied to the piezoelectric element material 40 is generated between each electrode 41, 42 and 43, 44. .

Since the piezoelectric element having such a structure is electrically constituted by two piezoelectric elements made of one piezoelectric element material, it has the advantage that it is easy to manufacture and can be made compact as a whole.

The principle of measuring the flow rate in the device configured as described above is to detect the force of the liquid (proportional to the square of the flow rate) applied to the orifice 2 installed in the pipe line 1.

That is, the force F applied to the orifice 2 is expressed by equation (1).

However, K: proportionality constant gn: standard free fall acceleration (9,8 m/, 2) rf
: Specific weight of the fluid kg/rrt Area of the surface of the Ao nitric orifice 2 facing the flow (m') ■ Velocity of the two fluids (m/S) Here, the force F that the orifice 2 receives is the force that causes the orifice to flexibly deform. As shown in Figure 3, the inside of the orifice has different polarities on the left and right, centered on the center line l parallel to the surface facing the flow of the orifice, and the magnitude of the force A stress δ corresponding to F is generated.

Here, since the piezoelectric element 40 is located inside the orifice 2 and has an integral structure with this orifice, it receives stress +δ and -δ generated inside the orifice, and due to the piezoelectric effect, a voltage E corresponding to this stress δ is generated. occurs between each electrode.

This voltage E is expressed by equation (2). However, D: Piezoelectric constant: Distance between electrodes Therefore, if the voltage E generated between each electrode 41, 42 and 43° 44 is measured differentially, the stress δ, that is, the electrical signal corresponding to the flow rate and flow rate. can be obtained.

Furthermore, when the voltage generated between each electrode is measured differentially,
With respect to mechanical noise transmitted to the orifice 2, since it acts on the two piezoelectric elements in the same phase, they cancel each other out and are not influenced by these elements.

FIG. 6 is a connection diagram showing an example of an electric circuit when a piezoelectric element as shown in FIG. 4 is used as the stress detection means.

Here, in the piezoelectric element 4, a parallel connection is adopted in which electrodes 42 and 43 are connected to a common line, electrodes 41 and 44 are connected, and an electric signal corresponding to stress is obtained from there.

In this figure, SW is a switch having contacts a, b, and c, DC is a charge detection circuit, ME is a charge storage and holding circuit, and CK is an arithmetic circuit.

The switch SW is connected to the contacts a and c for a short time as shown in FIG. 7A.

Now, when switch SW is connected to contact a in a state where a charge Q corresponding to the stress is generated in the piezoelectric element 4, a current as shown in the opening of Fig. 7 flows, and its discharge characteristics are determined by the charge amount detection circuit. Determined by DC input impedance.

Here, the current peak value A1 at the moment when the switch SW is connected to the contact a corresponds to the stress δ1 generated inside the orifice or target.

The charge storage/holding circuit ME stores and holds the current peak value A1 as shown in FIG.

The switch SW is then connected to the contact C, and after discharging the electric charge of the piezoelectric element, is connected to the contact S.

Next, when switch SW is connected to contact a, if stress δ1 has changed from δ1 by +△δ1, a new charge amount corresponding to +△δ1 is generated in the piezoelectric element. Therefore, a current having a current peak value A2 corresponding to +δ1 is detected from the charge amount detection circuit DC as shown at the beginning of FIG. 7, and is stored in the charge amount storage holding circuit ME.

The arithmetic circuit CK receives signals corresponding to each peak value from the electric charge storage holding circuit ME, and can obtain a signal corresponding to the differential pressure by calculating these signals.

That is, A2. A3. -A4 represents the deviation value from stress δ1, and A1. A2. A3. -A4 can be sequentially added to obtain an electric signal corresponding to the absolute value of stress, that is, the square of the flow velocity or flow rate.

In the above embodiment, a larger number of stress detection means 3 may be arranged in the orifice, and electrical signals may be obtained by appropriately calculating these signals depending on the stress distribution, for example.

Moreover, although the fluid force is received by the orifice here, other shapes of obstruction walls may be used.

As described above, according to the present invention, a flow rate measuring device having a simple structure and low manufacturing cost can be realized.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of the configuration of an embodiment of the present invention, Fig. 2 is a perspective view showing a partial cross section, Fig. 3 is an enlarged view of the vicinity of the stress detection section in Fig. 1, and Fig. 4 is a main A configuration diagram showing an example of a piezoelectric element used in the invention, FIG. 5 is an electric circuit diagram of the piezoelectric element shown in FIG. 4, and FIG. 6 is a block diagram showing an example of the electric circuit.
FIG. 7 is an operational waveform diagram of the circuit of FIG. 6. 1... Conduit, 2... Orifice, 21
...Mounting flange, 3...Stress detection section, 4...Piezoelectric element.

Claims (1)

[Claims] 1. An obstacle wall configured so as not to be flexibly deformed is placed in the pipe through which the fluid to be measured flows, and a stress detection means composed of two piezoelectric elements sharing the same piezoelectric element material is used as a piezoelectric element. The material is arranged in the obstacle wall so as to be integrated with the obstacle wall so that the center of the material coincides with a center line parallel to the surface of the obstacle wall facing the flow, and the stress generated in the obstacle wall is reduced. A flow rate measuring device configured to perform differential detection using two piezoelectric elements constituting the stress detection means.