JPH0648351Y2 - Vortex flowmeter signal amplification circuit - Google Patents

Description

TECHNICAL FIELD The present invention relates to a signal amplification circuit of a vortex flowmeter, and more specifically, to the vibration noise of a cantilever type vortex detector separately formed from a vortex generator from the vortex signal. The present invention relates to a signal amplification circuit that removes and amplifies.

2. Description of the Related Art Conventionally, as a vortex detecting method of a vortex flowmeter, a method of detecting as a strain signal due to a fluctuating pressure generated due to the generation of a vortex has been widely adopted. This is because it has high reliability because it does not come into contact with. In this method, a vortex generator is used as a flexure element, and a detection element that detects a vortex as a change in strain or stress generated in the flexure element is embedded inside or outside the vortex generator to be integrated. The vortex generator, which is configured separately from the vortex generator, is inserted into the perforated pressure detection chamber without contact with the inner wall, and one end is fixed to the vortex generator end or the flow tube wall. The vortex fluctuating pressure acting through the pressure communicating hole that opens to both sides of the vortex generator and communicates with the pressure detection chamber is detected.The vortex fluctuating pressure is detected by fixing one end to the wake side of the vortex generator. There is a method to do. The vortex detector separate from the vortex generator, which will be described later, applies the same vortex detector to a wide range of flowmeters, and is small and flexible. Since it can be used as a detector, it has an advantage that it is easy to detect a vortex with high sensitivity. In particular, the above-mentioned second method in which the vortex detector is separately configured and inserted in the vortex generator can be configured integrally with the vortex generator, so that the first method in which the vortex detecting element is embedded is used. Similarly, a simple and small vortex flowmeter can be constructed. The second method is disclosed in Japanese Patent Publication No. Sho 63-31726 previously proposed by the present applicant. The vortex detector of the publication is a strain detection system in which a strain detection element having a strain detection element fixed to a strip-shaped base material is inserted in a flexible cylinder. Further, the vortex detector proposed in Japanese Patent Laid-Open No. 62-215829 is composed of a flexible cylinder that responds to vortex fluctuation pressure, and an electrode support member that is loosely inserted in the flexible cylinder, and outputs a vortex signal. This is a static strain capacitance detection method in which at least one fixed electrode and a flexible cylinder provided on the electrode support member are used as variable electrodes to detect a change in capacitance. In the method in which such a vortex detector is provided separately from the vortex generator, the vortex fluctuation pressure can be detected with high sensitivity, so that the flow rate can be measured in a small flow rate range and the flow rate measurement range can be expanded. Since the vortex fluctuation pressure is proportional to the square of the flow velocity, if the vortex detector can obtain an output proportional to the pressure, the vortex signal will be +40 dB / Dec in proportion to the square of the measurement range.
Increases with the slope of. On the other hand, it is desirable that the preamplifier that processes this vortex signal has a gain characteristic that the signal level is constant in the measurement range of the flow velocity, but in order to exclude pipe vibration noise in the low range, fluid vibration noise in the high range, etc. As shown in Fig. 7, it has a preamplifier with an amplification characteristic that increases by +20 dB / Dec toward the cutoff frequency fa at a predetermined vortex frequency in the low frequency range, and has a cutoff frequency fb at the predetermined vortex frequency in the high frequency range from -40 to A suitable frequency characteristic is given by combining an active filter that attenuates at -80 dB / Dec.

Problems of the Prior Art As described above, the vortex flowmeter having the vortex generator and the vortex detector separately provided responds to minute pressure with high sensitivity and improves small flow sensitivity, but vortex detection since the natural frequency f ₀ of the vessel exacerbates the S / N becomes noise, the upper limit of the high basin adjacent the frequency of the vortex signal to said intrinsic vibration frequency f ₀ is limited. In order to extend the high flow region, the natural frequency of the vortex detector is increased, but this increases rigidity, which lowers the measurement limit for small flow rates, and the maximum vortex signal frequency f is f = 0.
The limit was 2f ₀ .

8 and 9 show an example of the relationship between the frequency f and the frequency component of the natural frequency f _{0 at} a predetermined flow rate ((a)) and the vortex signal waveform ((b)). In FIG. 8, f = 0.
In the case of 182f ₀ , it is shown that the noise component of natural frequency f ₀ = 3200Hz has already disturbed the vortex signal. Further, FIG. 9 shows the case of f = 0.344f ₀ , but in this case, it is difficult to distinguish the eddy signal from the character.

As mentioned above, the natural vibration of the vortex detector is the main noise source in the high flow region, and in order to remove this noise, it is necessary to add a filter with higher-order attenuation. Has the drawback of being complicated and expensive.

Means for Solving Problems The present invention has been made in view of the above-mentioned problems of the conventional technology, and removes the natural frequency component of the vortex detector to improve the S / N and impair the sensitivity of a small flow rate. It is an object of the present invention to provide a vortex flowmeter with an excellent flow rate range at low cost by expanding the flow rate measurement in a large flow rate range without any need. That is, the flow tube and the vortex generator disposed in the flow tube so as to face the flow are fixed at one end to the former flow tube or vortex generator, and the other end is displaced in response to the fluctuating pressure of the vortex. A cantilever type vortex detector for detecting the large displacement of the flexible body, and a vortex converter having a filter circuit for removing a noise component contained in the vortex signal detected by the vortex detector. In a vortex flowmeter that consists of a vortex signal that changes according to the flow rate, a vortex flowmeter signal amplification circuit with a notch filter whose natural frequency of the cantilever vortex detector is nu11 frequency Is provided.

Embodiment FIG. 1 is a configuration diagram showing a cross-sectional view in the flow direction of a vortex flowmeter 10 as an example to which the present invention is applied, and FIG. 2 is an enlarged view of a II portion of FIG. A conduit, which is sandwiched between pipes to be measured (not shown) and forms the main body of the vortex flowmeter 10. A vortex generator 2 is press-fitted and fixed in the conduit 1 with the diameter of the cross section as an axis, and a hollow chamber 25 is bored on the axis.
Pressure guiding holes 21, 22, 23, 24 penetrate through the hollow chamber 25. In the hollow chamber 25 of the vortex generator 2, a flexible cylinder 3 fixed by a mounting flange 31 to a mounting seat 11 formed by cutting the upper portion of the conduit 1 into a plane is inserted with a gap. Further, in the flexible cylinder 3, another mounting flange is mounted on the upper side of the mounting flange 31.
The fixed column 4 fixed by 41 is inserted. The fixed column 4
Electrodes 42 and 43 are attached to the left and right side surfaces facing the flow at the end of the, to form a capacitance using the flexible tube 3 as another common electrode. The lead wires 44, 45 of the electrodes 42, 43 are inserted into the fixed column 4 and electrically connected to the preamplifier 6. The preamplifier 6 is fixed to the conduit 1 by a mounting cylinder 5.

The above-mentioned vortex flowmeter 10 introduces the fluctuating pressure generated by the vortex generator into the hollow chamber 25 through the pressure guiding holes 21 to 24, and is fixed in a cantilever manner upon receiving the fluctuating pressure introduced. The changing displacement of the flexible cylinder 3 is detected by the electrodes 42 and 43 of the fixed column 4 as a change in electrostatic capacitance.

FIG. 3 shows a block diagram of the preamplifier 6, in which the signal from the vortex signal A has an amplification characteristic in the prior art having an approximate differential element B of the cutoff frequency fa and a secondary delay element C having the cutoff frequency fb. Input to the symmetrical Twin-T circuit D. The symmetrical Twin-T circuit is a well-known filter circuit,
The transfer function T (S) is a parallel T-type circuit consisting of a T-type circuit with a resistor R and a capacitance 2C and a T-type circuit with a capacitance C and a resistor R / 2 With a null frequency To be chosen. At this frequency f _0, the flexible cylinder 3 has a mounting flange 31
Is the natural frequency with the support as the detection frequency f = 0.33
Detection up to f ₀ is possible, and the frequency characteristics shown in Fig. 4 are obtained.

Figures 5 and 6 show the flow rates shown in Figures 8 and 9, respectively, at the same flow rates of 583Hz (0.182f ₀ ) and 1100Hz (0.34).
4f ₀ ), the f ₀ noise component of the natural frequency of the flexible cylinder 3 is reduced in the frequency component diagram of FIG. (A), and the improvement of S / N is shown in FIG. 8 and FIG. Seen in comparison with Figure 9. The comparison circuit of FIG. 3E and the output circuit of F are known circuits, and are output as eddy pulse signals from the Out terminal.

The above-described preamplifier of the present invention is also applied to the vortex flow type disclosed in the above-mentioned Japanese Patent Publication No. 63-31726 in the vortex detection method. That is, even in the strain detection method in which the strain detecting element is fixed to the strip-shaped base material in the flexible cylinder 3, the cantilevered natural frequency of which the flexible cylinder 3 uses the mounting flange 31 as a support portion. Therefore, the natural frequency mixes in the vortex signal as a noise component and deteriorates the S / N. It should be noted that the method other than the above method can be applied when the natural vibration noise in the detection element is mixed in the vortex signal.

Effects As is apparent from the above description, according to the present invention, the natural vibration noise f ₀ of the flexible cylinder included in the detection element is effectively removed, and the conventionally detectable vortex frequency f is f = 0.2f _0. In contrast to the limit of the degree, it is possible to measure at a high range flow rate of f = 0.4f _{0 to} 0.45f ₀ . In addition, by adding a simple symmetrical Twin-T circuit, extremely effective characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an example of a vortex flowmeter to which the vortex flowmeter signal amplification circuit of the present invention is applied, FIG. 2 is an enlarged view of a II portion of FIG. 1, and FIG. 3 is a block diagram of the signal amplification circuit. FIG. 4 is a diagram showing a frequency characteristic, FIGS. 5 and 6 are diagrams showing an eddy signal when the amplifier circuit of the present invention is used, and FIG. 7 is a frequency characteristic diagram of a conventional technique. FIG. 8 and FIG. 9 are diagrams showing vortex signals when a conventional amplifier circuit is used. 1 ... Conduit, 2 ... Vortex generator, 3 ... Flexible tube, 4 ... Fixed column, 6 ... Preamplifier, 10 ... Vortex flowmeter.

Claims (3)

[Scope of utility model registration request] 1. A vortex generator having a hollow chamber, which is disposed in a conduit through which a fluid flows, and into which a fluctuating pressure due to a generated Karman vortex is introduced, and a vortex generator which is inserted into the hollow chamber and has one end on one side thereof. A flexible body that is held and supported, a vortex detection unit that detects an alternating displacement of the flexible body that is displaced in response to the fluctuating pressure, and the number of vortices generated per unit time detected by the vortex detection unit. In the vortex flowmeter, which comprises a signal amplification circuit for obtaining a flow rate by means of the signal amplification circuit, an amplification circuit for amplifying the alternating displacement signal of the flexible body detected by the vortex detection means to a predetermined level, and the amplification circuit. The natural frequency of the flexible body included in the signal amplified by
1) A vortex flowmeter signal amplification circuit characterized by having a symmetrical twin (Twin) / T filter circuit with a frequency. 2. A flexible cylinder inserted into the hollow chamber of the vortex generator is a flexible cylinder, and means for detecting an alternating displacement of the flexible cylinder is provided.
2. The vortex according to claim 1, wherein the flexible body is a movable electrode, and the electrostatic detector is composed of a fixed electrode that is insulated and fixed to a side surface of a fixed column inserted into the flexible cylinder. Flowmeter signal amplification circuit. 3. A flexible cylinder inserted into the hollow chamber of the vortex generator is a flexible cylinder, and means for detecting an alternating displacement of the flexible cylinder is provided.
The vortex flowmeter signal amplification circuit according to claim 1, wherein the strain detection element is a strain detection element that is inserted into the flexible body and fixed to a strip-shaped base material that responds to an alternating displacement of the flexible body.