JPH0630725U - Vortex flowmeter - Google Patents

Abstract

(57) [Abstract] [Purpose] An object of the present invention is to provide an improved vortex flowmeter capable of preventing a pulse drop caused by a vortex signal including fluctuation or beat. [Structure] Two sensors for detecting Karman vortices generated in a fluid to be measured, two charge-voltage conversion circuits for converting AC charges output from each sensor into AC voltages, and charge-voltage conversion circuits for these circuits. A summing amplifier for adding and amplifying output signals, a filter circuit for low-pass filtering the output of the summing amplifier, a phase circuit for shifting the phase of the output voltage of the filter circuit, and an output of the phase circuit for the first frequency A first Schmitt trigger circuit for converting into a signal, a second Schmitt trigger circuit for converting the output voltage of the previous filter circuit into into a second frequency signal, an inverter for inverting this second frequency signal, and an output signal of this inverter. A logical sum circuit for calculating a logical sum with the above first frequency signal is provided, and a flow rate signal corresponding to the flow rate of the preceding measured fluid is obtained from the output of this logical sum circuit. It

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a vortex flowmeter for measuring a flow rate of a measurement fluid by using a Karman vortex generated in the measurement fluid, and is particularly improved to prevent a pulse drop caused by a vortex signal including fluctuations or beats. Regarding vortex flowmeter.

[0002]

[Prior art]

 The vortex flowmeter utilizes the fact that the generation frequency of the Karman vortex generated behind the vortex generator arranged in the measurement fluid is proportional to the flow velocity, and has a simple structure and a wide measurable range. It is widely used for flow rate measurement of various fluids because of its high measurement accuracy.

FIG. 5 is a configuration diagram showing a configuration of a conventional vortex flowmeter. In the figure, sensors 1 and 2 detect Karman vortices generated in a measurement fluid as weak AC charges. The weak AC charge signals output from the sensors 1 and 2 are input to charge voltage conversion circuits 3 and 4, respectively, and converted into AC voltage signals.

The output signals of these charge-voltage conversion circuits 3 and 4 are input to a summing amplifier 5 and are summed and amplified. The output signal of the summing amplifier 5 is input to the analog filter circuit 6 to remove noise.

The output signal of the analog filter circuit 6 is input to the Schmitt trigger circuit 7 and converted into a pulse signal. The pulse signal output from the Schmitt trigger circuit 7 is input to the F / V converter 9 that converts the frequency into a voltage via the transformer 8 and is converted into a voltage signal again.

The output signal of the F / V converter 9 is input to the voltage / current converter 10 and converted into a current signal of, for example, 4 mA to 20 mA.

[0007]

[Problems to be solved by the device]

However, the vortex flowmeter as described above has the following problems. FIG. 6A shows a waveform when the output of the analog filter circuit 6 outputs a normal vortex signal. In such a case, the Schmitt trigger circuit 7 having the Schmitt width ΔH ₁ is shown in FIG. The output is normal with no pulse drop as shown in).

However, when the output of the analog filter circuit 6 has a waveform accompanied by fluctuation as shown in FIG. 7A, a pulse-falling waveform as shown in FIG. No vortex signal is obtained.

[0009]

[Means for Solving the Problems]

 The present invention has, as a configuration for solving the above problems, two sensors for detecting a Karman vortex generated in a measurement fluid and two sensors for converting an AC electric charge output from each sensor into an AC voltage. A charge-voltage conversion circuit, a summing amplifier that adds and amplifies the output signals of these charge-voltage conversion circuits, a filter circuit that low-pass filters the output of this summing amplifier, and the phase of the output voltage of this filter circuit. A phase circuit, a first Schmitt trigger circuit that converts the output of this phase circuit into a first frequency signal, and a second Schmitt trigger circuit that converts the output voltage of the previous filter circuit into a second frequency signal. An inverter for inverting the second frequency signal and a logical sum circuit for calculating the logical sum of the output signal of this inverter and the first frequency signal are provided, and the output of this logical sum circuit It is intended to obtain a flow rate signal corresponding to the flow rate of the constant fluid.

[0010]

[Work]

 The two sensors detect Karman vortices generated in the measurement fluid. The two charge-voltage conversion circuits convert the AC charge output from each sensor into an AC voltage. The summing amplifier adds the output signals of these charge-voltage conversion circuits and amplifies them.

Then, the filter circuit low-pass filters the output of the summing amplifier. The phase circuit shifts the phase of the output voltage of this filter circuit. The first Schmitt trigger circuit converts the output of this phase circuit into a first frequency signal.

The second Schmitt trigger circuit converts the output voltage of the previous filter circuit into a second frequency signal. The inverter inverts this second frequency signal. The logical sum circuit calculates the logical sum of the output signal of the inverter and the first frequency signal. Then, a flow rate signal corresponding to the flow rate of the fluid to be measured is obtained from the output of the logical sum circuit.

[0013]

【Example】

 Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of one embodiment. The parts having the same functions as those of the conventional vortex flowmeter shown in FIG. 5 are designated by the same reference numerals, and the description thereof will be appropriately omitted.

The sensors 1 and 2 detect Karman vortices generated in the measurement fluid as weak AC charges. The weak AC charge signals output from the sensors 1 and 2 are input to the charge voltage conversion circuits 3 and 4, respectively, and converted into AC voltage signals.

The output signals of these charge-voltage conversion circuits 3 and 4 are input to a summing amplifier 5 where they are summed and amplified, and the output of the summing amplifier 5 is further input to an analog filter circuit 6, where noise is removed. , Its output voltage V ₁ is output to the phase shift circuit 11.

The phase shift circuit 11 delays the phase of the output voltage V ₁ by 180 ° and outputs it to the Schmitt trigger circuit 12 as the output voltage V ₂ . The Schmitt trigger circuit 12 has a positive trigger level with a Schmitt width ΔH ₂ and is pulsed with this as a reference and outputs it as a pulse signal P ₁ .

On the other hand, the output voltage V ₁ of the analog filter circuit 6 is pulsed by the Schmitt trigger circuit 13 having a negative trigger level of the Schmitt width ΔH ₃ and output as a pulse signal P ₂ .

Further, the pulse signal P ₂ is inverted by the inverter 14 and output as a pulse signal <P ₂ >. The pulse signals P ₁ and P ₂ are logically ORed by the logical OR circuit 15 and output to the transformer 8 as the pulse signal P ₃ .

After that, it is insulated by the transformer 8 and output to the F / V converter 9 to be converted into a voltage signal again. This voltage signal is input to the voltage / current converter 10 and converted into a current signal of, for example, 4 mA to 20 mA.

The specific configuration of the phase shift circuit 11 is as shown in FIG. In the figure, Q ₁ is an operational amplifier, the non-inverting input terminal (−) of which the output voltage V ₁ is applied via a resistor R ₁ and is connected to the output terminal by a resistor R ₂ .

A piezoelectric voltage is applied to the inverting input terminal (+) by dividing the output voltage V ₁ by the capacitor C ₁ and the resistor R ₃ . With the above configuration, the phase characteristic shown in FIG. 3 is obtained. The horizontal axis shows the frequency f and the vertical axis shows the phase characteristic. In this embodiment, the phase is used in the frequency region R with a 180 ° delay. Here, f ₀ is represented by f ₀ = 1 / 2πC ₁ R _{3 when} R ₁ = R ₂ .

Next, the operation of the embodiment configured as described above will be described using the waveform chart shown in FIG. The eddy signal is filtered and output as an output voltage V ₁ (FIG. 4C) to the output terminal of the analog filter circuit 6.

The output voltage V ₁ is phase-shifted by 180 ° in the phase shift circuit 11, and is output as the output voltage V ₂ as shown in FIG. 4A. This output voltage V ₂ is pulsed by the Schmitt trigger circuit 12 at a positive trigger level of the Schmitt width ΔH ₂ as shown in FIG. 4 (a), and is logically ORed as a pulse signal P ₁ (FIG. 4 (b)). It is output to the circuit 15.

Further, the output voltage V ₁ is pulsed by the Schmitt trigger circuit 13 at the negative trigger level of the Schmitt width ΔH ₃ as shown in FIG. 4C, and the pulse signal P ₂ (FIG. 4D). Is output to the inverter 14.

The inverter 14 inverts the pulse signal P ₂ and outputs it as a pulse signal <P ₂ > (FIG. 4 (e)) to the OR circuit 15. The logical sum circuit 15 calculates the logical sum of the pulse signal P ₁ (FIG. 4 (b)) and the pulse signal <P ₂ > (FIG. 4 (e)) to obtain the pulse signal P ₃ (FIG. 4 (f)). Is output to the transformer 8.

Looking at the waveform of the pulse signal P ₃ shown in FIG. 4F, it can be seen that the pulse drop generated in the pulse signal P ₁ (FIG. 4B) of the Schmitt trigger circuit 12 has been removed. I understand.

[0027]

[Effect of device]

 As described above in detail with the embodiments, according to the present invention, since the Schmitt trigger circuit is duplicated and the logical sum of the Schmitt trigger circuits is used as the vortex frequency, there are fluctuations or beats in the vortex frequency. However, it is possible to prevent the pulse drop caused by this.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a specific configuration of the phase shift circuit shown in FIG.

FIG. 3 is a characteristic diagram showing characteristics of the phase shift circuit shown in FIG.

FIG. 4 is a waveform diagram explaining the operation of the embodiment shown in FIG.

FIG. 5 is a block diagram showing a configuration of a conventional vortex flowmeter.

FIG. 6 is a waveform diagram illustrating normal operation of the vortex flowmeter shown in FIG.

FIG. 7 is a waveform diagram illustrating an abnormal operation of the vortex flowmeter shown in FIG.

[Explanation of symbols]

 1, 2 Sensors 3, 4 Charge-voltage conversion circuit 5 Summing amplifier 6 Analog filter circuit 7 Schmitt trigger circuit 11 Transfer circuit 12, 13 Schmitt trigger circuit 14 Inverter 15 Logical sum circuit

Claims (1)

[Scope of utility model registration request] 1. A sensor for detecting a Karman vortex generated in a fluid to be measured, two charge-voltage conversion circuits for converting an AC charge output from each sensor into an AC voltage, and charge-voltage conversion of these. A summing amplifier that adds and amplifies the output signals of the circuit, a filter circuit that low-pass filters the output of the summing amplifier, a phase circuit that shifts the phase of the output voltage of the filter circuit, and an output of this phase circuit A first Schmitt trigger circuit for converting into one frequency signal, a second Schmitt trigger circuit for converting the output voltage of the filter circuit into into a second frequency signal, an inverter for inverting this second frequency signal, and an output signal for this inverter. And a logical sum circuit for calculating a logical sum of the first frequency signal and obtaining a flow rate signal corresponding to the flow rate of the measurement fluid from the output of the logical sum circuit. Vortex flowmeter which is characterized.