JPH01267420A - Filter circuit for vortex flowmeter - Google Patents

Abstract

PURPOSE:To remove a noise component overlapped with a vortex frequency at a low cost and with a high responsiveness, by combining a vortex signal with an output of a highpass filter through a limiter circuit and a switch after the removal of a noise component thereof with a lowpass filter. CONSTITUTION:A vortex signal from a vortex signal detection means is inputted into a limiter circuit 12c via an amplifier 12a and a lowpass filter 12b and inputted into a synthesizer 12e via a highpass filter 12d. An output of the limiter circuit 12c is turned ON/OFF by a switch 12f to be applied to the synthesizer 12e. The synthesizer 12e combines an output of the switch 12f and an output of the highpass filter 12d and outputs a vortex frequency signal with a specified frequency.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention particularly relates to a vortex control system for use in an engine that enables accurate and responsive detection of vortex frequencies by removing noise components and undulation components superimposed on vortex frequencies. This relates to a filter circuit for a flowmeter.

[Conventional technology]

Conventionally, as a vortex flowmeter used in an engine, for example, Japanese Patent Publication No. 58-5641 is known.

FIG. 1 is a block diagram of a filter circuit of the vortex 'fL quantity meter of the present invention, which will be described later. In this FIG. When explaining the technique, FIG. 1 will be referred to.

In FIG. 1, an ultrasonic transmitter 4 and an ultrasonic receiver 5 are arranged facing each other via a flowmeter 1 having a vortex generator 2, and a Karman vortex is generated downstream of the vortex generator 2. The ultrasonic transmitter 4 is excited by the ultrasonic oscillation circuit 6 so that the ultrasonic wave propagates across the flow in the row 3.

The ultrasonic wave that crosses the flow of the Karman vortex street 3 is phase-modulated by the Karman vortex street and is received by the ultrasound receiver 5. This received signal is waveform-shaped by a waveform shaping circuit 8 and then output to a phase comparator 9.

On the other hand, the output of the ultrasonic oscillation circuit 6 that excites the ultrasonic transmitter 4 is applied to the voltage controlled phase shift circuit 7.

This voltage-controlled phase shift circuit 7 maintains the high frequency stability of the ultrasonic oscillation frequency signal and controls only the phase shift angle. This voltage-controlled phase shift circuit shifts the phase of the output of the ultrasonic oscillation circuit 6 and applies it to the phase comparator 9.

A phase-locked loop is configured by a phase comparator 9, an ultrasonic oscillation circuit 6, a voltage-controlled phase shift circuit 7, and a loop filter IO. 11 is a low pass filter.

A phase comparator 9 compares the phases of the output of the waveform shaping circuit 8 and the output of the voltage controlled phase shift circuit 7, adds the comparison result to the loop filter 10, and removes unnecessary frequency components of the comparison result from the loop filter 10. Remove with .

The voltage controlled phase shift circuit 7 controls the phase shift angle of the output signal of the ultrasonic oscillation circuit 6 in accordance with the output voltage of the loop filter IO, and outputs it to the phase comparator 9.

Thereby, the output of the voltage controlled phase shift circuit 7 is synchronized with the ultrasonic reception signal, and as a result, the output of the loop filter 10 directly becomes the phase demodulated output.

Thus, the parts indicated by reference numerals 1 to 11 constitute an eddy signal detection means for detecting eddy signals.

[Problem to be solved by the invention]

Since the conventional vortex flow meter is configured as described above, there is a problem that the vortex frequency is disturbed by noise other than the signal received by the ultrasonic receiver 5 and low-frequency undulations caused by the flow direction of the fluid. there were.

This invention was made to solve the above problems, and eliminates the noise component superimposed on the vortex frequency accurately, with good responsiveness, and at low cost, without using any sensor or control system other than the vortex flowmeter. The object of the present invention is to obtain a filter circuit for an eddy flow needle that can faithfully detect eddy frequency even when the eddy frequency suddenly increases.

[Means to solve the problem]

A filter circuit for an eddy flowmeter according to the present invention includes a low-pass filter that removes noise from an eddy signal, a limiter circuit that limits the output voltage of the low-pass filter, a switch that cuts off the output voltage of the limiter circuit, and a switch that controls the output voltage of the eddy signal. It is provided with a high-pass filter that removes waviness components and a synthesizer that combines the outputs of the switch and the high-pass filter.

[For production]

The low-pass filter in this invention removes the noise component superimposed on the eddy signal, limits the output voltage of this low-pass filter with a limiter circuit, and then connects it to the synthesizer by switching it on and off using a switch. The high-pass filter output is applied to a synthesizer, and the synthesizer combines the output of the high-pass filter and the output of the switch to detect a desired vortex frequency.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings. FIG. 1 is a block diagram showing the overall configuration, and in this first episode, vortex signal detection means 10 indicated by reference numerals 1 to 11
The 0 part has already been described in the [Prior Art] column, and redundant explanation of that part will be avoided.

In FIG. 1, the parts starting from the reference numeral 12 will be mainly described.

The output of the phase comparator 9 is input to the loop filter 1°, and is also passed through the low-pass filter 11 to the filter group 1.
2 is also entered. This filter group 1
The output of 2 is input to a waveform shaping circuit 13.

A Karman vortex frequency signal corresponding to the flow rate of the flowmeter 1 is output from the waveform shaping circuit 13. Further, the Karman vortex frequency signal is input to a filter switching determination circuit 14, and the determination result is input to a switching circuit 15.

The switching circuit 15 switches fixed terminals 15a to 15n that lead the output of each filter of the filter group 12 with the output of the filter switching determination circuit 14, and connects a movable terminal 150 that leads the output of one of the filters to the waveform shaping circuit 13. have. This switching circuit 15 switches the filter group 12.

With this configuration, as described above, the vortex signal, that is, the phase demodulation signal, generated in accordance with the flow rate of the fluid to be measured flowing through the flowmeter 1 is input to the filter group 12 via the low-pass filter 11.

By the way, in an engine, for example, in a low flow region such as when idling, there is no ultrasonic noise or undulation, and a stable vortex frequency can be measured. Therefore, the vortex frequency can be detected based on this correct value.

Normally, when the engine is idling, the air valve angle is extremely small, so the air that has passed through the flow meter is once throttled by the valve (not shown) before being sent to the engine, so the throttle effect causes air to be generated in the engine. Pulsating flow and ultrasonic noise downstream of the air valve do not propagate upstream. Therefore, the flowmeter provides stable output.

If the pass band of the filter group 12 is determined based on the obtained frequency output, as the engine rotation speed increases and the output frequency increases, the filter group 12 will switch accordingly, so that it will always be outside the signal output frequency. The noise cannot pass through the filter group 12.

Therefore, in the embodiment shown in FIG. 1, the waveform shaping circuit 13 shapes the output of the filter group to obtain a vortex frequency output, and this vortex frequency output is applied to the filter switching determination circuit 14 to determine filter switching. This filter switching determination result is manually input to the switching circuit 15.

By controlling the pass band by switching the filter group 12 using the switching circuit 15, noise other than the signal output frequency always does not pass through the filter group 12, as described above.

FIG. 2 is a block diagram showing the internal configuration of the filter group 12. In FIG. 2, T1 is an input terminal to which the output of the eddy signal detection means in FIG. 1, that is, the eddy signal from the output end of the low-pass filter 11 is input.

The vortex signal is input to a limiter circuit 12c via an amplifier 12a and a low-pass filter 12b, and is also input to a synthesizer 12e via a high-pass filter 12d.

Further, the 0 combiner 12e, which connects the output of the limiter circuit 12c to the combiner 12e intermittently with a switch 12f, combines the output of the switch 12f with the high-pass filter 12.
d and is combined to output a vortex frequency signal of a predetermined frequency, which is applied to the switching circuit 15 in FIG.

Next, the operation shown in FIG. 2 will be explained. Input terminal T
The vortex signal introduced into the amplifier 12a is input to the amplifier 12a.

This amplifier 12a amplifies a small high wave voltage when the vortex frequency is low and outputs it to the low pass filter 12b.

The low-pass filter 12b removes a noise signal when the vortex frequency is low and outputs it to the limiter circuit 12c. This limiter circuit 12c limits the signal amplitude to a certain voltage when the output amplitude of the low-pass filter 12b exceeds a certain voltage.

The output of this limiter circuit 12c is turned on and off by a switch 12f, and is applied to a combiner 12e. That is, the switch 12f connects the output of the limiter circuit 12c and the combiner 12e.
Intermittent signal line with.

On the other hand, the high-pass filter 12d removes the undulation component of the eddy signal and applies it to the synthesizer 12e. The synthesizer 12e synthesizes the output of the high-pass filter 12d and the output of the switch 12f, and outputs a vortex signal of a predetermined frequency.

FIG. 3 shows the amplifier 12a and low-pass filter 12 in FIG.
The characteristic a of the high-pass filter 12d and the characteristic a of the high-pass filter 12d are shown. The low-pass filter 12b has a function of removing noise components having a high frequency relative to the vortex frequency, and the high-pass filter 12d has a function of removing undulation components having a low frequency relative to the vortex frequency.

In addition, the switching of the switch 12f is determined by the vortex frequency, and the switching between the low-pass filter 12b and the high-pass filter 12d is determined by the vortex frequency.
It is at the intersection of the characteristics of

Now, as shown in FIG. 4(a), the input terminal T in FIG.
When the vortex frequency of the vortex signal introduced into I becomes high and a vortex signal with a undulation component A is input during the change, the undulation component A with a low frequency is greatly amplified by the amplifier 12a, but the limiter By circuit 12C, the fourth
The output voltage is limited as shown in Figure (b)).

On the other hand, the signal that has passed through the high-pass filter 12d passes high frequencies as is, and is combined with the signal limited by the limiter circuit 12c in the synthesizer 12e, as shown in FIG.
), and the original signal waveform can be output without distortion.

〔Effect of the invention〕

As described above, according to the present invention, after the noise component of the vortex signal is removed by a low-pass filter, the limiter circuit creates an amplitude limit and is intermittent by a switch, and the undulation component is removed by a high-pass filter. Since the output of the vortex flowmeter and the output of the switch are combined using a synthesizer to obtain a vortex signal of a predetermined frequency, it is accurate and responsive without using any sensor or control system other than the vortex flowmeter. The noise component superimposed on the vortex frequency can be removed at low cost, and the vortex frequency can be detected faithfully even when the vortex frequency suddenly increases.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the overall configuration of a filter circuit of a vortex flow meter according to an embodiment of the present invention, and FIG. 2 is a block diagram showing the internal configuration of one filter circuit of a filter group in the same embodiment. , FIG. 3 is a characteristic diagram showing the characteristics of the amplifier, low-pass filter, and high-pass filter in FIG. 2, and FIG. 4 is a waveform diagram for explaining the operation of the filter circuit of FIG. 2. 1... Flow meter, 12... Filter group, 12a...
Amplifier, 12b...Low pass filter, 12c...
Limiter circuit, 12d... High pass filter, 12e
...Synthesizer, 12f...switch. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] an eddy signal detection means for detecting an eddy signal generated in response to the flow rate of the fluid to be measured; an amplifier for amplifying the eddy signal detected by the eddy signal detection means; and a noise component removed from the output signal of the amplifier. a low-pass filter that limits the output voltage of the low-pass filter, a limiter circuit that limits the output voltage of the low-pass filter, and a switch that switches on and off the output of the limiter circuit;
A filter circuit for a vortex flowmeter, comprising: a high-pass filter that removes the undulation component of the vortex signal detected by the vortex signal detection means; and a synthesizer that combines the output signals of the switch and the high-pass filter.