JPH01267421A - Filter circuit for vortex flow meter - Google Patents

Abstract

PURPOSE:To enable detection of a vortex frequency faithfully, by removing a noise component of a vortex current through a lowpass filter and a beat component through a highpass filter to switch and outputting outputs thereof selectively. CONSTITUTION:A vortex signal from a vortex signal detection means is inputted at an input terminal 11 to remove a noise component through a lowpass filter 12b while a beat component is removed through a highpass filter 12c. Outputs of the lowpass filter 12b and the highpass filter 12c are switched with a switching circuit 15 to be taken out. When an output voltage of the switching circuit 15 exceeds a specified voltage, it is detected with a voltage detection circuit 12a to switch the switching circuit 15 forcibly to the position of the highpass filter 12c.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is designed to eliminate malfunctions when switching between a low-pass filter that removes noise components superimposed on eddy frequencies and a high-pass filter that removes waviness components. The present invention relates to a filter circuit for a vortex flow meter.

[Prior Art] Conventionally, as a vortex flowmeter used in an engine, for example, Japanese Patent Publication No. 5B-5641 is known.

FIG. 1 is a block diagram of a filter circuit of the vortex flowmeter of the present invention, which will be described later. In this FIG. When explaining, 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 phase comparison H
Output to 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.

The phase comparator 9, the ultrasonic oscillation circuit 6, the voltage controlled phase shift circuit 7, and the loop filter 10 constitute a phase locked loop. 11 is a low pass filter.

A phase comparator 9 compares the phases of the output of the waveform shaping circuit and the output of the voltage controlled phase shift circuit 7, and 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 .

Depending on the output voltage of the loop filter 10, the voltage controlled phase shift circuit 7 controls the phase shift angle of the output signal of the ultrasonic oscillation circuit 6 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.

In this way, the parts indicated by reference numerals 1 to 11 constitute an eddy signal detection means 100 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 a vortex flow meter that can faithfully detect vortex frequency even when the vortex frequency suddenly increases.

[Means to solve the problem]

A filter circuit for a vortex flowmeter according to the present invention includes a low-pass filter that removes noise in an eddy signal, a high-pass filter that removes undulations in the eddy signal, a switching circuit that switches the output of the low-pass filter and the output of the high-pass filter, and A voltage detection circuit that detects the output voltage of the switching circuit and drives the switching circuit is provided.

(Function) The low-pass filter of the present invention removes the noise component superimposed on the eddy signal, removes the undulation component of the eddy signal with a high-pass filter, and switches the output of the low-pass filter and the output of the high-pass filter with a switching circuit. The voltage of this switching circuit is detected by a voltage detection circuit, and when this voltage exceeds a predetermined voltage, the switching circuit is forcibly switched to the high-pass filter side by the voltage detection circuit.

〔Example] Hereinafter, one embodiment of the present invention will be explained based on the drawings.

The first part is a block diagram showing the overall configuration.
The part 00 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 a loop filter 10, and is also passed through a low-pass filter 11 to a 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 the filter switching determination circuit 14, and the determination result is input to the switching circuit 15.

The switching circuit 15 conducts the output of each filter in the filter group 12 (fixed terminals 15 a to 15 n are switched by the output of the switching determination circuit 14 and is a movable terminal that guides the output of one of the filters to the waveform shaping circuit 13 ). 150. 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 inputted 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, so the flow meter provides a 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 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 one of the filters 12. As shown in FIG. In FIG. 2, T1 is an input terminal to which the output of the eddy 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 applied to the fixed terminal 15a+ of the switching circuit 15 via the amplifier 12a50 and the pass filter 12b.

Further, the vortex signal is applied to the fixed terminal 15a2 of the switching circuit 15 through the high-pass filter 12c. This switching circuit 15 is the switching circuit shown in FIG. 1, and is switched by the filter switching determination circuit 14, but is also switched by a voltage detection circuit 12d, which will be described later.

By switching the movable terminal 150 of the switching circuit 15 by the filter switching determination circuit 14, the low-pass filter 12b
The output of the high-pass filter 12c and the output of the high-pass filter 12c are outputted to the waveform shaping circuit 13 shown in FIG.

The voltage of the movable terminal 150 is detected by the voltage detection circuit 12d, and when the voltage of the movable terminal 150 exceeds a predetermined voltage, the voltage detection circuit 12d forcibly moves the movable terminal 150 of the switching circuit 15 to the fixed terminal 15a2 side. In other words, the signal is switched to the high-pass filter 12c side.

Next, the operation shown in FIG. 2 will be explained. The vortex signal is input to and amplified by amplifier 12a, which amplifies small transient voltages when the vortex frequency is low and outputs it to low pass filter 12b.

The low-pass filter 12b removes a noise signal when the vortex frequency is low and outputs it to the fixed terminal 15a of the switching circuit 15.

On the other hand, a vortex signal is also input to the high-pass filter 12c,
The undulation component of the vortex signal is removed and outputted to the fixed terminal 15a of the switching circuit 15. As already mentioned, the movable terminal 150 of the switching circuit 15 is switched by the output of the filter switching determination circuit 14, and guides the output of the low-pass filter 12b or the high-pass filter 12c to the waveform shaping circuit 13 of FIG.

At this time, the voltage of the movable terminal 150 of the switching circuit 15 and the output voltage of the switching circuit 15 are detected by the voltage detection circuit 12d, and when it is detected that this output voltage is higher than a predetermined voltage, the voltage detection circuit 12d outputs Accordingly, the switching circuit 15
The movable terminal 150 is forcibly switched to the fixed terminal 15az side (high-pass filter 12c side).

FIG. 3 shows characteristics a of the amplifier 12a and low-pass filter 12b, and characteristics a of the high-pass filter 12c. This third
As is clear from the figure, the low-pass filter 12b removes noise components having a high frequency with respect to the vortex frequency, and uses the bypass filter? 12c has a function of removing low-frequency undulation components with respect to the eddy frequency.

Further, the switching of the switching circuit 15 is determined by the vortex frequency, and is located at the point where the characteristics of the low-pass filter 12b and the high-pass filter 12c intersect.

Now, if the vortex frequency suddenly increases as shown in FIG.
It is assumed that the output voltage of the switching circuit 15 is greatly amplified by the signal a, and the output voltage of the switching circuit 15 follows GND as shown in FIG. 4(b).

The voltage detection circuit 12d detects this voltage and immediately switches the movable terminal 150 of the switching circuit 15 to the fixed terminal 15az side, that is, to the high-pass filter 12c side, to follow the sudden change in vortex frequency.

〔Effect of the invention〕

As described above, according to the present invention, the noise component of the vortex signal is removed by a low-pass filter, the undulation component is removed by a high-pass filter, and the outputs of the low-pass filter and high-pass filter are switched and extracted by a switching circuit, and When the output voltage of the circuit exceeds a predetermined voltage, the voltage detection circuit is configured to forcibly switch the switching circuit to the high-pass filter side, so even if the vortex frequency suddenly increases, the vortex frequency can be faithfully detected. Moreover, the device can be made at low cost and has the advantage of being highly accurate.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the overall configuration of a filter 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 and the low-pass filter and the characteristics of the high-pass filter in FIG. 2, and FIG. 4 is a waveform diagram for explaining the operation of the filter circuit in FIG. 2. 1... Flow meter, 12... Filter group, 12a...
Amplifier, 12b...Low pass filter, 12c...
High pass filter, 12d... Voltage detection circuit, 15.
...Switching circuit. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Agent Masuo Oiwa Figure 3 1IIIO Procedural amendment (voluntary)

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 low-pass filter for removing noise components of the amplifier. , a high-pass filter for removing the undulation component of the eddy signal detected by the eddy signal detection means, a switching circuit for switching between the output of the low-pass filter and the output of the high-pass filter, and detecting the output voltage of the switching circuit. and a voltage detection circuit that drives a switching circuit.