JPS6332126B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bandpass automatic tracking filter that automatically synchronizes the fundamental frequency due to the vortices to the bandpass filter, particularly when measuring flow using a vortex flow meter.

The vortex detection signal of a vortex flowmeter, which utilizes the fact that the frequency of Karman vortices is proportional to flow velocity, contains low-frequency and high-frequency noise components such as flow velocity fluctuations and turbulent vortices contained in the flow superimposed on them. The correct vortex signal cannot be detected unless the noise component is removed. Therefore, the simplest method is to use a fixed band filter by connecting a high-pass filter and a low-pass filter in series to remove noise components other than the eddy frequency corresponding to the measurable flow velocity range. In a wide-range vortex flowmeter, even with this method, the vortex signal contains noise within the band, and the noise in the vortex signal is included as an erroneous signal, making it impossible to measure the flow rate correctly.

For this purpose, a method can be considered in which only the eddy signal is correctly detected by narrowing the bandwidth and automatically following the fundamental frequency caused by the eddy. Patent application 48-
No. 54725 "Filter Device" describes "bandwidth automatic tracking filter that adjusts the filter band by DA converting the frequency of the signal extracted from the middle of the high-pass filter and the low-pass filter" be. However, in this example, the resistance values that define the time constants of the high-pass filter and the low-pass filter are obtained by a single resistance value selected by AD converting the signals passed through the high-pass filter and the low-pass filter. ing.
In this case, the single resistance value is a secondary circuit element obtained by electrically insulating the A-D conversion output, so the conversion accuracy is low, and it is difficult to obtain a specified resistance value for the output voltage. It was necessary to select from among the conversion elements. For this reason, the yield is poor,
The problem was that it was time-consuming and expensive.

In order to solve the above-mentioned problems, the present invention connects in series a resistor element and a capacitor, which are made by connecting multiple circuit elements in parallel with a switching element with an accurate resistance value that defines the cutoff area of the filter. death,
To provide an automatic band tracking filter that automatically tracks a bandwidth simply and accurately by performing a switching operation by selecting an integration amount within a specified time of a counter proportional to a signal frequency.

Hereinafter, the details of the present invention will be specifically explained with reference to the drawings.

FIG. 1 is a partially cutaway perspective view of a vortex flowmeter in which a filter according to the present invention is used, FIG. 2 is a lateral sectional view thereof, FIG. 3 is an output waveform diagram thereof, and FIG. 4 is a diagram according to the present invention. FIG. 5 is a circuit diagram showing one embodiment of the automatic band tracking filter, and FIG. 5 is a partial circuit diagram showing another embodiment.

First, the explanation will be given with reference to FIGS. 1 and 2.

In FIGS. 1 and 2, denotes a pipe having a flow path with a circular cross section perpendicular to the axis, denotes a triangular prism installed in the pipe, denotes a thermistor sensor for detecting a vortex, and denotes a fluid.

Due to the flow of fluid, Karman vortices are generated on the left and right sides of the triangular prism installed in the pipe, and as a result, the fluid that flows in from the upstream side of the triangular prism flows out to the downstream side of the triangular prism, but the vortex Due to generation and separation, this flow velocity changes alternately on the left and right sides, and the heat radiation coefficient of the thermistor sensor changes. This change in heat dissipation coefficient is detected as a change in resistance of the thermistor sensor,
Furthermore, it is converted into a voltage change and detected.

Thereafter, by amplifying and shaping the detected voltage change and extracting it as a pulse proportional to the flow velocity, the flow rate or flow velocity can be determined.

However, this output voltage has a poor S/N ratio as shown in FIG. In FIG. 3, N is noise caused by pulsating flow, etc., and S is a vortex generation signal.

Therefore, it is necessary to remove the noise component from this output signal and extract and count only the vortex generation signal.
However, since this noise component includes frequency components within the measurement range of the flowmeter, it is necessary to remove this noise by using a band automatic tracking filter that passes only the frequency of the vortex signal that is currently occurring.

Next, FIG. 4 will be explained.

1 is an input terminal, 2 is an amplifier, 3 is a high-pass filter, 3a is a capacitor, 3b is a resistance selection circuit,
3-0, 3-1, 3-2, 3-3, 3-4 are resistors, 4 is a low-pass filter, 4a is a capacitor,
4b is a resistance selection circuit, 4-0, 4-1, 4-2,
4-3, 4-4 are resistors, 5 is a fixed low-pass filter, 6 and 7 are Schmitt trigger circuits, 8 is a frequency multiplier circuit, 9 is an analog switch switching circuit, 10 is an input negator, 11 is an AND gate, 1
2 is a dynamic pulse oscillation circuit, 13 is a delay circuit, 14 is a counting circuit, 15 is a latch circuit for controlling analog switching elements, 15-1, 15-
2,15-3,15-4 and 15-1',15
-2', 15-3', and 15-4' are analog switching elements, 16 is a gate circuit, and 17 is an output terminal.

The vortex signal detected by the vortex flow meter and converted into a voltage change is input from the input terminal 1 and amplified by the amplifier 2. After that, the vortex signal that has passed through the amplifier 2 is passed through the high pass filter 3.
is input.

The high pass filter 3 includes a capacitor 3a and analog switching elements 15-1 and 15-, respectively.
Resistors 3-1, 3 to 2, 15-3, 15- respectively
-2, 3-3 and 3-4 are connected in series, and the resistor selection circuit 3b is formed by connecting circuit elements in parallel to each other. One end of the capacitor 3a is connected to an input terminal connected to the amplifier 2, and the other end is connected to an output terminal connected to the low-pass filter 3. Further, the resistance selection circuit 3b is inserted between the output side connection of the capacitor 3a and the ground, and is connected to the analog switching elements 15-1, 15-2, 15-3 and 1.
5-4 and the corresponding resistors 3-1, 3-2,
The cutoff frequency can be adjusted by selectively connecting 3-3 and 3-4.

The signal input to the high-pass filter 3 has low frequency noise removed therein, and is input to the fixed low-pass filter 5 and the low-pass filter 4. The fixed low-pass filter 5 is configured to set the vortex signal frequency at the maximum flow rate of the vortex flowmeter as a cutoff frequency, and removes high frequency noise. However, since the fixed low-pass filter 5 is a fixed filter, its output still contains some noise.

On the other hand, the low-pass filter 4 includes analog switching elements 15-1,', 15-2', 15-3',
Resistors 4-1, 4-2, 4- to 15-4' respectively
Resistor selection circuit 4 configured by connecting circuit elements 3 and 4-4 in series in parallel with each other.
b and a capacitor 4a, the resistance selection circuit 4b is inserted between the input terminal of the low-pass filter 4, and the capacitor 4a is inserted between the output terminal side connection of the resistance selection circuit 4b and the ground. There is. Similarly to the high-pass filter 3, the cut-off frequency of the low-pass filter 4 can be adjusted.

The signal that has passed through the fixed low-pass filter 5 is input to the Schmitt trigger circuit 6, and its waveform is converted into a shaped pulse signal and input to the frequency multiplier circuit 8. The frequency multiplier circuit 8 is provided to improve transient response, and multiplies the frequency of the pulse signal output by the above-mentioned Schmitt trigger circuit 6 and sends it to the AND gate 11.

The AND gate circuit 11 outputs a pulse signal to the counting circuit 14 while controlling the signal multiplied by the frequency multiplier 8 as explained later.

The counting circuit 14 counts the frequency multiplier circuit output pulses via the AND gate 11 and outputs the counted value to the latch circuit 15. The latch terminal of the latch circuit is connected to the oscillation circuit 12, and the count value of the counting circuit is latched by the latch pulse until the next latch pulse is input.

The reset signal of the counting circuit is slightly delayed by the delay circuit 13, the count value is reset with a slight delay after being latched, and the counting circuit counts the output pulses of the frequency multiplier circuit until the next reset pulse is input.

The latch circuit 15 latches the counting result of the counting circuit 14 and switches the analog switching elements 15-1, 15-2, 1 according to the latch input frequency.
5-3, 15-4 and 15-1', 15-2',
By turning on and off appropriate analog switching elements 15-3' and 15-4', the cutoff frequencies of the high-pass filter 3 and low-pass filter 4 are switched, and the frequency of the vortex signal that is currently being generated is changed. The band is the pass band.

The output of the gate circuit 16 is always in the state 0, but when the count value of the counting circuit 14 reaches a predetermined set value, it becomes the state 1, and at that time, the output of the frequency multiplier circuit 8 is in the AND state. It becomes impossible to pass through the gate 11, and the operation of the counting circuit 14 stops. This gate circuit 16 prevents the counting circuit 14 from overflowing, but in some cases it may be used to limit the maximum tuning frequency.

In addition to the circuit configuration shown in FIG. 4, the analog switch switching circuit 9 may have a circuit configuration as shown in FIG. 5.

In Fig. 5, 18 is a frequency-voltage conversion circuit;
a is its input terminal, 19 is a voltage comparison circuit,
19a is its output terminal.

The input terminal 18a of the frequency-voltage conversion circuit 18 is connected to the frequency multiplier circuit 8, and the output terminal 19a of the voltage comparison circuit 19 is connected to analog switching elements 15-1, 15-2, 15-3, 1
5-4 and 15-1', 15-2', 15-3',
15-4', and connect it to the voltage comparator circuit 1.
Similar effects can be obtained by switching the cutoff frequencies of the high-pass filter 3 and the low-pass filter 4 by turning on and off the analog switching element according to the output of the filter 9.

As described above, the present invention digitally obtains the period of the vortex signal that has passed through the high-frequency and low-frequency fixed filters, and based on this, resistors constituting the band filter connected in cascade to the high-frequency and low-frequency filters. Since it is possible to select a known one, in the conventional examples (Japanese Patent Application No. 48-54725, Japanese Patent Publication No. 60-27212), the resistance value is made up of photoelectric conversion elements and analog feedback circuit elements. Since it has a configuration in which three photoelectric conversion elements are connected in series, the inefficient work of having to select those with matching resistance value characteristics is eliminated.
Therefore, it is possible to construct a tracking type bandpass filter that is extremely efficient and inexpensive.

Note that the present invention is not limited to the embodiments described above, and the configurations of the high-pass filter and low-pass filter, the counting method of the counting circuit, etc. can be freely changed within the scope of the purpose of the present invention. However, the present invention encompasses all of them.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway perspective view of a vortex flowmeter in which a filter according to the present invention is used, FIG. 2 is a lateral sectional view thereof, FIG. 3 is an output waveform diagram thereof, and FIG. 4 is a diagram according to the present invention. FIG. 5 is a circuit diagram showing one embodiment of the automatic band tracking filter, and FIG. 5 is a partial circuit diagram showing another embodiment. ...Pipe, ...Triangular prism, ...Thermistor sensor, ...Fluid, 1...Input terminal, 2...Amplifier, 3...
High pass filter, 3a, 4a... Capacitor, 3
b, 4b...resistance selection circuit, 3-0, 3-1, 3-
3,3-4,3-5...Resistor, 4...Low pass filter, 4a...Capacitor, 4-0,4-1,4-
3, 4-4, 4-5...Resistor, 5...Fixed low-pass filter, 6,7...Shutdown trigger circuit, 9...Analog switch switching circuit, 11...AND gate, 12...Oscillation circuit, 13...Delay circuit, 14...Counter circuit, 15... latch circuit, 16... gate circuit,
17...Output terminal.

Claims (1)

[Scope of Claims] 1. An automatic band tracking filter characterized by comprising the components described in the following items (a) to (d). (a) It consists of a capacitor with one pole connected to the input terminal side and the other pole connected to the output terminal side, and a plurality of circuit elements connected in parallel to each other, each consisting of a resistor connected in series to a switching element or contact. , comprising a resistor selection circuit inserted between the output side connection of the capacitor and the ground, and the cutoff frequency is adjusted by controlling the switching element or contact to select and connect the corresponding resistor. high pass filter. (b) A resistor selection circuit, which is made up of a plurality of circuit elements connected in parallel to each other, each consisting of a resistor connected in series to a switching element or contact, and inserted and connected between an input terminal and an output terminal, and the above-mentioned resistor selection circuit. It comprises a capacitor inserted between the output terminal side connection of the circuit and the ground, is connected after the high-pass filter, and controls the switching element or contact to select and connect the corresponding resistor. A low-pass filter whose cut-off frequency can be adjusted by. (c) A constant-area low-pass filter with a constant cutoff frequency, which is connected to the output side of the high-pass filter together with the low-pass filter. (d) A control circuit that detects the frequency of the output signal of the fixed-area low-pass filter and opens and closes the switching elements or contacts of the high-pass filter and low-pass filter so that a band in the vicinity of the detected frequency is set as a pass band. 2. The control circuit includes a waveform shaping circuit, a circuit that multiplies the frequency of the output pulse of the waveform shaping circuit, and the output of the frequency multiplication circuit that is reset periodically and until a predetermined count is reached before being reset. 2. The automatic band following filter according to claim 1, comprising an arithmetic circuit that counts pulses and opens and closes switching elements or contacts of a high-pass filter and a low-pass filter in accordance with the counted value. 3. The control circuit includes a waveform shaping circuit, a circuit that multiplies the frequency of the output pulse of the waveform shaping circuit, a frequency/voltage conversion circuit that receives the output pulse of the frequency multiplication circuit, and a frequency/voltage converter that responds to the output of the frequency/voltage converter. 3. The automatic band following filter according to claim 2, comprising an output circuit that opens and closes switching elements or contacts of a high-pass filter and a low-pass filter.