JPH0882538A - Vortex flowmeter - Google Patents

Abstract

PURPOSE: To provide a vortex flowmeter, which can cut the erroneously detected signal generated by vibration or the like without increasing the lower-limit value of a measuring range. CONSTITUTION: A Karman vortex is generated in fluid flowing through a pipe and detected with a sensor 1. The sensor signal outputted from the sensor 1 is inputted into a converter 20, and the sensor signal is converted into the pulse signal based on the specified crest value. The flow rate is measured based on the frequency component of the pulse signal. In this vortex flowmeter, a low-frequency cutting means 21, which cuts the signal component, whose frequency is lower than a preset frequency, from the pulse signal, is provided in the converter 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vortex flowmeter for measuring the flow rate of a fluid by utilizing a Karman vortex generated in the fluid flowing through a pipe.

[0002]

2. Description of the Related Art FIG. 4 is a diagram showing a configuration example of a conventional vortex flowmeter. In this vortex flowmeter, a Karman vortex is generated from a fluid flowing in a pipe, and the Karman vortex is detected by a sensor 1 installed in the pipe. The sensor signal output from the sensor 1 is input to the converter 2 and converted into a pulse signal having a frequency component proportional to the flow rate. The pulse signal is transmitted from the converter to the measurement system and converted into a flow rate signal according to the frequency component of the pulse signal in the measurement system.

In the converter 2, the sensor signal sent from the sensor 1 is amplified by the amplifier circuit 3 to a predetermined level as shown in FIG. 5 (a), and the amplified signal is input to the waveform shaping circuit 4. A signal waveform as shown in FIG. 5B from which the high frequency component has been removed is processed. Then, the output of the waveform shaping circuit 4 is cut at a certain crest level in the filter circuit 5,
The filter output of the filter circuit 5 is converted into a pulse conversion circuit 6
Is converted into a pulse signal with.

As described above, in a general vortex flowmeter, the sensor signal whose frequency increases in proportion to the flow rate of the pipe and the crest value increases accordingly is standardized by the converter 2 and the flow rate is detected by the frequency. Signal processing is performed so that it can be done.

Here, when the flow rate is small, the noise component and the original signal component cannot be distinguished because the peak value of the sensor signal is low. Therefore, in order to prevent the noise component from being mistakenly recognized as the signal component, the filter circuit 5 is used. All values below a certain peak value are cut. The peak value cut by the filter circuit 5 is the lower limit value of the measurement range for ensuring accuracy. Normally,
The cut level of the filter circuit 5 is set so that the converter output becomes zero when the flow rate is zero.

However, if vibration or the like is applied to the sensor 1 for some reason, a sensor signal is generated even if the flow rate is zero, and the output of the converter 2 does not become zero. In order to completely cut such a signal, the cut level of the filter circuit 5 must be increased. But,
When the cut level of the filter circuit 5 is increased, there is a problem that the lower limit value of the measurement range for ensuring accuracy is increased.

[0007]

As described above, the conventional vortex flowmeter has a problem that the lower limit value of the measurement range increases when trying to remove the signal component generated by pulsation, vibration or the like. The present invention has been made in view of the above circumstances, it is possible to cut an erroneous detection signal generated by vibration or the like without increasing the measurement range lower limit value,
Another object of the present invention is to provide a vortex flowmeter that can cope with the need for cutting low flow rates without adding an instrument.

[0008]

The present invention has taken the following means in order to achieve the above object. According to the present invention corresponding to claim 1, a Karman vortex is generated in a fluid flowing through a pipe and detected by a sensor, a sensor signal output from the sensor is input to a converter, and the sensor signal has a predetermined peak value. In the vortex flowmeter for converting into a pulse signal based on the pulse signal and measuring the flow rate based on the frequency component of the pulse signal, a signal component having a frequency lower than a preset frequency provided from the pulse signal is provided in the converter. It is configured by including a low frequency component cutting means that cuts.

[0009]

The present invention has the following effects by taking the above measures. According to the present invention corresponding to claim 1, the Karman vortex of the fluid flowing through the pipe is detected by the sensor, and the sensor signal output from the sensor is input to the converter. In the converter, the sensor signal is cut at a predetermined peak value to remove a noise component having a low peak value, and a pulse signal is generated from a signal component larger than the peak value. This pulse signal is output from the converter via the low frequency component cutting means. On the other hand, when a signal (erroneous detection signal) is generated in the sensor due to vibration or the like, if the peak value of the error detection signal is larger than the cut level, it is input to the low frequency component cutting means as a pulse signal. The low-frequency component cutting means functions to cut a signal component having a frequency lower than a preset frequency for the pulse signal, and therefore, based on an erroneous detection signal having no periodicity or a very large period. The pulse signal thus generated is removed by the low frequency component cutting means.

[0010]

Embodiments of the present invention will be described below. FIG. 1 shows the configuration of a vortex flowmeter according to an embodiment of the present invention. The parts having the same functions as those of the vortex flowmeter shown in FIG. 4 are designated by the same reference numerals.

That is, the vortex flowmeter of this embodiment is a sensor 1 for detecting the Karman vortex generated in the fluid flowing through the pipe.
And a converter 20 for processing the sensor signal output from the sensor 1.

The converter 20 includes an amplifying circuit 3 for amplifying a sensor signal sent from the sensor 1, a waveform shaping circuit 4 for shaping the output signal of the amplifying circuit 3 to remove high frequency noise, and a waveform shaping circuit 4. A filter circuit 5 that cuts the output signal at a certain crest level, a pulse conversion circuit 6 that converts the output signal of the filter circuit 5 into a pulse signal, and a signal component having a preset cut frequency or less from the pulse signal of the pulse conversion circuit 6 A low-cut circuit 21 for cutting is provided.

The filter circuit 5 is set with a cut level (peak value) capable of discriminating a signal component and a noise component corresponding to the minimum flow rate. Specifically, the cut level at which the converter output becomes zero when the flow rate is zero is the filter circuit 5.
Is set to

The low-cut circuit 21 is composed of a high-pass filter, and the following cut frequencies are set. That is, a cut frequency having a cycle slightly longer than the pulse frequency for the sensor signal corresponding to the minimum detectable flow rate is set. The cut frequency value can be set to any value.

Next, the operation of the present embodiment configured as described above will be described. When the Karman vortex generated from the fluid flowing in the pipe is detected by the sensor 1, the sensor 1 has a cycle corresponding to the flow rate from the sensor 1 to the converter 20.
A sensor signal having a waveform as shown in (a) is input.

The sensor signal input to the converter 20 is amplified by the amplifier circuit 3, the high-frequency noise is removed by the waveform shaping circuit 4, and the noise, which is a signal component below the cut level, is cut by the filter circuit 5. The signal of the filter circuit 5 is converted by the pulse conversion circuit 6 into a pulse signal as shown in FIG. This pulse signal is input to the low cut circuit 21. Here, the pulse signal shown in FIG. 3B has a cycle corresponding to the sensor signal that has detected the actual flow rate, and therefore has a frequency higher than the cut frequency due to the above-mentioned setting conditions. Therefore, the signal is directly transmitted to the receiver of the measurement system without being cut by the low cut circuit 21. In the measurement system, the period of the pulse signal received by the receiver is detected and a flow rate signal corresponding to the detected period is generated.

On the other hand, the operation when the fluid is not flowing in the pipe will be described. If the fluid is not flowing, a noise component having an extremely low peak value appears in the output of the sensor 1 as compared with the actual flow rate detection signal. Since this sensor output is smaller than the cut level set in the filter circuit 5, it is cut by the filter circuit 5 and the converter output becomes zero.

However, when a vibration is applied to the sensor 1, for example, a signal having a peak value higher than the cut level set in the filter circuit 5 (hereinafter, referred to as an "erroneous detection signal") is generated in the sensor output. To do. When the sensor 1 is vibrated and an erroneous detection signal having a signal waveform shown in FIG. 2A is input to the converter 20, a signal component exceeding the cut level in the filter circuit 5 is input to the pulse conversion circuit 6.
Is input to The pulse conversion circuit 6 outputs the pulse signal shown in FIG. 2B from the output of the filter circuit 5. Since this pulse signal is generated only when the sensor 1 is vibrated, the low cut circuit 21 cuts the pulse signal at the cut frequency. As a result, the output of the converter 20 is maintained in the zero state with respect to the input of the false detection signal.

The waveform and cycle of the erroneous detection signal vary depending on the state of vibration and the like, and the pulse-shaped waveform as shown in FIG. 2A is not always obtained. As described above, according to the present embodiment, the converter 20 is provided with the low-cut circuit 21, and the frequency component below the preset cut frequency is cut from the pulse signal of the pulse conversion circuit 6. An erroneous detection signal generated by vibration or the like of the sensor 1 can be removed without raising the temperature.

According to this embodiment, by adjusting the cut frequency set in the low cut circuit 21, it is possible to cut a low flow rate without adding an instrument. The present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention.

[0021]

As described above in detail, according to the present invention, an erroneous detection signal generated by vibration or the like can be cut without increasing the lower limit value of the measurement range, and when it is necessary to cut a low flow rate. Can provide a vortex flowmeter that can be used without adding an instrument.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a vortex flowmeter according to an embodiment of the present invention.

FIG. 2 is a diagram showing a waveform of an erroneous detection signal caused by vibration of a sensor and a pulse signal corresponding to the erroneous detection signal.

FIG. 3 is a diagram showing a waveform of a sensor signal corresponding to a flow rate and a pulse signal corresponding to the sensor signal.

FIG. 4 is a configuration diagram of a conventional vortex flowmeter.

FIG. 5 is a diagram showing a waveform of a sensor signal, a waveform shaping signal corresponding to the sensor signal, and a pulse signal thereof.

[Explanation of symbols]

1 ... Sensor, 2, 20 ... Converter, 3 ... Amplifying circuit, 4 ... Waveform shaping circuit, 5 ... Filter circuit, 6 ... Pulse conversion circuit,
21 ... Low-cut circuit.

Claims (1)

[Claims] 1. A Karman vortex is generated in a fluid flowing through a pipe and detected by a sensor, and a sensor signal output from the sensor is input to a converter to convert the sensor signal into a pulse signal based on a predetermined peak value. In the vortex flowmeter for converting and measuring the flow rate based on the frequency component of the pulse signal, a low frequency which is provided in the converter and cuts a signal component of a frequency lower than a preset frequency set from the pulse signal. A vortex flowmeter comprising a component cutting means.