JPS6032572Y2 - vortex flow meter - Google Patents

Description

[Detailed description of the invention] The principle of flow velocity detection of the sensor used in a vortex flowmeter is completely different from that of other flowmeter sensors.

To explain this simply, a vortex generator is inserted into a pipe through which fluid flows, and a sensor connected to one end of the vortex generator detects it as an alternating current signal of frequency r.

A proportional relationship holds between the vortex generation frequency r and the flow velocity V over a wide range of the flow velocity V.

For example, even if the flow velocity changes from about 0.2 m/s to 100 rr1/s, the relationship between the two can be expressed by the following formula.

f = kv ・・・・・・・・・ (1) However, k
is a proportionality constant.

Therefore, one of the features of the vortex flow meter is the possibility of measuring a wide range of flow rates using the same sensor.

However, the sensor for detecting the vortex frequency signal has the characteristic of sensing vibration noise, cavitation noise, fluid fluctuation, etc.

Therefore, the output signal of the sensor contains a large amount of these noise components in addition to the eddy frequency signal, and unless these noise components are removed, highly accurate flow rate measurement results cannot be obtained.

Also, the strength of the sensor's vortex frequency signal is small at low flow rates and increases as the flow rate increases.

This is also a drawback of flow measurement.

Conventionally, as a means of removing noise components contained in the vortex flowmeter sensor output, as shown in Fig. 1, the output of the sensor SD is guided to a bandpass filter BF, and the frequency signal of this filter is The lower limit frequency f and upper limit frequency f2 of the transmission range are selected to be appropriate frequencies for noise removal, and the noise components in the frequency range below f1 and the noise components in the range 12 or above are removed and the filter output is set to f1 to f2. A waveform shaping circuit ST using a Schmitt trigger selectively generates a vortex frequency signal included in a frequency range of The method that occurs in the output is adopted.

The measurement range of the eddy frequency signal e1 that can be measured with the circuit shown in Fig. 1 is above the bandpass filter BF with respect to the measurement line @fS1 to fS2 of the eddy frequency fs corresponding to the flow velocity measurement range that can be detected with the same sensor. The frequency compaction between the lower limits is limited to a relatively limited narrow range of ~f2.

As a means of widening the range of flow measurement by this bandpass filter, a method has also been proposed in which a swept bandpass filter is used instead of a bandpass filter with a fixed transmission bandwidth as shown in FIG.

A swept bandpass filter has a transmission band frequency width Δf /fm (
However, fm is the center frequency of the transmission range, and Δf is the difference between the upper and lower limit frequencies of the transmission range. This is a variable transmission range filter that can continuously change the transmission range of the filter over a range.

A bandpass filter having this configuration is abbreviated as 'l'-BF.

FIG. 2 shows an example of the frequency transmission characteristics of '['-BF.

In the figure, the horizontal axis shows the frequency f1, the vertical axis shows the input signal of T-BF, the ratio e2/e1 of the output signal e2, and the control signal ip
It shows that the transmission characteristic curve of T-BF moves from 1 to 2 to 3 as the value of IPt changes from Ip□ to Ip3.

T-BF has good frequency selectivity because the frequency width of the transmission range is narrow, and the usable frequency range fmin-fmx is wide, so it is effective in removing noise components included in the vortex frequency signal.
This method uses the frequency f of the vortex frequency signal corresponding to the measured flow rate.
If the change in frequency is rapid, the characteristics of the bandpass filter may no longer be able to follow the input frequency, or a complex control circuit may be required to automatically match the transmission range of the T-BF to the vortex frequency at the start of measurement. There is a certain difficulty.

Therefore, it is difficult to apply this to portable instruments used at measurement sites.

The present invention eliminates the above-mentioned drawbacks, and combines a microcomputer (hereinafter referred to as μmCPU) with the above-mentioned conversion circuit CON that converts the eddy frequency signal ef into a pulse output signal, and gives this μmCPU a half-cutting function. C.O.
The main purpose of this invention is to realize a portable vortex flowmeter that enables the application of 'l'-BF to N and can be applied to a wide measurement flow rate range.

In addition, by using the calculation function of the μm CPU, it is possible to calculate mass flow rate from a signal representing volumetric flow rate converted into a pulse signal, temperature correction calculation, and other calculations, realizing a portable vortex flowmeter with a wide range of applications. This is what I am trying to do.

The present invention will be explained below with reference to the drawings.

FIG. 3 shows a schematic configuration of an embodiment of the present invention.

In the figure, SD is a vortex frequency signal detection sensor, T-BF
is a swept bandpass filter, VA is a variable gain circuit such as a variable gain amplifier, and ST is a waveform shaping circuit, specifically, a scimitar trigger is used for this.

μmCPU is a microcomputer, DL is an input interface circuit provided to read the ST output signal (serial pulse signal) into μmCPU, (1) is an output interface circuit, CU is a control unit, and μmCPU
Control signal I that sets the transmission range of T-BF based on the command of
p, and a control signal IA for setting the gain of the variable gain circuit VA, which is applied to 'l'-BF and VA, respectively.

The operation of this embodiment will be explained below.

Now, the eddy frequency signal e included in the output of the sensor SD
If the frequency f of , is outside the transmission range of 'l'-BF, the output of the wave shaping circuit T does not generate a pulse output signal corresponding to the vortex frequency f.

Since the μmCPU reads the output of the ST via the input interface, the μmCPU has a function of determining the presence or absence of the pulse output signal of the ST.

Therefore, if it is determined that a pulse output signal is being generated, the pulse output signal corresponding to the input signal read from the DI is sent to the outside through the output interface circuit (1).

Also, if the input signal does not arrive from DI, μmC
The PU gives a command to the control unit CU to continuously change the value of the control signal UP and change the transmission range of the 'l'-BF so that the frequency within the transmission range of the T-BF matches the vortex frequency f.

Thus, once the signal from the ST output starts to be generated, μmC
The PU thereby confirms that the '['-BF is operating in a normal state, and sends a pulse output signal to the outside through (1).

Also, if the output from DI to ST stops inputting to the μm CPU during the operation, the signal corresponding to the input signal from DI before the input signal stops arriving is held in (1), and the same process as before is carried out. Scan the transmission range of l'-BF, and if the input signal from DI starts inputting to μmCPU, T-BF
After confirming that the signal has returned to normal, the output signal corresponding to the input signal from the DI is outputted from (1) to the outside, and in other cases, the signal is held at zero.

In this way, by adding an abnormality processing routine for restoring the abnormal operation of 'l'-EF to the μm CPU, a portable vortex flowmeter capable of measuring a wide flow rate range can be realized.

Furthermore, if a variable gain circuit VA is provided and its gain is controlled in accordance with the pulse repetition period of the ST pulse output signal Pr, the S/N value of the 'l'-BF output signal can be adjusted at any frequency of the vortex frequency. If it exceeds l, flow rate measurement becomes possible in principle.

As explained above, the conversion circuit CON and μm that convert the output signal er of the eddy frequency signal detection sensor SD consisting of T-BF, VA and ST of the vortex flowmeter into a pulse output signal
By combining the μm CPU with a judgment function, it is possible to put into practical use a vortex flowmeter that can be used in a wide flow velocity range originally provided by a frequency signal detection sensor.

Furthermore, if you use the calculation function of the μm CPU, you can calculate not only the pulse output signal such as the meter output shown in Figure 3, but also the integrated value of the scaled flow rate, the calculation of the instantaneous flow rate value, and the D/A.
By correcting the nonlinearity of the conversion and reading the pressure measurement signal and temperature measurement signal of the fluid flowing through the pipe into the μm CPU, it becomes possible to calculate the mass flow rate, and the industrial value of the vortex flowmeter can be increased.

[Brief explanation of drawings]

FIG. 1 shows the configuration of a conventional vortex flowmeter. FIG. 2 shows a diagram illustrating the characteristics of the swept bandpass filter used in the present invention. FIG. 3 shows a schematic configuration of an embodiment of the present invention. SD...Eddy frequency signal detection sensor, T-B
F...Sweep type bandpass filter, VA,...Variable gain circuit, ST...Waveform shaping circuit, μmCP
U...Microcomputer, DI...
-Interface input circuit, (1)...Interface output signal.

Claims (1)

[Scope of utility model registration request] The output signal of the sensor for detecting the vortex frequency signal is applied to the input of a swept bandpass filter, and the output signal of the filter is applied to a waveform shaping circuit through a variable gain circuit, and the waveform shaping circuit corresponds to the output signal of the sensor. A digital signal corresponding to the pulse output signal is read into the input of a microcomputer, and the microcomputer responds to the digital signal to provide a signal to the swept bandpass filter in the transmission range of the filter. A vortex flowmeter configured to provide a signal for setting a frequency band and a signal for setting a gain of the variable gain circuit.