JPH0658785A - Fluidic flowmeter - Google Patents

Abstract

PURPOSE:To obtain a fluidic flowmeter, which can improve an SN ratio in the entire region from the low flow-rate region to the high flow-rate region and can perform the highly accurate measurement of the flow rate. CONSTITUTION:A sensor 2 converts the vibration of fluid of a fluidic oscillating element 1 into the electric signal. An amplifier 31 having the low-pass filter characteristic amplifies the output of the sensor. An operating circuit 4 operates the flow rate based on the output of the amplifier. These parts are provided. With respect to the increase in output value of the sensor 2, the gain of the amplifier 31 is changed into the decreasing direction, and the cut-off frequency of the amplifier is changed into the increasing direction at the same time. The high-frequency noises in the low flow-rate region are attenuated, and the gain of the low-frequency noises in the high flow-rate region is suppressed. The changes of the gain and the cut-off frequency are continuously performed based on the resistance change of a voltage-resistance converting element. Thus, the more accurate measurement can be performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluidic flowmeter using a fluidic oscillator.

[0002]

2. Description of the Related Art As gas and other flow meters,
The fluidic flowmeter, which has recently been drawing attention, is configured to detect fluid pressure oscillation of a fluidic oscillation element with a sensor, convert it into an electrical signal, and count the electrical signal to calculate the flow rate. ing.

In such a fluidic flow meter, the electrical signal obtained by the fluidic oscillation element through the sensor changes its voltage level remarkably according to the change in the flow rate of the fluid, as shown in FIG. 5 (a). The level is small in the low flow rate range, and increases as the flow rate increases. In addition, since the flow rate and the vibration period of the fluidic oscillator, that is, the output frequency of the sensor, are in a proportional relationship as shown in FIG. 6B, there is a correlation between the output frequency of the sensor and the output voltage. The output voltage increases as the voltage rises. For this reason, in particular, a configuration is generally adopted in which an amplifier is interposed in order to make a voltage level in a low flow rate region, that is, a low frequency region into a logic level capable of arithmetic processing, and a sensor output is amplified by the amplifier and input to an arithmetic circuit. .

However, if the noise in the high frequency range is mixed in the low flow rate region by simply interposing the amplifier, this noise is also amplified, so that there is a problem that the SN ratio is deteriorated particularly in the low flow rate region. is there.

Therefore, in order to improve the SN ratio in the low flow rate region, the voltage level in the high flow rate region can be lowered by adding a low-pass filter function having a frequency characteristic as shown in FIG. 6 to the amplifier. It is being appreciated.

However, in this case, when low frequency noise is mixed in during measurement in the high flow rate region, that is, in the high frequency region, this low frequency noise is amplified, and conversely the SN ratio in the high flow rate region deteriorates. It was a new defect.

The present invention has been made in view of the above technical background, and it is possible to improve the SN ratio in all regions from a low flow rate region to a high flow rate region, and to perform a highly accurate flow rate measurement. The purpose is to provide a Dick flow meter.

[0008]

In order to achieve the above object, the present invention provides a sensor (2) for converting fluid vibration of a fluidic oscillation element (1) into an electric signal and an output of the sensor. Amplifier with low-pass filter characteristics (3
A fluidic flowmeter comprising: 1) and a calculation circuit (4) for calculating a flow rate based on the output of the amplifier, wherein the amplifier (31) is provided in response to an increase in the output value of the sensor (2). Is a fluidic flowmeter characterized in that its gain is changed in a decreasing direction and its cutoff frequency is increased in a simultaneous manner.

Further, the gain change and the cutoff frequency change of the above-mentioned amplifier are caused by the sensor (2) or the amplifier (3
It is preferable to carry out continuously based on the resistance change of the voltage resistance conversion element whose resistance value continuously changes according to the magnitude of the output value of 1).

[0010]

In the low flow rate range, the fluid vibration of the fluidic oscillation element (1) is small and the output voltage of the sensor (2) is also small. Therefore, the resistance value of the voltage resistance conversion element in the gain control circuit (32) is extremely large. Has become. Therefore, the gain of the amplifier (31) becomes large, the cutoff frequency is lowered, the frequency characteristic of the amplifier (31) becomes as shown in FIG. 4, and even if a high level high frequency noise is mixed, the noise is attenuated. .

Next, when the fluid flow rate increases, both the output voltage value and the output frequency of the sensor (2) increase, but the resistance value of the voltage resistance conversion element in the gain control circuit (32) increases the output voltage of the sensor. The amplifier (3
The gain of 1) decreases, but the cutoff frequency increases. Therefore, as the fluid flow rate increases, the frequency characteristic of the amplifier (31) changes as shown in (b) and (c) of FIG. At this time, even if low-frequency noise is mixed, the gain of the low-frequency region is suppressed, so that the gain of the noise is also reduced and the S / N ratio is not deteriorated.

[0012]

Embodiments of the present invention will be described below.

In FIG. 1 showing the basic configuration of the present invention,
(1) is a fluidic oscillation element that generates pressure oscillation according to the fluid flow rate, and (2) is a sensor that detects fluid pressure oscillation of the fluidic oscillation element and converts it into an electrical signal. The fluid pressure oscillation of the fluidic oscillating element (1) is small when the flow rate is small and is large when the flow rate is large, and accordingly, the output voltage and the output frequency of the sensor are small when the flow rate is small and increase when the flow rate is large. , As shown in FIG. 5, it significantly changes according to the flow rate.

(3) is an amplifier circuit for amplifying the output of the sensor (2). As shown in FIG. 2, the amplifier circuit (3) has an amplifier (31) for receiving the sensor output and an external feedback of the amplifier. A gain control circuit (32) connected to the circuit and a capacitor (33) connected in parallel to the gain control circuit are provided. The gain control circuit (32) includes a voltage resistance conversion element whose resistance value continuously changes according to the input voltage of the amplifier (31), that is, the output voltage of the sensor (2). It is said that the change continuously changes the gain of the amplifier. Specifically, when the output voltage of the sensor (2) increases, the resistance value decreases and the gain decreases, and when the output voltage of the sensor decreases, the resistance value increases and the gain increases. Such a voltage resistance conversion element can be easily configured by using, for example, a field effect transistor, and the configuration is not particularly limited.

The gain control circuit (32), together with the capacitor (33), gives the amplifier a transfer characteristic as a low-pass filter. Thus, the cutoff frequency of this low-pass filter is uniquely determined by the resistance value of the voltage resistance conversion element and the capacitance value of the capacitor (33) in the gain control circuit (32), but the resistance value of the voltage resistance conversion element is Since the output voltage of the sensor (2) decreases with an increase in the output voltage, the cutoff frequency increases with an increase in the output voltage of the sensor, decreases with an decrease in the output voltage, and continuously changes with a change in the sensor output voltage. It is supposed to do.

Next, the operation of the fluidic flowmeter shown in FIGS. 1 and 2 will be described with reference to the graph shown in FIG.

In the low flow rate region, the fluid vibration of the fluidic oscillation element (1) is small and the output voltage of the sensor (2) is also small. Although the resistance value of the voltage resistance conversion element in the gain control circuit (32) is determined by the magnitude of the output voltage of the sensor (2), the resistance value is extremely large because the sensor output is small. As a result, the gain of the amplifier (31) increases, but the cutoff frequency decreases. Therefore, the frequency characteristic of the amplifier (31) at this time is as shown in Fig. 4B,
The low frequency output from the sensor (2) in the low flow region is amplified to a constant level. Even if high frequency noise is mixed in when measuring in such a low flow rate range, the noise is attenuated,
The S / N ratio does not deteriorate.

Next, when the fluid flow rate increases, both the output voltage value and the output frequency of the sensor (2) increase, but the resistance value of the voltage resistance conversion element in the gain control circuit (32) increases the output voltage of the sensor. The amplifier (3
The gain of 1) decreases, but the cutoff frequency increases. Therefore, the frequency characteristic of the amplifier (31) at this time is as shown in (b) of FIG. The output voltage of the amplifier (31) is maintained in a substantially constant range because the output voltage of the sensor itself is increasing although the gain is lower than that of b.

Next, when the fluid flow rate further increases, both the output voltage value and the output frequency of the sensor (2) further increase, the resistance value of the voltage resistance conversion element of the gain control circuit (32) further decreases, and the amplifier ( The gain of 31) becomes lower and the cutoff frequency becomes higher. Therefore, the amplifier (31) at this time
The frequency characteristic of is as shown in C of FIG. Even if low-frequency noise is mixed during measurement in such a high flow rate range, the gain of the low-frequency range is suppressed and the gain of the noise is reduced, so that the S / N ratio does not deteriorate. Rather, since the input voltage of the amplifier (31) is originally high in the high frequency range,
On the contrary, the N ratio will be improved. Of course, even if the gain is decreased, the input voltage of the amplifier (31) is originally high as described above, so that the output of the amplifier (31) is maintained at a constant level.

As described above, the frequency characteristic of the amplifier (31) continuously changes from a to b and then to c and vice versa according to the magnitude of the sensor output. As a result, the level of the output voltage of the amplifier is almost the same. It is controlled within a fixed range, and the SN ratio is maintained well regardless of the frequency range.

FIG. 3 shows a modification of the amplifier circuit. In this example, the voltage resistance conversion element of the gain control circuit (32) receives the output of the amplifier (31) and changes its resistance value. Has been done. Even with such a configuration, the same operational effect as that shown in FIG. 2 can be exhibited.

Note that the embodiments shown in FIGS. 2 and 3 exemplify the basic configuration of the present invention, and the circuit configuration of the external feedback circuit is not limited to those shown in the drawings. May be configured so that the resistance value of the voltage-resistance conversion element increases with an increase in the gain, the gain may be reduced, and the frequency may be increased. In addition, various modifications are possible without departing from the concept of the present invention. is there.

[0023]

As described above, according to the present invention, as the output value of the sensor increases, the amplifier simultaneously changes its gain in the decreasing direction and its cut-off frequency in the increasing direction. Therefore, even if high-frequency noise is mixed in the low flow rate region, the noise is attenuated by the reduction of the cutoff frequency, so that the SN ratio can be maintained in a good condition. On the other hand, in the high flow rate region, even if low frequency noise is mixed, the gain in the low frequency region is suppressed, so that the gain of the noise is also suppressed, and the SN ratio can be maintained well. as a result,
It is possible to obtain a high-quality flow meter with high measurement accuracy, which can maintain a good SN ratio while securing the output level of the amplifier in a constant range in all areas from the low flow rate range to the high flow rate range.

The change in gain and the change in cutoff frequency are
When continuously performed based on the resistance change of the voltage resistance conversion element, the frequency characteristic of the amplifier can be continuously changed, and more accurate measurement can be guaranteed.

[Brief description of drawings]

FIG. 1 is a block diagram showing a basic configuration of the present invention.

FIG. 2 is a specific circuit configuration diagram of an amplifier circuit in FIG.

FIG. 3 is another specific circuit configuration diagram of the amplifier circuit.

FIG. 4 is a graph showing frequency characteristics of the amplifier according to the present invention.

FIG. 5 (a) shows the relationship between fluid flow rate and sensor output,
(B) is a graph showing the relationship between the flow rate and the frequency.

FIG. 6 is a graph showing frequency characteristics of an amplifier in a conventional example.

[Explanation of symbols]

 1 ... Fluidic oscillation element 2 ... Sensor 31 ... Amplifier 32 ... Gain control circuit (voltage resistance conversion element)

Claims (2)

[Claims] 1. A sensor (2) for converting fluid vibration of a fluidic oscillation element (1) into an electric signal, and an amplifier (31) with a low-pass filter characteristic for amplifying the output of the sensor.
And a calculation circuit (4) for calculating a flow rate based on the output of the amplifier, wherein the amplifier (31) is provided with an increase in the output value of the sensor (2). A fluidic flow meter characterized in that the gain is changed in the decreasing direction and the cutoff frequency is increased in the increasing direction at the same time. 2. A voltage-resistance conversion element in which a change in the gain of the amplifier (31) and a change in the cutoff frequency change continuously in resistance according to the magnitude of the output value of the sensor (2) or the amplifier (31). The continuous operation is performed based on the resistance change.
The fluidic flow meter described in.