JPS6261890B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a device for measuring the flow rate or flow rate by detecting the number of generated vortices, and in particular detects the number of generated Karman vortices or swirl vortices using, for example, a hot wire to measure the flow rate or flow rate. The present invention relates to a device for measuring .

FIG. 1 is a configuration diagram showing a conventional flow rate or flow rate measuring device, and FIG. 2 shows the flow rate or flow rate measuring device 1 installed in a conduit 2, and a fluid such as air flowing in the direction of the arrow in the conduit 2. This shows the case of measuring the flow rate or flow velocity. In FIG. 1, 3 is a vortex generator, 4 and 5 are heat wires, and 6 is this heat wire 4.
and 5 are supports, and 7 is a measuring circuit whose detailed circuit is shown in FIG.

In the measurement circuit 7 shown in FIG. 3, 8 is a power supply terminal for power supply voltage Vcc, 9a to 9z are resistors, and 1
0a to 10d are operational amplifiers, 11a and 11b
is a capacitor, 12a and 12b are transistors, 13 is a node from which the first signal V ₁ shown in FIG. 4a is output, 14 is a node from which the second signal V ₂ shown in FIG. The third signal shown in c
16 is the first output terminal from which the _fourth signal V ₄ shown in FIG. 4d is output, 17 is the fourth
The second output terminal 18 outputs the fifth analog voltage signal V ₅ shown in FIG. e, and the third output terminal 18 outputs the demodulated signal Vpp.

The resistors 9a, 9b, 9d and the operational amplifier 10a constitute a first bridge circuit that controls the temperature difference between the temperature of the hot wire 4 and the intake air to be substantially constant. Similarly, the resistors 9q, 9
r, 9t and the operational amplifier 10b, the heating wire 5
A second bridge circuit is configured to control the temperature difference between the temperature of the intake air and the intake air to be substantially constant. Also,
The resistors 9f, 9e and the transistor 12a constitute a first amplifier circuit that current amplifies the output of the first bridge circuit. Similarly, the resistor 9
u, 9v and the transistor 12b constitute a second amplification circuit for current amplifying the output of the second bridge circuit. In addition, the resistor 9c is as shown in FIG.
This stabilizes the first signal V ₁ shown in FIG. Similarly, resistor 9s stabilizes the second signal V ₂ shown in FIG. 4b. Further, the circuit composed of the hot wire 4, the first bridge circuit, the first amplifier circuit, and the resistor 9c detects the first signal V ₁ of the one-sided Karman vortex street generated on the downstream side of the vortex generator 3. itself constitutes the detection circuit of the hot wire flowmeter. Similarly, a circuit composed of the hot wire 5, the second bridge circuit, the second amplifier circuit, and the resistor 9s detects the second signal V ₂ of the Karman vortex street on the other side generated on the downstream side of the vortex generator 3. However, it constitutes the detection circuit of a hot wire flowmeter by itself. Also,
With the resistors 9g, 9h, 9m, 9n, 9p, operational amplifier 10c, and capacitors 11a, 11b,
A first differential circuit is configured to amplify a difference signal between the first signal V ₁ and the second signal V ₂ and output a third signal V ₃ . The resistors 9i, 9j, 9k, and 9l and the operational amplifier 10d constitute a waveform shaping circuit that shapes the third signal _V3 and outputs the fourth signal _V4 . In addition, the voltage input to the (+) input terminal of the operational amplifier 10a is controlled by the resistors 9x, 9y, and 9z.
An adder circuit is configured to take the average of V ₊ and the voltage V ₊ input to the (+) input terminal of the operational amplifier 10b and output a fifth signal V ₅ . Further, the first bridge circuit equilibrium condition is as follows: Value of resistor (9a)/value of resistor (9b)=resistance value of hot wire (4)/value of resistor (9b).

Similarly, the equilibrium condition of the second bridge circuit is as follows: Value of resistance (9q)/value of resistance (9r)=resistance value of hot wire (5)/value of resistance (9t).

Next, the operation of the flow rate or flow rate measuring device having the above configuration will be explained. First, if the temperature coefficient of resistance of the hot wire 4 and the temperature coefficient of resistance of the resistor 9a are set equal, the temperature control of the hot wire 4 constitutes the temperature control of the temperature difference change method called a hot wire anemometer, and the first of the Karman vortex street on one side At the same time as detecting the signal V ₁ (see Figure 4 a), the current I _H1 flowing through the hot wire 4 is the temperature of the intake air;
Regardless of the change in pressure, the value corresponds to the mass flow rate, and the voltage V ₊ or V _- of the operational amplifier 10a has a value corresponding to the mass flow rate. Similarly, if the temperature coefficient of resistance of the hot wire 5 and the temperature coefficient of resistance of the resistor 9a are set equal, the temperature control of the hot wire 5 constitutes the temperature control of the temperature difference change method called a hot wire anemometer, and the Karman vortex street on the other side The second signal V ₂ (see Fig. 4b) is detected, and the current I _{H2 flowing through the hot wire 4 becomes a value corresponding to the mass flow rate regardless of changes in the temperature and pressure of the intake air, and the current I H2} flowing through the hot wire 4 becomes a value corresponding to the mass flow rate, Voltage V ₊
Alternatively, V _- will be a value corresponding to the mass flow rate. On the other hand, a laterally symmetrical and regular Karman vortex street is generated in the wake of the vortex generator 3. Therefore, the hot wires 4 and 5 are simultaneously cooled by the average flow velocity and alternately cooled by the high frequency vortex frequency. Therefore, the first signal V ₁ and the second signal V 2 for keeping the hot wires 4 and 5 at a predetermined temperature have components 1 and ₂ corresponding to the average flow velocity, and components ΔV ₁ and ΔV ₂ corresponding to the flow velocity change due to the Karman _vortex . It consists of ΔV ₂ . The components ΔV ₁ and ΔV ₂ have opposite polarity;
A third signal V ₃ (see FIG. 4c) is obtained from K ₁ ×(ΔV ₁ −ΔV ₂ ). This third signal V ₃ is waveform-shaped by a waveform shaping circuit to obtain a fourth signal V ₄ (see FIG. 4d) which is a frequency signal. The ratio between the frequency of this fourth signal _V4 and the flow velocity of the intake air is approximately constant. A frequency signal is then obtained which is equal to the volumetric flow rate of the intake air per unit time. Next, if the temperature coefficient of resistance of the hot wire 4 and the temperature coefficient of resistance of the resistor 9a are made equal, and the temperature coefficient of resistance of the hot wire 5 and the temperature coefficient of resistance of the resistor 9q are made equal, the hot wire 4 and the hot wire 5 will each This is a so-called hot wire anemometer temperature difference change method in which the temperature difference increases little by little as the temperature of the intake air increases. Therefore, the mass flow rate of the intake air can be detected regardless of the temperature and pressure of the intake air. A function of this mass flow rate is the control current of the hot wire, and the terminal voltage of resistors 9d and 9t is also a function of the mass flow rate. Then, the fifth signal V ₅ of the analog voltage whose modulation due to the vortex has been canceled by the addition circuit is V ₅ = (A + BU〓)〓 However, U: (Kg/hr)
Therefore, it is possible to obtain the same analog output as a normal hot wire anemometer.

However, according to conventional flow rate or current velocity measurement devices, as the flow velocity of the fluid to be measured increases and the vortex frequency increases, the amplitude of the third signal V ₃ decreases above a certain frequency due to responsiveness limitations. Eventually, it becomes undetectable. This detection upper limit is determined by the responsiveness of the hot wire feedback circuit, which is determined by the responsiveness of the hot wires 4 and 5, the responsiveness of the operational amplifiers 10a and 10b, and the like. Since there are limits to the responsivity of the hot wires 4 and 5 and the responsivity of the operational amplifiers 10a and 10b, there is a natural limit to the upper limit of detection, resulting in drawbacks such as unstable detection at large flow rates. Ta.

Therefore, an object of the present invention is to provide a flow rate or flow velocity control device that can increase the amplitude of the detection voltage on the high frequency side of the vortex frequency and widen the detectable range with a simple configuration. .

In order to achieve such an object, the present invention provides a circuit network whose impedance changes depending on the frequency on at least one side of the bridge circuit constituting the hot wire temperature control circuit, and adjusts the set temperature of the hot wire as the vortex frequency increases. This will be explained in detail below using examples.

FIG. 5 is a circuit diagram showing an embodiment of a measuring circuit used in the flow rate or flow rate measuring device according to the present invention. In the same figure, 19a to 19d are resistors, 20
a and 20b are capacitors.

As shown in FIG. 1, this measurement circuit is incorporated into a vortex generator 3, hot wires 4 and 5, and a support 6 to constitute a flow rate or flow rate measuring device according to the present invention. Furthermore, it goes without saying that the operation without the capacitors 20a and 20b is similar to that shown in FIG. Moreover, FIG. 6 is a diagram showing the output characteristics of the measuring circuit shown in FIG. 5, where the vertical axis shows the detection output V, and the horizontal axis shows the flow velocity v or the flow rate p or the vortex frequency f. The straight line A shows the fifth signal V ₅ , the curve B shows the phase lead compensated third signal V ₃ in FIG. 5, and the curve C shows the third signal V 3 in FIG. ₃ .

Next, the operation of the flow rate or flow rate measuring device having the above configuration will be explained. First, in the first bridge circuit, the impedance of the sides of the resistors 19a and 19b on the high frequency side becomes small due to the action of the capacitor 20a, and the impedance of the hot wire 4 on the high frequency side becomes large. In other words, on the high frequency side, the impedance of the capacitor 20a becomes small, and frequency compensation, that is, phase lead compensation is performed in the feedback amplifier circuit of the first bridge circuit. Therefore, the set temperature of the hot wire 4 is increased on the high frequency side, and as shown by curve B in FIG. 6, the detection sensitivity can be increased. Similarly, in the second bridge circuit, due to the action of the capacitor 20b, the impedance of the sides of the resistors 19c and 19d on the high frequency side becomes small, and the impedance of the hot wire 5 on the high frequency side becomes large. In other words, on the high frequency side, the impedance of the capacitor 20b becomes smaller,
Frequency compensation, ie phase lead compensation, is performed on the feedback amplifier circuit of the second bridge circuit. Therefore,
The set temperature of the hot wire 5 is increased on the high frequency side, and as shown by curve B in FIG. 6, the detection sensitivity can be increased.

In addition, in the above embodiment, a phase compensation circuit (resistors 19a, 19
b, capacitor 20a and resistors 19c, 19
d, capacitor 20b) is used, but it goes without saying that the same effect can be achieved by providing a phase compensation circuit consisting of a desired two-terminal network on other sides as well. Further, in the above embodiments, the case where Karman vortices are detected using two hot wires has been described, but it goes without saying that the detection of swirl vortices can be similarly performed even when one hot wire is used.

As explained in detail above, the flow rate or current velocity measuring device according to the present invention has a simple configuration in which frequency compensation is performed on the feedback amplifier circuit of the bridge circuit that controls the temperature of the hot wire, and thereby the flow rate or current velocity measuring device according to the present invention can be used to measure the vortex frequency on the high frequency side. Since the amplitude of the detection voltage can be increased, there are effects such as being able to widen the flow rate detection range.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing a conventional flow rate or flow rate measuring device, Fig. 2 is a plan view showing the case where this flow rate or flow rate measuring device is installed in a conduit, and Fig. 3 is a block diagram showing a conventional flow rate or flow rate measuring device.
A detailed circuit diagram of the measurement circuit shown in FIG.
FIG. 5 is a circuit diagram showing an embodiment of the measuring circuit used in the flow rate or flow rate measuring device according to the present invention, and FIG. 6 is a diagram showing the output characteristics of the measuring circuit shown in FIG. 5. 1... Flow rate or flow rate measuring device, 2... Conduit, 3
... Vortex generator, 4 and 5 ... Heat wire, 6 ... Support body, 7 ... Measurement circuit, 8 ... Power terminal, 9a to 9
z...Resistance, 10a-10d...Operation amplifier, 1
1a and 11b...capacitors, 13-15...
...Node, 16-18...Output terminal, 19a-1
9d...Resistor, 20a and 20b...Capacitor. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1 A vortex generator installed in the fluid to be measured causes
The flow rate is detected as a change in a fluid-like vortex, the change in this fluid-like vortex is detected as a change in the frequency of an electric signal by at least one heat-sensitive element, and the detection is obtained by using cooling of this heat-sensitive element. In a device that measures a flow rate or flow velocity by amplifying a signal with an operational amplifier and feeding back the output of the operational amplifier so that the difference between the temperature of the heat-sensitive element and the temperature of the fluid to be measured takes a desired value, a heating wire is used. A flow rate or flow velocity measurement characterized in that a circuit network whose impedance changes depending on the frequency is provided on at least one side of a bridge circuit constituting a temperature control circuit, and the set temperature of the hot wire is increased as the vortex frequency increases. Device.