JPS58158519A - Device for measuring flow rate or flow speed - Google Patents

Abstract

PURPOSE:To improve initial starting and operation stability,by imparting a desired offset voltage between the input signals to the two input terminals of an operation amplifier constituting a bridge circuit. CONSTITUTION:A circuit, which controls a hot wire at an approximately constant temperature, is constituted by a resistor 101, the hot wire 102, resistors 103 and 104, and the operation amplifier 106. A diode 503 is connected between the noninverted input terminal of the operation amplifier 106 and the connecting point of resistors 501 and 502. The resistors 501 and 502 form a series circuit. To one end of the series circuit, a voltage Vcc is applied, and the other end is grounded.

Description

DETAILED DESCRIPTION OF THE INVENTION In particular, the present invention detects the generated number of Karman vortices or swirl vortices using a hot wire, and
The present invention relates to a flow velocity or original sound measuring device which is designed to have a good flow rate and to operate stably even when there is a burr.

This type of device is proposed in Japanese Utility Model Publication No. 48-14448. The method disclosed in this conventional example is that a hot wire gold film is placed inside the negative through hole provided in the columnar object that constructs the extraction body.
It was a method to detect the number of simplifications produced.

As pointed out in the above-mentioned Japanese Utility Model Publication No. 48-14448, the method of detecting analog cooling changes of hot wires by arranging them in the fluid to be measured does not allow turbulence to occur due to changes in flow velocity. There were drawbacks such as changes in signal detection sensitivity in response to changes in the signal and poor frequency characteristics.

In addition, a pair of bare heating edges is provided downstream of the #J generator, and both heating wires are controlled at a constant temperature, so that the entire vortex signal is determined by the difference signal of IIJ Gohgo of each heating wire. When attempting to detect the hot wires, there is a drawback that stable detection cannot be expected because differences in the characteristics of the operational amplifiers used for the respective hot wires cause differences in the respective detection signals. Furthermore, it may not start due to variations in the offset voltage of the operational amplifier.

Here, according to Fig. 1, the flow velocity of the secondary rice, fc, is the flow rate m++'
The iE device will be described. In this figure 1, 4°5
are hot wires, and each end of both hot wires 4 and 5 is grounded, and the other end of the hot wire 4 is connected to the inverting input terminal of the operational amplifier 21, and connected to the transistor via &[23 gold. 39 emitters.

Connection point φ! between the emitter of the transistor 39 and the resistor 23!
is grounded through resistors 25 to 27, and resistor 25
1) The thermistor 31 is tilted. resistance 2
The connection point between 6 and 27 is connected to the non-inverting input terminal of the operational amplifier 21.

The output end of the operational amplifier 21 is grounded via a resistor 36 and is also connected to the base of a transistor 390 via a resistor 35. The collector of the transistor 39 is connected to Vc.
A voltage of c is applied.

Thus, the hot edge 4, the resistors 23, 25 to 27, and the thermistor 31 form a bridge N path, and the feedback path is formed mainly from the arithmetic amplifier 21 and the transistor 39. Circuit toyoji, heat l1ll
! i! 4 to a constant temperature. The detection output v1 of the heat &4 is applied to the emitter of the transistor 39.

This emitter is connected to a non-inverting input terminal of an operational amplifier 48 via a capacitor 41 and a resistor 42.

Similarly, the other end of the hot wire 5 is connected to the inverting input terminal of the operational amplifier 22, and is also connected to the emitter of the transistor 40 via the resistor 24. The connection point with this emitter total resistance 24 is grounded via resistors 28 to 30, and a thermistor 32 is connected to the resistor 28 in parallel with the 6° resistor 28 and 29. Connected to the input end.

The output terminal of the operational amplifier 22 is grounded through a resistor 38 and connected to the base of a transistor 40 through a resistor 37. A voltage of Vcc is applied to the collector of this transistor 40.

Thus, hot wire 5, resistance 24.28-30 samister 32
A bridge circuit 9 is constituted by the above, and a feedback circuit is constituted mainly by the operational amplifier 22 and the transistor 40. This bridge N path and the feedback circuit control the hot wire 5 to a constant temperature. The detection output V2B of the hot wire 5 is set to appear at the emitter of the transistor 40.

The emitter of transistor 40 is connected to capacitor 44 and resistor 4.
5 to the non-inverting input terminal of the operational amplifier 48. A voltage of Vcc is applied to this non-inverting input terminal via a resistor 46, and is also grounded via a resistor 47.

A resistor 4 is connected between the output terminal and the inverting input terminal of this operational amplifier 48.
3 is connected. Operational amplifier 48 and resistors 42 and 43
．． The circuit with 45 to 47 and capacitors 41 and 44 is as follows:
This circuit extracts and amplifies only the detection output of the Karman vortex contained in the outputs Vl and Vz, and outputs it to the output terminal of the operational amplifier 48 as an output V3.

This output v3 is applied to the inverting input terminal of the voltage comparator 49. A non-inverting input terminal of the voltage comparator 49 is connected between the connection point of resistors 50 and 51, and is also connected to the output terminal via a resistor 52. resistance 50
and 511rs form a series circuit, one end of which is connected to Vcc.
voltage is applied, and the other end is grounded. A voltage of Vcc is applied to the output terminal of the voltage comparator 49 via a resistor 53.

This circuit consisting of the voltage comparator 49 and the resistors 50 to 53 constitutes a waveform shaping circuit that converts the output (3) to the output V4 (pulse output), and this output No. 7 is a frequency output.

The thermistors 31 and 32 are used to detect the temperature of the object to be measured, and thereby correct the control 4I temperature of the hot wires 4 and 5 to an appropriate value according to the temperature of the fluid.

In the conventional flow rate or flow rate measurement device configured as described above, a case will be considered in which variations in the offset bias current, offset bias current, etc. exist in the operational amplifiers 21 and 22.

Since the circuit for controlling the heating wires 4 and 5 to a substantially constant temperature has exactly the same configuration, this basic circuit is shown in FIG. 2 for ease of explanation.

In this Fig. 2, 101 is a resistor whose resistance value is R
3, 102 is a hot wire whose resistance (In is RH), 103 is a resistor whose resistance value is IRI, 104 is a resistor with R2, and 106 is an operational amplifier whose input/output terminal voltage is V
+, V-, Vo. 105 is V ten.

■Let the offset voltage Vos appear between one terminal.

In this case, RH V-E□Vo...(2) R3+
RH In the steady state, the relational expression V+=V-...(3)' holds true.

This relational expression and the offset voltage VO8% terminal voltage Vo
Figures 3 (a) to (C) show the relationship between When used as a current meter, this relationship must be met.

However, as VO8 approaches 0, Vos<O as shown in Figure 3(e) finally occurs, and when vo approaches 0, V->V0 (V-=V+ is the stable point). As a result, the circuit becomes permanently inoperable. Therefore, in order for this circuit to operate stably, VO8 must be 0.

Furthermore, as shown in FIG. 3(b), the field value of Vos>O changes. This means that the sensitivity of both Kalman detection signals is VO3.
This means that the detection output changes depending on the zero value, and when detection is performed using two hot wires 4 and 5 as shown in FIG. The disadvantage is that the balance is disrupted.

In addition, if this device is to be applied to an automobile intake air amount measurement device, it must be a device that operates stably over a wide temperature range, and the operational amplifiers 21 and 22 are also inexpensive and general-purpose products that can be manufactured in Tendo. Must. Therefore, it is not possible to adjust the offset voltage using the operational amplifier itself.
Furthermore, there is no good adjustment method in cases where the VOR changes depending on the magnitude of the values of 10 and V-.

This invention was made in order to eliminate the above-mentioned drawbacks of the conventional technology, and either applies the entire offset voltage or adds a control circuit so that the Hiraga point of the bridge (b) has a desired value. By doing this, the disadvantage that the detection sensitivity of the cormorant signal changes due to the offset voltage or frequency characteristics of the P5 operational amplifier is eliminated, and
It is possible to improve the detection sensitivity so that there is no difference in detection sensitivity when detecting all the signals by using two heat-sensitive elements, and also to create a flow velocity or original sound measuring device that can stably start up under any circumstances. The entire purpose is to provide.

Embodiments of the flow rate or flow rate measuring device of the present invention will be described below with reference to the drawings. FIG. 4(a) is a diagram showing a vortex generator in a fluid applied to the embodiment.
Figure (b) is an enlarged perspective view of the yarn generator. This fourth
In both figures (a) and 4(b), 1 is a conduit, and fluid flows in the direction indicated by arrow A through this conduit. A vortex generator 2 is provided in one circle of this conduit, and regular Karman waves are generated behind and on the side of the vortex generator 2. As is clear from FIG. 4(b), the vortex generator 2 is provided with a pair of heating wires 4, 5, and these heat 1fM4, 5 are connected to the support 3, respectively.
It is widely supported. The support column 3Vi is fixed to the vortex generator 2. The hot wires 4 and 5 are regularly cooled alternately by the left and right vortices 1''.

Figure 5 shows the thermal iIMffi attached to the above-mentioned vortex generator 2.
This is a circuit diagram showing the basic configuration of one embodiment of the flow velocity or flow rate measuring device of the present invention used, and corresponds to the above-mentioned FIG. 2. In FIG. 5, parts that are the same as those in FIG. 2 are given the same reference numerals, and their explanation will be omitted, and the newly added parts will be described with emphasis on all parts.

In this FIG. 5, 501 and 502 are resistors, and 50
3 is a diode. Diode 503 is connected between the non-inverting input terminal of operational amplifier 106 and the connection point between resistors 501 and 502. The resistors 501 and 502 form a direct current circuit, and a voltage of Vcc is applied to one end of this direct current circuit, and the other end is grounded.

If VO8 in Fig. 5 is Vos < 0, then when the power is turned on, when p vo = o, V -> V0, and it will not start forever, but due to the effects of the added resistors 501 and 502 and the diode, Vos < OTh It is possible to compensate so that V0 is lifted so as to cancel it out, and the relationship of V-<V0 is established.

FIG. 6 shows the functional relationship of the voltages V+ and V- shown in FIG. 5 with respect to the output voltage Vo. According to this, it is clearly understood that until the diode 503 is reverse biased, the slope of 10 is raised as shown by the dotted line, and Vos compensates for VO8≧0.

As shown in Figure 5, the effect of the added circuit is apparent.

This allows the circuit to be started stably in any case. Of course, depending on the VccO value at the connection point of the resistor 501 shown in FIG. 5, the same effect can be expected even if the resistor 501 alone increases the voltage at the V point.

Next, even if vos≧0, if the value of VO8 is different,
Let us consider the reason why the detection sensitivity differs depending on the magnitude of the voO value. The cases shown in FIGS. 3(a) and 3(b) correspond to typical examples of this case. In the case of Fig. 3(a), the slope of V- is always constant regardless of vO so that V0 = V-,
FIG. 3 (In bJ, the slope of V- for V+=V- decreases as vO increases.

According to the inventor's experimental results, V to make this V0=V-
It is best for the stability of detection sensitivity to detect vortex signals when the slope of - changes slightly decreasing in response to an increase in VO. It is also known that the disadvantage of narrowing the detectable frequency range is that it narrows the detectable frequency range.

FIG. 7 is a basic configuration diagram of another embodiment of the present invention. In this Figure 7, 701 is a resistor with a resistance value R5, 702
is a diode and its forward voltage is the total VF. The non-inverting input terminal of the operational amplifier 106 is further connected to the resistor 7 in the circuit of FIG.
01 and a diode 702 in series.

In this case, the functional relationship μ between V and VO is shown in FIG. In this FIG. 8, the corrected V0 is VosVF
If Vo≧VF, the line becomes a solid line.If Vo≧VF, the line becomes a dotted line.

By adjusting this vF or RsO value,
Offset voltage and other variations in the 1m meter 106 can be corrected as desired. When the hot wires are stretched in parallel on the left and right sides, it is possible to arbitrarily adjust the unbalanced detection signals obtained from the left and right sides.

FIG. 9 shows the output waveform fll of a circuit in which a vortex signal is detected using the basic circuit adjusted by VC as shown in FIGS. 7 and 8. FIG. 9(a) shows the average value of flow rate versus output voltage VQ (Vo
) is shown. In this case, the flow rate on the horizontal axis may be the flow velocity, or may be proportional to the vortex frequency F.

Vo on the vertical axis corresponds to the output of a normal hot wire anemometer, and is expressed by the King 0 equation. Figure 9 (
Figure 9(b) shows an example of detecting vortex signals at points a and b in &).
Shown below. The flow rates at points a and b are approximately 1:2.

As described above, if VO5 is not an appropriate value, the amplitude of the vortex signal is unstable, and the waveform may become distorted, including abnormal high-wave components. This situation can occur if VO8≦0.

With the correction shown in FIGS. 5 and 7, #t of 1st shift,
Lid characteristics (frequency characteristics), waveform distortion, etc. are improved.

FIG. 10 is a circuit diagram showing the overall electrical path of another embodiment of the present invention, corresponding to FIG. In FIG. 10, in order to avoid duplication, the same parts as those in FIG. 1 are given the same reference numerals and their explanations are omitted, and the parts different from those in FIG. 1 will be mainly described.

In FIG. 10, as is clear from the explanation of FIGS. 5 and 7, the non-inverting input terminals of the corner devices 21 and 22 are different from those in FIG. ,
In FIG. 10, the non-inverting input terminal of the operational amplifier 21 is further grounded to the circuit of FIG.
A voltage of Vcc is applied via.

Similarly, the non-inverting input terminal of the operational amplifier 22 is connected to the resistor 63.
It is grounded through a direct circuit of a diode 64 and a voltage of Vcc is applied through a resistor 66.

By doing this, the positive offset voltage VO8≧0 is forcibly applied to the non-inverting input terminal side of the bridge circuit by the resistors 66 and 67. It is assumed that the offset voltage of the operational amplifier itself and other unbalanced components are added to this, and that the added components are different between the bridge of the four hot wires and the five hot wires.

In this case, each bridge (b) path can be activated easily, but since there is an imbalance as described above, a difference occurs in the detection sensitivity corresponding to the flow rate (that is, the vortex frequency) of the detection outputs Vl and V2. This difference can be easily balanced by adjusting the value of the resistor 61 or 63.

FIG. 11 is a circuit diagram of still another embodiment of the present invention, and the difference from FIG. 10 is that the connection point of the bridge circuit including the hot wire 4.5 is connected to the non-inverting input terminal of the operational amplifier 21.220. The point is that the bridge circuit is configured as follows.

That is, the resistors 65 and 66 are used to apply a positive offset voltage, thereby ensuring initial start-up when the power is turned on, and further ensuring the balance and stability of the output voltages v1 and V2. However, with only the resistors 65 and 66, the offset voltage and other effects w' can be corrected only on one side. The means for correcting the reverse direction are resistors 61.63 and diodes 62.64.

With both of these, it is possible to easily reduce the imbalance occurring in the outputs Vl and V2.

These effects and countermeasure principles can be easily understood by graphing the characteristics of (10) and (2) - with respect to Vo as described above. No matter how many places P)r the offset voltage is applied to, no matter where it is on the bridge circuit,
Similar effects can be expected.

It would be better to have more fine control depending on the VoO value.

Further, the heating wire may be a thermistor, a bossostar, a diode, a transistor, or other heat-sensitive element.

In each of the above embodiments, the Karman flow rate of 1゜ using two hot ray sounds was described, but it goes without saying that the same effect can be expected even with one ray sound or with the swirl type Sakiryu Sokei. Nor.

As explained above, according to the flow velocity or flow rate measuring device of the present invention, the output of the operational amplifier is connected between the input signals of the two input terminals of the operational amplifier constituting the bridge circuit for controlling the temperature of the hot wire to a constant temperature. With a simple configuration that provides a desired offset voltage in response to the number of times w! This has the effect of significantly improving the initial start-up and operation stability of the r operation.

Furthermore, when trying to detect the difference signal between two hot wires of Karman vortices, for example, even if the two operational amplifiers have irregularities in offset voltage, frequency characteristics, etc., they can be easily balanced independently. This has the effect that the detection sensitivity of the dog is not affected by the temperature change of the constant fluid to be subjected to 1111.

1'Also, even if the operational amplifier itself is not equipped with an offset voltage adjustment function, all settings can be made using external input/output terminals, so the desired function can be achieved using inexpensive general-purpose elements.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a conventional flow rate or flow rate measuring device;
The figure is a basic circuit diagram of the main parts of the flow rate or flow rate measuring device shown in Fig. 1, and Fig. 3 (a, 1 to 3 (e) is a basic circuit diagram for explaining the operation of the operational amplifier in the basic circuit of Fig. 2. FIG. 4(a) is a diagram showing operating characteristics for explaining the relationship between input/output voltage and offset voltage. A diagram showing the state that occurs, FIG. 4 (b, l are enlarged perspective views of the same vortex generator as above, FIG. 5 is a basic circuit diagram of the main part in an embodiment of the flow velocity or flow rate mlJl installation of the present invention,
Figure 6 is an operating characteristic diagram for explaining the relationship between the input/output voltage, offset frost, and pressure of the operational amplifier in the basic circuit diagram of Figure 5, and Figure 7 is the second diagram of the flow velocity or flow rate measuring device of the present invention. The basic circuit diagram of the main part in the embodiment, FIG.
FIG. 9 (a
] and FIG. 9(b) are diagrams showing the output-pressure waveform of the operational amplifier in the basic circuit of FIG. 7, and FIG.
1 is an overall circuit diagram of a different embodiment of a flow rate or flow rate measuring device according to the invention, respectively. 1... Conduit, 2... Vortex generator, 4, 5... Heat wire,
21゜22.48,106... operational amplifier, 23~3
0°35~38.42.43.45~47.50~53
゜61.63, 65, 66.501-503...Resistor, 31.32...Thermistor, 39.40-...Transistor, 62.63.503...Diode. In addition, the same reference numerals in the figures indicate the same or equivalent parts. Figure 9 (a) 0, sb, s, Qoc■oqF (b)

Claims (1)

[Claims] tl+ A vortex generator provided in the fluid to be measured; this vortex generator detects a fluid change in the flow velocity or flow rate of the fluid to be measured, and detects it as a change in the frequency of an electrical signal. At least one heat-sensitive element, a bridge circuit on one side of the heat-sensitive resistor, the unbalanced voltage of the bridge are respectively applied to the inverting and non-inverting input terminals of the operational amplifier, and the output of the operational amplifier is all returned to the bridge circuit. Means for controlling the temperature of the heat-sensitive element so as to maintain a substantially constant temperature, and detecting a frequency corresponding to the number of occurrences of #8 in the output of the operational amplifier; means for applying a desired offset voltage between the inverting and non-inverting input terminals of the operational amplifier so that the Pritsuno circuit is activated even when the output of the operational amplifier is below a specified voltage; When the node J is controlled so that the f-direction of the output of the operational amplifier becomes the desired one-direction, the means for controlling the equilibrium point of the bridge circuit to a desired value are also changed. (2) The heat-sensitive element is composed of heating wires arranged symmetrically with respect to the IH generator, and is used to compensate for the fluctuation of the left and right heating wires and the offset voltage and characteristic fluctuations of the performance hall. The inverting and non-inverting inputs of the operational amplifier 1@
Means for applying the entire desired offset voltage between the bridges and means for applying the entire desired offset voltage to the output of the operational amplifier so that the offset voltage changes to the desired value is provided. A flow rate or flow rate 1t (11 constant device) according to claim 1, characterized in that the device is provided in an intake passage of an automobile, and is designed to completely plan the intake air of the automobile. range 1
2. A device for measuring flow velocity or flow velocity according to paragraphs 2 and 2.