JP2582971B2 - Fluid flow rate detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluid flow detecting device capable of accurately detecting the flow rates of various fluids.

[0002]

2. Description of the Related Art Conventionally, the configuration of a device for detecting a fluid flow rate is as shown in FIG. 7, for example. For example, heating resistors 101A and 101B are connected to a sensor pipe 100 branched from a bypass pipe through which a gas (fluid) supplied to a semiconductor flows.
Is wound (or provided in the tube 100). The resistors 102 and 103 are connected so as to form a bridge circuit with the heating resistors 101A and 101B. A current flows from the constant current source 104 to the bridge circuit. The impedance of the elements constituting the bridge circuit is set so that the bridge circuit is balanced when no fluid is flowing through the sensor tube 100. The balanced output of the bridge circuit is taken into an operational amplifier 107 constituting a differential amplifier via resistors 105 and 106. If no fluid flows, the differential amplifier will produce a zero output at its output terminal out due to the equilibrium state of the bridge circuit. However, when the fluid flows out, the heating resistor 101A located on the upstream side in the sensor tube 100
Is cooled (or heated) more than the heating resistor 101B located on the downstream side, and the equilibrium state of the bridge circuit is broken. The above cooling is proportional to the mass flow rate of the fluid flowing through the sensor tube 100, and the output signal obtained from the output terminal out of the differential amplifier is proportional to the mass flow rate of the fluid flowing through the sensor tube and thus flowing through a bypass pipe (not shown). Will have a proportional value.

[0003]

However, in the above-described conventional fluid flow rate detecting device, the output of the differential amplifier is equal to the flow rate Q.
As shown in “OUT PUT” of FIG. 8A, there is a problem that the linear output Oi departs from the ideal linear output Oi and has an error ε. FIG. 8B shows that the error ε increases as the flow rate Q increases.

Therefore, conventionally, two methods, (1) correction by a broken line approximation circuit and (2) correction by feedback adjustment, have been performed.

First, in the correction by the broken line approximation circuit, FIG.
Amplifier 901 _1, 901 _2, adding ... a a respective diode voltage -V ₁ having amplification characteristic close to the ideal straight line predetermined voltage V _1, V _2, ... for each as, -V _2, switched ... by. Note that the amplifier 902 is an inverting amplifier. According to such a circuit, when a single amplifier circuit, while away from the ideal line Oi as O ₁ of FIG. 10 (a), each voltage interval O _1, O _2, O _3, separated by ... And the error ε
As shown in FIG. 10 (b), it can be suppressed within a small range for each section.

However, according to this method, if the error is reduced, the number of switching amplifiers increases, which causes a problem that the circuit configuration becomes large and complicated.

On the other hand, a circuit for performing correction by feedback adjustment is shown in FIG. That is, a configuration is added to the configuration of the fluid flow control device shown in FIG. 7 in which the output of the differential amplifier is fed back to the constant flow source 104 via the variable resistor Rv to control the amount of current flowing through the bridge circuit. According to such a configuration, a device that outputs an output signal that is linear with respect to the flow rate Q by increasing the value of the current flowing through the bridge circuit as the fluid flow rate increases is realized with a simple configuration.

However, according to this method, there is a problem that the temperature of the heating resistors 101A and 101B rises due to a change in the current value, and it takes time until the temperature becomes constant again, resulting in a slow response.

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the conventional fluid flow rate detecting device, and has as its object to provide a fluid having a quick response and a relatively simple structure. The object is to provide a flow detection device.

[0010]

According to the present invention, there are provided two heating resistors provided in a sensor tube through which a fluid flows, a resistor connected to these heating resistors and constituting a bridge circuit together with the heating resistors, An output extracting means for obtaining a balanced output of the bridge circuit; and a signal V ₀₂ (V ₀₂₎ corresponding to a linear error with respect to the flow rate based on the output V ₀₁ obtained by the output extracting means.
_{= V 01 (V 01 -V F1} ) (V 01 -V F2) ... (V 01 -
V _Fn )), a linear error generator for generating a linear error signal with respect to the flow rate from the signal V ₀₂ generated by the error corresponding signal generator, and an output obtained by the output extracting means. A fluid flow rate detection device is provided by including a subtraction means for subtracting the signal created by the linear error creation means from V ₀₁ to obtain a linear output of the flow rate.

[0011]

According to the above construction, an error signal is created, and this is subtracted from the output of the conventional fluid flow rate detection device to obtain an error signal.
It is possible to detect an appropriate fluid flow rate.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A fluid flow detecting device according to an embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows a fluid flow detecting device according to an embodiment of the present invention. 7, the same components as those in the conventional example of FIG. 7 are denoted by the same reference numerals, and the description thereof will be omitted. In the present embodiment, the detection signal V ₀₁ output from the operational amplifier 107
Plots a characteristic curve as shown in FIG.
It is assumed that it changes with respect to the flow rate Q as shown in FIG. In this case, the detection signal V ₀₁ is squared to obtain a linear error ε.
(V ₀₁ ) ² similar to the above is obtained. That is, a countermeasure in a case where the linear error ε is similar to y = x ² having the origin (O, O) as a vertex is obtained as follows.

That is, the output of the operational amplifier 107 is led to the two-input multiplier 1 to obtain the output (V ₀₁ ) ² . The output (V ₀₁ ) ² is led to a required point of the resistor R ₂ connecting between the inverting and non-inverting terminals of the operational amplifier 2 via the resistor R ₁ . The operational amplifier 2 basically constitutes a differential amplifier together with the resistors R ₃ and R ₄ , and the resistors R ₁ and R ₂ are variable resistors connected to the inverting input terminal, and the resistance value due to these is represented by ( R ₁₂ ), the feedback resistor R
_{Assuming that} the resistance value of No. ₄ is (R ₄ ), the gain of the inverting amplifier is G = − (R ₄ ) / (R ₁₂ ). The output V ₀₃ of the amplification by such a gain corresponds to the movement of the connection point to the resistor R _{2 in} the P and N directions.
The characteristics are as shown in FIG. That is, V ₀₃ = ± GV ₀₂ . Thus, by changing the position of the connection point for the resistor R ₃ of the resistor R _1, it produces an output V ₀₃ corresponding to the linear error epsilon. That is, the connection point location Ikan, making the corresponding signal linear error required by changing the magnitude and sign of V ₀₃ (polar).

The output signal V ₀₃ is supplied via a resistor R ₅ to
This is supplied to an operational amplifier 3 constituting a differential amplifier together with the resistors R ₆ , R ₇ and R ₈ . Here, the differential amplifier acts as a subtractor, and its output signal V ₀₄ is obtained as V ₀₄ = V ₀₁ −V ₀₃ . Here, since the gain of the operational amplifier 2 is adjusted so that V ₀₃ is a linear error ε, the output signal V ₀₄ is a detection output from which the linear error ε has been subtracted, and FIG.
The characteristic shown in (d) is exhibited. Thus the sign of the output signal V ₀₃ corresponding to the linear error ε may use an adder.

Next, a fluid flow detecting device according to another embodiment will be described with reference to FIGS. In this embodiment, the output characteristic of the device shown in FIG. 7 changes so as to exceed the ideal characteristic Oi as shown in FIG.
This is to deal with the case where the value has a positive value as shown in FIG. Therefore, in the present embodiment, the configuration of the error-corresponding signal generating means 10 is changed to 10A in FIG. 3 in the configuration of the apparatus shown in FIG. That is, to one input terminal of the multiplier 1 provides an output signal V ₀₁ of the operational amplifier 107 as it is.
And, the other input terminal of the multiplier 1
(V ₀₁ -V _F ). Here V _F represents the voltage when Oi and the V ₀₁ was intersected at other than the origin in FIG. 4 (a). Such a voltage − (V ₀₁ −V _F ) is obtained from V _{01 as} follows. Reference numeral 11 denotes an operational amplifier that constitutes an inverting amplifier. The non-inverting input terminal of the operational amplifier 11 is grounded to the inverting input terminal, with V ₀₁ is applied via a resistor R _11, via a resistor R ₁₂ Voltage (-V
_F ) is applied. Therefore, the input signal is (V ₀₁ −V
_F ), which is inverted and eventually becomes-(V ₀₁ -V _F ). Multiplier 1, V ₀₁ and - (V ₀₁ -V _F) and multiplication is performed, the output V ₀₂ becomes _{V 02 = -V 01 (V 01} -V F). In the following, as in the embodiment of FIG.
Amplification is performed by a gain G (| G | <1) using an amplification circuit centered on the resistor R ₁ and the resistor R ₂ as shown in FIG.
The movement of the contact point (movement in the P or N direction) with _V03
Make adjustments. The output signal V ₀₃ is supplied to the subtracter around the operational amplifier _{3, V 04 = V 01 -V} 03 is performed. As a result, V ₀₃ becomes a linear error ε,
The output signal V ₀₄ has a linear characteristic that does not include a linear error, as shown in FIG.

Next, a fluid flow detecting device according to another embodiment will be described with reference to FIGS. In this embodiment, the output characteristics of the device shown in FIG.
6 (a), and the linear error ε changes as shown in FIG. 6 (b), which is a combination of FIG. 2 (b) and FIG. 3 (b). is there. Therefore, in the present embodiment, in the configuration of the apparatus shown in FIG. 1, the configuration of the error-corresponding signal generating means 10 is changed as shown in 10B of FIG. here,
3 using multipliers 1A inputs, giving it an output signal V ₀₁ of the operational amplifier 107 to its one input terminal.
Then, − (V ₀₁ −V _F1 ) is given to the second input terminal of the multiplier 1A, and − (V ₀₁ −V _F1 ) is given to the third input terminal.
(V ₀₁ -V _F2 ). Here, the V _F1 in FIG. 6 (a), the represents the voltage when the the Oi and V ₀₁ initially intersect other than the origin, V _F2 represents the voltage when the next and Oi and V ₀₁ intersect. The above-(V ₀₁ -V _F1 ),-(V ₀₁ -V
_F2 ) is the same as that of FIG.
It is obtained in the same manner as in FIG. In multipliers 1A, V ₀₁ and - (V
₀₁ -V _F1 ) is multiplied by-(V ₀₁ -V _F2 ), and the output V ₀₂ is V ₀₂ = V ₀₁ (V ₀₁ -V _F1 ) (V ₀₁ -V _F2 ). In the following, amplification is performed by a gain G (| G | <1) in an amplifier circuit centered on the operational amplifier 2, and FIG.
V ₀₃ equals the error signal ε is performed suppression of the error corresponding signal (c) is obtained. The output signal V ₀₃ is V ₀₄ = V ₀₁ -V ₀₃ are given to the subtracter around the operational amplifier 3 is performed. As a result, since V ₀₃ is a linear error ε,
The output signal V ₀₄ has a linear characteristic that does not include a linear error as shown in FIG.

[0018] As described above, in this embodiment, the output characteristic curve of the fluid flow sensing device correcting circuit is not added by the voltage at the time of crossing the ideal characteristics Oi - (V ₀₁ -
V _Fn ) is produced and multiplied by V ₀₁ to obtain a linear error corresponding signal V ₀₁ (V ₀₁ −V _F1 ) (V ₀₁ −V _F2 )... (V ₀₁ −V _Fn ). This was G times by the amplifier to create a V ₀₃ equal to the linear error signal epsilon, by subtracting the V ₀₃ from V _01, system for a linear characteristics can be obtained. Note that n is an arbitrary number, but Oi and V ₀₁ are generally about twice at most (n = 2).
However, the configuration does not become complicated due to the increase in n.

Although the constant current type has been described above, the present invention can also be applied to a constant temperature heating type.

[0020]

As described above, according to the present invention, a signal corresponding to a linear error is simply generated from the output _V01 ,
Since obtaining a signal equal to the linear error by suppressing a signal corresponding to the linear error, which can be obtained only by linear without precisely the error output subtracted from V _01.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is a waveform chart of each part according to an embodiment of the present invention.

FIG. 3 is a main part block diagram of another embodiment of the present invention.

FIG. 4 is a waveform chart of each part of the embodiment using the main parts shown in FIG. 3;

FIG. 5 is a main part block diagram of another embodiment of the present invention.

FIG. 6 is a waveform chart of each part of the embodiment using the main parts shown in FIG. 5;

FIG. 7 is a block diagram of a conventional fluid flow detection device.

8 is a waveform chart of each part of the conventional example of FIG.

FIG. 9 is a block diagram of a fluid flow detection device including a correction circuit according to a conventional example.

FIG. 10 is a waveform chart for explaining the operation of FIG. 9;

FIG. 11 is a block diagram of a fluid flow detection device provided with another conventional correction circuit.

[Explanation of symbols]

 1, 1A Multiplier 2 Operational amplifier (linear error generating means) 3 Operational amplifier (subtractor) 10, 10A, 10B Error-corresponding signal generating means 100 Sensor tube 101A, 101B Heating resistor 104 Constant current source 107 Operational amplifier (output extracting means) )

Claims (5)

(57) [Claims] 1. A heating element provided in a sensor tube through which a fluid flows, a resistor connected to the heating element to form a bridge circuit together with the heating element, and a balanced output of the bridge circuit. an output take-out means, the signal V ₀₂ corresponding to the linear error to the flow rate on the basis of the output V ₀₁ of the output extracting means to obtain _{(V 02 = V 01 (V} 01 -
V _F1 ) (V ₀₁ −V _F2 )... (V ₀₁ −V _Fn )), and a signal of a linear error with respect to the flow rate is generated from the signal V ₀₂ generated by the error corresponding signal generation unit. fluid flow to the linear error preparing means, characterized in that it comprises a subtraction means from the output V ₀₁ of the output extracting means to obtain obtain the linear output of the flow rate by performing addition or subtraction of said linear signal error producing means for Detection device. Wherein error corresponding signal generating means, V as V ₀₂
Fluid flow sensing device according to claim 1, characterized in that it consists multipliers to create a ₀₁ ^2. 3. An error-corresponding signal generating means, comprising: V ₀₁ to V _F1
A subtractor for subtracting the fluid flow sensing device according to claim 1, characterized in that it comprises a multiplier for creating V ₀₁ (V ₀₁ -V _F1) from the output of the subtracter the V ₀₁ Prefecture. 4. An error-corresponding signal generating means, comprising: V ₀₁ to V _F1
, A second subtractor for subtracting V _F2 from V ₀₁ , the output of the first and second subtractors and the V _{01
V 01 (V 01 -V F1)} (V 01 -V F2) fluid flow sensing device according to claim 1, characterized in that it comprises a multiplier for creating from a. 5. A linear error generating means, comprising: an inverting amplifier constituted by an operational amplifier; a first resistor connected between the inverting and non-inverting input terminals of the operational amplifier; A second resistor connected between the first resistor and an output of the creating means, the second resistor being capable of moving a connection point to an arbitrary position of the first resistor.
The fluid flow detecting device according to claim 1.