JPH0143885B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device that measures a flow rate by transferring heat between a temperature-dependent resistor provided in a fluid and the fluid, such as an intake air amount of an automobile, a cooling water flow rate, a gasoline flow rate, a lubricating oil flow rate, etc. This is used to measure the flow rate, etc.

BACKGROUND ART Conventionally, a device that measures a flow rate by transferring heat to and from a fluid has been used to measure the intake air amount of an automobile. Special Publication No. 49-48893 and No. 56-
18723 hot wire flowmeters are known. These flow meters (shown in Figures 1 and 2) include a heater/temperature detection resistor (30 in Figure 1, R _H in Figure 2) and a fluid temperature detection resistor (18 in Figure 1, R H in Figure 2). R _K ′) and 2
Fixed resistors (19 and 21 in Figure 1, 14 and 16 in Figure 2) are installed on each side of the bridge to equalize the branch point voltage of the bridge, that is, the temperature of the fluid temperature detection resistor and the heater An error amplifier (2 in Figure 1) is installed so that the difference between the temperature of the temperature detection resistor and the
6. In step 19 in Figure 2, the error is amplified, the voltage applied to the bridge is controlled, the current flowing into the heater/temperature detection resistor is controlled, and the self-heating of the heater/temperature detection resistor is controlled, and the heater/temperature detection resistor is controlled. The flow rate is detected from the current flowing through the detection resistor.

Therefore, in the configurations shown in Figures 1 and 2, in order to keep the temperature difference between the fluid temperature detection resistor and the heater/temperature detection resistor constant, it is necessary to reduce the current flowing through the fluid temperature detection resistor to suppress self-heating as much as possible. Therefore, it is necessary to make the resistance value of the fluid temperature detection resistor larger than the resistance value of the heater/temperature detection resistor, and the temperature coefficients have to be made equal.

In addition, to eliminate the above-mentioned drawbacks, a heater/temperature detection resistor and a fluid temperature detection resistor having the same shape and the same resistance value are used to make the temperature difference between the two temperature detection resistors constant, as shown in Figure 3. Composition of JP-A-1985-
There are 43447.

In this configuration, since the feedback resistor added to the operational amplifier 12 is a fluid temperature detection resistor, when determining the gain of the amplifier circuit, it cannot be determined by the circuit alone, and active trimming integrated with the sensor section is required, reducing adjustment costs. There was a problem with getting bigger.

Further, in this type of device, the output signal is generally a current value flowing through a heater/temperature detection resistor in consideration of temperature characteristics, and a current detection resistor is provided, and the voltage across the resistor is used as an output signal. However, in order to increase the output, the current detection resistor must be increased.
In order to increase the sensitivity of the heater/temperature detection resistor, it is necessary to increase the voltage applied to the heater/temperature detection resistor, and due to contradictory events, the current detection resistor becomes a somewhat small value, and the output signal of the device changes to the current detection value. It becomes necessary to amplify the output of the resistor.

Furthermore, since one input signal of the operational amplifier 8 is outputted from a resistor circuit, and the other input signal is passed through one stage of operational amplifiers, the same frequency characteristics cannot be obtained, resulting in unstable control.

The present invention has been made in view of the above-mentioned problems, and includes a first temperature-dependent resistor that is provided in a conduit through which a fluid to be measured flows and that generates heat by itself when energized;
A second resistor, which is provided in the conduit and whose resistance changes with the temperature of the fluid to be measured, is not affected by the thermal influence of the temperature-dependent resistance.
temperature-dependent resistors, and measures the flow rate of the fluid to be measured from voltage signals across both temperature-dependent resistors generated by constant current control of both temperature-dependent resistors, the flow rate flowing through the first temperature-dependent resistor a first voltage/current converter that controls current; a second voltage/current converter that controls current flowing through the second temperature-dependent resistor; and a voltage across the first temperature resistor that divides the voltage across the first temperature resistor at a predetermined voltage division ratio. a first attenuator; an error amplifier for amplifying the difference between the output signal of the first attenuator and the output voltage of the second temperature-dependent resistor; and a second output to the second voltage/current converter.
By configuring the attenuator and the attenuator, the same shape and characteristics can be used for the first and second temperature-dependent resistors, and the cost is low.In addition, the current detection resistor can be made small, and the output can be easily increased using only the attenuator. The purpose of the present invention is to provide a flow rate measuring device that can measure the flow rate well.

An embodiment of the present invention will be described with reference to the drawings. Fourth
The figure is an electrical wiring diagram of the present invention, and FIG. 5 is its block diagram. 1 is a first temperature-dependent resistor that also serves as a heater and measures temperature. 2 is a second temperature-dependent resistor that detects the fluid temperature of the fluid to be measured. 3 is a conduit through which the fluid to be measured passes. Both the first and second temperature dependent resistors 1 and 2 have the same shape and the same electrical characteristics, for example, the diameter is
It uses a platinum resistance wire of 40 μm to 150 μm, and may be wound around a bobbin of ceramic or the like, or may be strung around an electrically insulated pin-shaped support in a conduit.

Reference numeral 4 denotes a measuring circuit that measures the flow rate of the fluid to be measured from the terminal voltages of the first and second temperature-dependent resistors 1 and 2, respectively. 41 is a first voltage-current converter, which converts a current _iH according to the input voltage signal from _J11 to the first temperature-dependent resistor 1.
It sucks from the flowing terminal J ₁₂ , and the operational amplifier OP
2, resistors R4 and R5, and a transistor _T2 . 42 is a second voltage-current converter;
It has the same function as the first voltage-current converter 41, and a current i _C corresponding to the input voltage signal is passed from the terminal 21 to the second temperature-dependent resistor 2 and absorbed from the terminal J ₂₂ .
It consists of an operational amplifier OP1, resistors R ₁ , R ₂ , R ₃ and a transistor T ₁ . A first attenuator 43 is composed of resistors R ₆ and R ₇ and divides the voltage across the first temperature-dependent resistor. 44 is an error amplifier, which is composed of an operational amplifier OP3 and input resistors R ₈ and R ₉ , and connects the voltage between terminal J ₂₁ and the ground, and the voltage between the connection point G of the resistors R ₆ and R ₇ of the first attenuator 43 and the ground. The difference with the voltage is amplified and output using the open loop gain of the operational amplifier OP3. Reference numeral 45 denotes a second attenuator, which is composed of resistors R ₁ 0 and R ₁ 1, and divides the output voltage of the error amplifier 44 into the first and second attenuators.
to inputs D and A of each of the voltage-current converters. J ₃ is the power input terminal of measurement circuit 4. J ₄ is the flow rate signal output terminal. J ₅ is the ground terminal of the measuring circuit 4.

The operation of the above configuration will be described below. In the first voltage-current converter 41, a voltage V _D is applied to the input terminal D.
is applied, the output of the operational amplifier OP2 is power-amplified by the transistor _T2 , and a voltage V _E is applied to the series circuit of the first temperature-dependent resistor 1 and the resistor _R4 . At this time, the resistance value of the first temperature dependent resistor is R _H
If the flowing current is _iH , then the following equation holds true.

V _E =i _H・(R _H +R ₄ )...(1) Also, the voltage V _F at terminal F of resistor R ₄ is given by the following formula.

V _F =i _H ·R ₄ (2) Since the configuration is such that the voltage V _F is fed back to the inverting input of the operational amplifier OP2, the following equation holds true.

V _D = V _F …(3) From equations (2) and (3), V _D = i _H・R ₄ , and if the resistance value of resistor R ₄ is constant, the current i _H flowing through the first temperature-dependent resistor 1 is It is proportional to the input voltage of the first voltage-current converter 41.

In the second voltage-current converter 42, similarly to the first voltage-current converter 41, when the resistance value of the second temperature-dependent resistor 2 is R _C and the flowing current is i _C , the following equation holds true.

V _B =i _C・(R _C +R ₁ +R ₂ ) …(4) (However, V _B is the voltage at terminal B) V _C =i _C・R ₂ , V _C =V _A …(5) That is, the second temperature The current i _C flowing through the dependent resistor 2 is the second
It is proportional to the input voltage V _A of the voltage-current converter 42.
Further, the voltages at points A, C, D, and F in the first and second voltage-current converters 41 and 42 are equal. Therefore, the output voltage of the first attenuator that divides the voltage across the first temperature-dependent resistor (voltage between point G and ground)
V _G is given by the following formula.

V _G = V _F + (V _E −V _F )×K ₁ (6) where K ₁ is the proportionality constant of the second attenuator and is expressed by the following equation.

K ₁ = R ₇ / (R ₆ + R ₇ ) …(7) Transforming equation (6) using (1)(2)(3)(4)(5), V _G =V ₀ +i _H・_{R H}・K ₁ …(8) (However, V ₀ = V _A = V _C = V _D = V _F ) Also, from equations (4) and (5), V _B = V _{0 +} i _C ) ...(9) Here, the error amplification circuit 44 converts the difference between the voltage V _B and the voltage V _G into the open loop gain K ₂ of the operational amplifier OP3.
Since the voltage is amplified by the second attenuator 45, divided by the voltage division ratio _K3 , and fed back to the first and second voltage-current converters 41 and 42, the right-hand sides of equations (8) and (9) are equal, and the following equation is obtained: The formula holds true.

K ₁・i _H・R _H = i _C・(R _C +R ₁ )...(10) If K ₁・i _H = i _C in equation (10), the following equation holds true.

R _H = R _C + R ₁ …(11) Here, to set K ₁・i _H = i _C , in equations (2) and (5), set V _F = V _C and i _H・R ₄ = i _C・R ₂ becomes i _C /i _H =
Since R ₄ /R ₂ , formula (11) is satisfied by choosing K ₁ = R ₄ /R ₂ .

Resistance values R _H of the first and second temperature dependent resistors 1 and 2,
When R _C is described by introducing a temperature coefficient α, the following equation is obtained.

R _H = R ₀ (1+KTa+K・ΔT) …(12) R _C = R ₀ (HKTa) …(13) However, R ₀ is 0°C of the first and second temperature dependent resistances 1 and 2.
Use one with the same resistance value and characteristics. ΔT is the temperature difference between both temperature dependent resistors.

Therefore, by substituting equations (12) and (13) into equation (11), we obtain the following equation.

ΔT=R ₁ /(R ₀・K) …(14) That is, the first temperature dependent resistance 1 is the second temperature dependent resistance 2
Compared to , the temperature is always controlled to rise to a constant value by ΔT. At this time, the current i _H flowing through the first temperature dependent resistor 1 is related to the flow rate. From equation (2), the current i _H is the voltage
Since it is proportional to V _F and equal to the voltage V _K at the output terminal K point of the second attenuator 45, V _K = i _H・R ₄ (15) Relationship between the output voltage V _H of the error amplifier 44 and the voltage V _K is determined by the partial pressure ratio _K3 of the second attenuator, and is expressed by the following equation.

V _K = K ₃ · V _H (K ₃ = R11/R10 + R11; constant) ...(16) The following equation is obtained from equations (15) and (16).

V _H = R ₄ /K ₃ ·i _H (17) That is, by adjusting the partial pressure ratio K ₃ of the second attenuator, the output signal corresponding to the flow rate of this device can be amplified to an arbitrary magnitude.

When the flow rate increases when the device is in a stable state, the self-heated heat of the first temperature-dependent resistor 1 flows out into the fluid, and the resistance value of the first temperature-dependent resistor 1 decreases. Then, the voltage V _E at point E becomes smaller, and the voltage V _G at the output point G of the first attenuator also becomes smaller. If the temperature of the fluid is constant, the second voltage-current converter 4
2, the state does not change and the voltage V _B at point B does not change.
Therefore, the output of the error amplifier 44 increases and the second
The output voltage V _K of the attenuator 45 increases.
Therefore, the input signals of the first and second voltage-current converters 41 and 42 increase, and the currents flowing through the first and second temperature-dependent resistors each increase. Then, the amount of self-heating of the first temperature-dependent resistor 1 increases, and the first voltage-current converter 4
The voltage V _E at point E at point 1 increases, and the output of the first attenuator 43 increases, while the voltage V B at point _B of the second voltage-current converter 42 also increases. However, the amount of increase in voltage V _G is larger, and when voltage V _B and voltage V _G become equal, that is, when the temperature difference ΔT between the first and second temperature dependent resistors 1 and 2 becomes equal to the set value. The device becomes stable. Conversely, when the flow rate decreases from a certain steady state, the current in the first temperature-dependent resistor 1 similarly decreases, the voltage V _H decreases, and the temperature difference ΔT becomes stable when it becomes equal to the set value.

In this way, the temperature difference between the first temperature-dependent resistor 1 and the second temperature-dependent resistor 2 is kept constant, and the error amplifier 4
The flow rate of the fluid can be determined from the output voltage of 4.

In this embodiment, the first and second voltage-current converters are voltage-follower type voltage-current converters using operational amplifiers, but the same effect can be obtained by using other methods such as a current mirror type. You can get it.

Furthermore, fluids can be measured regardless of whether they are gases or liquids.

As described above, the present invention provides a first temperature-dependent resistance that self-heats due to electricity supply in a conduit through which a fluid to be measured flows, and a resistance that increases at the temperature of the fluid to be measured in a conduit that is not thermally affected by this first temperature resistance. changing second
A measurement circuit that includes a temperature-dependent resistor and measures the flow rate of the fluid to be measured from voltage signals across both temperature-dependent resistors; a first voltage-current converter that controls the current flowing through the first temperature-dependent resistor; a second voltage-current converter that controls the current flowing through the resistor;
A first attenuator that divides the voltage across the temperature-dependent resistor, and an output signal of the first attenuator and a second attenuator.
It is equipped with an error amplifier that amplifies the difference between the output voltage of the temperature-dependent resistor and a second attenuator that divides the output signal of the error amplifier and outputs it to the first and second voltage-current converters. According to the above, by assigning appropriate weights to the respective output current values of the first and second voltage power converters, the second temperature-dependent resistor does not self-heat and the temperature difference between the two temperature-dependent resistors is accurately maintained constant. Moreover, since the same shape and characteristics can be used, the thermal response to sudden changes in fluid temperature can be the same, and since both temperature-dependent resistors are constant current driven, the current detection resistor can be small, and the second attenuator Since the output signal can be amplified with just one, there is no need for an amplifier for output amplification, so there is no need to worry about drift, temperature characteristics, etc., and the flow rate can be measured with high precision, which is an excellent effect.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of the prior art related to the device of the present invention, FIG. 2 is a second schematic configuration diagram of the prior art related to the device of the present invention, and FIG. 3 is a schematic configuration diagram of the prior art related to the device of the present invention. The third schematic configuration diagram, FIG. 4 are detailed electrical wiring diagrams showing one embodiment of the present invention, and FIG. 5 is a block diagram of the embodiment shown in FIG. 4, respectively. DESCRIPTION OF SYMBOLS 1... First temperature dependent resistance, 2... Second temperature dependent resistance, 3... Conduit, 4... Measurement circuit, 41... First voltage current converter, 42... Second voltage current converter, 43 ...first attenuator, 44...error amplifier, 45...second attenuator.

Claims (1)

[Scope of Claims] 1. A first temperature-dependent resistor that is provided in a conduit through which a fluid to be measured flows and that generates heat by itself when energized; A to-be-measured resistor that is provided in the conduit and is not thermally affected by the first temperature-dependent resistance. a second temperature-dependent resistor whose resistance changes with the temperature of the fluid; and a flow rate measuring device that measures the flow rate of the fluid to be measured from voltage signals across both temperature-dependent resistors generated by constant current control of both temperature-dependent resistors. a first voltage/current converter that controls the current flowing through the first temperature dependent resistor; a second voltage/current converter that controls the current flowing through the second temperature dependent resistor; a first attenuator that divides the voltage at both ends at a predetermined voltage division ratio; an error amplifier that amplifies the difference between the output signal of the first attenuator and the output voltage of the second temperature-dependent resistor; and a predetermined output signal of the error amplifier. a second attenuator that divides the voltage at a partial pressure ratio and outputs the divided voltage to the first and second voltage/current converters.