JPH0749977B2 - Flow velocity sensor-Drive system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a flow velocity sensor driving method for measuring a flow velocity of a fluid with low power consumption by using a flow velocity sensor.

<Prior Art> As a method of heating the heating resistor and utilizing the change in the amount of heat transferred from the heating resistor to the fluid to determine the flow velocity of the fluid, the temperature difference between the fluid and the heating element should be constant. A method of measuring the flow velocity of the fluid at the same time as compensating the influence of the fluid temperature by connecting the resistance temperature detector and the heating resistor in the bridge circuit and amplifying and feeding back the output from the bridge circuit has been adopted.

However, in this method, it is necessary to constantly energize the bridge circuit, the feedback circuit, and the like, and this is not practical for a current meter that requires portability because the battery is exhausted.

<Object of the Invention> It is an object of the present invention to provide a flow velocity sensor driving method that is capable of measuring the flow velocity of a fluid with low power consumption by improving the above-mentioned conventional technique.

<Embodiment> FIG. 1 is a circuit configuration diagram of a flow velocity sensor drive circuit showing an embodiment of the present invention.

In the figure, 1 is a dry battery, 2 is a switch element, and 3 to 7 are resistors that form a bridge circuit.

Among them, 3 and 4 may be fixed resistors and 5 may be fixed resistors or semi-fixed resistors. Reference numerals 6 and 7 are resistance temperature detectors, and those having the same resistance value and temperature coefficient are used.

Reference numeral 8 is a differential amplifier, and 9 is a heating resistor, which generates heat by Joule heat. This temperature is to be arranged very close to Rs so that it is transmitted to the resistance temperature detector 7 (temperature measurement resistance value Rs). To do.

When the switch element 2 is open, that is, when the circuit is not powered, each resistance value is selected under the condition of R ₁ = R ₂ and Rf = Rs.

Now, when the switch element 2 is closed, the two voltages v ₁ and v ₂ generated at the positive input terminal and the negative input terminal of the differential amplifier 8 shown in the figure have the following relationship.

v ₁ > v ₂ (1) If the voltage of the power supply 1 is E, v ₁ and v ₂ are expressed by the following equation.

Since the value of v ₁ −v ₂ changes depending on the value of R ₃ , the differential input voltage to the differential amplifier 8 changes.

Considering now in a windless state, if R ₃ is increased, the differential input voltage is increased and accordingly the output voltage of the differential amplifier 8 is increased, which increases the Joule heat in the heating resistor 9 (R _H ). . As a result, this amount of heat heats the resistance temperature detector (Rs) 7, the resistance value of the resistance temperature detector 7 increases, and v ₁ −v ₂ moves in the direction of decreasing, and finally v ₁ -V ₂ 0 and the entire circuit is in equilibrium. In this state, the output voltage V ₀ of the differential amplifier 8 has a constant value.

Here, if the amplification degree of the differential amplifier 8 is α, the following equation holds.

V ₀ = α (V ₁ −V ₂ ) (4) Therefore, the larger the amplification factor α, the closer V ₁ −V ₂ becomes to zero.

If R ₃ is operated with a constant value, R ₃
Since the voltage V ₀ determined by the value of is obtained at the output, the voltage V ₀ at this time can be used as the reference output in the windless state.

Next, when a fluid of a certain temperature flows in the resistance temperature detectors Rf and Rs to generate a wind velocity, the operation described below occurs.

The resistance value Rf of the resistance temperature detector 6 changes according to the temperature of the fluid, but the rate of change is the same as Rs of the resistance temperature detector 7.
(However, this is when considering the case where there is no heating from the heating resistor 9 from R _H. ) Therefore, V ₂ changes, but V ₁ also changes, so V ₂ −V ₁ does not change. From this, the dependence of the fluid temperature on temperature can be ignored.

With respect to the flow velocity of the fluid, the larger this value is, the larger the amount of heat taken from the resistance temperature detector Rs becomes.
The temperature of Rs decreases, and the resistance value naturally decreases due to the temperature coefficient.

As a result, V ₁ also decreases and V ₂ −V ₁ increases. Since feedback is applied to the circuit as a whole so that V ₂ −V ₁ becomes zero, an increase in the output voltage V ₀ causes an increase in heat generation of the heating resistor R _H.
Rs is heated, its resistance value increases, V ₂ rises, and finally V ₁ −V ₂ satisfies the equilibrium state.

That is, if there is a flow velocity, the output voltage V ₀ of the differential amplifier 8 changes according to its magnitude. Therefore, it becomes possible to measure the flow velocity of the fluid from the value of V ₀ .

The above is the principle of measuring the flow velocity of the fluid by the feedback control by the resistance bridge and the differential amplifier 8.

Next, a method of reducing power consumption will be described based on the above-mentioned feedback control circuit.

This can be realized by turning on (ON) -off (OFF) the switch element 2. That is, the switch element 2 is closed for a short time (3 to 5 seconds) only when it is desired to measure the flow velocity. Next, if the output voltage V ₀ immediately before opening the switch element 2 is read by means such as sample hold, the flow velocity can be measured with considerable accuracy. According to an experiment by the present inventor, the switching element 2
When the closed time is 3 seconds, the wind speed of the fluid is 20 cm /
It was confirmed that the error was 1% or less when the time was longer than 2 seconds.

In a system that is not normally subjected to feedback control, when a constant voltage is applied to the heating resistor 9 ( _RH ), the transient response of the temperature rise of the heating resistor 9 is exponential as shown in FIG. It takes a considerable time to draw a curve and reach a certain value. Experiments conducted by the present inventor have confirmed that it takes 10 to 20 seconds. Since the thermodynamic response speed is slow,
To accelerate this, it is necessary to adopt a method in which a transiently high voltage is applied, the initially generated Joule heat is set large, the temperature is raised quickly, and the applied voltage is gradually lowered.

This is shown in the voltage waveform of FIG.

Such a voltage waveform is automatically obtained by the drive circuit of this embodiment.

That is, in FIG. 1, the transient response after the switch element 2 is open and no power is applied to the entire circuit and after the switch element is closed can be explained as follows.

Since the power supply is connected to the circuit from the moment when the switch element 2 is closed, the heating resistor 9 does not generate heat when the switch element 2 is open, so that v ₂ is a low voltage, and v ₁ − v ₂ has a large value. Therefore, the differential amplifier 8
The output voltage V ₀ of V is much larger than V ₀ = α (v ₁ −v ₂ ). Since R _H generates heat due to this large value of V ₀ , the temperature of the resistance temperature detector Rs rises rapidly.
Therefore, the resistance value of the resistor Rs also increases rapidly, and v ₂ also increases at the same speed. In this way, v ₁ −v ₂ rapidly decreases and reaches the equilibrium state quickly. That is, by applying the feedback control, the equilibrium point is reached within a short time. Therefore, the time during which the switch element 2 is closed may be shortened accordingly.

As a result, the battery used for the power supply has a long life, and the flow velocity can be measured with low power consumption.

<Effects of the Invention> As described in detail above, the present invention consumes extremely little power because the flow velocity of the fluid can be measured within a short time. Therefore, it is most suitable for applications such as dry cell driving which requires portability.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of a flow velocity sensor drive circuit showing one embodiment of the present invention. FIG. 2 is an explanatory diagram showing how the temperature rises due to Joule heat when a constant voltage is applied to the heating resistor. FIG. 3 is a waveform diagram showing a voltage waveform applied to the heating resistor. 1 ... Dry battery, 2 ... Switch element, 3,4,5 ... Fixed resistance, 6,7
... Resistance temperature detector, 8 ... Differential amplifier, 9 ... Heating resistor

Claims (1)

[Claims] 1. A first resistance temperature detector, a first resistance connected to the first resistance temperature detector, and a second resistance having the same temperature coefficient as that of the first resistance temperature detector. A resistance bridge circuit including a temperature resistance element and a second resistance connected to the second resistance temperature element, a differential amplifier for amplifying an output from the resistance bridge circuit, and the differential amplifier Flow rate sensor drive, comprising a heating resistor for heating the second temperature measuring resistor of the resistance bridge circuit by the output voltage of the switch and a switching means for turning on / off the power source of the bridge circuit and the differential amplifier. method.