JPH02653Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to an improvement in the burning-off mechanism of hot-wire adhering dust in a hot-wire current meter.

In order to eliminate measurement errors caused by debris adhering to the hot wire in a hot wire anemometer, a method of burning off the debris by passing a rather large burnout current through the hot wire to raise the temperature of the hot wire. has been put into practical use. However, with conventional garbage burning-off mechanisms, the temperature of the hot wire does not rise sufficiently even when a burning current is applied due to the influence of the temperature of the measured fluid, which is the hot wire atmosphere, so that the burning and removal of garbage cannot be performed satisfactorily. On the other hand, the heat rays may heat up excessively and shorten their lifespan. This point will be explained in detail using FIG. 1. This figure is a schematic diagram of this kind of conventional hot-wire flow velocity meter equipped with a hot-wire attached dust burning-off mechanism applied to measuring the flow velocity of engine intake air.
The configuration and functions will be briefly explained below. As shown in the figure, an ambient temperature dependent resistance 1 and a hot wire H are installed in the measurement fluid passage A (in this case, the intake air passage),
Bridge resistors 2 and 3 are provided to form a bridge for measurement. And both neutral points a of the bridge,
b is connected to the input terminal of an operational amplifier 4, and its output terminal is connected to a transistor 5 driven by a power supply S.
The bridge is configured to be connected to and energize the bridge. Thus, by compensating for changes in the intake air temperature by the ambient temperature dependent resistor 1 and reading the voltage appearing across the bridge resistor 3, the flow rate of the intake air is measured.

Next, in order to send a burnout current to the hot wire H to burn and remove the dust attached to the hot wire H, a transistor 6 is connected to the burnout current control resistor 7 in parallel with the bridge resistor 2 as shown in the figure. put. In this case, if a burnout signal is applied to point c according to a predetermined pattern at a desired time (after the engine has stopped, that is, when intake air is not flowing) to turn on transistor 6, the neutral points a and b can be turned on. The equilibrium of the potential between them is broken, and a burning current flows through the hot wire H, making it possible to remove dust attached to it.

However, in such a conventional burn-off mechanism,
The resistance value of the ambient temperature dependent resistor 1 changes depending on the intake air temperature, and as a result, the temperature rise due to the burning current of the hot wire H becomes unstable. That is, when it is cold, the burn-off temperature of the hot wire may be insufficient and dust cannot be completely removed.On the other hand, when it is hot, the burn-off temperature may rise too much, leading to a reduction in the life of the hot wire.

The purpose of this invention is to provide a heat ray-adhered dust burn-off mechanism that eliminates the drawbacks of the conventional burn-off mechanism described above and can perform stable dust burn-off. In order to achieve this purpose, the present invention is characterized by providing a resistance for controlling the burnout current in the measurement fluid passage, and furthermore, by selecting the temperature coefficient of the resistance within a predetermined range, a stable Garbage burning can be done.

Hereinafter, the present invention will be explained in detail with reference to Examples. FIG. 2 shows a schematic configuration of an embodiment of the present invention, in which a burnout current control resistor 7 is installed in the measuring fluid passage A.
This makes it possible to depend on the ambient temperature. Now, the resistance value R of the hot wire H when the intake air temperature is 20° C. during burning out is expressed by the following formula.

R=R ₁・R ₃ (R ₂ +R _K )/R ₂・R _K ...(1) Here, R ₁ and R _K are the ambient temperature dependent resistance 1 and the reference temperature 20 of the burnout current control resistance 7, respectively. This is the resistance value at °C.

Regarding the above, the resistance value R' of the hot wire H when the intake air temperature changes by +Δt is R'=R ₁ (1+α ₁ Δt)・R ₃ /R ₂・R _K (1+α _K Δt) {R ₂ +R _K ( 1+α _K Δt)} ...(2). Here, α ₁ and α _K are the temperature coefficients of resistance of resistor 1 and resistor 7 at a reference temperature of 20° C., respectively.

On the other hand, if the temperature of the hot wire H is t _b and the resistance value of the hot wire at 20° C. is R _H0 , then R _H =R _H0 {1+α _H (t _b −20)}. Here, α _H is the temperature coefficient of resistance of the hot wire H at a reference temperature of 20°C. From the above equation, t _b = (R _H /R _H0 -1)/α _H +20...(3) is obtained.

Hot wire temperature t _b at intake air temperature 20℃ during grilling
Substituting equation (1) into equation (3) (where R _H = R), t _b {R ₁・R ₃ (R ₂ +R _K )/R ₂・R _K /R _H0 −1} / α _H +20 ...(4) In addition, the hot wire temperature t _b ′ when the intake air temperature changes by +Δt is calculated similarly (however, R _H = R′) t _b ′ = {R ₁・R ₃ / R ₂・R _K・R _H0・(1+α ₁ Δt)/(
1+α _K Δt) ・(R ₂ +R _K +R _K・α _K・Δt)−1)} /α _H +20 ……(5). Here, if we set R ₁・R ₃ /R ₂・R _K・R _H0 = A and R ₂ +R _K = B, equations (4) and (5) become t _b = (A・B−1)/ α _H +20 ……(6) t _b ′={A・1+α ₁ Δt/1+α _K Δt(B+R _K・α _K・Δt)−1}±/α _H +20 ……(7)

Therefore, the difference in burning temperature depending on the atmosphere Δt _b =
Calculating t _b ′−t _b from equations (6) and (7), Δt _b = A・Δt/α _H (1+α _K・Δt) × (R _K・α _K +α ₁・B+α ₁・R _K・α _K・Δt−B・α _K ) ...(8) is obtained, and by rewriting equation (8), Δt _b = A/α _H {α ₁・R _K・Δt−R ₂ +R ₂ (1+α ₁・Δ
t) /Δt・α _K +1}=R ₁・R ₃ /α _H・R ₂・R _K・R _H0 {α ₁・R _K・Δt−R ₂ +R ₂ (1+α ₁・Δt)/Δt・
α _K +1}...(9) is obtained.

FIG. 3 shows an example in which the relationship between Δt _b and α _K in the above equation (9) is illustrated with Δt _b on the vertical axis and α _K on the horizontal axis, and the change in intake air temperature Δt as a parameter. Here, α _H is 0.003620/℃ (platinum wire temperature coefficient), R ₂
is 770Ω, R _K is 7700Ω, R _H0 is 2Ω, R ₁ is 713.5
Ω, R ₃ is 4Ω, and α ₁ is 0.003620/°C. Also,
Δt is 60℃ (i.e. intake air temperature 80℃), 20
℃ (intake air temperature 40℃) and -20℃ (intake air temperature 0℃). This figure shows that when α _K is very small,
Due to the fluctuation of the intake air temperature from 0℃ to 80℃, Δt _b is approximately
This causes a fluctuation of 160°C, whereas when α _K is 0.03,
It shows that the variation of Δt _b decreases to about 60°C. Since the burn-off temperature is generally set at about 1000°C, it is extremely effective if the variation in Δt _b is within about 60°C. Therefore, it can be seen that by selecting α _K , that is, the temperature coefficient of the burnout current control resistor 7, within a predetermined range, the influence of temperature changes due to the ambient temperature of the hot wire H can be reduced to a level that poses no practical problem. That is, by providing the burn-off current control resistor 7 in the measuring fluid passage A and selecting its temperature coefficient within a predetermined range, stable burn-off of hot wire adhering dust becomes possible.

In addition, in order to select α _K within the above-mentioned predetermined range, it is sufficient to select a material for the resistor 7 whose temperature coefficient is within the predetermined range, or to connect several types of resistors with different temperature coefficients in parallel, for example. There is no problem even if the temperature coefficient obtained by connecting and synthesizing the temperature coefficient has a value within a predetermined range.

As is clear from the above explanation, according to the present invention,
Since the heating of the hot wire due to the burning current is stable regardless of the ambient temperature, garbage can always be burned off reliably without impairing the life of the hot wire. Moreover, it has the advantage that the modification of the conventional mechanism to the present mechanism is extremely simple in terms of circuitry.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing a conventional burn-off mechanism;
The figure is a schematic diagram showing the mechanism of one embodiment of the present invention.
The figure is a graph showing the relationship between the change in hot wire temperature and the temperature coefficient of the resistance for controlling the burnout current. A: Measuring fluid passage, H: Hot wire, 1: Atmosphere temperature dependent resistance, 2, 3: Bridge resistance, 4: Operational amplifier, 5, 6: Transistor, 7: Resistor for controlling burnout current, S: Power supply.

Claims (1)

[Scope of utility model registration request] A bridge constituted by an ambient temperature dependent resistor 1 and a hot wire H installed in the measuring fluid passage A and bridge resistors 2 and 3 is energized by a power supply S via an operational amplifier 4 and a transistor 5. , in a hot-wire anemometer formed to generate a burnout current in response to a predetermined burnout signal via a burnout current control transistor 6 and a resistor 7, the burnout current control resistor 7 is It is installed in the measurement fluid passage A, and the temperature coefficient of the burnout current control resistor 7 is selected within a predetermined range so that the burnout temperature of the hot wire adhering dust is not affected by the temperature of the measurement fluid. A mechanism for burning off hot wire adhering debris in a hot wire current meter.