JPS5950939B2 - hot wire current meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hot-wire anemometer that measures flow velocity using the resistance-temperature characteristics of a predetermined metal wire disposed in a fluid.

A hot wire anemometer is one of the devices for measuring the flow velocity of a fluid.

In this current meter, a metal wire such as platinum having a predetermined resistance temperature characteristic is placed in the fluid as a hot wire, and this hot wire is cooled to a degree according to the flow velocity of the fluid, making use of the property that the resistance value changes. There is. Hot wire anemometers have a structure in which a metal wire, i.e. a hot wire, is exposed to the fluid and is constantly in contact with high-speed fluid, so in order to accurately measure the flow velocity and prevent damage to the hot wire portion, it is necessary to It is necessary to keep the hot wire part clean at all times to prevent an increase in heat capacity and frictional resistance with the fluid.

In particular, when a hot-wire anemometer is used to measure the intake air flow rate of an internal combustion engine, the rate of dust contamination in the intake air is high, and foreign matter adheres to the hot wire each time the measurement is performed, causing deterioration over time and resulting in measured values. reliability decreases.

Therefore, at the end of the measurement, it is necessary to remove foreign matter such as dust attached to the hot wire.・Therefore, a hot-wire anemometer has been devised in which a large current is passed through a predetermined metal wire to raise the temperature to a high temperature, thereby burning off foreign matter such as dust that adheres during fluid measurement.

A conventional hot wire current meter will be explained below with reference to FIG.

In Fig. 1, the hot wire current meter has a hot wire RH arranged in one branch and resistances R, , R.

, and R. are placed in each of the remaining three branches, and the above hot wire RH
There is a resistance R in the branch opposite to . resistor R in parallel with. and a transistor Tl, a drive pulse generating means 1 connected to the base of the transistor Ti and generating a pulse for driving the transistor Tl, and a branch circuit having a hot wire RH of the block circuit and a hot wire. The junction point a with the branch path which has a resistance R, which faces the hot wire RH, has a resistance R, which faces the hot wire RH. branch with resistance R. The resistance R is opposite to. a constant voltage source VB that supplies a predetermined voltage between a junction point b with the branch having the hot wire RH of the bridge circuit, and the resistor R and the branch having the hot wire RH of the bridge circuit. a junction point c with a branch path having a resistance R, and a branch path having a junction point c with the resistance R;
' and is connected to the junction point d with the branch road having the junction point a? , b, and compares the voltage at the junction point c with the voltage at the junction point d to control the current flowing from the constant voltage source VB into the bridge circuit. The current control circuit 2 includes a transistor T forming a Darlington connection with the operational amplifier OP.

and T. And further resistance R. The junction c is connected to the negative input terminal of the operational amplifier 0P, the junction d is connected to the positive input terminal, and the output of the operational amplifier 0P is connected to the base of the transistor T2. The emitter is a transistor T. connected to the base of the transistor T.
The collector of transistor T is connected to the collector of transistor T3. The emitter is resistance R. A transistor T is connected to the junction a of the bridge circuit through the transistor T. The collector of is connected to the junction b. It is most effective to start the burnout at the end of the flow velocity measurement, for example, when the ignition key of the internal combustion engine is turned off and the fluid flow velocity becomes zero.

This is because there is no heat dissipation. When a drive pulse is supplied from the drive pulse generating means 1 to the transistor T for a predetermined time at the above timing, the transistor T is turned on.

Then, the resistance R of the bridge circuit. and the resistance R of the bypass circuit
. Since these are combined in parallel, the balance of the bridge circuit collapses and the resistances R and R are combined in parallel. A large current flows through and R. In the current control circuit 2, a predetermined current flows through the resistor R when the balance is balanced, but when the balance is broken, the positive input terminal side of the operational amplifier 0P has a higher potential than the negative input terminal side, so the output becomes a high potential. Become.
For this reason, the transistor T. The collector-emitter voltage VCE increases and the resistance R increases. The current flowing in the bridge circuit decreases, and the current flowing in the bridge circuit increases. Therefore, a large current flows through the hot wire RH and the resistor R.
The temperature of H rises rapidly, and foreign matter such as dust is burned off.
When the temperature of the hot wire RH exceeds 1,000℃, the hot wire R
Any foreign matter such as dust attached to the H will be completely burned off. However, if the burnout is performed in accordance with the above method each time the ignition key of the internal combustion engine is turned off, the hot wire RH will always be heated to a temperature of 1,000° C. or more.

Therefore, platinum was used for the hot wire RH. The surface of the wire evaporates, causing a change in resistance, and the lifespan of the wire is shortened by the number of times the wire evaporates. SUMMARY OF THE INVENTION An object of the present invention is to provide a long-life hot wire current meter that solves the above-mentioned problems.

In order to achieve the above objective, the number of times the ignition switch of the internal combustion engine is turned off is increased to about 1,000 degrees Celsius each time metal wires such as platinum are burnt out, considering the service life of vehicles such as automobiles. Considering that the resistance value change often exceeds the allowable value, the pulse width or peak value of at least one of the burn-off current pulses applied to the metal wire is increased during burn-off to eliminate foreign matter such as dust on the metal wire. The structure is such that the temperature at which the material is burnt off is set to two different temperatures: about 1,000°C and about 800°C or less. Hereinafter, a second embodiment of the present invention will be described.
This will be explained with reference to the figures.

In FIG. 2, the circuit configuration of the present invention includes a bridge circuit, a drive pulse generating means 1, a current control circuit 2, a power supply voltage supply circuit 3, and an ignition key SWI.

Ignition key SW, battery etc. DC power supply voltage VB
is supplied to the ignition device 5. In addition, the current control circuit 2
Unlike the case in FIG. 1, there is a branch circuit with a hot wire RH of the bridge circuit and a resistor R. The base of the transistor T is connected to the junction C with the branch having the transistor T. The emitter of the transistor T5 is connected to the base of the transistor T5. emitter and resistance R. is connected to the junction A of the branch with the hot wire RH of the bridge circuit and the branch with the resistor R opposite to the hot wire RH, through which the collectors of the transistor T4 and the collector of the transistor T5 are connected together, and the resistor of the bridge circuit is It is connected to the junction B of the branch with R2 and the branch with resistance R,. Further, the power supply voltage supply circuit 3 is a power switch SW.

and a drive signal generating means 4, including a power switch SW. The battery power supply VB and the ignition key SW are connected to the input terminal of the circuit, the junction point A of the bridge circuit is connected to the output terminal, the drive signal generation means 4 is connected to the control terminal, and the input of the drive signal generation means 4 is connected. It is connected between the ignition key SW and the ignition device 5, and is also connected to the drive pulse generating means 1. When measuring the flow velocity, use the power switch SW of the power supply voltage supply circuit 3.

A voltage is applied between the junction points A and B of the bridge circuit including the hot wire RH from the DC power source VB through the bridge circuit. The current flowing through the bridge circuit is controlled by a current control circuit 2, and the flow velocity of the fluid is calculated by detecting a change in the resistance value of the hot wire RH of the bridge circuit from a change in voltage at a junction point C, for example. Now, when the ignition key SW of the internal combustion engine is turned off, a drive signal is sent from the drive signal generation means 4 of the power supply circuit 3 to the drive pulse generation means 1.

A predetermined time T has elapsed since the drive pulse generating means 1 turned off the ignition key SW1.

A driving pulse having a rear pulse width B is applied to a junction point D between a branch circuit having a resistance R1 and a branch circuit having a resistance R2 of the bridge circuit.
The signal is sent to the base of the transistor T1 of the bypass circuit connected between the junction point B and the junction point B. At this time, the transistor T1 is turned on and the resistors R2 and R4 are combined in parallel. Then, the balance of the bridge circuit collapses, the current flowing through the resistor R3 temporarily decreases, and the base current of the transistor T4 of the current control circuit 2 decreases. This causes transistor T5
Colletata emitsutata question voltage. E increases and transistor T
5, that is, the current flowing through the resistor R6 decreases. On the other hand, in the bridge circuit, the current from the DC power supply VB increases, and the hot wire RH becomes high in temperature, thereby burning off foreign matter such as dust. Since the burnout temperature in this case is proportional to the time during which the burnout current is passed through the hot wire RH, it can be adjusted by varying the pulse width τ of the drive pulse. For example, according to an example of the present invention, the pulse width τ required to raise the platinum used in the hot wire to 1,000° C. and completely burn off foreign matter such as dust attached to the platinum was about 1 second. The drive pulse generating means 1 counts the number of times the hot wire RH is burnt out, and when it has counted a predetermined number of times, it switches the pulse width τ of the drive pulse to reduce the heat wire RH by approximately 1.
The pulse signal is sufficient to raise the temperature up to ,000°C, and during the remaining burnout, a pulse signal is generated to raise the temperature to an appropriate value of about 800°C or less.

For this purpose, counters and one-shot multis are used, for example. After the hot wire is burnt out, a signal indicating the completion is sent from the drive pulse generation means 1 to the drive signal generation means 4 of the power supply voltage supply circuit 3.

When the drive signal generating means 4 receives the above signal, it cuts off the signal sent to the control terminal of the power switch SW2, thereby turning off the power switch SW2. As another example, in a bypass circuit consisting of a resistor R4 of a bridge circuit and a transistor T1, the width of the driving pulse applied to the base of the transistor T1 is set to a predetermined value, and the value of the resistor R4 is changed to reduce the burnout flowing to the hot wire RH. Even a configuration in which the current values are made different can bring about the same effect because of the characteristic that the temperature of the hot wire rises in proportion to the value of the current flowing through the hot wire.

As mentioned above, the temperature at which the hot wire of the hot wire type anemometer burns out is set to a high temperature of about 1,000 degrees Celsius for one predetermined number of burnouts, and is set to an appropriate value lower than the above temperature for other burnouts. As a result, foreign matter such as dust attached to the hot wire can be completely removed, and changes in resistance value due to burning out of the hot wire can be suppressed as low as possible.

[Brief explanation of the drawing]

FIG. 1 shows a conventional hot-wire type current meter, and FIG. 2 shows an embodiment of the hot-wire type current meter of the present invention. Explanation of symbols of main parts, RH...Heat wire, T1~
T5...Transistor, 0P...Operation amplifier, SWl...Ignition key, R1~
R2... Resistor, SW2... Power switch, A, B, C, D, a, b, c, d... Junction, 1... Drive pulse generating means, 2...
・Current control circuit, 3... Power supply voltage supply circuit, 4
..."... Drive signal generating means, 5... Ignition device, 8... DC power supply.

Claims (1)

[Claims] 1. A metal wire having a predetermined resistance-temperature characteristic disposed in a fluid passage, a constant voltage source connected to the metal wire and supplying a predetermined voltage to both ends, and A hot wire anemometer comprising a metal wire burnout current pulse generating means for supplying a burnout current pulse to the wire, wherein at least one of the N (N≧2) generated burnout current pulses has a pulse width or A device characterized in that its peak value is larger than other pulse widths or peak values.