CN85101114A - Airometer circuitry with temperature-compensation circuit - Google Patents

Abstract

Airometer circuitry with temperature-compensation circuit comprises: an air meter testing circuit that produces output signal according to airshed; An output circuit that is used to amplify air meter testing circuit output signal, its output signal value are adjusted to input signal values becomes a predetermined relation; A normal threshold voltage circuit of predetermined reference voltage being provided for air meter testing circuit and output circuit.In order to compensate the Airometer circuitry variation of output signals that produces owing to the influence of air meter testing circuit and output circuit component temperature coefficient, regulate the temperature coefficient of normal threshold voltage circuit output signal, thereby offset the temperature coefficient of Airometer circuitry each several part.

Description

Airometer circuitry with temperature-compensation circuit

Generally speaking, the present invention relates to a kind of Airometer circuitry with temperature-compensation circuit, specifically, the present invention relates to a kind of temperature-compensation circuit, this circuit is used to compensate the variation of output signals that causes owing to whole Airometer circuitry variation of temperature.

For instance, in internal combustion engine, to the input airshed of internal combustion engine be detected, and with its work that comes controlling combustion engine as a parameter.In order to detect the input airshed, can use the hot wire air flow meter.In this hot wire air flow meter, a heated filament that is heated to predetermined temperature in advance is placed on the intake channel, the electric current that detects in the heated filament that flows through heating just can detect airshed.As example, such air meter is awarded in Bamboo grass mountain people's such as (Sasayama) United States Patent (USP) " NO 4,297,881 " on January 3rd, 1981 and is discussed to some extent.Because the value of detected airshed is to change with the variation of importing temperature in air meter, way up to now is the output signal that compensation is subjected to the intake air temperature variable effect.Generally speaking, in the hot wire air flow meter, except having a heated filament, a cold silk is housed also, this cold silk also is installed in the same intake channel, thereby realizes the detection to temperature in compensation.Usually, the temperature compensation of this type has also obtained application in the input air meter of multiple other type.

Even if had the compensation of input temperature, in fact still exist a problem, promptly when variation of ambient temperature, the components and parts value of Airometer circuitry will change, and for example the resistance of resistance will change with temperature Change.Like this, because the relation of each components and parts temperature characterisitic, in fact the pass between airshed and output signal value is fastened and is also existed a temperature characterisitic, is called " temperature correlation ".Especially use in internal combustion engine under the situation of air meter, the air meter parts are contained in the engine room, are subjected to very big influence of temperature variation, and therefore, the problem of this temperature correlation is very serious.

The inventor has had been found that this temperature correlation has a significant impact for the precision of air meter, and has recognized the necessity that compensates this temperature characterisitic.

In addition, be compared to general temperature-compensation circuit for the air meter temperature-compensation circuit higher accuracy requirement is arranged, this is that this funtcional relationship will be illustrated with reference to formula below because the output signal value of airshed and airflow detection circuit is the relation of a bipyramid exponential function.Therefore, in order to measure the flow that reaches 4% precision, accuracy of detection must remain on 1%.In addition, because the temperature coefficient of an air meter and the temperature coefficient of other air meter are not quite similar, so ideal situation is to carry out desired adjustment to temperature coefficient easily, and the predetermined relation between airshed and the output signal value is never upset in temperature compensation.Yet, before this, make a high-precision temperature-compensation circuit, make it to be adapted to above-mentioned specific condition this purpose that the air meter temperature-compensation circuit is produced a very large impact and still be unrealized.

The present invention has realized such intention: solves by the new exercise question that the inventor found, and satisfies whole Airometer circuitry is carried out the requirement of temperature compensation, and the requirement of satisfying high-precision temperature compensation circuit equipment.

Therefore, an object of the present invention is to provide an Airometer circuitry with temperature compensation, this circuit can satisfy the requirement of aforesaid exercise question.

Another object of the present invention provides a high-precision temperature compensation circuit, and this circuit structurally is simple, and is easy to adjust.

In order to achieve the above object, according to the present invention, a temperature-compensation circuit is housed in the Airometer circuitry, this circuit structurally is simple, and can adjust, so that make its temperature coefficient reach desired value, thereby compensated the temperature coefficient of other circuit rather than temperature-compensation circuit, made the temperature coefficient of whole Airometer circuitry reduce to zero.In order to obtain temperature-compensation circuit simple in structure of the present invention, the inventor has utilized a feature of Zener diode, be that Zener voltage temperature coefficient (Zener voltage variation/variation of temperature) changes with the Zener current value, realized a kind of by adjusting the circuit that Zener current arbitrarily is provided with temperature coefficient.

By the reference accompanying drawing, read the following part that is described in detail, can be well understood to the present invention.In the accompanying drawings:

Fig. 1 is a block diagram, has represented the structure of Airometer circuitry;

Fig. 2 is a circuit diagram, according to concrete device of the present invention, has represented an Airometer circuitry with temperature-compensation circuit;

Fig. 3 is a circuit diagram, is used for explaining the present invention's temperature-compensation circuit;

Fig. 4 is a diagram, has represented the concrete instance of the temperature coefficient characteristics of a Zener diode.

Referring to Fig. 1, the output signal of airflow detection circuit 20 is connected to the input end of " zero interval circuit " 30.The reference voltage that presets from a stabilized voltage supply 10 is provided on testing circuit 20 and the zero interval circuit.

Tested air-flow shown in wave-like line arrow among Fig. 1 hits on the air flow detecting device of testing circuit 20 (this pick-up unit is not shown), this detected airshed is converted into an electric signal, the signal of this detection inputs to zero interval circuit 30, in this circuit, the relation of input value and output valve is adjusted to a predetermined relation, will determine the characteristic degree of tilt of zero point and input value and output valve especially.Zero at interval this predetermined relationship of circuit 30 be that request by an independent controling circuit realizes, this independently control circuit (not illustrating in the drawings) be connected to zero output terminal of circuit 30 at interval.

According to the present invention, Fig. 2 has represented an air meter optimum implementation with temperature-compensation circuit.In this embodiment, foregoing hot wire air flow meter is used for as air meter.

Referring to Fig. 2, supply voltage V ₊Be applied to transistor Tr ₁Collector on, Tr ₁Emitter receive a heated filament RH who places current path and go up (this path figure does not illustrate), the other end of this heated filament passes through resistance R ₁Ground connection.Resistance R ₁₂Cross-over connection is in transistor Tr ₁Collector and base stage on.Resistance R ₂And R ₁₀What link together one is connected to transistor Tr ₁Emitter.Resistance R ₂The other end pass through resistance R ₉Be connected to an operational amplifier OP ₁Inverting input.Resistance R ₂The other end also receive variable resistor R ₃An end.Variable resistor R ₃The other end pass through resistance R ₂₁Receive operational amplifier OP ₄In-phase input end.Variable resistor R ₃And resistance R ₂₁Between contact and heated filament RH and resistance R ₁Between contact be connected.Because electric current is by heated filament RH and resistance R ₁And the voltage drop V that produces ₂Pass through resistance R ₂₁Be applied to operational amplifier OP ₄In-phase input end.Resistance R ₁₀The other end receive operational amplifier OP ₁Inverting input.Capacitor C ₅Be connected across operational amplifier OP ₁Two input ends on.

Operational amplifier OP ₁In-phase input end receive resistance R ₁₁An end, resistance R ₁₁The other end be connected to resistance R ₁₄Resistance R ₄An output terminal that is connected to a normal threshold voltage circuit 100 (normal threshold voltage circuit is enclosed by dot-and-dash line), resistance R ₄The other end be connected to resistance R ₆With variable resistor R ₅Resistance R ₆The other end receive operational amplifier OP ₂Inverting input, this operational amplifier OP ₂In-phase input end receive heated filament RH and resistance R ₁Between contact on.At operational amplifier OP ₂Output terminal and inverting input between, be connected in series a cold silk RC and resistance R ₈, on the position that cold silk is installed, the temperature of tested air-flow can be detected.Operational amplifier OP ₂Output terminal also pass through resistance R ₁₁Receive operational amplifier OP ₁In-phase input end, and pass through resistance R ₁₄Ground connection.Resistance R ₇An end and capacitor C ₁An end, all receive operational amplifier OP ₂Inverting input, and the equal ground connection of their other end.

Transistor Tr ₁, on the heated filament RH, cold silk RC, resistance R ₁To R ₁₄, capacitor C ₁And C ₅And operational amplifier OP ₁And OP ₂Constitute a feedback circuit 200, this circuit control electric current I H remains unchanged the temperature of heated filament RH.Like this, because current flowing resistance R ₁And the voltage drop V that produces ₂Just characterized flow detecting signal.Specifically, when air-flow percussion heated filament, heated filament is taken away a part of heat by atmospheric molecule, so temperature decreases, the heater current amount of temperature that is used to compensate reduction is corresponding to airshed.This feedback circuit 200 is corresponding to airflow detection circuit shown in Figure 1 20.

Resistance R with feedback circuit 200 ₄What be connected is resistance R ₁₈An end and operational amplifier OP ₃Output terminal, the output terminal of just normal threshold voltage circuit 100.Variable resistor R ₁₉And resistance R ₂₀Be connected one terminate to resistance R ₁₈The other end.Variable resistor R ₁₉Other end ground connection, resistance R ₂₀The other end and operational amplifier OP ₄Inverting input join.

Operational amplifier OP ₃Output terminal and inverting input pass through resistance R ₁₆Link together the resistance R of this inverting input by being connected in series ₁₅With diode D ₁Ground connection.Supply voltage V ₊Pass through resistance R ₂₇Be connected to operational amplifier OP ₃In-phase input end, the Zener diode ZD of this in-phase input end by a reversal connection simultaneously ₁Ground connection.Variable resistor R ₁₇Be connected operational amplifier OP ₃Output terminal and Zener diode ZD ₁Negative pole between.Variable resistor R ₁₇With Zener diode ZD ₁Negative pole between tie point and capacitor C ₂The other end join capacitor C ₂Other end ground connection.Supply voltage V ₊Also pass through resistance R ₂₈Feed-in operational amplifier OP ₃Resistance R ₂₈An end and capacitor C ₃An end all with Zener diode ZD ₂Negative pole join capacitor C ₃The other end and Zener diode ZD ₂Anodal all ground connection.Capacitor C ₃With Zener diode ZD ₂Effect be protection operational amplifier OP ₃, make it not to be subjected to influence from the surge voltage of power supply.Normal threshold voltage circuit 100 so constitutes.

Simultaneously, operational amplifier OP ₄Inverting input also with the variable resistor R that connects ₂₂And resistance R ₂₃Join resistance R ₂₃Zener diode ZD by reversal connection ₃Ground connection.Zener diode ZD ₃Negative pole pass through resistance ₂₄Receive operational amplifier OP ₄Output terminal, this output terminal passes through resistance R ₂₅Ground connection.Resistance R ₂₄With resistance R ₂₆An end join resistance R ₂₆The other end receive output terminal V ₀Resistance R ₁₈To R ₂₆, Zener diode ZD ₃With operational amplifier OP ₄Constituted zero interval circuit 300.With operational amplifier OP ₃The same, operational amplifier OP ₁, OP ₂And OP ₄All be by supply voltage V ₊Provide power supply, but in order to make figure clearer, feeder line does not draw.

The circuit working principle of Fig. 2 will be below brief description in addition.

In order to explain the principle of work of top feedback circuit 200, at first should clear and definite heated filament RH and cold silk RC all have platinum line on the aluminum coil frame, and be placed in the inlet channel, so that make it be subjected to enough airflow influences.Heated filament and cold silk all have the resistance of oneself, and all have positive temperature characterisitic.In other words, their resistance rises with temperature increases.

Transistor Tr ₁With the electric current I of the value of putting in advance _HFeed-in heated filament RH makes it be heated to certain temperature, and this temperature exceeds a predetermined value △ I than the temperature of air-flow _HIn addition, because cold silk RC is connected on operational amplifier OP as a feedback resistance ₂On, the electric current that flows through cold silk RC is very little, so the temperature of cold silk is not subjected to the influence of this electric current basically, and is keeping and the air-flow consistent temperature.

Because electric current flows into resistance R from heated filament RH ₁And the voltage V that produces ₂, through operational amplifier OP ₂Amplify, then feed-in operational amplifier OP ₁In-phase input end.Because resistance R ₂With R ₃The resistance sum and be far longer than the resistance of heated filament RH, so flow through resistance R ₁Electric current be exactly the electric current I that flows through on the heated filament RH basically _H

Operational amplifier OP ₂Have a determined feedback quantity of resistance during work, thereby compensated the influence that intake air temperature changes by cold silk RC.

Operational amplifier OP ₁With the resistance R of heated filament cross-over connection ₂, R ₃On the voltage drop dividing potential drop after voltage and operational amplifier OP ₂Output voltage compare, produce a output voltage corresponding to their difference, this voltage is by transistor Tr ₁Feed-in heated filament RH.Like this, flow through the electric current I of heated filament RH _HJust be controlled, make the temperature of heated filament RH exceed a steady state value △ I than intake air temperature _H

As a result, when charge flow rate changed, the heat of being taken away by air inlet on the heated filament also changed to some extent, electric current I _HVariation say the variation of having offset the heat that is pulled away on the heated filament in some sense.In fact, electric current I _HA function as charge flow rate changes.Owing to flow through resistance R ₁Electric current be substantially equal to I _HSo, resistance R ₁On voltage drop represented charge flow rate.It is to be noted charge flow rate Q and voltage V especially ₂Relation be V ₂α

, like this, be fed into operational amplifier OP ₄Voltage V ₂Just produced an airshed signal V at output terminal after being exaggerated ₀This signal can be given the microcomputer that is used for engine control, for example is used for pilot-gas/fuel ratio.

The principle of work of zero interval circuit 300 will be described below.This circuit is an in-phase amplification circuit that uses operational amplifier.By adjusting the variable resistor R on the inverting input ₁₉, make operational amplifier OP ₄Bias voltage change, thereby make output signal V ₀Reach a desired level.And then, by adjusting operational amplifier OP ₄Feed back the variable resistor R in the widely different road ₂₂, can change the gain of in-phase amplifier, thereby output signal V optionally is set ₀For input signal V ₂Rate of change, i.e. I/O characteristic.Exactly because this adjustment has been arranged, just make the output characteristics of air meter to be complementary with the specification of a control circuit, this control circuit (not illustrating in the drawings) is accepted output signal V ₀Control.Operational amplifier OP ₄The Zener diode ZD of output terminal ₃Be used for absorbing the high-voltage noise that enters zero interval circuit 300 by the outside.

The following describes the principle of work of normal threshold voltage circuit 100.The effect of this circuit is not only for reference voltage being provided for the operational amplifier in feedback circuit 200 and the zero interval circuit 300, still in order to finish the task of whole Airometer circuitry being carried out temperature compensation.This is also of the present invention just will put the place.In fact, the temperature coefficient of reference voltage can be adjusted, thereby goes to compensate the temperature effect of whole Airometer circuitry.For the detailed description problem, please referring to Fig. 3 and Fig. 4.

In Fig. 3, for simplicity, supply voltage feeder line and resistance R ₂₈Not illustrate, equally not illustrate in order protecting operational amplifier to make it not influenced by surge and the Zener diode ZD that is connected in parallel that is provided with yet ₂With capacitor C ₃, noise protective condenser C is not shown yet ₂And power supply " opened " resistance R that starting current that " pass " produce in the threshold voltage circuit often plays the bypass effect ₂₇, all above-mentioned parts of not showing all are not main for the present invention.

The HZ2B-LL type Zener diode of producing with Hitachi, Ltd (Hitachi) is an example, temperature coefficient characteristics Y ₂(mv/ ℃) and the Zener diode electric current I z(mA that plays basic role in the present invention) relation as shown in Figure 4, in this figure, the abscissa of logarithmic scale is represented Zener current, the Temperature Coefficient of Zener Voltage that the ordinate representative changes with Zener current.

According to this family curve, the Zener diode temperature coefficient can be shown by formula (1):

γz＝α·lnIz+β ……（1）

In the formula: α=4.78 * 10 ^-4β=2.54 * 10 ^-4

The embodiment of Fig. 3 has comprised operational amplifier OP, resistance R _A, R _BAnd R _C, diode D ₁With Zener diode ZD ₁If diode D ₁Forward voltage drop be V _F, the Zener voltage of Zener diode is V _Z, output voltage is V _S, following result is then arranged:

$\mathrm{Vs\; =\; -}\frac{R_B}{R_A}{V}_F\mathrm{+\; (1+}\frac{R_B}{R_A}{\mathrm{)V}}_Z\mathrm{\dots \dots (2\; )}$

Negligible resistance R _AAnd R _BTemperature coefficient, the output voltage temperature coefficient γ of this normal threshold voltage circuit _sCan draw from following formula:

${\gamma }_S=\frac{{\mathrm{dV}}_S}{d_T}=\frac{R_B}{R_A}(\frac{{\mathrm{SV}}_Z}{S_T}-\frac{{\mathrm{SV}}_F}{S_T})$

$=\frac{R_B}{R_A}{\mathrm{(\gamma }}_Z\mathrm{-\gamma }{}_F\mathrm{)\; \dots \dots (3)}$

γ in the formula _FRepresent diode D ₁Temperature coefficient.

From equation (3) as can be seen, by changing Zener diode ZD ₁Temperature characterisitic γ _ZJust temperature coefficient γ that can the normal threshold voltage circuit of regulated at will _SFor example, consider the temperature coefficient γ of diode _FGenerally, can make γ z=-2mv/ ℃ by regulating Zener current Iz, at this moment the temperature coefficient γ of output voltage V s in-2mv/ ℃ magnitude _SJust can be transferred to about Omv/ ℃.Yet γ z=-2mv/ ℃ of this value gone out the scope of control shown in Figure 4, is approximately Omv/ ℃ of this value in order to obtain γ s, can be with diode D ₁Short circuit (without diode) makes the γ in the equation (3) _FEqual zero, then by regulating variable resistor R _CMake Zener current Iz reach about 5mA, so just make γ z be substantially equal to zero.The circuit of Fig. 3 and Fig. 2 has used diode D ₁, this is because if do not use diode D ₁, for the normal threshold voltage circuit that provides to have positive temperature coefficient (PTC), just must make Zener current greater than 5mA, this has just increased the power attenuation of power circuit.Used diode D shown in Figure 2 ₁, under the situation of Zener current, can easily carry out the adjusting of positive temperature coefficient (PTC) less than 5mA.For example, at R _B/ R _A=1.0, V _F=0.7V under the situation of Vz=2V, in order to obtain positive temperature coefficient (PTC), then has:

γs＝1×（γz+2）（mv/℃） ……（4）

Draw from the family curve of Fig. 4: during Iz=1mA, γ z=0.77mv/ ℃ then can obtain:

γs＝1.23mv/℃ ……（5）

This γ s is positive.

In view of the above, by regulating variable resistor R _CChange Zener current Iz, just can be arbitrarily with the temperature coefficient γ s of normal threshold voltage circuit just be arranged to, zero or negative value.

Because variable resistor R _CAdjusting to voltage V is set _SAbsolute value do not have what the influence (in fact, the small increase of the internal resistance of Zener diode and Zener voltage can be ignored), temperature-compensation circuit shown in Figure 3 require to suppress in the circuit of temperature correlated characteristic so can be applied to one, regulate variable resistor Rc in order to carry out temperature compensation, thereby suppressed temperature correlation.Airometer circuitry of the present invention shown in Figure 2 has been implemented the ultimate principle of temperature compensation described above.

In the circuit of Fig. 2, the output signal Vo of zero interval circuit 300 is:

$V_0\mathrm{=\; 1+}\frac{R_{\mathrm{22}}}{R_{\mathrm{20}}{\mathrm{+\; (<figure-callout\; id="18"\; label="R"\; filenames="85101114\_DRIMG3.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{18}}{\mathrm{//\; R}}_{\mathrm{19}})}{\mathrm{·\; R}}_1\mathrm{·I}{}_H$

$-\frac{R_{\mathrm{22}}}{R_{\mathrm{20}}{\mathrm{+(<figure-callout\; id="18"\; label="R"\; filenames="85101114\_DRIMG3.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{18}}{\mathrm{\parallel R}}_{\mathrm{19}})}·\frac{R_{\mathrm{19}}}{{\mathrm{<figure-callout\; id="18"\; label="R"\; filenames="85101114\_DRIMG3.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{18}}{\mathrm{+R}}_{\mathrm{19}}}{V}_Z\mathrm{\dots \dots (6)}$

In the formula: I _HBe the electric current that flows through heated filament RH, Vz is Zener diode ZD ₁Zener voltage, symbol " ∥ " expression resistance R ₁₈And R ₁₉Parallel connection, R just ₁₈∥ R ₁₉=R ₁₈R ₁₉/ R ₁₈+ R ₁₉

Suppose:

$\mathrm{1\; +}\frac{R_{\mathrm{22}}}{R_{\mathrm{20}}{\mathrm{+\; (<figure-callout\; id="18"\; label="R"\; filenames="85101114\_DRIMG3.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{18}}{\mathrm{//\; R}}_{\mathrm{19}})}\mathrm{=\; C}$

$\frac{R_{\mathrm{22}}}{R_{\mathrm{20}}{\mathrm{+\; (<figure-callout\; id="18"\; label="R"\; filenames="85101114\_DRIMG3.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{18}}{\mathrm{//R}}_{\mathrm{19}})}·\frac{R_{\mathrm{19}}}{{\mathrm{<figure-callout\; id="18"\; label="R"\; filenames="85101114\_DRIMG3.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{18}}{\mathrm{+\; R}}_{\mathrm{19}}}\mathrm{=\; D}$

Equation (6) then is reduced to:

Vo＝C·Vz-D·Vz ……（7）

In the formula: V ₂It is foregoing resistance R ₁On voltage drop.

According to fundamental formular (King ' s formula), air-flow detects output signal V ₂And the relation between the airshed Q is:

${\mathrm{<figure-callout\; id="2"\; label="V"\; filenames="85101114\_DRIMG3.png"\; state="\{\{state\}\}">V</figure-callout>}}_2{}^2\mathrm{=\; A+B}\sqrt{Q}$ ……（8）

In the formula: the unit of Q be the kg/h(kilogram/hour), A and B are coefficients, V ₂Provide by following formula:

V ₂＝I _H×R ₁……（9）

The result is the electric current I among the heated filament RH _HWith the relation of airshed Q be the funtcional relationship of fourth root, coefficient A, B, C and D are determined by the resistance that constitutes Airometer circuitry.

When the temperature variation of air meter parts, parameter under the influence of circuit component temperature coefficient (especially C, D, I _HAnd R ₁) also change, the result also changes the output signal Vo of Airometer circuitry.With reference to equation (2) and (3), the temperature coefficient γ s of the output voltage V s by regulating normal threshold voltage circuit 100 can offset the variation of output signal Vo.

If the output voltage V o that is caused by temperature variation is changed to △ Vo, can draw from equation (7) and (9):

△Vo＝CR ₁△I _H+I _H（C△R ₁+R ₁△A）-△D·Vs-D·△Vs……（10）

By adjusting the temperature correlation variation △ Vs that temperature coefficient γ s changes normal threshold voltage circuit 100 output voltage V s, the Airometer circuitry output voltage that just equation (10) can be provided changes △ Vo and is reduced to zero.

In fact, at first Airometer circuitry is placed in the specific environment temperature, confirm its output voltage, then it is placed in the different environment temperature, regulate variable resistor Rc, make the value of circuit output voltage in a back environment temperature equal the output voltage values of this circuit in previous environment temperature.

As mentioned above, according to the present invention, can provide a kind of Airometer circuitry that not influenced by temperature correlation.Owing to compensated temperature correlation, output signal does not just change with variation of ambient temperature.According to the present invention, can also provide high-precision temperature-compensation circuit.This temperature-compensation circuit not only can be used for Airometer circuitry, can also be used for various control circuits, and in these control circuits, people do not wish to produce the variation of output signals that occurs owing to temperature variation.In addition, the temperature coefficient of temperature-compensation circuit can arbitrarily be provided with, and this characteristic can be applied to temperature coefficient is had in the circuit of specific (special) requirements.

Be noted that further the present invention never only limits to the embodiment of being narrated, it can comprise and essence of the present invention and the consistent modification of claim scope.For example, the present invention can be used for the air meter rather than the foregoing hot wire air flow meter of other type.In addition, by the variable resistor (embodiment as the aforementioned) that adjusting and operational amplifier output terminal and Zener diode join, can regulate Zener current.If but Zener current does not need adjusting, variable resistor just can replace with a fixed resistance, then this resistance is repaired a little.On the other hand, also can regulate Zener current by the independent combination of a normal value power supply and current control device.

Claims (17)

1, Airometer circuitry comprises:

A gas flow detection circuit that produces output signal according to airshed;

An output circuit, this circuit is used as input signal to the output signal of described gas flow detection circuit, receives and amplifies this signal to produce an output signal, regulates the value of this output signal, makes it and input signal values become a predetermined relationship;

A normal threshold voltage circuit that is used for providing pre-permanent threshold voltage to described testing circuit and output circuit;

Its characteristic is: the temperature compensation means that also comprises the temperature coefficient that is used to regulate normal threshold voltage circuit output signal in described Airometer circuitry, thereby offset the temperature coefficient of testing circuit and output circuit, the variation of output signals that causes owing to whole described Airometer circuitry temperature variation has been reduced to zero basically.

2, according to the air-flow circuit of claim 1, described normal threshold voltage circuit has a Zener diode, the Zener voltage of this Zener diode is as reference voltage, described temperature compensation means has the normal threshold voltage source and the current control device that are connected in series, normal threshold voltage source that this is connected in series and current control device and Zener diode join, regulate current control device and go to change Zener current, thereby can be set to a predetermined value to the temperature coefficient of the output signal of described normal threshold voltage circuit.

3, according to the Airometer circuitry of claim 2, described normal threshold voltage source is provided by the output voltage of described normal threshold voltage circuit, and described current control device comprises a variable resistor.

4, according to the Airometer circuitry of claim 3, described airflow detection circuit comprises a hot wire air flow testing circuit, this hot wire air flow testing circuit has a heated filament that is heated to predetermined temperature, when air-flow percussion heated filament, the electric current that flows through this heated filament changes to some extent, goes to detect the variation of this electric current in order to measure airshed.

5, according to the Airometer circuitry of claim 1, described output circuit comprises an in-phase amplification circuit with operational amplifier, also comprise the device that is used to change described in-phase amplification circuit feedback quantity and input reference voltage, thereby the relation of input value and output valve just can be adjusted to predetermined relation.

6, according to the Airometer circuitry of claim 2, described output circuit comprises an in-phase amplification circuit with operational amplifier, also comprise the device that is used to change described in-phase amplification circuit feedback quantity and input reference voltage, thereby the relation of input value and output valve just can be adjusted to predetermined relation.

7, according to the Airometer circuitry of claim 3, described output circuit comprises an in-phase amplification circuit with operational amplifier, also comprise the device that is used to change described in-phase amplification circuit feedback quantity and input reference voltage, thereby the relation of input value and output valve just can be adjusted to predetermined relation.

8, according to the Airometer circuitry of claim 4, described output circuit comprises an in-phase amplification circuit with operational amplifier, also comprise the device that is used to change described in-phase amplification circuit feedback quantity and input reference voltage, thereby the relation of input value and output valve just can be adjusted to predetermined relation.

9, according to the Airometer circuitry of claim 5, the output voltage of described normal threshold voltage circuit is used as the reference voltage of described operational amplifier.

10, according to the Airometer circuitry of claim 6, the output voltage of described normal threshold voltage circuit is used as the reference voltage of described operational amplifier.

11, according to the Airometer circuitry of claim 7, the output voltage of described normal threshold voltage circuit is used as the reference voltage of described operational amplifier.

12, according to the Airometer circuitry of claim 8, the output voltage of described normal threshold voltage circuit is used as the reference voltage of described operational amplifier.

13, temperature-compensation circuit comprises:

Amplifier and one are used for providing the Zener diode of normal value reference voltage to this amp.in;

It is characterized in that: also comprise the device of the Zener current of regulating described Zener diode in the described temperature-compensation circuit, thereby can be arranged on a predetermined value to the output temperature coefficient of described amplifier.

14, according to the temperature-compensation circuit of claim 13, described amplifier comprises an operational amplifier, the in-phase input end of this operational amplifier links to each other with the negative pole of described Zener diode, the device of described adjusting Zener current is in series by a normal threshold voltage source and current control device, by a feedback circuit, the part output signal of described operational amplifier is admitted to the inverting input of this operational amplifier.

15, according to the temperature-compensation circuit of claim 14, described normal threshold voltage source is provided by the output of described operational amplifier, and described current control device comprises a variable resistor.

16, according to the temperature-compensation circuit of claim 14, described feedback circuit comprises resistance and a diode, and this diode has predetermined temperature coefficient.

17, according to the temperature-compensation circuit of claim 15, described feedback circuit comprises resistance and a diode, and this diode has predetermined temperature coefficient.

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