JPH11271126A - Air flow rate-measuring apparatus of heating resistor type - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air flow rate-measuring apparatus of a heating resistor type which can output a singular point and inform an apparatus abnormality, etc., outside in a system carrying out digital trimming and outputting after modulating a pulse width by software. SOLUTION: A signal of a sucked air flow rate of an internal combustion engine detected by an air flow rate sensor 100 is converted digitally into an air flow rate signal by a numeric value operation means 300 and an error of the flow rate is digitally corrected. An analog output means 400 is constituted of a timer output port 410 which outputs an analog signal of output data of the numeric value operation means 300 according to a pulse width modulation system by a timer function by software and an I/O port 420 which outputs an analog signal of a level preliminarily set on the basis of the output data of the numeric value operation means 300, and therefore the analog output means outputs after converting the output data of numeric value operation means 300 to analog data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating resistor type air flow measuring device for measuring an air flow rate based on a heat radiation amount from a heating wire to air using a heating wire or the like, and more particularly, to a heating resistor type air flow measuring device for an internal combustion engine of an automobile. The present invention relates to a heating resistor type air flow measuring device suitable for measuring an air flow to be performed.

[0002]

2. Description of the Related Art In a conventional heating resistor type air flow measuring device, a current flowing through a heating wire or the like is controlled by a driving circuit using an operational amplifier or the like so that the temperature of the heating wire becomes a predetermined temperature. The air flow is measured using the current. Here, the operational amplifiers used in the drive circuit have individual offsets, and the resistors used in the drive circuit also have variations in resistance value. Therefore, in the conventional heating resistor type air flow measuring device,
Due to the offset and the variation of the resistance value, each heating resistor type air flow measuring device has a measurement error. Therefore, at the time of shipment of the heating resistor type air flow measuring device, the characteristics are checked for each unit, and adjustment is performed so as to be within the specification range.

[0003] As an adjustment method at the time of shipment, conventionally,
Resistance trimming had been performed. By this resistance trimming, the zero point and the span of the output of the heating resistor type air flow measuring device are adjusted so as to be within the specification range. However, the resistance trimming is not easy to perform an adjustment operation and includes an adjustment error.

Thus, for example, US Pat. No. 4,669,
As described in the specification of Japanese Patent No. 052, electronic trimming for performing multi-point correction using digital data by using numerical calculation means is known.

[0005]

However, when the electronic trimming is performed, the output of the heating resistor type air flow measuring device becomes digital data. Since the output of the conventional heating resistor type air flow measurement device is analog data, the interface for taking in the air flow data measured by the heating resistor type air flow measurement device into the engine control unit is to take in analog data. ,
In this state, the conventional interface cannot be used. In general, a sensor such as a heating resistor type air flow measuring device needs to be compatible with an engine control unit using the output of the sensor, so that it is necessary to convert data corrected by digital trimming into analog data. Come up.

A well-known method for converting digital data into analog data is PWM (Puls).
There is a pulse width modulation method called e Width Modulation). Using a numerical operation device such as a microcomputer,
As a method of converting digital data into analog data by a pulse width modulation method, there is an output method of pulse width modulation by software using a timer function. This software method can be easily used when the numerical operation device does not have a dedicated pulse width modulation function.

However, in the method of outputting pulse width modulation by software, a dead zone where pulse width modulation cannot be output occurs during the processing time of the software itself, and singularities of 0% and 100% are generated. There is a problem that data cannot be output. In the conventional heating resistor type air flow measurement device, when the air flow measurement device itself is abnormal, an output with an output value fixed to 0 V or Vcc is output to notify the engine control device of the abnormality of the air flow measurement device. The formula was taken,
In the method of outputting pulse width modulation by software, since a singular point cannot be output, there is a problem that an external device such as an engine control device cannot be notified of an abnormal state of the air flow measuring device.

SUMMARY OF THE INVENTION An object of the present invention is to provide a heating resistor type air flow measuring device which uses a method of performing digital trimming and outputting pulse width modulation by software, and capable of outputting a singular point. It is an object of the present invention to provide a heating resistor type air flow measuring device which can be notified to the public.

[0009]

(1) In order to achieve the above object, the present invention provides an air flow sensor for detecting an intake air flow rate of an internal combustion engine using a heating resistor, and an output of the air flow sensor. A heating resistor type air flow rate measuring device having a numerical value calculating means for digitally converting a signal into an air flow rate signal and digitally correcting a flow rate error by converting output data of the numerical value calculating means into analog data; An analog output means for outputting, based on the output data of the numerical operation means, a timer output port for outputting the output data of the numerical operation means in analog by a pulse width modulation method by a timer function by software; It comprises an I / O port for outputting a signal of a preset level in analog form. . With this configuration, the digital trimming is performed by using the numerical calculation means, and the analog output means can output the pulse width modulation by software from the timer output port and output the singular point from the I / O port. Becomes

(2) In the above (1), preferably,
The I / O port outputs a signal of a level that cannot be output by the timer output port.

(3) In the above (2), preferably,
The level output from the I / O port is a level of a singular point that is not used as an air flow signal.

(4) In the above (3), preferably,
The I / O port alternately outputs a binary value of a singular point which is not used as an air flow signal.

(5) In the above (1), preferably,
The I / O port alternately outputs two values within a range that can be output by the timer output port.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction of a heating resistor type air flow measuring device according to an embodiment of the present invention will be described below with reference to FIGS. First, the overall configuration of the heating resistor type air flow measuring device according to the present embodiment will be described with reference to FIG. FIG. 1 is a block diagram showing the overall configuration of a heating resistor type air flow measuring device according to one embodiment of the present invention.

The air flow sensor 100 measures the flow rate of air taken into the intake pipe by using, for example, a hot wire disposed in the intake pipe of the internal combustion engine, and outputs the air flow sensor voltage (AFS).
Voltage: Vt). The detailed configuration of the air flow sensor 100 will be described later with reference to FIGS. The AFS voltage output from the air flow sensor 100 is converted into a digital signal by the A / D converter 200 and input to the numerical operation means 300.

The numerical operation means 300 comprises an air flow rate conversion operation means 310, a voltage output correction operation means 320, and a correction data holding means 330. When the power is turned on, the correction data holding means 330 includes
The data is read from the correction data storage unit 500 provided outside the storage device, and data to be used during the execution of the correction calculation is held. The data held in the correction data holding unit 330 is erased when the power is turned off, but the correction data storage unit 5
The data stored in 00 is retained even when the power is turned off.

The air flow rate conversion operation means 310 outputs the AFS converted to a digital signal by the A / D converter 200.
The voltage Vt is converted into an air flow rate QaTbl using an air flow rate conversion table set in a program area in advance. The air flow rate conversion table is set for each model of the heating resistor type air flow rate measuring device, and from this data, based on the AFS voltage which is the output of the air flow rate sensor 100,
The air flow value is obtained by linear interpolation.

The voltage output correction calculating means 320 comprises an error calculating means 322 and a flow rate correcting means 324. The error calculating means 322 includes the air flow rate conversion calculating means 31.
0, and the flow rate correction data QaMap (q, a, b) set and stored in the correction data storage means 500 in advance and held in the correction data holding means 330 after the power is turned on. Then, an error in the obtained air flow value is obtained. Flow rate correction data QaMa used here
Correction data holding means 330 storing p (q, a, b)
For example, a non-volatile memory capable of reading and writing data even after assembly is used, and after completion of a product, characteristics of each unit are checked and data for correcting an error is stored. The flow rate correction data includes a flow point, a gradient at that point, and an intercept, and calculates a flow error by linear interpolation from the input air flow data. The flow correction means 324 calculates the corrected flow value QaRef based on the flow error obtained by the error calculation means 322 and the air flow value data measured by the air flow sensor 100. Therefore,
The process adjusted by the conventional resistance trimming is replaced with a process of storing correction data in a nonvolatile memory, which can be referred to as electronic trimming.

The numerical operation means 300 has a self-diagnosis function. For example, when the reading of the correction data from the correction data holding means 330 is defective, the numerical calculation means 300
The output data of “0” is “0”. When the result of the correction operation inside the voltage output correction operation means 320 overflows, the output data is changed to a predetermined value (for example, FIG. 7).
"A5"), and when the result of the correction operation is a negative value, the output data is set to "0". If the output data is "0" or the like, it is a value that is not used as a normal air flow signal. By outputting this data to the outside, an abnormality of the air flow measurement device can be notified.

Here, the corrected air flow value QaRef calculated by the numerical calculation means 300 is digital data and is different from the voltage value of analog data which is the output value of the conventional heating resistor type air flow measurement device. When the air flow measuring device of the present invention is used as an input signal of the engine control unit instead of the conventional air flow measuring device, the output form is different as it is. Since it is not easy to change the engine control unit to receive the digital data, in the present embodiment, the corrected air flow value QaRef, which is digital data, is converted into analog data by using the analog output means 400. Like that. The analog output means 40
The configuration and operation of 0 will be described later with reference to FIGS.

Next, the configuration of the air flow sensor 100 used in this embodiment will be described with reference to FIG. FIG.
1 is a circuit configuration diagram showing a configuration of an air flow sensor used in a heating resistor type air flow measurement device according to an embodiment of the present invention.

The air flow sensor 100 is provided with a heating resistor R for measuring the intake air flow rate, which is disposed in the intake pipe TB.
H, a temperature-sensitive resistor RC for compensating the intake air temperature, and a drive circuit 110. Drive circuit 110
Consists of a bridge circuit and a feedback circuit. A bridge circuit is formed by the heating resistor RH, the temperature-sensitive resistor RC, and the resistors R1 and R2. The voltage across the resistor R1 and the voltage across the resistor R2 are input to the operational amplifier OP1, and the operational amplifier OP1 applies feedback to the heating resistor RH and the temperature-sensitive resistor R2.
A feedback circuit is configured to supply a heating current Ih to the heating resistor RH so as to maintain a constant temperature difference between C. Here, when the flow velocity of the air flowing through the intake pipe TB is high, the amount of heat taken from the heating resistor RH increases, so that a large amount of the heating current Ih flows. Since the amount of heat to be consumed is small, the heating current Ih also decreases. That is, the heating current Ih is proportional to the flow rate of the air flowing through the intake pipe TB. Therefore, the heating current I
h is detected as a voltage across the resistor R1 and output as an air flow sensor voltage (AFS voltage) Vt.

Since the amount of heat taken from the heating resistor Rh is the same regardless of the direction of air flow in the forward flow Vf and the backward flow Vb, the heating current Ih flows even in the backward flow. An excessive detection error of the device occurs.

Next, the state of attachment of the heating resistor type air flow measuring device according to the present embodiment to the intake pipe will be described with reference to FIGS. FIG. 3 is a front view showing a state in which the heating resistor type air flow measuring device according to one embodiment of the present invention is attached to an intake pipe, and FIG. 4 is a cross sectional view showing a partial cross section of FIG.

As shown in FIG. 3, a hole is formed in the wall surface of the main air constituting member constituting the intake pipe TB, and the heating resistor type air flow measuring device AFM is provided with a hole formed in the wall surface from the outside of the intake pipe TB. Inserted from. The heating resistor type air flow measuring device AFM is fixed to the wall surface of the intake pipe TB with screws or the like so as to maintain mechanical strength.

Next, as shown in FIG. 4, the components of the heating resistor type air flow measuring device AFM include the A / D converter 200, the numerical operation means 300, the analog output means 400, and the like shown in FIG. A housing member HOS containing a circuit board CB constituting the drive circuit 110 shown in FIG.
Sub air passage component BP formed by non-conductive member
Etc. A heating resistor RH for detecting the air flow rate and a temperature-sensitive resistor RC for compensating the intake air temperature are arranged in the sub air passage component BP. The heating resistor RH and the temperature-sensitive resistor RC are electrically connected to the circuit board CB via a support SPT made of a conductive member. The housing HOS, the circuit board CB, the auxiliary air passage BP, the heating resistor RH, the temperature sensing resistor RC and the like are configured as an integrated module as a heating resistor type air flow measuring device AFM.

Here, a heating resistor type air flow measuring device A
The intake pipe TB, which is the main air passage portion into which the FM is inserted, is substantially a cylindrical pipe, and the effective cross-sectional area of the main air passage through which the air flows is substantially the same at the location of the entrance and exit of the sub air passage BP.

Next, the operation of the analog output means 400 according to the present embodiment will be described with reference to FIGS.
As shown in FIG. 1, the analog output unit 400 includes a timer output port 410, an I / O port 420, a determination unit 430, a setting unit 440, and a switching unit 450.

Timer output port 410 converts digital data into PWM by software using a timer function.
(Pulse Width Modulation) is output to convert the analog data into a voltage value. However, the timer output port 410 that outputs pulse width modulation by software cannot output a singular point such as 0 V or Vcc. Therefore, in the present embodiment, the I / O port 420 is further provided. I
The / O port 420 receives 0 V or Vc from the setting unit 430.
It is possible to set a singular point such as c. By switching the switch SW to the timer output port 410 side by the switching means 430, a PWM output can be obtained, and by switching the switch SW to the I / O port 420 side, a voltage such as 0V or Vcc can be obtained. The singular point is output.

The operation of the timer output port 410 according to the present embodiment will now be described with reference to FIGS. FIG. 5 is an output waveform diagram of the timer output port 410 of the analog output means of the heating resistor type air flow measuring device according to one embodiment of the present invention, and FIG. 6 is a heating resistor type air flow according to one embodiment of the present invention. 5 is a flowchart illustrating a process of an output unit of a timer output port 410 of an analog output unit of the measurement device.

As shown in FIG. 5, the timer output port 41
0 indicates that the output voltage is turned ON / OFF by software by a timer function and PWM (Pulse Width Modulat
ion), and the total output averaged by changing the ON time TON and the cycle T1 is converted into a predetermined analog voltage value. The period T1 is, for example, 50 μs to 1
00 μs. In the present embodiment, the period T of the PWM output is
The output voltage value is controlled by changing the ON time TON while keeping 1 constant.

In this embodiment, as a method of turning on / off the output voltage by a timer function of software, a free running timer (FR)
T: Output compare match (OC) of a timer that automatically counts up at the initial set time
M: interrupt processing is executed when the timer reaches the set value, and at the same time, the set level is output from the output port).

Next, referring to FIG. 6, a description will be given of a process at the time of executing an interrupt process by the OCM of the timer output port 410. At step 610, the timer output port 410 outputs "High" due to the OCM interrupt.
It is determined whether the signal has reached the “h” level or the “Low” level.If the “High” level has been output, the process proceeds to step 620, and if the “Low” level has been output, the process proceeds to step 640.

When the “High” level is output, in step 620, the timer output port 410
Set the time until the next comparison is performed. This time corresponds to the ON time of the duty control. For example,
In the example illustrated in FIG. 5, when the “High” level is output at time t1, the timer output port 410
The time TON until the next comparison is performed is set.
At step 630, the set time has elapsed, and the timer output port 410 becomes “L” at the next compare match.
In other words, in the example shown in Fig. 5, when the time TON elapses from the time t1, the "Low" level is output by a compare match.

If it is determined in step 610 that a "Low" level has been output, the process proceeds to step 64.
At 0, the timer output port 410 sets a cycle as the time until the next comparison is performed, and the cycle holds the time from when the output level becomes the “High” level and the remaining “Low” level. Therefore, a value obtained by subtracting the previously set duty ON time from the cycle is set. This value corresponds to the duty control (cycle T1-ON time TON). For example, in the example shown in FIG. 5, when the timer output port 410 outputs the “Low” level at the time t2, the time (T1-T1) until the next comparison is performed.
TON).

In step 650, the timer output port 410 is set to output the "High" level at the next compare match after the set time has elapsed. That is, in the example shown in FIG. 5, the time (T1
−TON), and at time T3, output a “High” level in a compare match.

By repeating the above-described processing, PWM output becomes possible by the timer function (OCM function of FRT).

In the PWM output by the timer function, since the processing is performed by software by interruption, the PWM output for a shorter time than the processing time cannot be performed. That is, a singular point such as 0 V or Vcc cannot be output. That is, the logic in the above description is an algorithm that is realized on the premise that the minimum and maximum pulse widths of the PWM output are sufficient to secure the processing time by software.
However, in reality, PWM output of other pulse widths may be required, and when the above algorithm is executed to output such a value, the time for the next comparison to be executed has passed. Sets the time at which the compare is to be executed, and as a result, the compare does not occur until after one cycle of the timer. Then, the initially set cycle of the PWM output does not become as set, which affects the PWM output itself. Therefore, in order to avoid such a situation, an upper limit value and a lower limit value are set in advance for the PWM output, and the pulse width output shorter than the processing time of the software is fixed to a possible minimum value or a maximum value. Is prevented from being disturbed.

Here, the PWM output by the timer function will be described with reference to FIG. FIG. 7 is a diagram showing an input / output relationship by analog output means of the heating resistor type air flow measuring device according to one embodiment of the present invention.

In FIG. 7, the data on the horizontal axis is digital data input to the analog output means 400, that is, digital data output from the flow rate correction means 324 in FIG. The vertical axis indicates the PWM analog output (voltage) output from the analog output means 400. When the output data is in the range of a2 to a3, the PWM output (analog voltage) of the timer output port 410 is proportional to the output data. However, if the output data is a
PWM output (analog voltage) in the range less than 2
Becomes V1 constant, and in a range larger than a3, V2
It will be constant. Here, the maximum value a5 of the output data is set to 100
Assuming%, a2 is, for example, 7%, and a3 is, for example, 93%.

Accordingly, it is impossible to output 0 V or the power supply voltage of the microcomputer which is the numerical operation means 300, which is equivalent to the maximum output voltage Vcc. 0V or V
The output corresponding to cc can be recognized as an impossible value for the engine control system, which is an external system that receives data from the air flow measurement device according to the present embodiment, and can be used for failure diagnosis of the air flow measurement device. Therefore, 0V or Vc
The inability to output a singular point corresponding to c means that there is no means for transmitting a failure of the measuring apparatus to the external system.

Next, the processing of the analog output means 400 according to the present embodiment will be described with reference to FIG. FIG.
5 is a flowchart showing a process of an analog output unit of the heating resistor type air flow measuring device according to one embodiment of the present invention.

As shown in FIG. 7, when the output data is between a2 and a3, the PWM output by the timer output port 410 is in a normal range. Output data is less than a2,
Alternatively, a range exceeding a3 is a dead zone region where PWM output cannot be performed. Therefore, in the present embodiment,
When the output data becomes less than a1, the output becomes 0V, a
When the number becomes 4 or more, a process is executed so that the output becomes equivalent to Vcc.

In step 810, the determination means 430 of the analog output means 400 shown in FIG. 1 determines whether or not the output data is equal to or larger than a4 at which a singular point corresponding to Vcc needs to be output. If the output data is equal to or larger than a4, the process proceeds to step 870. If the output data is smaller than a4, the process proceeds to step 815.

Here, the case of less than a4 will be described first. In step 815, the determination means 430
It is necessary to output a singular point whose output data is equivalent to 0V.
It is determined whether the value is less than 1. If the output data is less than a1, the process proceeds to step 880. If the output data is a1 or more, the process proceeds to step 820.

Here, the case of a1 or more will be described first. At this time, the output data is a1 or more, and
Since it is less than a4, in step 820,
The determining means 430 determines whether the output data exceeds a3.

If the output data exceeds a3,
In step 825, the setting unit 440 sets the output data of the timer output port 410 to V2 corresponding to the maximum value of the PWM output, and proceeds to step 840.

On the other hand, when the output data does not exceed a3, the process proceeds to step 830, and the determination means 430 determines whether the output data is less than a2.

If it is less than a2, in step 835, the judging means 430 sets the output data of the timer output port 410 to V1 corresponding to the minimum PWM output possible value, and proceeds to step 840.

At step 840, the judgment means 430
Determines whether the output port by the switching of the switch SW by the switching unit 450 is set to the level output by the comparison, that is, the timer output port 410 side. If the timer output port 410 has not been set, the switching unit 450 changes the setting to the timer output port 410 in step 845 so that the level output can be performed by a compare match.
Proceed to. If the output has not been changed and the output port is in a state where level output by compare match is possible, the process proceeds to step 600.

The details of step 600 are as described in the flowchart of FIG. 6. The timer output port 410 outputs the PWM output to the outside via the switch SW based on the output data.

If it is determined in step 810 that the output data is equal to or larger than a4, in step 870, the switching unit 450 sets the output port to the I / O port 42.
Change to 0.

Next, in step 875, the setting means 440 outputs “H” to the I / O port 420 as output data.
The output is set to output the “high” level, and the process ends.

Further, when it is determined in step 815 that the output data is less than a1, in step 880, the switching unit 450 sets the output port to the I / O port 42.
Change to 0.

Next, in step 885, the setting means 440 outputs “L” to the I / O port 420 as output data.
ou "level is set to be output, and the process ends.

According to the processing described above, even when PWM output is performed by the timer function, data can be output at a singular point such as 0 V or Vcc as shown by the solid line in FIG.

In the above description, the duty is ON.
Although the period has been described as the “High” level, a circuit configuration in which a buffer is interposed between the microcomputer and the external output stage to reduce the influence of an external connection circuit is often adopted. Can be adopted. In this case, the above-described “High” level can be dealt with by using negative logic in which the logic is inverted to “Low” level, and conversely, “Low” level is inverted to “High” level.

In the above description, since the output is out of the normal flow rate range, it is possible to notify an external system device of an abnormal state of the measuring device. As a means for notifying this abnormality, in addition to the fixed output of the above-mentioned singular points such as 0V and Vcc, the singular points are alternately output at a predetermined cycle (for example, a 50 ms cycle) to thereby provide an external device. It is also possible to notify the other system devices. Further, of the values within the flow rate range that is normally used even if it is not a singular point, for example, two values such as 1 V and 4 V are similarly determined at a predetermined cycle (for example, 50 V).
It is also possible to output the information alternately at an interval of (ms) to notify an external system device.

As described above, according to the present embodiment, a software timer function is used to perform digital trimming in place of the conventional resistance trimming and to convert the output of the heating resistor type air flow measuring device into analog data. Thus, even when the output of the pulse width modulation is performed, the abnormality of the device or the like can be notified to the outside.

[0060]

As described above, according to the present invention,
In a heating resistor type air flow measuring device using a method of performing digital trimming and outputting pulse width modulation by software, it is possible to output a singular point, and to notify an abnormality of the device to the outside.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an overall configuration of a heating resistor type air flow measuring device according to an embodiment of the present invention.

FIG. 2 is a circuit configuration diagram showing a configuration of an air flow sensor used in a heating resistor type air flow measurement device according to an embodiment of the present invention.

FIG. 3 is a front view showing a state in which a heating resistor type air flow measuring device according to an embodiment of the present invention is attached to an intake pipe.

FIG. 4 is a transverse sectional view showing a partial section of FIG. 3;

FIG. 5 is a timer output port 41 of an analog output unit of the heating resistor type air flow measuring device according to one embodiment of the present invention.
FIG. 11 is an output waveform diagram of 0.

FIG. 6 shows a timer output port 41 of an analog output means of the heating resistor type air flow measuring device according to one embodiment of the present invention.
6 is a flowchart illustrating processing of an output unit of 0.

FIG. 7 is a diagram showing an input / output relationship of analog output means of the heating resistor type air flow measuring device according to one embodiment of the present invention.

FIG. 8 is a flowchart showing a process of an analog output unit of the heating resistor type air flow measuring device according to the embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 air flow sensor 110 drive circuit 300 numerical calculation means 310 air flow conversion calculation means 320 voltage output correction calculation means 322 error calculation means 324 flow correction means 330 correction data holding means 400 analog output means 410 ... Timer output port 420 ... I / O port 430 ... Determining means 440 ... Setting means 450 ... Switching means 500 ... Correction data storage means RH ... Heating resistor RC ... Temperature sensitive resistor

Claims (5)

[Claims] An air flow sensor for detecting an intake air flow rate of an internal combustion engine using a heating resistor, an output signal of the air flow sensor is digitally converted into an air flow signal, and a flow error is digitally corrected. A heating element type air flow measuring device having a numerical operation means for performing the following: an analog output means for converting the output data of the numerical operation means into analog data and outputting the analog data, wherein the analog output means is provided by a timer function by software. A timer output port for analog output of the output data of the numerical operation means by a pulse width modulation method,
A heating resistor type air flow measuring device, comprising: an I / O port for outputting a signal of a preset level in analog form based on output data of the numerical operation means. 2. A heating resistor type air flow measuring device according to claim 1, wherein said I / O port outputs a signal of a level which cannot be output by said timer output port. apparatus. 3. A heating element according to claim 2, wherein the level output from said I / O port is a level of a singular point which is not used as an air flow signal. Resistor type air flow measurement device. 4. The heating resistor type air flow measuring device according to claim 3, wherein said I / O port alternately outputs two levels of a singular point which is not used as an air flow signal. Heating resistor type air flow measurement device. 5. A heating resistor type air flow measuring device according to claim 1, wherein said I / O port alternately outputs two values within a range that can be output by said timer output port. Body air flow measurement device.