JPH05142006A - Offset voltage measuring device - Google Patents

Abstract

(57) [Abstract] [Purpose] The purpose is to directly measure the input offset voltage of the constant temperature control circuit of the air flow meter and the heating set temperature of the heating resistor. [Structure] The heating resistor is removed from the air flow meter, two types of voltage V ₂ of large and small are applied to the constant temperature control circuit 1, and the output V ₁ of the constant temperature control circuit 1 for each is divided by the voltage dividing resistors 15 and 16. The input offset voltage V _TOFF of the constant temperature control circuit 1 is obtained by calculating and amplifying the difference voltage between the voltages V ₃ and V ₂
To detect. [Effect] Since the input offset voltage of the constant temperature control circuit and the heating set temperature of the heating resistor can be directly measured, the responsiveness of the flow meter and the heating set temperature of the heating resistor can be measured without flowing air. it can.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for adjusting an electronic circuit of a hot wire type air flow meter used in an electronic fuel control system for an automobile.

[0002]

2. Description of the Related Art The conventional technology is "transistor technology, 19
77, August issue, p265-p275, the relationship between the flow rate change responsiveness of the constant temperature hot wire air flow meter and the input offset voltage of the constant temperature control circuit is known, and in order to adjust the responsiveness. Adjusting the input offset voltage.

[0003]

The conventional technique operates as a flow meter when it is difficult to directly measure the input offset voltage, such as when an air temperature correction circuit is included in the constant temperature control circuit. The response adjustment is performed by adjusting the input offset voltage of the constant temperature control circuit while observing the output waveform in the state, and it is necessary to flow air after the flow meter is assembled and then adjust the response. It was Further, if the offset voltage is obtained by directly measuring the output voltage of the constant temperature control circuit, the ratio of the offset voltage to the operating voltage is small, so that accurate measurement is difficult. An object of the present invention is to provide a device that directly measures the input offset voltage of a constant temperature control circuit and adjusts the responsiveness of a flow meter simply and reliably. In addition, in the input offset voltage detection device, it is necessary to adjust the resistance value of the voltage dividing resistor of the measurement circuit according to the characteristics of the non-measurement circuit. It becomes easy. When the measuring device itself automatically adjusts the resistance value, if the electronic circuit forming the measuring device is saturated, the measured value may become inappropriate and the self-adjustment function of the voltage dividing resistor may not operate. In order to solve this problem, it is detected that the electronic circuit exceeds a certain voltage range, and the voltage dividing resistor is automatically adjusted based on the saturation mode. Further, when the amplification factor of the constant temperature control circuit that determines the heating temperature of the heating resistor is also measured at the same time as the response adjustment, the adjustment work can be performed at one time, and the work efficiency is further improved.

[0004]

In order to achieve the above object, two types of input voltage, large and small, are applied to a constant temperature control circuit,
The voltage obtained by amplifying the difference between the input voltage and the value obtained by dividing the output of the constant temperature control circuit by the voltage dividing resistor with a voltage division ratio close to its amplification factor is sample-held for each large and small input, and analog calculation is performed. By doing so, the input offset voltage of the constant temperature control circuit is detected. Next, a sliding variable resistor is used as the voltage dividing resistor that is adjusted according to the amplification characteristic of the constant temperature control circuit of the non-measured sample, and it is configured to be driven by a stepping motor. The rotation direction of the stepping motor is controlled so that the voltage dividing ratio of the voltage dividing resistor becomes equal. Further, the voltage dividing resistance is composed of a plurality of fixed resistance switches, and the switch is controlled by using an up-down counter, whereby the voltage division ratio is adjusted quickly.

Further, in order to cope with the case where the electronic circuit in the measuring device is saturated, the differential voltage between the divided voltage sampled and held for each large and small input voltage and the input voltage exceeds a certain voltage range. This is detected by the comparator, the saturation mode is discriminated, and the adjusting direction of the voltage dividing resistor is determined.

[0006]

The constant temperature control circuit of the constant temperature hot wire air flow meter outputs the voltage V ₁ obtained by DC amplifying V ₂ with respect to the voltage V ₂ detected by the current detecting resistor for the heating current of the heating resistor. Is applied to the heating resistor and the current detection resistor to heat the heating resistor to a constant resistance value, that is, a constant temperature.
Constant temperature control circuit to the magnitude two kinds of voltages V _2a, is applied to V _2b alternately output V _1a that DC amplifying the input and divided by dividing resistors this because V _1b is obtained each V _3a, V _{Get 3b} The input offset voltage V _TOFF of the constant temperature control circuit is analog from the ratio (V _2a / V _2b ) of the difference voltages V _4a and V _4b between the voltage division V _{3 of the} voltage _dividing resistor and the input voltage V ₂ and the two large and small input voltages. It can be calculated. At this time, the closer the value of the voltage dividing resistor is to the amplification factor of the constant temperature control circuit, the more accurately the input offset voltage can be detected.
The value of the _voltage dividing resistor is adjusted so that (ΔV ₄ = V _4a −V _4b ) becomes smaller. To make this adjustment, a sliding variable resistor driven by a stepping motor or a fixed resistor switched by an up / down counter is used.

When V ₁ is represented by the amplification factor A of the constant temperature control circuit,

[0008]

[Equation 1]

[0009] When the large and small voltages V _2a and V _2b are alternately applied to the constant temperature control circuit, the voltages V _1a and V _1b obtained by DC amplifying the input voltage are obtained.

[0010]

[Equation 2]

[0011]

[Equation 3]

The output voltage V ₁ of the constant temperature control circuit is divided by the voltage division ratio K.
The voltage is divided by a voltage dividing resistor and the difference from the input V ₂ is differentially amplified by m times to obtain V ₄ .

[0013]

[Equation 4]

[0014]

[Equation 5]

An input offset voltage can be obtained by performing an analog operation after sampling and holding V _4a and V _4b . If the ratio of the magnitudes of V _2a and V _2b is n,

[0016]

[Equation 6]

[Mathematical formula-see original document] If V _TOFF is obtained from _equations 4 and 5,

[0018]

[Equation 7]

The closer the value of A · K = 1 is, the closer the value of Expression 7 becomes to the value of Expression 8.

[0020]

[Equation 8]

The value of equation 8 can be obtained by performing differential amplification using an operational amplifier.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a circuit configuration when the device of the present invention is connected to a constant temperature control circuit except a heating resistor from a hot wire air flow meter, and FIG. 2 is a timing chart of voltage signals used for measurement. In FIG. 1, operational amplifier 11, transistor 19 and resistor 18 are resistors 12, 13 and transistor 14, respectively.
In order to apply the predetermined voltages V _2a and V _2b generated in accordance with the clock signal Ck ₁ to the input terminal of the constant temperature control circuit 1, a current flows from the V ₁ terminal to the V ₂ terminal of the constant temperature control circuit 1. Here, in order to simplify the calculation, the resistors 12 and 13 are selected to have substantially equal values, and n = 2 in the equation (6).

The voltages V _3a and V _3b and the inputs V _2a and V _2b obtained by dividing the output voltages V _1a and V _1b of the constant temperature control circuit 1 upon application of V _2a and V _2b by resistors 15 and 16, respectively. The difference between
In this embodiment, the differential amplifier circuit 17 is used to amplify the signal 100 times to obtain V _4a and V _4b . The voltage waveform of each part at this time is shown in FIG. 2. The output voltage of the differential amplifier circuit 17 with respect to the clock signal Ck ₁ for switching V ₂ changes like V ₄ shown in FIG. 2, from V ₄ to V _4a , In order to take out V _4b as a DC voltage, the switches 20 and 23 are opened and closed at the timings shown in the clocks Ck ₂ and Ck _{3 so} as to open the capacitors 21 and 24.
To charge. When the switches are turned on when the clocks Ck ₂ and Ck ₃ are Hi, the output voltages of the operational amplifiers 22 and 25 are held at V _4a and V _4b , respectively. Since the circuit of the embodiment of FIG. 1 corresponds to the case where n = 2 and m = 100 in the equation 7, substituting this into the equation 7,

[0024]

[Equation 9]

[0025] Since the denominator of the value of the equation 9 can be approximated to 1 when the value of V _4a −V _4b is sufficiently small, the output of the operational amplifier 28 becomes

[0026]

[Equation 10]

_Therefore , the input offset voltage V _TOFF of the constant temperature control circuit 1 can be detected. For the expression 10 to be effective, ΔV ₄ = V _4a obtained by the differential amplifier circuit 29.
Adjust resistor 15 so that −V _4b approaches zero.

An embodiment of a device for changing the resistance 15 so that ΔV ₄ approaches 0 based on the values of ΔV ₄ and V _4a , V _4b will be described with reference to FIG. FIG. 3 shows a saturation detection circuit 2 for detecting that V _4a and V _4b exceed a certain voltage range, a direction detection circuit 3 for detecting the positive / negative of ΔV _{4, and} a voltage dividing resistor composed of a rotary sliding resistor. The rotation direction of the stepping motor 6 is determined based on the outputs of the winding control circuit 5, the saturation detection circuit 2 and the direction detection circuit 3 which supply current to the stepping motor 6 and the stepping motor 6, and a signal is sent to the winding control circuit 5. ΔV ₄ when it is composed of the discrimination circuit 4 for outputting
And a device for changing the resistance 15 so that ΔV ₄ approaches 0 based on the values of V _4a and V _4b .

The signals output from the saturation detection circuit 2 for the magnitudes of V _4a and V _4b are respectively D ₁ and V when V _{4a is} excessive.
_4a under-time and _{D 2, V 4b D 3,} V 4b D 4 when the under-case excessive, the output for the [Delta] V ₄ of the direction detection circuit 3, [Delta] V
_{When 4} is smaller than the practical value of approximate expression 10 and Q _L , and when larger than Q _H , outputs Q _OK , Q _{NG of} the discrimination circuit 4,
Q _F is, respectively, when ΔV ₄ is sufficiently small and the voltage division ratio is appropriate,

[0030]

[Equation 11]

When the adjustment of the voltage division ratio is impossible,

[0032]

[Equation 12]

However, @ = EOR.

When the voltage division ratio should be changed in the direction of increasing ΔV ₄ ,

[0035]

[Equation 13]

It becomes

When the winding current of the stepping motor 6 is supplied by the winding control circuit 5 based on the outputs Q _OK , Q _NG , and Q _F obtained by the discrimination circuit 4 as described above, the stepping motor 6 changes the winding current. The division ratio of the voltage dividing resistor is 1
It is adjusted so that 0 is valid. By implementing the circuit configuration of FIG. 3, the voltage dividing resistor 15 of the input offset voltage detection circuit is automatically adjusted, and the operation of Equation 9 can be substituted by Equation 10, and the input offset voltage of the constant temperature control circuit is shown in FIG. It can be obtained by an operational amplifier circuit.

Another embodiment of the present invention will be described with reference to FIG. FIG. 4 shows an up / down counter 3 which is a means for changing the voltage dividing resistance constituted by the winding control circuit 5, the stepping motor 6 and the rotary sliding resistor in the embodiment of FIG.
4 and resistors 32a to 32i and switches 33b to 33i. In the embodiment of FIG. 4, the resistor 32
By increasing the resistance value of a to _32i from R _32a to R _{32i in} accordance with a binary number, a resistance value of 256 levels can be obtained, and the resistance 3
The division ratio by 1, 32, 16 is output by the discrimination circuit 4 ΔV ₄
= It can be adjusted according to the V _4a -V _4b. According to the embodiment of FIG. 4, there is no delay due to mechanical parts, backlash, etc., and the division ratio can be adjusted faster.

Another embodiment of the present invention will be described with reference to FIG. In addition to the embodiment of FIG. 1, FIG. 5 shows a circuit that outputs a voltage difference between V ₁ and V ₂ when V _2a is applied.
1, a switch 42, a capacitor 43, and an operational amplifier 44. V ₁ and V ₂ of the constant temperature control circuit 1
Since a heating resistor is connected between the terminals to control heating during operation of the flowmeter, a heating resistor is connected between the voltage V ₂ of the current detection resistor 1a and V _H = V ₁ -V ₂ . Resistance value is R
_{If H} ,

[0040]

[Equation 14]

Is satisfied. Further, when the temperature coefficient of the heating resistor which is a temperature dependent resistor is α and the resistance value at 0 ° C. is R _H0 , the resistance value R _H is obtained by using the temperature T _H of the heating resistor.

[0042]

[Equation 15]

Therefore, the control temperature of the heating resistor set by the constant temperature control circuit 1 can be known by sample-holding V _H when V _{2a is} applied. The input offset voltage of the constant temperature control circuit 1 is adjusted by the adjusting resistors 1d and 1e, and the heating temperature of the heating resistor is adjusted by the adjusting resistors 1b and 1e.
Since the input offset voltage and the heating temperature are set by c and interfere with each other due to the adjustment of the other, these two characteristic adjustments should be performed simultaneously. By implementing the invention of FIG. 5, both the input offset voltage of the constant temperature control circuit of the flowmeter and the heating set temperature can be measured continuously and simultaneously, so the responsiveness of the constant temperature hot wire air flowmeter And the heating set temperature of the heating resistor can be quickly adjusted.

[0044]

By implementing the present invention, the input offset voltage of the constant temperature control circuit can be directly measured with high accuracy, so that a constant temperature hot wire type air flow meter can be used without flowing air and changing the flow rate. The responsiveness of can be known, and by automatically adjusting the voltage dividing ratio of the voltage dividing resistor, it is possible to always obtain an accurate measured value. In addition, since the difference between the input voltage and the output voltage of the constant temperature control circuit is sampled and held, the response of the hot wire air flow meter and the heating set temperature of the heating resistor can be adjusted as the characteristics of the electronic circuit only.
The hot wire type air flow meter can be assembled and the constant temperature control circuit can be adjusted accurately and quickly without flowing air.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of an embodiment of the present invention.

FIG. 2 is a timing chart of the embodiment of FIG.

FIG. 3 is a circuit configuration diagram of another embodiment of the present invention.

FIG. 4 is a circuit configuration diagram of another embodiment of the present invention.

FIG. 5 is a circuit configuration diagram of another embodiment of the present invention.

[Explanation of symbols]

1 ... Constant temperature control circuit, 2 ... Saturation detection circuit, 3 ... Direction detection circuit, 4 ... Discrimination circuit, 5 ... Winding control circuit, 6 ... Stepping motor.

Claims (6)

[Claims] 1. In a constant temperature hot wire type air flow meter, two kinds of voltage, large and small, are alternately applied to a constant temperature control circuit of a heating resistor, and an output voltage of the constant temperature control circuit for each input voltage is changed. The voltage obtained by dividing the voltage obtained by dividing the voltage with a voltage divider having a voltage division ratio close to the amplification factor of the constant temperature control circuit and the voltage obtained by amplifying the voltage input to the constant temperature control circuit is sample-held for each input. An offset voltage measuring device characterized by arithmetically amplifying voltage. 2. A voltage dividing resistor for dividing the output voltage of the constant temperature control circuit is constituted by a variable resistor so that the voltage dividing ratio becomes equal to the ratio of the heating resistor and the current detecting resistor set by the constant temperature control circuit. The offset voltage measuring device according to claim 1, wherein the variable resistance is automatically adjusted. 3. A stepping motor in which a voltage dividing resistor for dividing the output of the constant temperature control circuit is constituted by a sliding variable resistor driven by a stepping motor, and the voltage dividing ratio is equal to the amplification factor of the constant temperature control circuit. The offset voltage measuring device according to claim 1, wherein the offset voltage measuring device is controlled. 4. A voltage dividing resistor for dividing the output of the constant temperature control circuit is composed of a fixed resistor and a switch controlled by the counter, and the counter is controlled so that the voltage dividing ratio becomes equal to the amplification factor of the constant temperature control circuit. The offset voltage measuring device according to claim 1, wherein 5. A voltage dividing resistor is detected based on a saturation condition by detecting saturation of a circuit for amplifying a difference between a voltage dividing resistor for dividing the output of the constant temperature control circuit and a voltage input to the constant temperature control circuit. 2. The offset voltage measuring device according to claim 1, wherein the adjusting direction of the voltage division ratio is determined. 6. A constant temperature control circuit is applied with two types of input voltage, large and small, alternately to detect an input offset voltage, and at the same time, a difference between the output voltage of the constant temperature control circuit and the input voltage is sample-held to perform constant temperature control. The offset voltage measuring device according to claim 1, wherein the amplification factor of the circuit is detected.