JPH11311559A - Sensor circuit system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To extremely reduced fluctuation in a digital detection signal without using a correction circuit even when the voltage of a power supply is fluctuated, to simplify a circuit configuration, to reduce power consumption, to eliminate the need for increasing the dimensions of a sensor, to simplify circuit adjustment, and to appropriately maintain the reliability of a circuit system in the flow-rate sensor circuit system. SOLUTION: A sensor circuit system is provided with an analog circuit at a sensor side that includes a flow-rate detection circuit for outputting an analog electric signal corresponding to a flow rate and a constant-voltage circuit for the flow-rate detection circuit, and a digital circuit at a microcomputer side that includes an A/D conversion circuit for converting the analog electric signal being outputted from the flow-rate detection circuit to a digital electric signal. In the sensor circuit system, the output of the constant-voltage circuit is used as a + side reference voltage of the A/D conversion circuit, and the output of the constant-voltage circuit is utilized as reference in the digital circuit, thus obtaining a digital detection signal corresponding to the flow rate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an electric circuit system associated with various sensors for outputting an electric signal corresponding to a detected amount. Examples of the sensor include a thermal flow sensor such as an indirectly heated flow sensor.

[0002]

2. Description of the Related Art
Flow sensors (or flow sensors) that measure the flow (or flow velocity) of various fluids, especially liquids (or gases)
Although various types are used, a so-called thermal (particularly indirectly heated) flow sensor is used because it is easy to reduce the cost.

As the indirectly heated flow sensor, a sensor in which a thin-film heating element and a thin-film temperature sensing element are laminated on a substrate by using a thin-film technology via an insulating layer, and the substrate is attached to a pipe is used. I have. By energizing the heating element, the temperature sensing element is heated to change the electrical characteristics of the temperature sensing element, for example, the value of electrical resistance. This change in the electric resistance value (based on the temperature rise of the temperature sensing element) changes according to the flow rate (flow velocity) of the fluid flowing in the pipe. This is because a part of the calorific value of the heating element is transmitted to the fluid via the substrate, and the amount of heat diffused into the fluid changes according to the flow rate (flow velocity) of the fluid. This is because the amount of heat supplied to the body changes and the electric resistance value of the thermosensitive body changes. The change in the electric resistance value of the temperature sensing element also differs depending on the temperature of the fluid. Therefore, a temperature sensing element for temperature compensation is incorporated in an electric circuit for measuring the change in the electric resistance value of the temperature sensing element. It has also been practiced to minimize the change in the flow measurement value due to the temperature of the fluid.

[0004] Such an indirectly heated flow sensor using a thin film element is disclosed in, for example, Japanese Patent Application Laid-Open No. 8-146,026.
There is a description in the publication.

[0005] In recent years, analog outputs of various types of sensors that output electric signals corresponding to detection amounts, such as the above-mentioned indirectly heated type thermal flow sensors and the like, are based on the detection amounts of the sensors. Perform various controls,
The detected amount is converted into a digital signal so that it is convenient to communicate the detected amount to a remote place or to display the detected amount.

[0006] Such conversion into a digital signal is performed by a microcomputer (microcomputer), which has progressed rapidly in recent years. In general, the sensor and the microcomputer are manufactured as separate units at different manufacturing sites, and these wiring terminals are electrically connected to each other by soldering or the like to form a sensor circuit system (sensor circuit and its peripheral circuit system). Are formed.

In a sensor as a measuring device, a voltage from a power supply is generated by using an internal reference voltage circuit (constant voltage circuit: stabilized power supply circuit) to generate a constant voltage with extremely small voltage fluctuation in order to ensure measurement accuracy. doing. An analog signal, which is a detection signal output from the sensor, is A / A on the microcomputer side.
It is converted into a digital signal by the D conversion circuit. This A /
Conventionally, a power supply voltage supplied to the microcomputer has been used as a reference voltage of the D conversion circuit.

For this reason, if the power supply voltage fluctuates (for example, 5%), the A / D conversion circuit digitizes the input signal from the sensor based on the fluctuating reference voltage. However, there is a problem that the value of the digital signal to be changed also changes accordingly.

Even if the supply voltage fluctuates, A /
In order to make the output signal from the D conversion circuit correspond to the input signal from the sensor (that is, the detection signal) as much as possible, a correction circuit is added on the sensor side, and the sensor output is compensated for the power supply voltage variation by the correction circuit. It is conceivable that the value is corrected to the input value and then input to the A / D converter on the microcomputer side.

FIG. 8 is a block diagram showing the configuration of a sensor circuit system using a flow sensor having such a correction circuit.

In FIG. 8, in an analog circuit (sensor side), a constant voltage is generated by a constant voltage circuit from a power supply (Vcc) and supplied to a flow rate detection circuit. An analog electric signal corresponding to the detected amount is output from the flow rate detection circuit, and this output is input to the correction circuit. An input is also made from the Vcc and the constant voltage circuit to the correction circuit, and a compensated detection amount signal in which the voltage fluctuation of the Vcc is compensated by analog operation is output. In digital circuits (microcomputer side),
The compensation detection amount signal from the analog circuit is input to the A / D conversion circuit, where it is A / D converted, and a digital signal output is obtained. In the A / D conversion circuit, A / D conversion is performed using a reference voltage supplied from Vcc on the microcomputer side. For this reason, even if the voltage of Vcc fluctuates, the amount of the fluctuation is compensated in advance by the compensation detection amount signal input to the A / D conversion circuit, and the output of the A / D conversion circuit has a value corresponding to the detection amount. Becomes

However, when such a configuration is adopted,
For example, an analog multiplication / division circuit used as a correction circuit uses an amplifier, a transistor, a resistor, and many other components (including a peripheral circuit for adjusting input / output levels). However, there are disadvantages such as an increase in the power consumption, an increase in the size of the sensor, difficulty in adjusting the analog circuit, and a decrease in the reliability of the circuit system.

Accordingly, an object of the present invention is to provide a sensor circuit system in which, even if the voltage of a power supply changes, the digital detection signal fluctuates very little without using a correction circuit, and the circuit configuration is simplified. An object of the present invention is to reduce power consumption, eliminate the need to increase the size of a sensor, simplify circuit adjustment, and maintain good circuit system reliability.

[0014]

According to the present invention, there is provided a detecting circuit for outputting an analog electric signal corresponding to a detected amount, and a constant voltage circuit for the detecting circuit. And a digital circuit including an A / D conversion circuit for converting an analog electric signal output from the detection circuit into a digital electric signal, wherein the digital circuit includes the analog circuit. A sensor circuit system characterized in that a digital detection signal corresponding to the detection amount is obtained by using an output of the voltage circuit as a reference.

According to the present invention, there is provided an analog circuit including a detection circuit for outputting an analog electric signal corresponding to a detection amount and a constant voltage circuit for the detection circuit. And a digital circuit including an A / D conversion circuit that converts an analog electric signal output from the detection circuit into a digital electric signal, wherein the reference voltage of the A / D conversion circuit is A sensor circuit system using the output of the constant voltage circuit is provided.

According to the present invention, there is provided an analog circuit including a detection circuit for outputting an analog electric signal corresponding to a detection amount and a constant voltage circuit for the detection circuit. And a digital circuit including an A / D conversion circuit for converting an analog electric signal output from the detection circuit into a digital electric signal, wherein the output of the detection circuit and the constant voltage circuit are provided. And the output of A
/ D conversion circuit, and a digital signal corresponding to the output of the detection circuit output from the A / D conversion circuit before or after the reference with respect to the digital signal corresponding to the constant voltage circuit output from the A / D conversion circuit. A sensor circuit system that calculates a ratio of magnitudes and obtains a digital detection signal corresponding to the detection amount based on a calibration curve stored in advance;
Is provided.

In one embodiment of the present invention, an output terminal of the constant voltage circuit and an output terminal of the detection circuit of the sensor having the analog circuit are respectively connected to two input terminals of a microcomputer having the digital circuit. ing.

In one embodiment of the present invention, the detection circuit is a flow rate detection circuit of an indirectly heated flow sensor, and the indirectly heated flow sensor is arranged so as to be affected by the heating element and the heat generated by the heating element. A flow path for the fluid to be detected is formed such that heat from the heating element is transmitted to and absorbed by the fluid to be detected. A heat generation control for controlling the heat generation of the heating element in a path for supplying a current to the heating element, wherein the temperature sensing affected by the heat absorption by the fluid to be detected based on the heat generation of the body is executed in the flow sensing element. Means are connected,
The heat generation control means controls a current supplied to the heating element based on the result of the temperature sensing so that the result of the temperature sensing matches a target, and a flow rate of the fluid to be detected based on a control state of the heat control means. And outputs an analog electric signal corresponding to the detected amount.

In one embodiment of the present invention, a voltage applied to the heating element is used to indicate a control state of the heating control means.

In one embodiment of the present invention, each of the heating element and the temperature sensing element for flow rate detection is formed of a thin film, and the heating element and the temperature sensing element for flow rate detection are laminated on a substrate via an insulating layer. Have been.

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a first embodiment of a sensor circuit system according to the present invention.
It is a block diagram showing an embodiment.

In FIG. 1, in an analog circuit (sensor side), a constant voltage is generated by a constant voltage circuit from a power supply (Vcc) and supplied to a flow rate detection circuit. The flow rate detection circuit outputs an analog electric signal corresponding to the detected flow rate. On the other hand, in the digital circuit (microcomputer side),
The output of the constant voltage circuit of the analog circuit is +
It is input as a reference voltage (not shown, but a ground potential is input as a negative reference voltage of an A / D conversion circuit), and a flow detection signal is input from a flow detection circuit of an analog circuit. A / D-converts the detection signal based on the reference voltage. For this reason,
Even if the voltage of Vcc fluctuates, the A / D converter uses the constant voltage generated by the constant voltage circuit as the reference voltage, so that the digital voltage accurately corresponds to the detected amount without being affected by the voltage fluctuation of Vcc. A signal is output from the A / D conversion circuit. The A / D conversion circuit outputs, for example, an 8-bit digital signal. Using the output of the A / D conversion circuit, the CPU performs (or controls) desired processing such as integration, flow control, communication, storage, display, and the like.

As shown in FIG. 1, in this embodiment, in addition to the connection between the output terminal of the flow rate detection circuit of the analog circuit and the signal input terminal of the A / D conversion circuit of the digital circuit, The output terminal of the constant voltage circuit of the analog circuit is connected to the reference terminal of the A / D conversion circuit of the digital circuit. This connection can be made by soldering or a coupler attached to the terminal.

FIG. 2 is a circuit diagram showing one embodiment of a flow sensor constituting a circuit system according to the present invention. The power supply (Vcc) is, for example, +5 V (± 5%), and is supplied to the constant voltage circuit 102. The constant voltage circuit 102 has an output of 0.1 W at +4 V (± 0.5%), for example, and the output is supplied to a bridge circuit 104. The bridge circuit 104 includes a temperature sensing element 104-1 for flow rate detection, a temperature sensing element 104-2 for temperature compensation, and variable resistors 104-3 and 104-4.

The voltages at points a and b of the bridge circuit 104 are input to the differential amplifier circuit 106. The differential amplifier circuit 106
Is made variable by a variable resistor 106a. The output of the differential amplification circuit 106 is input to the integration circuit 108. The variable amplification factor differential amplifier circuit 106 and the integration circuit 108 function as responsiveness setting means as described later.

On the other hand, the power supply is connected to the collector of the NPN transistor 110, and the emitter of the transistor 110 is connected to the heating element 112. The output of the integration circuit 108 is input to the base of the transistor 110. That is, the power supply supplies current to the heating element 112 via the transistor 110, and the voltage applied to the heating element 112 is
It is controlled by a partial pressure of zero. And transistor 1
The voltage division of 10 is controlled by the current of the output of the integration circuit 108 input to the base via the resistor, and the transistor 110 functions as a variable resistor and functions as heat generation control means for controlling heat generation of the heat generator 112. I do.

FIG. 5 is a partially cutaway plan view showing the structure of the flow sensor according to the present embodiment, and FIGS. 3 and 4 are a partially cutaway side view and a sectional view, respectively.

In these figures, reference numeral 2 denotes a casing main body, and a pipe 4 penetrating the casing main body and serving as a flow path of the fluid to be detected is formed. The pipe 4 extends to both ends of the casing body 2. At both ends of the casing main body, connecting portions 6a and 6b for connecting to an external pipe are formed. An element housing portion is formed in the casing 2 above the conduit 4, and a casing lid 8 is fixed to the housing portion by screws. The casing lid 8 and the casing main body 2 constitute a casing.

A flow rate detector 12 is disposed in the casing. As shown in FIG. 6, the flow rate detecting unit 12 includes an insulating layer 1 on the upper surface (first surface) of the substrate 12-1.
2-2, a thin-film heating element 12-3 is formed thereon, and a pair of electrode layers 12- for the thin-film heating element is formed thereon.
4, 12-5, an insulating layer 12-6 is formed thereon, and a thin film temperature sensing element 12-7 for flow rate detection is formed thereon,
It is made of a chip having an insulating layer 12-8 formed thereon. As the substrate 12-1, for example, a substrate made of silicon or alumina having a thickness of about 0.5 mm and a size of about 2 to 3 mm square can be used (when an insulating substrate such as alumina is used, the insulating layer 12- 2 can be omitted), the thin-film heating element 12-3 can be made of a cermet having a thickness of about 1 μm and patterned into a desired shape, and the electrode layers 12-4 and 12-5 have a thickness of about 1 μm. A layer made of nickel of about 0.5 μm or a layer of gold having a thickness of about 0.1 μm can be used, and the insulating layers 12-2, 12-6, and 12-8 have a thickness of about 1 μm. A film made of SiO ₂ can be used, and the thin film thermosensitive body 12-7 has a thickness of 0.5 to 1 μm.
It is possible to use a stable metal resistance film having a large temperature coefficient such as platinum or nickel patterned in a desired shape, for example, a meandering shape (or a manganese oxide-based NTC).
What consists of a thermistor can also be used). As described above, since the thin-film heating element 12-3 and the thin-film thermosensitive element 12-7 are disposed very close to each other with the thin-film insulating layer 12-6 interposed therebetween, the thin-film thermosensitive element 12-7 is thin-film. Heating element 12
-3 immediately.

As shown in FIGS. 3 and 4, the lower surface of the flow rate detector 12, that is, the lower surface of the substrate 12-1 (second
A fin plate 14 as a heat transfer member is joined to the surface (surface) by a joining material 16 having good heat conductivity. As the fin plate 14, for example, copper, duralumin, copper-
A material made of a tungsten alloy can be used. As the bonding material 16, for example, a silver paste can be used. The casing body 2 includes the flow rate detector 12.
At the position where is disposed, an opening through which the fin plate 14 passes is formed, and the opening is filled with sealing glass in a state where the fin plate 14 is inserted, and a glass seal 18 is formed. .

The fin plate 14 is bent substantially at a right angle at the center, the upper horizontal portion is joined to the flow detecting section 12, and the lower vertical portion extends into the conduit 4. The fin plate 14 extends across the line 4 from the top to the bottom through the center of the cross section in the line 4 having a substantially circular cross section. However, the pipe 4 does not necessarily have to have a circular cross section, and may have an appropriate cross section. In the pipe 4, the dimension L ₁ of the fin plate 14 in the pipe direction is the thickness L _{2 of the} fin plate 14.
Bigger than enough. For this reason, the fin plate 14 can satisfactorily transfer heat between the flow rate detection unit 12 and the fluid without significantly affecting the flow of the fluid in the pipeline 4.

A fluid temperature detecting section 22 is disposed in the casing at a position separated from the flow rate detecting section 12 along the pipeline 4. The temperature detecting section 22 is provided on the same substrate as the flow rate detecting section 12 on the same thin film thermosensitive element (corresponding to the temperature compensating thermosensitive element 104-2 in FIG. 1).
Is formed in a chip shape. Further, the temperature detecting portion 22 is joined to a thin portion just above the pipe line 4 of the casing main body portion 2 for improving heat transfer via a joining material having good heat conductivity. The fluid temperature detection unit 22 includes:
It is preferable to arrange on the upstream side with respect to the fluid flow direction in the pipeline 4.

Incidentally, the resin coating 20 and the resin coating 20 are respectively covered so as to cover the flow rate detecting section 12 and the temperature detecting section 22 as described above.
24 are formed. In FIG. 5, these resin coatings are not shown.

In the casing, a wiring board 26 is fixedly disposed at a portion other than the flow rate detecting section 12 and the temperature detecting section 22. Some of the electrodes of the wiring board 26 are electrically connected to the electrodes of the flow rate detecting section 12 by bonding wires 28, and similarly to the electrodes of the temperature detecting section 22 by bonding wires. Have been. These bonding wires 28
It is sealed by the resin coatings 20, 24. Some of the electrodes of the wiring board 26 are connected to the external lead wires 30.
And the external lead 30 extends out of the casing.

That is, in the flow rate detecting section 12, the thin film heating element 1-3 is affected by the heat absorption of the fluid to be detected via the fin plate 14 based on the heat generated by the thin film heating element 12-3.
The temperature sensing according to 2-7 is executed. As a result of the temperature sensing, a difference between voltages Va and Vb at points a and b of the bridge circuit 104 shown in FIG. 1 is obtained.

The value of (Va-Vb) changes as the temperature of the flow sensing temperature sensing element 104-1 changes according to the flow rate of the fluid. By appropriately setting the resistance values of the variable resistors 104-3 and 104-4 in advance, the value of (Va-Vb) can be set to zero in the case of a desired reference fluid flow rate. At this reference flow rate, the output of the differential amplifier circuit 106 is zero, the output of the integration circuit 108 is constant, and the resistance value of the transistor 110 is also constant. In that case, the partial pressure applied to the heating element also becomes constant, and the flow rate output at this time indicates the above-mentioned reference flow rate.

When the fluid flow rate increases or decreases from the reference flow rate, the output of the differential amplifier circuit 106 differs depending on the polarity (the resistance-temperature characteristic of the flow rate detecting temperature sensing element 104-1) depending on the value of (Va-Vb). ) And the magnitude changes, and the output of the integration circuit 108 changes accordingly. The rate of change of the output of the integrating circuit 108 is determined by the variable resistor 106a of the differential amplifier 106.
Can be adjusted by setting the amplification factor. The response characteristics of the control system are set by the integrating circuit 108 and the differential amplifier circuit 106.

If the flow rate of the fluid increases, the temperature of the temperature sensing element 104-1 decreases, so that the amount of heat generated by the heating element 112 is increased (that is, the amount of current is increased).
From the integration circuit 108, a control input is made to the base of the transistor 110 so as to reduce the resistance of the transistor 110.

On the other hand, when the flow rate of the fluid decreases, the temperature of the flow rate detecting temperature sensing element 104-1 increases.
12 to reduce the amount of heat generation (that is, reduce the amount of current)
As described above, a control input for increasing the resistance of the transistor 110 is made from the integration circuit 108 to the base of the transistor 110.

As described above, the heat generation of the heating element 112 is feedback-controlled so that the temperature detected by the flow rate detecting temperature sensor 104-1 always becomes the target value regardless of the change in the fluid flow rate. (If necessary, the polarity of the output of the differential amplifier circuit 106 is appropriately inverted according to the positive / negative of the resistance-temperature characteristic of the temperature sensing element 104-1 for flow rate detection). Since the voltage applied to the heating element 112 at this time corresponds to the fluid flow rate, this is taken out as a flow rate output.

This flow rate output is input to the A / D conversion circuit of the digital circuit of FIG. 1 as a flow rate detection output of the sensor. 1. The output of the constant voltage circuit 102 of FIG. 2 is input as the + side reference voltage of the A / D conversion circuit of the digital circuit of FIG.

According to the above embodiment, the temperature of the flow sensing temperature sensing element 104-1 around the heating element 112 is maintained substantially constant regardless of the flow rate of the fluid to be sensed. Of the flammable fluid to be detected can be prevented from igniting and exploding.

In the present embodiment, the heating element 11
2 does not require a constant voltage circuit.
There is an advantage that a low-output constant voltage circuit 102 for P.4 may be used. For this reason, the calorific value of the constant voltage circuit can be reduced, and the flow rate detection accuracy can be maintained well even if the flow rate sensor is downsized. In addition, high-speed operation is possible by reducing the size of the flow sensor.

In the above embodiment, even if the voltage of Vcc fluctuates, the digital detection signal hardly fluctuates, the circuit configuration is simple, the power consumption is small, the sensor size does not need to be increased, and the circuit adjustment is not required. Is also simplified, and the reliability of the circuit system is improved. Further, since the power consumption of the A / D conversion circuit is small, the operation of the sensor is not adversely affected.

FIG. 7 shows a second embodiment of the sensor circuit system according to the present invention.
It is a block diagram showing an embodiment.

This embodiment differs from the first embodiment in the configuration of the digital circuit. That is, the + of the A / D conversion circuit
Vcc is connected to the side reference terminal. The output of the constant voltage circuit of the analog circuit and the output of the flow rate detection circuit are connected to each other via a changeover switch (changeover SW).
It is connected to the signal input terminal of the D conversion circuit. This changeover switch is controlled by the CPU.

In the present embodiment, by operating the changeover switch, the output of the constant voltage circuit and the output of the flow rate detection circuit are alternately input to the signal input terminal of the A / D conversion circuit. After being D-converted, it is input to the CPU. By appropriately setting the time interval between the time when the constant voltage circuit output is input and the time when the flow rate detection circuit output is input, it is possible to sufficiently reduce the voltage fluctuation of Vcc in these input time intervals.

The CPU calculates the ratio of these two signals, compares it with a calibration curve stored in advance in a built-in memory, and obtains a digital signal corresponding to the output of the flow rate detection circuit.

As described above, in the present embodiment, at the output stage of the A / D conversion circuit, two types (a signal corresponding to the output of the constant voltage circuit [reference signal] and a flow rate detection circuit) are affected by the voltage fluctuation of Vcc. Although a digital signal corresponding to the output is output (detection data signal), these two types of signals are substantially equally affected by the fluctuation of the Vcc voltage on the microcomputer side. (That is, the ratio of the detection data signal to the reference signal is obtained), it is possible to substantially eliminate the influence of the voltage fluctuation of Vcc, and to obtain a digital signal accurately corresponding to the detection amount.

Also in this embodiment, the circuit configuration is simple, the power consumption is small, there is no need to increase the sensor size, the circuit adjustment is simplified, and the reliability of the circuit system is improved.

[0052]

As described above, according to the sensor circuit system of the present invention, the output of the constant voltage circuit included in the analog circuit on the sensor side is used for A / D conversion by the digital circuit on the microcomputer side. By using the reference voltage as the reference voltage or using the reference signal for the calculation in the CPU by the A / D conversion circuit, it is possible to sufficiently prevent the influence of the voltage fluctuation of the power supply. Moreover, such effects,
The circuit configuration can be simplified, the power consumption can be reduced, the sensor dimensions can be kept small, the circuit adjustment can be simplified, and the reliability of the circuit system can be improved while being improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of a sensor circuit system according to the present invention.

FIG. 2 is a circuit diagram showing one embodiment of a flow sensor constituting a circuit system according to the present invention.

FIG. 3 is a partially cutaway side view showing a structural portion of one embodiment of a flow sensor constituting a circuit system according to the present invention.

FIG. 4 is a cross-sectional view showing a structural portion of an embodiment of a flow sensor constituting a circuit system according to the present invention.

FIG. 5 is a partially cutaway plan view showing a structural portion of one embodiment of a flow sensor constituting a circuit system according to the present invention.

FIG. 6 is an exploded perspective view of a flow detection unit of one embodiment of a flow sensor constituting a circuit system according to the present invention.

FIG. 7 is a block diagram showing a second embodiment of the sensor circuit system according to the present invention.

FIG. 8 is a configuration block diagram of a sensor circuit system using a flow sensor having a correction circuit.

[Explanation of symbols]

 Reference Signs List 2 Casing body 4 Pipe 6a, 6b Connection 8 Casing lid 12 Flow rate detector 12-1 Substrate 12-2 Insulating layer 12-3 Thin film heating element 12-4, 12-5 Electrode layer 12-6 Insulating layer 12-7 Thin film temperature sensing element for flow rate detection 12-8 Insulating layer 13 Housing 14 Fin plate 16 Bonding material 18 Glass seal 20 Resin coating 22 Fluid temperature detecting unit 24 Resin coating 26 Wiring board 28 Bonding wire 30 External lead wire 102 Constant voltage Circuit 104 Bridge circuit 104-1 Flow sensing temperature sensing element 104-2 Temperature compensation temperature sensing element 104-3, 104-4 Variable resistor 106 Differential amplifier circuit 108 Integrating circuit 110 Transistor 112 Heating element

Claims (7)

[Claims] An analog circuit including a detection circuit that outputs an analog electric signal corresponding to a detection amount, a constant voltage circuit for the detection circuit, and a digital electric signal output from the detection circuit. A / D to convert to
A digital circuit including a conversion circuit, wherein the digital circuit obtains a digital detection signal corresponding to the detection amount by using an output of the constant voltage circuit as a reference. Sensor circuit system to do. 2. An analog circuit including a detection circuit for outputting an analog electric signal corresponding to a detected amount, a constant voltage circuit for the detection circuit, and a digital electric signal output from the detection circuit. A / D to convert to
A sensor circuit system having a digital circuit including a conversion circuit, wherein an output of the constant voltage circuit is used as a reference voltage of the A / D conversion circuit. 3. An analog circuit including a detection circuit for outputting an analog electric signal corresponding to a detection amount, a constant voltage circuit for the detection circuit, and a digital electric signal output from the detection circuit. A / D to convert to
A sensor circuit system having a digital circuit including a conversion circuit, wherein an output of the detection circuit and an output of the constant voltage circuit are alternately input to the A / D conversion circuit via a changeover switch; The ratio of the magnitude of the digital signal corresponding to the output of the detection circuit output from the A / D conversion circuit before or after the reference is calculated based on the digital signal corresponding to the constant voltage circuit output from the A / D conversion circuit, and A sensor circuit system for obtaining a digital detection signal corresponding to the detected amount based on a stored calibration curve. 4. An output terminal of the constant voltage circuit and an output terminal of the detection circuit of the sensor having the analog circuit are connected to the microcomputer 2 having the digital circuit, respectively.
The sensor circuit system according to claim 1, wherein the sensor circuit system is connected to two input terminals. 5. The flow rate detection circuit of an indirectly heated flow rate sensor, wherein the indirectly heated flow rate sensor is provided with a heating element and a flow rate detection sensor arranged so as to be affected by heat generated by the heating element. And a flow path for the fluid to be detected is formed such that heat from the heating element is transmitted to and absorbed by the fluid to be detected. Temperature sensing affected by heat absorption by the fluid to be detected is executed in the temperature sensing element for flow rate detection, and heat generation control means for controlling heat generation of the heating element is connected to a path for supplying current to the heating element. The heat generation control means controls a current supplied to the heating element based on the result of the temperature sensitivity so that the result of the temperature sensitivity matches a target, and controls the current of the fluid to be detected based on a control state of the heat generation control means. Detects flow rate and is detected by this The sensor circuit system according to claim 1, wherein an analog electric signal corresponding to the detected amount is output. 6. The sensor circuit system according to claim 5, wherein a voltage applied to said heating element is used to indicate a control state by said heat generation control means. 7. The heating element and the temperature sensing element for flow rate detection are each formed of a thin film, and the heating element and the temperature sensing element for flow rate detection are laminated on a substrate via an insulating layer. The sensor circuit system according to claim 5, wherein