JPH08247801A - Transducer and gas meter using the same - Google Patents

Abstract

(57) [Abstract] [Purpose] To eliminate the differential amplifier circuit and provide a transducer that obtains an output signal in which the measured value is expressed by the pulse width or the number of pulses with a simple circuit centered on a logic circuit. A bridge-type sensor circuit 1 mainly composed of piezoresistive elements connected in a bridge-type, two comparators 3a and 3b having two corner voltages Va and Vb of the bridge-type sensor circuit 1 as one input, respectively, A ramp voltage generating circuit 4 that generates a ramp voltage Vr that gradually increases or decreases at a rate of change and applies the ramp voltage Vr to the other input of both comparators 3a and 3b, and both comparators 3a and 3b.
and a gate circuit G2 that outputs a signal having a pulse width T corresponding to the time from when one output of b is inverted to when the other output is inverted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transducer for detecting a mechanical quantity such as pressure or acceleration by a sensor and outputting a measurement signal to an application system such as a microcomputer, and a gas meter using the transducer, and more particularly to a bridge type The present invention relates to a circuit technology for processing the output of a bridge-type sensor circuit mainly composed of a piezoresistive element connected to.

[0002]

2. Description of the Related Art As disclosed in Japanese Patent Application Laid-Open No. 3-135745, there is a mechanical quantity sensor in which a plurality of piezoresistive elements are arranged on a semiconductor diaphragm to form a bridge circuit, which is widely used as a pressure sensor or the like. It is applied. As disclosed in Japanese Patent Laid-Open No. 5-87586, the output circuit of this type of bridge-type sensor circuit is designed so that the difference between two corner voltages of the bridge circuit (so-called bridge voltage) is taken out by a differential amplifier circuit. ing.

As is well known, in many electronic circuit devices and systems, an analog voltage signal of a sensor output is digitally converted and digitally processed by a microcomputer. The same applies to the case of the bridge type sensor circuit described above,
The bridge voltage (sensor output) extracted by the differential amplifier circuit is often converted into a digital value by an A / D converter incorporated in a microcomputer or an external A / D converter.

However, there is a problem in that a high-grade and expensive A / D converter is required to A / D convert a bridge voltage that changes over a wide range with high resolution. Wide area
A voltage / frequency conversion method is often used in various electronic circuit devices as a method for easily and inexpensively realizing high-resolution A / D conversion.

That is, a voltage control type variable frequency oscillation circuit is provided, and the oscillation frequency thereof is variably controlled by the bridge voltage (sensor output) taken out by the differential amplifier circuit.
If this oscillation output is input to the counter input port of the microcomputer and the number of input pulses per fixed time is counted by the counter built in the microcomputer, the sensor output is digitally converted.

[0006]

Conventionally, since the bridge voltage of the bridge type sensor circuit is taken out by the differential amplifier circuit, there are the following problems. Of particular importance in this type of sensor circuit is that the output circuit does not adversely affect the accuracy or stability of the bridge circuit. Therefore, the input impedance of the differential amplifier circuit that extracts the bridge voltage must be sufficiently high. However, it is extremely difficult to realize a highly accurate and highly stable differential amplifier circuit with high input impedance, and it is complicated by using multiple expensive and expensive operational amplifiers and adding various correction circuits and compensation circuits around them. It becomes an analog circuit. Therefore, it is more difficult to stably maintain a highly accurate operation for a long period of time. Also, since the circuit scale becomes large, it is difficult to realize a small transducer by integrally mounting the bridge type sensor circuit.

The present invention has been made in view of the above background, and an object thereof is to solve the above problems and to eliminate a differential amplifier circuit for extracting a bridge voltage of a bridge type sensor circuit. It is an object of the present invention to provide a transducer capable of obtaining an output signal in which a measured value is expressed by a pulse width or a pulse number with a simple circuit centering on a logic circuit and a gas meter using the transducer.

[0008]

In order to achieve the above object, in a transducer according to the present invention, a bridge type sensor circuit mainly composed of piezoresistive elements connected in a bridge type, and a bridge type sensor circuit Two comparators each having two corner voltages as one input, a ramp voltage generation circuit that generates a ramp voltage that gradually increases or decreases at a predetermined change rate and applies the ramp voltage to the other input of each of the comparators, and And a gate circuit that outputs a signal having a pulse width corresponding to the time from when one output of the comparator is inverted to when the other output is inverted.

Here, the lamp voltage generating circuit may be configured to output the lamp voltage only once after a predetermined time has elapsed after power is turned on, or may be configured to repeatedly output the lamp voltage at an appropriate cycle. In the latter case, it is desirable to provide a circuit that outputs a synchronization signal in synchronization with the operation cycle of the lamp voltage generation circuit.

If a delay time variable type delay circuit for appropriately delaying the change point of the output signal of the comparator is provided, the overall input / output characteristics of the transducer can be adjusted appropriately.

Further, if an oscillation circuit that oscillates at a relatively high frequency is provided and the oscillation signal is output to the outside for the period of the pulse width of the gate circuit, the measured value is expressed in the number of pulses. Can generate signals. in this case,
If the oscillation circuit is a voltage-controlled variable frequency circuit and the frequency changes according to the drive voltage of the bridge type sensor circuit, the output drift of the sensor circuit due to the fluctuation of the power supply voltage can be corrected.

Further, in the gas meter according to the present invention, in the gas meter capable of detecting at least the gas flow rate and the gas pressure, a sensor for detecting the gas pressure may be used.
7 is used, the bridge type sensor circuit mounted on the transducer is a pressure sensor in which the piezoresistive element is changed by pressure, and the pulse output from the transducer is used. It is configured to include an arithmetic processing unit that receives and performs a predetermined arithmetic processing.

[0013]

The two corner voltages of the bridge type sensor circuit are input to the two comparators, respectively, and compared with the ramp voltage to be binarized. That is, the output of one comparator is inverted when one corner voltage becomes equal to the ramp voltage, and the output of the other comparator is inverted when the other corner voltage becomes equal to the ramp voltage. The time difference between the output inversions of the two comparators corresponds to the difference between the two corner voltages (that is, the bridge voltage).

That is, an output in which the measured value by the bridge type sensor circuit is expressed by the pulse width is obtained from the gate circuit. Further, in the case of the configuration according to claim 6, the pulse width signal is converted into the number of pulses and output. That is, when the pulse output from the gate circuit is on,
When the oscillation signal of the oscillation circuit that oscillates at a predetermined high frequency is output to the outside, the output pulse train is
If the frequency of the oscillator circuit is constant, the number of pulses will depend on the length of the pulse width output from the gate circuit. Therefore,
Since the pulse width corresponds to the measured value as described above, the number of pulses also corresponds to the measured value.

When outputting a signal in which the measured value is expressed in pulse width, this is input to the timer input port of the microcomputer,
By counting the pulse width with the timer built in the microcomputer, the sensor measurement value is converted into digital.
In addition, when outputting a signal that represents the measured value in pulses, input this to the counter input port of the microcomputer and count the number of pulses with the counter built in the microcomputer to convert the sensor measured value to digital. Become.
When a pulse signal is input from the transducer to the microcomputer as described above, an optical transmission system or a photocoupler can be used as the signal transmission system.

Further, in the gas meter of the present invention, the detection sensitivity of the sensor is higher than that of the mechanical type, and the output thereof is the pulse width or pulse train (number) as described above, and therefore the output is directly processed. When input to the device, the arithmetic processing unit operates using the input value as it is without using an expensive AD converter or the like, and therefore the handling is easy, and the transducer of the present invention has a circuit configuration of Since it can be made simple, small and inexpensive, the gas meter using it can also be made smaller and the cost can be reduced.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of a transducer and a gas meter using the same according to the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 shows a circuit configuration of an embodiment of a transducer according to the present invention, and FIG. 2 shows operation waveforms of its main part. This transducer includes a bridge type sensor circuit 1 mainly composed of piezoresistive elements connected in a bridge type and resistors (characteristic correction resistors R1, R2, R).
3 is added), a sensor drive circuit 2 for applying a drive voltage to the bridge type sensor circuit 1, and two comparators 3a having two corner voltages Va and Vb of the bridge type sensor circuit 1 as one input respectively. , 3b
And a ramp voltage Vr that gradually increases or decreases at a predetermined change rate.
Of the lamp voltage generating circuit 4 for generating the voltage and applying it to the other input of each of the comparators 3a and 3b, and the power for supplying the trigger signal St to the lamp voltage generating circuit 4 only once after a certain time has passed since the power was turned on to the transducer. The on-trigger circuit 5 and the gate circuits G1 and G2 that output a signal having a pulse width corresponding to the time from the inversion of one output of the comparators 3a and 3b to the inversion of the other output. In the embodiment shown in FIG. 1, a constant voltage type drive circuit is used as the sensor drive circuit, but a constant current type drive circuit operates similarly.

As shown in the timing chart of FIG.
When the power supply voltage Vcc is applied to the transducer, a trigger signal St is applied from the power-on trigger circuit 5 to the lamp voltage generating circuit 4 after a predetermined time when each part starts to function normally, and in response to this, the circuit 4 receives a constant change rate. The lamp voltage Vr that decreases with is output. This lamp voltage Vr and two corner voltages Va and Vb of the bridge type sensor circuit 1
And are compared by comparators 3a and 3b, respectively.

One corner voltage Va is the lamp voltage Vr.
The output of the one comparator 3a is inverted at the time when it becomes equal to, and the output of the other comparator 3b is inverted at the time when the other corner voltage Vb becomes equal to the ramp voltage Vr. The time difference T of the output inversion of these two comparators corresponds to the difference Va-Vb (that is, bridge voltage) of the two corner voltages. An output signal OUT1 having a pulse width T is output from the gate circuit G2. This is a signal expressing the sensor measurement value in pulse width.

Next, a modification of the above embodiment will be described. As shown in FIG. 3A, the comparators 3a, 3a
If delay circuits 5a and 5b of variable delay time for appropriately delaying the changing point of the output signal of b are provided, the signals at each point in the circuit become as shown in FIG. R
The output can be delayed by shifting the phase by the C time constant. This allows the total input / output characteristics of the transducer to be adjusted appropriately.

Further, the characteristic adjusting function is not limited to the above-mentioned one, but is constituted so that the voltage change rate of the lamp voltage generating circuit 4 can be variably adjusted, and further, as shown in FIG. It is also possible to provide variable gain amplifiers 9a and 9b on the input side. The modified examples shown in FIGS. 3 and 4 can be similarly applied to each of the following embodiments.

FIG. 5 shows a second embodiment of the present invention.
This embodiment differs from the above-mentioned embodiments in that the pulse train (number) corresponding to the sensor measurement value is output. As shown in the figure, the circuit of the first embodiment described above was used as it is (denoted by the same reference numeral), and a pulse width-pulse train conversion circuit was provided at its output (gate circuit G2). This pulse width-pulse train conversion circuit includes a gate circuit G
3 and an oscillating circuit 8 that oscillates at a relatively high frequency. The oscillating signal Vs and the output (signal OUT1) of the gate circuit G2 are input to the gate circuit G3 to output the signal OUT1.
The pulse train synchronized with the oscillation signal Vs is output from the gate circuit G3 to the outside only for the period of the pulse width T (see the timing chart shown in FIG. 6). That is, the signal OUT that represents the sensor measurement value by the number of pulses from the gate circuit G3.
It is configured to output 2. Since the other configurations and effects are the same as those of the above-described first embodiment, the same reference numerals are given and detailed description thereof will be omitted.

FIG. 7 shows a third embodiment of the present invention.
7 is shown in a block diagram, it is basically the same as that of the second embodiment described above, and the specific circuit configuration of each block diagram is shown in FIG. Is the same as. In this embodiment, unlike the second embodiment, a voltage-controlled variable frequency circuit is used as the oscillation circuit 8'for controlling the output section (gate circuit) G3.
That is, in the second embodiment described above, when the power supply voltage changes, the voltage applied to the bridge-type sensor circuit 1 also changes, so that the sensitivity of the transducer changes due to the power supply voltage fluctuation. Therefore, in the present embodiment, the function of canceling the change in sensitivity due to the fluctuation of the power supply voltage (changing the oscillation frequency) is provided in the oscillation circuit 8'for outputting the pulse train so that the sensitivity of the transducer is kept constant. . That is, even if the mechanical quantity to be measured is constant, if the pulse width output from the gate circuit G2 becomes large due to fluctuations in the power supply voltage, the oscillation frequency is delayed and the output signal Vs is output per unit time. When the number of pulses is controlled to be small, the number of pulses output from the gate circuit G3 does not depend on the fluctuation of the power supply voltage and becomes the same if the mechanical amount is constant.

The concrete construction of the oscillation circuit 8'for exhibiting such a function comprises a control voltage generation circuit 8a and a voltage control type oscillation circuit 8b, and the concrete circuit construction of each circuit 8a, 8b is as follows. Is as shown in FIG.
With this configuration, when the power supply voltage Vcc changes, the output Vi of the amplifier circuit also changes. Therefore, the voltage control type oscillation circuit 8b is driven at the oscillation frequency according to the input voltage,
When Vi changes as described above, the oscillation frequency of the voltage control type oscillation circuit 8b changes accordingly. Therefore, by appropriately setting the amplification factor of the amplifier circuit, the output drift of the sensor circuit due to the fluctuation of the power supply voltage Vcc can be corrected, and the transducer can be independent or less dependent on the fluctuation of the power supply voltage.

FIG. 9 shows a fourth embodiment of the present invention.
As shown in the figure, in the present embodiment, the above-described second and third
Similar to the embodiment, it is for outputting the signal OUT2 represented by the number of pulses (pulse train) according to the sensor measurement value. Specifically, the power-on trigger circuit 5 used in the second and third embodiments is used. Instead, a synchronization signal generation circuit 7 and a timing signal generation circuit 10 are provided.

That is, when power is applied to the transducer, each section operates and the synchronizing signal generating circuit 7 outputs a square wave signal St with a duty ratio of 50% at a sufficiently low constant frequency, which is supplied to the ramp voltage generating circuit 4. It becomes an input. The circuit 4 integrates the square wave signal St to generate a ramp voltage Vr that repeatedly increases and decreases at a constant rate of change. The ramp voltage Vr and the two corner voltages Va and Vb of the bridge type sensor circuit 1 are compared by the comparators 3a and 3b, respectively (see the timing chart shown in FIG. 10).

Further, the output S of the synchronizing signal generating circuit 7
By supplying t to the timing signal generation circuit 10, as shown in the timing chart of FIG. 10, it is possible to detect the rising edge of St and output a single trigger pulse (synchronization signal) Sp. Then, as shown in FIG. 11, for example, when the transducer 12 and the microcomputer 13 for processing the output are connected, the synchronizing signal Sp is a synchronizing signal Sp and an output for notifying the microcomputer 13 of sampling timing. The signals OUT1 and OUT2 are given,
The microcomputer 13 performs sampling for a certain period of time after receiving the synchronization signal Sp, and outputs the number of pulses OUT
2, the pulse width OUT1 is measured, and a predetermined process is performed based on the measured pulse width OUT1.

In this embodiment, an example of outputting a pulse train is shown, but as shown by the broken line in the figure, the output OUT1 of the gate circuit G2 is taken out (oscillation circuit 8 and gate circuit G3 are not provided). Thus, the pulse width based on the sensor measurement value may be output as in the first embodiment.

In addition, as shown in FIGS. 12A and 12B, a light emitting element,
Of course, optical transmission technology such as a photocoupler can be easily used. Further, in the fourth embodiment, the timing signal Sp is output from the sensor (trussducer) side and the output signals OUT1 and OUT2 based on the actual measurement values are given to the microcomputer 13, but as shown in FIG. , Sensor (transducer) from the output port of the microcomputer 13
Alternatively, the power may be output to the power source on the side for a certain period of time to operate, and the output at that time may be returned to the input port of the microcomputer.
In this way, either one may be active.

FIG. 14 shows an embodiment of the gas meter according to the present invention. As shown in the figure, the gas meter measures the flow rate (gas flow rate per unit time) of the gas flowing in the gas pipe 15 and the metering unit 16 that measures the amount of gas flowing in the gas pipe 15 (total gas amount). It is composed of a flow rate sensor 17, a transducer 12 incorporating a pressure sensor according to the present invention for measuring the gas pressure in the gas pipe 15, a seismograph 18 for detecting an earthquake, and the like.

The total amount of gas flowing in the gas pipe 15 is measured by the measuring unit 16 and displayed on a display unit (not shown) such as a meter. The gas flow rate and gas pressure in the gas pipe 15 are measured by the flow rate sensor 17 and the pressure sensor in the transducer 12, respectively, and the controller 13
Is constantly monitored by If a gas leak occurs, the flow rate of the gas flowing through the gas pipe 15 increases abnormally. Also, if you forget to turn off the gas appliances, the gas will continue to flow for an abnormal time. Furthermore, the gas pressure flowing through the gas pipe 15 decreases before and after the gas leak and the restoration of the gas pipe construction.

In this gas meter, when the controller 13 detects an abnormality in the gas flow rate or a decrease in the gas pressure, the warning lamp 20 is turned on to give an alarm, and the shutoff valve 19 is closed. Further, even when an earthquake is detected by the seismograph 18, the warning lamp 20 is turned on to notify the alarm and the shutoff valve 19 is closed. In this way, when an abnormality occurs in the gas flow rate or gas pressure, the gas pipe 15 can be automatically closed to prevent the risk of explosion or the like.

Further, as shown in FIG. 14, the shut-off valve 19 is closed or a warning is issued by detecting an external signal 21 from a gas alarm installed in a room or an incomplete combustion alarm installed in a gas appliance. The lamp 20 may be turned on.

With such a configuration, in the case of the transducer 12 of the present invention, its output is a pulse signal (pulse width, pulse train (number)) based on the measurement value of the pressure sensor, so that the controller (one-chip microcomputer or the like) is used as it is. Input to the arithmetic processing unit 13), it is not necessary to perform AD conversion on the controller 13 side, the load on the controller 13 side is small, and high-speed processing is possible.

[0035]

As described above, in the transducer of the present invention, the two corner voltages of the bridge type sensor circuit are two.
It is input to each of the two comparators and compared with the lamp voltage to be binarized. That is, the output of one comparator is inverted when one corner voltage becomes equal to the ramp voltage, and the output of the other comparator is inverted when the other corner voltage becomes equal to the ramp voltage. The time difference between the output inversions of these two comparators is the difference between the two corner voltages (that is, the bridge voltage).
It corresponds to.

In this way, the comparator which compares one corner voltage of the bridge circuit with the ramp voltage and binarizes it has an extremely high input impedance due to its non-linear circuit principle, and has a simple structure and operates stably. To do. Therefore, highly accurate measurement can be stably performed over a long period of time without substantially disturbing the accuracy of the bridge type sensor circuit having the critical characteristic. In addition, the sensor output reading and conversion circuit system, which is mainly composed of a comparator, is much simpler and cheaper than a high input impedance type differential amplifier circuit, and is an ultra-compact transducer that is integrated with a bridge type sensor circuit. Can be easily realized.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing a first embodiment of a transducer according to the present invention.

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

FIG. 3 is a circuit configuration diagram showing a main part of a modified example.

FIG. 4 is a circuit configuration diagram showing a main part of still another modification.

FIG. 5 is a circuit configuration diagram showing a second embodiment of the transducer according to the present invention.

FIG. 6 is a timing chart of the second embodiment.

FIG. 7 is a block diagram showing a third embodiment of the transducer according to the present invention.

FIG. 8 is a circuit configuration diagram showing a main part thereof.

FIG. 9 is a block diagram showing a fourth embodiment of the transducer according to the present invention.

FIG. 10 is a timing chart of the third embodiment.

FIG. 11 is a diagram showing an application example.

FIG. 12 is a diagram showing an application example.

FIG. 13 is a diagram showing an application example.

FIG. 14 is a diagram showing an embodiment of a gas meter according to the present invention.

[Explanation of symbols]

 1 Bridge type sensor circuit 2 Sensor drive circuit 3a, 3b Comparator 4 Lamp voltage generation circuit 5 Power-on trigger circuit 6a, 6b Delay circuit 7 Synchronous signal generation circuit 8 Oscillation circuit G1, G2, G3 Gate circuit Va, Vb Bridge corner voltage Vr Lamp voltage OUT1 Output signal expressing measured value in pulse width OUT2 Output signal expressing measured value in pulse width

Claims (8)

[Claims] 1. A bridge type sensor circuit mainly composed of piezoresistive elements connected in a bridge type, two comparators each having two corner voltages of the bridge type sensor circuit as one input, and a predetermined rate of change. A ramp voltage generating circuit that generates a ramp voltage that gradually increases or decreases and applies the ramp voltage to the other input of each of the comparators, and the time from when one output of both comparators is inverted until the other output is inverted. And a gate circuit that outputs a signal having a corresponding pulse width. 2. The transducer according to claim 1, wherein the lamp voltage generating circuit outputs the lamp voltage only once after a lapse of a certain time after power is turned on. 3. The transducer according to claim 1, wherein the ramp voltage generating circuit repeatedly outputs the ramp voltage at an appropriate cycle. 4. The transducer according to claim 3, further comprising a circuit that outputs a synchronization signal in synchronization with an operation cycle of the ramp voltage generation circuit. 5. The transducer according to claim 1, further comprising a delay time variable delay circuit that appropriately delays a change point of the output signal of the comparator. 6. An oscillating circuit which oscillates at a relatively high frequency is provided, and the oscillating signal is output to the outside only for the period of the pulse width of the gate circuit. The transducer according to item 1. 7. The transducer according to claim 6, wherein the oscillating circuit is a voltage-controlled variable frequency type circuit, and the frequency changes according to a drive voltage of the bridge type sensor circuit. 8. A gas meter capable of detecting at least gas flow rate and gas pressure, wherein the transducer according to any one of claims 1 to 7 is used as a sensor for detecting the gas pressure, and The bridge-type sensor circuit to be mounted is a pressure sensor in which the piezoresistive element changes according to pressure, and further comprises arithmetic processing means for receiving a pulse output from the transducer and performing predetermined arithmetic processing. Gas meter to do.