JP3038408B2 - Capacitive sensor circuit for gas meter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas sensor capacitive sensor circuit used as a gas meter monitoring circuit.

[Conventional technology]

2. Description of the Related Art In recent years, gas meters provided with a safety mechanism for preventing accidents of city gas and propane gas have become widespread. Specifically, it detects pressure drops due to earthquakes and rubber hoses coming off,
It is designed to shut off gas. However, since these sensors for detecting vibration and pressure are all mechanical sensors, they are not preferable in terms of accuracy and reliability.

Therefore, it is conceivable to use an acceleration sensor for detecting vibration and a pressure sensor for detecting gas pressure to obtain an analog electric signal.

[Problems to be solved by the invention]

However, gas meters are generally powered by batteries,
The electronic circuit is required to operate with low power consumption. For example,
When the capacitive type is used for the acceleration sensor and the pressure sensor, the capacitance / period conversion circuit that is frequently used has a problem that the current consumption is several hundred μA or more because of continuous oscillation, which makes the battery impractical. Was.

The present invention has been made in view of the above points, and an object of the present invention is to provide a gas meter capacity type capable of realizing low power consumption when extracting a signal using a capacity type sensor such as an acceleration sensor or a pressure sensor. It is to provide a sensor circuit.

[Means for solving the problem]

In order to achieve the above object, a capacitance type sensor circuit for a gas meter according to the present invention includes a sensor capacitance whose capacitance value changes according to a change in a measurement target, voltage applying means for intermittently applying a voltage to the sensor capacitance, and a sensor. Amplifying means for transferring the charge stored when a voltage is applied to the capacitance to a fixed capacitor, amplifying the voltage based on the capacitance value of the sensor capacitor and the capacitance value of the fixed capacitor, and outputting the output of the amplifying means. A / D converter that converts and outputs digital data and this A / D
It has a latch circuit that stores the output of the converter, and a window comparator that determines the level of the output of the amplifying means and drives the A / D converter only when this level exceeds a predetermined range.

Further, a capacitance type sensor circuit for a gas meter according to the second invention of the present invention includes a capacitance circuit in which a capacitance value that changes in accordance with a change of a measurement target and a capacitance circuit in which a fixed capacitor is connected in series, and a sensor capacitance of the capacitance circuit. Voltage applying means for intermittently applying a voltage to the fixed capacitor, an A / D converter for converting the midpoint voltage between the sensor capacitance of the capacitance circuit and the fixed capacitor into digital data and outputting the digital data, A latch circuit for storing the output of the capacitor, and a window comparator for determining the midpoint voltage of the capacitance circuit and driving the A / D converter only when the voltage exceeds a predetermined range.

[Action]

In the present invention, the sensor capacity is intermittently driven,
Only when the signal based on the capacitance value of the sensor capacitance exceeds a predetermined range, the signal is digitally processed and stored, thereby enabling the circuit to operate with low power consumption.

〔Example〕

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

FIG. 1 is a basic circuit diagram of an amplifier showing one embodiment of a capacitive sensor circuit according to the present invention. In Figure 1, 1 is capacitive sensor clogging sensor capacitance change of the capacitance value C _S in accordance with the measured vibration and gas pressure in the gas meter 2 and the second fixed capacitor as a reference capacitance, 4 be an operational amplifier , S _{1 to} S ₅ are switches. That is, the sensor capacitance 1 with one end connected in series to the capacitor 2 via a switch S _1, is connected to the non-inverting input of the operational amplifier 4 is further connected to a reference voltage V _R through the switch S _2. The other end of the sensor capacitor 1 is connected to the inverting input of the operational amplifier 4 via a switch S _3, further switch
It is grounded via the S _4. Wherein both ends of the capacitor 2 is connected is switch S _5, these switches S ₁ to S
Numeral ₅ turns on and off in the operation modes (phases) φ ₁ and φ ₂ shown in Table 1 below.

Here, all the circuits in FIG. 1 are normally off. The measurement is performed in two stages (φ ₁ , φ ₂ ). That is, assuming that each switch S ₁ to S ₅ are operated as Table 1, phi ₁ In the fixed capacitor 2 of the first stage is reset, the sensor capacitor 1 is charged by the reference voltage V _R. In the second stage φ ₂ , all charges of the sensor capacitance 1 are transferred to the fixed capacitor 2, and the operational amplifier 4
The output V _O of is as follows.

Here, C _I is the capacitance value of the fixed capacitor 2.

Therefore, after the output V _O of the operational amplifier 4, and the level determination by the third two comparators 5 ₁ constituting the window comparator 5, as shown in FIG, 5 _2, flip-flops 6 _and 62 the result of the determination Latching is performed by the latch circuit 6 and stored until the next measurement. Thereafter, the same operation is repeated.

Therefore, if the latch circuit 6 is constituted by CMOS and the power supply other than the latch circuit is cut off, the current consumption becomes almost zero. If the number of comparators 5 ₁ and 5 ₂ is increased, the output V _O of the operational amplifier can be determined at a plurality of levels. However, if more detailed determination is required, the A / D converter 7 is used as shown in FIG. A
The digital data can be stored in the latch circuit 8 by performing the / D conversion. In the figure, V _A and V _B are the comparators 5
_1, 5 ₂ after being set to the lower limit reference voltage, CK denotes a clock for driving the latch circuit 6, A / D converter 7.

On the other hand, in the case of a phenomenon that hardly occurs, such as an earthquake,
The window comparator 5 shown in FIG.
Output is monitored periodically, and a certain level value or more (abnormal value)
Only when the signal of (A) is output, the A / D converter 7
It may be configured to read the analog value after / D conversion. In this way, the operation time of the A / D converter that consumes a relatively large amount of current can be reduced.

Also, regarding the gas pressure, normally, an abnormal upper and lower value may be monitored by the comparator 5, and the analog value may be obtained by A / D conversion only when telemetering is necessary.

Thus, according to the above embodiments, intermittently the reference voltage V _R applied by the switch S ₁ to S ₅ in the sensor capacitance 1, transferred the charge accumulated in the fixed capacitor 2, the voltage of the capacitor 2 Is amplified by the operational amplifier 4, converted into digital data by the comparator 5 or the A / D converter 7, and the data is held by the latch circuits 6 and 8, so that the average power consumption is 10 μA or less. In addition, a high-reliability and high-accuracy capacitive sensor circuit can be obtained as compared with a conventional mechanical sensor.

FIG. 2 is a circuit diagram of an amplifier corresponding to FIG. 1 showing another embodiment of the present invention. The point of difference between FIG. 1, a third fixed capacitor 3 is provided to the sensor capacitor 1, in the sensor capacitor 1 was added intermittently reference voltage V _R, the second capacitor a charge stored in it By transferring the voltage to the second and second capacitors 3, the voltage is amplified by the operational amplifier 4. That is, when the change in the sensor capacitance 1 is very small, the output of the operational amplifier 4 does not change significantly in the circuit of FIG. Therefore, in the circuit of FIG. 2, with the third capacitor 3 having substantially equal capacitance value C _R and the sensor capacitor 1 is configured to obtain an output of large changes to changes in the sensor capacitance 1. In the figure, S ₆
To S ₁₂ are switch, these switches S ₆ to S ₁₂ second
It is turned on and off in the operation modes φ ₁ and φ ₂ shown in the table.

According to the circuit configuration of FIG. 2, to charge the reference voltage V _R to the sensor capacitor 1 in phi ₁ of the first stage, second and third capacitors 2 and 3 are reset. Then, in phi ₂ of the second stage, to move the charge stored in the sensor capacitor 1 to the second and third capacitor 2,3. As a result, the output V _{O of the} operational amplifier 4
Is as follows.

Therefore, as is apparent from the above equation (2), if the capacitance value C _I of the second capacitor 2 is made smaller than each of the above C _S and C _R , a large output V _{O will} be generated with respect to this change in C _S. Change can be obtained.

Also, when the change of the sensor capacitance 1 is large, as in FIG. 5, the reference voltage V _R of the sensor capacitor 1 and the fixed capacitor 3 is provided a capacitive circuit connected in series to each switch S ₁₃ to the capacitance circuit intermittently configured to apply a voltage by to S _15, the comparators and the midpoint voltage clogging output V _O
5 _1, by discriminating at 5 _2, operational amplifier is not required, the circuit is simplified. In this case, the output V _O is as follows.

Note that the same or corresponding portions in the drawings denote the same reference numerals, switch S ₁₃ to S ₁₅ mode phi ₁ shown in Table 3, on at phi _2,
Operate off.

In the fifth Fig comparator 5 _1, 5 ₂ of the reference voltage V _A,
Although V _B was configured for generating the power source, as shown in Figure 6, together with the series connected capacitors 11 to 13 against the charging reference voltage V _R, switch S ₁₆ to reset these capacitors 11-13 the to S ₁₈ is provided, a connection point a, the reference voltage b of the voltage, respectively V _a, as V _B may be configured to be added to the comparators 5 _1, 5 _2. In this case, each switch S _{13 to} S ₁₈
Are turned on and off in the modes φ ₁ and φ ₂ shown in Table 4.

In FIG. 5, an A / D converter can be used instead of the window comparator 5. Also, as in the embodiment of the present invention, the output V _O is periodically monitored by the window comparator 5 and is equal to or higher than a certain level value (abnormal value).
A / D conversion may be performed by the A / D converter only when the signal of (1) is output, and then an analog value may be read.

〔The invention's effect〕

As described above, according to the present invention, a voltage is intermittently applied to the sensor capacitance, and only when a signal based on the capacitance value of the sensor capacitance exceeds a predetermined range, the signal is converted into digital data by the A / D converter. Since the data is converted and stored, the current consumption can be significantly reduced and the life of the battery can be prolonged as compared with the analog type using a conventional capacity / period conversion circuit.

Further, according to the second aspect of the present invention, a voltage is intermittently applied to a capacitance circuit in which a sensor capacitance and a fixed capacitor are connected in series, and only when the intermediate voltage of the capacitance circuit exceeds a predetermined range, the voltage is digitally converted. Since it is converted into data and stored, current consumption can be greatly reduced,
Battery life can be extended. In addition, since the intermediate voltage is directly converted into digital data, an amplifier is not required, so that the circuit can be simplified.

[Brief description of the drawings]

FIG. 1 is a basic circuit diagram of an amplifying section showing one embodiment of the present invention,
FIG. 2 is a circuit diagram corresponding to FIG. 1 showing another embodiment of the present invention, FIGS. 3 and 4 are configuration diagrams for converting the output of the above embodiment into digital data, and FIG. FIG. 6 is a circuit diagram showing another embodiment of the present invention, and FIG. 6 is a circuit diagram showing a modification of FIG. 1 ... sensor capacity, 2, 3 ... fixed capacitor, 4 ... operational amplifier, 5 ... window comparator, 6, 8 ... latch circuit, 7 ... A / D converter, 11 to 13 ... reference voltage Generation capacitor, S _{1 to} S ₁₈ … Switch, V _R …… Reference voltage for charging.

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G01R 27/26 F16K 17/36 G01F 15/00 G08B 21/00

Claims (2)

(57) [Claims] 1. A sensor capacity whose capacitance value changes according to a change in a measurement object; voltage applying means for intermittently applying a voltage to the sensor capacity; and a voltage stored when the voltage is applied to the sensor capacity. Amplifying means for transferring the electric charge to the fixed capacitor and amplifying and outputting the voltage based on the capacitance value of the sensor capacitance and the capacitance value of the fixed capacitor; A for converting the output of the amplifying means into digital data and outputting the digital data An A / D converter, a latch circuit for storing the output of the A / D converter, and a drive circuit for determining the level of the output of the amplifying means and driving the A / D converter only when this level exceeds a predetermined range. And a window comparator for the gas meter. 2. A capacitance circuit in which a sensor capacitance and a fixed capacitor whose capacitance value changes according to a change in a measurement object are connected in series, and voltage applying means for intermittently applying a voltage to the sensor capacitance and the fixed capacitor of the capacitance circuit. An A / D converter that converts a midpoint voltage between the sensor capacitance of the capacitance circuit and the fixed capacitor into digital data and outputs the digital data; a latch circuit that stores the output of the A / D converter; and the capacitance circuit Window voltage that drives the A / D converter only when this voltage exceeds a predetermined range.
A capacitive sensor circuit for a gas meter, comprising a comparator.