JP2007017208A - Gas detection system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reconcile low electric power consumption with wide concentration range measurement, as to a sensor device with an electric source built therein. <P>SOLUTION: The sensor device is made by combining an FET-system sensor of low electric power consumption having sensitivity in a low concentration zone and a sensor having sensitivity in a high concentration zone and requiring heater heating. An exemplary operation is shown below. Normally, in detecting gas leakage, the sensor for a low concentration zone is operated while interrupting the energization of a heater. When the FET-system sensor detects a value exceeding the first set threshold, the heater heating is started. If the temperature of the heater exceeds the second threshold, the start-up of the high concentration zone sensor is determined to have been completed. Thereafter, an output value of the FET-system sensor is used as an output value of the sensor device if concentration is equal to or less than the third set threshold while using an output value of the zone sensor as an output value of the sensor device if the concentration is equal to or more than the third set threshold. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a system for detecting a change in gas concentration, and more particularly to a gas concentration measurement system in which a power supply is mounted on a sensor device and wirelessly transmits signals to the outside.

  There are various types of gas sensors. For example, for combustible gas sensors, there are contact combustion type, semiconductor type, heat conduction type, infrared absorption type, etc. as described in JIS M 7626 “Stationary type combustible gas detection alarm”. Are known. In addition, as a method using a thin film or thick film, a gas sensitive film is formed on the gate electrode of FET (Field Effect Transistor) described in pages 15 to 20 of Sensors and Actuators magazine B1 volume. The hydrogen responsiveness of the method of reading the potential change with FET (hereinafter referred to as FET method) has been reported. Japanese Journal of Applied Physics, Vol. 40, pages L1232 to L1234, a method of reading the temperature rise of the thermoelectric conversion film by the target gas as a voltage (hereinafter referred to as a thermoelectric method) has been proposed (Non-Patent Document 2). ). The FET method has high sensitivity, and for example, on pages 10 to 11 of the 18th Eurosensors International Conference Abstracts, 5 ppm hydrogen can be detected with a sensor using palladium as the gate electrode (Non-patent Document 3). . In the thermoelectric system, it is reported in the above-mentioned document that 3% hydrogen can be detected using platinum.

  The above example relates to a single sensor, but as an example of using a plurality of sensors, a method of detecting hydrogen gas in a wide concentration range using a plurality of sensors having different output linear regions with respect to the concentration (Japanese Patent Application Laid-Open No. 2002-2002). No. 357576) is disclosed (Patent Document 1). The example of FIG. 2 is this example. The sensor 201 includes a resistance-type hydrogen sensor 202 made of palladium alloy and an oxide semiconductor-type hydrogen sensor 203 made of tin oxide. The sensor 201 determines which sensor output uses the gas concentration of the atmosphere and switches the signal. A discriminator 205 and a switching unit 206 are arranged. A signal related to the gas concentration is output from the switch 206.

  In addition to measuring the gas concentration at a specific location, a detection system that measures the gas concentration distribution in the entire facility and uses this result to monitor leak diffusion and identify leak locations will become more popular in the future. It is expected that. A hydrogen station that supplies hydrogen gas to a fuel cell vehicle is a good example of a facility that requires such a detection system because it is built in an urban area and requires high safety. A technique for connecting a plurality of gas sensors by wireless communication and monitoring a gas concentration distribution is described, for example, on pages 94 to 95 of the 10th Chemical Sensor International Conference Technical Abstracts (Non-Patent Document 4). In this example, it is proposed that several types of sensors such as electrochemical sensors and photoionization sensors be hybridized to construct odor and VOC monitoring systems for wastewater treatment plants, waste disposal plants, livestock houses, clean rooms, etc.

JP 2002-357576 A Sensors and Actuators, Vol. B1, pp. 15-20 Japanese Journal of Applied Physics Vol. 40, pp. L1232-1234 XVIII EUROSENSORS, Digest of Technical Papers, (2004) pp. 10-11 The 10th International Meeting on Chemical Sensors, Technical Digest, pp. 94-95

  When tens to hundreds of sensors are arranged to measure the gas concentration distribution, the sensor-equipped small wireless terminal (hereinafter referred to as sensor node) has a built-in sensor, wireless function, and power supply. This eliminates the need for wiring and facilitates the placement of sensor nodes. One of the important issues in a sensor node (hereinafter referred to as a sensor device) incorporating such a power supply is a reduction in power consumption.

The reduction in power consumption includes a reduction in wireless communication power and a reduction in power consumption of the sensor itself. In general, the instantaneous maximum power consumption is determined by the power consumption of the wireless portion, but it is the power consumption of the sensor that has a large effect on the accumulated power consumption over a long period of time. This is because the wireless portion consumes power when periodically transmitting, but the sensor portion always consumes power.
In addition, as described above, there are several types of gas sensors. Especially in gas sensors using an electrochemical reaction such as a semiconductor type or a thermoelectric type, the temperature is important because the chemical reaction is affected by the temperature. . Therefore, it is necessary to heat and use the sensor, and the power consumption of the sensor heating heater becomes enormous.

  That is, in order to reduce power consumption, it is effective to use a sensor with low power consumption and suppress heater heating.

  Among the sensors described above, the FET method has the lowest power consumption and can be suppressed to about several tens of microwatts. However, as described on pages 10 to 11 of the 18th Eurosensors International Conference Technical Abstract, the FET method is sensitive to the low concentration range and is not suitable for measurement in the high concentration range.

  An object of the present invention is to realize a sensor device that can measure over a wide concentration range even in the absence of power supply from the outside.

  By combining a low power consumption FET type gas sensor corresponding to a low concentration range with a semiconductor type or thermoelectric type gas sensor corresponding to a high concentration range, power consumption is suppressed in a control sequence. Specifically, only the FET type gas sensor corresponding to the low gas concentration is always activated, the semiconductor type or thermoelectric type sensor is stopped, a certain gas concentration range is set as a threshold value, and the threshold value is set. When it exceeds, the sensor in the high concentration area is activated and detected by both sensors.

  In a safety monitoring system such as gas leak detection, it is important to always measure only the low gas concentration, and in that case, the sensor corresponding to the high concentration region where heater overheating is required should be stopped. Thus, power consumption can be suppressed.

  The main aspects of the present invention are listed as follows.

  That is, the essence is at least a power source, a FET-type first gas sensor that measures low-concentration gas, a second gas sensor that measures high-concentration gas heated by a heater, a temperature sensor, a comparator, And the first gas sensor is switched between the first gas sensor and the second gas sensor by confirming the start of heating of the second gas sensor by the temperature sensor. This is a gas detection system.

  In this case, a sensor having at least the power source, a first gas sensor of FET type that measures low concentration gas, a second gas sensor that measures high concentration gas heated by a heater, a temperature sensor, and a comparator. It can be configured as a device, further provided with a communication function unit, wirelessly transmitting various data to a server, and generating and transmitting data processing and control signals necessary for control in this server. It is. In this example, a form having a gas sensor device, a communication device that exchanges information by communication, a server that accumulates or analyzes the output of the sensor device, and a monitor that displays a gas concentration is useful.

  The high-concentration gas is practically set at a gas concentration of 1% or more, and is frequently used.

  The first and second gas sensors are switched as follows, for example. Each of the plurality of comparators controls the first comparator to start a heater unit for a second gas sensor that measures the high-concentration gas to be heated by the heater, and the second comparator measures the high-concentration gas. Confirm that the temperature of the heater unit is appropriate for the second gas sensor, that is, the transition of the second gas sensor to normal operation, and the third comparator detects the FET-type first gas sensor and the high-concentration gas. This has a function of selecting the output of the second gas sensor to be measured.

  Conventionally, an apparatus that combines a plurality of sensors has been described in Patent Document 1 described above, but it has only a function of always starting each sensor and switching in a density region suitable for each sensor. On the other hand, the present invention is equipped with a battery and a wireless communication function, and further, by adding a plurality of sensors and a control sequence for switching between them, a wide concentration can be obtained without external power supply. A sensor device corresponding to a region can be realized.

  According to the gas detection system of the present invention, detection in a wide concentration range is possible, and low power consumption can be realized.

  Prior to specific description of embodiments of the present invention, various gas sensors used in the present invention will be briefly described. A semiconductor sensor (sometimes referred to as an oxide semiconductor sensor) measures a change in resistance of a sintered body of tin oxide or zinc oxide, for example. For example, it is used that the resistance is changed by heating to 300 ° C. with a platinum wire heater or the like, and gas adsorbing on the surface of tin oxide. For this reason, the power consumption in the heater cannot be ignored. A thermoelectric sensor is a material that has a catalytic action on gas and is placed on the thermoelectric material.For example, when hydrogen gas dissociates and adsorbs on the platinum surface, heat is generated and the temperature changes. Is detected. Even in this sensor, in order to improve the sensitivity to hydrogen and the response speed, it is necessary to heat the catalyst material, and power consumption due to heater heating increases. As described above, the present invention aims to reduce power consumption while taking advantage of the features of the gas sensor.

  On the other hand, the FET gas sensor uses a gas-sensitive material for the gate electrode of a field effect transistor, and gas is adsorbed and dissociated on the surface of the gate electrode, and the effect is observed as a gate voltage shift. In the case of detecting hydrogen gas, a hydrogen catalyst material such as platinum or palladium is used for the gate electrode. When hydrogen is dissociatively adsorbed on the platinum surface and becomes hydrogen atoms, the channel conductivity of the transistor changes due to the influence of the dipole, so that it can be considered that the gate voltage has changed relatively. The FET type gas sensor can reduce the current consumption to 100 μA or less, and can reduce the power consumption of the sensor.

<Example 1>
Hereinafter, examples of embodiments of the present invention will be described.
FIG. 1 is a conceptual diagram showing a configuration of a sensor device of a gas detection system of the present invention. The sensor device includes a power supply 103, a wireless unit 102, a control unit 104, and a sensor unit 105. The sensor unit 105 includes a FET type sensor 109, a sensor 110 corresponding to a high concentration region, a heater 111, and a temperature sensor 112. The control unit 104 includes at least three comparators 106, 107, and 108. The first comparator 106 compares the data detected by the FET sensor 109 with the first threshold value, and outputs the output 114 of the sensor device, the high concentration sensor 110, or the heater 111 for the high concentration sensor through the controller 113. This is for outputting instructions for heating. The second comparator 107 measures the temperature change caused by the heater 111 with the temperature sensor 112, and whether the temperature of the temperature sensor 112 exceeds the second threshold, that is, the high concentration sensor 110 can be normally measured. It is for detecting that. The third comparator 108 compares the output of the FET sensor 109 with the third threshold value, determines whether the FET sensor 109 is within the appropriate measured concentration range, and connects the FET sensor 109 to the output terminal 114 of the sensor device. This is for selecting either the output or the output of the high concentration range sensor 110.

An outline of a control sequence for determining the sensor output value of the sensor device of the present invention will be described with reference to FIG. In this embodiment, a case where a thermoelectric sensor is used as the high-concentration sensor 110 will be described. Both the FET sensor 109 and the high concentration region sensor 110 transfer the output value of each sensor (FET type sensor output value: S _F , high concentration region sensor output: S _H ) (step 1) to the control unit 104. The first comparator 106 compares the first threshold value (S _T1 ) with the FET system (109) sensor output (S _F ) (step 2). When S _F ≦ S _T1 , the output of the sensor device is S = S _F (step 3).

If S _F > S _T1 , the heater of the high concentration sensor 110 is activated and heating is started (step 4). Here, the first threshold value is a set value for starting activation of the high-concentration area sensor 110 and needs to be determined in consideration of the activation time of the heater within the appropriate concentration range of the FET sensor 109.

Further, when S _F > S _T1 , the second comparator 107 is used to determine whether the output of the temperature sensor 112 exceeds the second threshold value. If not, the output of the sensor device is set to S. = S _F. When the output of the temperature sensor 112 exceeds the second threshold value, the output of the sensor device is set to S by the third comparator 108, and the output of the FET sensor (S _F ) or the output of the high concentration region sensor 112 ( S _H ). Here, the second threshold value is a temperature at which an appropriate output is obtained for the measurement of the high concentration range sensor 110.

The third comparator 108 compares the third threshold value (S _T2 ) with the FET sensor output (S _F ), and if S _F ≦ S _T2 , the sensor device output S = S _F ( Step 8) If S _F > S _T2 , S = S _H (Step 9). Here, the third threshold value can be arbitrarily determined from the overlapping region of the appropriate concentration region of the FET sensor 109 and the appropriate concentration region of the high concentration sensor 110.

  When used for hydrogen leakage detection, the appropriate concentration range of the FET sensor 109 is 1% or less, and the operating temperature range of the thermoelectric sensor 110 is 100 to 150 ° C. or more, so the first threshold is 500 to 1000 ppm, The threshold value may be 80 to 120 ° C. as 80% or more of the operating temperature range, and the third threshold value may be selected in the range of 5000 ppm to 1%. When a semiconductor sensor is selected as the sensor 110 for the high concentration region, the proper use temperature of the semiconductor sensor is 200 ° C. to 400 ° C., and the second threshold is preferably set to about 160 ° C. to 360 ° C. . In order to control to these temperatures, in addition to the first to third comparators described above, a comparator for controlling energization of the heater based on the output of the temperature sensor may be added.

  In this embodiment, the output value of the FET sensor 109 and the output value of the high-concentration area sensor 110 are compared with the threshold value based on the information converted into the concentration. However, the sensor output value is handled as the voltage or current value. The threshold value may be processed as a voltage or current value corresponding to the concentration of each sensor using a signal before being converted into the concentration.

  Furthermore, since the output value of each sensor is temperature-dependent, it goes without saying that a calibration table based on temperature is stored in the control unit, and the value subjected to calibration is used as the output of the sensor device.

<Example 2>
An example of a gas detection system including the sensor device described in the first embodiment as a constituent element will be described with reference to FIG. The gas detection system includes at least a plurality of sensor devices (Node # 1, Node # 2, to Node # n) 301 to 303, a communication device 304 that exchanges signals with each sensor device, and stores and analyzes data. The server 305 includes a display system 306 that displays the gas concentration of each sensor device. Furthermore, by connecting the server 305 to a network, the state of the sensor device and the gas concentration can be confirmed and controlled from a remote location. Here, the sensor devices (Node # 1, Node # 2, to Node # n) 301 to 303 are the sensor devices described in the first embodiment.

  In such a gas detection system in which the sensor devices 301 to 303 and the server 305 are connected wirelessly, data analysis on the server side can be performed at high speed. For this reason, as shown in the first embodiment, without having a comparator inside the sensor, the state and output value of each sensor are transmitted to the server 305 and compared in software in the server. It is also possible to transmit a heater activation signal to 301 to 303 or select an output value of the sensor device.

The sensor device with built-in power supply, FET type sensor, high-concentration range sensor with heater and temperature sensor output value is configured with comparator or software configured with hardware inside sensor device or server The following functions should just be implemented using a comparator.
(1) Control the activation of the heater for the gas sensor. The form of the heater for heating differs depending on the form of the gas sensor, but in any case, it is important to control the activation of the corresponding heater. That is, in the case of a gas sensor corresponding to a high concentration region in which a heater is incorporated, a heater built in the built-in sensor, or a gas sensor in a form in which the heater is provided separately from the gas sensor main body, The activation of the heater provided separately is controlled.
(2) It is determined whether the operation state of the high-concentration range sensor having a heater is appropriate.

Alternatively, the temperature of the heater may be managed and determined to be appropriate.
(3) Select the gas concentration output of the FET sensor and the high concentration range sensor.

  Since the low-concentration gas leakage detection is routinely performed, the power consumption of the sensor device can be kept low. For this reason, even a power source built in the sensor device can be operated for a long time. By using a sensor device with a built-in power supply and wireless function, for example, a gas detection system for a hydrogen station can be configured. Since the connection is not required, it can be arranged freely without limiting the installation location, and the concentration distribution of each sensor device can be displayed on a server, or remote location monitoring can be performed.

  Although the present invention has been described above, the effects of the embodiments of the present invention are described in detail as follows.

  In a gas sensor device that supports the high concentration range even when there is no external power supply, low concentration measurement is always performed with low power consumption.When a certain threshold concentration is exceeded, high power consumption corresponding to the high concentration region is high. By starting the sensor, the sensor device can be operated with a small battery (for example, a dry cell). Therefore, the sensor device can also be reduced in size, and the sensor installation location can be freely selected together with the wireless communication function.

  Further, when the gas leak detection system is configured, it is sufficient to replace the sensor device calibrated in advance without worrying about wiring, and the system maintenance is facilitated.

  Furthermore, a control sequence in which a FET gas sensor is constantly measured and a sensor suitable for a high concentration region is activated when a set threshold value is exceeded is also effective in reducing power consumption of a wired sensor device.

FIG. 1 is a conceptual diagram showing a configuration example of a sensor device of the present invention. FIG. 2 is a conceptual diagram of a sensor configuration showing a conventional example. FIG. 3 is a flowchart showing a part of the control sequence of the sensor device of the present invention. FIG. 4 is a conceptual diagram showing a configuration example of a gas detection system using the sensor device of the present invention.

Explanation of symbols

101: sensor device, 102: wireless unit, 103: power supply, 104: control unit, 105: sensor unit, 106: first comparator, 107: second comparator, 108: third comparator, 109: FET type sensor, 110: high concentration range sensor, 111: heater, 112: temperature sensor, 113: controller, 114: output terminal, 201: measurement point of conventional example, 202: resistance type hydrogen sensor using palladium alloy of conventional example, 203: Oxide semiconductor hydrogen sensor using tin oxide, 205: Switch of conventional example, 206: Discriminator of conventional example, 207: Output of conventional example, 301: First sensor device, 302: Second sensor device 303: n-th sensor device 304: communication device 305: server 306: display system

Claims (5)

At least a power supply, a FET-type first gas sensor that measures low-concentration gas, a second gas sensor that measures high-concentration gas heated by a heater, a temperature sensor, and a comparator, and The first gas sensor and the second gas sensor are switched and used by determining the start of heating of the heater with respect to the second gas sensor by a comparator and confirming the start of the second gas sensor by the temperature sensor. Gas detection system. At least the power source, the communication function unit, a FET-type first gas sensor that measures low-concentration gas, a second gas sensor that measures high-concentration gas heated by a heater, a temperature sensor, and a comparator The gas detection system according to claim 1, wherein the sensor device has a component of the gas detection system. The gas detection system according to claim 1, wherein a gas concentration of the high-concentration gas is 1% or more. Each of the plurality of comparators performs control to activate a heater unit for a second gas sensor that measures the high concentration gas heated by the first comparator, and the second comparator measures the high concentration gas. Confirming the transition of the heater to the appropriate temperature for the second gas sensor, the third comparator selects the output of the FET-type first gas sensor and the second gas sensor that measures the high-concentration gas. It has a function, The gas detection system of Claim 1 characterized by the above-mentioned. A gas detection system comprising: the gas sensor device according to claim 2; a communication device that exchanges information by communication; a server that accumulates or analyzes the output of the sensor device; and a monitor that displays a gas concentration.

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