JP4270712B2 - Gas detection method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention provides a semiconductor type gas detection element, energizes the gas detection element to obtain an output from the gas detection element, and also provides a gas detection circuit that allows the gas detection element to be electrically heated. The present invention relates to a gas detection device provided with an alarm device that issues an alarm based on an output from a gas detection element, and a gas detection method using the gas detection device.
[0002]
[Prior art]
Conventionally, as this type of gas detection device, a first energization state in which the gas detection element is purge-heated and a second energization state in which the gas detection element is maintained in an adsorption state in which atmospheric gas is adsorbed are alternately repeated. While performing the heating control, the stable output (base output) from the gas detection element in the second energization state in clean air where the concentration of the gas to be detected is less than negligible is the first output, and the second energization A second output from the gas detection element with respect to the gas to be detected at the end of the state is obtained, and the difference is calculated as an output based on the gas to be detected.
However, according to such a method, fluctuations in the first output due to deterioration of the gas detection element or the like cannot be offset, and there is a possibility that an accurate gas concentration cannot be obtained gradually. Further, in order to prevent the influence due to the fluctuation of the first output, the fluctuation of the base output in the second energization state is measured with time, and the average value is taken as the first output, and the second output and It is considered that the gas concentration can be obtained more accurately over a long period of time, and a gas detection device capable of performing these controls is considered.
[0003]
[Problems to be solved by the invention]
However, for example, when the measurement of the gas concentration is performed for the purpose of issuing an alarm, even if the gas detection method as described above is adopted, the gas to be detected is detected in the space to be detected. When the gas to be detected is present in a small amount in advance below the alarm level, or when it becomes a characteristic that the gas is sensitively detected due to deterioration over time, the base output gradually increases over time. Thus, there was a situation in which the output was greatly different at the start and end of the second energized state. Therefore, in such a case, the amount of gas to be measured to be measured is calculated based on the average value of the fluctuating base output, so that the first output serving as a reference for assuming that the gas concentration is 0 is accurately obtained. In other words, it was a factor that fluctuated, and the reliability in concentration measurement was still not sufficient.
In particular, when it is desired to detect a high concentration gas, the base output of the gas detection element rapidly rises in a short period of time. Even if the gas detection element is not deteriorated, the base output is stable. In many cases, it is difficult to obtain the state, and it is difficult to accurately obtain the first output, and it is not possible to obtain an accurate gas concentration, and the reliability in concentration measurement is still not sufficient. It was.
[0004]
Accordingly, an object of the present invention is to provide a technique capable of measuring the concentration of a gas to be detected with higher reliability even when detecting a gas having a high concentration, in view of the above-described drawbacks. is there.
[0005]
[Means for Solving the Problems]
In order to achieve this object, the characteristic means of the gas detection method of the present invention includes:
A semiconductor type gas detection element is provided, and a current is supplied to the gas detection element to obtain an output from the gas detection element, and a gas detection circuit is provided for making the gas detection element freely energized and heated. A gas detection method using a gas detection device provided with an alarm device for issuing an alarm based on the output of
Conducting heating control for alternately repeating a first energized state in which the gas detecting element is purge-heated and a second energized state in which the gas detecting element is adsorbed to adsorb atmospheric gas,
In a state where the gas detection element is disposed in the detected gas atmosphere, after the gas detection element is switched from the second energized state to the first energized state, at least the gas detecting element detects the detected gas. Obtain the standby time until the temperature rises to disappear, maintaining the first energized state over the standby time ,
After obtaining the first output from the gas detection element after the standby time has elapsed after starting the first energized state,
Obtain the second output from the gas detection element in the second energized state,
The difference between the first and second outputs is the output from the gas detection element to the gas to be detected.
[0006]
In addition, the characteristic configuration of the gas detection device of the present invention for achieving the above object is as follows:
A semiconductor type gas detection element is provided, and a current is supplied to the gas detection element to obtain an output from the gas detection element, and a gas detection circuit is provided for making the gas detection element freely energized and heated. A gas detection device provided with an alarm device for issuing an alarm based on the output of
Conducting heating control for alternately repeating a first energized state in which the gas detecting element is purge-heated and a second energized state in which the gas detecting element is allowed to adsorb atmospheric gas is performed, and the gas detecting element is After the gas detecting element is switched from the second energized state to the first energized state in a state where the gas detecting element is arranged in the detected gas atmosphere, the gas detecting element rises to a temperature at which the detected gas is no longer detected. to previously obtain the time advance, as the waiting time the time, after the start first energized state, the obtaining a first output from the gas sensing element in said first energized state at the time elapsed the waiting time, the second A control device is provided that calculates a difference between the first and second outputs by obtaining a second output from the gas detection element in a two-energized state.
[0007]
[Function and effect]
In other words, when the energization heating control is performed in which the first energization state in which the gas detection element is purge-heated and the second energization state in which the gas detection element is adsorbed to hold the atmospheric gas are alternately performed, the gas detection is performed. Even if the element tends to deteriorate due to long-term use or the like, in the first energized state, the gas detection element is exposed to a high temperature, and deposits adhering to the surface thereof are oxidized and removed, and the gas detection is performed. It becomes easy to maintain the amount of moisture adhering to the surface of the element itself in a constant state. Further, in the second heating state, when the gas detection element adsorbs the gas to be detected in the atmosphere and an output detection voltage is applied, the gas detection element is caused by an oxidation reaction of the gas to be detected on the surface of the gas detection element. Since the change in the electronic state is reflected in the current, an output corresponding to the concentration of the gas to be detected is exhibited and high gas selectivity can be exhibited. Therefore, in this way, the gas to be detected can be detected stably, and a highly reliable detection result can be provided over a long period of time.
[0008]
In this case, when the output of the gas detection element in a state where the gas detection element is arranged in clean air is obtained, the gas detection element from the gas detection element when the concentration of the gas to be detected is 0 You can know the output. Here, immediately after the gas detection element is switched from the first energized state to the second energized state, the output is unstable, and an output corresponding to a detected gas concentration of 0 is obtained. It's hard to say. In addition, when the detected gas is present at a high concentration in the atmosphere in the second energized state, the base output rapidly rises and it is difficult to obtain an output with respect to the detected gas concentration of 0. Therefore, the present inventors stabilize the output from the gas detection element in the purge state where the temperature of the gas detection element rises until the detection gas is no longer detected regardless of the presence or absence of the detection gas. We came up with the point of being in a state and completed the present invention.
[0009]
That is, according to the present invention, if the gas detection element is heated to a temperature at which the detected gas is not detected in the first energized state, the first output obtained at that temperature is detected. Since it can be regarded as corresponding to a gas concentration of 0, if a second output as an output for the gas to be measured is obtained while the gas detection element is maintained in the second energized state, the detected object The output based on the gas is added to the base output, and the difference between the first and second outputs becomes the output by the detected gas. When obtaining the difference between the first output and the second output, if the difference between the first output and the second output obtained in one cycle of the first and second energized states is obtained, it is for the convenience of control. Either may be obtained first.
[0010]
Therefore, the difference between the first and second outputs is obtained in a state where the base output does not depend on the concentration of the detected gas in the atmosphere, and is precisely adapted to the concentration of the detected gas. It can be said that. Therefore, accurate determination can be made even when determining the concentration of the gas to be detected.
[0011]
When the gas detection element is heated to the purge state, the gas detection element is heated to about 300 ° C. to 450 ° C., and when the gas detection element is maintained in the adsorption state, the gas detection element is heated to room temperature to about 300 ° C. Depending on the characteristics of the gas sensing element, it has a unique temperature range.
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
As shown in FIG. 1, the gas detection device of the present invention is provided with a semiconductor type gas detection element 1, energizes the gas detection element 1 to obtain an output from the gas detection element 1, and the gas detection device. A control device 3 is provided that includes a gas detection circuit 2 including a bridge circuit that allows the element 1 to be heated and energized, and determines whether or not an alarm is required based on an output from the gas detection element 1. And an alarm device 4 for generating an alarm are provided.
[0012]
The control device 3 alternately repeats a first energization state in which a voltage is applied to the gas detection element 1 to perform purge heating and a second energization state in which the gas detection element 1 is maintained in an adsorption state in which atmospheric gas is adsorbed. An energization heating control unit 31 is provided.
[0013]
After the gas detection element is placed in the gas to be detected and the gas detection element is switched from the second energized state to the first energized state, the temperature of the gas detection element detects the detected gas. Find the waiting time until it rises until it runs out,
After obtaining the first output from the gas detection element after the standby time has elapsed after starting the first energized state,
A timer 32 and an output unit 33 for obtaining a second output from the gas detection element in the second energized state are provided, and a calculation unit 34 for calculating a difference between the first and second outputs is provided.
[0014]
Specifically, the first energized state lasts for 5 seconds at 2.0 V, and the second energized state continues for 5 seconds without applying voltage. Here, the first output is obtained as the base output from 2.8 seconds (standby time) to 5 seconds after the start of the first energized state. Further, the second output is obtained in the second energization state.
A difference between the first and second outputs is obtained from the obtained output by the arithmetic unit 33. Further, based on the difference, judgment of an alarm is performed, and when an alarm needs to be issued, an alarm output is output to the alarm device 4 to issue an alarm such as an alarm sound.
[0015]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
Covering a platinum wire coil 11 having a diameter of about 30 μm as the gas detection element 1, a tin oxide semiconductor is provided in a diameter of 0.5 mm, and the tin oxide semiconductor is baked at 600 ° C. for 1 hour to form a gas sensitive portion 12. In addition, a hot-wire semiconductor gas detection element having a normal temperature operation type, in which 0.05 mol% of palladium is added to the gas sensitive part 12 and having a carbon monoxide gas (detected gas) selectivity, is provided (see FIG. 2). When the first energization state was performed, the output progress as shown in FIG. 3 was shown in clean air and in the gas to be detected. This gas detection element 1 is found to be heated to 300 ° C. or higher after 2.8 seconds (standby time), and this gas detection element exhibits an output only near room temperature and produces a gas output at 300 ° C. or higher. Therefore, it can be seen that the output at the concentration 0 of the detected gas can be obtained accurately. It can be seen that the first output decreases as the temperature of the gas sensing element rises, and reaches the output of clean air (Air) and stabilizes after 2.8 seconds while drawing an attenuation curve. Therefore, the standby time is set to 2.8 seconds, and the first output can be determined with the output from the start of the first energization state to 5 seconds later.
[0016]
Further, when the output progress of the gas detection element after the start of the second energization state is obtained, it is as shown in FIG. 4, and the temperature of the gas detection element returns to room temperature in about 3 seconds, and the second output can be measured. As a result, the output progress for the gas to be detected was obtained by applying a pulsed voltage for several milliseconds, and after 3 seconds, an output capable of determining the concentration of the gas to be detected having a sufficiently high concentration was obtained. You can see that
[0017]
[Another embodiment]
The gas detection element is not limited to such a room temperature drive type carbon monoxide gas detection element, and various elements can be used. The standby time can be determined for each gas detection element.
[Brief description of the drawings]
[Fig. 1] Conceptual diagram of a gas detection device [Fig. 2] Schematic diagram of a gas detection element [Fig. 3] Temperature and output progress graph in a first energization state [Fig. Explanation of]
1 Gas detection element 2 Gas detection circuit 3 Control device 4 Alarm device

Claims (2)

A semiconductor type gas detection element is provided, and a current is supplied to the gas detection element to obtain an output from the gas detection element, and a gas detection circuit is provided for making the gas detection element freely energized and heated. A gas detection method using a gas detection device provided with an alarm device for issuing an alarm based on the output of
Conducting heating control for alternately repeating a first energized state in which the gas detecting element is purge-heated and a second energized state in which the gas detecting element is adsorbed to adsorb atmospheric gas,
In a state where the gas detection element is disposed in the detected gas atmosphere, after the gas detection element is switched from the second energized state to the first energized state, at least the gas detecting element detects the detected gas. Obtain the standby time until the temperature rises to disappear, maintaining the first energized state over the standby time ,
After obtaining the first output from the gas detection element after the standby time has elapsed after starting the first energized state,
Obtain the second output from the gas detection element in the second energized state,
A gas detection method in which the difference between the first and second outputs is output to the detected gas by the gas detection element. A semiconductor type gas detection element is provided, and a current is supplied to the gas detection element to obtain an output from the gas detection element, and a gas detection circuit is provided for making the gas detection element freely energized and heated. A gas detection device provided with an alarm device for issuing an alarm based on the output of
Conducting heating control for alternately repeating a first energized state in which the gas detecting element is purge-heated and a second energized state in which the gas detecting element is allowed to adsorb atmospheric gas is performed, and the gas detecting element is After the gas detecting element is switched from the second energized state to the first energized state in a state where the gas detecting element is arranged in the detected gas atmosphere, the gas detecting element rises to a temperature at which the detected gas is no longer detected. to previously obtain the time advance, as the waiting time the time, after the start first energized state, the obtaining a first output from the gas sensing element in said first energized state at the time elapsed the waiting time, the second A gas detection device provided with a control device for obtaining a second output from the gas detection element in a two-energized state and calculating a difference between the first and second outputs.

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