GB2285508A - Corrosive gas detector - Google Patents
Corrosive gas detector Download PDFInfo
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- GB2285508A GB2285508A GB9424857A GB9424857A GB2285508A GB 2285508 A GB2285508 A GB 2285508A GB 9424857 A GB9424857 A GB 9424857A GB 9424857 A GB9424857 A GB 9424857A GB 2285508 A GB2285508 A GB 2285508A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N17/00—Investigating resistance of materials to the weather, to corrosion, or to light
- G01N17/04—Corrosion probes
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/04—Analysing solids
- G01N29/12—Analysing solids by measuring frequency or resonance of acoustic waves
Description
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DESCRIPTION
METHOD AND APPARATUS FOR DETERMINING THE PRESENCE OF CORROSIVE GAS 2285508 The present invention relates to a method and apparatus for determining the presence of corrosive gas. More particularly, the present invention relates to a method and apparatus which is capable of determining correctly the presence of corrosive gas at an early stage by determining promptly and precisely a charge in frequency detected by a corrosive gas sensor.
With the development of industry, accidents and disasters due to various kinds of inflammable or toxic gases, and oxygen deficiency have been increased. Especially, corrosive gas exerts various adverse effects on the human body and corrodes metals even when it is contained in our living environment and working environment in extremely small quantities. Therefore, corrosive gas causes troubles to electronic circuits of manufacturing facilities, computers or the like.
As an example of generation of corrosive gas, abnormal heating of power cables of electrical appliances, which is one of the causes of a fire, may be considered. Generally, PVC (polyvinyl chloride), which is a flame retardant material, is used for power cables of electrical appliances. It is widely known that HCl (hydrogen chloride), which is corrosive gas, is generated upon heating PVC.
As a device for detecting such corrosive gas as described above, for example, a corrosive gas sensor of crystal resonator type is known.
The corrosive gas sensor of crystal resonator type includes a crystal resonator as a resonator. At a center portion of the crystal resonator, for example, a chromium film and a gold film are deposited byevaporation. At both end portions thereof, metal films to be corroded by corrosive gas are deposited. Then, the crystal resonator is oscillated by an oscillation circuit, and the oscillation frequency is counted by a frequency counter.
When the metal films deposited on the crystal resonator are corroded by corrosive gas, the crystal resonator increases in weight. The frequency of the crystal resonator decreases with the increase in weight of the crystal resonator. The decrease in the frequency is taken out as a change in the natural frequency. The presence of corrosive gas is detected by detecting the change in the natural frequency.
Such a conventional corrosive gas sensor as described above outputs corrosive gas detecting signals when the frequency difference between the initial frequency of the crystal resonator and the natural frequency of the same when the crystal resonator is corroded becomes lower than a predetermined threshold (negative level), that is, the frequency difference exceeds a fixed level. And, some conventional corrosive gas sensors capture the frequency difference by a relation with the time, and detect the presence of corrosive gas by an inclination of the change in frequency.
However, the conventional corrosive gas sensor of a crystal resonator type decides the presence of corrosive gas by the frequency difference between the initial frequency and the natural frequency of the crystal resonator. Thus, a predetermined threshold should be set to a higher level to remove influences of temperature and humidity. Accordingly, 3- the corrosive gas detecting signal is not output until considerable change in frequency, and the presence of corrosive gas can not be detected correctly at an early stage.
An object of the present invention is to provide a method and an apparatus for determining the presence of corrosive gas capable of correctly determining the presence of corrosive gas at an early stage by capturing precisely an unusual decrease in frequency from a detected frequency of a corrosive gas sensor.
According to the present invention, there is provided an apparatus for determining the presence of corrosive gas which comprises: a corrosive gas sensor for detecting corrosive gas by a change in oscillation frequency; an oscillating means for oscillating the corrosive gas sensor; a sampling means for sampling the frequency detected by the corrosive gas sensor in a predetermined cycle; a frequency difference detecting means for detecting a frequency difference between the detected frequency and a reference frequency each time the detected frequency being sampled by the sampling means; a corrosive gas deciding means for deciding the presence of corrosive gas when the frequency difference detected by the frequency difference detecting means exceeds a predetermined threshold; and a reference frequency operating section for operating and setting the next reference frequency to be compared with the detected frequency, based on the frequency difference when the frequency difference is detected next time.
In the apparatus according to the present invention, the reference frequency operating section may be preferably formed by a reference frequency correcting means for correcting the reference frequency by multiplying the frequency difference by a predetermined coefficient lower than 1 and adding the obtained level to the reference frequency, and a reference frequency setting means for setting the level of the corrected reference frequency operated by the reference frequency correcting means as the next reference frequency.
The apparatus according to the present invention may be preferably applied to hydrogen chloride among corrosive gases.
The apparatus according to the present invention may comprise also a maximum value controlling means for controlling a change in the frequency detected by the sampling means when the change in the detected frequency exceeds the predetermined level, and a running average operating means for operating running average every time a predetermined plurality of detection data are obtained. in this case, the maximum value controlling means may control change in the detected frequency when the detected frequency contains noise elements and change in the frequency exceeds the predetermined level.
Further, the apparatus according to the present invention may comprise a duration measuring means for outputting a decision of the presence of corrosive gas only when the decision of the presence of corrosive gas from the corrosive gas deciding means continues for a predetermined period of time or longer.
Still further, the apparatus according to the present invention may comprise the corrosive gas sensor and the oscillating means formed by a plurality of corrosive gas detectors including a plurality of corrosive gas detecting sections and a plurality of transmission circuits each circuits having a predetermined address all its own, a receiving means as the sampling means calling each of the corrosive gas detectors, respectively, to collect detection outputs thereof and storing each of the outputs in each of the corrosive gas detectors, and a detector number counting means outputting the decision of the presence of corrosive gas only when the number of decision of the presence of corrosive gas exceeds a predetermined number upon detecting outputs of each of the corrosive gas detectors, respectively, with the corrosive gas deciding means.
Furthermore, the apparatus according to the present invention may comprise a crystal resonator for a reference signal sending a reference signal to be compared with the frequency detected by the corrosive gas sensor, an oscillating means for oscillating the crystal resonator for a reference signal, a mixture means for mixing the frequency from the oscillating means of the corrosive gas sensor and the frequency from the oscillating means of the crystal resonator for a reference signal, and a change signal selecting means for taking out the change in frequency of the corrosive gas sensor due to corrosive gas from the output signal after mixing.
In addition, the apparatus according to the present invention may comprise a maintenance level determining means for comparing said detected frequency of the corrosive gas sensor with a predetermined maintenance level, and a maintenance signal output means for outputting maintenance signal in accordance with the decision output from the maintenance level determining means. In this case, the maintenance level determining means outputs the decision when the detected frequency exceeds the maintenance level.
According to a second aspect of the present invention,_ there is provided a method for determining the presence of corrosive gas comprising the steps of: oscillating a corrosive gas sensor for detecting corrosive gas by a change in oscillation frequency with oscillating means; sampling the frequency detected by the corrosive gas sensor in a predetermined cycle; detecting a frequency difference between the detected frequency and a reference frequency each time the detected frequency being sampled by the sampling means; deciding the presence of corrosive gas when the frequency difference detected by the frequency difference detecting means exceeds a predetermined threshold; and operating and setting the next reference frequency to be compared with the detected frequency based on the frequency difference when the frequency difference is detected next time. In the method according to the present invention, the next reference frequency may be preferably operated and set by multiplying the frequency difference by a predetermined coefficient lower than I and adding the obtained level to the reference frequency.
The method according to the present invention may be preferably applied to hydrogen chloride.
The method accordina to the iDresent invention may comprise also the steps of: controlling a change in frequency of the detected frequency when the change in the detected frequency exceeds the predetermined level; and operating running average every time a predetermined plurality of detection data are obtained. In this case, the change in the detected frequency may be controlled when the detected frequency contains noise elements and change in the detected frequency exceeds the predetermined level.
Further, the method according to the present invention may comprise the step of outputting a decision of the presence of corrosive gas only when the decision of the presence of corrosive gas from the corrosive gas deciding means continues for a predetermined period of time or longer.
Still further, the method according to the present invention may comprise the steps of: forming the corrosive gas sensor and the oscillating means by a plurality of corrosive gas detectors including a plurality of corrosive gas detecting sections and a plurality of transmission circuits each circuits having a predetermined address all its own; calling each of the corrosive gas detectors, respectively to collect detection outputs thereof and storing each of the outputs in each of the corrosive gas detectors; and outputting the decision of the presence of corrosive gas only when the number of decision of the presence of corrosive gas exceeds a predetermined number upon detecting outputs of each of the corrosive gas detectors, respectively with the corrosive gas deciding means.
Furthermore, the method according to the present invention may use a crystal resonator for a reference signal sending a reference signal to be compared with the frequency detected by the corrosive gas sensor, and oscillating means for oscillating the crystal resonator for a reference signal, and comprise the steps of: mixing the frequency from the oscillating means of the corrosive gas sensor and the frequency from the oscillating means of the crystal resonator for a reference signal; and taking out the change in frequency of the corrosive gas sensor due to corrosive gas from the output signal after mixing.
Moreover, the method according to the present invention may comprise the steps of: comparing said detected frequency of said corrosive gas sensor with a predetermined maintenance level; and outputting maintenance signal when said detected frequency exceeds said maintenance level determining means.
In the method and apparatus for determining the presence of corrosive gas according to the present invention having constitution as described above, the frequency difference A F between the detected frequency Fn of the corrosive gas sensor and the reference frequency Fr every time the detected frequency Fn is sampled in a predetermined cycle, for example, in a cycle of five seconds. When the frequency difference L F becomes lower than the predetermined threshold (negative level), an alarm is issued to stop generation of corrosive gas. The next reference frequency is operated in such a manner that the frequency difference L F between the detected frequency Fn and the reference frequency Fr is multiplied by a predetermined coefficient lower than 1, for example, 0.03 and that the obtained value is added to the original reference frequency.
Assuming that the detected frequency Fn linearly decreases, the frequency difference L F increases with the passage of time. And, the reference frequency Fr to be operated based on the detected frequency Fn shows a characteristic of decreasing with the same inclination as that of the detected frequency Fn after the passage of certain period of time.
In this case, the frequency difference L F until the reference frequency Fr decreases with the same inclination as that of the detected frequency Fn decreases as the decreasing speed (inclination) of the detected frequency Fn increases. As the decreasing speed of the detected frequency decreases, the frequency difference L F shows a characteristic of approaching zero.
According to the present invention, the presence of corrosive gas is determined by comparing the difference frequency L F between the detected frequency Fn and the reference frequency Fr with a predetermined threshold Fs. That is, a change with time in the frequency difference L F decreases exponentially at first, but converges to a fixed level after the passage of certain period of time. And the convergent level decreases as the decreasing speed of the 9 detected frequency Fn increases, and approaches zero as the decreasing speed decreases.
Therefore, according to a method of the present invention, the presence of corrosive gas can be precisely detected by setting the threshold for determining the corrosive gas to the level lower than the convergent level (negative level) of the frequency difference A F due to the decrease of the frequency to be usually expected.
And, detection sensitivity of corrosive gas may be freely determined by varying the threshold Fs.
According to the apparatus for determining the presence of corrosive gas, a change in frequency is controlled when the detected frequency Fn detected by the sampling means includes noise elements and change in the detected frequency exceeds the predetermined level, and running average is operated every time a predetermined plurality of detection data are obtained in order to control the change in frequency and then the presence of corrosive gas is determined. By this, wrong information about corrosive gas issued by temporary noises due to fluctuations of temperature, humidity and a power source may be avoided, thereby improving reliability of determining of corrosive Further, according to the apparatus of the present invention, the presence of corrosive gas is determined when the corrosive gas is detected for a predetermined period of time or longer. By this, wrong information about corrosive gas issued by temporary noises due to fluctuations of temperature, humidity and a power source may be avoided, thereby improving reliability of determining of corrosive gas.
Still further, according to the apparatus of the present invention, the presence of corrosive gas is determined when a number of corrosive gas detectors, more than the predetermined number, detect corrosive gas. By this, wrong information about corrosive gas issued by temporary noises due to partially fluctuations of temperature, humidity and a power source and due to fluctuation of sensitivity of detectors may be avoided, thereby improving reliability of determining of corrosive gas.
Furthermore, according to the apparatus of the present invention, a change in frequency due to corrosive gas is taken out from the frequency output from the corrosive gas sensor and the frequency from the crystal resonator for reference signal, and the presence of corrosive gas is determined when the data exceeds a predetermined alarm level. By this, a simple and cheap frequency counting circuit having a resolution of at most 1 [Hzj at 5 [kHz] may be used in place of a complicated and expensive frequency counting circuit having a resolution of 1 [Hz] around 10 [MHz]. Furthermore, since the change in frequency by noises due to fluctuations of temperature, humidity, and a power source occurs in both the corrosive gas sensor and the crystal resonator for a reference signal, noises may be removed by taking the difference between the frequency of the corrosive gas sensor and that of the crystal resonator for a reference signal.
Moreover, according to the apparatus of the present invention, the maintenance signal is generated when the frequency data of the corrosive gas sensor exceeds a predetermined maintenance level due to the secular deterioration of the crystal resonator, thereby replacing immediately the corrosive gas sensor which is outside the stable frequency range and is no longer capable of detecting corrosive gas.
The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which:- Fig. 1 is a block diagram illustrating the principle of the present invention; Fig 2a illustrates a corrosive gas sensor according to a first embodiment of the present invention; Fig. 2b illustrates a corrosive gas sensor according to another example of the present invention; Fig. 3 is a block diagram showing a corrosive gas determining apparatus according to a first embodiment of the present invention; Fig. 4 is a graph showing changes in reference frequency, detected frequency and frequency difference; Fig. 5 is a graph showing a change in frequency difference when decreasing speed of the detected frequency is a parameter; Fig. 6 is a graph showing a difference in time required for determining the presence of corrosive gas with the correction coefficient of the reference frequency; Fig. 7 is a schematic diagram showing a case where the present invention is applied to a fire detecting device; Fig. 8 is a schematic diagram showing a case where the present invention is applied to a semiconductor processing plant; Fig. 9 is a block diagram showing a corrosive gas determining apparatus according to a second embodiment of the present invention; Fig. 10 is a block diagram showing a corrosive gas determining apparatus according to a third embodiment of the present invention; Fig. 11 is a"block diagram showing a corrosive gas determining apparatus according to a fourth embodiment of the present invention;.
Fig. 12 is a block diagram showing a corrosive gas determining apparatus according to a fifth embodiment of the present invention; and Fig. 13 is a block diagram showing a corrosive gas determining apparatus according to a sixth embodiment of the present invention; Figs. 2 to 8 show one embodiment of the present invention.
Figs. 2a and 2b illustrate a first embodiment of a corrosive gas sensor according to the present invention.
Fig. 1 is a block diagram illustrating the overall principle of an apparatus in accordance with the present invention.
The apparatus of Fig. 1 for determining the presence of corrosive gas comprises a corrosive gas sensor 1 for detecting corrosive gas by a change in oscillation frequency; and oscillating means 7 for oscillating the corrosive gas sensor; a sampling means 11 for sampling the frequency detected by the corrosive gas sensor in a predetermined cycle; a frequency difference detecting means 12 for detecting the frequency difference between the detected frequency and a reference frequency from a reference frequency setting means 15 each time the detected frequency is sampled by the sampling means 11; a corrosive gas deciding means 13 for deciding upon the presence of corrosive gas when the frequency difference detected by the frequency difference detecting means 12 exceeds a predetermined threshold; and a reference frequency operating section 14 for operating and setting the next reference frequency to be compared with the detected frequency, based on the frequency difference when the frequency difference is detected next time.
Referring to Fig. 2a, there is shown a corrosive gas sensor 1 of a crystal resonator type. It is constituted by a laminated film comprising a crystal resonator 2, a chromium (Cr) film 3, and a gold (Au) film 4 and zinc (Zn), films 5 and 6.
At a center portion of the crystal resonator 2, Cr film 3 and Au film 4 are deposited to be laminated. At both end portions of the upper surface of the crystal resonator 2, Zn films 5 and 6 are deposited, respectively.
As shown in Fig. 2b, the Cr film and the Au films may be entirely covered with the Zn films 5 and 6, thereby enlarging the area of the Zn films 5 and 6 to be reacted with corrosive gas. Therefore, the corrosive gas sensor of Fig. 2b is more highly sensitive to corrosive gas than that of Fig. 2a.
7 is an oscillation circuit as an oscillation means. The oscillation circuit 7 is connected to the crystal resonator 2 through the connecting lines 8, Au film 4 and Cr film 3. The crystal resonator 2 is set into oscillation at its natural frequency by the oscillation circuit 7.
When corrosive gas 9 is generated, it chemically reacts with Zn deposited on the crystal resonator 2 to form a compound. For example, when the corrosive gas 9 is hydrogen chloride, it reacts with Zn to form zinc chloride (ZnC12) Since the mass of this compound is heavier than Zn, oscillation frequency of the crystal resonator 2 decreases. The decrease in the oscillation frequency is captured by the corrosive gas sensor 1, thereby detecting the generation of the corrosive gas 9. The change of oscillation frequency is output from the oscillation circuit 7.
Examples of the corrosive gas 9 to be captured by the corrosive gas sensor 1 includes a gas containing halogen (F, Cl, Br, I and At) as a compound such as hydrogen chloride (HCl), hydrogen fluoride (HF) and phosphorus tribromide (PBr3); and a gas which is easy to react with zinc (Zn) such as hydrogen sulf ide (H25) and ammonia NH3.
Fig. 3 is a block diagram of a corrosive gas determining apparatus using the above-described corrosive gas sensor 1.
Referring to Fig. 3, there is shown a corrosive gas determining apparatus 10. It is constituted by a corrosive gas sensor 1 of the crystal resonator type, an oscillation circuit 7 as an oscillating means, a frequency data input section 11 as a sampling means, a frequency difference detecting section 12 as a frequency difference detecting means, a corrosive gas deciding section 13 as a corrosive gas deciding means, a reference frequency correcting section 14 as a reference frequency correction means, a reference frequency setting section 15 as a reference frequency setting means, and an alarm output section 16.
The corrosive gas sensor 1 of the crystal resonator type oscillates at the normal frequency by the oscillation circuit 7. A frequency detected by the corrosive gas sensor 1 is supplied to the frequency data input section 11. The frequency data input section 11 samples the detected frequency from the corrosive gas sensor 1 in a predetermined cycle, for example, in a cycle of five seconds, to change it into digital frequency data and then outputs the data.
The frequency data sampled and changed into digital data by the frequency data input section 11 is supplied to the frequency difference detecting section 12. The frequency difference detecting section 12 detects a frequency difference A F between the detected frequency Fn and a reference frequency Fr set by the reference frequency setting section 15 which is described later. The reference frequency Fr to be used for detecting the frequency difference A F is produced by a reference frequency operating section 50. The reference frequency operating section 50 is constituted by the reference frequency correcting section 14 and the reference frequency setting section 15.
The reference frequency correcting section 14 updates the reference frequency Fr each time the frequency difference A F is obtained through the frequency difference detecting section 12 by the following equation (l):
Fr next = (Fn-Fr) x K + Fr... (1) = AF x K + Fr where Fn is the frequency detected this time, Fr is the reference frequency of this time, Fr next is the reference frequency of the next time and K is a correction coefficient.
In the equation (1), the frequency difference A F between the detected frequency Fn and the reference frequency Fr obtained by the frequency difference detecting section 12 is multiplied by a predetermined coefficient lower than 1, for example, 3/100 = 0.03 as the correction coefficient K and added to the original reference frequency Fr. The reference frequency Fr next corrected by the reference frequency correcting section 14 is set by the reference frequency setting section 15 as the reference frequency of the next time, that is, the time when the next frequency difference A F between the detected frequency Fn and the reference frequency Fr is detected.
The correction coefficient K is determined by a threshold Fs of the corrosive gas deciding section 13 described hereinafter and a sampling cycle of the frequency data, etc.
An output from the frequency difference detecting section 12 is supplied to the corrosive gas deciding section 13. The corrosive gas deciding section 13 compares a predetermined threshold Fs with the frequency difference AF. When the frequency difference A F becomes the threshold Fs or less, the corrosive gas deciding section 13 decides that there is corrosive gas exceeding a predetermined density, and then outputs the corrosive gas decision to the alarm output section 16. On the basis of this output, an alarm about the corrosive gas is issued by the alarm output section 16.
The operation of the corrosive gas determining apparatus according to the embodiment shown in Fig. 3 will now be described.
Fig. 4 is a graph showing changes with time in the reference frequency Fr and the frequency difference A F detected by the frequency difference detecting section 13 when the detected frequency Fn from the corrosive gas sensor 1 linearly decreases.
In Fig. 4, the axis of abscissas represents the time [sec], and the axis of ordinates represents the frequency [Hz]. Suppose the detected frequency Fn linearly decreases with a predetermined inclination as shown by a solid line. The reference frequency Fr next changes at first in such a manner that the frequency difference L F between the reference frequency Fr next and the detected frequency Fn increases with the passage of time, as shown by the dotted lines. After the passage of a certain period of time, the reference frequency Fr next decreases with the same inclination as that of the detected frequency Fn while maintaining a constant frequency difference A F.
Therefore, the frequency difference between the detected frequency Fn and the reference frequency Fr decreases exponentially in accordance with the decrease in of the detected frequency Fn and converges to a fixed value after a set period of time.
Fig. 5 is a graph showing a change with time in the frequency difference LF between the detected frequency Fn regarding a decreasing speed (rate of change) as a parameter and the reference frequency Fr next in which:
the axis of abscissas represents the time [sec]; the axis of ordinates represents the frequency [Hz]; L F1 is a change with time in the frequency difference when decreasing speed is -1.0 [Hz/sec]; 6 F2 is a change with time in the frequency difference when decreasing speed is -2. 0 [Hz/sec]; L F3 is a change with time in the frequency difference when decreasing speed is -3.0 [Hz/sec]; L F4 is a change with time in the frequencydifference when decreasing speed is -5.0 [Hz/sec]; and L F5 is a change with time in the frequency difference when decreasing speed is - 7.0 [Hz/sec].
As apparent from Fig. 5, as the decreasing speed of the detected frequency Fn increases, the decreasing rate of the frequency difference L F increases and the convergent value thereof decreases. On the other hand, as the decreasing speed of the detected frequency Fn decreases, the decreasing rate of the frequency difference A F decreases and the convergent -value thereof approaches zero. Therefore, the threshold Fs of the corrosive gas deciding section 13 in the embodiment of Fig. 3 may be determined by characteristics of the frequency difference L F shown in Fig. 5. For example, when the limit level of the decreasing speed of the frequency to be usually expected and the decreasing speed of the frequency due to corrosive gas is -1 [Hz/sec], the threshold Fs may be set to the level lower than the convergent value of the frequency difference A F of the decreasing speed of -1 [Hz/sec] (about -150 [Hz]), for example, -200 [Hz].
of course, in order to improve the detection sensitivity, the threshold Fs may be set more close to the convergent level of the frequency difference A F. On the other hand, in order to decrease the detection sensitivity, still lower threshold Fs may be set.
A method for determining the correction coefficient K will now be described. Fig. 6 is a graph showing a relation between the value of the correction coefficient K of the reference frequency and the deciding time required to decide the presence of corrosive gas (curves A, B and C) in which: the axis of abscissas represents the deciding time required to decide the presence of corrosive gas; the axis of ordinates represents the detected frequency [Hz] of the corrosive gas sensor, the reason why the difference from the initial frequency is used is to get rid of the change of initial natural frequency of each sensor; F11 is a change of the decreasing speed of the detected frequency by time when the decreasing speed of the detected frequency is -0.6 [Hz/sec]; F12 is the change by time when the decreasing speed is -0.8 [Hz/sec]; F13 is the change by time when the decreasing speed is -1.0 [Hz/sec]; F14 is the change by time when the decreasing speed is -2.0 [Hz/sec]; F15 is the change by time when the decreasing speed is -3.0 [Hz/sec]; and F16 is the change by time when the decreasing speed is -6.0 [Hz/sec].
In addition, Fs is the threshold (-150 [Hz]). Fo2:', example, the intersection of the Fs and F11 shows the deciding time required to decide the presence of corrosive gas when the Fs is set to -150 [Hz] and the decreasing speed of the detected frequency is -0.6 [Hz/sec].
-Eurther, a curve A shows characteristic of the corrosive gas deciding time when the threshold Fs is set to -100 [Hz] and the correction coefficient K of the reference frequency is set to 0.03. The curve A is obtained by connecting round marks each showing the corrosive gas deciding time obtained with respect to each of the frequency differences F under the conditions of Fs = -100 [Hz] and K = 0.03.
The curve B shows characteristic of the corrosive gas deciding time when the threshold Fs is set to -100 [Hz] and the correction coefficient K of the reference frequency is set to 0.04. The curve B is obtained by connecting triangular marks each showing the corrosive gas deciding time obtained with respect to each of the frequency differences F under the conditions of Fs = -100 [Hz] and K 0.04.
The curve C shows characteristic of the corrosive gas deciding time when the threshold Fs is set to -100 [Hz] and the correction coefficient K of the reference frequency is set to 0.05. The curve C is obtained by connecting square marks each showing the corrosive gas deciding time obtained with respect to each of the frequency differences F under the conditions of Fs = -100 [Hz] and K = 0.05.
The curve B in which K is set to 0.04 intersects the straight line F13 showing the change of the deciding time when the lowering speed of the detected frequency is -1.0 [Hz/sec]. That is to say, an alarm is issued after the deciding time shown by the intersection of the curve B and the straight line F13. On the other hand, the curve B does not intersect the straight lines F11 and F12 each showing the change of the deciding time when the decreasing speed of y the detected frequency is -0.8 [Hz/sec] or less. This means that the alarm is not issued when the detected frequency decreases at a low speed.
The corrosive gas deciding time has the following characteristics. When the correction coefficient K is reduced, for example, to 0.03, the corrosive gas deciding time may be shortenedhs shown by the curve A. In this case, the alarm is issued at the decreasing speed of -0.8 [Hz/sec]... but is not issued at the decreasing speed of -6.0 Conversely, when the correction [Hz/sec] orless.,,. coefficient is increased, for example, to 0.05, the corrosive gas deciding time is prolonged as shown by the curve C. However, the alarm is not issued at the decreasing speed of -1.0 [Hz/sec] or úess- --' Accordingly, the correction coefficient K in the reference frequency correcting section 14 of the embodiment of Fig. 3 may be determined by a relation between the different rate of decreasing of the frequency (straight lines F 11, etc.) and the corrosive gas deciding time and the issuance of the alarm (the curves A to C) as shown in Fig. 6.
For example, when the limit level of the decreasing speed of the frequency to be usually expected and that of the decreasing speed of the frequency due to corrosive gas are both -1 O[Hz/sec], the correction coefficient K may be set 0.05 or more at the decreasing speed of -1 O[Hz/sec] where no alarm is issued.
of course, in order to improve the detection sensitivity, the correction coefficient K may be set more close to 0.05. On the other hand, in order to decrease the detection sensitivity, still larger correction coefficient K may be set.
Further, comparing the result of conventional determination by only setting the thresholdt.
-t-with the determination by the reference frequency, when thhreshold Fs is set to -150 [Hz] and compared with the above-described curve A connecting round marks, both of deciding time are equally 25 seconds in case that decreasing speed of the detected frequency is -6.0 [Hz/sec], however, in case that decreasing speed of the detected frequency is -3.0 [Hz/sec], the corrosive gas deciding time due to the threshold 11 S 50 seconds, while the time due to the reference frequency is 45 seconds, which is 5 seconds faster. In case that the decreasing speed is -2.0 [Hz/sec], the corrosive gas deciding time due to the reference frequency is 70 seconds, in contrast to 80 seconds due to the threshold.L On the other hand, in case that the decreasing speed is -1.0 [Hz/sec], the corrosive gas deciding time due to the reference frequency is 160 seconds, in contrast to 150 seconds due to the thresholdl In case that the decreasing speed is -0.6 [Hz/sec] set by the effect of change of environment such as temperature and humidity or the like, information about corrosive gas is not issued, while corrosive gas deciding time is 250 seconds due to the thresholdL\ k I C;, - -, -. / - As described above, a change with time in the frequency difference L F between the detected frequency Fn and the reference frequency Fr, in this embodiment, decreases exponentially at first but converges to a fixed level after the passage of certain period of time. The convergent level of the frequency difference n F decreases as the decreasing speed of the detected frequency Fn increases, and approaches zero as the decreasing speed decreases. The issuance of the alarm and the time required for the issuance of the alarm may be controlledby suitably setting the correction coefficient K. Therefore, the presence of corrosive gas can be correctly detected at an early stage by setting the threshold Fs for determining the corrosive gas to the level lower than the convergent level (negative level) of the frequency difference Z5 F due to the decrease of the frequency to be usually expected. Further, by setting the correction coefficient K, a system for determining the presence of corrosive gas can be controlled so as to issue information about corrosive gas earlier than the decision of corrosive gas by simply setting the threshold when the detected frequency decreases at a high speed, and so as to issue information about corrosive gas later than the decision of corrosive gas by simply setting the threshold, or not to issue information when the detected frequency decreases at a low speed.
Fig. 7 is a schematic diagram of the above-described corrosive gas determining apparatus 10 as applied to a fire detecting device for detecting corrosive gas generated when a fire breaks out.
Referring to Fig. 7, there is shown the corrosive gas determining apparatus 10, a monitor and control board 17, signal lines 18 connecting the corrosive gas determining apparatus 10 and the monitor and control board 17, and a substance generating corrosive gases 9 when a fire breaks out and power cables are abnormally heated, such as PVC generating hydrogen chloride.
The corrosive gas determining apparatus is located on a suitable place such as a ceiling surface of a warning area. Suppose the cables using a substance 19, such as PVC, as an insulating material is abnormally heated due to excess current, thereby generating corrosive gas typified by HCl. The corrosive gas determining apparatus 10 detects the corrosive gas in the manner as described above upon generation of the corrosive gas, and the monitor and control board 17 issues an alarm. In this case, a breaker of a power board may be pulled down to stop the flow of current and a fire distinguishing equipment may be actuated in -23 addition to the issuance of the alarm.
Fig. 8 is a schematic diagram of the corrosive gas determining apparatus 10 as applied to a semiconductor processing plant.
Referring to Fig. 8, there are shown the corrosive gas determining apparatus 10 detecting the corrosive gases 9, the monitor and control board 17, the signal lines 18 connecting the corrosive gas determining apparatus 10 and the monitor and control board 17, a valve for preventing a leakage of corrosive gas 9, signal lines 21 connecting the monitor and control board and the valve 20, a cylinder 22 for storing corrosive gases 9, manufacturing equipments 23 and 24 such as CVD/Epi furnace, a pipeline 25 for introducing corrosive gas 9 into the manufacturing equipments through the valve 20, and a pipeline 26 for introducing corrosive gases 9 into a detoxifying device.
When something is wrong with the pipelines 25 and 26 which are flowing line of corrosive gas 9 and the leakage of corrosive gas 9 is occurred, the corrosive gas determining apparatus detects the leakage, and then the monitor and control board 17 actuates the valve 20 to close the passage of corrosive gas 9.
Fig. 9 is a block diagram showing a second embodiment of the present invention.
In this embodiment, a maximum value controlling section as a maximum value controlling means and a running average operating section as a running average operating means are added to the corrosive gas determining apparatus 10 shown in Fig. 3.
Referring to Fig. 9, there is shown a maximum value controlling section 27 consecutively provided to the frequency data input section 11. When the frequency detected in the frequency data input section 11 includes noise elements, and the change in the detected frequency exceeds a predetermined level, the maximum value controlling section 27 controls the change in the frequency. There is also shown a running average operating section 28 provided between the maximum value operating section 27 and the frequency difference detecting section 12. The r unn ing average operating section 28 operates the running average every time a predetermined plurality of detection data are obtained in order to control the change in frequency when the frequency detected in the frequency data input section 11 includes noise components and the change in the detected frequency exceeds a predetermined level.
The frequency data sampled and changed into digital data by the frequency data input section 11 is supplied to the maximum value controlling section 27 and the running average operating section 28. In the maximum value controlling section 27 and the running average operating section 28, the maximum level of the change in frequency is controlled and subjected to a running average processing to remove shocking noise elements such as a temporary noise or a shot noise incident to analog detection.
Accordingly, in this embodiment, wrong information about corrosive gas issued by temporary noises due to fluctuations of temperature, humidity and a power source may be avoided, thereby improving reliability of determining of corrosive gas.
Fig. 10 is a block diagram showing a third embodiment of the present invention.
In this embodiment, a duration measuring section 29 as a duration measuring means is added to the corrosive gas determining apparatus 10 shown in Fig. 3.
Referring to Fig. 10,.there is shown a duration measuring section 29 provided between the corrosive gas deciding section 13 and the alarm output section 16. Only when the decision of the presence of corrosive gas from the corrosive gas deciding section 13 continues for a predetermined period of time or longer, the duration measuring section 29 outputs the decision to the alarm output section 16.
In this embodiment, when corrosive gas is detected for a predetermined period of time or longer, the presence of corrosive gas is determined. Accordingly, in this embodiment, wrong information about corrosive gas issued by temporary noises due to fluctuations of temperature, humidity and a power source may be avoided, thereby improving reliability of determining of corrosive gas.
Fig. 11 is a block diagram showing a fourth embodiment of the present invention.
In this embodiment, the corrosive gas sensor 1 and the oscillation circuit 7 shown in Fig. 3 are constituted by a plurality of corrosive gas detecting sections and a plurality of corrosive gas detectors comprising a plurality of transmission circuits each having a predetermined address all its own. And, in this embodiment, a receiving section is provided as the frequency data input section which is a sampling means, and a detector number counting section 26 is provided between the corrosive gas deciding section and the alarm output section.
Referring to Fig. 11, a control panel 30 is connected to a plurality of corrosive gas detectors 32a, 32b... 32n through a signal line 31. Each of the corrosive gas detectors 32a, 32b,-32n contains a corrosive gas detecting section 33 for detecting corrosive gas in an analog fashion, and a transmission circuits 34 for transmitting an output from the corrosive gas detecting section 33 to the control panel 30. Each of the transmission circuits 34 to be contained in a plurality of corrosive gas detectors 32a, 32b,-32n has a predetermined address all its own. The transmission circuit 34 counts the number of call pulses from the control panel 30. When the counting value agrees with the address of the transmission circuit 34, the transmission circuit 34 sends out an analog detection output to a vacant time which is a pulse interval of the call pulses.
The inner structure of the control panel 30 will now be described.
The receiving section 35 as a receiving means sends out call pulses to a plurality of corrosive gas detectors 32a, 32b,...32n. And, the receiving section 35 collects the analog detection outputs from each of the corrosive gas detectors 32a, 32b,-32n by a polling method and converts them to digital data.
On the other hand, the receiving section 35 contains a storage section and stores the analog detection output converted to digital data in each of the corrosive gas detectors 32a, 32b,...32n, and then, supplies the converted data to the frequency difference detecting section 12. In the frequency difference detecting section 12, the frequency difference A F between the detected frequency Fn and the reference frequency Fr is detected. The reference frequency Fr to be used for detecting the frequency difference A F is produced by the reference frequency correcting section 14 and the reference frequency setting section 15. The reference frequency operating section 50 is constituted by the the reference frequency correcting section 14 and the reference frequency setting section 15.
The output from the frequency difference detecting section 12 is supplied to the corrosive gas deciding section 13. The corrosive gas deciding section 13 compares the predetermined threshold Fs with the frequency difference A F. When the frequency difference L F becomes the threshold Fs or less, the corrosive gas deciding section 13 decides that there is corrosive gas exceeding a predetermined density, and outputs the decision to the detector number counting section 36. The detector number counting section 36 counts the number of the detectors deciding the presence of corrosive gas among the detectors 32a, 32b,...32n. When the number of the detectors deciding the presence of corrosive gas is more than the predetermined number, the detector number counting section 36 outputs the decision to the alarm output section 16. An alarm about the presence of corrosive gas is issued by the alarm output section 16 in accordance with the decision from the detector number counting section 36.
In this embodiment, the presence of corrosive gas is determined when a number of corrosive gas detectors, more than the predetermined number among the detectors 32a, 32b,...32n detect corrosive gas. Therefore, wrong information about corrosive gas issued by temporary noises due to partially fluctuation of temperature, humidity and a power source can be avoided, thereby improving reliability of determining of corrosive gas.
Fig. 12 is a block diagram of a fifth embodiment of the present invention.
In this embodiment, a crystal resonator 37 for reference signal, an oscillation circuit as an oscillation means for oscillating the crystal resonator 37, a mixing circuit as a mixture means for mixing the frequency from the oscillation circuit 38 and the frequency from the oscillation circuit 7 for oscillating the corrosive gas sensor 1, and a high-pass circuit 40 as change signal selecting means for taking out the change in frequency due to corrosive gas from the mixing circuit 39 are added to the corrosive gas determining apparatus 10 shown in Fig. 3.
Referring to Fig. 12, the corrosive gas sensor 1 of a crystal resonator type which is set into oscillation by the oscillation circuit 7 at a frequency of the combination of the natural frequency (about 10 [MHz]), the frequency changed by the influence of noise or the like and the frequency changed by the influence of corrosive gas.
The crystal resonator 37 for reference signal is set into oscillation by the oscillation circuit 38 at a frequency of the combination of the natural frequency (about 10 [MHz] and the frequency changed by the influence of noise or the like.
The mixing circuit 38 such as DBM (double balanced mixer) mixes the signal from the oscillation circuit 7 and the signal from the oscillation circuit 38 to produce a signal having a summation frequency (the combination of the natural frequency of 20 [MHz], the frequency changed by the influence of noise or the like multiplied by 2 and the frequency changed by the influence of corrosive gas) and a signal having a difference frequency (the frequency changed by the influence of corrosive gas), respectively.
The high-pass circuit 40 removes the summation frequency from the mixing circuit 39 and takes out only the difference frequency.
The frequency data input section 11 samples the difference frequency from the high-pass circuit 40 in a predetermined cycle, for example in a cycle of five seconds, to change it into digital signal data and then outputs the data.
In this embodiment, a change in frequency due to corrosive gas is taken out from the frequency output from the corrosive gas sensor 1 of the crystal resonator type and the frequency from the crystal resonator 37 for reference signal, and the presence of corrosive gas is determined when the data exceeds the predetermined alarm level. Accordingly, in this embodiment, a simple and cheap frequency counting circuit having a resolution of at most 1 [Hz] at 5 [kHz] may be used in place of a complicated and expensive frequency counting circuit having a resolution of 1 [Hz] around 10 [MHz]. Further, since the change in frequency by noises due to fluctuations of temperature, humidity, and a power source occurs in both the corrosive gas sensor 1 and the crystal resonator 37 for a reference signal, noises may be removed by taking the difference between the frequency of the corrosive gas sensor and that of the crystal resonator for a reference signal.
Fig. 13 is a block diagram showing a sixth embodiment of the present invention.
In this embodiment, a maintenance signal of the corrosive gas sensor 1 is output in accordance with the secular deterioration of the crystal resonator. Also in this embodiment, a maintenance level determining section 41 as a maintenance level determining means and a maintenance level output section 42 as a maintenance level output means are added to the corrosive gas determining apparatus 10 shown in Fig. 3.
In Fig. 13, the maintenance level determining section 41 compares the frequency detected by the corrosive gas sensor 1 with a predetermined maintenance level of the frequency.
The maintenance signal output section 42 outputs the maintenance signal in accordance with the output from the maintenance level determining section 41.
The frequency data sampled and changed into digital data by the frequency data input section 11 is supplied to the frequency difference detecting section 12 and the maintenance level determining section 41. The maintenance level determining section 41 compares the output value of the frequency with the initial value thereof. When the frequency level outside the range of satisfying a desired performance of the crystal resonator due to a secular deterioration of the crystal resonator is detected, the -30maintenance level determining section 41 outputs the decision to the maintenance signal output section 42. The maintenance signal output section 42 outputs a maintenance signal in accordance with the output from the maintenance level determining section 41.
In this embodiment, when the frequency data of the corrosive gas sensor 1 of the crystal resonator type exceeds the predetermined maintenance level due to the secular deterioration of the.crystal resonator, the maintenance signal is generated. Accordingly, in this embodiment, the corrosive gas sensor which is outside the stable frequency range and is no longer capable of detecting corrosive gas may be immediately replaced.
According to this embodiment, the maintenance level determining section 41 and the maintenance signal output section 42 are added to the first embodiment shown in Fig. 3. However, the maintenance level determining section 41 and the maintenance signal output section 42 may be added to the second to fifth embodiments according to the present invention.
Claims (21)
1. An apparatus for determining the presence of corrosive gas, comprising: a corrosive gas sensor for detecting corrosive gas by a change in oscillation frequency; an oscillating means for oscillating said corrosive gas sensor; a sampling means for sampling the frequency detected by said corrosive gas sensor in a predetermined cycle; a frequency difference detecting means for detecting a frequency difference between said detected frequency and a reference frequency each time said detected frequency is being sampled by said sampling means; a corrosive gas deciding means for deciding the presence of corrosive gas when the frequency difference detected by said frequency difference detecting means exceeds a predetermined threshold; and a reference frequency operating section for operating and setting the next reference frequency to be compared with the detected frequency, based on said frequency difference when the frequency difference is detected next time.
2. An apparatus according to claim 1, wherein said reference frequency operating section comprises: a reference frequency correcting means for correcting said reference frequency by multiplying said frequency difference by a predetermined coefficient lower than 1 and adding the obtained level to said reference frequency; and a reference frequency setting means for setting the level of the corrected reference frequency operated by said reference frequency correcting means as the next reference frequency.
An apparatus according to claim wherein said corrosive gas is hydrogen chloride (HCl).
4. An apparatus according to any of claims 1 to 3, further comprising: a maximum value controlling means for controlling a change in the frequency detected by said sampling means when the change in the detected frequency exceeds the predetermined level; and a running average operating means for operating a running average every time a predetermined plurality of detection data are obtained.
5. An apparatus according to claim 4, wherein said maximum value controlling means controls change in the detected frequency when the detected frequency contains noise elements and change in the frequency exceeds the predetermined level.
6. An apparatus according to any of claims 1 to 3, further comprising a duration measuring means for outputting a decision of the presence of corrosive gas only when the decision of the presence of corrosive gas from said corrosive gas deciding means continues for a predetermined period of time or longer.
7. An apparatus according toany of claims 1 to 3, further comprising: said corrosive gas sensor and said oscillating means formed by a plurality of corrosive gas detectors including a plurality of corrosive gas detecting sections and a plurality of transmission circuits each circuits having a predetermined address all its own; a receiving means as said sampling means calling each of said corrosive gas detectors, respectively, to collect detection outputs thereof and storing each of said outputs in each of said corrosive gas detectors; and a detector number counting means outputting the decision of the presence of corrosive gas only when the number of decision of the presence of corrosive gas exceeds a predetermined number upon detecting outputs of each of said corrosive gas detectors, respectively, with said corrosive gas deciding means.
8. An apparatus according toany of claims 1 to 3, further comprising: a crystal resonator for a reference signal sending a reference signal to be compared with the frequency detected by said corrosive gas sensor; an oscillating means for oscillating said crystal resonator for a reference signal; a mixture means for mixing the frequency from said oscillating means of said corrosive gas sensor and the frequency from said oscillating means of said crystal resonator for a reference signal; and a change signal selecting means for taking out the change in frequency of said corrosive gas sensor due to corrosive gas from the output signal after mixing.
9. An apparatus according to any of claims 1 to 8, furr.her comprising: a maintenance level determining means for comparing said detected frequency of said corrosive gas sensor with a predetermined maintenance level; and a maintenance signal output means for outputting maintenance signal in accordance with the decision output from said maintenance level determining means.
10. An apparatus according to claim, wherein said maintenance level determining means outputs said decision when said detected frequency exceeds said maintenance level.
11. A method for determining the presence of corrosive gas, comprising the steps of: oscillating a corrosive gas sensor for detecting corrosive gas by a change in oscillation frequency with oscillating means; sampling the frequency detected by said corrosive gas sensor in a predetermined cycle; detecting a frequency difference between said detected frequency and a reference frequency each time said detected frequency is sampled by said sampling means; deciding the presence of corrosive gas when the frequency difference detected by said frequency difference detecting means exceeds a predetermined threshold; and operating and setting the next reference frequency to be compared with the detected frequency based on said frequency difference when the frequency difference is detected next time.
12. A method according to claim 11, wherein next reference frequency is operated and set by multiplying said frequency difference by a predetermined coefficient lower than 1 and adding the obtained value to said reference frequency.
13. A method according to claim 11, wherein said corrosive gas is hydrogen chloride.
14. A method according to any of claims 11 to 13, further comprising the steps of: controlling a change in frequency of the detected frequency when the change in the detected frequency exceeds the predetermined level; and operating running average every time a predetermined plurality of detection data are obtained.
15. A method according to claim 14, further comprising the step of controlling the change in the detected frequency when the detected frequency contains noise elements and change in the detected frequency exceeds the predetermined level.
16. A method according to any of claims 11 to 13, further comprising the step of outputting a decision of the presence of corrosive gas only when the decision of the presence of corrosive gas from said corrosive gas deciding means continues for a predetermined period of time or longer.
17. A method according to any of claims 11 to 13, further comprising the steps of: forming said corrosive gas sensor and said oscillating means by a plurality of corrosive gas detectors including a plurality of corrosive gas detecting sections and a plurality of transmission circuits each circuits having a predetermined address all its own; calling each of said corrosive gas detectors, respectively to collect detection outputs thereof and storing each of said outputs in each of said corrosive gas detectors; and outputting the decision of the presence of corrosive gas only when the number of decision of the presence of corrosive gas exceeds a predetermined number upon detecting outputs of each of said corrosive gas detectors,. respectively with said corrosi.ve gas deciding means.
18. A method according toany of claims 11 to 13, using a crystal resonator for a reference signal sending a reference signal to be compared with the frequency detected by said corrosive gas sensor, and oscillating means for oscillating said crystal resonator for a reference signal, wherein said method comprises the steps of: mixing the frequency from said oscillating means of said corrosive gas sensor and the frequency from said oscillating means of said crystal resonator for a reference signal; and taking out the change in frequency of said corrosive gas sensor due to corrosive gas from the output signal after mixing.
19. A method according to any of claims 11 to 18, further comprising the steps of: comparing said detected frequency of said corrosive gas sensor with a predetermined maintenance level; and outputting maintenance signal when said detected frequency exceeds said maintenance level determining means.
20. An apparatus for determining the presence of corrosive gas, substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawings.
21. A method for determining the presence of corrosive gas, substantially as hereinbefore described, with reference to the accompanying drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP31145393 | 1993-12-13 |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB9424857D0 GB9424857D0 (en) | 1995-02-08 |
| GB2285508A true GB2285508A (en) | 1995-07-12 |
| GB2285508B GB2285508B (en) | 1997-05-28 |
Family
ID=18017407
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9424857A Expired - Fee Related GB2285508B (en) | 1993-12-13 | 1994-12-09 | Method and apparatus for determining the presence of corrosive gas |
Country Status (2)
| Country | Link |
|---|---|
| DE (1) | DE4444224A1 (en) |
| GB (1) | GB2285508B (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2328018A (en) * | 1997-08-08 | 1999-02-10 | Bio Rad Laboratories | DSP technique for photo-acoustic spectroscopy (PAS) |
| US6025913A (en) * | 1997-08-08 | 2000-02-15 | Bio-Rad Laboratories | Digital signal processing (DSP) techniques for FT-IR multiple modulation measurements using a photoelastic modulator |
| EP1999453A4 (en) * | 2006-02-28 | 2016-01-06 | Exxonmobil Res & Eng Co | Metal loss rate sensor and measurement using a mechanical oscillator |
| US10006885B2 (en) | 2012-08-10 | 2018-06-26 | Fujitsu Limited | QCM sensor and method of manufacturing the same |
| US20220236225A1 (en) * | 2019-04-22 | 2022-07-28 | Taiyo Yuden Co., Ltd. | Arithmetic device, arithmetic method, and gas detection system |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH09180080A (en) * | 1995-12-26 | 1997-07-11 | Hochiki Corp | Hci sensor |
| WO2009109203A1 (en) * | 2008-03-06 | 2009-09-11 | Siemens Aktiengesellschaft | Corrosion detection device and method |
| US10627368B2 (en) * | 2018-02-17 | 2020-04-21 | Applied Nanotech, Inc. | Methane gas sensor |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1991017423A1 (en) * | 1990-05-08 | 1991-11-14 | Purafil, Inc. | Method and apparatus for monitoring corrosion and reporting same according to accepted industry standards |
-
1994
- 1994-12-09 GB GB9424857A patent/GB2285508B/en not_active Expired - Fee Related
- 1994-12-13 DE DE19944444224 patent/DE4444224A1/en not_active Withdrawn
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1991017423A1 (en) * | 1990-05-08 | 1991-11-14 | Purafil, Inc. | Method and apparatus for monitoring corrosion and reporting same according to accepted industry standards |
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2328018A (en) * | 1997-08-08 | 1999-02-10 | Bio Rad Laboratories | DSP technique for photo-acoustic spectroscopy (PAS) |
| US6025913A (en) * | 1997-08-08 | 2000-02-15 | Bio-Rad Laboratories | Digital signal processing (DSP) techniques for FT-IR multiple modulation measurements using a photoelastic modulator |
| US6043884A (en) * | 1997-08-08 | 2000-03-28 | Bio-Rad Laboratories, Inc. | DSP technique for photoacoustic spectroscopy (PAS) sample pulse response for depth profiling |
| GB2328018B (en) * | 1997-08-08 | 2001-07-25 | Bio Rad Laboratories | DSP technique for photoacoustic spectroscopy (PAS) sample pulse response for depth profiling |
| EP1999453A4 (en) * | 2006-02-28 | 2016-01-06 | Exxonmobil Res & Eng Co | Metal loss rate sensor and measurement using a mechanical oscillator |
| US10006885B2 (en) | 2012-08-10 | 2018-06-26 | Fujitsu Limited | QCM sensor and method of manufacturing the same |
| US20220236225A1 (en) * | 2019-04-22 | 2022-07-28 | Taiyo Yuden Co., Ltd. | Arithmetic device, arithmetic method, and gas detection system |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9424857D0 (en) | 1995-02-08 |
| DE4444224A1 (en) | 1995-06-14 |
| GB2285508B (en) | 1997-05-28 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20131209 |