Patent Description:
In the process of manufacturing semiconductors and materials that react easily with water, moisture analyzers are used for controlling trace moisture in the process gases as recited in non-patent literature (NPL) <NUM>, and on-site calibration is required to achieve the reliability. Generally, the calibration is performed where the output-response to trace moisture has reached a sufficient equilibrium by maintaining the moisture concentration in the sensor cell for several hours (NPL2).

However, while such static calibration method enables accurate calibration, it is difficult to apply the static calibration method to on-site calibration because the calibration system is huge and the calibration takes as long as ten hours. In addition, since the earlier calibration system needs a large amount of calibration gases, it is difficult to apply it to processes using special gases for which there is no existing calibration system, or it is not easy to obtain a large amount of calibration gases.

<CIT> discloses an apparatus and a method for calibrating a moisture sensor in a measuring device without removing the measuring device from its operating position, by means of a calibrating sensor coupled by means of a tube to said measuring device so as to expose the calibrating sensor to the same process air as the sensor to be calibrated, wherein a processor compares the data detected by the calibrating sensor to the data detected by the sensor to be calibrated.

In view of the above problems, an object of the present invention is to provide a system, and a method for calibrating a moisture sensor, which can be performed in a short time and are applicable to on-site calibrations.

The first aspect of the present invention is defined in claim <NUM> and inheres in a system for calibrating a moisture sensor encompassing a processing unit. The processing unit pertaining to the first aspect includes (a) a logic circuit configured to obtain reference data, which indicate temporal variation of moisture concentrations, after injecting water-vapor with known concentrations into an analyzer, (b) a logic circuit configured to measure subject data indicating temporal variation of output-responses of a subject sensor element of the analyzer under test, the subject data are obtained under same condition with the reference data was obtained, (c) a logic circuit configured to compare the subject data with the reference data, with same time-duration for obtaining the reference data, the time-duration is measured from a timing at which the water-vapor with the known concentrations is injected for calculating relationships between the output-responses of the subject sensor element and the known concentrations.

The second aspect of the present invention: is defined in claim <NUM> and inheres in a method for calibration of a moisture sensor, including (a) obtaining reference data, which indicate temporal variation of moisture concentrations, after injecting water-vapor with known concentrations into an analyzer of a calibration system, (b) measuring subject data indicating temporal variation of output-responses of a subject sensor element of the analyzer under test, the subject data are obtained under same condition with the reference data was obtained, (c) comparing the subject data with the reference data, with same time-duration for obtaining the reference data, the time-duration is measured from a timing at which the water-vapor with the known concentrations is injected, and (d) calculating relationships between the output-responses of the subject sensor element and the known concentrations.

There is also described herein a non-transitory computer readable storage medium storing a calibration program of system for calibrating a moisture sensor, the calibration program causing a processing unit in the system to execute processing for calibration by a series of instructions for performing calibration. The series of instructions encompasses (a) obtaining reference data, which indicate temporal variation of moisture concentrations, after injecting water-vapor with known concentrations into an analyzer of a calibration system, (b) measuring subject data indicating temporal variation of output-responses of a subject sensor element of the analyzer under test, the subject data are obtained under same condition with the reference data was obtained,(c) comparing the subject data with the reference data, with same time-duration for obtaining the reference data, the time-duration is measured from a timing at which the water-vapor with the known concentrations is injected, and (d) calculating relationships between the output-responses of the subject sensor element and the known concentrations.

According to the present invention, it is possible to provide the system, and the method for calibrating the moisture sensor, which can be performed in a short time and are applicable to the on-site calibrations.

Before describing first and second embodiments of the present invention, with reference to <FIG>, <FIG>, 5A and 5B, we will introduce an illustrative example for static calibration system, which does not fall under the scope of the present invention but has led to the first and second embodiments of the present invention.

As illustrated in <FIG>, a static calibration system pertaining to the illustrative example includes a first mass flow controller (MFC) 55a, a second MFC 55b, a third MFC 55c, a fourth MFC 55d, a fifth MFC <NUM>, a first automatic pressure regulator (APR) <NUM> and a second APR <NUM> so as to implement a wet gas line through the fourth MFC 55d, a first dry gas line through the first MFC 55a and a second dry gas line through the third MFC 55c. The second dry gas line and the wet gas line are connected to implement a first mixed gas line through the second MFC 55b. The first dry gas line and the first mixed gas line are connected to implement a second mixed gas line through the fifth MFC <NUM>. The first mixed gas line is branched to an exhaust gas line through the first APR <NUM>.

The exhaust gas line and the second mixed gas line are bypassed by a pressure control line through the second APR <NUM>. The moisture concentration around the calibrating sensor <NUM> can be changed by controlling the flow ratio between the wet gas line through a saturator <NUM> and the first and second dry gas lines and the first mixed gas line. The saturator <NUM> is a <NUM> (<NUM>/<NUM> inch) stainless steel pipe containing pure water and introduces a constant concentration of saturated water-vapor by controlling the temperature with a Peltier device.

<FIG> is an example of the sensor response when the moisture concentration is changed stepwise using the system illustrated in <FIG>. The graph illustrated in <FIG> illustrates the temporal variation of the attenuation Alpha[GREEK] as the output-response of the ball SAW sensor in ten hours when the moisture concentration evaluated as the frost point (FP) was changed in steps from -<NUM> degrees centigrade to - <NUM> degrees centigrade. From the data illustrated in <FIG>, a calibration curve of the relationship between the FP and the attenuation Alpha can be obtained. While the system illustrated in <FIG> is capable of accurate calibration, it is too huge to apply to on-site calibration.

In <FIG>, the relationships between the FP and the attenuation Alpha of the ball SAW sensor, which are obtained by the static calibration system illustrated in <FIG>, are plotted as open circles. In <FIG>, we found that the relationship indicated as a dotted curve can be expressed as a function of the attenuation Alpha given by
[Math. <NUM>] <MAT> where A, B, C, and D are coefficients, which are characteristics of each sensor.

That is, the calibration of the ball SAW sensor means the determination of the coefficients A, B, C, and D. When the FP is above -<NUM> degrees centigrade, the FP can be approximated to be almost linear to the attenuation Alpha neglecting the exponential term of Eq. (<NUM>) as
[Math. <NUM>] <MAT>.

Therefore, the coefficients A and B can be determined by a least squares fitting of the data in the high concentration range. Furthermore, Eq. (<NUM>) can be transformed to
[Math. <NUM>] <MAT> expressing the exponential term of Eq. (<NUM>) as a linear function. <FIG> illustrates the relationship between the attenuation Alpha and the values on the left-hand side of Eq. (<NUM>) using data in the low FP range.

Therefore, the coefficients C and D can be determined by a least squares fitting. By using the coefficients A, B, C, and D, we can obtain the calibration curve for the sensor as
[Math. <NUM>] <MAT>.

Now, embodiments of the present invention will be described below with reference to the drawings. In the descriptions of the following drawings, the same or similar reference numerals are assigned to the same or similar portions. However, the drawings are diagrammatic, and attention should be paid to a fact that the relations between thicknesses and plan view dimensions, the configuration of the apparatus and the like differ from the actual data. Thus, the specific thicknesses and dimensions should be judged by considering the following descriptions.

Also, even between the mutual drawings, the portions in which the relations and rates between the mutual dimensions are different are naturally included. Also, the embodiment as described below exemplify the apparatuses and methods for embodying the technical ideas of the present invention, and in the technical ideas of the present invention, the materials, shapes, structures, arrangements and the like of configuration parts are not limited to the followings.

In the following description, the "horizontal" direction or the "vertical" direction is simply assigned for convenience of explanation and does not limit the technical spirit of the present invention. Therefore, for example, when the plane of paper is rotated <NUM> degrees, the "horizontal" direction is changed to the "vertical" direction and the "vertical" direction is changed to the "horizontal" direction. When the plane of paper is rotated <NUM> degrees, the "left" side is changed to the "right" side and the "right" side is changed to the "left" side. Therefore, various changes can be added to the technical ideas of the present invention, within the technical scope prescribed by claims.

As illustrated in <FIG>, a calibration system pertaining to a first embodiment of the present invention encompasses, a first pipe 45a through which background gas flows, a flowmeter <NUM> installed between the first pipe 45a and a second pipe 45b, an inlet <NUM> installed between the second pipe 45b and a third pipe 45c, an injector <NUM> for injecting a constant volume of the calibration gas to the inlet <NUM>, and a quick response moisture sensor <NUM> installed at downstream of the inlet <NUM> through the third pipe 45c, which serve as "an introduction pipe".

As illustrated in <FIG>, the calibration system pertaining to the first embodiment further encompasses a processing unit <NUM> connected to the moisture sensor <NUM>, a reference data memory <NUM> connected to the processing unit <NUM>, and a subject data memory <NUM> connected to the processing unit <NUM>. The moisture sensor <NUM>, the processing unit <NUM>, the reference data memory <NUM> and the subject data memory <NUM> implement a moisture analyzer <NUM>.

The water-vapor generator <NUM> illustrated in <FIG> produces saturated water-vapor in background gases on the head space provided above water, the water is contained in the lower portion of the water-vapor generator <NUM>. At an upper portion of the water-vapor generator <NUM>, a thermometer <NUM> is attached. The thermometer <NUM> measures temperature of the background gases saturated with water-vapor. Prior to conducting calibration with the calibration system illustrated in <FIG>, the tip of the injector <NUM> is supposed to be inserted in the water-vapor generator <NUM>. And, by the injector <NUM>, the saturated water-vapor is sampled from the water-vapor generator <NUM>.

Thereafter, the background gas is introduced into the first pipe 45a illustrated in <FIG>, and the background gas flows at a controlled flow rate through the first pipe 45a, as the flow of the background gas is controlled or measured by the flowmeter <NUM>. And, when the saturated water-vapor is injected by the injector <NUM> into inlet <NUM>, the water-vapor is carried through the third pipe 45c to the moisture sensor <NUM> by diffusion and drifting, and output-responses are obtained by the moisture sensor <NUM>.

As illustrated in <FIG>, the processing unit <NUM> include a reference-data obtaining logic-circuit (LCKT) <NUM>, a subject-data obtaining logic-circuit (LCKT) <NUM>, a relationship calculating logic-circuit (LCKT) <NUM> and control circuit configured to control time sequence of the operations of the reference-data obtaining LCKT <NUM>, the subject-data obtaining LCKT <NUM> and the relationship calculating LCKT <NUM>.

The reference-data obtaining LCKT <NUM> obtains reference data, which indicate temporal memory of moisture concentrations, after injecting water-vapor with known concentrations into an analyzer of a calibration system. The subject-data obtaining LCKT <NUM> measures subject data indicating temporal variation of output-responses of a subject sensor element of the analyzer under test, the subject data are obtained under same condition with the reference data was obtained.

The relationship calculating LCKT <NUM> compares the subject data with the reference data, with same time-duration for obtaining the reference data, the time-duration is measured from a timing at which the water-vapor with the known concentrations is injected. And the relationship calculating LCKT <NUM> further calculates relationships between the output-responses of the subject sensor element and the known concentrations. The reference data memory <NUM> stores the reference data obtained by reference-data obtaining LCKT <NUM>. The subject data memory <NUM> stores the subject data obtained by the subject-data obtaining LCKT <NUM>.

The moisture sensor <NUM> is implemented by a ball SAW sensor illustrated in <FIG>, and the output-responses vary with time owing to the change in moisture concentration. As illustrated in <FIG>, in the ball SAW sensor implementing the moisture sensor <NUM>, a SAW is excited by the sensor electrode <NUM> with the specific condition. The SAW generates a naturally collimated beam <NUM> around the piezoelectric ball <NUM> so that multiple roundtrips along the equator of the ball can be realized. Since the sensitive film <NUM> coated on the propagation route of the SAW change the viscoelasticity due to adsorption of water, the concentration of moisture can be evaluated by the attenuation Alpha of the SAW.

The processing unit <NUM> may be, for example, a central processing unit (CPU) of a computer system. The reference-data obtaining LCKT <NUM>, the subject-data obtaining LCKT <NUM> and the relationship calculating LCKT <NUM> may be achieved by functional logical circuits arranged in a general-purpose semiconductor integrated circuit. For example, the processor may include a programmable logic device (PLD) such as a field-programmable gate array (FPGA).

The FPGA is an integrated circuit designed to be configured by a customer or a designer after manufacturing. The FPGA configuration is generally specified using a hardware description language (HDL), similar to that used for an application-specific integrated circuit (ASIC). Similar to the configuration of FPGAs, the processing unit <NUM> may contain the reference-data obtaining LCKT <NUM>, the subject-data obtaining LCKT <NUM> and the relationship calculating LCKT <NUM> as an array of programmable logic blocks.

That is, like software, the electronic hardware of the reference-data obtaining LCKT <NUM>, the subject-data obtaining LCKT <NUM> and the relationship calculating LCKT <NUM> can be designed modularly, by creating subcomponents and then higher-level components to instantiate them. In a case where the processing unit <NUM> is housed in a PC, the output units <NUM> may be built in the PC, or may be composed integrally with the PC. Meanwhile, in a case where the processing unit <NUM> is merged with the hybrid IC or module, it is also possible to assemble the processing unit <NUM> in an inside of the moisture analyzer <NUM>. Alternatively, the reference-data obtaining LCKT <NUM>, the subject-data obtaining LCKT <NUM> and the relationship calculating LCKT <NUM> may be implemented by architecture of a software program.

Though not illustrated, in a similar way to a usual computer system, a set of registers, cache memory and a main memory (data memory) as the primary storage, and further a program memory are connected to or built in the processing unit <NUM> according to the first embodiment of the present invention. The primary storage is directly connected to the processing unit <NUM> of the calibration system embodied by computer system. The set of registers are internal to the processing unit <NUM>. Registers contain information that the arithmetic and logic unit needs to carry out the current instruction.

Registers are technically the fastest of all forms of computer storage, being switching transistors integrated on the CPU's silicon chip, and functioning as electronic "flip-flops". Cache memory is a special type of internal memory used by processing unit <NUM> to increase the performance or "throughput". Some of the information in the main memory is duplicated in the cache memory, which is slightly slower but of much greater capacity than the processor registers, and faster but much smaller than main memory.

Although the illustration is omitted, the main memory contains the current data and instructions that are currently being run, and is directly connected to the data bus 348a, 348b. The arithmetic LCKTs <NUM>, <NUM> and <NUM> can very quickly transfer information between the set of register and locations in main storage, also known as a "memory addresses".

The program memory can be composed of semiconductor memories, magnetic disks, optical disks, magneto-optical disks, magnetic tapes, and the like. Hence, a calibration program for drive-controlling the reference-data obtaining LCKT <NUM>, the subject-data obtaining LCKT <NUM> and the relationship calculating LCKT <NUM>, which are illustrated in <FIG>, and causing the LCKTs <NUM>, <NUM>, <NUM> to calibrating the moisture sensor, according to the first embodiment just needs to be stored in the program memory (not illustrated) of a computer system that implements the moisture analyzer34. Meanwhile, varieties of input/output data and parameters, which are necessary for calibration, data under computation, and the like, can be stored in the data memory such as SRAM.

The processing unit <NUM> according to the first embodiment of the present invention is configurable of the computer system such as the PC, and accordingly, illustration of the PC is omitted. However, the processing unit <NUM> may further include input units such as a PC keyboard, a mouse, and a light pen. Specifically, the mouse is clicked for the operator notation displayed on the output units <NUM>, whereby measurement conditions or sensor specifications can be entered. Moreover, as another output unit, a printer device or the like may be provided as well as the output units <NUM> illustrated in <FIG>.

According to the calibration system pertaining to the first embodiment, the effectiveness such that a measurement time as short as ten minutes can be achieved, while ten hours are required for static calibration pertaining to the illustrative examples. Since the calibration system pertaining to the first embodiment implemented by a small number of simple components, it is possible to downsize the scale of the calibration system, and apply the calibration system to on-site calibration. Moreover, since the calibration system pertaining to the first embodiment uses saturated water-vapor as calibration gases, it is easy to prepare high precision calibrated gases in the field without a detailed control.

As the water-vapor generator <NUM> illustrated in <FIG>, we use a sampling gas bag for gas analysis, whose inner surface was inactivated, as illustrated in <FIG>. After purging the gas bag with nitrogen gas, pure water is injected into the bag and the bag is saturated with water-vapor at room temperature controlled by an air conditioner. As the injector <NUM> illustrated in <FIG> and <FIG>, we use a gas-tight syringe, with which we can control the injection volume using the scale of the syringe. The saturated water-vapor is extracted from the gas bag using the gas-tight syringe serving as the injector <NUM>, and injected into the inlet <NUM> provided <NUM> upstream of the ball SAW sensor as the moisture sensor <NUM> connected to the third pipe 45c. The nitrogen gas flow through the first pipe 45a, the second pipe 45b and third pipe 45c is controlled using a mass flow controller as the flow meter <NUM>.

We installed a ball SAW sensor as the moisture sensor <NUM> in the system pertaining to the first embodiment, and measured responses by injection of saturated water-vapor. The injection volume was <NUM> and the flow rate of the background gas was <NUM> · min-<NUM>. At the measurement, the room temperature was <NUM> degrees centigrade. Response time was evaluated as the time within which a <NUM>% to <NUM>% increase in the FP was observed after the injection of saturated water-vapor.

<FIG> illustrates a temporal variation of the FP due to the injection of saturated water-vapor measured using the moisture sensor <NUM>. The FP increased immediately after injection and then decreased gradually. The decrease took about ten minutes and is considered to represent a process at which the water adsorbed on the pipe surface was gradually desorbed.

The expanded view of the peak is illustrated in <FIG>. The response time taken for <NUM>% to <NUM>% of the FP change from -<NUM> to <NUM> degrees centigrade was only <NUM>. Since the response time is less than one second, it can be regarded that the equilibrium between the moisture concentration within the sensitive film and that in the atmosphere is rapidly reached at any instance of the dynamic calibration process pertaining to the first embodiment, which takes ten minutes. This rapid equilibrium is the basis for the validity of the dynamic calibration process pertaining to the first embodiment.

First, to obtain a reference data for a dynamic calibration method pertaining to the first embodiment, we install a reference sensor element implemented by the ball SAW sensor as the moisture sensor <NUM> illustrated in <FIG>. In Step <NUM> of the procedure illustrated in <FIG> the reference-data obtaining LCKT <NUM> obtains reference data, which indicate temporal variation of moisture concentrations, after injecting water-vapor, which has known concentrations, into an analyzer under test.

The reference sensor element has been already calibrated by the static calibration method pertaining to the illustrative example, which has been illustrated in <FIG>. The calibration system may be the dynamic calibration system pertaining to the first embodiment. Then, the calibration system measures the temporal variation of the attenuation Alpha by the injection of saturated water-vapor. The temporal variation of the FP can be obtained by substituting the attenuation Alpha at each time in Eq. (<NUM>). The reference-data obtaining LCKT <NUM> stores the obtained reference data into the reference data memory <NUM>.

The measurement result for the reference data is illustrated in <FIG> and <FIG> at a background gas flow rate of <NUM> · min-<NUM>, a saturated water-vapor injection volume of <NUM>, and a room temperature of <NUM> degrees centigrade. From the temporal variation of the attenuation Alpha after the injection of saturated water-vapor, as illustrated in <FIG>, the temporal variation of FP was obtained using the calibration curve obtained using Eq. (<NUM>), as illustrated in <FIG>. Since the rising part of the peak changes rapidly, the rising part is not used for the calibration, and the gradually decreasing part of the curve illustrated in solid curve is used as reference data.

Next, the reference sensor element is replaced with a subject sensor element to be calibrated, In Step <NUM> of the procedure illustrated in <FIG> the subject-data obtaining LCKT <NUM> measures subject data indicating temporal variation of output-responses of a subject sensor element of an analyzer under test, the subject data are obtained under same condition with the reference data was obtained. For example, the temporal variation of the attenuation Alpha is measured for ten minutes under the same conditions as the condition when the reference data was measured. The subject sensor element is implemented by the ball SAW sensor. The subject-data obtaining LCKT <NUM> stores the obtained subject data into the subject data memory <NUM>. The attenuation Alpha of a new sensor - -or the subject moisture sensor - - under the same condition as the measurement for the reference data is illustrated by the solid curve in <FIG>.

In Step <NUM> of the procedure illustrated in <FIG>, the relationship calculating LCKT <NUM> reads out the reference data from the reference data memory <NUM>, and furthermore, the relationship calculating LCKT <NUM> reads out the subject data from the subject data memory <NUM>. Thereafter, the relationship calculating LCKT <NUM> compares the subject data with the reference data, with same time-duration for obtaining the reference data, the time-duration is measured from a timing at which the water-vapor with the known concentrations is injected.

And, furthermore, in Step <NUM> of the procedure illustrated in <FIG>, the relationship calculating LCKT <NUM> further calculates relationships between the output-responses of the subject sensor element and the known concentrations.

Using the reference data illustrated by the dotted curve at same time-duration, we obtained the FP at the right ordinate. <FIG> illustrates the relationship between the attenuation Alpha and the FP in the high concentration range as illustrated by closed circles.

Since the relationship illustrated in <FIG> is almost linear, the coefficients of calibration curves A and B were determined to be A = <NUM> and B = -<NUM> by a least squares fitting. On the other hand, <FIG> illustrates the relationship between the attenuation Alpha and the values obtained by the functional expression represented on the left-hand side of Eq. (<NUM>) in the low concentration range as illustrated by open circles. Since the relationship illustrated in <FIG> is also linear, coefficients C and D were determined to be C = -<NUM> and D = <NUM> by a least squares fitting.

In Step <NUM> of the procedure illustrated in <FIG>, the relationship calculating LCKT <NUM> further defines the calibration data. That is, the calibration curve of the new sensor element obtained by the dynamic calibration method is given by
[Math. <NUM>] <MAT>.

The calibration curve of the subject sensor element is derived as the relationship between the attenuation Alpha and the FP of the reference data at same time-duration.

The relationship calculating LCKT <NUM> further send the defined calibration data toward the output unit <NUM>. Alternatively, the defined calibration data may be stored in a calibration data memory, although the illustration of the calibration data memory is omitted.

Finally, the subject sensor element is calibrated again by the static calibration method. The calibration curve of the same subject sensor element obtained by the static calibration method is given by
[Math. <NUM>] <MAT> and the calibration curve obtained is compared with that obtained by the dynamic calibration method pertaining to the first embodiment.

In <FIG>, the result of dynamic calibration curve using Eq. (<NUM>) is illustrated as a solid curve and the result of static calibration curve using Eq. (<NUM>) is illustrated as a dotted curve. These two curves look nearly identical.

<FIG> illustrates the error between the set FP and the measured FP calculated by the substitution of the attenuation Alpha into each calibration curve. The abscissa illustrates the set FP and the ordinate illustrates the measured FP. If there is no error, the measured FP should be plotted on the <NUM> degrees line illustrated by the dotted line. Open circles illustrate results obtained by the dynamic calibration and closed circles illustrate those obtained by the static calibration. In the FP range from -<NUM> to -<NUM> degrees centigrade, the root-mean-square (RMS) errors of the static and dynamic calibration methods were <NUM> degrees centigrade and <NUM> degrees centigrade, respectively.

The RMS error of <NUM> degrees centigrade of the dynamic calibration in the FP range from -<NUM> to -<NUM> degrees centigrade is acceptable for a rough estimate of the sensor condition. Since this error is considered to be the accumulation of errors in the calibration curve obtained using Eq. (<NUM>) acquired as the reference data, errors in the amount of injected saturated water-vapor as the calibration gas, and subtle differences in temperature and atmospheric pressure, it can be reduced by improving the system components.

According to the dynamic calibration method pertaining to the first embodiment, the effectiveness such that a measurement time as short as ten minutes can be achieved, while ten hours are required for static calibration pertaining to the illustrative examples. Therefore, it is possible to apply the dynamic calibration method to on-site calibration. Moreover, since the dynamic calibration method pertaining to the first embodiment uses saturated water-vapor as calibration gases, it is easy to prepare high precision calibrated gases in the field without a detailed control.

For example, the calibration program used with the first embodiment of the present invention is stored in a non-transitory computer readable storage medium, and the program memory of the processing unit <NUM> is caused to read a content recorded in the external recording medium, whereby the calibration program concerned can execute a series of processing of the calibration of the present invention.

Namely, the calibration program, which causes the processing unit <NUM> in the calibration system pertaining to the first embodiment to execute processing for calibration, includes a series of instructions for performing the procedure of the calibration. The series of instructions may include instructions to the reference-data obtaining LCKT <NUM> so that the reference-data obtaining LCKT <NUM> obtains reference data, which indicate temporal variation of moisture concentrations, after injecting water-vapor with known concentrations into an analyzer of a calibration system.

The series of instructions further includes instructions to the subject-data obtaining LCKT <NUM> so that the subject-data obtaining LCKT <NUM> measures subject data indicating temporal variation of output-responses of a subject sensor element of an analyzer under test, the subject data are obtained under same condition with the reference data was obtained.

The series of instructions still further includes instructions to the relationship calculating LCKT <NUM> so that compares the subject data with the reference data, with same time-duration for obtaining the reference data, the time-duration is measured from a timing at which the water-vapor with the known concentrations is injected, The series of instructions yet still further includes instructions to the relationship calculating LCKT <NUM> so that the relationship calculating LCKT 347calculates relationships between the output-responses of the subject sensor element and the known concentrations.

Here, the "non-transitory computer readable storage medium" means such a medium that can record a program. The non-transitory computer readable storage medium includes, for example, an external memory device of a computer, a semiconductor memory, a magnetic disk, an optical disk, a magneto-optical disk, a magnetic tape, and the like. Specifically, a flexible disk, a CD-ROM, an MO disk, an open-reel tape and the like are included in the "non-transitory computer readable storage medium".

For example, a main body of the processing unit <NUM> can be configured to build therein a flexible disk device and an optical disk device or to cause the flexible disk device and the optical disk device to be externally connected thereto. The flexible disk is inserted into the flexible disk drive from an insertion slot thereof, and the CD-ROM is inserted into the optical disk drive from an insertion slot thereof, and both of them are subjected to a predetermined reading operation, whereby the programs stored in these external recording mediums can be installed into the program memory that implements the processing unit <NUM>.

Moreover, a predetermined drive device is connected to the processing unit <NUM>, whereby, for example, the ROM and the magnetic tape device can be used as external recording mediums. Furthermore, it is possible to store the calibration program in the program memory via an information processing network such as the Internet in place of using the external recording medium.

According to the calibration program used with the first embodiment, the effectiveness such that a measurement time as short as ten minutes can be achieved, while ten hours are required for static calibration pertaining to the illustrative examples. Therefore, it is possible to apply the calibration program to on-site calibration. Moreover, it is easy to prepare high precision calibrated gases in the field without a detailed control.

As illustrated in <FIG>, a calibration system pertaining to a second embodiment of the present invention encompasses a first pipe 44a through which background gas flows, a flowmeter <NUM> installed between the first pipe 44a and a second pipe 44b. The second pipe 44b is branched into a first branched pipe 44e having a first valve <NUM>, and another branch of the second pipe 44b is connected to a third pipe 44c via a second valve <NUM>.

The third pipe 44c is branched into a second branched pipe 44f having a third valve <NUM>, and another branch of the third pipe 44c is connected to a moisture analyzer <NUM>, and therefore the third pipe 44c serve as "an introduction pipe" for the moisture analyzer <NUM>. In the calibration system pertaining to the second embodiment further encompasses an inlet <NUM> installed between the first branched pipe 44e and the second branched pipe 44f and an injector <NUM> for injecting a constant volume of the calibration gas to the inlet <NUM>.

By branching the pipe at upstream and downstream of the inlet <NUM> and switching the flow path using the first valve <NUM>, the second valve <NUM> and the third valve <NUM>, it is possible to adopt configuration which allows replacement and maintenance of the inlet <NUM> on-line, as the moisture analyzer <NUM> is installed at downstream of the inlet <NUM> through the third pipe 44c.

The water-vapor generator <NUM>, which was illustrated in <FIG> in the explanation of the first embodiment, produces the saturated water-vapor in background gases on the head space of water, the water is contained in the lower portion of the water-vapor generator <NUM>. Prior to conducting calibration with the calibration system illustrated in <FIG>, the tip of the injector <NUM> is supposed to be inserted in the water-vapor generator <NUM>. And, by the injector <NUM>, the saturated water-vapor is sampled from the water-vapor generator <NUM>.

Thereafter, the background gas is introduced into the first pipe 44a illustrated in <FIG>, and the background gas flows at a controlled flow rate through the first pipe 44a, as the flow of the background gas is controlled or measured by the flowmeter <NUM>. And, when the saturated water-vapor is injected by the injector <NUM> into inlet <NUM>, the water-vapor is carried through the third pipe 45c to the moisture analyzer <NUM> by diffusion and drifting, and output-responses are obtained by the moisture analyzer <NUM>.

The moisture analyzer <NUM> is implemented by a ball SAW sensor illustrated in <FIG> as the moisture sensor <NUM> of the first embodiment, and the output-responses vary with time owing to the change in moisture concentration. Although the illustration is omitted, similar to the configuration explained in the first embodiment, the moisture analyzer <NUM> further includes the processing unit <NUM>, the reference data memory <NUM> and the subject data memory <NUM>.

And, the processing unit <NUM> encompasses the reference-data obtaining LCKT <NUM>, the subject-data obtaining LCKT <NUM> and the relationship calculating LCKT <NUM>, which are explained in the first embodiment. Since the calibration system pertaining to the second embodiment embraces simple components, it is possible to downsize the calibration system, and apply the calibration system to on-site calibration. Moreover, since the calibration system pertaining to the second embodiment uses saturated water vapor as calibration gases, it is easy to prepare high precision calibrated gases in the field without a detailed control.

According to the calibration system pertaining to the second embodiment, the effectiveness such that a measurement time as short as ten minutes can be achieved, while ten hours are required for static calibration pertaining to the illustrative examples. Since the calibration system pertaining to the second embodiment implemented by a small number of simple components, it is possible to downsize the scale of the calibration system, and apply the calibration system to on-site calibration. Moreover, since the calibration system pertaining to the second embodiment uses saturated water-vapor as calibration gases, it is easy to prepare high precision calibrated gases in the field without a detailed control.

When the injected water concentration is CW and the injection volume is VS, total injected water content VW is given by <MAT>.

On the other hand, the water vapor injected into the pipe with the background gases passing through at the flow rate F<NUM>, diffuses in the flow direction and reaches the sensor while adsorbed to / desorbed from the pipe wall surface, so the moisture concentration around the sensor changes with the time. Since concentration integration IC is the time integral of response curve Cm (t) <MAT> and, the product of the concentration integration Ic and the gas flow rate F<NUM> equals to VW, the concentration integration IC is given by <MAT>.

In a condition that the boll SAW sensor illustrated in <FIG> is connected to the calibration system pertaining to the second embodiment, saturated water vapor gas was injected in the calibration system. The flow rate of background gas was changed to <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>/min using a mass flow controller. <FIG> illustrates a temporal variation of moisture concentration calculated from the output-responses of the ball SAW sensor. Each of the output-responses is plotted after shifted by <NUM> ppmv. The moisture concentration of injected calibration gas was calculated as CW=<NUM> ppmv from the saturated water vapor pressure at room temperature of <NUM> degrees centigrade.

When the gas flow rate is <NUM>/min, the total moisture content is <NUM> from Eq. (<NUM>), and the theoretical value of concentration integration Ic is <NUM> ppm min from Eq. (<NUM>). The value of <NUM> ppm min is almost equal to Ic=<NUM> ppm min obtained from the response curve by Eq. (<NUM>). <FIG> illustrates the result of carrying out similar measurement at each flow rate. The measured values at all flow rates, which are indicated by open circles, almost agreed with the theoretical values indicated by the solid curve. Consequently, it was illustrated that operation of the calibration system pertaining to the second embodiment follows the theoretical prediction.

Therefore, a similar method for calibration of moisture sensor as the dynamic calibration method pertaining to the first embodiment can be executed. That is, the dynamic calibration method pertaining to the second embodiment includes the step of the reference-data obtaining LCKT <NUM> obtains reference data, which indicate temporal variation of moisture concentrations, after injecting water-vapor with known concentrations into an analyzer of a calibration system. And, the dynamic calibration method pertaining to the second embodiment includes the step of the subject-data obtaining LCKT <NUM> measures subject data indicating temporal variation of responses of a subject sensor element of an analyzer under test, the subject data are obtained under same condition with the reference data was obtained.

Furthermore, the dynamic calibration method pertaining to the second embodiment includes the step of the relationship calculating LCKT <NUM> comparers the subject data with the reference data, with same time-duration for obtaining the reference data, the time-duration is measured from a timing at which the water-vapor with the known concentrations is injected. Furthermore, the dynamic calibration method pertaining to the second embodiment includes the step of the relationship calculating LCKT <NUM> calculates relationships between the responses of the subject sensor element and the known concentrations.

According to the dynamic calibration method pertaining to the second embodiment, the effectiveness such that a measurement time as short as ten minutes can be achieved, while ten hours are required for static calibration pertaining to the illustrative examples. Therefore, it is possible to apply the dynamic calibration method to on-site calibration. Moreover, since the dynamic calibration method pertaining to the second embodiment uses saturated water-vapor as calibration gases, it is easy to prepare high precision calibrated gases in the field without a detailed control.

According to the calibration program used with the second embodiment, the effectiveness such that a measurement time as short as ten minutes can be achieved, while ten hours are required for static calibration pertaining to the illustrative examples. Therefore, it is possible to apply the calibration program to on-site calibration. Moreover, it is easy to prepare high precision calibrated gases in the field without a detailed control.

The dynamic calibration method can be executed by the processing unit <NUM> by a calibration program pertaining to the second embodiment, which is essentially same as the calibration program pertaining to the first embodiment. Therefore, duplicated explanation of the calibration program is omitted. And, a series of instructions for performing the dynamic calibration method shall be stored in a non-transitory computer readable storage medium.

Claim 1:
A dynamic calibration system for calibrating a moisture sensor comprising a programmable logic device as a processing unit (<NUM>), and an analyzer (<NUM>) comprising a moisture sensor (<NUM>) configured to accept a subject sensor element, wherein an output of the moisture sensor (<NUM>) is connected to the processing unit (<NUM>), the processing unit including:
a functional logic circuit (<NUM>) of said programmable logic device configured to obtain reference data from a calibrated reference sensor element installed as the moisture sensor (<NUM>), which indicate temporal variation of moisture concentrations, after injecting water-vapor with known concentrations into the analyzer (<NUM>);
a functional logic circuit (<NUM>) of said programmable logic device configured to obtain subject data indicating temporal variation of output-responses of a subject sensor element to be calibrated installed as the moisture sensor (<NUM>) of the analyzer (<NUM>, wherein the subject data are obtained under the same condition as the reference data; and
a functional logic circuit (<NUM>) of said programmable logic device configured to compare the subject data to the reference data with same time-duration measured from a timing at which the water-vapor with the known concentrations is injected for calculating relationships between the output-responses of the subject sensor element and the known concentrations,
the system further comprising:
an injector (<NUM>) configured to inject a constant volume of a calibration gas to
an inlet (<NUM>) configured to receive a tip of the injector (<NUM>) ;
a flowmeter (<NUM>) configured to control a flow rate of a background gas;
a first pipe (44a) for introducing the background gas to the flowmeter (<NUM>);
a second pipe (44b) connecting the flowmeter (<NUM>) with the inlet (<NUM>), configured to flow the background gas at a controlled flow rate by the flowmeter (<NUM>); and
a third pipe (44c) connecting the inlet (<NUM>) with the moisture sensor (<NUM>), configured to introduce the background gas and the calibration gas into the moisture sensor (<NUM>).