Patent Description:
A zirconia-type oxygen analyzer is an oxygen analyzer that utilizes the property whereby a zirconia element exhibits conductivity with regard to oxygen ions at high temperatures. When a platinum electrode is attached to both sides of a zirconia element and heated, and a gas with a different oxygen partial pressure is brought into contact with each side of the zirconia element, the effect of an oxygen concentration cell is generated. The zirconia-type oxygen analyzer measures the electromotive force generated between the two electrodes by this effect to measure the oxygen partial pressure on the measurement gas side.

In zirconia-type oxygen analyzers, deterioration of the zirconia sensor (zirconia oxygen sensor) occurs due to use over an extended period of time, resulting in a shift (drift) of the oxygen concentration. To maintain an accurate display of oxygen concentration, calibration needs to be performed by periodically causing a gas of known concentration to flow on the measurement gas side and electrically correcting the output. For example, patent literature (PTL) <NUM> discloses a technique for calibrating a zirconia-type oxygen analyzer.

The zirconia-type oxygen analyzer can usually be maintained in a normal condition through periodic performance of such calibration, but as the degree of deterioration of the zirconia sensor increases, the effect of drift cannot be sufficiently compensated for even by calibration, resulting in measurement failure, errors, and the like. In such a situation, the zirconia sensor itself needs to be replaced.

Maintenance, such as calibration and replacement of the zirconia sensor, thus needs to be done at the appropriate timing. On the other hand, maintenance work is time-consuming and costly and hence should be kept to a minimum.

It is known, however, that the timing and content of the required maintenance varies greatly depending on the environment in which the zirconia-type oxygen analyzer is used. For example, the calibration cycle and sensor replacement timing of a zirconia-type oxygen analyzer for process gases used in boilers, power plants, or the like are greatly dependent on the operating environment, such as the components included in the gas to be measured, the temperature, and moisture. Currently, it is common for users to determine the timing and content of maintenance according to conditions.

PTL <NUM>: <CIT>
Further prior art may be found in <CIT> which describes a calibration method and zirconia-type oxygen analyzer using this method, in <CIT> which describes a zirconia type oxygen meter and in <CIT> which describes an oxygen sensor controlling apparatus, oxygen sensor controlling method and computer readable recording medium.

Users typically have little knowledge and skill regarding the behavior of zirconia sensors, however, and are therefore unable to properly set the timing and content of appropriate maintenance. As a result, users may perform excessive calibration or sensor replacement, or continue to use the zirconia sensor until an error occurs, which may lead to suspended operation of equipment in the plant.

The manufacturer of a zirconia-type oxygen analyzer could propose necessary maintenance to the user at the appropriate timing. For the manufacturer to propose appropriate maintenance, however, detailed information would need to be shared on the operating environment of the zirconia-type oxygen analyzer, the status of calibration, the degree of sensor deterioration, and the like. In reality, it is difficult to share information constantly from the start of operation to replacement of equipment.

It would be helpful to provide a maintenance method for a zirconia-type oxygen analyzer, a maintenance system, and a zirconia-type oxygen analyzer that enable maintenance of a zirconia-type oxygen analyzer to be appropriately performed. The present invention is defined by appended independent claims <NUM> and <NUM>. The dependent claims describe optional features and distinct embodiments. The zirconia-type oxygen analyzers described herein below are for technical illustration only and not part of the claimed invention.

A maintenance method, according to an embodiment, for a zirconia-type oxygen analyzer is a maintenance method for a zirconia-type oxygen analyzer that uses a zirconia sensor to measure an oxygen concentration of a gas to be measured and includes storing in a memory, by the zirconia-type oxygen analyzer, an internal resistance present in the zirconia sensor and/or a calibration coefficient for correcting, based on a measured value of a physical quantity measured by the zirconia sensor for a standard gas having a known oxygen concentration, a conversion formula for converting a measured value of a physical quantity measured by the zirconia sensor into the oxygen concentration of the gas to be measured, determining, by an information processing apparatus, a timing at which maintenance should be performed on the zirconia sensor based on a change over time in the internal resistance and/or the calibration coefficient stored in the memory, and presenting, by the information processing apparatus, the timing at which maintenance should be performed on the zirconia sensor. The timing at which maintenance should be performed on the zirconia sensor, as determined based on the internal resistance and/or the calibration coefficient, is thus presented so that the user can appropriately perform maintenance on the zirconia-type oxygen analyzer by performing the maintenance at the presented timing.

In the maintenance method for a zirconia-type oxygen analyzer according to an embodiment, the information processing apparatus approximates the change over time in the internal resistance by a quadratic curve, and determines a timing at which a value of the internal resistance, estimated by the quadratic curve for the change over time in the internal resistance, reaches a predetermined upper limit of the internal resistance as the timing at which maintenance should be performed on the zirconia sensor. In this way, the change over time in the internal resistance is approximated by a quadratic curve, the timing when the internal resistance reaches the upper limit is estimated using the quadratic curve, and the timing at which maintenance should be performed is determined. The timing of required maintenance can thus be appropriately determined and presented.

In the maintenance method for a zirconia-type oxygen analyzer according to an embodiment, the information processing apparatus approximates the change over time in the calibration coefficient by a quadratic curve, and determines a timing at which a rate of change of the calibration coefficient, estimated by the quadratic curve for the change over time in the calibration coefficient, reaches a predetermined upper limit of the rate of change as the timing at which the zirconia sensor should be calibrated. In this way, the change over time in the calibration coefficient is approximated by a quadratic curve, the timing at which the rate of change of the calibration coefficient reaches the upper limit is estimated using the quadratic curve, and the timing for calibrating the zirconia sensor is determined. The timing and content of required maintenance can thus be appropriately determined and presented.

In the maintenance method for a zirconia-type oxygen analyzer according to an embodiment, the information processing apparatus approximates the change over time in the calibration coefficient by a quadratic curve, and determines a timing at which a variation range of the calibration coefficient, estimated by the quadratic curve for the change over time in the calibration coefficient, reaches a predetermined upper limit of the variation range as a timing at which the zirconia sensor should be replaced. In this way, the change over time in the calibration coefficient is approximated by a quadratic curve, the timing at which the variation range of the calibration coefficient reaches the upper limit is estimated using the quadratic curve, and the timing at which the zirconia sensor should be replaced is determined. The timing and content of required maintenance can thus be appropriately determined and presented.

In the maintenance method for a zirconia-type oxygen analyzer according to an embodiment, the zirconia-type oxygen analyzer determines a coefficient for correcting the conversion formula as the calibration coefficient based on a first measured value that is a measured value of the physical quantity measured by the zirconia sensor for a first standard gas having a known first oxygen concentration and a second measured value that is a measured value of the physical quantity measured by the zirconia sensor for a second standard gas having a known second oxygen concentration, and stores the determined calibration coefficient in the memory. In this way, the calibration coefficient is determined based on the measured value of the physical quantity measured by the zirconia sensor for two standard gases with different concentrations, and the timing at which maintenance should be performed is determined based on such a calibration coefficient. The timing of required maintenance can thus be appropriately determined and presented.

A maintenance system for a zirconia-type oxygen analyzer according to an embodiment is a maintenance system including a zirconia-type oxygen analyzer that uses a zirconia sensor to measure an oxygen concentration of a gas to be measured, and an information processing apparatus, wherein the zirconia-type oxygen analyzer stores, in a memory, an internal resistance present in the zirconia sensor, and/or a calibration coefficient for correcting, based on a measured value of a physical quantity measured by the zirconia sensor for a standard gas having a known oxygen concentration, a conversion formula for converting a measured value of a physical quantity measured by the zirconia sensor into the oxygen concentration of the gas to be measured, and the information processing apparatus determines a timing at which maintenance should be performed on the zirconia sensor based on a change over time in the internal resistance and/or the calibration coefficient stored in the memory and presents the timing at which maintenance should be performed on the zirconia sensor. The timing at which maintenance should be performed on the zirconia sensor, as determined based on the internal resistance and/or the calibration coefficient, is thus presented so that the user can appropriately perform maintenance on the zirconia-type oxygen analyzer by performing the maintenance at the presented timing.

A zirconia-type oxygen analyzer according to an embodiment is a zirconia-type oxygen analyzer that uses a zirconia sensor to measure an oxygen concentration of a gas to be measured, the zirconia-type oxygen analyzer including a controller configured to measure, at a predetermined timing, an internal resistance present in the zirconia sensor, and store the measured internal resistance in a memory. Therefore, the change in the internal resistance stored in the memory can be analyzed to properly determine the timing and content of maintenance that should be performed.

A zirconia-type oxygen analyzer according to an embodiment is a zirconia-type oxygen analyzer that uses a zirconia sensor to measure an oxygen concentration of a gas to be measured, the zirconia-type oxygen analyzer including a controller configured to measure a physical quantity, using the zirconia sensor, for a standard gas having a known oxygen concentration, calculate, based on the measured physical quantity and the known oxygen concentration, a calibration coefficient for correcting a conversion formula for converting a measured value of the physical quantity measured by the zirconia sensor into the oxygen concentration of the gas to be measured, and store the calculated calibration coefficient in a memory. Therefore, the change in the calibration coefficient stored in the memory can be analyzed to properly determine the timing and content of maintenance that should be performed.

According to an embodiment of the present disclosure, maintenance of a zirconia-type oxygen analyzer can be appropriately performed.

<FIG> is a diagram illustrating the maintenance flow of a zirconia-type oxygen analyzer according to a comparative example. In the comparative example, when the manufacturer delivers the equipment for the zirconia-type oxygen analyzer, the user starts operating the equipment. The user performs calibration periodically at the user's discretion, but the zirconia sensor deteriorates with continued use. As deterioration progresses, it becomes impossible to sufficiently compensate for the effect of drift even by calibration, and errors eventually occur during measurement by the zirconia-type oxygen analyzer. The user confirms the occurrence of an error and orders a new zirconia sensor from the manufacturer. The manufacturer receives the order and delivers the new zirconia sensor. The user installs the new zirconia sensor and resumes operation of the equipment. In the comparative example, this cycle is repeated.

In this configuration according to the comparative example, the user performs the calibration of the zirconia sensor at the user's discretion. However, users do not necessarily have sufficient knowledge and skill regarding maintenance of zirconia sensors. Users might therefore perform excessively frequent maintenance or not perform maintenance frequently enough. Furthermore, as illustrated in the maintenance flow in <FIG>, users might continue to use the zirconia-type oxygen analyzer until an error occurs, which may lead to suspended operation of equipment in the plant. In the configuration according to the comparative example, it might therefore not be possible to perform appropriate maintenance.

Embodiments of the present disclosure are now described with reference to the drawings. Identical or equivalent portions in the drawings are labeled with the same reference signs. In the explanation of the embodiments, a description of identical or equivalent portions is omitted or simplified as appropriate.

<FIG> is a diagram illustrating an example configuration of a maintenance system <NUM> according to an embodiment of the present disclosure. The maintenance system <NUM> includes a zirconia-type oxygen analyzer <NUM> and a management apparatus <NUM> as an information processing apparatus in the present embodiment. The zirconia-type oxygen analyzer <NUM> includes a zirconia sensor <NUM>, a converter <NUM>, and a gas-filled cylinder <NUM>. The zirconia sensor <NUM> and the converter <NUM> are connected by a power cable <NUM>. The zirconia sensor <NUM> and the gas-filled cylinder <NUM> are connected by a gas cable <NUM> provided with pressure reducing valves <NUM>, <NUM>. When a gas with a different oxygen partial pressure is brought into contact with each side of the zirconia element in the zirconia sensor <NUM>, the effect of an oxygen concentration cell is generated. The zirconia sensor <NUM> transmits an electromotive force corresponding to this effect (hereinafter referred to as "cell electromotive force") to the converter <NUM>. Based on the electromotive force and the oxygen partial pressure of a comparison gas, the converter <NUM> measures (calculates) the oxygen partial pressure of the gas to be measured. The converter <NUM> also generates a log data file according to the calibration or constant deterioration diagnosis of the zirconia sensor <NUM>, as described below, and stores the log data file in the memory <NUM> (see <FIG>).

The gas-filled cylinder <NUM> is a source of gas with a known value of oxygen partial pressure, which is used as a reference at the time of measuring the oxygen partial pressure of the gas to be measured. For example, the gas-filled cylinder <NUM> stores a span gas and a zero gas, selects one of the gases as a comparison gas, and supplies the selected gas to the zirconia sensor <NUM>. The span gas is a gas containing <NUM>% oxygen, nitrogen, and the like. Air is mainly used. The zero gas is a gas containing <NUM>% oxygen, nitrogen, and the like. The span gas and zero gas can be used as standard gases with a known oxygen concentration.

The management apparatus <NUM> is an information processing apparatus for managing the maintenance of the zirconia-type oxygen analyzer <NUM>, for example, which is maintained by the manufacturer of the zirconia-type oxygen analyzer <NUM>. The management apparatus <NUM> determines and presents the timing at which maintenance should be performed on the zirconia sensor <NUM> based on the log data file generated by the converter <NUM>. Here, the timing at which maintenance should be performed may include the timing at which the zirconia sensor <NUM> should be calibrated, the timing at which the zirconia sensor <NUM> should be replaced, and the like. The management apparatus <NUM> determines the calibration timing, replacement timing, and the like of the zirconia sensor <NUM> and determines the timing of maintenance based on these timings. Therefore, according to the configuration of the present embodiment, the user can appropriately perform maintenance on the zirconia-type oxygen analyzer by performing maintenance at the presented timing.

<FIG> illustrates an example configuration of the zirconia sensor <NUM> in <FIG>. <FIG> illustrates the measurement principle of the zirconia sensor <NUM> by way of a cross-sectional view. In <FIG>, the zirconia sensor <NUM> includes a zirconia tube <NUM> and electrodes <NUM>, <NUM> provided on the inner and outer periphery thereof. Typically, porous platinum electrodes are used for the electrodes <NUM>, <NUM>. In the zirconia sensor <NUM> with this configuration, the zirconia tube <NUM> is first heated to a high temperature of approximately <NUM>. A comparison gas G2 is then passed outside the tube (comparison gas channel), and a gas to be measured G1 is passed inside the tube (measurement gas channel). Consequently, an electromotive force Vout corresponding to the difference in oxygen concentration between the comparison gas G2 and the gas to be measured G1 is generated between the electrodes <NUM>, <NUM>. This electromotive force Vout is proportional to the logarithm of the oxygen concentration ratio. By using a gas (for example, a span gas) with a known oxygen concentration, such as air, as the comparison gas G2, the oxygen concentration in the gas to be measured G1 can be determined from the magnitude of the electromotive force Vout. Specifically, in the case of the temperature of the zirconia sensor <NUM> being <NUM>, PX is given by Mathematical Formula (<NUM>) below, based on the Nernst equation, where PX is the oxygen partial pressure of the gas to be measured G1 and PA is the oxygen partial pressure of the comparison gas G2.

<FIG> is a block diagram illustrating an example configuration of the converter <NUM> in <FIG>. The converter <NUM> includes a controller <NUM>, a memory <NUM>, a sensor <NUM>, a Human Machine Interface (HMI) <NUM>, an input/output interface <NUM>, and a communication interface <NUM>.

The controller <NUM> includes one or more processors. The "processor" in an embodiment is a general purpose processor, such as a central processing unit (CPU), or a dedicated processor specialized for particular processing, but these examples are not limiting. The controller <NUM> is communicably connected with each component of the converter <NUM> and controls operations of the converter <NUM> overall. The controller <NUM> controls operations of each component of the zirconia-type oxygen analyzer <NUM> according to application programs and data for realizing the functions of the zirconia-type oxygen analyzer <NUM>. For example, the controller <NUM> may measure the oxygen concentration from the magnitude of the electromotive force Vout of the zirconia sensor <NUM>, calculate the calibration coefficient, calculate the internal resistance of the zirconia sensor <NUM>, and/or display the results of the processing on a display of the HMI <NUM>.

The memory <NUM> includes any appropriate storage module, including random access memory (RAM), read-only memory (ROM), a hard disk drive (HDD), and a solid state drive (SSD). The memory <NUM> may, for example, function as a main memory, an auxiliary memory, or a cache memory. The memory <NUM> stores any information used for operations of the converter <NUM> or resulting from operations of the converter <NUM>. For example, the memory <NUM> may store system programs, log data files, various data received from the manufacturer, measurement data measured in the sensor <NUM>, various types of information received by the communication interface <NUM>, and the like. The memory <NUM> is not limited to being built into the converter <NUM>, but may instead be an external database, such as a Secure Digital (SD) card or Universal Serial Bus (USB) memory, or an external storage module.

The sensor <NUM> measures the electromotive force Vout, the internal resistance, and the like of the zirconia sensor <NUM>. The sensor <NUM> is connected to the zirconia sensor <NUM>. The configuration of the sensor <NUM> for measuring the internal resistance of the zirconia sensor <NUM> will be described later. The data measured in the sensor <NUM> is stored in the memory <NUM>.

The HMI <NUM> is a user interface. The HMI <NUM> includes components such as an operation interface that receives user operations and a display that displays the oxygen concentration measured by the zirconia sensor <NUM> and information on maintenance, such as the calibration cycle.

The input/output interface <NUM> is an interface for inputting and outputting data to and from other apparatuses or storage media. For example, the input/output interface <NUM> includes a slot for an SD card, a USB interface, or the like.

The communication interface <NUM> includes any appropriate communication module capable of connecting and communicating with other apparatuses by any appropriate communication technology. The communication interface <NUM> may further include a communication control module for controlling communication with other apparatuses and a storage module for storing communication data, such as identification information, necessary for communicating with other apparatuses. An example in which the communication interface <NUM> is implemented by a wireless local area network (LAN) communication device connectable to the Internet is described below. However, the communication interface <NUM> may, for example, be implemented by a wired LAN or other communication methods, including Bluetooth communication.

<FIG> is a block diagram illustrating an example configuration of the management apparatus <NUM> in <FIG>. The management apparatus <NUM> is one server apparatus or a plurality of communicably connected server apparatuses. Instead of this configuration, the management apparatus <NUM> may be any general purpose electronic device, such as a personal computer (PC), or any other dedicated electronic device. As illustrated in <FIG>, the management apparatus <NUM> includes a controller <NUM>, a memory <NUM>, a communication interface <NUM>, an input interface <NUM>, and an output interface <NUM>.

The controller <NUM> includes one or more processors. The "processor" in an embodiment is a general purpose processor or a dedicated processor specialized for particular processing, but these examples are not limiting. The controller <NUM> is communicably connected with each component of the management apparatus <NUM> and controls operations of the management apparatus <NUM> overall.

The memory <NUM> includes appropriate storage module, including an HDD, SSD, ROM, electrically erasable programmable read-only memory (EEPROM), and/or RAM. The memory <NUM> may, for example, function as a main memory, an auxiliary memory, or a cache memory. The memory <NUM> stores any information used for operations of the management apparatus <NUM> or resulting from operations of the management apparatus <NUM>. For example, the memory <NUM> may store a system program, an application program, various types of information received by the communication interface <NUM>, and the like. The memory <NUM> is not limited to being internal to the management apparatus <NUM> and may be an external database or an external storage module connected through a digital input/output port or the like, such as USB.

The communication interface <NUM> includes any appropriate communication module capable of connecting and communicating with other apparatuses, such as the converter <NUM> of the zirconia-type oxygen analyzer <NUM> or the cloud, by any appropriate communication technology. The communication interface <NUM> may further include a communication control module for controlling communication with other apparatuses and a storage module for storing communication data, such as identification information, necessary for communicating with other apparatuses.

The input interface <NUM> includes one or more input interfaces that receive a user input operation and acquire input information based on the user operation. For example, the input interface <NUM> may be physical keys, capacitive keys, a pointing device, a touch screen integrally provided with a display of the output interface <NUM>, a microphone that receives audio input, or the like, but is not limited to these.

The output interface <NUM> includes one or more output interfaces that output information to the user to notify the user. For example, the output interface <NUM> may be a display that outputs information as images, a speaker that outputs information as sound, or the like, but these examples are not limiting. The input interface <NUM> and/or the output interface <NUM> described above may be formed integrally with the management apparatus <NUM> or be provided separately.

The functions of the management apparatus <NUM> can be implemented by the processor included in the controller <NUM> executing a computer program (program) that can be used to implement the functions of the maintenance system <NUM> according to the present embodiment. That is, the functions of the management apparatus <NUM> can be implemented by software. The program causes a computer to execute the processing of the steps included in the operations of the management apparatus <NUM> to implement the functions corresponding to the processing of the steps. That is, the computer program is a program for causing a computer to function as the management apparatus <NUM> according to the present embodiment.

The computer program can be recorded on a computer-readable recording medium. The computer-readable recording medium is, for example, a magnetic recording apparatus, an optical disc, a magneto-optical recording medium, or a semiconductor memory. The program can, for example, be distributed by the sale, transfer, or lending of a portable recording medium such as a digital versatile disk (DVD) or a compact disk read only memory (CD-ROM) on which the program is recorded. The program may be distributed by being stored on a storage of a server and transferred from the server to another computer over a network. The program may be provided as a program product.

For example, the computer can temporarily store, in the main memory, the program recorded on the portable recording medium or transferred from the server. The computer uses a processor to read the program stored in the main memory and executes processing with the processor in accordance with the read program. The computer may read the program directly from the portable recording medium and execute processing in accordance with the program. Each time the program is transferred from the server to the computer, the computer may sequentially execute processing in accordance with the received program. Such processing may be executed by an application service provider (ASP) type of service that implements functions only via execution instructions and result acquisition, without transferring the program from the server to the computer. Examples of the program include an equivalent to the program represented as information provided for processing by an electronic computer. For example, data that is not a direct command for a computer but that has the property of specifying processing by the computer corresponds to the "equivalent to the program".

A portion or all of the functions of the management apparatus <NUM> may be implemented by a dedicated circuit included in the controller <NUM>. In other words, a portion or all of the functions of the management apparatus <NUM> may be implemented by hardware. Furthermore, the management apparatus <NUM> may be implemented by a single information processing apparatus or implemented by cooperation between a plurality of information processing apparatuses.

<FIG> is a diagram illustrating the maintenance flow of the zirconia-type oxygen analyzer <NUM> according to an embodiment of the present disclosure. The operations of the zirconia-type oxygen analyzer <NUM> and the management apparatus <NUM> described with reference to <FIG> correspond to the maintenance method of the present embodiment. In the present embodiment, when the manufacturer delivers the equipment for the zirconia-type oxygen analyzer <NUM> (S1), the user starts operating the equipment (S2).

After the start of operation, the zirconia-type oxygen analyzer <NUM> according to the present embodiment performs a constant deterioration diagnosis on the zirconia sensor <NUM> and the like (S3). The constant deterioration diagnosis is a process for the controller <NUM> of the converter <NUM> to automatically measure the internal resistance present in the zirconia sensor <NUM> at a predetermined timing and store the measured internal resistance in the memory <NUM>. As described below, it is known that the internal resistance of the zirconia sensor <NUM> increases as the zirconia sensor <NUM> is used. By storing such internal resistance in the memory <NUM> as a log data file, the zirconia-type oxygen analyzer <NUM> can analyze the changes in internal resistance to appropriately determine the timing and content of maintenance that should be performed.

After the start of operation, the user calibrates the zirconia sensor <NUM> periodically (S4). During the calibration of the zirconia sensor <NUM>, the controller <NUM> of the converter <NUM> measures a physical quantity (such as electromotive force) of a standard gas with known oxygen concentration using the zirconia sensor <NUM>. The controller <NUM> calculates, based on the measured physical quantity and the known oxygen concentration, calibration coefficients for correcting a conversion formula for converting the measured value of the physical quantity measured by the zirconia sensor <NUM> into the oxygen concentration of the gas to be measured. The controller <NUM> then stores the calculated calibration coefficients in the memory <NUM>. As described below, it is known that these calibration coefficients change as the zirconia sensor <NUM> is used. The zirconia-type oxygen analyzer <NUM> stores the calibration coefficients used in each such calibration in the memory <NUM> as a log data file. The changes in the calibration coefficients can thus be analyzed to appropriately determine the timing and content of maintenance that should be performed based on the variation range and rate of change of the calibration coefficients.

To appropriately determine the timing and content of maintenance that should be performed, the controller <NUM> of the converter <NUM> may also store information such as the calibration cycle and process measurement values, in addition to the calibration coefficients and constant deterioration diagnosis information, in the memory <NUM> as the log data file. The calibration cycle is the time interval of the calibration of the zirconia sensor <NUM> performed by the user. The process measurement values are the measured values of the electromotive force Vout, measured by the zirconia sensor <NUM> during the operation of the zirconia-type oxygen analyzer <NUM>, and data illustrating the transition of the oxygen concentration calculated from the electromotive force Vout. Such log data files are extracted to an external destination using a recording medium, such as an SD card or USB memory. The user loads the log data file onto an information processing apparatus that can be connected to the Internet, such as a PC, tablet, or smartphone, and transmits the log data file to the manufacturer through a website or the like provided by the manufacturer (S5).

The manufacturer analyzes the log data file received from the user (S6) and proposes a recommended calibration cycle, sensor replacement cycle, and the like to the user (S7). Details of the analysis of the log data file are described below. The user calibrates the zirconia sensor <NUM> according to the recommended calibration cycle proposed by the manufacturer and orders a replacement zirconia sensor <NUM> according to the sensor replacement cycle (S8). Upon delivery of the zirconia sensor <NUM> (S9), the user installs the zirconia sensor <NUM> and starts operation of the zirconia-type oxygen analyzer (S10).

In this way, in the maintenance system <NUM> according to the present embodiment, the zirconia-type oxygen analyzer <NUM> performs constant deterioration diagnosis of the zirconia sensor <NUM> and the like and records information, such as calibration coefficients, information on constant deterioration diagnosis, the calibration cycle, and process measurement values, as a log data file. The manufacturer's management apparatus <NUM> then proposes a recommended calibration cycle, a sensor replacement cycle, and the like to the user based on this information. Therefore, according to the configuration of the present embodiment, the timing and content of maintenance on the zirconia-type oxygen analyzer <NUM> can be appropriately determined and implemented.

The calibration of the zirconia-type oxygen analyzer <NUM> is performed by measuring the electromotive force Vout using the gas to be measured G1 as a span gas or zero gas and the comparison gas G2 as a span gas. The span gas and zero gas are used as standard gases with a known oxygen concentration. In other words, when the gas to be measured G1 is used as a span gas, the converter <NUM> is calibrated (span calibration) against the sensor output corresponding to the oxygen concentration of the span gas. When the gas to be measured G1 is used as a zero gas, the converter <NUM> is calibrated (zero calibration) against the sensor output corresponding to the oxygen concentration of the zero gas.

<FIG> is a diagram illustrating calculation of a calibration coefficient for the zirconia-type oxygen analyzer. In <FIG>, the vertical axis represents the electromotive force (cell electromotive force) Vout [mV] of the zirconia sensor <NUM>. The horizontal axis represents the oxygen concentration [vol%] of the gas to be measured G1. The horizontal axis is indicated by a logarithmic scale.

In <FIG>, the corrected calibration curve indicates the theoretical calibration curve corresponding to the straight line obtained by Mathematical Formula (<NUM>) below, which is a variation of Mathematical Formula (<NUM>).

Here, the oxygen partial pressure PX of the gas to be measured G1 and the oxygen partial pressure PA of the comparison gas G2 correspond to the oxygen concentration of the gas to be measured G1 and the oxygen concentration of the comparison gas G2. The mathematical formula corresponding to the theoretical calibration curve may be used as a conversion formula for converting the measured value of a physical quantity (such as the cell electromotive force Vout) measured by the zirconia sensor <NUM> into the oxygen concentration of the gas to be measured.

As illustrated in <FIG>, in a case in which the oxygen concentration values are expressed on a logarithmic scale, the corrected calibration curve is a straight line passing through the points (<NUM> [vol%], <NUM> [mV]) and (<NUM> [vol%], <NUM> [mV]), which represent (oxygen concentration [vol%], cell electromotive force [mV]). The theoretical value of the cell electromotive force (<NUM> [mV]) when the gas concentration of the gas to be measured is a zero gas concentration (<NUM> [vol%]) is referred to as the zero base point, and the theoretical value of the cell electromotive force (<NUM> [mV]) when the gas concentration is a span gas concentration (<NUM> [vol%]) is referred to as the span base point.

The pre-correction calibration curve illustrates the characteristics of the cell electromotive force of the deteriorated zirconia sensor <NUM>. In <FIG>, the deteriorated zirconia sensor <NUM> exhibits a cell electromotive force es [mV] when the oxygen concentration of the gas to be measured G1 is the span gas concentration (<NUM> [vol%]) and exhibits a cell electromotive force ez [mV] when the oxygen concentration is the zero gas concentration (<NUM> [vol%]). In the example in <FIG>, a larger cell electromotive force e1 [mV] than the theoretical value is observed when the oxygen concentration of the gas to be measured is p1 [vol%]. Therefore, if the oxygen concentration is calculated using the theoretical calibration curve based on the measured cell electromotive force, the calculated oxygen concentration will deviate from the actual oxygen concentration.

The zirconia-type oxygen analyzer <NUM> according to the present embodiment corrects and calibrates the oxygen concentration of the gas to be measured based on the deviation of the pre-correction calibration curve from the zero base point and the span base point. In other words, the zirconia-type oxygen analyzer <NUM> corrects the pre-correction calibration curve to the corrected calibration curve based on the measured value of a physical quantity (such as cell electromotive force) measured by the zirconia sensor <NUM> for the zero gas and span gas as standard gases. The ratio, expressed as a percentage, of a difference (B) between the cell electromotive force (ez) for the zero gas concentration and the cell electromotive force (es) for the span gas concentration in the pre-correction calibration curve to a difference (A) between the zero base point and the span base point in the theoretical calibration curve is referred to as the zero point correction factor. The ratio, expressed as a percentage, of the cell electromotive force (C) for the span gas concentration in the pre-correction calibration curve to the difference (A) between the zero base point and the span base point in the theoretical calibration curve is referred to as the span point correction factor. Here, A = <NUM> [mV], B = ez - es [mV], and C = es [mV]. In other words, the zero point correction factor and the span point correction factor are indicated by Mathematical Formulas (<NUM>) below.

The zirconia-type oxygen analyzer <NUM> according to the present embodiment calculates the aforementioned zero point correction factor and span point correction factor as calibration coefficients. The zirconia-type oxygen analyzer <NUM> calculates the oxygen concentration y [vol%] of the gas to be measured from the measured cell electromotive force E [mV] by the following Mathematical Formula (<NUM>), using the above-described zero point correction factor and span point correction factor.

Here, Kz = zero point correction factor/<NUM>, and Ks = span point correction factor × <NUM>/<NUM>. Kz is referred to as the zero point correction coefficient, and Ks is referred to as the span point correction coefficient. The zero point correction coefficient and the span point correction coefficient can also be used as calibration coefficients.

In the zirconia sensor <NUM> that operates according to theory, the zero point correction factor is <NUM>%, and the span point correction factor is <NUM>%. As the zero point and span point correction factors move away from these theoretical values, the zirconia sensor <NUM> deteriorates and becomes difficult to calibrate. In the present embodiment, a threshold is set in advance for the difference from the theoretical values of the correctable zero point correction factor and span point correction factor, and when the zero point correction factor or span point correction factor differs from the theoretical value by more than the threshold, it may be determined that the zirconia sensor <NUM> needs to be replaced. For example, the threshold for the zero point correction factor may be <NUM>%. In this case, the correctable range for the zero point correction factor is <NUM>% to <NUM>%. For example, the threshold for the span point correction factor may be <NUM>%. In this case, the correctable range for the span point correction factor is <NUM>% to <NUM>%.

As the zirconia sensor <NUM> deteriorates due to use, the difference between the calibration coefficients, such as the aforementioned zero point correction factor and span point correction factor, and theoretical values thereof increases. It is known that the difference between the calibration coefficients and their theoretical values increases over time in the form of a quadratic curve. Therefore, the management apparatus <NUM> that receives the log data file including the calibration coefficients may approximate the change over time in a calibration coefficient by a quadratic curve. The management apparatus <NUM> may then determine the timing at which the variation range of the calibration coefficient, estimated based on the quadratic curve for the change over time in the calibration coefficient, reaches the upper limit of a predetermined variation range as the timing at which the zirconia sensor <NUM> should be replaced. For example, the upper limit of the variation range of the zero point correction factor may be <NUM>%. The upper limit of the variation range of the span point correction factor may be <NUM>%. The management apparatus <NUM> may determine the timing at which the rate of change of the calibration coefficient, estimated based on the quadratic curve for the change over time in the calibration coefficient, reaches the upper limit of a predetermined rate of change as the timing at which the zirconia sensor <NUM> should be calibrated. For example, the upper limit of the rate of change of the zero point correction factor and the span point correction factor may be a value between <NUM>% and <NUM>% (for example, <NUM>%). In this way, the management apparatus <NUM> approximates the change over time in the calibration coefficient by a quadratic curve to estimate the timing at which the zirconia sensor <NUM> should be replaced or calibrated. The timing and content of required maintenance can thereby be appropriately determined and presented to the user. In the determination of the timing and content of maintenance based on the change over time in the calibration coefficients, the change over time in the calibration coefficients can be estimated more accurately by use of the log data file after calibration has been performed three or more times.

The zirconia-type oxygen analyzer <NUM> determines a coefficient for correcting the conversion formula as the calibration coefficient based on first and second measured values, which are measured values of the physical quantity measured by the zirconia sensor <NUM> for first and second standard gases having known oxygen concentrations, and stores the determined calibration coefficient in the memory <NUM>. Such first and second standard gases may, for example, be the above-described zero gas and span gas. In this way, the zirconia-type oxygen analyzer <NUM> determines the calibration coefficient based on the measured value of the physical quantity measured by the zirconia sensor <NUM> for two standard gases with different concentrations, and the timing at which maintenance should be performed is determined based on such a calibration coefficient. According to the configuration of the present embodiment, the timing of required maintenance can thus be appropriately determined and presented.

<FIG> is a schematic diagram illustrating the electrical connection between the zirconia sensor <NUM> and the converter <NUM> of <FIG>. Several items are used to evaluate the soundness of the zirconia sensor <NUM>. One such item is the internal resistance of the zirconia sensor <NUM>. The internal resistance of a good zirconia sensor <NUM> is low, usually <NUM>Ω or less. However, the internal resistance of the zirconia sensor <NUM> tends to increase when the sensor characteristics deteriorate due to various factors such as dirt on the sensor electrodes, cracks, or changes in sensor properties upon continued use in an actual gas. The internal resistance of a deteriorated zirconia sensor <NUM> is generally several thousand Ω or higher. Therefore, the zirconia-type oxygen analyzer <NUM> according to the present embodiment may perform a self-diagnosis of the internal resistance periodically (for example, once a week or month) to confirm the soundness of the zirconia sensor <NUM>.

Here, with reference to <FIG>, a resistor shunt method is described as an example of a method for measuring internal resistance. <FIG> illustrates an excerpt of only the parts of <FIG> that are related to the sensor signals of the zirconia sensor <NUM> and the converter <NUM>. In <FIG>, an equivalent circuit of the zirconia sensor <NUM> is represented by an internal resistor <NUM> and a voltage source <NUM>, which are connected in series with each other. The voltage source <NUM> is an equivalent circuit that outputs the electromotive force Vout of the zirconia sensor <NUM>. The two terminals <NUM>, <NUM> of the internal resistor <NUM> and the voltage source <NUM>, which are connected in series with each other, are connected via the power cable <NUM> to a measurement circuit <NUM> of the sensor <NUM> provided in the converter <NUM>. As illustrated in <FIG>, the internal resistor <NUM> and voltage source <NUM>, which are connected in series with each other, are connected in parallel with a shunt resistor <NUM> and a switch <NUM>, which are connected in series with each other in the converter <NUM>. The shunt resistor <NUM> and the switch <NUM> are also included in the sensor <NUM>. The measurement circuit <NUM> switches the switch <NUM> on and off, and based on the change in the electromotive force Vout of the voltage source <NUM> observed between when the shunt resistor <NUM> is and is not connected electrically to the internal resistor <NUM> and the voltage source <NUM>, the measurement circuit <NUM> calculates the resistance of the internal resistor <NUM>.

For such measurement to be performed, the electromotive force Vout of the voltage source <NUM> needs to be at a measurable level. However, since a span gas with the same composition as air, for example, is used as the comparison gas G2, the electromotive force Vout of the voltage source <NUM> may be <NUM> mV, or a low level near <NUM> mV, in the case in which the gas to be measured G1 is an actual gas. In such a case, it is difficult to calculate the resistance of the internal resistor <NUM> by the resistor shunt method. The electromotive force Vout of the zirconia sensor <NUM> is maximized when a zero gas is used as the gas to be measured G1. Hence, in the case of using the resistor shunt method, the gas to be measured G1 is typically a zero gas. The following Mathematical Formula (<NUM>) holds, where the internal resistance of the zirconia sensor <NUM> is Rcell, the electromotive force of the zirconia sensor <NUM> is Vzero when a zero gas is used as the measurement gas G1, the resistance of the shunt resistor <NUM> is Rs, and the voltage between the terminals <NUM>, <NUM> is Vcell when the switch <NUM> is ON and the shunt resistor <NUM> is connected in parallel with the internal resistor <NUM> and the voltage source <NUM>.

Based on the above-described principle, the zirconia-type oxygen analyzer <NUM> according to the present embodiment may measure the internal resistance Rcell of the zirconia sensor <NUM> at a predetermined timing and store the measured value in the memory <NUM>. The method of measuring the internal resistance of the zirconia sensor <NUM> is not limited to the resistor shunt method, and other methods may be used. As described above, the value of the internal resistance Rcell of the zirconia sensor <NUM> may be transmitted to the management apparatus <NUM> as a log data file and used by the management apparatus <NUM> to estimate the sensor replacement cycle or the like.

As the zirconia sensor <NUM> deteriorates with use, the internal resistance of the zirconia sensor <NUM> increases. It is known that the internal resistance increases over time in the form of a quadratic curve. Therefore, the management apparatus <NUM> that receives the log data file including the internal resistance may approximate the change over time in the internal resistance by a quadratic curve. The management apparatus <NUM> may then determine the timing at which the internal resistance, estimated based on the quadratic curve for the change over time in the internal resistance, reaches the upper limit of a predetermined internal resistance as the timing at which maintenance should be performed on the zirconia sensor <NUM>. In this way, the management apparatus <NUM> approximates the change over time in the internal resistance by a quadratic curve to estimate the timing at which maintenance should be performed on the zirconia sensor <NUM>. The timing of required maintenance can thereby be appropriately determined and presented to the user.

<FIG> is a diagram illustrating estimation of the replacement timing of the zirconia sensor <NUM>. The horizontal axis in <FIG> represents time. The vertical axis represents the internal resistance (sensor resistance) [Ω] of the zirconia sensor <NUM>. In <FIG>, the black circle plot indicates the actual measured values (log data) of the internal resistance Rcell of the zirconia sensor <NUM>. The dotted curve is an approximate curve of the actual measured values of the internal resistance Rcell. In <FIG>, the approximate curve is illustrated by a quadratic curve. In the example of <FIG>, <NUM>Ω is set as the upper limit of the internal resistance, and maintenance such as replacement of the zirconia sensor <NUM> is recommended at a recommended replacement timing at which the internal resistance is predicted to reach <NUM>Ω. The period from the start of use of the zirconia sensor <NUM> to the recommended replacement timing corresponds to the time cycle over which replacement of the sensor is recommended. Based on the change over time in the internal resistance, the management apparatus <NUM> can thus calculate and present to the user the recommended replacement timing and recommended replacement cycle of the zirconia sensor <NUM>.

As described above, the maintenance system <NUM> according to the present embodiment includes the zirconia-type oxygen analyzer <NUM> that uses the zirconia sensor <NUM> to measure the oxygen concentration of a gas to be measured, and the management apparatus <NUM>. The zirconia-type oxygen analyzer <NUM> stores, in the memory <NUM>, the internal resistance of the zirconia sensor <NUM> and/or a calibration coefficient for correcting, based on the measured value of the physical quantity measured by the zirconia sensor <NUM> for a standard gas, a conversion formula for converting a measured value of a physical quantity measured by the zirconia sensor <NUM> into the oxygen concentration of the gas to be measured. The management apparatus <NUM> determines and presents the timing at which maintenance should be performed on the zirconia sensor <NUM> based on the change over time in the internal resistance and/or the correction coefficient stored in the memory <NUM>. The timing at which maintenance should be performed on the zirconia sensor, as determined based on the internal resistance and/or the calibration coefficient, is thus presented so that the user can appropriately perform maintenance on the zirconia-type oxygen analyzer by performing the maintenance at the presented timing.

In a conventional configuration, the user and the manufacturer need to share detailed information in order to know the status of calibration by the user, the degree of deterioration of the zirconia sensor <NUM>, and the like. In contrast, according to the configuration of the present embodiment, the usage status of the zirconia-type oxygen analyzer <NUM> by the user can easily be recognized simply by transmission of the log data file. Also, according to the configuration of the present embodiment, the manufacturer can propose an appropriate calibration cycle, sensor replacement timing, and the like to the user by receiving and analyzing the log data file. Therefore, maintenance on the zirconia-type oxygen analyzer <NUM> can be optimized on the user's side. Furthermore, according to the configuration of the present embodiment, a history of calibration, changes in internal resistance, and the like of the zirconia-type oxygen analyzer <NUM> can be obtained as a log data file. This enables data analysis to be performed with high accuracy and maintenance to be performed appropriately. According to the configuration of the present embodiment, the appropriate calibration cycle, sensor replacement timing, and the like can also be set regardless of the user's knowledge or skill regarding the behavior of the zirconia sensor <NUM>. It is therefore possible to reduce labor and costs due to excessive calibration and replacement of the zirconia sensor <NUM> and to avoid problems such as defective measurement values due to a delay in calibration timing and equipment suspension due to a delay in replacement of the zirconia sensor <NUM>.

In the example described in the first embodiment, the log data file is extracted to an external destination using a recording medium, such as an SD card. The user loads the log data file onto an information processing apparatus, such as a PC, and transmits the log data file to the manufacturer through a website or the like. However, such extraction and transmission of the log data file may be automated so that the timing of calibration, replacement of the zirconia sensor <NUM>, and the like can be presented automatically, without the user having to perform the steps for extraction and transmission.

<FIG> illustrates the details of the maintenance flow of a zirconia-type oxygen analyzer in which such extraction and transmission of the log data file is not automated. During configuration of the zirconia-type oxygen analyzer <NUM> (S11), the user operates the HMI <NUM> to perform an operation to output the log data file (S12). The user extracts the log data file (S13) and stores the log data in a storage medium, such as an SD card (S14). The user loads the log data file onto an information processing apparatus that can be connected to the Internet, such as a PC, and transmits the log data file to the manufacturer through a website or the like provided by the manufacturer (S15).

Upon receiving the log data file (S16), the manufacturer analyzes the log data file (S17), checks the analysis results (S18), and transmits the analysis results to the user (S19). The analysis results can be transmitted electronically by e-mail or other means via the Internet, or can be sent by mail or the like. Upon receiving the analysis results (S20), the user reflects the results in the maintenance plan for the zirconia-type oxygen analyzer <NUM> (S21).

Work thus needs to be done manually if maintenance of the zirconia-type oxygen analyzer <NUM> is not automated. In contrast, the amount of labor can be reduced by automation of the maintenance of the zirconia-type oxygen analyzer <NUM>.

<FIG> illustrates an automated maintenance flow of the zirconia-type oxygen analyzer <NUM>. The operations of the zirconia-type oxygen analyzer <NUM> and the management apparatus <NUM> described with reference to <FIG> correspond to the maintenance method of the present embodiment.

In <FIG>, when the user performs calibration work (S31), the controller <NUM> of the converter <NUM> automatically outputs a log data file (S32) and transmits the log data file to the management apparatus <NUM> managed by the manufacturer (S33). The log data file is transmitted by the communication interface <NUM>, such as a wireless LAN connected to the Internet, based on control by the controller <NUM>.

Upon receiving the log data file (S34), the controller <NUM> of the management apparatus <NUM> analyzes the log data file (S35). The controller <NUM> may analyze the log data file by, for example, controlling the management apparatus <NUM> in accordance with a predetermined program for analyzing the log data file, as described in the first embodiment. The analysis results may include a recommended maintenance plan (timing, content, and the like of maintenance). After the analysis, the controller <NUM> transmits the analysis results to the converter <NUM> managed by the user (S36). The analysis results are transmitted by the communication interface <NUM> based on control by the controller <NUM>.

Upon receiving the analysis results of the log data file (S37), the controller <NUM> of the converter <NUM> displays the content of the recommended maintenance plan on the HMI <NUM> of the converter <NUM> (S38). The user reflects the displayed maintenance plan in the maintenance of the zirconia-type oxygen analyzer <NUM> (S39).

In this way, the amount of manual work can be reduced by automating the tasks of extracting log data and transmitting the log data to the manufacturer, along with automatically informing the user of the timing of calibration, replacement of the zirconia sensor <NUM>, and the like. The amount of labor can thus be reduced, and human error can also be prevented.

Claim 1:
A maintenance method for a zirconia-type oxygen analyzer that uses a zirconia sensor to measure an oxygen concentration of a gas to be measured, the maintenance method comprising:
storing in a memory, by the zirconia-type oxygen analyzer, an internal resistance present in the zirconia sensor;
determining, by an information processing apparatus, a timing at which maintenance should be performed on the zirconia sensor based on a change over time in the internal resistance stored in the memory; and
presenting, by the information processing apparatus, the timing at which maintenance should be performed on the zirconia sensor.