Patent Application
20140025318
The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2012-159329, filed Jul. 18, 2012, which is incorporated herein by reference in its entirety.
The present invention relates to a pressure guiding tube blockage diagnosing device and blockage diagnosing method, for diagnosing a blockage in a pressure guiding tube for guiding, to a pressure detecting portion, a pressure to be measured, wherein there are fluctuations in the pressure.
Conventionally, in the process industry field, pressure transmitting devices and differential pressure transmitting devices have been used in order to control processes by detecting, for example, the amounts of variations in processes. Pressure transmitting devices are also known as pressure forwarding devices, and differential pressure transmitting devices are also known as differential pressure forwarding devices. A pressure transmitting device measures an absolute pressure or a gauge pressure, and a differential pressure transmitting device measures a pressure difference between two points, and they are used to measure variable quantities in processes such as pressure, flow rate, fluid level, specific gravity, and so forth. Typically when a process variable quantity is measured using a pressure or differential pressure transmitting device (hereinafter termed simply a “transmitting device” when referred to in general), the pressure to be measured is guided to the transmitting device (the pressure detecting portion) through a thin tube, known as the pressure guiding tube, from the process tube in which is flowing a fluid that is to be measured.
In this type of device structure, blockages in the pressure guiding tubes may result from the adherence, to the interior of the pressure guiding tubes, of solid objects, or the like, by that which is being measured. If a pressure guiding tube becomes completely blocked, then it becomes impossible to measure the process variable quantities accurately, which can have a serious impact on the plant. However, because pressure is still transmitted to the transmitting device up until the point wherein the pressure guiding tube becomes completely blocked, the impact of the blockage tends to not appear in the process variable quantity measurement values.
Remote seal-type pressure transmitting devices wherein pressure guiding tubes are not required have been developed in response to this type of problem. However, an extremely large number of plants measure process variable quantities using pressure guiding tubes, and thus there is the need to be able to perform pressure guiding tube blockage diagnostic functions on-line.
In response to this problem, there have already been proposals for methods and devices for diagnosing blockages in pressure guiding tubes using pressure fluctuations in the fluid.
For example, the ability to detect a blockage in a pressure guiding tube from a reduction in the maximum fluctuation amplitude (the difference between the maximum value and the minimum value) of a pressure signal is shown in Japanese Examined Patent Application Publication H7-11473 (“the JP '473”). Devices and methods for detecting and diagnosing blockages in pressure guiding tubes using the magnitudes of fluctuations in pressure or differential pressure, and using parameters calculated therefrom, are described in Japanese Patent 3139597 (“the JP '597”) and Japanese Patent 3129121 (“the JP '121”).
A device and a method for diagnosing the state of a pressure guiding tube from a statistical quantity or a function that reflects the magnitude of the fluctuations, that being the standard deviation or the power spectrum density of the fluctuations, derived from a differential pressure, are described in Japanese Unexamined Patent Application Publication 2002-538420 (“the JP '420”).
A device and method for diagnosing a blockage from the speed of fluctuations, such as the rising/falling frequency of the pressure fluctuations, are shown in Japanese Unexamined Patent Application Publication 2010-127893 (“the JP '893”). Note that the invention described in the JP '893, although differing from the inventions described in the above-noted JP '473, the JP '597, the JP '121 and the JP '420” in the point in that it is based on the speed (frequency) of the fluctuations rather than the amplitudes of the fluctuations in pressure or differential pressure, shares the point that it uses fluctuations in pressure or differential pressure.
However, in most of these conventional devices and methods for detecting blockages in pressure guiding tubes from fluctuations in pressure, there is a problem in that there is a certain amount of time lag produced between the occurrence of the blockage and the detection thereof. This time lag results from factors such as described below.
Many of the devices and methods for diagnosing blockages in pressure guiding tubes use fluctuations in pressure of a fluid. Because properties of a fluid (pressure or differential pressure) that are irregular signals are used as the data underlying the diagnostics, the “feature quantities (feature quantities indicating the state of fluctuation of the pressure)” that are produced by the pressure fluctuations (for example, the rising/falling frequency of the pressure fluctuations, first-order difference fluctuations (fluctuations calculated from the measured value the previous time Dp(i−1) and the measured value the current time Dp(i), that is Dp(i)−Dp(i−1)), or second-order difference fluctuations (the backward differences after the first-order difference fluctuations, that is, fluctuations calculated from the measured values the time before last, Dp(i−2), the measured values the previous time, Dp(i−1), and the measured values the current time, Dp(i), namely, Dp(i)−2Dp(i−1)+Dp(i−2)), and the like include variability other than that which is caused by a blockage. Because of this, the feature quantities are difficult to use as-is in diagnostics.
Given this, an “indicator value” (an indicator value indicating the state of blockage of the pressure guiding tube) calculated from the feature quantities over a specific time interval (for example, a moving average, over a specific interval, of the rising/falling frequency, the root mean square, over a specific interval, of a first-order difference fluctuation, the root mean square, over a specific interval, of a second-order difference fluctuation, or the like) is used in diagnostics.
If the time interval for calculating the indicator value is long, then the diagnostics will be accurate because of the ability to suppress variability in the indicator value. On the other hand, if time interval for calculating the indicator value is long, the time until the effects of a blockage will be reflected in the indicator value will be long. As a result, when attempts are made to secure some degree of accuracy in the diagnostics, some amount of time will be required until the effects of the blockage are reflected in the indicator value. Consequently, there is a given time lag between the occurrence of a blockage and the detection of the blockage.
If, at this time, the blockage progresses gradually enough then the time lag from the occurrence of the blockage to the detection of the blockage will be of a magnitude that can be ignored, so there will be no problem. However, if the blockage progresses rapidly, then the time lag from the occurrence of the blockage to the detection of the blockage will be of a magnitude that cannot be ignored.
The present invention was created in order to solve such a problem, and an aspect thereof is to provide a pressure guiding tube blockage diagnosing device and blockage diagnosing method able to reduce the time lag between the occurrence of a blockage and the detection of the blockage when a blockage progresses rapidly.
In order to achieve such an aspect, the present invention provides a pressure guiding tube blockage diagnosing device for diagnosing a blockage in a pressure guiding tube for guiding, to a pressure detecting portion, a pressure to be measured, wherein there are fluctuations in the pressure. The pressure guiding tube blockage diagnosing device includes a receiving portion that receives pressure data from the pressure detecting portion, a feature quantity calculating portion that partitions a time series of pressure data, received by the receiving portion, into a plurality of intervals, and calculates, for each interval, a feature quantity indicating the state of fluctuation of the pressure, a change rate calculating portion that performs, for each interval, a smoothing process on the feature quantities over a specific time interval up to that interval, and calculates, from the feature quantities that have been subjected to the smoothing process, a change rate, for each interval, indicating the change of state of blockage of the pressure guiding tube therein, and an evaluating portion that evaluates the state of blockage of the pressure guiding tube based on the change rate calculated by the change rate calculating portion.
In order to reduce the time lag between the occurrence of a blockage and the detection of the blockage, occurring when the blockage progresses rapidly, the present invention focuses on the change rate of the indicator value that indicates the state of blockage of the pressure guiding tube. The circumstances leading up to this focus on the change rate of the indicator value are as described below. When a blockage progresses, the indicator value changes toward an abnormal range from a normal range. At this time, if the type of progress of the blockage is sudden, then even though there will be the time lag described above, the indicator value will change over a relatively short period of time. Changing over a short period of time means that even a change that would have a small difference when the indicator value is viewed would have a change rate that is a large value of a degree not normally seen. Moreover, often the point in time at which the change rate becomes large is a point in time that is prior to the indicator value reaching the abnormal range. The result is the understanding that it is possible to detect a rapidly progressing blockage more quickly through detecting a change rate having a larger value than normal in the indicator value than through detecting the indicator value going into the abnormal range.
Moreover, it struck the inventors that, rather than simply calculating the change rate of the indicator value, it would be effective to use a smoothing process, such as a moving average process or the least-squares method, to calculate the change rate after smoothing the indicator value over a given time width. The reasons why it is necessary to calculate the change rate after smoothing are the following. When calculating the change rate, there would be a problem in that the change rate that occurs only because of the blockage could not be calculated well by merely taking a simple difference (a forward difference or a backward difference). The reason for this is that variability in the data that is caused by dealing with a fluid (an irregular signal) is included in the indicator values. Even if the variability in the indicator values is low, when a difference (a forward difference or a backward difference) is simply calculated from the indicator value, often the variability in the difference will be appear larger than the difference in the indicator value.
As an example by which to explain the variability becoming large when taking a difference, let us consider data wherein the values in the range between −0.5 and 0.5, as illustrated in
Calculating the change rate after smoothing makes it possible to take only the change in the indicator value that is due to the effect of the blockage in the pressure guiding tube, which is what is actually of interest, while eliminating the variability from an indicator value that has variability. In addition to focusing on the change rate of the indicator value, the ability to skillfully take only the change due to blockage of the pressure guiding tube from the change rate of the indicator value makes it possible to reduce the lag time between the occurrence of a blockage until the discovery of the blockage when the blockage progresses rapidly.
The present invention is based on such an understanding, and effects identical to those of diagnostics through the change rate in the indicator value, described above, are obtained through the change rate calculated directly from the feature quantities, without passing through the indicator values. The reason for this is as follows. An indicator value is calculated through performing a filtering process, such as a moving average or an average sum of squares. Further calculating a change rate through performing a filtering process on the indicator values that are thus obtained ultimately applies two filters. Here often processes that are performed by these two filters can be combined into a single equivalent filtering process. For example, performing a moving average process twice can be replaced with performing once an equivalent weighted moving average. This equivalent weighted moving average can be performed to calculate the change rate directly from the feature quantities, without passing through the indicator values. Even if not combined into a single equivalent filter, it is often possible to think of a filter that produces essentially equivalent effects. For example, when one considers the linear slope that is obtained through the application of the least-squares method after applying a moving average to the data and a linear slope calculated through the application of the least-squares method to the original data, the two slopes that are produced will not be exactly the same, but in the point that a change rate of the original data is calculated by either process, the meanings of the results obtained are essentially identical, and, in practice, essentially identical values are obtained, despite there being a slight difference.
As a result, even if there is variability in the feature quantity, it is possible to reduce the time lag from the occurrence of a blockage until the discovery of a blockage, when the blockage is progressing rapidly, through calculating a change rate where in there is relatively little variability, even from feature quantities over a shorter time interval.
Note that in the present invention devices and means for detecting pressures and differential pressures, such as differential pressure transmitters and pressure transmitters, are termed, in general, “pressure detecting portions,” where the pressure data from a pressure detecting portion is defined as including differential pressure data. That is, if a pressure detecting portion detects a differential pressure, “pressure data” means a differential pressure between two points, where if the pressure detecting portion is that which detects pressure, “pressure data” means either an absolute pressure or a gauge pressure. In the present invention, not just absolute pressure or gauge pressure, but differential pressure as well, are included in “pressure data.”
Moreover, the present invention provides not only a pressure guiding tube blockage diagnosing device, but also provides a pressure guiding tube blockage diagnosing method.
Given the present invention, the time series of the pressure data received from the receiving portion is partitioned into a plurality of intervals, a feature quantity indicating the state of fluctuation of the pressure is calculated for each interval, a smoothing process for smoothing the feature quantities over a specific time interval up until that interval is performed for each individual interval, a change rate indicating a change in the state of blockage of the pressure guiding tube is calculated for each interval from the feature quantities on which the smoothing process has been performed, and the state of blockage of the pressure guiding tube is evaluated based on the calculated change rate, and thus only the change in the indicator value due to the effect of blockage of the pressure guiding tube, which is the actual interest, is taken, making it possible to reduce the time lag from the occurrence of a blockage to the detection of the blockage when a blockage progresses suddenly.
Examples of the present invention will be explained in detail below based on the drawings.
The receiving portion 6 receives differential pressure data from the differential pressure transmitting device 5. The differential pressure data from the differential pressure transmitting device 5 corresponds to the pressure data from the pressure detecting portion as stated in the present invention. The feature quantity calculating portion 7 partitions the time series differential pressure data, received by the receiving portion 6, into a plurality of intervals and calculates, for each interval, a feature quantity indicating the state of fluctuation of the pressure therein. In the present example, the rising/falling frequencies of the fluctuations are calculated as the feature quantities. The method for calculating the rising/falling frequencies of the fluctuations is set forth as a specific method in the JP '893, already proposed by the present applicant, and thus the detailed explanation thereof is omitted here.
The change rate calculating portion 8 obtains the feature quantities calculated by the feature quantity calculating portion 7, performs, for each individual interval, a smoothing process on the feature quantities for a given time interval up until that interval, and calculates, from the feature quantities on which the smoothing process has been performed, a change rate that indicates a change in the state of blockage of the pressure guiding tubes for the individual intervals.
The “change rate” calculated by the change rate calculating portion 8 is not a simple change rate obtained from a difference in feature quantities (a forward difference, a backward difference, or the like), but rather is a change rate calculated by performing a smoothing process on “feature quantities” over a specific time interval (a specific number of samples or a specific interval). In the present example, the change rate calculating portion 8 calculates the change rate, as Zk, through Equation (1), below, from the feature quantities from the feature quantity calculating portion 7. This change rate Zk is a backward difference of triangular moving averages (wherein the moving average is applied twice) of the feature quantities.
where n1 and n2 are integers that satisfy n1−1>n2>1.
With the “feature quantity” as uk, it is defined as follows.
Zk:=Yk−Yk−1:The backwards difference of the triangular moving averages of the “feature quantities” (*) . . . (4)
*Where a “triangular moving difference” is where a moving average is applied twice
Equation (1) is the result of substituting Equation (2) and Equation (3) into Equation (4).
In the evaluating portion 9, the functions are different at the time of calculating reference characteristics and at the time of performing an evaluation, and operate as follows.
(1) An average value μ and a standard deviation α are calculated from the change rates obtained from the differential pressure data when no blockage has occurred.
(2) “μ−3σ” and “μ+3σ” are calculated from the average value μ and the standard deviation σ obtained in (1).
(3) “μ±3σ,” obtained in (2), is outputted as the reference characteristic to the reference characteristic storing portion 10.
A check is performed as to whether or not the change rate obtained from the differential pressure data for which the evaluation as to whether or not there is a blockage is to be performed is within the range of the reference characteristic “μ±3σ,” obtained from the reference characteristic storing portion 10, to evaluate whether or not there is a change in the state of blockage of the pressure guiding tube. In this case, if the change rate is within the range of “μ±3σ,” then the evaluation is that “there is no change in the state of blockage of the pressure guiding tube,” but if the change rate is outside of the range of “μ±3σ,” then the evaluation is that “there is a change in the state of blockage of the pressure guiding tube.”
The reference characteristic storing portion 10, at the time at which the reference characteristic is calculated, stores the reference characteristic, “μ±3σ,” obtained from the evaluating portion 9, and, at the time at which the evaluation is performed, outputs, to the evaluating portion 9, the reference characteristic, “μ±3σ,” that was stored at the time at which the reference characteristic was calculated.
The warning outputting portion 11, upon an evaluation that “there is a change in the state of blockage of the pressure guiding tube,” based on the evaluation result by the evaluating portion 9, begins to output a blockage warning, and continues to output the blockage warning until the warning is resetted thereafter. When the blockage warning is outputted, this can be considered to be “abnormal (a blockage has occurred).” When the blockage warning is not outputted, this can be considered to be “normal (no blockage).”
The pressure guiding tube blockage diagnosing device 100 receives such differential pressure data by the receiving portion 6, to diagnose the pressure guiding tube blockage. In the below, the situation wherein the pressure guiding tube blockage is diagnosed will be explained following the flow of calculations in the various portions in the pressure guiding tube blockage diagnosing device 100.
The change rates calculated by the change rate calculating portion 8 are sent to the evaluating portion 9. The reference characteristic, “μ±3σ,” obtained at the time of calculation of the reference characteristic, is stored in the reference characteristic storing portion 10. The evaluating portion 9 reads in the reference characteristic, “μ±3σ,” that is, the average value ±3σ for the normal data, which is stored in the reference characteristic storing portion 10, to check whether or not the change rate from the change rate calculating portion 8 is within the range of the reference characteristic “μ±3σ.” Here if the change rate is within the range of “μ±3σ,” then the evaluating portion 9 evaluates that “there is no change in the state of blockage of the pressure guiding tube,” but if the change rate is outside of the range of “μ±3σ,” then the evaluation is that “there has been a change in the state of blockage of the pressure guiding tube.”
For moving average data, the average value ±3σ for the normal data is defined as a reference characteristic, and the evaluation is performed by defining a blockage as having occurred if the moving average value goes outside of the range of the average ±3σ of the normal data. In this case, after 50 seconds after the blockage has occurred (on the 650th second after the start of the data) the moving average value for the rising/falling frequency goes outside of the average value ±3σ of the normal data, and the blockage is detected. In this case, there is a 50-second time lag from the occurrence of the blockage until the detection of the blockage.
As can be understood by comparing the change in the change rate, shown in
While in the above example the change rate was calculated using a triangular moving average process as the smoothing process in the change rate calculating portion 8, in another example the change rate is calculated using the least-squares method as the smoothing process. Note that in the another example the difference is only in the process within the change rate calculating portion 8, and the structure is identical to that illustrated in
In the another example, the change rate calculating portion 8 applies the least-squares method as the smoothing process for the feature quantities for the specific time interval up until the given interval, for each interval, for the feature quantities obtained from the feature quantity calculating portion 7, where the slope of the line obtained is defined as the change rate for the interval.
An example of a case wherein the change rate is calculated through the application of the least-squares method is illustrated in
When the least-squares method is applied to the first through 10th indicator values, the line that is shown by the solid line in
Even for the data thereafter, the same process is repeated, shifting by one data each time. The slopes of the lines produced in this way are used as the change rates.
The change rates calculated by the change rate calculating portion 8 are sent to the evaluating portion 9. The reference characteristic, “μ+3σ,” obtained at the time of calculation of the reference characteristic, is stored in the reference characteristic storing portion 10. The evaluating portion 9 reads in the reference characteristic, “μ±3σ,” that is, the average value ±3σ for the normal data, which is stored in the reference characteristic storing portion 10, to check whether or not the change rate from the change rate calculating portion 8 is within the range of the reference characteristic “μ±3σ.” Here if the change rate is within the range of “μ±3σ,” then the evaluating portion 9 evaluates that “there is no change in the state of blockage of the pressure guiding tube,” but if the change rate is outside of the range of “μ±3σ,” then the evaluation is that “there has been a change in the state of blockage of the pressure guiding tube.”
As can be understood by comparing the change in the moving average value for the rising/falling frequency, shown in
Note that while in the examples set forth above the explanations were for examples wherein a differential pressure transmitter was used as the pressure detecting portion and differential pressure data was received by the receiving portion from the differential pressure transmitter, instead the diagnosis of blockage of the pressure guiding tube can be performed similarly also in the case wherein a pressure transmitting device is used as the pressure detecting portion and pressure data is received, by the receiving portion, from the pressure transmitting device.
Moreover, while in the examples set forth above the explanation was for an example wherein a pressure transmitting device or differential pressure transmitting device was used as the pressure detecting portion and data from these transmitting devices was received by a receiving portion of a pressure guiding tube blockage diagnosing device that is external to the transmitting device, instead a pressure sensor or differential pressure sensor internal to the transmitting device may be used as pressure detecting portion, and the output of that sensor may be received by a receiving portion within the transmitting device, and some or all of the calculations may be performed within the transmitting device.
Moreover, while in the examples set forth above the explanation was for an example of a method that used, as the feature quantity, the rising/falling frequency of the pressure, as set forth in the JP '893, the example of the present invention is not limited to this method. The present invention can be applied insofar as the feature quantity is based on pressure fluctuations, and feature quantities that have been used in conventional methods, such as first-order difference fluctuations or second-order difference fluctuations of pressure or differential pressure may be used instead. Moreover, examples of reference characteristics include the maximum value, the minimum value, and the like, rather than just μ±3σ.
While the present invention has been explained above in reference to examples, the present invention is not limited to the examples set forth above. The structures and details in the present invention may be varied in a variety of ways, as can be understood by one skilled in the art, within the scope of technology in the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-159329 | Jul 2012 | JP | national |
