JPS6368907A - Variation rate detection method for analog information - Google Patents

Abstract

PURPOSE:To detect both long-period variation and short-period variation by comparing a sampled value obtained at a short period with a comparison reference value obtained at a period which is an integral multiple of said period, and obtaining variation rate information. CONSTITUTION:A CPU 3 reads a process value out of an interface 1 at every constant period. Then the current sampled value and a count value of the number of times of sampling are stored in a RAM 5 and the current sampled value is compared with the comparison reference value stored in the RAM 5 to check whether or not the absolute value of the difference between the both exceeds a prescribed variation rate limit value. Then when the absolute value exceeds the limited value, the variation rate is diagnosed as an abnormal value to output an alarm-on signal and when not, it the normalcy of the variation rate is judged to output an alarm-off signal. Then, the comparison reference value is updated into the current sample value at a reference value update period and the new comparison reference value is stored in the RAM 5. Consequently, the rate from long-period variation to short-period variation is securely grasped at every reference value update period and reflected upon the variation rate diagnosis.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method for detecting a rate of change in analog information, which is applied to, for example, diagnosing the rate of change in human-powered analog information of a digital controller.

(Prior Art) For example, when diagnosing the rate of change of an input process value in a digital controller that performs process control, the rate of change is conventionally detected as shown in FIG. That is,
The analog changing process value Pv is sampled every predetermined change rate check period T1, and the current sample value PV is
The difference Δ1 between I and the previous sample value PvO is determined. Then, it is diagnosed whether this difference exceeds a prescribed change rate limit value. In this way, conventionally, the rate of change has been detected by comparing the previous sample value and the current sample value b (Problem to be solved by the invention) However, in the above conventional detection method, If there is a change in a period shorter than the change rate check period T1, such a change cannot be detected. Therefore, if the rate of change check period T1 is set to be short, such as T2, the rate of change over a long period cannot be detected.

An object of the present invention is to provide a method for detecting a rate of change in analog information that can detect both long-cycle changes and short-cycle changes.

[Structure of the invention]

(Means for Solving the Problems) The present invention includes a process of sampling analog information at a predetermined period, a process of obtaining change rate information by comparing the current sample value and a comparison reference value, and a process of sampling analog information at a predetermined period. The gist of the method is to include a process of updating a comparison reference value to the sample value collected every time. In other words, the gist is that the rate of change information is obtained by comparing a sample value collected in a certain sampling period with a comparison reference value collected in a period that is an integral multiple of the sampling period.

(Function) The sample value represents an analog information value for each sampling period, and the comparison reference value represents an analog information value for each period that is a predetermined integral multiple of the sampling period.

When the first sampling is performed after the comparison reference value is updated, the first sample value and the comparison reference value are compared. This comparison result represents the rate of change of analog information from the time when the comparison reference value is updated until after one sampling period. Next, when the second sampling is performed, the second sample value is compared with the comparison reference value. This second comparison result represents the rate of change from the time of the update to two sampling periods later. Thereafter, the same comparison is repeated every time the comparison reference value is updated until the next update time of the comparison reference value arrives, and comparison results indicating the rate of change of longer cycles are successively obtained. In this way, during one update cycle from update to update of the comparison reference value,
A predetermined integer number of comparison results are obtained that indicate the rate of change of different cycles from short cycles to long cycles.

Then, a predetermined integer number of comparison results having different cycles are obtained for each update cycle.

(Example) The present invention will be described below with reference to an example in which the present invention is applied to diagnosis of the rate of change of an input process value of a digital controller.

FIG. 3 shows a schematic configuration of the digital controller.

In the figure, an input interface 1 takes in process values necessary for control from the outside, processes them, and transmits them to a CPU 3, and is composed of an A/D converter and the like. The output interface 2 processes the control information and change rate diagnosis results output from the CPU 3 and outputs them to external equipment, such as a D/A converter for analog signal conversion and a photocoupler for digital signal conversion. It consists of

The CPU 3 performs processing based on input information from the input interface 1 using a control algorithm (not shown), processing using a change rate diagnosis algorithm shown in FIG. 1, and the like. The ROM 4 stores program programs for the control algorithm and rate of change diagnosis algorithm used by the CPU 3.

The RAM 5 temporarily stores sample values 6, comparison reference values 7, count values 8, etc. used when the CPU 3 performs processing.

In this configuration, the CPU 3 performs rate of change diagnosis in accordance with the procedure shown in FIG.

First, the CPU 3 reads process values from the input interface 1 at regular sampling intervals (step S
8. SL). Then, the process value just read (current sample value) and the count value of the number of sampling times are stored in the RAM.
5 (step 2) and store the current sample value in R
It is compared with the comparison reference value stored in AM5, and it is checked whether the absolute value of the difference between the two exceeds a prescribed change rate limit value Δ1I11 (step S3). As a result of the check, if the rate of change is exceeded, the rate of change is diagnosed as abnormal and an alarm-on signal is output (Step S4); if the rate of change is not exceeded, the rate of change is determined to be normal and an alarm-off signal is output (Step S4).
5).

Next, it is stored in RAM5 to determine whether it is time to update the standard value.
A check is made based on the count value within (step S6).

At this time, the reference value update cycle is set to, for example, three times the sampling cycle.

In other words, the reference value update time comes every three times sampling is performed. Then, when the reference value update time comes, the comparison reference value is updated to the current sample value in step S.
7) Store the updated comparison reference value in the RAM 5.

Such change rate diagnosis processing is repeated every sampling period (step S8). Further, during this sampling period, processing by the control program is performed.

FIG. 2 shows the state of sampling in the rate of change diagnosis process described above, together with specific changes over time in the process value Pv.

As shown in the figure, the sample values PVIO, PVI1 . ... is loaded. Also, every time sampling is performed three times at each reference value update period T4, which is three times the sampling period T3, the sample values PVIO, PV13. ... is set as a comparison reference value. Then, the set comparison reference values PVIO, PV13. ...and each sample value PVII read between that setting and the next setting.

PV12 is compared, and the difference between the two is Δ11. Δ12°...
・A rate of change diagnosis is performed based on.

The difference that forms the basis of this change rate diagnosis, for example Δ11°Δ12
．． Δ13 is the rate of change from the time when the comparison reference value was updated to PVIO] for Δ]1 until after the sampling cycle, or for Δ12, the rate of change from the time of the update to two sampling cycles later. , and Δ13 indicate the rate of change after three sampling cycles from the above-mentioned update time, that is, until the next update time. That is, the difference Δ]1°Δ12. Δ13 indicates the rate of change of different cycles within the reference value update cycle from a short cycle corresponding to the sampling cycle T3 to a long cycle corresponding to the reference value update cycle T4. Therefore, according to this embodiment, it is possible to reliably capture the rate of change from a long period to a short period at each reference value update period and reflect it in the rate of change diagnosis.

FIG. 4 shows an algorithm for diagnosing the rate of change of a digital controller to which another embodiment of the present invention is applied, which is a method of using the previous sample value as a second comparison reference value to the above embodiment. This is a flowchart showing.

The difference between this algorithm and the one shown in FIG. , further convert the current sample value into the second
The difference is compared with the previous sample value as a comparison reference value, and it is also checked whether the difference does not exceed the change rate limit value Δ1m (step S9). If the result of step S9 is that it is exceeded, an alarm on signal is output (step S4), and if the result is that it is not exceeded, an alarm off signal is output (step 5). .

By adding the step of checking the difference between the previous sample value and the current sample value in this way, it is possible to prevent the detection sensitivity from decreasing with respect to short cycle changes. That is, for example, as shown in FIG. 5, the reference value update period T4
If there is a short-period rapid change in the latter half of , this change cannot be captured by the difference Δ23 between the comparison reference value PV20 and the current sample value PV23.

Therefore, the previous sample value PV22 and the current sample value PV
By checking the difference Δ23' from 23 at the same time, sudden changes will not be overlooked, and a highly reliable rate of change diagnosis can be performed.

〔Effect of the invention〕

As explained above, according to the present invention, sample values collected at short intervals are compared with comparison reference values collected at intervals longer than the sample values by an integer multiple, so changes in short intervals are also long. This has the effect of being able to detect changes in the cycle.

[Brief explanation of drawings]

FIG. 1 is a flowchart showing an algorithm for rate of change diagnosis to which an embodiment of the present invention is applied; FIG. 2 is a diagram showing the sampling status of rate of change diagnosis in FIG. 1; FIG. 4 is a flowchart showing an algorithm for rate of change diagnosis applying another embodiment of the present invention, FIG. 5 is a diagram showing a sampling situation for rate of change diagnosis in FIG. 4, and FIG. FIG. 7 is a diagram for explaining the problems of the conventional method of FIG. 6. 1... Input interface, 2... Output interface, 3... CPU, 4... ROM, 7...
RAM. Pv...Process value, PvO-PV23...Sample value, T3...Sampling period, T4...Reference value update period, Δ1-Δ23. Δ23'...difference. Applicant's agent Mr. Sato Figure 1 Special opening U63-68907 (5) 1--77-d Figure 6

Claims (1)

[Claims] 1. A step of sampling analog information at predetermined intervals, a step of comparing the current sample value with a comparison reference value to obtain information regarding the rate of change, and sampling at a predetermined integer number of times of said sampling. A method for detecting a rate of change in analog information, comprising the step of updating the comparison reference value to the sampled value. 2. A method for detecting a rate of change in analog information according to claim 1, further comprising the step of comparing the current sample value and the previous sample value to obtain information regarding the rate of change.