JPH0720048B2 - Transient change tracking digital filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to a digital filter for filtering a digitized signal.

(Prior Art) Since a signal measured by an instrumentation system generally has a large or small fluctuation even in a steady state, there is a case where a fluctuation suppressing process is performed by a filter in order to improve measurement accuracy. is there. However, if the time constant of the filter is made too large to suppress fluctuations too much, it is impossible to follow the transient change.

(Problems to be Solved by the Invention) Therefore, a transient change tracking digital filter has been proposed. In the method using the transient change tracking digital filter, a rapid transient change is tracked, but a relatively gentle change is made. However, there was a problem that the change was delayed in tracking.

The present invention has been made to solve the above problems,
Its purpose is to provide a transient change tracking type digital filter that has excellent smoothness in a steady state of a signal, excellent followability in a transient state of a signal, and excellent followability even in a relatively gentle transient change. is there.

[Structure of the Invention] (Means and Actions for Solving Problems) In order to achieve the above object, the present invention provides a digital filter for filtering a digitized signal, in which an input signal and an output signal of the digital filter are A transient change detecting section for detecting a transient change from the difference; an input / output deviation detecting section for integrating a deviation between the input signal and the output signal of the digital filter and detecting a large deviation from an integrated value of the deviation; and the transient change detecting section. Time and a large deviation is detected, a filter processing unit that sequentially changes the time constant of the digital filter for each sampling of the signal is provided, and by increasing the time constant of the digital filter, the input signal of the digital filter is smoothed in a steady state. In addition, when the transient state or large deviation of the input signal is detected, It is characterized in that it has configured to improve tracking of the output signal to the input signal by sequentially decreasing the number.

(Example) The Example of this invention is described with reference to drawings.

FIG. 1 shows a block diagram of an embodiment of the present invention. Whether the input section 1 and the output section 5 use a digital interface or an A / D converter depending on whether the external signal is a digital signal or an analog signal. Alternatively, a D / A converter is used.

In the transient change detection unit 2, the absolute value D of the difference between the input signal xi from the input unit 1 to the filter processing unit 3 and the output signal yi from the filter processing unit 3 to the output unit 5, that is, D = | xi−yi | When it exceeds the reference value Do, it is determined that a transient change has occurred, and a signal notifying the detection of the transient change is input to the filter processing unit 3. As the reference value Dο, for example, a value n times the reference deviation σx of the input signal xi, that is, a value such as Dο = nσx is used. Here, n is a value determined depending on which of smoothness and followability is important. When the input signal contains high frequency noise, a low pass filter may be provided in front of the transient change detector 2 to remove the high frequency noise.

The filter processing unit 3 is basically composed of a conventional digital film, but a signal for detecting a transient change is input from the transient change detecting unit 2 or a signal having a large deviation from the input / output deviation detecting unit 4. When is entered, a function for sequentially changing the time constant is added in order to improve followability. As a method of changing the time constant, there is a method of multiplying the time constant by 1 / k for each sampling process, that is, Ti ₊₁ = 1 / kTi. Here, Ti is a time constant, and k is a value determined from the degree of request for the followability of the output signal yi.

In the input / output deviation detection unit 4, the integrated value S of the difference between the input signal xi from the input unit 1 to the filter processing unit 3 and the output signal yi from the filter processing unit 3 to the output unit 5, that is, Is determined, and if it exceeds the reference value S0, it is determined that the deviation is large, and a signal notifying the detection of the large deviation is sent to the filter processing unit 3
To enter. However, t is a value smaller than the time constant T,
This is the cycle for determining a large deviation. The reference value Sο is, for example, m times the standard deviation δx of the input signal xi, that is, Sο =
Use a value such as mδx. Here, m is set as a coefficient of the standard deviation δx to what extent the input and the output are allowed.

FIG. 2 compares the characteristics of the transient change tracking digital filter of the present invention, the transient change tracking filter up to now, and the conventional first-order lag filter. On the other hand, the output 7 of the conventional transient change tracking type filter and the output 8 of the transient change tracking type digital filter of the present invention immediately follow, but the output 9 of the conventional first-order lag filter takes a considerable time to follow. It depends. Further, the output 7 of the transient change following type digital filter according to the present invention is not able to follow the ramp change (slow change) 7 of the transient change following type filter output so far. Follows well.

As described above, the transient change tracking type digital filter of the present invention has good smoothness in a steady state, and immediately and reliably follows a rapid transient change, and also can follow a gentle transient change well. The present invention can be applied to the flow control of the above or to the neutron flux signal in a nuclear reactor, etc. to contribute to the safety of the plant and the nuclear reactor.

[Effects of the Invention] As described above, according to the transient change tracking type digital filter of the present invention, the digital filter having excellent smoothness in a steady state and excellent tracking property in a rapid transient or a gentle transient change. Due to its characteristics, it has large fluctuations in steady state, but it prevents false alarms of signals that must be triggered by reliably capturing transient changes, and preprocessing for stable control in control systems using similar signals. Has an excellent effect on.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a diagram showing three types of a transient change tracking digital filter of the present invention, a conventional transient change tracking filter, and a conventional first-order lag digital filter. It is a figure which compared the characteristic of a filter. 1 ... Input part 2 ... Transient change detection part 3 ... Filter processing part 4 ... Input / output deviation detection part 5 ... Output part 6 ... Input signal

Claims (1)

[Claims] 1. A digital filter for filtering a digitized signal, wherein a transient change detector for detecting a transient change from a difference between an input signal and an output signal of the digital filter, and an input signal and an output signal of the digital filter. An input / output deviation detection unit that integrates the deviation and detects a large deviation from the integrated value of the deviation, and a filter that sequentially changes the time constant of the digital filter at the time of the transient change detection and the large deviation detection every sampling of the signal. The input signal of the digital filter has smoothness in a steady state by providing a processing unit and a large time constant of the digital filter, and when the input signal is in a transient state or a large deviation is detected, By gradually decreasing the constant, the followability of the output signal to the input signal will be improved. Transient tracking digital filter, characterized by being configured to.