JPH0683018B2 - Transient change tracking type digital filter - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a digital filter for filtering a digitized signal.

[Technical background of the invention and its problems] Generally, a signal measured by an instrumentation system has a large or small fluctuation even in a steady state. Therefore, a fluctuation is increased by a filter in order to improve measurement accuracy. In some cases, processing to suppress it may be performed. 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.

[Object of the Invention] The present invention has been made to solve the above problems,
It is an object of the present invention to provide a transient change tracking type digital filter having excellent smoothness in a steady state of a signal and excellent tracking ability in a transient state of a signal.

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention detects a transient change from a difference between an input signal and an output signal, and sequentially changes the time constant of a digital filter at a constant rate when a transient change is detected. The present invention relates to a transient change tracking type digital filtering which has a filter characteristic that is smooth in a steady state and good in a transient state.

Embodiments of the Invention Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. The input section 1 and the output section 4 use an 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.

The transient change detection unit 2 obtains an 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 4, that is, D = xi−yi. When it exceeds the reference value D ₀ , 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 D ₀ , for example, the input signal
A value such that n times the standard deviation σx of xi D ₀ = 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 basically consists of a conventional digital filter, but when a signal for transient change detection is input from the transient change detection unit 2, it has a function of sequentially changing the time constant in order to improve followability. Has been added. As a method of changing the time constant, the time constant is 1 / k for each processing of one sample.
The method of doubling Ti ₊₁ = 1 / kTi. Here, k is a value determined from the degree of followability of the output signal yi, Ti is the time constant at time i, and Ti ₊₁ is time i.
It is a time constant of +1.

FIG. 2 shows the step response of the first-order lag digital filter when k = 2 and k = 4. As can be seen from this figure, the change at the beginning is small, but the follow-up becomes faster, and at the end, it catches up smoothly. Such follow-up is the third
As a matter of course, the characteristic is different from the step response of the conventional invariant time constant first-order lag digital filter shown in the figure. Further, as an advantage of the method of sequentially multiplying such a time constant by 1 / k, since the initial tracking is suppressed,
Even if the transient change detection unit 2 erroneously determines that it is in a transient state due to noise or the like, it does not have to significantly affect the output signal, and the followability in the latter half becomes faster. It is to arrive faster.

By the way, whether or not the output signal yi can sufficiently follow the input signal xi is determined by the transient change detection unit 2 whether or not the absolute value D of the difference between the input signal xi and the output signal yi becomes smaller than the reference value D _1. To do. Here, as the reference value D ₁ , for example, a value such that m times the standard deviation σx of the input signal xi D ₁ = mσx is used. In general, it is better to adopt a value smaller than n for this m, but the same value may be used.

In addition, when the transient change end signal enters the filter processing unit 3 in the transient change detection unit 2, as an example of how to return the time constant, the time constant is multiplied by k for each processing of one sample. Returns to a constant.

When the standard deviation σx is calculated, it is better to calculate and update the standard deviation σx at an appropriate time so as to cope with a change with time.

FIG. 4 compares both the filter according to the present invention and the conventional first-order lag filter, and the output (c) of the conventional first-order lag filter follows the transient change of the input signal (a). Although it is quite time consuming, it can be seen that the filter output (b) of the present invention follows immediately.

As described above, the transient change tracking type digital filter of the present invention has good followability in normal conditions and can reliably follow transient changes immediately, so that it is applied to, for example, flow control of a plant or neutron flux signal in a nuclear reactor. Can contribute to the safety of the plant and the reactor.

[Effects of the Invention] As described above, according to the transient change tracking type digital filter of the present invention, since it has a digital filter characteristic that is excellent in smoothness in a steady state and excellent in followability in a transient state, fluctuations also occur in a steady state. The present invention has excellent effects in preventing false alarms of signals that must reliably detect a large transient change and issuing an alarm, or in preprocessing for stable control in a control system that uses similar signals.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a diagram showing a step response of a first-order lag digital filter of the present invention, and FIG. 3 is a step response of a conventional first-order lag digital filter. FIG. 4 and FIG. 4 are diagrams for comparing the filter output of the present invention with the output of the conventional first-order lag filter. 1 ... Input section, 2 ... Transient change detection section 3 ... Filter processing section, 4 ... Output section

Claims (1)

[Claims] In a digital filter for filtering a digitized signal, a transient change detector for detecting a transient change when an absolute value of a difference between an input signal and an output signal of the digital filter exceeds a reference value, and the transient. A filter processing unit that sequentially changes the time constant of the digital filter at a constant rate when a change is detected is provided, which has smoothness in the steady state of the input signal and the time constant of the digital filter in the transient state of the input signal. A transient change tracking type digital filter characterized in that it is configured so as to improve the trackability of an output signal with respect to an input signal by sequentially changing it at a constant rate.