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A Calculation Method of Low-pass Filter Cutoff Frequency for Slowly Varying Process Signals

A low-pass filtering, process signal technology, applied in electrical program control, program control in sequence/logic controllers, etc., can solve problems such as inability to obtain accurate and effective signal bandwidth values, and improve process variable measurement and control accuracy, The effect of suppressing high-frequency noise and reducing calculation time

Active Publication Date: 2018-05-15
SOUTH CHINA UNIV OF TECH
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, in the actual process, it is usually impossible to obtain an accurate effective signal bandwidth value, and it can only be roughly estimated based on the knowledge of the controlled object; for example, it can be estimated that the effective signal bandwidth value of a certain process does not exceed 1Hz, but the effective signal bandwidth value cannot be known exactly Is it 0.5Hz or 0.1Hz

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  • A Calculation Method of Low-pass Filter Cutoff Frequency for Slowly Varying Process Signals
  • A Calculation Method of Low-pass Filter Cutoff Frequency for Slowly Varying Process Signals
  • A Calculation Method of Low-pass Filter Cutoff Frequency for Slowly Varying Process Signals

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Embodiment 1

[0041] A low-pass filter cut-off frequency calculation method for slowly changing process signals, the process is as follows figure 2 shown, including the following steps:

[0042] In the first step, at the sampling frequency f s Collect process variables to obtain sampled signals X(k), k∈{1,...,N+1}, where N is a positive integer;

[0043] Sampling frequency f s means, f s =c s f Bh ;

[0044] Among them, f Bh is the estimated value of the bandwidth upper limit of the process variable; c s is the preset coefficient two, c s >5. The sampling frequency f of the calculation method of the present invention s You only need to estimate the upper limit of the bandwidth of the process variable and multiply it by the preset coefficient 2 to get it. The method is simple and can guarantee the sampling frequency f s Meet the sampling density requirements;

[0045] In order to facilitate the application of fast Fourier transform and further shorten the calculation time, the val...

Embodiment 2

[0065] Extrusion exit temperature is a key process variable in aluminum alloy extrusion and can reflect the quality of the processed product. The emissivity of aluminum alloy is low and has a wide range of variation, and the surface temperature is very easy to radiate. The appearance of aluminum at the extrusion exit is bright, and the temperature is relatively low. Affected by factors such as changes in the surface state, unstable target emissivity, and the medium between the temperature measuring device and the measured object (such as dust, smoke, water vapor, etc.), the output of the thermometer will fluctuate slightly.

[0066] This kind of fluctuation changes rapidly and does not reflect the real change of the extrusion outlet temperature, which is not conducive to the control of the extrusion process and the quality management of the product, so it needs to be filtered. The extrusion process control program usually runs on the PLC. Because the storage space of the PLC ...

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Abstract

The present invention provides a low-pass filter cutoff frequency calculation method for a slow change process signal. The method is characterized by comprising the steps of firstly collecting a process variable to obtain a sample signal, carrying out singular value processing on the sample signal to obtain a signal to be analyzed and calculating the frequency spectrum of the signal to be analyzed, then carrying out subtraction on the values of two adjacent times of the signal to be analyzed to form a difference signal and calculating the frequency spectrum of the difference signal, finally comparing the frequency spectrums of the signal to be analyzed and the difference signal, wherein the an obvious different frequency band of the two frequency spectrums is the frequency band of an effective signal, and a frequency band frequency maximum value is taken as the cutoff frequency of low-pass filter. According to the low-pass filter cutoff frequency calculation method, the cutoff frequency of low-pass filter can be determined through processing and analyzing the sample signal of the process variable, thus the low-pass filter can be realized, the calculation method is simple, the amount of calculation is small, and the real-time requirement of control can be satisfied.

Description

technical field [0001] The invention relates to the technical field of process control and signal processing, and more specifically relates to a low-pass filter cut-off frequency calculation method for slow-varying process signals. Background technique [0002] In the production process, accurate measurement of the controlled variable is a prerequisite for its effective control. There are a large number of slow-changing objects in process control, such as outlet temperature control of aluminum profile extrusion, boiler furnace temperature control, etc. The effective signal bandwidth of these variables is concentrated in the lower frequency bands, and their sampled signals usually need to be low-pass filtered to suppress high-frequency noise. Therefore, determining the cut-off frequency of low-pass filtering is often the key link in the measurement and control of these variables. [0003] If the effective signal bandwidth can be accurately known, the upper limit of the effe...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): G05B19/05
CPCG05B19/05
Inventor 莫鸿强杜启亮
Owner SOUTH CHINA UNIV OF TECH