Boots – shoes – and leggings
Patent
1996-06-28
1998-06-09
Ngo, Chuong Dinh
Boots, shoes, and leggings
G06F 1710
Patent
active
057645523
DESCRIPTION:
BRIEF SUMMARY
This is a 371 of PCT/US 94/00284 filed Jan 4, 1994.
BACKGROUND OF THE INVENTION
The invention relates to a method for adjusting an adaptive exponential filter and an adaptive exponential filter. The invention is useful in the reduction of the noise component in a signal representing the value of the measurement. The input of the filter is supplied with a series of time-discrete input signals containing both a data component (or the value representing the measurement) and a noise component (or a distortion of the value representing the measurement). Within a process control context, the invention further relates to the use of the adaptive exponential filter in a control loop, a control loop, and a method for controlling a control loop.
Adaptive filters are filters that have the ability to adjust their own parameters automatically. They can be used to diminish the adverse effects of noise distortion in processing signals in a number of applications such as noise cancellation or noise reduction, echo canceller, leakage compensation, line equalization, speech processing, or the like. In this connection the term "noise" is used to signify all forms of interference.
In the case of process control, noise signals can either be produced in the process system (to which measurements are applied) as process noise or in the measurement system as measurement noise. It is usually not possible to identify the source of noise in a signal through the use of conventional analytical techniques on the time discrete signals themselves. Usually, noise will demonstrate an oscillatory or vibrational characteristic when a series of discrete signals is analyzed as a function of time; usually, the overall oscillatory pattern can be resolved into a set of sine waves having characteristic frequencies.
Process noise is produced from transient variations in the process system itself in the regions Droximate to the location of the measuring sensor. There are a variety of factors that can contribute to such variations in the process system itself such as the presence of entrained gas bubbles in a liquid, local variations in a liquid density as in the case of agitated oil/water mixtures, local variations in liquid temperature, turbulence, or the like.
Measurement noise is produced in each stage of the measurement system. The measurement noise is usually a function of the quality of the measurement system.
Current methods used to measure process variables such as temperature, pressure, and flow inherently yield signals which incorporate both process noise and measurement noise in their magnitude. Hence, using a process signal corrupted by noise is a long-standing problem of process control engineers. When steady state or average values are needed by the system receiving the measurements, as in the case where an energy or mass balance is to be calculated, conventional filtering techniques will reduce the effects of the higher frequency portion of the noisy signal significantly. However, response by such filters to lower frequency process fluctuation noise will have a considerable phase lag which will continue to induce uncertainty in the representative character of the value of the signal being output from the filter.
The successful design of a filter to minimize the effects of the noisy signal is based upon the understanding of the types and nature of the noise in the measurement of chemical processes, operating equipment, machinery, or the like.
Natural phenomena, such as noise, are usually not uniformly distributed. Instead, they are more likely to follow a normal distribution also known as Gaussian Distribution which has well-known bell-shaped distribution properties. Random numbers generated by this distribution tend to cluster about the mean or average value of the entire group. As values depart from the mean, they occur less frequently.
The most commonly used filter for noise reduction in the field of process control is an exponential filter. Such exponential filters are designed to filter digital (usually time-discrete) input signa
REFERENCES:
patent: 4679136 (1987-07-01), Shigemasa
patent: 4719561 (1988-01-01), Shigemasa
patent: 5150317 (1992-09-01), Countryman
patent: 5237524 (1993-08-01), Heinemann
Nazer Yahya
Quelle Ernst
Walter Hilger A.
Ngo Chuong Dinh
Schultz Dale H.
The Dow Chemical Company
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