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Common Applications of Filter

Author: Apogeeweb Date: 26 Feb 2019  8510

signal filtering

Warm hints: This article contains about 4500 words and reading time is about 20 mins.

Ⅰ Introduction

Filtering is a fundamental and important technique in signal processing. Filtering technology can extract the desired signal from various signals and filter out unwanted interference signals. A filter is an important component in the frequency domain analysis of a signal. 

Classification and Application of Filters

Catalog

Ⅰ Introduction

Ⅱ Applications of Filter

2.1 Communications Industry

2.2 Semiconductor Industry

2.3 Petrochemical Industry

2.4 Chemical Fiber Industry

2.5 Steel / Intermediate Frequency Heating Industry

2.6 Automotive Manufacturing

2.7 DC Motor Harmonic Control

2.8 Hospital System

2.9 Theater/Sports Hall

2.10 Speech Signal Processing

2.11 Image Processing

2.12 TV, Radar

2.13 Music

2.14 Airport

2.15 FIR Filter in Audio System

2.16 Adaptive Filtering in Signal Processing

2.17 FBAR Filter in Smart Phone


 

There are many kinds of filters, and various filters have different performance characteristics. Therefore, when selecting filters, it is usually necessary to comprehensively consider the customer's actual use environment and customer performance requirements in order to make correct, effective, and reliable choices.

filter

Filters are divided into analog filters and digital filters. Analog filters are used to process analog signals or continuous signals. Digital filters are used to process discrete digital signals.

 

Ⅱ Applications of Filter

Analog filters can be widely used in industrial, commercial and institutional distribution networks, such as: power systems, electrolytic plating companies, water treatment equipment, petrochemical companies, large shopping malls and office buildings, precision electronics companies, airports / ports Systems, medical institutions, etc.

2.1 Communications Industry

Communications Industry

In order to meet the operational needs of large-scale data center equipment rooms, the UPS usage capacity in the communication power distribution system has increased significantly. According to the survey, the main harmonic source equipment of the communication low-voltage power distribution system is UPS, switching power supply, inverter air conditioner and so on.

The harmonic content generated is high, and the displacement power factor of these harmonic source devices is extremely high. By using active filters, the stability of communication systems and power distribution systems can be improved, the service life of communication equipment and power equipment can be extended, and the power distribution system can be more in line with the design specifications of harmonic environments.

 

2.2 Semiconductor Industry

The triple harmonics of most semiconductor industries is very serious, mainly due to the large number of single-phase rectifiers used in the enterprise. The triple harmonics belongs to the zero-order harmonic, which has the characteristics of collecting in the neutral line, causing the neutral line pressure to be too large, and even sparking phenomenon, which has great production safety hazards.

filter

Triple harmonics can also cause the circuit breaker to trip, delaying production time. The triple harmonics forms a circulation in the transformer, which accelerates the aging of the transformer. Severe harmonic pollution will inevitably affect the efficiency and longevity of equipment in power distribution systems.

 

2.3 Petrochemical Industry

Petrochemical Industry

Due to the need of production, there are a large number of pump loads in the petrochemical industry, and many pump loads are equipped with variable-frequency drive. The large number of applications of variable-frequency drive has greatly increased the harmonic content in the distribution system of the petrochemical industry.

At present, most of the variable-frequency drive rectification links use 6 pulses to convert AC into DC, so the harmonics generated are mainly 5, 7 and 11 times. The main hazards are manifestations of hazards to electrical equipment and deviations in metering. This problem can be well solved by using an active filter.

 

2.4 Chemical Fiber Industry

Chemical Fiber Industry

 

In order to greatly increase the melting rate, increase the melting quality of the glass, and extend the age of the furnace and save energy, electric flux heating equipment is commonly used in the chemical fiber industry, and electricity is directly fed into the fuel-heated glass tank kiln by means of electrodes. These devices generate a large amount of harmonics, and the spectrum and amplitude difference of the three-phase harmonics are relatively large.

 

2.5 Steel / Intermediate Frequency Heating Industry

Steel / Intermediate Frequency Heating Industry

The medium frequency furnace, rolling mill, electric arc furnace and other equipment commonly used in the steel industry will have a major impact on the power quality of the power grid, causing frequent overload protection actions of the capacitor compensation cabinet, serious heat generation of the transformer and power supply lines, frequent fuses, etc., and even causing The voltage drops and flickers.

 

2.6 Automotive Manufacturing

Automotive Manufacturing

The welding machine is an indispensable equipment in the automobile manufacturing industry. Due to the randomness, rapidity and impact characteristics of the welding machine, a large number of welding machines are used to cause serious power quality problems, resulting in unstable welding quality and high degree of automation. The power compensation system cannot work due to unstable voltage, and the reactive power compensation system cannot be used normally.

 

2.7 DC Motor Harmonic Control

Large DC motor places need to convert AC power to DC power through rectification equipment. Because of the large load capacity of such projects, there are serious harmonic pollution on the AC side, causing voltage distortion and causing accidents in severe cases.

In the case of automated production lines and precision equipment, harmonics can affect their normal use, causing faults in intelligent control systems, PLC systems, etc.

 

2.8 Hospital System

The hospital has very strict requirements on the continuity and reliability of power supply. The automatic recovery time of class 0 is T≤15S, the time of automatic recovery of class 1 is 0.5S≤T≤15S, and the time of automatic recovery of class 2 is T≤0.5. S, voltage total harmonic distortion rate THDu ≤ 3%, X-ray machine, CT machine, nuclear magnetic resonance are loads with extremely high harmonic content.

 

2.9 Theater/Sports Hall

Theater/Sports Hall

The thyristor dimming system and large LED equipment are harmonic sources. During the operation, a large number of third harmonics will be generated, which will not only cause the power equipment of the power distribution system to be inefficient, but also cause the strobe of the lights to be communicated. The weak electric circuit such as cable TV generates noise and even causes malfunction.

In modern telecom equipment and various control systems, digital filter applications are also extremely extensive, and some of the most successful applications are listed here.

 

2.10 Speech Signal Processing

Speech Signal Processing

Speech processing is one of the earliest fields of application of digital filters, and one of the first areas to promote the development of digital signal processing theory. The field mainly includes five aspects:

First, speech signal analysis. That is, the waveform characteristics, statistical characteristics, model parameters, etc. of the speech signal are analyzed and calculated;

Second, speech synthesis. That is, using dedicated digital hardware or running software on a general purpose computer to generate speech;

Third, speech recognition. That is, using dedicated hardware or a computer to recognize the words spoken by the person, or to identify the person speaking;

Fourth, voice enhancement. That is, the masked speech signal is extracted from noise or interference.

Fifth, speech coding. Mainly used for voice data compression, a series of international standards for speech coding have been established, which are widely used for communication and audio processing.

 

2.11 Image Processing

Digital filtering technology is successfully applied to the recovery and enhancement of still images and moving images, data compression, noise and interference, image recognition and tomography, and is also successfully applied to radar, sonar, ultrasonic and infrared signals. Visible image imaging.

In the field of modern communication technology, almost no branch is not affected by digital filtering techniques. Digital sources, such as digital communication, network communication, image communication, multimedia communication, etc., are widely used in source coding, channel coding, modulation, multiplexing, data compression, and adaptive channel equalization. The digital filter is almost impossible. Among them, the software radio technology, which is considered to be the future development direction of communication technology, is based on digital filtering technology.

 

2.12 TV, Radar

TV, Radar

The replacement of analog TV by digital TV is an inevitable trend. The popularity of high-definition television is just around the corner, and the accompanying video disc technology has formed an industry with a huge market; videophones and conference TV products are constantly being updated.

The achievements and standardization of video compression and audio compression technologies have led to the booming industry in the TV industry, and digital filters and related technologies are important foundations for video compression and audio compression technologies.

The radar signal occupies a very wide frequency band and the data transmission rate is also very high. Therefore, compressing the data volume and reducing the data transmission rate are the primary problems faced by the digital processing of the radar signal. Telling the emergence of digital devices has spurred advances in radar signal processing technology.

In modern radar systems, the digital signal processing part is indispensable because digital signal filtering technology is indispensable from signal generation, filtering, processing, estimation of target parameters and target imaging display. Digital filters for radar signals are one of the most active research areas today. Sonar signal processing is divided into two categories, active sonar signal processing and passive sonar signal processing. Many of the theories and techniques involved in active sonar systems are the same as radar systems.

 

2.13 Music

The digital filter has opened up a new situation for the music field. The digital filtering technology has shown great power in editing, synthesizing, and adding special effects such as reverberation and chorus in music. Digital filters can also be used to compose, record, and play back, or to restore the sound quality of old tapes.

 

2.14 Airport

The root cause of power system harmonic generation is some power transmission and distribution and power equipment with nonlinear volt-ampere characteristics. When a current flows through a non-linear load, it does not have a linear relationship with the applied voltage, and a non-sinusoidal current is formed, thereby generating harmonics. Harmonic pollution is increasingly threatening the safety, stability, and economic operation of power systems, which has a significant impact on the linear load of the same network and other users.

airport

As a convenient means of transportation, the aircraft has brought a variety of choices to people's daily transportation life, and the airport is also expanding year by year. However, in the low-voltage power distribution system of the airport, there are a large number of harmonic sources, such as airport navigation lights, DC motors, electric furnaces, rolling mills, electric welders, etc. These harmonic sources have large current distortion and wide harmonic spectrum range. The characteristics of reactive power change are fast.

The harmonics generated by such loads endanger the normal operation of the power distribution system and even cause serious electrical accidents. Taking the airport navigation lighting system as an example, the navigation light load equipment is increasing, and the airport lighting station uses a large number of thyristor dimming equipment, resulting in a large amount of harmonic current, which pollutes the power quality, while adding current and additional The thermal effect also poses a certain hazard to the safety of various electrical equipment and cable lines. Therefore, it is extremely important to analyze and manage the power harmonics of the airport navigation light station.

filter

At present, there are two main mainstream methods for harmonic control of power systems: passive filtering technology and active filtering technology. High-power  semiconductor dimming equipment used in airport lighting stations generates a large number of high-order harmonics (mainly all odd-order harmonics other than 3 times harmonics), while passive filters are separate for each harmonic. Designing a single resonant filter, the design parameters are related to the system impedance (the calculation of the system impedance is very cumbersome, and the system is expanded year by year, the system impedance will also change); passive filtering can not completely eliminate the harmonics, but there is the danger of amplifying the resonance; The aging of the capacitor will also make the original design resonance point offset and fail to filter out the target harmonics; the passive filter system is suitable for single-load and stable applications.

Compared with passive filters, the active filter system has high controllability and fast response (≤1ms), can compensate for each harmonic, can suppress flicker, compensate reactive power, has a multi-functional feature; The cost performance is more reasonable; the filtering characteristics are not affected by the system impedance, and the danger of resonance with the system impedance can be eliminated; and the adaptive function can automatically track and compensate for the changed harmonics.

The basic principle is to detect the harmonic current from the load circuit of the harmonic source (compensated object), and the compensation device generates a compensation current waveform with the same magnitude and opposite phase of the harmonic current to cancel the harmonic source load. The harmonic current is generated so that the grid side current contains only the fundamental component.

 

2.15 FIR Filter in Audio System

Application of FIR Filter in Audio System

Normally, we use the IIR EQ to correct the frequency response curve of the sound system or a certain channel. This is the purpose of using this equalizer. In fact, in most cases, it can help us achieve this goal. In actual use, there is a certain difference between PEQ and GEQ, but no matter which form of EQ, as long as it is powerful enough, it can basically achieve the purpose we expected.

But unfortunately, while the IIR EQ corrects the frequency response curve of the system or channel according to our own will, it also brings a by-product – the phase response of the sound system or channel is destroyed. Moreover, the general rule is that the greater the change in the frequency response of the IIR EQ, the more severe the damage to the phase response of the corresponding system or channel.

filter

The effect of the high-pass filter (also considered to be a type of IIR EQ) on the phase in the sound system

However, in today's highly developed technology, FIR, which has been widely used in other fields such as communications, can be applied to audio systems, which is indeed a good thing.

Because it solves the problem that IIR EQ can't solve, that is, as another type of EQ, it can correct only the frequency response of the sound system without affecting its phase response; it can also only phase the sound system. Make corrections without affecting the frequency response (isn't this similar to the "all-pass filter"? Yes, but it's more flexible and functional than the AP); it also corrects the system's frequency response and phase response. .

In this way, the FIR EQ is almost omnipotent except that it does not have the ability to correct the impulse response of the system. This is true, but it also has side effects.

filter

Comparison of frequency response and phase processing of signals above 500 Hz using FIR processor

Because the FIR filter is a digital filter that cannot be implemented with analog circuitry, it will cost more or less time to process the signal. In other words, the audio system using the FIR filter will have additional delays, and the IIR can be implemented with analog circuits. There is no such problem. Everything has two sides. If there is a good side, it will be bad. The other side. Although, the cost of time is also a factor we must consider, but at least for the medium and high frequency signals, we do not need to be too distressed for the time cost of a few milliseconds.

The specific time cost required depends mainly on the frequency range in which FIR processing is required. The lower the frequency, the longer the period of the sound. Very simple, we can think that as the FIR of the digital signal processor, at least one period of time corresponding to the lower limit frequency of the sound signal is required to process it. For example, in an ideal situation, for a 500 Hz sound signal, the FIR filter needs to be processed for at least 2 ms. Of course, this time lag is generally acceptable. But if you want to deal with signals as low as 50Hz, it may take 20ms or even longer, which will become a very annoying problem for live performances.

Generally speaking, the audio industry must be constantly making choices. Because there is never a best solution, only a more appropriate solution for the moment. For a better frequency response phase response, we will consider using a FIR filter, but at the same time we don't want too much delay in the system. Therefore, in reality, many manufacturers choose to use the FIR to process the mid-high frequency part of the system, while the IIR EQ and the classic crossover circuit handle the low frequency and ultra low frequency parts.

 

2.16 Adaptive Filtering in Signal Processing

The various applications of adaptive filters mainly include:

1. System modeling, in which an adaptive filter is used as a model to estimate the characteristics of an unknown system.

2. An adaptive noise canceller, wherein the adaptive filter is used to estimate and cancel a noise component in the desired signal.

 

 

Frequently Asked Questions about Common Applications of Filter

1. What are the applications of low pass filter?
Low pass filters are used to filter noise from a circuit. 'Noise' is a high frequency signal. When passed through a low pass filter most of the noise is removed and a clear sound is produced. high-cut or treble cut filters.

 

2. What is the application of high pass filter?
Applications of Active High Pass Filters are in audio amplifiers, equalizers or speaker systems to direct the high frequency signals to the smaller tweeter speakers or to reduce any low frequency noise or “rumble” type distortion.

 

3. Which filter is used in radio?
Radio Frequency filters are a special kind of a circuit that allows the right signals to pass while they cancel out undesired signals. When it comes to the filter topology, there are four basic RF filter types, i.e. high pass filter, low pass filter, band pass filter, and band reject.

 

4. What should I set my low pass filter to?
As a general rule, the Low-Pass Filter should be set at a value approximately equal to (or below) 70% of your main speaker's lowest frequency response. For example, your speaker's frequency response goes down to 43Hz. 70% of 43Hz equals 30.1, so you should set the subwoofer's low pass filter to 30Hz.

 

5. What is the transfer function of low pass filter?
Low Pass Filters and their Transfer Functions
As its name implies, a low pass filter is an electronic device that allows low frequency AC signals to pass a current through the filter circuit. The output from the filter circuit will be attenuated, depending on the frequency of the input signal.

 

6. What does an RF filter do?
RF filters are electronic components that are used to allow or prevent selected signals or frequencies in order to eliminate noise or pass through of unwanted signals. For effective filtering of signals, choose from the exclusive selection of RF filters from reputed manufacturers available at Future Electronics.

 

7. What are low pass filters used for?
Low pass filters are used to filter noise from a circuit. 'Noise' is a high frequency signal. When passed through a low pass filter most of the noise is removed and a clear sound is produced.

 

8. What are high and low pass filters used for?
Difference between Low pass filter and High pass filter:

Difference between Low pass filter and High pass filter

 

9. How do you make a low pass filter?
A simple 1st order low pass filter can be made using a single resistor in series with a single non-polarized capacitor (or any single reactive component) across an input signal Vin, whilst the output signal Vout is taken from across the capacitor.

 

10. What is the cutoff frequency of a low pass filter?
The cutoff frequency for a low-pass filter is that frequency at which the output (load) voltage equals 70.7% of the input (source) voltage. Above the cutoff frequency, the output voltage is lower than 70.7% of the input, and vice versa.

Ordering & Quality

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