signal cond filters
DESCRIPTION
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INSTRUMENTATION AND CONTROL(MCT 3224)SIGNAL CONDITIONING : PASSIVE FILTERSNadzril SulaimanDepartment of Mechatronics Engineering,International Islamic University Malaysia
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ContentConcept of filtersLow-pass filterHigh-pass filterBand-pass filterBand-reject filter
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Objectives of topicExplain terms related to filterIdentify the circuit of different types of filtersExplain the characteristics of each type of filtersDesign different types of filters based on the design requirements
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Soil sieving analogy
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Introduction to filtersFilters pass, reject, and attenuate signals at various frequencies
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Characteristics of filtersCommon types of filters:Low-pass - Allow low frequency signal; eliminate high frequency signal
High-pass - Allow high frequencies; eliminate low frequencies
Band-pass - Allow/Pass some particular range of frequencies; eliminate other frequencies outside that band
Band-rejection (Band-Stop) - Stop a range of frequencies; pass all other frequencies
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Characteristics of filtersIdeal filters
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Characteristics of filtersPractical filters
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Important termsPass band frequencies passedStop band frequencies eliminated / attenuatedCutoff Frequency, fc (critical @ corner frequency) point in the stop band where frequencies have been attenuated by 3 dB (or frequency at which gain = 0.707)
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Important termsBand width distance (in Hz) between 2 fc in Band-pass and Band-reject (Band-stop) filters
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Passive filter circuitsLow-pass filter
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Low-pass filterCharacteristics:
It blocks high frequencies and passes low frequencies All signals with frequency above some critical value are simply rejected
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Design low-pass filterDesign Methods: 1) Find the cutoff frequency that will satisfy the design criteria 2) Select a standard value of C in F or pF 3) Calculate the value of R using equation of cutoff frequency * Choose another value of capacitor if the resistance value is below 1k or above 1M
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Design low-pass filterCutoff / critical frequencyVoltage ratio / Magnitude of TF* f is the frequency of the signal under considerationResponse of the low-pass filter as a function of the frequency ratio ( f/fc ).
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Design low-pass filterExample 1:
A student measures signal from a microphone. The measured signal contains noise at 0.5MHz. The desired information signal is at 400Hz.Develop a low-pass RC filter to attenuate the noise by 97%.
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High-pass filterCharacteristics:
It blocks low frequencies and passes high frequencies All signals with frequency below some critical value are simply rejected
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Design high-pass filterDesign Methods: 1) Find the cutoff frequency that will satisfy the design criteria 2) Select a standard value of C in F or pF 3) Calculate the value of R using equation of cutoff frequency * Choose another value of capacitor if the resistance value is below 1k or above 1M
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Design high-pass filterCutoff / critical frequencyVoltage ratio / Magnitude of TF* f is the frequency of the signal under considerationResponse of the high-pass filter as a function of the frequency ratio ( f/fc ).
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Design high-pass filterExample 2:
Pulses for a stepping motor are being transmitted at 2000 Hz, in which at this frequency the output is attenuated by 3dB . Design a filter to reduce the noise that present at 60Hz.
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Band-pass filterCharacteristics:
A low-pass filter followed by a high-pass filter Blocks frequency below low limit and above high limit Frequencies between limits are passed
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Design band-pass filterDesign Methods: 1) Find fL and fH that will satisfy the design criteria 2) Select a standard value of R that will satisfy the limit (RH / RL < 0.01) 3) Calculate the value of C using equation of cutoff frequency
* Choose another value of resistor if the capacitor value is not in the F or F range
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Design band-pass filter* Resistor ratio, RH / RL must be kept below 0.01
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Design band-pass filterExample 3:
A signal conditioning system use a frequency variation from 6 kHz to 60 kHz to carry measurement information.There is considerable noise at 120 Hz and at 1 MHz. Design a band-pass filter to reduce the noise by 90%.
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Design band-reject filter (Twin-T)Design Method:
1) Find cutoff frequency that will satisfy the design criteria.
2) Select a standard value of C in F or pF 3) Calculate the value of R using equation of cutoff frequency
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Design band-reject filter (Twin-T)Design Method:
4) Calculate the value of grounding components, R1 and C1 using the respective equation
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Design band-reject filter (Twin-T)Example 4 :
A single line is multiplexed to carry sensor signal in a frequency range below 1kHz and communication signals ranging from 10kHz to 50kHz. There is a large noise component at 4.5kHz from a turbine in the plant. Design a twin-T notch filter to attenuate the 4.5kHz noise.
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Filter-end