6 Element Intermediate.ppt

1

Courtesy of Khairul Saleh

Fisika fMIPA UNSRI 2

These include: Amplifiers for amplifying the transducer output.

which may be small. Filters, for filtering out unwanted portions of the

signal. AD/DA converters, for converting analog type

signals to digital form

1. Introduction


Amplifiers are intermediate elements that increase the magnitude of the signal from a transducer so that it can be conveniently displayed or recorded. These may be of mechanical, hydraulic, pneumatic, optical or eletricallelectronic types, depending on the type of transducer. In cases where a reduction is needed in the magnitude of the signal from the transducers, these are called attenuators.

2. Amplifier


2.1. Mechanical Amplifier Elementshow a lever mechanism that is a typical

mechanical amplifier. As seen from the figure, the output signal Xo is given by:


2. 2. Hydroulic Amplifying Elementshows a typical hydraulic type element, in which

the output signal X, is given by


2. 3. Pneumatic Amplifying Elemet


2. 4. Optical Amplifying Element A ray of light gets deflected by 2 from a mirror attached to the moving

member and the distance X0 moved by the light spot on the scale is given by

where R is the distance between the scale and the mirror. By proper choice of the distance R. X0 can be made as large as desired.


2. 5. Electrical Amplifying ElementCurrently, most of the electrical amplifiers are either transistor based or

employ suitable integrated circuits (ICs) or both Vacuum tubes have now become obsolete and are employed in certain special applications only. Presently a wide variety of amplifiers are available to meet the specific requirements in the signal conditioning element of the instrument systems. The following are the characteristics of an ideal amphfer i.e. it should have:

(i) infinite input impedance, i.e. it should have no loading effect on the transducer.

(ii) zero output impedance(iii) a very large gain (theoretically infinite) to improve resolution(iv) zero output for zero input(v) ability to filter spurious inputs(vi) instant response.



Operational Amplifier - An operational amplifier(op amp) is a high gain differential amplifier withnearly ideal external characteristics. Internally theop amp is constructed using many transistors.

Terminology:V+ = non-inverting input voltageV- = inverting input voltageVo = output voltageIo = output currentI+ = non-inverting input currentI- = inverting input current±VDC = positive and negative DCsupply voltages used to powerthe op amp (typically ±5V to±30V)ΔV = V+ - V- = difference voltage

3. Operational Amplifiers


The Op-Amp Symbol


Internal Model of a Real Op-Amp

Zin is the input impedance (very large ≈ 2 MΩ)Zout is the output impedance (very small ≈ 75 Ω)Aol is the open-loop gain


Op-Amps Nearly ideal

An operational amplifier has a very high input impedance and a very high gain.

High gain: up to 105-106 High input impedance: 4MΩ Low output impedance: ∼500 Ω Stable

Op-Amp is short for operational amplifier. An operational amplifier is modeled as a voltage controlled voltage source. The exact gain is often unpredictable.


3.1 Inverting Amplifier


3.2 Non-inverting Amplifier


3.3 Differential (or Difference) Amplifier


3.4 Voltage followerThis is simply a noninverting amplifier with Rg= ∞ and Rf = 0

This unity gain amplifier is sometimes used asan input buffer as it has very high inputimpedance and low output impedance


3.5 Summing amplifier


3.6 Integrator


IntegratorSince the inverting input is at virtual ground

Applying Kirchhoff's Current Law (KCL) at the inverting input


3.7 Differentiator


DifferentiatorSince the inverting input is at virtual ground

Applying KCL at the inverting input


3.8 Instrumentation AmplifierMain aim is to improve the input impedance while maintaining a good common mode rejection


APPLICATION: Interfacing Strain Gauges in a Bridge Circuit


4. Filter

Macam-macam Filter Low-pass Filters (Tapis Lolos Rendah) High-pass Filters (Tapis Lolos Tinggi) Band-pass Filters (Tapis Lolos Pita) Band-stop Filters (Tapis Sekat Pita)


Filters: Intuitive Understanding

Transfer Function:

Impedance:

Low-pass filters: CRVi Vo



Low-pass filters:

L

RVi Vo

Dimensionless Frequency:

At low frequency:

At high frequency:



High-pass filters: C

R VoVi

VoL

R

Vi

At low frequency:

At high frequency:



C

R

L

VoVi

Band-pass or Band-stop Filters:

C

R VoVi

L

RVi Vo

}High-pass

Low-pass

Low-passHigh-pass

High-passLow-pass



C

R

L

VoVi

Band-pass or Band-stop Filters:

Band-pass Band-stopHigh-passLow-pass


Complex Frequency and Laplace Transform

Phasor and Impedance

What if

Define complex frequency


Transfer FunctionC

R

L

VoVi



Active filters:

CR1

ViVo

+-

R2

Low pass filter


Active Band-pass or Band-stop Filters:

CR1

ViVo

+-

R2

C

R VoVi

}High-pass

Low-passC2

R1

ViVo

+-

R2

C1

Transfer Function? Quiz

Transfer Function


Filter order ? Determined by the or of the Denominator of the transfer function

Cascade Connections

High Order FiltersC

R

L

VoVi

C

R

L

Vi

C

R

L

Vo

C2R1

Vi+-

R2

C1 C2R1

Vo+-

R2

C1

Loading


Band Pass Filter C

R

L

VoVi

Center Frequency?

Transfer Function

What if the transfer function is described as


5. ADC dan DAC

ADC : A/D Converter ; Analog to Digital Converters : Pengubah besaran /kuantitas/ sinyal analog (sinyal kontinue) menjadi sinyal digital (sinyal diskrit).

DAC : D/A Converter ; Digital to Analog Converter : Pengubah besaran / sinyal digital menjadi sinyal Analog.


5.1 Binary-Weighed D/A Converters


5.2. R/2R Ladder D/A Converters


5.3 Integreted-Circuit D/A Converters


IC D/A C MC1408


5.4. Parallel-Encoded A/D Converters


5.5. Counter-Ramp A/D Converters


5.6. Successive-Approximation A/D C


5.7. Integrated-Circuit A/D Converters


IC ADC 0804


Data Acquisition System


Sumber


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6 Element Intermediate.ppt

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