Chapter 7 Signal Conditioning ● ●
What is and why signal conditioning ? Signal conditioning circuits ● ● ● ● ● ● ● ●
Current sensitive circuits Ballast circuits Voltage-dividing circuits Bridge circuits Resonant circuits Amplifier circuits Filters etc. 1
What is and why signal conditioning ?
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Definition. Why signal conditioning ? Mechanical signal conditioning. Electrical signal conditioning. Why electrical signal conditioning ?
2
Why signal conditioning ? Instrument and other requirements ● ● ● ● ● ● ●
Input to instrument must be voltage. Range matching to instrument. Impedance matching Bandwidth limitation of instrument Signal isolation Signal preprocessing Removal of undesirable signals 3
Signal conditioning circuits ●
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Voltage to voltage conversion (a) Voltage amplification (b) Filters Current to voltage conversion Resistance to voltage Capacitance to voltage Comparators Signal energy to voltage
4
Signal conditioning circuits Two types of transducers: Passive transducers Active transducers Signal conditioning circuits ● Current sensitive circuits ● Ballast circuits ● Voltage-dividing circuits ● Bridge circuits ● Resonant circuits ● Amplifier circuits ● Filters ● etc.
5
Simple current sensitive circuits Rm
ei
Current indicator or recorder
ei i o= kR t R m
io
kRt Resistance-type transducer
Rm : meter and circuit resistance
ei k =0, ⇒ i max = Rm io io Rm 1 = = i max ei 1 R t / R m k
Note : (1) The relationship is nonlinear ! (2) ei must be kept precisely constant ! 6
Ballast circuits Resistance-type transducer
Rm i ei
kRt
eo
Rm : ballast resistance
Voltage indicator or recorder
ei i= kR t R m e i kR t e o =ikR t = R m kR t eo kR t / R m = e i 1 kR t / R m
Note : (1) The relationship is nonlinear ! (2) ei must be kept precisely constant !
7
Voltage-dividing circuits
i
ei i= R 1 R 2
R1
ei R2
eo
ei R 2 e o =iR 2 = R 1 R 2 eo R2 / R1 = e i 1 R 2 / R 1
8
Voltage-dividing potentiometer (Linear Potentiometer)
i ei
Rp
kR p
eo
kR p e i eo= =ke i Rp
9