Transcript 07-Chapter 3, 3 of 3x

ELECTRONIC INSTRUMENTATION
EKT 314/4
WEEK 7 : CHAPTER 3
SIGNAL CONDITIONING
Chapter 3 Content
 Introduction
 Signal Conditioning Circuit (SCC) Function
 Preliminary Requirement
 Signal Conditioning (SC) System Type
 Amplifier
 Modulator
 Filter
Filter
 A network designed to attenuate certain frequencies but pass
others without attenuation is called a filter.
 Possess at least one pass band (band of frequencies in which
the output is approximately equal to the input) and an
attenuation band in which output is zero (attenuation is
infinite).
 The frequencie(s) that separate the various pass and
attenuation bands are called the cutoff frequencies.
Types of Filters
 Low pass
 High pass
 Band pass
 Band stop
 All pass
Ideal Response – Low Pass
Low Pass Filter
Ideal Response – High Pass
High Pass Filter
Ideal Response – Band Pass
Band Pass Filter
Ideal Response – Band Stop
Ideal Response – All Pass
Filter – Classifications
 Passive Filters
 Active Filters
Passive Filters
 A passive filter is a kind of electronic filter that is made only
from passive elements.
 It does not require an external power source (beyond the
signal).
 Since most filters are linear, in most cases, passive filters are
composed of just the four basic linear elements – resistors,
capacitors, inductors, and transformers.
 More complex passive filters may involve nonlinear
elements, or more complex linear elements, such as
transmission lines.
Passive Filter Advantages
A passive filter has several advantages over an active filter:
 Guaranteed stability
 Passive filters scale better to large signals (tens of amperes,
hundreds of volts), where active devices are often impractical
 No power consumption, but the desired signal is invariably
attenuated. If no resistors are used, the amount of signal loss
is directly related to the quality (and the price) of the
components used.
 Inexpensive (unless large coils are required)
 For linear filters, generally, more linear than filters including
active (and therefore non-linear) elements
Active Filters
 An active filter is a type of analog electronic filter,
distinguished by the use of one or more active components
i.e. voltage amplifiers or buffer amplifiers.
 Typically this will be a vacuum tube, or solid-state (transistor
or operational amplifier).
Active Filter Advantages
 Inductors can be avoided. Passive filters without inductors cannot
obtain a high Q (low damping), but with them are often large and
expensive (at low frequencies), may have significant internal
resistance, and may pick up surrounding electromagnetic signals.
 The shape of the response, the Q (Quality factor), and the tuned
frequency can often be set easily by varying resistors, in some
filters one parameter can be adjusted without affecting the others.
Variable inductances for low frequency filters are not practical.
 The amplifier powering the filter can be used to buffer the filter
from the electronic components it drives or is fed from, variations
in which could otherwise significantly affect the shape of the
frequency response.
ELECTRONIC INSTRUMENTATION
EKT 314/4
WEEK 7 : CHAPTER 3
END