8255.ppt

ELECTRONIC INSTRUMENTATION &
CONTROL SYSTEMS
(WLE-306)
Presented by:
Mr. Shahnawaz Uddin
1

Unit-4
MISCELLANEOUS INSTRUMENTS
2

Amplitude Distortion
• Distortion is the alteration of the original shape (or other characteristic)
of a signal, waveform, or other form of information
• Distortion is usually unwanted and in practice, many methods are
employed to minimize it
• In signal processing, a noise-free system can be characterized by a
transfer function, such that the output y(t) can be written as a function of
the input x(t) as: y(t) = F(x(t))
• When the transfer function comprises only a gain (A) and delay (T), then
the output is undistorted
• Distortion occurs when the transfer function F is more complicated than
this, e.g., if F is a linear function of frequency (for instance a filter whose
gain and/or delay varies with frequency), then the signal will experience
linear distortion
• The linear distortion will not change the shape of a single sinuosoid, but
will usually change the shape of a multi-tone signal
3

• Amplitude distortion is distortion occurring in a system, subsystem,
or device when the output amplitude is not a linear function of the
input amplitude
• For example, in case of a transistor, output is a linear function of
input only for a fixed portion of the transfer characteristic, i.e., Ic = βIb
• When output is not in this portion, two forms of amplitude distortion
might arise:
(i) Harmonic Distortion, & (ii) Intermodulation Distortion
(i) Harmonic distortion:
• The creation of harmonics of the fundamental frequency of a
sinusoidal wave to a system
(ii) Intermodulation distortion:
• This form of distortion occurs when two sinusoidal waves of
frequencies f1 and f2 are present at the input, resulting in the creation
of several other frequency components, whose frequencies include
(f1 + f2 ), (f1 - f2 ), (2f1 - f2 ), (2f2 – f1), and in general (mf1 ± nf2) for
integer m and n
Amplitude Distortion (-contd.)
4

• Generally the strength of the unwanted output falls rapidly as m and n
increase
• Amplitude distortion is measured with the system operating under
steady-state conditions with a sinusoidal input signal
• When other frequencies are present, the term "amplitude" refers to
the amplitude of fundamental frequency component only
• It can be shown mathematically (Fourier Series Analysis) that any
complex waveform is made up of a fundamental frequency (f0)
component and its harmonics (2f0, 3f0, 4f0, …)
• It is often desired to measure the amplitude of fundamental or each
harmonic individually, and can be performed by instruments called
wave analyzers
• Wave analyzers are also referred to as frequency selective
voltmeters, carrier frequency voltmeters, or selective level
voltmeters
• Some wave analyzers have the facility of automatic frequency
control, in which the tuning automatically locks to the signal
5

• This makes it possible to measure the amplitude of signals that are
drifting in frequency by amounts that would carry them outside the
widest pass-band available
• Harmonic distortion analyzers measure the total harmonic content in
the waveforms
• Harmonic distortion can be quantitatively measured very accurately with
harmonic distortion analyzer, generally called a distortion analyzer
• The total harmonic distortion (THD) is given by
where, D2, D3, D4, … represent 2nd, 3rd, 4th, harmonics
• The harmonic distortion analyzer measures the total harmonic distortion
without individually the amplitude & frequency of each component
• These analyzers can be used along with a frequency generator or a source
of white (or pseudo-random) noise to measure the frequency response of
amplifiers, filters, etc.
...
D
D
D
D 2
4
2
3
2
2 



6

Fig. (4.1) Graph of a Waveform and the distorted versions of the same waveform
7

Basic Wave Analyzer
• A basic wave analyzer is shown in fig. (9.1a), and consists of a
primary detector (a simple LC circuit)
• This LC circuit is adjusted for resonance at the frequency of the
particular harmonic component to be measured
• The intermediate stage is a full wave rectifier, to obtain the
average value of the input signal
• The indicating device is a simple dc voltmeter that is calibrated
to read the peak value of the sinusoidal input voltage
• Since, the LC circuit is tuned to a single frequency, it passes
only the frequency to which it is tuned and rejects all other
frequencies
• A number of tuned filters, connected to the indicating device
through a selector switch, would be required for a Wave
Analyzer
8

Basic Wave Analyzer (-contd.)
Fig. (9.1a) Basic Wave Analyzer
9

Basic Wave Analyzer (-contd.)
10

Frequency Selective Wave Analyzer
• Wave analyzer (fig. 9.1b) consists of a very narrow pass-band
filter section which can be tuned to a particular frequency within
the audible frequency range (20 Hz -20 kHz)
• The complex wave to be analyzed is passed through an adjustable
attenuator, which serves as a range multiplier and permits a large
range of signal amplitudes to be analyzed without loading the
amplifier
• The driver amplifier applies the attenuated input signal to a high-Q
active filter (a low pass filter, which allows the selected frequency
to pass and reject all others)
• The magnitude of this selected frequency is indicated by the meter
and the filter section identifies the frequency of the component
• The filter circuit consists of a cascaded RC resonant circuits and
amplifiers
11

• The capacitors are varied for range changing (i.e., coarse tuning)
& the potentiometer is used to change the frequency within the
selected pass-band (i.e., fine tuning), hence, this wave analyzer is
also called a frequency selective voltmeter
• The selected signal output from the final amplifier stage is applied
to the meter circuit & to an un-tuned buffer amplifier
• The main function of the buffer amplifier is to drive output devices,
such as recorders or electronics counters
• The meter has several voltage ranges as well as decibel scales
marked on it
• It is driven by an average reading rectifier type detector
• The bandwidth of the instrument is very narrow, typically about 1%
of the selective band given in response characteristics (fig. 9.2)
Frequency Selective Wave Analyzer (-contd.)
12

13

14

Heterodyne Wave Analyzer
• The wave analyzers are useful for measurement in the audio
frequency range only, i.e., for measurements in the RF range and
above (MHz range), an ordinary wave analyzer can’t be used
• Hence, special types of wave analyzers working on the principle of
heterodyning (mixing) are used, which are known as Heterodyne
wave analyzers
• In Heterodyne wave analyzer, the input signal to be analyzed is
heterodyned with the signal from the internal tunable local oscillator
in the mixer stage to produce a higher IF frequency
• By tuning the local oscillator frequency, various signal frequency
components can be shifted within the pass-band of the IF amplifier
• The output of the IF amplifier is rectified and applied to the meter
circuit
• An instrument that involves the principle of heterodyning is the
Heterodyning tuned voltmeter (shown in fig. 9.3)
• The input signal is heterodyned to the known IF by means of a
tunable local oscillator
15

• The amplitude of the unknown component is indicated by the
VTVM (Vacuum Tube Voltmeter) or output meter
• The frequency of the component is identified by the local oscillator
frequency, i.e., the local oscillator frequency is varied so that all
the components can be identified
• The fixed frequency amplifier is a multistage amplifier, which can
be designed conveniently because of its frequency characteristics
• With the use of a suitable attenuator, a wide range of voltage
amplitudes can be covered
• Their disadvantage is the occurrence of spurious cross-modulation
products, setting a lower limit to the amplitude that can be
measured
Heterodyne Wave Analyzer (-contd.)
16

• Two types of frequency-selective amplifiers find use in Heterodyne
wave analyzers
• The first type employs a crystal filter (band-pass arrangement),
having a center frequency of 50 kHz; another type uses a resonant
circuit in which the effective Q has been made high and is controlled
by negative feedback
• When a knowledge of the individual amplitudes of the component
frequency is desired, a heterodyne wave analyzer is used
• A modified heterodyne wave analyzer is shown in fig. 9.4
• In this analyzer, the attenuator provides the required input signal for
heterodyning in the first mixer stage, with the signal from a local
oscillator having a frequency of 30-48 MHz
• The first mixer stage produces an output which is the difference of
the local oscillator frequency and the input signal, to produce an IF
signal of 30 MHz
17

• This IF frequency is uniformly amplified by the IF amplifier
• This amplified IF signal is fed to the second mixer stage, where it
is again heterodyned to produce a difference frequency or IF of
zero frequency
• The selected component is then passed to the meter amplifier and
detector circuit through an active filter having a controlled band-
width
• The meter detector output can then be read off on a db-calibrated
scale, or may be applied to a secondary device such as a recorder
• This wave analyzer is operated in the RF range of 10 kHz -18 MHz
with 18 overlapping bands selected by the frequency range control
of the local oscillator
• The bandwidth, which is controlled by the active filter, can be
selected at 200 Hz, 1 kHz, and 3 kHz
18

19

20

Harmonic Distortion Analyzer
Fundamental Suppression Type:
• Distortion analyzer measures the total harmonic power present in the
test wave rather than the distortion caused by each component
• The simplest method to suppress the fundamental frequency by
means of a high pass filter whose cut-off frequency is a little above
the fundamental frequency
• Thus, the high pass filter allows only the harmonics to pass and the
total harmonic distortion (THD) can then be measured
• The most commonly used harmonic distortion analyzers based on
fundamental suppression are as follow:
(i) Employing a Resonance Bridge, (ii) Wien's Bridge Method
(iii) Bridged T -Network Method
(i) Employing a Resonance Bridge:
• The bridge, shown in fig. (9.5), is balanced for the fundamental
frequency, i.e., L & C are tuned to the fundamental frequency
21

• The bridge is unbalanced for the harmonics, i.e., only harmonic
power will be available at the output terminal and can be measured
• If the fundamental frequency is changed, the bridge must be
balanced again by varying L & C
• If L & C are fixed components, then this method is suitable only when
the test wave has a fixed frequency
• Indicators can be thermocouples or square law VTVMs (Vacuum
Tube Volte Meters), which indicate the rms value of all harmonics
• When a continuous adjustment of the fundamental frequency is
desired, a Wien bridge arrangement is used (shown in fig. 9.6)
(ii) Wien's Bridge Method:
• The bridge is balanced for the fundamental frequency, therefore,
fundamental energy is dissipated in the bridge circuit elements
• Only the harmonic components reach the output terminals
Harmonic Distortion Analyzer (-contd.)
22

• The harmonic distortion output can then be measured with a meter
• For balance at the fundamental frequency:
C1 = C2 = C, R1 = R2 = R, R3 = 2R4
(iii) Bridged T -Network Method:
• As shown in fig. (9.7), L & C's are tuned to the fundamental
frequency, and R is adjusted to bypass fundamental frequency
• The tank circuit being tuned to the fundamental frequency, the
fundamental energy will circulate in the tank and is bypassed by the
resistance
• Only harmonic components will reach the output terminals and the
distorted output can be measured by the meter
• The Q of the resonant circuit must be at least 3-5
• One method of using a bridge T-network is given in fig. (9.8)
• The switch S is first connected to point A so that the attenuator is
excluded and the bridge T-network is adjusted for full suppression of
the fundamental frequency, i.e., minimum output
23

• Minimum output indicates that the bridged T-network is tuned to the
fundamental frequency & fundamental frequency is fully suppressed
• The switch is next connected to terminal B, i.e. the bridged T-network
is excluded
• Attenuation is adjusted until the same reading is obtained on the
meter
• The attenuator reading indicates the total rms distortion
Note:
• Distortion measurement can also be obtained by means of a wave
analyzer; knowing the amplitude & frequency of each component; the
harmonic distortion can be calculated
• However, distortion meters based on fundamental suppression are
simpler to design and less expensive than wave analyzers
• The disadvantage with the harmonic distortion analyzers is that they
give only the total distortion and not the amplitude of individual
distortion components
24

Fig. (9.5) Resonance Bridge
25

Fig. (9.6) Wien’s Bridge Method 26

27

28

Spectrum Analyzer
• The most common way of observing signals is to display them on an
oscilloscope, with time on the x-axis (i.e., amplitude of the signal
versus time)
• It is also useful to display signals in the frequency domain; the
instrument providing this frequency domain view is the spectrum
analyzer
• A spectrum analyzer provides a calibrated graphical display on its
CRT, with frequency on the horizontal axis and amplitude (voltage)
on the vertical axis
• Displayed as vertical lines against these coordinates are sinusoidal
components of which the input signal is composed
• The height represents the absolute magnitude, and the horizontal
location represents the frequency
• These instruments provide a display of the frequency spectrum over
given frequency band
• Spectrum analyzers use either (i) a parallel filter bank, or (ii) a
swept frequency technique 29

(i) Spectrum Analyzer using Parallel Filter Bank:
• In a parallel filter bank analyzer, the frequency range is covered by a
series of filters whose central frequencies and bandwidths are so
selected that they overlap each other (as shown in Fig. 9.9a)
• Typically, an audio analyzer will have 32 of these filters, each covering
one third of an octave
• For wide band narrow resolution analysis, particularly at RF or
microwave signals, the swept technique is preferred
(ii) Spectrum Analyzer using Swept Receiver Design:
• As shown in fig. (9.9b), the sawtooth generator provides the sawtooth
voltage which drives the horizontal axis element of the scope and this
sawtooth voltage is frequency controlled element of the voltage tuned
oscillator
• As the oscillator sweeps from fmin to fmax of its frequency band at a linear
recurring rate, it beats with the frequency component of the input signal
& produces an IF, whenever a frequency component is met during its
sweep
Spectrum Analyzer (-contd.)
30

• The IF corresponding to the frequency component is amplified and
detected if necessary, and then applied to the vertical plates of the
CRO, producing a display of amplitude versus frequency
• One of the principal applications of spectrum analyzers has been in
the study of the RF spectrum produced in microwave instruments
• In a microwave instrument, the horizontal axis can display a wide
range (2-3 GHz) for a broad survey and a narrow range (30 kHz) as
well for a highly magnified view of any small portion of the spectrum
• Signals at microwave frequency separated by only a few kHz can be
seen individually
• The basic block diagram of an RF spectrum analyzer (fig. 9.13)
covers the range 500 kHz to 1 GHz, which is representative of a
super-heterodyne type
• The input signal is fed into a mixer which is driven by a local oscillator
(which is linearly tunable electrically over the range 2-3 GHz)
31

• The mixer provides two signals at its output that are proportional in
amplitude to the input signal but of frequencies which are the sum
and difference of the input signal & local oscillator frequency
• The IF amplifier is tuned to a narrow band around 2 GHz, since the
local oscillator is tuned over the range of 2-3 GHz, only the inputs
that are separated from the local oscillator frequency by 2 GHz will be
converted to IF frequency band, pass through the IF frequency
amplifier, get rectified & produce a vertical deflection on the CRT
• From this, it is observed that as the sawtooth signal sweeps, the local
oscillator also sweeps linearly from 2-3 GHz
• The tuning of the spectrum analyzer is a swept receiver, which
sweeps linearly from 0 to 1 GHz
• The sawtooth scanning signal is also applied to the horizontal plates
of the CRT to form the frequency axis
• Spectrum analyzers are widely used in radars, oceanography, and
bio-medical fields
32

33

Basic Spectrum Analyzer Using Swept Receiver Design
34

35

Fig. (9.12) Test Waveform as seen on X-axis (time) & Z-axis (frequency)
Fig. (9.13) RF Spectrum Analyzer
36

Q-METER
• The overall efficiency of coils and capacitors intended for RF
applications is best evaluated using the Q-value
• The Q-meter is an instrument designed to measure some electrical
properties of coils and capacitors
• The principle of Q-meter is based on series resonance; the voltage
drop across the coil or capacitor is Q-times the applied voltage
(where Q is the ratio of reactance to resistance, XL/R)
• If a fixed voltage is applied to the circuit, a voltmeter across the
capacitor can be calibrated to read Q directly
• At resonance XL = XC and EL = I XL , EC = I XC , E = IR
• Therefore,
• From the above equation, if E is kept constant, the voltage across the
capacitor can be measured by a voltmeter calibrated to read directly
in terms of Q
E
E
R
X
R
X
Q C
C
L



37

• A practical Q-meter circuit is shown in fig.(10.7)
• The wide range oscillator, with frequency range from 50 kHz to 50 MHz,
delivers a current to the shunt resistance (Rsh) having a value of 0.02 Ω
• Rsh introduces almost no resistance into the tank circuit and therefore,
represents a voltage source of magnitude ‘e’ with a small internal
resistance
• The voltage across the capacitor is measured by an electronic voltmeter
corresponding to EC and calibrated directly to read Q
• The circuit is tuned to resonance by varying C until the electronic
voltmeter reads the maximum value
• The resonance output voltage E, corresponding to EC , is E = Q x e
• That is, Q = E/e
• Since, ‘e’ is known, the electronic voltmeter can be calibrated to read Q
directly
• The inductance of the coil can be determined by connecting it to the test
terminals of the instrument
Q-METER (-contd.)
38

• The circuit is tuned to resonance by varying either the capacitance or the
oscillator frequency
• If the capacitance is varied, the oscillator frequency is set to a given
frequency & resonance is obtained
• If the capacitance is preset to a desired value, the oscillator frequency is
varied until resonance occurs
• The inductance of the coil can be calculated from known values of the
resonant frequency & resonating capacitor (C)
• The Q indicated is not the actual Q, because the losses of the resonating
capacitor, voltmeter and inserted resistance are all included in the
measuring circuit
• The actual Q of the measured coil is somewhat greater than the
indicated Q
• This difference is negligible except where the resistance of the coil is
relatively small compared to the inserted resistance Rsh
Q-METER (-contd.)
C
)
f
2
(
1
L
or
,
LC
2
1
f
,
X
X 2
C
L





39

Q-METER (-contd.)
Fig. (10.7) Circuit Diagram of a Q-meter
40

Factors Causing Error during Q-measurement:
(1) At high frequencies the electronic voltmeter may suffer from losses
due to the transit time effect
The effect of Rsh is to introduce an additional resistance in the tank
circuit, as shown in fig. (10.8)
• To make the Qobs value as close as possible to Qact , Rsh should be
made as small as possible (Rsh value of 0.02-0.04 Ω introduces
negligible error)
(2) Another source of error, and probably the most important one, is the
distributed capacitance or self capacitance of the measuring circuit
Q-METER (-contd.)
)
R
R
1
(
Q
Q
,
Hence
R
R
1
R
R
R
Q
Q
R
R
L
Q
and
R
L
Q
sh
obs
act
sh
sh
obs
act
sh
obs
act












41

• The presence of distributed or stray capacitances modifies the actual
Q and the inductance of the coil
• At the resonant frequency, at which the self capacitance and inductance
of the coil are equal, the circuit impedance is purely resistive; this
characteristic can be used to measure the distributed capacitance
• One of the simplest methods of determining the distributed capacitance
(Cs) of a coil involves the plotting of a graph of 1/f2 against C (in pF) as
shown in fig. (10.9a)
• The frequency of the oscillator in the Q meter is varied and the
corresponding value of C for resonance is noted
• The straight line produced to intercept the x-axis gives the value of Cs
Q-METER (-contd.)
s
2
s
2
2
s
2
2
C
C
then
,
0
f
1
If
)
C
C
(
L
4
f
1
or
,
)
C
C
(
L
2
1
f
and
L
4
Slope
,
therefore
,
4
Slope
L













43

• The value of unknown can also be determined from the above
equation
• Another method of determining the stray or distributed capacitance
(Cs) of a coil involves making two measurements at different
frequencies
• The capacitor C of the Q-meter is calibrated to indicate the
capacitance value
• The test coil is connected to the Q-meter terminals as shown in
fig.(10.9b)
• The tuning capacitor is set to a high value position (to its maximum)
and the circuit is resonated by varying the oscillator frequency
• Suppose the meter indicates resonance & the oscillator frequency is
found to be f1 & the capacitance value to be C1
• The oscillator frequency of the Q-meter is now increased to twice the
original frequency, i.e., f2 = 2f1 , and the capacitor is varied until
resonance occurs at C2
Q-METER (-contd.)
44

• The resonant frequency of an LC circuit is given by
• Therefore, for the initial resonance condition, the total capacitance of the
circuit is (C1+ Cs) and the resonant frequency is given by
• After the oscillator and the tuning capacitor are varied for the new value
of resonance, the capacitance is (C2 + Cs), therefore,
• But f2 = 2f1 , therefore,
• Hence, C1 + Cs = 4 (C2 + Cs)
• The distributed capacitance can be calculated using the above equation
Q-METER (-contd.)
LC
2
1
f


)
C
C
(
L
2
1
f
s
1
1



)
C
C
(
L
2
1
f
s
2
2



)
C
C
(
L
2
1
2
)
C
C
(
L
2
1
s
1
s
2 





3
C
4
C
C 2
1
s



45

Examples
Ex. 10.1: The self capacitance of a coil is measured by using the
outlined in the previous section. The first measurement is at f1=1 MHz
& C1=500 pF. The second measurement is at f2=2 MHz & C2=110 pF.
Find the distributed capacitance. Also calculate the value L.
(Ans. 20 pF, 48.712 µH)
Ex. 10.2: Calculate the value of the self capacitance when the following
measurements are performed:
• f1=2 MHz & C1=500 pF
• f2=6 MHz & C2=50 pF
(Ans. 6.25 pF)
Problem-1: The distributed capacitance was found to be 20 pF by use
of a Q-meter. The first resonance occurred at C1=300 pF & f1 was
half the second resonance frequency. Determine the value of f2 at the
second resonance (given L=40 µH) (Ans. 2.8 MHz) 47

Electroencephalogram (EEG)
• An electroencephalogram (EEG) is a test that measures and records
the electrical activity of the brain
• Special sensors (electrodes) are attached to your head and hooked
by wires to a computer
• The computer records your brain's electrical activity on the screen or
on paper as wavy lines
• Certain conditions, such as seizures, can be seen by the changes in
the normal pattern of the brain's electrical activity
EEG may be done to:
• Diagnose epilepsy and see what type of seizures are occurring
• Check for problems with loss of consciousness or dementia
• Find out if a person who is in a coma is brain-dead
• Study sleep disorders, such as narcolepsy
• Watch brain activity while a person is receiving general
anesthesia during brain surgery
48

• Help find out if a person has a physical problem (problems in the
brain, spinal cord, or nervous system) or a mental health problem
How EEG is Done?
• The EEG record is read by a doctor who is specially trained to
diagnose and treat disorders affecting the nervous system
(neurologist)
• You will be asked to lie on your back on a bed or table or relax in a
chair with your eyes closed
• The EEG technologist will attach 10 to 20 flat metal discs (electrodes)
to different places on your head, using a sticky electrolyte paste or
jelly to hold the electrodes in place (A cap with fixed electrodes may
be placed on your head instead of individual electrodes)
• The electrodes are hooked by wires to an EEG machine that records
the brain activity drawn by a row of pens on a moving piece of paper
or as an image on the computer screen
EEG (-contd.)
49

• You may be asked to breathe deeply and rapidly (hyperventilate), usually
20 breaths a minute for 3 minutes
• You may be asked to look at a bright, flashing light called a strobe
(photic or stroboscopic stimulation)
Results: There are several types of brain waves:
• Alpha Waves have a frequency of 8 to 12 cycles per second. Alpha
waves are present only in the waking state when your eyes are closed
but you are mentally alert. Alpha waves go away when your eyes are
open or you are concentrating.
• Beta Waves have a frequency of 13 to 30 cycles per second. These
waves are normally found when you are alert or have taken high doses
of certain medicines, such as benzodiazepines.
• Delta Waves have a frequency of less than 3 cycles per second. These
waves are normally found only when you are asleep or in young children.
• Theta Waves have a frequency of 4 to 7 cycles per second. These
waves are seen in drowsiness or arousal in older children and adults; it
can also be seen in meditation
EEG (-contd.)
50

Fig. (1) The cerebrum contains the frontal, parietal, temporal and occipital lobes
51

Fig. (2) The 10–20 electrode system for measuring the EEG
52

Fig. (3) A man undergoing an EEG, wearing a cap equipped with electrodes
53

Fig. 4(a) Four types of EEG waves
Fig. 4(b) When the eyes are
opened, alpha waves disappear
54

Normal In adults who are awake, the EEG shows mostly alpha waves and beta
waves.
The two sides of the brain show similar patterns of electrical activity.
There are no abnormal bursts of electrical activity and no slow brain
waves on the EEG tracing.
If flashing lights (photic stimulation) are used during the test, one area
of the brain (the occipital region) may have a brief response after each
flash of light, but the brain waves are normal.
Abnormal The two sides of the brain show different patterns of electrical
activity. This may mean a problem in one area or side of the brain is
present.
The EEG shows sudden bursts of electrical activity (spikes) or sudden
slowing of brain waves in the brain. These changes may be caused by
a brain tumor, infection, injury, stroke, or epilepsy.
55

Abnormal The EEG records changes in the brain waves that may not be in
just one area of the brain. A problem affecting the entire brain-
such as drug intoxication, infections (encephalitis), or metabolic
disorders (such as diabetic ketoacidosis) that change the chemical
balance in the body, including the brain-may cause these kinds of
changes.
The EEG shows delta waves or too many theta waves in adults
who are awake. These results may mean brain injury or a brain
illness is present. Some medicines can also cause this.
The EEG shows no electrical activity in the brain (a "flat" or
"straight-line" EEG). This means that brain function has stopped,
which is usually caused by lack of oxygen or blood flow inside
the brain. This may happen when a person has been in a coma. In
some cases, severe drug-induced sedation can cause a flat EEG.
56

What factors may affect the EEG Test?
• Reasons why the results may not be helpful include:
(i) Moving too much
(ii) Taking some medicines, such as those used to treat seizures
(antiepileptic medicines) or sedatives, tranquilizers, and barbiturates
(iii) Being unconscious from severe drug poisoning or a very low body
temperature (hypothermia)
(iv) Having hair that is dirty, oily, or covered with hairspray or other hair
preparations. This can cause a problem with the placement of the
electrodes.
EEG (-contd.)
57

Electrocardiography
• An electrocardiogram (ECG or EKG) is an electrical recording of the
heart activity over time and is used in the investigation of heart
disease
• British physiologist Augustus D. Waller was the pioneer of
electrocardiography and in 1887 published the first human
electrocardiogram
• In 1903 Dutch physiologist, Willem Einthoven, transformed this
curious physiologic phenomenon into an indispensable clinical
recording device that is still used today
• ECG is a surface measurement of the electrical potential generated
by electrical activity in cardiac tissue
• The human heart can be considered as a large muscle whose
beating is simply a muscular contraction which develops a potential
to be measured in the form of ECG
58

Three Leeds of ECG:
• The differential potential is
measured between the right and left
arm, between the right arm and the
left leg and between left arm and left
leg
• These three measurements are
referred to as leads I, II, III
respectively
• The signal from the body is being
amplified because the signals from
the body are small and weak,
ranging from 0.5 mV to 5.0 mV
• Signals are filtered to remove the
noise, then after digital conversion
through ADC the digital signal is
sent to computer
Electrocardiography (-contd.)
Fig. (2)
60

Fig. (3) Block diagram of an electrocardiograph. The normal locations for
surface electrodes are right arm (RA), right leg (RL), left arm (LA), and left
leg (LL). Physicians usually attach several electrodes on the chest of the
patients as well.
Resistors
and switch
Amp ADC
Signal
processor
Monitor
Printer
Storage
LA
LL
RA
RL
61

Fig. (4) Schematic representation of normal ECG
62

Types of ECG Recordings
• Bipolar Leads record
voltage between electrodes
placed on wrists & legs
(right leg is grounded)
• Lead I records between
right arm & left arm
• Lead II: right arm & left leg
• Lead III: left arm & left leg
Fig. (5) 63

Fig. (6) Einthoven’s triangle. Lead I is from RA to LA, lead II is from RA to
LL, and lead III is from LA to LL.
0
III
II
I 


64

Causes of Cardiac
Cycle
• 3 distinct waves are
produced during cardiac
cycle
• P wave caused by atrial
depolarization
• QRS complex caused by
ventricular depolarization
• T wave results from
ventricular repolarization
Fig. (7) 65

P wave: (Depolarization of both atria)
• Relationship between P and QRS helps distinguish various cardiac
arrhythmias
• Shape and duration of P may indicate atrial enlargement
PR interval: (from onset of P wave to onset of QRS)
• Normal duration = 0.12 – 0.2 sec
• Represents atria to ventricular conduction time (through His
bundle)
• Prolonged PR interval may indicate a 1st degree heart block
QRS complex: (Ventricular depolarization)
• Larger than P wave because of greater muscle mass of ventricles
• Normal duration = 0.08 - 0.12 sec
Elements of the ECG
66

• Its duration, amplitude, and morphology are useful in diagnosing
cardiac arrhythmia, ventricular hypertrophy, Myocardial Infarction
(MI), electrolyte derangement, etc.
• Q wave greater than 1/3 the height of the R wave, greater than
0.04 sec are abnormal and may represent MI
ST segment:
• Connects the QRS complex and T wave
• Duration of 0.08-0.12 sec
T wave:
• Represents repolarization or recovery of ventricles
• Interval from beginning of QRS to apex of T is referred to as the
absolute refractory period
QT Interval:
• Measured from beginning of QRS to the end of the T wave
• Normal QT is usually about 0.40 sec
• QT interval varies based on heart rate
Elements of the ECG (-contd.)
67

Ultrasound System
• Ultrasound is one of the most widely used modalities in medical imaging,
which is regularly used in cardiology, obstetrics, gynaecology, abdominal
imaging, etc.
• Mostly, it is used in non-invasive techniques, although an invasive
technique like intra-vascular imaging is also possible
• Ultrasound systems are signal processing intensive with various imaging
modalities and different processing requirements in each modality, digital
signal processors (DSP) are finding increasing use in such systems
• The advent of low power system-on-chip (SoC) with DSP and RISC
processors is providing portable and low cost systems without
compromising the image quality necessary for clinical applications
• The term ultrasound refers to frequencies that are greater than 20 kHz,
which is commonly accepted to be the upper frequency limit the human
ear can hear
• Typically, ultrasound systems operate in the 2 MHz to 20 MHz frequency
range, although some systems are approaching 40 MHz for harmonic
imaging 69

Ultrasound System: Basic Functionality
70

• Fig.(1 ) shows the basic functionality of an ultrasound system, which
demonstrates how transducers focus sound waves along scan lines
in the region of interest
• In principle, the ultrasound system focuses sound waves along a
given scan line so that the waves constructively add together at the
desired focal point
• As the sound waves propagate towards the focal point, they reflect
off on any object they encounter along their propagation path
• Once all of the sound waves along the given scan line have been
measured, the ultrasound system focuses along a new scan line until
all of the scan lines in the desired region of interest have been
measured
• To focus the sound waves towards a particular focal point, a set of
transducer elements are energized with a set of time-delayed pulses
to produce a set of sound waves that propagate through the region of
interest, which is typically the desired organ and the surrounding
tissue 71

• This process of using multiple sound waves to steer and focus a
beam of sound is commonly referred to as beam-forming
• Once the transducers have generated their respective sound
waves, they become sensors that detect any reflected sound
waves that are created when the transmitted sound waves
encounter a change in tissue density within the region of interest
• By properly time delaying the pulses to each active transducer, the
resulting time-delayed sound waves meet at the desired focal
point that resides at a pre-computed depth along a known scan
line
• The amplitude of the reflected sound waves forms the basis for the
ultrasound image at this focal point location
• Envelope detection is used to detect the peaks in the received
signal and then log compression is used to reduce the dynamic
range of the received signals for efficient display and can be
analysed by the doctor or technician
72

Ultrasound System: System Components
73

• The beam-former control unit, as shown in Fig. (2), is responsible for
synchronizing the generation of the sound waves and the reflected
wave measurements
• The controller knows the region of interest in terms of width and
depth and gets translated into a desired number of scan lines and a
desired number of focal points per scan line
• The beam-former controller begins with the first scan line and excites
an array of piezo-electric transducers with a sequence of high-voltage
pulses (of the order ±100 V & ±2 A) via transmit amplifiers
• The pulses go through a Tx/Rx switch, which prevents the high-
voltage pulses from damaging the receive electronics
• Note that these high-voltage pulses have been properly time delayed
so that the resulting sound waves can be focused along the desired
scan line to produce a narrowly focused beam at the desired focal
point
74

• The beam-former controller determines which transducer elements to
energize at a given time and the proper time delay value for each
element to properly steer the sound waves towards the desired focal
point
• As the sound waves propagate toward the desired focal point, they
migrate through materials with different densities; with each change
in density, the sound wave has a slight change in direction &
produces a reflected sound wave
• Some of the reflected sound waves propagate back to the transducer
& form the input to the piezo-electric elements in the transducer
• The resulting low voltage signals are scaled using a variable
controlled amplifier (VCA) before being sampled by ADCs
• The VCA is configured so that the gain profile being applied to the
received signal is a function of the sample time since the signal
strength decreases with time (e.g., it has travelled through more
tissue)
75

• The number of VCA and ADC combinations determines the number
of active channels used for beam-forming
• It is usual to run the ADC sampling rate 4 times or higher than the
transducer centre frequency
• Once the received signals reach the Rx beam-former, the signals are
scaled and appropriately delayed to permit a coherent summation of
the signals
• This new signal represents the beam-formed signal for one or more
focal points along a particular specific scan line
• Once the data is beam-formed, depending on the imaging modes,
various processings are carried out, e.g., it is common to run the
beam-formed data through various filtering operation to reduce out
band noise
• In B (Brightness) mode, demodulation followed by envelope detection
and log compression is the most common practice
76

• Several 2D noise reduction and image enhancement functions are
also performed in this mode
• In spectral mode, a windowed Fast Fourier Transform (FFT) is
performed on the demodulated signal & displayed separately
• It is also common to present the data on a speaker after
separation of forward and reverse flow
• In these systems, a repeated set of pulse is sent through the
transducer
• In between the pulses, the received signal is recorded
• There is an alternate mode where a continuous pulse sets are
transmitted, which are known as continuous wave (CW) systems
• These systems are used where a more accurate measurement of
velocity information is desired using Doppler techniques
• The disadvantage of this system is that it loses the ability to
localize the velocity information
77

• In these systems, a separate set of transducers are used for
transmission and reception
• Due to large immediate reflection from the surface of the
transducer, the dynamic range requirement becomes very high to
use ADC to digitize the reflected ultrasound signal and maintain
enough signal to noise (SNR) for estimating the velocity
information
• Therefore, an analog beam-forming is usually used for CW
systems followed by analog demodulation
• Such systems can then use lower sampling rate (usually in kHz
range) ADCs with higher dynamic range
78

79

A-mode (Amplitude) Imaging:
• It displays the amplitude of a sampled voltage signal for a single
sound wave as a function of time
• This mode is considered 1D and used to measure the distance
between two objects by dividing the speed of sound by half of the
measured time between the peaks in the A-mode plot, which
represents the two objects in question
• This mode is no longer used in ultrasound systems
B-mode (Brightness) Imaging:
• It is the same as A-mode, except that brightness is used to represent
the amplitude of the sampled signal
• B-mode imaging is performed by sweeping the transmitted sound
wave over the plane to produce a 2D image
• Typically, multiple sets of pulses are generated to produce sound
waves for each scan line, each set of pulses are intended for a
unique focal point along the scan line
Ultrasound System: Imaging Modes
80

CW (Continuous Wave) Doppler:
• In this mode, a sound wave at a single frequency is continuously
transmitted from one piezo-electric element and a second piezo-
electric element is used to continuously record the reflected sound
wave
• By continuously recording the received signal, there is no aliasing in
the received signal
• Using this signal, the blood flow in veins can be estimated using the
Doppler frequency
• However, since the sensor is continuously receiving data from
various depths, the velocity location cannot be determined
PW (Pulse Wave) Doppler:
• For this several pulses are transmitted along each scan line and the
Doppler frequency is estimated from the relative time between the
received signals
• Since pulses are used for the signaling, the velocity location can also
be determined
81

Color Doppler:
• For this, the PW Doppler is used to create a color image that is super-
imposed on top of B-mode image
• A color code is used to denote the direction and magnitude of the flow,
e.g., red typically denotes flow towards the transducer and blue denotes
flow away from it
• A darker color usually denotes a larger magnitude while a lighter color
denotes a smaller magnitude
Power Doppler:
• In this, instead of estimating the actual velocity of the motion, the
strength or the power of the motion is estimated and displayed
• It is useful to display small motion and there is no directional information
in this measurement
Spectral Doppler:
• It shows the spectrum of the measured velocity in a time varying manner
• Both PW & CW Doppler systems are capable of showing spectral
Doppler
82

M-mode:
• This display refers to scanning a single line in the object and then
displaying the resulting amplitudes successively, which shows the
movement of a structure such as a heart
• Because of its high pulse frequency (up to 1000 pulses per second),
this is useful in assessing rates and motion and is still used
extensively in cardiac and fetal cardiac imaging
Harmonic Imaging:
• It is a new modality where the B-mode imaging is performed on the
second (or possibly other) harmonics of the imaging
• Due to the usual high frequency of the harmonic, these images have
higher resolution than conventional imaging, however, due to higher
loss, the depth of imaging is limited
• Some modern ultrasound systems switch between harmonic and
conventional imaging based on depth of scanning
83

• This system imposes stringent linearity requirements on the signal
chain components
Elasticity/Strain Imaging:
• It is a new modality where some measures of elasticity (like Young’s
modulus) of the tissue (usually under compression) is estimated and
displayed as an image
• These types of imaging have been shown to be able to distinguish
between normal and malignant tissues
• This is currently a very active area of research both on clinical
applications and in real-time system implementation
84

Basic Ultrasound Machine
Basic Ultrasound Machine Components:
• Central Processing Unit (CPU)
• Transducer probe
• Transducer Pulse Controls
• Display
• Keyboard/Cursor
• Disk Storage
• Printers
85

What is an EEG?
• An electroencephalogram is a measure of the brain's
voltage fluctuations as detected from the electrodes.
• It is an approximation of the cumulative electrical
activity of neurons.
• Background
– 1875 - Richard Caton discovered electrical
properties of exposed cerebral
hemispheres of rabbits and monkeys.
– 1924 - German Psychiatrist Hans Berger
discovered alpha waves in humans and
coined the term “electroencephalogram”
– 1950s - Walter Grey Walter developed
“EEG topography” - mapping electrical
activity of the brain.

Human Brain
Frontal Lobes
Personality, emotions, problem solving.
Parietal lobes
Cognition, spatial relationships and
mathematical abilities, nonverbal
memory.
Occipital lobes
Vision, color, shape and movement.
Temporal lobes
Speech and auditory processing,
language comprehension, long-term
memory.

Different waves in EEG
Slowest but highest
amplitude waves,
deepest stages of sleep
it tends to appear during
drowsy, meditative, or
sleeping states.
Predominantly originates
From occipital lobe during
wakeful relaxation with
closed eyes.
associated with active, busy,
or anxious thinking and
active concentration.
relate to neural consciousness
via the mechanism for
conscious attention

Problems with EEG
• Electrical activity generated by complex system
of billions of neurons.
• Difficult to “register” electrode location.
• Artifacts from motion, eye blinks, swallows, heart
beat, sweating…
• Food, age, time of day, fatigue, motivation of
subject.
• Advantages of EEG
• Many EEG studies have reported reproducible
changes in brain dynamics that are task dependent!
• People are able to control their brainwaves via
biofeedback!

90
Fig. Basic structure of the heart. RA is the right atrium, RV is the right
ventricle; LA is the left atrium, and LV is the left ventricle. Basic pacing rates
are also shown.

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