bme unit-1

8/4/2019 bme unit-1

1/123

INTRODUCTION TO

BIOMEDICAL ENGINEERING

8/4/2019 bme unit-1

2/123

Why Biomedical Engineering?

Promising future developments

Improve medicine, save lives

Numerous possibilities based upon level of biology and

engineering specialty

Hybridization of skills and knowledge

8/4/2019 bme unit-1

3/123

Types of problems

Interface between biological and non-biological materials

Design, modeling, and construction of biologically-analogoustechnologies

Understanding and improving upon biological limitations

Medical tools and diagnostics

8/4/2019 bme unit-1

4/123

TerminologyBiomedical engineering

Bioengineering

Also, biological engineering and others . . .

Biotechnology

Often used interchangeably with biomedical engineering. When distinguishing

between the two, typically bioengineering tends to refer to engineering using

biological substances, often at a higher level of biology than biotechnology.

The use of engineering science and math to tackle problems in medicine. When

distinguished from bioengineering, focuses more on the machine/device/non-

biological type of research.

Term that is generally similar to bioengineering, but, in comparison, refers mostspecifically to direct manipulation and use of living biological substances.

8/4/2019 bme unit-1

5/123

UNIT I

Physiology and Transducers

8/4/2019 bme unit-1

6/123

Human Anatomy & Physiology

Cell

8/4/2019 bme unit-1

7/123

Human body develops from union ofSPERM + OVUM=FIRST CELL OF HUMAN

BODY

Group of cells

Tissues

Organs

Systems

8/4/2019 bme unit-1

8/123

Structure of Cell

Cell is a structural & Functional unit of human body, capable of

carrying out functions of life independently. Nucleus

Cytoplasm

Cell Membrane

Functions of Cell- Production of Bio-Energy- Storage- Multiplication

- Specific function according to location

8/4/2019 bme unit-1

9/123

8/4/2019 bme unit-1

10/123

8/4/2019 bme unit-1

11/123

Membrane Potentials

1. Resting Membrane Potential2. Excitatory Post-synaptic Potential (EPSP)3. Inhibitory Post-synaptic Potential (IPSP)4. Action Potential

8/4/2019 bme unit-1

12/123

Levels of Investigation

Organism Systems(e.g. Vision)

Cell Synapsis

Next weeks

Today

Molecule

Next weeks

8/4/2019 bme unit-1

13/123

Click on animation website or main website (here)

Neurons have a selectively permeable membrane

During resting conditions membrane is: permeable to potassium (K+) (channels are open)

impermeable to sodium (Na+) (channels are closed)

Diffusion force pushes K+ out (concentration gradient)

This creates a positively charged extra-cellular space.

Electrostatic force pushes K+ in

Thus, there is a dynamic equilibrium with zero netmovement of ions.

The resting membrane potential is negative (- 60mv)

1. Resting Membrane Potential
http://bcs.whfreeman.com/thelifewire/content/chp44/4401s.swfhttp://www18.homepage.villanova.edu/diego.fernandezduque/Teaching/Teach_Index.htmhttp://www18.homepage.villanova.edu/diego.fernandezduque/Teaching/Teach_Index.htmhttp://bcs.whfreeman.com/thelifewire/content/chp44/4401s.swf

8/4/2019 bme unit-1

14/123

Copyright Allyn & Bacon 2004

Cell Membrane

8/4/2019 bme unit-1

15/123

15

OUTSIDE

INSIDE

K+ = Potassium; Na+ = Sodium; Cl- = Chloride; Pr- = proteins

Na+

Na+

K+

K+

Force of Diffusion

Electrostatic Force

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -- - - - - - -

Cl-

Force of Diffusion

Cl-

Electrostatic Force

Pr-

Closedchannel

openchannel

openchannel

nochannel

3Na/2Kpump

Resting Membrane Potential

- 65 mV

8/4/2019 bme unit-1

16/123

Resting membrane potential:(things you need to know)

a. Concept of Selective membrane

b. How permeable the membrane is to proteins, K+, andNa+

c. Diffusion and electrostatic forces and how they act on

K+ and Na+d. Concept of Dynamic equilibrium

e. Concept of Membrane potential

f. ATP Na/K pump and its role in maintaining the

membrane potential

8/4/2019 bme unit-1

17/123


8/4/2019 bme unit-1

18/123


Membrane Potentials

1.RestingPotential(justdescribed)

2.ExcitatoryPost-synapticpotential

threshold4.InhibitoryPost-synapticpotential

3.ActionPotential

8/4/2019 bme unit-1

19/123

2. Excitatory Post-synaptic Potential (EPSP)

Post-synaptic neuron

Pre-synaptic neuron

8/4/2019 bme unit-1

20/123

1. The pre-synaptic neuron releases aneurotransmitter.

2. Neurotransmitter diffuses acrossextra-cellular space - synaptic cleft.

3. Neurotransmitter binds to post-synaptic receptor.

4. Binding of neurotransmitter causes

Na+ channels in post-synapticmembrane to open.

5. Depolarization occurs (excitatory

potential)

Post-synaptic neuron

Pre-synaptic neuron

Excitatory Post-synaptic Potential (EPSP)

8/4/2019 bme unit-1

21/123

21

OUTSIDE

INSIDE

K+ = Potassium; Na+ = Sodium; Cl- = Chloride; Pr- = proteins

Na+

Na+

K+

K+

Force of Diffusion

Electrostatic Force

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -- - - - - - -

Cl-

Force of Diffusion

Cl-

Electrostatic Force

Pr-

Closedchannel

openchannel

openchannel

nochannel

OPEN Na+CHANNEL

+ + +

- 65 mV- 50 mV

1. Resting Membrane PotentialExcitatory Post-Synaptic Potential (EPSP)

8/4/2019 bme unit-1

22/123

EPSP

EPSP is a graded potential

Multiple EPSPs are integrated acrossspace and time.

ExcitatoryPost-synapticpotential

Integration

Once the threshold isreached, voltage-dependent sodiumchannels are opened

The cell is depolarized(action potential)

8/4/2019 bme unit-1

23/123

3. Inbibitory Post-synaptic Potential (IPSP)

8/4/2019 bme unit-1

24/123


Nervous System

8/4/2019 bme unit-1

25/123

8/4/2019 bme unit-1

26/123

Nervous system

Central processing unit of body. Controls andbalance of body functions.

Divisions Central nervous system (CNS)

Peripheral nervous system (PNS)

Autonomic nervous system (ANS)

Components

Nerve cell

Sensory nerve

Brain

Motor nerve

End organ

8/4/2019 bme unit-1

27/123

Functions of Nervous system

Control over voluntary and involuntaryfunctions / actions.

To control body movements, respiration,circulation, digestion, hormone secretion,

body temperature To receive stimuli from sense organs,

perceive them and respond accordingly

Higher mental functions like memory,receptivity, perception & thinking.

8/4/2019 bme unit-1

28/123

8/4/2019 bme unit-1

29/123

Parts of CNS

Cerebrum

Cerebellum

Mid brain

Pones

Medulla oblongata

Spinal cord

8/4/2019 bme unit-1

30/123

Brain Protected by skull

Three coverings of brain called meninges

Dura Arachnoid

Pia matter

Cerebro spinal fluid (CSF) between the Pia

meter and Arachnoid CSF acts as a shock absorber and provides

nutrition to the brain

8/4/2019 bme unit-1

31/123

8/4/2019 bme unit-1

32/123

8/4/2019 bme unit-1

33/123

8/4/2019 bme unit-1

34/123

8/4/2019 bme unit-1

35/123

Cerebrum

Biggest part of brain, divided into two hemispheres

Contra lateral control

Outer surface is grey due to cells

Internally white due to fibers

Surface is folded to increase the area

Functions of cerebrum Intellect, memory, will power, imagination, emotion &

other psychological functions

Receive and perceive the stimuli

To give command for reaction with the help of pastexperience

To control over other parts of nervous system

8/4/2019 bme unit-1

36/123

Cerebellum

Situated below and behind the cerebrum

Functions of cerebellum Controls tone muscles

Helps coordination of body movements

Helps balancing the body

Mid brain

Underneath the cerebrum and above pons Functions of mid brain

To control involuntary functions

8/4/2019 bme unit-1

37/123

Pons

Below mid brain

Functions of pons Control of consciousness

Control level of concentration

Medulla oblongata Lowest part of CNS just above the spinal cord

Functions of Medulla oblongata

Control of respiration Control of circulation

Control of swallowing and vomiting

8/4/2019 bme unit-1

38/123

Spinal cord Located safely in spinal canal

Length is 45cm, which extends up to firstlumber vertebra

31 pairs of peripheral nerves starts fromspinal cord

Functions of spinal cord To propagate sensory stimuli from organs to

the brain

To carry commands from the brain towardsthe organs

Reflex action

8/4/2019 bme unit-1

39/123

Reflex action

Protective function of the spinal cord

Sensory organ

Afferent nerve

Sensory cell in posterior horn of spinal cord Connector nerve

Motor cell in anterior horn of spinal cord

Efferent nerve

End organ of reaction

8/4/2019 bme unit-1

40/123

Autonomic nervous system(Involuntary nervous system) It has control over

Digestion

Respiration

Circulation

Hormone secretion

Maintenance of body temperature

Maintenance of water balance

Peripheral nervous system 12 pairs of cranial nerves from brain (cranial

nerves)

31 pairs of spinal nerves from spinal cord

(spinal nerves)

8/4/2019 bme unit-1

41/123

8/4/2019 bme unit-1

42/123

Billons of nerve cells

Billons of connections

Maximum utilization of brain is 10%

90 % brain is in dormant state

8/4/2019 bme unit-1

43/123


Circulatory System

8/4/2019 bme unit-1

44/123

8/4/2019 bme unit-1

45/123

Components of blood

Total volume of blood 5 to 6 liters

Components Plasma 55-60 %

Blood cells 40-45 %

RBC

WBC

Platelets

R B C (R d bl d ll )

8/4/2019 bme unit-1

46/123

R.B.C. (Red blood cells)

Colour of blood due to RBC

4 to 5 millions / c.c. Hemoglobin carry 90% Oxygen

Dumbbell shaped cells with no nucleus

W.B.C. (White blood cells) White colored

6000 to 9000 / c.c.

Kills the bacteria (protective role) No specific shape, with central nucleus

8/4/2019 bme unit-1

47/123

Platelets

1,00,000 to 2,00,000 / c.c.

Helps in clotting of blood(Enzyme Thrombokinase)

Circular shape

Plasma 90 to 92 % water

8 to 10 % dissolved organic & inorganic

matter (proteins, glucose, salts & hormones) Presence of antibodies

8/4/2019 bme unit-1

48/123

Functions of Blood To carry Oxygen from lungs to cells and to

carry CO2

from cells to lungs

To carry nutrients from Digestive system tocells

To carry excretory products (waste material)

from cells to excretory organs To carry hormones

To maintain water balance in the body

To maintain body temperature

To protect the body from infections

Clotting the blood after injury

8/4/2019 bme unit-1

49/123

Difference between Arteries & Veins

Arteries

Carry blood from heartto other organs

Carry oxygenatedblood

Have thick walls

Do not have valves

Veins

Carry blood from otherorgans to heart

Carry de-oxygenatedblood

Have thin walls

Presence of valves

8/4/2019 bme unit-1

50/123

8/4/2019 bme unit-1

51/123

Heart

Situated in the rib cage of chest on the left

side Embedded in lungs

Size of heart is equal to the size of clenchedfist

Connected with many big (giant )bloodvessels

Made up of involuntary muscle

Heart starts beating from 4th month of IU life.

Duration of one heart beat is 0.8sec.

8/4/2019 bme unit-1

52/123

8/4/2019 bme unit-1

53/123

4 Chambers of Heart

Auricles to receive blood

Ventricles to pump blood Left side oxygenated blood

Right side deoxygenated blood

8/4/2019 bme unit-1

54/123

8/4/2019 bme unit-1

55/123

Circulation of Blood

Continuous circulation

Force of circulation due to pumping action ofheart

From left ventricle Aorta Branches &Sub branches Artery Small arteryArteriole Capillaries CELLSVenouls Small veins union of many veins Superior & Inferior venacava Right auricle

Right ventricle Pulmonary arteryLungs (oxygenation) Pulmonary veins Left auricle Left ventricle

8/4/2019 bme unit-1

56/123


Respiratory System

8/4/2019 bme unit-1

57/123

8/4/2019 bme unit-1

58/123

Copyright 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Structure and function of the respiratory pumps

How gases are exchanged with blood The role of pressures and surfactants in rate of

exchange

How respiration is regulated

8/4/2019 bme unit-1

59/123


Respiratory System: Overview

Lungs: exchange surface

75 m2

Thin walled

Moist

Ribs & skin protect

Diaphragm & ribs pump air

8/4/2019 bme unit-1

60/123


Respiratory System: Overview

Figure 17-2 b: Anatomy Summary

8/4/2019 bme unit-1

61/123

Functions

8/4/2019 bme unit-1

62/123

Functions Supply of Oxygen

To remove CO2 and water vapour

Purification of blood

Protective function- coughing, sneezing

Talking

Organs of Respiration Nose

Throat

Larynx

Trachea with its branching system

lungs

(diagram of Respiratory System)

Nose

8/4/2019 bme unit-1

63/123

Nose

Two nasal cavities separated by nasal septum

The Nasal Septum is made up of cartilage &bone

Function

Warming of Air Filtration of Air

To keep nasal passage moist

Sensation of smell

8/4/2019 bme unit-1

64/123

8/4/2019 bme unit-1

65/123

Throat & Larynx

Throat (seven passages)

Larynx Oesophagus

Mouth

Left Eustachian tube

Right Eustachian tube

Left nostril

Right nostril

8/4/2019 bme unit-1

66/123

Trachea

Made up of cartilage and muscles Two main branches- Left and Right bronchus

Branching and sub branching ending in alveoli

8/4/2019 bme unit-1

67/123

8/4/2019 bme unit-1

68/123

Inspiration

8/4/2019 bme unit-1

69/123

Inspiration

Active process by muscular action

Contraction of diaphragm

Increase in vertical diameter

Contraction of intercostals muscles

Elevation of ribs and sternum

Increase in antero-posterior and transverse diameter

Expansion of lungs due to negative pressure

Air drawn inwards Expiration

Passive process

Elastic recoil of the lungs due to Relaxation of diaphragm andinter costal muscle.

Positive pressure created in lungs

Control of Respiration

Control of Inspiration and Expiration by medulla oblongata

L V l

8/4/2019 bme unit-1

70/123

Lung Volumes

Tidal capacity : 500c.c.

Dead space : 150c.c. Vital capacity : 4500c.c.

Total lung capacity : 6000c.c.

Residual volume : 1350c.c. Expiratory reserve : 1500c.c.

Inspiratory capacity : 3000c.c.

8/4/2019 bme unit-1

71/123

Analysis of gases in respiration

O2

N2

CO2Inspired air 21% 79% -

Exhaled air 16% 79% 5%

Effects of Pranayama More oxygenation of blood

Improvement in function of all organs

Life span increases because of more supplyof oxygen

F ti f th R i t S t O i

8/4/2019 bme unit-1

72/123


Functions of the Respiratory System: Overview

Figure 17-1: Overview of external and cellular respiration

Exchange O2

Air to blood

Blood to cells

Exchange CO2 Cells to blood

Blood to air

Regulate blood pH Vocalizations

Protect alveoli

The Airways:C d ti f Ai f O t id t Al li

8/4/2019 bme unit-1

73/123


Filter, warm & moisten air

Nose, (mouth), trachea, bronchi & bronchioles

Huge increase in cross sectional area

Conduction of Air from Outside to Alveoli

Figure 17-4: Branching of the airways

8/4/2019 bme unit-1

74/123

Signal Acquisition

Medical Instrumentation typically entailsmonitoring a signal off the body which isanalog, converting it to an electricalsignal, and digitizing it to be analyzedby the computer.

8/4/2019 bme unit-1

75/123

Types of Sensors:

Electrodes: acquire an electrical signal

Transducers: acquire a non-electricalsignal (force, pressure, temp etc) andconverts it to an electrical signal

8/4/2019 bme unit-1

76/123

Active vs Passive Sensors:

Active Sensor: Requires an external AC or DC electrical

source to power the device

Strain gauge, blood pressure sensor

Passive Sensor:

Provides it own energy or derives energyfrom phenomenon being studied Thermocouple

8/4/2019 bme unit-1

77/123

Sensor Error Sources

Error: Difference between measured value

and true value.

8/4/2019 bme unit-1

78/123

5 Categories of Errors:1. Insertion Error

2. Application Error

3. Characteristic Error

4. Dynamic Error

5. Environmental Error

8/4/2019 bme unit-1

79/123

Insertion Error: Error occurring when inserting a

sensor

8/4/2019 bme unit-1

80/123

Application Error: Errors caused by Operator

8/4/2019 bme unit-1

81/123

Characteristic Error: Errors inherent to Device

8/4/2019 bme unit-1

82/123

Dynamic Error: Most instruments are calibrated in static

conditions if you are reading a thermistor ittakes time to change its value. If you readthis value to quickly an error will result.

8/4/2019 bme unit-1

83/123

Environmental Error: Errors caused by environment

heat, humidity

8/4/2019 bme unit-1

84/123

Sensor Terminology

Sensitivity:

Slope of output characteristic curve y/ x; Minimum input of physical parameter will

create a detectable output change

Blood pressure transducer may have asensitivity of 10 uV/V/mmHg so you will see a10 uV change for every V or mmHg applied to

the system.

8/4/2019 bme unit-1

85/123

Input

Output

Input

Output

Which is more sensitive? The left side onebecause youll have a larger change in y for agiven change in x

8/4/2019 bme unit-1

86/123

Sensor Terminology

Sensitivity Error = Departure from ideal

slope of a characteristic curve

Ideal Curve

Sensitivity Error

Output

Input

8/4/2019 bme unit-1

87/123

Sensor Terminology

Range = Maximum and Minimum values

of applied parameter that can bemeasured.

If an instrument can read up to 200 mmHgand the actual reading is 250 mmHg then youhave exceeded the range of the instrument.

8/4/2019 bme unit-1

88/123

Sensor Terminology

Dynamic Range: total range of sensor forminimum to maximum. Ie if your instrumentcan measure from -10V to +10 V your dynamic

range is 20V Precision = Degree of reproducibility denoted

as the range of one standard deviation

Resolution = smallest detectable incrementalchange of input parameter that can bedetected

8/4/2019 bme unit-1

89/123

Accuracy

Accuracy = maximum difference that

will exist between the actual value andthe indicated value of the sensor

XoXi

8/4/2019 bme unit-1

90/123

Offset Error

Offset error = output that will exist

when it should be zero

The characteristic curve had the samesensitive slope but had a y intercept

Zero offset errorOffset Error

Input Input

Output Output

8/4/2019 bme unit-1

91/123

Linearity

Linearity = Extent to which actualmeasure curved or calibration

curve departs from ideal curve.

8/4/2019 bme unit-1

92/123

Linearity

Nonlinearity (%) = (Din(Max) / INfs) * 100%

Nonlinearity is percentage of nonlinear Din(max) = maximum input deviation

INfs = maximum full-scale input

Input

Output Din(Max)

Full Scale Input

Transducers and other Sensors

8/4/2019 bme unit-1

93/123

Transducers and other Sensors

Transducers: sensors and are defined asa device that converts energy from someone form (temp., pressure, lights etc) into

electrical energy where as electrodesdirectly measure electrical information

8/4/2019 bme unit-1

94/123

Wheatstone Bridge

Basic Wheatstone Bridge uses one resistor ineach of four arms where battery excites thebridge connected across 2 opposite resistor

junctions (A and B). The bridge output Eoappears across C and D junction.

Es

R1

R2R4

R3

EC ED+-

A

B

Eo

Eo

R1R3

R2 R4

EC ED

Es

+ -

+ -

8/4/2019 bme unit-1

95/123

Strain Gauges

Definition: resistive element thatchanges resistance proportional to an

applied mechanical strain

8/4/2019 bme unit-1

96/123

Strain Gauges

Compression = decrease in length by DL andan increase in cross sectional area.

Rest ConditionL = length

L - DL = length Compression

8/4/2019 bme unit-1

97/123

Strain Gauges

Tension = increase in length by DL and adecrease in cross section area.

Rest ConditionL = length

TensionL + DL = length

Resistance of a metallic bar is

8/4/2019 bme unit-1

98/123


given in length and area

where R = Resistance units = ohms () = resistivity constant unique to type of

material used in bar units = ohm meter (m) L = length in meters (m) A = Cross sectional area in meters2 (m2 )

A

pLR


8/4/2019 bme unit-1

99/123


given in length and area

Example: find the resistance of a copper bar that has a crosssectional area of 0.5 mm2 and a length = 250 mm note the resistivityof copper is 1.7 x 10-8m

- 0085.0

1000

15.0

1000

1250

10*7.12

2

8

mm

mmm

mm

mmm

mA

LR

8/4/2019 bme unit-1

100/123

Piezoresistivity

Piezoresistivity = change in resistance for agiven change in size and shape denoted as h

Resistance in tension =

Resistance increases in tension

L = length;L = change in L; = resistivityA = Area;A = change in A

DDAALLhR

8/4/2019 bme unit-1

101/123

Resistance in compression =

Resistance decreases in compression

L = length;L = change in L; = resistivity

A = Area;A = change in A

DDAA

LLhR

Note: Textbook forgot the in equations 6-28 and 6-29 on page 110

Gauge Factor

8/4/2019 bme unit-1

102/123

Gauge Factor

Gauge Factor (GF) = a method of comparing onetransducer to a similar transducer

8/4/2019 bme unit-1

103/123

Gauge Factor

where

GF = Gauge Factor unitless

R = change in resistance ohms ()

R = unstrained resistance ohms () L = change in length meters (m) L = unstrained length meters (m)

DD

L

LR

R

GF

8/4/2019 bme unit-1

104/123

Gauge Factor

Where strain which is unitless GF gives relative sensitivity of a strain gauge where the

greater the change in resistance per unit length thegreater the sensitivity of element and the greater thegauge factor.

LL

RR

GF

D

D

T f St i G U b d d d

8/4/2019 bme unit-1

105/123

Types of Strain Gauges: Unbonded and

Bonded

Unbonded Strain Gauge: resistanceelement is a thin wire of special alloystretch taut between two flexiblesupports which is mounted on flexiblediaphram or drum head.


8/4/2019 bme unit-1

106/123


Bonded

When a Force F1 is applied todiaphram it will flex in a manner thatspreads support apart causing anincrease in tension and resistance

that is proportional to the forceapplied.

When a Force F2 is applied todiaphram the support ends will more

close and then decrease the tensionin taut wire (compression force) anddecrease resistance will decrease inamount proportional to applied force


8/4/2019 bme unit-1

107/123


Bonded

Bonded Strain Gauge:made by cementing athin wire or foil to a diaphragm thereforeflexing diaphragm deforms the element

causing changes in electrical resistance insame manner as unbonded strain gauge


8/4/2019 bme unit-1

108/123


Bonded

When a Force F1 is applied todiaphram it will flex in amanner that causes anincrease in tension of wirethen the increase in resistanceis proportional to the forceapplied.

When a Force F2 is applied todiaphram that cause a

decrease the tension in tautwire (compression force) thenthe decrease in resistance willdecrease in amountproportional to applied force

Comparison of Bonded vs Unbonded

8/4/2019 bme unit-1

109/123

Comparison of Bonded vs. Unbonded

Strain Gauges

1. Unbonded strain gauge can be builtwhere its linear over a wide range ofapplied force but they are delicate

2. Bonded strain gauge are linear over asmaller range but are more rugged

Bonded strain gauges are typically usedbecause designers prefer ruggedness.

8/4/2019 bme unit-1

110/123

Typical Configurations

R2 = SG2R4 = SG4

R3 = SG3

C+

-

A

B

Vo

R1 = SG1

DES

Electrical Circuit MechanicalConfiguration

4 strain gauges (SG) in Wheatstone Bridge:

8/4/2019 bme unit-1

111/123

Transducer Sensitivity

Transducer Sensitivity = rating thatallows us to predict the output voltagefrom knowledge of the excitation

voltage and the value of the appliedstimulus units = V/V*unit of appliedstimulus

8/4/2019 bme unit-1

112/123


Example if you have a force transducer calibrated ingrams (unit of mass) which allows calibration of forcetransducer then sensitivity denoted as = V/V*g(another ex = V/V*mmHg)

8/4/2019 bme unit-1

113/123


To calculate Output Potential use thefollowing equations:

where Eo = output potential in Volts (V)

E = excitation voltage

= sensitivity V/V*g F = applied force in grams (g)

FEEo **

8/4/2019 bme unit-1

114/123

Inductance Transducers

Inductance Transducers: inductance L canbe varied easily by physical movement of apermeable core within an inductor 3 basic

forms: Single Coil Reactive Wheatstone Bridge Linear Voltage Differential Transformer LVDT:

8/4/2019 bme unit-1

115/123

LVDT:

Diaphragm

Core External

Load

L2

L3

L1

Axis of Motion

AC Excitation

8/4/2019 bme unit-1

116/123

Capacitance Transducers

Quartz Pressure Sensors: capacitivelybased where sensor is made of fusedquartz

Capacitive Transducers: Capacitance Cvaries with stimulus

8/4/2019 bme unit-1

117/123

Capacitive Transducers:

Three examples: Solid Metal disc parallel to flexible metal

diaphragmseparated by air or vacuum (similar tocapacitor microphone) when force is applied they

will move closer or further away. Stationary metal plate and rotating moveable plate:

as you rotate capacitance will increase or decrease

Differential Capacitance:1 Moveable metal Plateplaced between 2 stationary Places where youhave 2 capacitors: C1 between P1 and P3 and C2between P2 and P3 where when a force is appliedto diaphragm P3 moves closer to one plate or viceversa

8/4/2019 bme unit-1

118/123

Temperature Transducers

3 Common Types: Thermocouples Thermistors Solid State PN Junctions

8/4/2019 bme unit-1

119/123

Thermocouple:

Thermocouple: 2 dissimilar conductor joinedtogether at 1 end.

The work functions of the 2 materials are different

thus a potential is generated when junction isheated (roughly linear over wide range)

8/4/2019 bme unit-1

120/123

Thermistors:

Thermistors: Resistors that change their valuebased on temperature where

Positive Temperature Coefficient (PTC) device willincrease its resistance with an increase intemperature

Negative Temperature Coefficient (NTC) device willdecrease its resistance with an increase intemperature

Most thermistors have nonlinear curve when plottedover a wide range but can assume linearity if within alimited range

8/4/2019 bme unit-1

121/123

BJT = Bipolar Junction Transistor

Transistor = invented in 1947by Bardeen, Brattain andSchockley of Bell Labs.

IC

VCB

VCE

VBE+

++

-

-

-IB

IE

B = BaseC = CollectorE = Emitter

IE = I B + I C

8/4/2019 bme unit-1

122/123

BJT = Bipolar Junction Transistor

Transistor rely on the free travel ofelectrons through crystalline solids calledsemiconductors. Transistors usually areconfigured as an amplifier or a switch.

Solid State PN Temperature

8/4/2019 bme unit-1

123/123

Solid State PN Temperature

Transducers

Solid State PN Junction Diode: thebase emitter voltage of a transistor isproportional to temperature. For adifferential pair the output voltage is:

q

IIKT

VC

C

BE

D2

1ln

K = Boltzmans Constant = 1.38 x10-23J/K

T = Temperature in KelvinIC1 = Collector current of BJT 1 mA

IC2 = Collector current of BJT 2 mA

VCB

VEE-

VBE+

+

+

- -

-VCB

VCC+

VBE

+

ccs1 ccs2

Ic1 Ic2

DVBE

bme unit-1

Documents

Transcript of bme unit-1