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1Dr. T. Elsarnagawy
Introduction to Biomedical Introduction to Biomedical Equipment TechnologyEquipment Technology
2Dr. T. Elsarnagawy
Text Books & ReferencesText Books & References
Introduction to biomedical equipment technology; J.J. Carr
Medical Instrumentation; Webster
Electronic devices; Boylestad
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Syllabus Syllabus
Introduction to biomedical instrumentation & measurement
Basic theories of measurement
Signals & noise
Electrodes, sensors and transducers
Pp 26-125
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What is biomendical engineeringWhat is biomendical engineeringIt is a cross-disciplinary field that incorporates
EngineeringBiologyChemistryMedicine
Biomedical instrumentation is used to take measurements that are used in
MonitoringDiagnostic meansTherapy
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Fields of biomedical engineeringFields of biomedical engineeringBioinstrumentation
Applies the fundamentals of measurement science to biomedical instrumentationEmphasizes the common principles with making measurements in living cells
BiomaterialsApplication of engineering materials in production of medical devices
BiomechanicsBehavior of biological tissues and fluidsErgonomics (design principles)
BiosignalsThe mechanisms of signal productionFundamental origins in of the variability in the signal
Rehabilitation engineeringDesign of equipments for disabled individuals
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Scientific NotationScientific Notation
The form of a number in scientific notation:
N X 10x {Unit}N: Numbers
10: Base
x: Exponent
Never forget to write the UNIT ……if it exists
10-x 1/10x
Prefixes:Nano-, micro-, milli-, centi-, …, kilo-, mega-, giga-, tera-
10-9 …………………………………………………………………………………..1012
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Metric PrefixesMetric Prefixes
Symbol Name Multiplication
p pico 1 x 10-12
n nano 1 x 10-9
μ micro 1 x 10-6
m milli 1 x 10-3
k kilo 1 x 103
M Mega 1 x 106
G Giga 1 x 109
T Tera 1 x 1012
8
UNITS AND PHYSICAL UNITS AND PHYSICAL CONSTANTSCONSTANTS
Dr. T. Elsarnagawy
9
SI UnitsSI Units
The standard unit system for medical, engineering and scientific practice is taken from the SI (Systeme Internationale) CGS or MKS (also called metric system)
SI depends on multiplying prefixes in the basic units (see metric prefixes table)
Dr. T. Elsarnagawy
10Dr. T. Elsarnagawy
Conversion to SI unitsConversion to SI units
11
Conversion from SI unitsConversion from SI units
Dr. T. Elsarnagawy
12
standard physical units
13
Physical constantsPhysical constants
Dr. T. Elsarnagawy
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DefinitionsDefinitionsMeasurand (Physical quantities):
Position, displacement
Temperature
Force
Pressure,…
Concentrations, chemicals,…,
Sensor:is a device that detects a change in a physical stimulus and turns it into a signal which can be measured or recorded
Signal conditioning:Amplifying, waveshaping, filtering, rectifying,…
A Transduceris a device that transfers power from one system to another in the same or in a different form.
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Common medical measurandsCommon medical measurands
The measurand is the measured quantity
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Generalized Instrumentation systemGeneralized Instrumentation system
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Instrumentation SystemInstrumentation System
A Measuring system is required to compare a quantity with a standard or to provide an output that can be related to the quantity being measured
The quantity to be measured is detected by an input transducer or sensor.
The detected quantity may be converted to a mechanical or electrical form of energy
Display
Recorder
Signal conditioner
Measurand
Sensor
Input Output
18Dr. T. Elsarnagawy
Medical Measurement ChainMedical Measurement Chain
A/DConverter
Oscilloscope
LCD
ProcessCircuitSensor
surface electrode pressure transducer
photocoupler temperature sensor press
ure gaugestrain gauge
:
EMGInstrument
ECGInstrument
Blood PressureInstrument
......
Clinical Instrument
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Generalized Instrumentation SystemGeneralized Instrumentation System
Dashed lines are optional for some application
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““Averages”Averages”in Biomedical Engineeringin Biomedical Engineering
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Types of AveragesTypes of Averages
DefinitionMost typical value or most expected value in a collection of numerical data
Different kinds of averageMean (arithmetic mean):
The sum of all values xn divided by the number n of different values
Ex.: mean average???
sum=125, n=28 Xmean=125/28=4.46
Types of AveragesTypes of Averages
Median:
The middle value in a data set
Mode:
The most frequently occurring value in a data set
If data is perfectly symmetrical ??
Which average is the best to use for which kind of data??
If data is symmetrical use mean average
If data is highly asymm. (outliers) median
If you need an answer to a question mode
Ex.: most common cause of death, or most popular TV show on Friday,…
Other types of averages:Geometric average biological studies
Harmonic mean (H.M.) when data are expressed in ratios (miles/hr, riyal/dozen,…)
Geometric average
Ex.: if you have 48$, spend half of your available money each day for 5 days.
Arithm. Mean= (48+24+..)/5=18.6
Geometric average
To find the Geometric average
To straighten the curve semilog paper
Harmonic mean (H.M.)
Is used when data is expressed in ratios (miles/hrs, riyals/dozen,…)
The expression of H.M.
Harmonic mean: example
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Integrated AverageIntegrated Average
This average is applied often in RC circuits
The area under the curve of a time dependent function divided by the segment of the range over which the average is taken
The output of the circuit ~ time average of the input signal
0
V
tt1 t2
TV1
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Used in electrical circuits and other technologies e.g.when comparing AC sine wave current with DC current the AC should be expressed in an equivalent value which is the rms.
Definition of rms:
Vrms: is the rms valueT: is the time interval t1 to t2V(t): is the time-varying voltage function
Special case: the rms value of a sine wave voltage is Vp/√2 or 0.707 Vp (Vp is the peak voltage)
Root-mean-square “rms”Root-mean-square “rms”
Root sum sqaure “rss”
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Logarithmic Representation of signal LevelsLogarithmic Representation of signal Levels“Decible Notation dB”“Decible Notation dB”
Original unit was “bel”
The prefix “deci” means one tenth
Hence, the “decible” is one tenth of a “bel”
dB expresses logarithmically the ratio between two signal levels (ex.: Vo/Vi = Gain)
dB is dimensionless
For voltage or current measurements
For power measurements
Review table 3-8 page 37 in IBET
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Common dB scales in electronicsCommon dB scales in electronicsdBmdBm, , dBmVdBmV
dBmdBm: 0 dBm refers to an input power of 1mW dissipated in 50Ω resistive load
What is the signal level 9mW as expressed in dBm?dBm = 10 log (9mV/1mW) = 9.54 dBm
Express a signal level of 800 μV in dBmUse P=V2/R
=0.00000064V/50Ω
=0.0000128mW
dBm = 10log(P/1mW)= -48.9
Review dBmV and examples page 38,39 in IBET
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Iin Io
Vo
Po
Vin
Pin
The basic equations to calculate The basic equations to calculate decibels (Logarithm)decibels (Logarithm)
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Calculation of the overall strength of a system and Calculation of the overall strength of a system and calculating the system gaincalculating the system gain
2001.0
2.011
inV
VA
5.02.0
1.0
1
2 V
VAtten
151.0
5.1
2
32 V
VA
45.1
6
33 V
VA o
600321 AAAttenAAV
6.55600log20 dBA
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Converting between dB and Gain notationConverting between dB and Gain notation
For dB = 20 log (Vo/Vin)if it is needed to convert from dB to output-input ratio i.e. Vo/Vin
Vo = Vin 10dB/20
or Vo = Vin EXP(dB/20)
Ex: calculate the output voltage Vo if the input voltage Vin=1mV and an amplifier of +20 dB is used:
Vo=(0.001V) 10(20/20)
=(0.001) (10) = 0.01V
Av=20dB
1 mVVo
?
Vin
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Special decibel scales: dBmSpecial decibel scales: dBm
dBmdBm: used in reference frequency measurements (RF)
0 dBm is defined as 1 mW of RF signal dissipated in 50-Ω resistive load
dBm = 10 log (P/1 mW)
EX: What is the signal level 9 mW as expressed in dBm?dBm = 10 log (P/1 mW)
dBm = 10 log (9 mW/1 mW) = 9.54 dBm
Data Classes
QualitiveNonnumerical or categorical (includes the presence or nonpresence of some factor, good or bad, defective or not defective, gender …)
Not inherently with numbers
Can be given a numerical flavor (1 or 0, yes or no)
Sometimes we assign some kind of scale
Data Classes
QuantitiveNaturally result in some number to represent a factor (amount of money, length, temperature, voltage, pressure, weight …)
Interval: referenced to a selected standard zero point (ex.: calendar is referred to date of birth of Christ or Hijra, temperature C is referred to the freezing or boiling point of water) note: centigrade: centi=100 (0-100 divisions from the arbitrarily set 0C to 100C)
Ratio: fixed to a natural zero point, such as weights, pressure, temperature (Kelvin) referred to the absolute zero (0 K) at which molecular motion ceases (-273.16C)
Variation and error
Variations (or random variation) are caused by certain errors in the measurement process.
Caused by type of meter used
Caused by variation in the process being measured
Random variation causes data obtained to disperse
how to represent this dispersion?
Histogram, normal distribution
Variation and error: Histograms & Normal distribution (Gaussian curve)
Data represented in fig.a Histogram
Data represented in fig.b normal distribution (Gaussian)
Set of data:
Variance & Standard deviation
The normal distribution gives a measure of data dispersionDispersion of data is summed up as variance and standard deviation of the data
Variance:
Standard deviation:
In case of small data sets
X : the mean
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Accuracy of a measurement is indicated by Accuracy of a measurement is indicated by the size of the size of ΔX
Xi: true value
X0: central value of successive measurements
ΔX: Error
As ΔX 0 then X0 Xi
X0Xi
ΔX
X
Y
Basics of measurements
Before we begin our look at biomedical instrumentation, we need to study
some general characteristics of instrumentation
System Characteristics
•Specific ch/cs
•General ch/cs
Specific Characteristics for a system
Specs for specific biomedical instrumentation as determined by the committee ………… ex: ECG
ECG specifications
Some specific Characteristics
For example
Dynamic range:Given is the input dynamic range -5mV to +5mV
If input signal exceeds the dynamic range so it will cause an error
The amplified signal is then called to be saturated
Some specific Characteristics
DC offsetIs the amount the signal may be moved from its baseline and still be amplified properly by the system
Without DC offset
With DC offset
Some specific Characteristics
Slew rateMaximum rate at which the system can observe a changing voltage per unit time
If the input signal exceed the given slew rate the output will be distorted
Frequency responseThe range of frequencies of the measurand the system can handle
General characteristics
These are characteristics all systems share
Linearity
Analog or digital system
Significant factors in measurements
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Measured/Calibration curve
Max deviation
I/p
O/p
Idealized curve(linear fit)
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1. Accuracy Closeness to the true value of measurand
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2. Precision
a measure of the degree of agreement within a group of measurements – repeatability of a system- (however no guarantee of accuracy)
Results have Low scatter excellent precision
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3. Sensitivity
Relation between change in output for a given change in input (scale factor, magnification).
The relation may be linear or nonlinear
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How to calculate Sensitivity (S)How to calculate Sensitivity (S)
I/p
O/p
I/p
O/p
S:sensitivity=ΔO/p/ΔI/p
Inverse Sens.=1/S
linear Non-linear
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4. Linearity:
An instr. is said to be linear when incremental changes in input and output are constant over the specified range
(i.e. Output in lin. prop to the input)
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5. Resolution
Smallest i/p increment change that gives some change in the o/p
Example:
Voltmeter scale with 100 divisions FS=200V, 1/10 of scale division can be estimated determine the resolution?
Solution:
1 division=200/100=2V
Resolution=1/10 scale division=1/10x2=0.2V
58Dr. T. Elsarnagawy
6. Threshold
Minimum input value below which no output can be detected.
7. Hystresis
Tendency for indications on an upward cycle to differ from the same points on the downward cycle
Causes: Friction, relaxation
Numeric value of Hyster.: % of full scale
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8.Drift:
Variation in output without change in input
(...Temp. Changes or component instability)
9. Zero Stability
Ability to return to zero when measurand = 0
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All togetherAll together
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10. Dynamic range:Rdyn=Ymax-Ymin
Given is the input dynamic range -5mV to +5mV
If input signal exceeds the dynamic range so it will cause an error in the output
The amplified signal is then called to be saturated
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11. DC offsetIs the amount the signal may be moved from its baseline and still be amplified properly by the system
Without DC offset
With DC offset
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13. Frequency response characteristics
The range of frequencies of the measurand the system can handle
Wideband
Band-pass
Typical for sensors
--- Phase distortion
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12. Slew rateMaximum rate at which the system can observe a changing voltage per unit time
If the input signal exceed the given slew rate the output will be distorted
Calibrationالمعـــايره
Measurements for calibration means
الحراره - قياساتTemperature
الخطى - المنحنى عن اإلنحراف Creep قياسات
Hystresis
الصفر - عن Zero drift اإلنحراف
- ) البدايه ) نقطه الصفر إلى الرجوع Zero error خطأ
القياسات - تكرار Reproducability خطأ
Calibration procedure
Reference standard
Transducer
Calibrationmeasurements
Calibration is used to detect the errors in a sensor Correction if possible
Sensor
Assignment for next weekMeasurement errors
Describe the four general categories of error
Dealing with measurement errors
Signals
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Sinusoidal waveformSinusoidal waveform
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Types of signalTypes of signal
a. Static: dc
b. Quasistatic
c. Periodic: sine, square,…v(t)=v(t+T)
d. Repetitive: quasiperiodic
e. Single event transient signal
f. Repetitive single event
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Waveform symmetryWaveform symmetry
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Signal samplingSignal samplingMost instrumentation transducers have analog output
At the interface between analog transducers and digital computers the signal must be digitized
So the signal is sampled at regular intervals
Each sample voltage is then converted into an equivalent digital value
The next sample cannot be taken until the conversion of the last sample is to digital form is completed
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Sampled signalsSampled signals
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Effect of the sampling rateEffect of the sampling rate
1 Sample/sec
12 sample/sec
If fsampling > fsignal o.k. Ideally fsampling = 2 fsignal
If fsampling < fsignal aliasing
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To reconstruct the original signal after sampling pass the sampled waveform through a low-pass filter that blocks fs
Sampling is used to formAM, PM,
Some applications don’t accept fsampling=2fsignal as in ECG =5fsignal
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Essential Electronics FormulaEssential Electronics Formula
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Essential Electronics FormulaEssential Electronics FormulaOhm's Law The first of these is Ohm's Law, which states that a voltage of 1V across a resistance of 1 Ohm will cause a current of 1 Amp to flow. The formula is
R = V / I
(where R = resistance in Ohms, V = Voltage in Volts, and I = current in Amps)
V = R * I
I = V / R
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ReactanceReactance
The impedance (reactance) of a capacitor, which varies inversely with frequency (as frequency is increased, the reactance falls and vice versa).
XC = 1 / (2 Π f C)where Xc is capacitive reactance in Ohms, (Π pi) is 3.14159, f is frequency in Hz, and C is capacitance in Farads.
Inductive reactance, being the reactance of an inductor. This is proportional to frequency.
XL = 2 Π f Lwhere XL is inductive reactance in Ohms, and L is inductance in Henrys
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Decibels (dB) dB = 20 log (V1 / V2) dB = 20 log (I1 / I2) dB = 10 log (P1 / P2)
Either way, a drop of 3dB represents half the power and vice versa.
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Frequency There are many different calculations for this, depending on the combination of components.
The -3dB frequency for resistance and capacitance (the most common in amplifier design) is determined by
fo = 1 / (2 Π R C) where fo is the -3dB frequency
When resistance and inductance are combined, the formula is
fo = R / (2 Π L)
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Power Power in any form can be calculated by a number of means:
P = V I P = V2 / R P = I2 R
where P is power in watts, V is voltage in Volts, and I is current in Amps.