1 Dr. T. Elsarnagawy Introduction to Biomedical Equipment Technology.

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

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UNITS AND PHYSICAL UNITS AND PHYSICAL CONSTANTSCONSTANTS

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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

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Conversion from SI unitsConversion from SI units

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standard physical units

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Physical constantsPhysical constants

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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.


Common medical measurandsCommon medical measurands

The measurand is the measured quantity


Generalized Instrumentation systemGeneralized Instrumentation system


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


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


Generalized Instrumentation SystemGeneralized Instrumentation System

Dashed lines are optional for some application


““Averages”Averages”in Biomedical Engineeringin Biomedical Engineering


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


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


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”


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


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


Iin Io

Vo

Po

Vin

Pin

The basic equations to calculate The basic equations to calculate decibels (Logarithm)decibels (Logarithm)


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


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


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


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


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


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


Measured/Calibration curve

Max deviation

I/p

O/p

Idealized curve(linear fit)


1. Accuracy Closeness to the true value of measurand


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


3. Sensitivity

Relation between change in output for a given change in input (scale factor, magnification).

The relation may be linear or nonlinear


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


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)


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


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


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


All togetherAll together


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


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


13. Frequency response characteristics

The range of frequencies of the measurand the system can handle

Wideband

Band-pass

Typical for sensors

--- Phase distortion


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


Sinusoidal waveformSinusoidal waveform



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


Waveform symmetryWaveform symmetry


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


Sampled signalsSampled signals


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


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


Essential Electronics FormulaEssential Electronics Formula


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


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


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.


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)


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.

1 Dr. T. Elsarnagawy Introduction to Biomedical Equipment Technology.

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nnano1 x

ggiga1 x

mmega1 x

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