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

2. Text Books & References
Introduction to biomedical equipment technology; J.J. Carr
Medical Instrumentation; Webster
Electronic devices; Boylestad
Dr. T. Elsarnagawy

3. Syllabus Introduction to biomedical instrumentation & measurement
Basic theories of measurement
Signals & noise
Electrodes, sensors and transducers Pp
Dr. T. Elsarnagawy

4. What is biomendical engineering
It is a cross-disciplinary field that incorporates
Engineering
Biology
Chemistry
Medicine
Biomedical instrumentation is used to take measurements that are used in
Monitoring
Diagnostic means
Therapy
Dr. T. Elsarnagawy

5. Fields of biomedical engineering
Bioinstrumentation
Applies the fundamentals of measurement science to biomedical instrumentation
Emphasizes the common principles with making measurements in living cells
Biomaterials
Application of engineering materials in production of medical devices
Biomechanics
Behavior of biological tissues and fluids
Ergonomics (design principles)
Biosignals
The mechanisms of signal production
Fundamental origins in of the variability in the signal
Rehabilitation engineering
Design of equipments for disabled individuals
Dr. T. Elsarnagawy

6. Scientific 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
Dr. T. Elsarnagawy

7. Metric Prefixes Symbol Name Multiplication p pico 1 x 10-12 n nanoμ
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
Dr. T. Elsarnagawy

8. Units and physical constants
Dr. T. Elsarnagawy

9. SI 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

10. Conversion to SI units
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11. Conversion from SI units
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12. standard physical units

13. Physical constants
Dr. T. Elsarnagawy

14. Definitions Measurand (Physical quantities): Sensor:
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 Transducer
is a device that transfers power from one system to another in the same or in a different form.
Dr. T. Elsarnagawy

15. Common medical measurands
The measurand is the measured quantity
Dr. T. Elsarnagawy

16. Generalized Instrumentation system
Dr. T. Elsarnagawy

17. Instrumentation 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
Dr. T. Elsarnagawy

18. Medical Measurement Chain
A/D Converter
Oscilloscope
LCD
Process Circuit
Sensor
surface electrode pressure transducer photocoupler temperature sensor pressure gauge
strain gauge ：
EMG Instrument
ECG Instrument
Blood Pressure Instrument
．．．．．．
Clinical Instrument
Dr. T. Elsarnagawy

19. Generalized Instrumentation System
Dashed lines are optional for some application
Dr. T. Elsarnagawy

20. “Averages” in Biomedical Engineering
Dr. T. Elsarnagawy

21. Types of Averages Definition
Most typical value or most expected value in a collection of numerical data
Different kinds of average
Mean (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
Dr. T. Elsarnagawy

22. Types of Averages If data is perfectly symmetrical  ?? Median:
The middle value in a data set
Mode:
The most frequently occurring value in a data set
If data is perfectly symmetrical  ??

23. 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,…)

24. Geometric average
Ex.: if you have 48$, spend half of your available money each day for 5 days.
Arithm. Mean= ( )/5=18.6

25. Geometric average To find the Geometric average
To straighten the curve  semilog paper

26. Harmonic mean (H.M.)
Is used when data is expressed in ratios (miles/hrs, riyals/dozen,…)
The expression of H.M.

27. Harmonic mean: example

28. Integrated 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 V t t1 t2 T V1
Dr. T. Elsarnagawy

29. Root-mean-square “rms”
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 value
T: is the time interval t1 to t2
V(t): is the time-varying voltage function
Special case: the rms value of a sine wave voltage is Vp/√2 or Vp (Vp is the peak voltage)
Dr. T. Elsarnagawy

30. Root sum sqaure “rss”

31. Logarithmic Representation of signal Levels “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
Dr. T. Elsarnagawy

32. Common dB scales in electronics dBm, dBmV
dBm: 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 dBm
Use P=V2/R
= V/50Ω
= mW
 dBm = 10log(P/1mW)= -48.9
Review dBmV and examples page 38,39 in IBET
Dr. T. Elsarnagawy

33. The basic equations to calculate decibels (Logarithm)
Iin Io Vo Po
Vin
Pin
Dr. T. Elsarnagawy

34. Calculation of the overall strength of a system and calculating the system gain
Dr. T. Elsarnagawy

35. Converting 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
Vin
Av=20dB Vo ?
1 mV
Dr. T. Elsarnagawy

36. Special decibel scales: dBm
dBm: 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 (9 mW/1 mW) = 9.54 dBm
Dr. T. Elsarnagawy

37. Data Classes Qualitive
Nonnumerical 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

38. Data Classes Quantitive
Naturally 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 ( C)

39. 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 

40. 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:

41. Variance & Standard deviation
The normal distribution gives a measure of data dispersion
Dispersion of data is summed up as variance and standard deviation of the data
Variance:
Standard deviation:
In case of small data sets
: the mean

42. Accuracy of a measurement is indicated by the size of ΔX
Xi: true value
X0: central value of successive measurements
ΔX: Error
As ΔX  0 then X0  Xi Y ΔX X0 X Xi
Dr. T. Elsarnagawy

43. Basics of measurements
Before we begin our look at biomedical instrumentation, we need to study some general characteristics of instrumentation

44. System Characteristics
Specific ch/cs
General ch/cs

45. Specific Characteristics for a system
Specs for specific biomedical instrumentation as determined by the committee ………… ex: ECG
ECG specifications

46. 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

47. Some specific Characteristics
DC offset
Is the amount the signal may be moved from its baseline and still be amplified properly by the system
Without DC offset
With DC offset

48. Some specific Characteristics
Slew rate
Maximum 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 response
The range of frequencies of the measurand the system can handle

49. General characteristics
These are characteristics all systems share
Linearity
Analog or digital system

50. Significant factors in measurements

51. Measured/ Calibration curve O/p Max deviation Idealized curve
(linear fit)
I/p
Dr. T. Elsarnagawy

52. Closeness to the true value of measurand
Accuracy
Closeness to the true value of measurand
Dr. T. Elsarnagawy

53. Results have Low scatter  excellent 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
Dr. T. Elsarnagawy

54. The relation may be linear or nonlinear
3. Sensitivity
Relation between change in output for a given change in input (scale factor, magnification).
The relation may be linear or nonlinear
Dr. T. Elsarnagawy

55. How to calculate Sensitivity (S)
Non-linear
linear
O/p
O/p
I/p
I/p
S:sensitivity=ΔO/p/ΔI/p
Inverse Sens.=1/S
Dr. T. Elsarnagawy

56. (i.e. Output in lin. prop to the input)
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)
Dr. T. Elsarnagawy

57. Smallest i/p increment change that gives some change in the o/p
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
Dr. T. Elsarnagawy

58. Minimum input value below which no output can be detected.
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
Dr. T. Elsarnagawy

59. Variation in output without change in input
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
Dr. T. Elsarnagawy

60. All together
Dr. T. Elsarnagawy

61. 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
Dr. T. Elsarnagawy

62. 11. DC offset
Is the amount the signal may be moved from its baseline and still be amplified properly by the system
Without DC offset
With DC offset
Dr. T. Elsarnagawy

63. 13. Frequency response characteristics
The range of frequencies of the measurand the system can handle
Wideband
Band-pass
--- Phase distortion
Typical for sensors
Dr. T. Elsarnagawy

64. 12. Slew rate
Maximum 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
Dr. T. Elsarnagawy

65. Measurements for calibration means
المعـــايره
Measurements for calibration means
- قياسات الإنحراف عن المنحنى الخطى Creep
- قياسات الحراره Temperature
Hystresis
- الإنحراف عن الصفر Zero drift
- خطأ الرجوع إلى الصفر (نقطه البدايه) Zero error
- خطأ تكرار القياسات Reproducability

66. Calibration procedure
Calibration is used to detect the errors in a sensor
 Correction if possible
Sensor
Transducer
Calibration
measurements
Reference standard

67. Assignment for next week Measurement errors
Describe the four general categories of error
Dealing with measurement errors

68. Signals

69. Sinusoidal waveform
Dr. T. Elsarnagawy

70.                                                                                                    
Dr. T. Elsarnagawy

71. Types of signal Static: dc Quasistatic Periodic: sine, square,…
v(t)=v(t+T)
d. Repetitive: quasiperiodic
e. Single event transient signal
f. Repetitive single event
Dr. T. Elsarnagawy

72. Waveform symmetry
Dr. T. Elsarnagawy

73. Signal sampling Most 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
Dr. T. Elsarnagawy

74. Sampled signals
Dr. T. Elsarnagawy

75. Effect of the sampling rate
12 sample/sec
1 Sample/sec
If fsampling > fsignal  o.k Ideally fsampling = 2 fsignal
If fsampling < fsignal  aliasing
Dr. T. Elsarnagawy

76. Sampling is used to form
To reconstruct the original signal after sampling  pass the sampled waveform through a low-pass filter that blocks fs
Sampling is used to form
AM, PM,
Some applications don’t accept fsampling=2fsignal as in ECG  =5fsignal
Dr. T. Elsarnagawy

77. Essential Electronics Formula
Dr. T. Elsarnagawy

78. Essential Electronics Formula
Ohm'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 
Dr. T. Elsarnagawy

79. Reactance
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 , 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 L
where XL is inductive reactance in Ohms, and L is inductance in Henrys
Dr. T. Elsarnagawy

80. Either way, a drop of 3dB represents half the power and vice versa.
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.
Dr. T. Elsarnagawy

81. When resistance and inductance are combined, the formula is
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)
Dr. T. Elsarnagawy

82. 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.
Dr. T. Elsarnagawy