1. Basics of Measuring Instrumentation System (2).pptx
1. Fundamental to Biomedical instrument
Basics of measuring instrumentation system
Kedir Ali
Department of Biomedical Engineering
Kombolcha Institute of Technology
Wollo University
2. Outlines
• Measurement
• Metrology
• Instrumentation
• Biomedical instrumentation system
• Components of Biomedical instrumentation system
• Types of medical instruments
3. History of measurement
• Measurement originate in 3rd & 4th millennium BC by ancient
people of Egypt, Mesopotamia, Indus Valley and Elam (Iran).
• They uses measurement for purposes of agriculture, construction
and trade.
Example: Cubit…
5. Measurement
• A process of gathering information from a physical world and
comparing with agreed standards.
• Obtain correct value of the measured physical quantity.
• Essential for observing and testing scientific and technological
investigations.
• Measurements are carried out by using instruments.
6. Standards of Measurement System
• A fundamental references for which all other measuring devices
are compared
• Used for calibrations of measuring instruments (minimizing
error)
• On the basis of their function and application, standards are
classified as; international, primary, secondary and working
standards.
7. Cont.
1. International standards
• Defined on the basis of international agreement
• Define units precisely
• Preserved carefully under standard atmospheric condition
• Not applicable for measurement (only for comparison)
2. Primary standards
• Used for calibrating secondary standards
• Not available outside of national laboratory
• Compared with international standards after long interval
8. Cont.
3. Secondary standards
• Basic reference standards used in industrial measurement laboratories
• Compared with primary standards on periodic basis
4. Working standards
• Used as a reference purpose in lab and workshops
• Has an accuracy lower than the rest three
• Material used to make the standards are lower graded & relatively
cheap
9. Measurement Errors
The result of every measurement by any measuring instrument
contains some uncertainty – error.
Absolute Error : difference between the measured value & true
value of a quantity.
Relative Error: ratio of absolute error to the true value of the
quantity.
10. Classification of Errors
There are three main classes of errors, namely:
1. Gross Errors
• Occurred due to human mistake during measurement
Arise due to:
• Carelessness of the measurer
• Luck of ability to use the tool
• Inability to interpret the measured result
11. Cont.
2. Systematic Errors
• Occurred by any factor that systematically affect measurement.
• Caused by defective instruments, inherent limitation of measuring
device, and wrong construction of device – instrumental.
• Imperfect method of observation, wrong selection of measurement
tool, error while reading values – observational.
• Environmental interference, external conditions (temperature,
humidity, sound, …) – environmental error.
12. Cont.
3. Random Errors
• Errors caused by any factors that randomly affect the
measurement.
• Normal or unavoidable errors due to unknown sources.
• Cannot determine under ordinary measurement process.
13. How to reduce errors in measurement
• Use standard and properly validated instrument
• Pre-test the instrument
• Double check measurement & measurement tool
• Check the reliability, sensitivity of the scale
• Etc.…
14. Metrology
• Metrology derived from two words “metro” which means
measure, and “logos” which means study.
• A science of measurement and its application.
• Focuses on advancing measurement science to improve quality of
life.
15. Types of metrology
Scientific metrology
• Concerned with the establishment of new units and methods of
measurement.
• Deals with the specification of new standards, their realization,
and the conveyance of these standards to users.
16. Cont.
Applied or industrial metrology
• Deals with the use of measurement and its application to
industrial and manufacturing processes.
• It seeks to establish the importance of measurement in general.
• Ensures the functionality of measuring equipment, proper calibration,
and quality control.
Metrology calibration?
• An act of assessing and standardizing the accuracy and precision of
measuring equipment.
17. Cont.
Legal metrology
• Concerned with the regulatory requirements of measurements.
• Includes measurement methods, and units of measurement.
• The regulations aim to ensure fair trade, furthermore to protect
consumer rights, ensure public safety, protect the environment
and enable taxation.
19. Medical Instrumentation system
• To measure or determine the presence of some physical quantity
that can assist the medical personnel to make better diagnosis
and treatment.
20. Components of instrumentation system
Measurand
• The physical quantity or condition that the instrumentation
system measures.
• The source for the measurand is the human body which
generates a variety of signals.
21. Cont.
Transducer
• A device that converts one form of energy to other.
• a piezo-electric crystal converts mechanical vibrations into
an electrical signal
• Provides a usable output in response to the measurand.
22. Cont.
Sensor
• Converts a physical measurand to an electrical signal.
• The sensor should be minimally invasive and interface with the
living system with minimum extraction of energy.
23. Cont.
Signal Conditioner
• Convert the output of the transducer into an electrical quantity
suitable for operation of the display or recording system.
• Includes amplification, filtering analog-to-digital and digital-to-
analog conversion or signal transmission circuitry.
24. Cont.
Display System
• Provides a visible representation of the quantity on the screen of
a cathode ray tube or in numerical form.
• Visual, audible signals from alarm
26. Cont.
Data transmission & Storage
• Maintains the data for future reference (hard copy or memories).
27. General concerns in the design of instrumentation systems
Accuracy
Range
• The range of an instrument is generally considered to include all
the levels of input amplitude and frequency over which the
device is expected to operate.
• The objective should be to provide an instrument that will give a
usable reading from the smallest expected value of the variable
or parameter being measured to the largest.
28. Cont.
Sensitivity
• The sensitivity of an instrument determines how small a variation
of a variable or parameter can be reliably measured.
• The sensitivity directly determines the resolution of the device,
which is the minimum variation that can accurately be read.
• Too high a sensitivity often results in nonlinearities or instability.
29. Cont.
Linearity
• The degree to which variations in the output of an instrument follow
input variations.
• In a linear system the sensitivity would be the same for all absolute
levels of input, whether in the high, middle, or low portion of the range.
• In some instruments a certain form of nonlinearity is purposely
introduced to create a desired effect.
30. Cont.
Hysteresis
• A characteristic of some instruments whereby a given value of
the measured variable results in a different reading when
reached in an ascending direction from that obtained when it is
reached in a descending direction.
• Mechanical friction in a meter, for example, can cause the
movement of the indicating needle to lag behind corresponding
changes in the measured variable, thus resulting in a hysteresis
error in the reading.
31. Cont.
Frequency Response
• A variation in sensitivity over the frequency range of the
measurement.
• Flat response An instrument system should be able to respond rapidly
enough to reproduce all frequency components of the waveform with
equal sensitivity.
33. Types of instruments
Instruments can be subdivided into separate classes according to
several criteria.
• Active vs Passive Instruments
• Analog and Digital Instruments
• …
34. Cont.
Active instruments
• Quantity to be measured activates the magnitude of external power
input source that produces the measurement.
• Additional external energy input source is required.
• Output adjusted by adjusting the external energy.
• High resolution
Passive instruments
• The output is entirely produced by the quantity being measured.
• Additional external energy input source is not required.
35. Cont.
Analog instruments
• Output varies continuously as the quantity being measured changes.
• Output can have infinite number of values within instrument range
• Recordings are made with linear bumps & dips.
• Information is exact
Digital instruments
• Output varies in discrete steps
• Output can have finite number of values
• Recordings are made with zeros & ones
• Information are not exact as analog information
36. Medical equipment in different dept. of hospital
• Outpatient Department (OPD)
• Radiology department
• Pharmacy department
• Inpatient service
• Medical department
• Pathology department
• …
37. Reading assignment
1.Difference between sensors & transducer
Quiz-1
1. What is the purpose of measurement, instrumentation &
metrology ?
2. What purpose of signal conditioning ?
