MET253
Measurements in Biomedical
Instruments
MEASUREMENT
 Defined as
1. The process of numerical evaluation of
dimension.
2. The process of comparison with standard
measuring instruments.
Measurement
 Why we need to measure things?
1. Estimate the required quantity
2. Validate the design
3. Convert the Physical parameter into
meaningful values
4. Evaluate the performance
Methods of measurements:
 Direct method
 Indirect method
 Comparative method
 Contact method
Direct method:
 Measurements are directly obtained
example: scales
Indirect method:
 Obtained by measuring other quantities
EX: weight= height X width X length X density
Comparative method:
 Obtained by comparing the unknown quantity with known quantity
EX: balance scale
Contact method:
 Obtained by placing sensor
EX: temperature sensors
CLASSIFICATION OF TYPES OF MEASUREMENT APPLICATIONS
 1. Monitoring of processes and operations.
 2. Control of processes and operations.
 3. Experimental engineering analysis
1. Monitoring of processes and operations.
 These application of measurement serve as a
monitoring application without any control
function
 They indicate the value or condition of
parameter under observation
 Example: voltmeter, water meter, electric
energy meter
2. Control of processes and operations.
 A very useful application of instruments is in
automatic control systems.
 There has been a very strong association
between measurement and control.
 Control systems usually contains feed back to
control the desired variable
3. Experimental engineering analysis
 To solve engineering problems, theoretical
and experimental methods are available.
 Many applications require application of
both the methods
Elements of measurement process
1. Measured quantity
2. Standard system
3. Measuring technology
4. Measuring instrument
1- Measured quantity
 Is the estimation of physical
parameter or phenomena.
 Ex: temperature, pressure, ..etc.
2- Standard System
 Is the agreed standard units that used to evaluate the
quantity.
 There are 4 types of these standards
1. International standards
2. Primary standards
3. Secondary standards
4. Working standards
Measurement units:
SI: fundamental units
Measurement units:
SI: derived units
3-Measuring Technology
 It aims to follow the procedures and
methods that are suitable for each
measured quantity.
 For example, the indication of current
value in electrical circuit is totally different
from the indication of the voltage.
4- Measuring instrument
 Is the proper tool that use to investigate the
magnitude of quantity.
 For example
 Multimeter
 Osclliscope
 Strain gauge
 Thermometer
 etc