1. Temperature measurements
Vital Signs
• Vital signs are measurements of the body's most basic functions. The
three main vital signs routinely monitored by medical professionals and
health care providers include the following: 1. Body Temperature 2.
Respiration Rate 3. Pulse Rate.
• Vital signs are useful in detecting or monitoring medical problems.
Temperature, respiration and pulse rate measurements.
Vital Sign Normal Result for Adults
Body temperature 97.8 F to 99.1 F, with an average of 98.6 F
Respiration (breathing) rate 12 to 18 breaths per minute
Pulse 60 to 100 beats per minute
Blood pressure 90/60 mmHg to 120/80 mmHg
2. Temperature measurements
• An adult’s temperature can be taken by mouth (oral), under
the arm (axillary), or in the ear canal (tympanic) using a digital
thermometer designed for these specific uses.
• The readings can vary depending on which one of these is
used.
• Oral: The generally accepted average oral temperature is 98.6
F, but normal may range from 97 F to 99 F. A temperature of
100.4 F most often indicates an infection or illness.
• Axillary: An armpit temperature is usually lower than the oral
temperature by half to one degree.
• Tympanic: An ear temperature is usually higher than the oral
temperature by half to one degree.
3. Temperature measurements
The Forehead Fallacy
• Laying a palm against someone’s forehead
may give an indication that their body
temperature is higher than normal, but it is
not a trusted method of determining illness.
Neither is using forehead thermometers,
which have been found to be unreliable.
4. Temperature measurements
Health Implications of Abnormal Body Temperature
• A body temperature that is higher than normal is called
a fever (pyrexia) and is typically a sign that the body is
trying to fight an illness or infection by killing the virus or
bacteria causing it. Fever also triggers the body’s immune
system.
Other potential causes of fever in adults include:
• Certain medications, such as antibiotics, blood pressure
medications, and anti-seizure drugs
• Heat illness (e.g., heat stroke, heat exhaustion)
• Autoimmune disease
• Cancer
5. Temperature measurements
• A temperature reading below 95 F can be an
indication the body is losing heat more quickly
than it is able to produce it—a medical
emergency known as hypothermia in which
the heart, nervous system, and other organs
can’t work normally.
• If left untreated, hypothermia can lead to
complete failure of the heart and respiratory
system, and eventually to death.
6. Fibre optic temperature sensors
Introduction
There are various methods of temperature measurement which include following.
1. Classic mercury glass thermometer
2. Infrared Pyrometer
3. Electronic thermometer (made of thermocouple, thermistor, RTD etc.)
• Above temperature measurement systems have very little immunity from nearby EM interference and
stray radiation.
• This leads to inaccurate measurements.
• Fibre optic temperature sensors offer excellent performance compare to above mentioned temperature
measurement techniques due to its many benefits outlined below.
• Hence such sensors are employed in various space applications and hazardous environments like high
voltage machines (e.g. generators, motors, transformers), nuclear power plants, chemical power plants
etc.
7. Fibre optic temperature sensors
• The fibre optic temperature sensors are mainly classified into
two types viz. Interferometric and non-interferometric.
• The figure depicts simple non-interferometric and non-
luminescent type fibre optic temperature sensor.
8. Fibre optic temperature sensors
• The simple non-interferometric type sensor consists of multi-
mode optical fibre and temperature sensitive material.
• The temperature sensing materials include GaAs, CdTe, Si etc.
• GaAs is preferred over others due to its better wavelength
variation with temperature.
• These materials exhibit changes in their optical parameters
such as absorption, transmission and reflection qualities with
variation in the temperature.
• The working principle depends on phenomenon of energy
bandgap shrinkage with increase in the temperature of such
semiconductor materials.
• The figure depicts schematic of such temperature sensor and
its temperature vs wavelength curve.
9. Fibre optic temperature sensors
• In this sensor type, thin semiconductor ship is used as active
element.
• This active element is sandwiched between light source (e.g.
LED or laser) and photodetector.
• In this sensor, constant intensity of light signal us modulated
by external temperature when it travels through the optical
fiber cable.
• Moreover its wavelength shifts towards higher side due to
gradual increase in the temperature.
• This is due to optical absorption edge.
10. Fibre optic temperature sensors
• The figure depicts Mach-Zehnder Interferometric temperature
sensor.
• This sensor offers flexible geometry and higher sensitivities.
• Hence it can be used for measurement of various
measuranads such as temperature, pressure, rotation, strain
etc.
11. Fibre optic temperature sensors
• It works based on phase modulation by external
measurands.
• Here phase of the beam through sensing fiber is
compared with the reference beam.
• Beam splitter is used in the design of such Mach-Zehnder
Interferometric sensor as shown in the figure.
• Beam splitter divides the light beam into two parts, one
is launched into the sensing part and the other is used as
reference.
12. Fibre optic temperature sensors
• Following are the benefits or advantages of Fiber Optic Temperature
Sensor:
➨It is immune from nearby EM (electromagnetic) and stray radiation.
➨It can be used in environments where high levels of electrical
interference exists or where intrinsic safety is a concern.
➨It (i.e. non-interferometric type) offers greater accuracy (+/- 1o) and
faster response time (~2 sec).
➨It is light in weight and compact in size.
➨It is cheaper due to low manufacturing cost.
➨It supports wide temperature range of measurement from -10 oC to
300 oC. The GaAs offers better wavelength variation with temperature.
13. Fibre optic temperature sensors
• Following are the drawbacks or disadvantages of Fiber Optic Temperature
Sensor:
➨The different types of optical temperature sensors will have different
temperature range of operation and their accuracy of measurements also
vary. These depend on their construction and materials used.
➨It is complex to develop measurement systems using fiber optic sensors.
➨The users require training before they start using such sensor types.
➨Some fibre optic temperature sensors are expensive.
