Thermal or Temperature Sensor
Temperature sensors or Temperature Sensors are simple device that sense the degree of cold or
heat and transform it into a simple unit. We employ them in various applications in our daily lives,
such as domestic water heaters, refrigerators, microwaves, or in the form of thermometers.
Generally, they have a wide range of usages, and the geotechnical controlling area is one of them.
They are utilized in this field to control the condition of concrete structures, bridges on soil or
water, etc., for structural variations in them according to seasonal changes.
Figure 1: Various types of temperature sensors
Temperature sensors are constructed to monitor a regular check on special structures like highway
bridges, railway tracks, concrete or soil dams, etc. A thermometer is the most common form of
them applied to sense the degree of temperature everywhere.
Construction
The construction of thermal sensors can vary based on the type of sensor, but a common type is
the thermocouple. Thermocouples consist of two different metallic conductors joined at one end.
This junction is exposed to the temperature to be measured, while the other ends are connected to
a voltage-measuring device. The voltage generated at the junction is directly proportional to the
temperature difference between the hot and cold junctions.
Other types of thermal sensors include:
1. Resistance Thermometer/Temperature Detector (RTD): Resistance thermometers, also
known as resistance temperature detectors (RTDs), are temperature sensors that operate on
the principle of the change in electrical resistance with temperature. The most common
type of resistance thermometer uses a fine wire or thin film made from a material with a
known and predictable temperature-resistance relationship.
Construction:
The construction of an RTD typically involves a temperature-sensitive element made of a
pure metal, such as platinum, nickel, or copper. Platinum is commonly used due to its
stability and linear resistance-temperature characteristics. The temperature-sensitive
element is often wound into a coil or deposited as a thin film on a ceramic substrate.
The RTD is then housed in a protective sheath, which may be made of materials like
stainless steel to shield the sensor from environmental factors and mechanical damage. The
sheath is usually filled with an insulating material to enhance thermal response.
2. Thermistor: Thermistors are made of semiconductor materials with resistance that varies
significantly with temperature. The resistance is measured to determine the temperature of
the thermistor.
3. Infrared (IR) Sensors: These sensors detect the infrared radiation emitted by an object to
determine its temperature. They often use special materials like thermopiles or pyroelectric
detectors.
Figure 1: Fundamental diagram of thermocouple
Working: The working principle of thermal sensors depends on the specific type:
•
Thermocouples: They operate based on the Seebeck effect, where a voltage is generated
at the junction of two dissimilar metals in response to a temperature difference.
•
RTDs: The resistance of the wire changes linearly with temperature, and by measuring
this resistance, the temperature can be determined.
•
Thermistors: The resistance of the thermistor changes exponentially with temperature,
allowing for accurate temperature measurements.
•
Infrared Sensors: These sensors detect the infrared radiation emitted by an object. The
amount of radiation is related to the object's temperature, and the sensor converts this
radiation into a temperature reading.
Applications: Thermal sensors find applications in various industries and technologies,
including:
1. Industrial Process Control: Monitoring and controlling temperatures in manufacturing
processes to ensure product quality.
2. Automotive: Engine temperature monitoring, climate control systems, and exhaust
temperature measurements.
3. Medical Devices: Body temperature measurement, environmental monitoring in
healthcare facilities.
4. Environmental Monitoring: Weather stations, climate research, and ecological studies.
5. Consumer Electronics: Temperature control in devices, such as laptops and
smartphones.
6. HVAC (Heating, Ventilation, and Air Conditioning): Controlling indoor climate by
monitoring temperature.
7. Energy Management: Monitoring temperature in power plants and electrical systems
for efficient operation.
8. Food Industry: Temperature control during food processing, storage, and
transportation to ensure safety and quality.