This document provides a comparative analysis of different temperature sensors, including liquid-in-glass thermometers, thermocouples, RTDs, thermistors, semiconductor devices, and radiation thermometers. It discusses the operating principles, advantages, disadvantages, accuracy, temperature range, response time, and applications of each sensor type. The key findings are that liquid-in-glass thermometers are inexpensive but slow and fragile, while thermocouples have a wide range but are prone to noise; RTDs are accurate but expensive; thermistors have fast response but a small range; and radiation thermometers can measure from far away but require careful calibration. The best sensor depends on the specific measurement needs and constraints.

1. 1
Assignment 01
Course name: Instrumentation Measurement
Course code: RME 2101
Submitted by: Azrin Zibat
Roll: RH-42
Date of submission: 28/02/2023

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Comparative Analysis of Different
Temperature Sensors
A temperature sensor is a type of electronic device that monitors the temperature of its
surroundings and turns the measured data into electronic data in order to record, monitor, or
communicate temperature changes. Instruments for measuring temperature can be classified
into following categories based on the physical principles behind the measurement techniques.
 Thermal expansion
 Thermoelectric effect
 Resistance change
 Sensitivity of semiconductor device
 Radiative heat emission
 Thermography
 Resonant frequency change
 Sensitivity of fiber-optic devices
 Color change
 Change of state of material
Temperature sensors come in a variety of shapes and sizes. Some temperature sensors (contact
temperature sensors) need direct touch with the actual thing being monitored, whilst others
measure an object's temperature indirectly (non-contact temperature sensors).
Contact sensors: The most common contact temperature sensors are liquid-in-glass
thermometers, thermocouples, RTDs, IC temperature sensors (LM35) and thermistors etc.
Non-contact sensors: Radiation thermometers, thermopiles, thermal images, fiber optic
sensors etc.
We have studied a few of the above-mentioned temperature measurement sensors which are
briefly discussed below, and a comparative analysis will follow.
1. Liquid in glass thermometers:
Typically the fluid used is often mercury or colored alcohol enclosed within a bulb and
capillary tube. The fluid expands along the capillary tube as the temperature rises, and
the meniscus level is measured against a calibrated scale engraved on the tube.
Advantages:
• Inexpensive
• Good repeatability

3. 3
• Calibration doesn’t drift often
• Portable
• Easy to use
• No external power source required
Disadvantages:
• Inaccuracy (It’s difficult to get an error lower than ±1%)
• Slow response time
• Unable to measure any surface temperature as it has to be submerged into the
object
• Limited temperature range; alcohol based (-112°C to 78°C), mercury based(-37°C
to 356°C)
• Fragile as it is made of glass
• Toxicity (Mercury, which is commonly used in liquid in glass thermometers, is a
toxic substance that can be hazardous if not handled properly)
• Can’t be automated
However, the greater inherent accuracy of liquid-in-glass types can only be realized if
the liquid meniscus level is read carefully.
2. Thermocouples:
Thermocouples are made up of two distinct metals that are connected together. When
heated, they produce a small voltage proportionate to the temperature difference
between the two ends. They mainly work depending on of Seebeck effect.
Advantages:
• Comparatively lower inaccuracy than glass thermometers (less or equal than
±0.75%)
• Long time stability and resolution of particular thermocouples( N type
thermometers have three times better life and stability than other
thermocouples)
• Wide range of temperature. In general from -200°C and up to 1400°C depending
on different types of thermocouples
Disadvantages:
• Non-linear output
• Provides low voltage
• Induced stain in hot junction causes error( it has to be put horizontally to reduce
the error)
• Can be sensitive to oxidizing or reducing atmospheres depending on the base
metals or alloys.

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• Very much prone to contamination in operating environment
• They require careful calibration
• Sensitivity to electromagnetic interference
• Expensive
The base metal thermocouple is the most regularly used temperature measuring
device in industry. Throughout the temperature range of 250 to 1200C, the typical
error is 0.5% of full scale. Noble metal thermocouples are substantially more
expensive, but they are chemically inert and can monitor temperatures up to 2300
degrees Celsius with an error of 0.2% on the entire scale. Unfortunately, because all
thermocouples have a low-level output voltage, they are susceptible to noise and
hence unsuitable for sensing minor temperature variations.
3. Thermopile:
A sensor made of multiple thermocouples connected in series.
Advantages:
• Non-contact measurement
• Higher sensitivity
• Fast response
• More durable than thermocouple
• Higher resolution
• Can measure temperature of a moving body
•
Disadvantages:
• Expensive
• Requires careful calibration
• sensitive to environmental noise
• More likely to response to environment temperature due to high sensitivity
4. RTD sensors:
A sensor made of a metal wire with a known resistance that changes with temperature.
Advantages:
• Wide range of temperature
Platinum: 270 to þ1000°C (although use above 650°C is uncommon)
Copper: 200 to þ260°C
Nickel: 200 to þ430°C
Tungsten: 270 to þ1100°C
• More stable
• More accurate

5. 5
• Linear output( more linear than thermocouples)
• Higher repeatability
Disadvantages:
• Slow response time than some other sensors
• Expensive
• Susceptible to self-heating
• Current source required
Resistance thermometers, with a measuring error of 0.5%, are also widely used in the
temperature range of 270 to 650°C. While their temperature range is narrower than
that of thermocouples, they are more stable and can detect slight temperature
variations. The platinum resistance thermometer is often recognized as having the
finest price-to-performance ratio for measuring temperatures ranging from 200 to
500°C
5. Thermistors:
A sensor made of a ceramic or polymer material that changes its resistance with
temperature. Resistance decreases with increase in temperature.
Advantages:
• Low cost
• Small in size
• Fast response
Disadvantages:
• Non-linear output
• Small temperature range(-55°C to 150°C)
• Sensitivity to self-heating
• Sensitivity to ambient temperature change
• Current source required
• thermistors have to be operated at generally lower current levels than resistance
thermometers
• Less sensitivity than RTDs
They give a fast output response to temperature changes, with good measurement
sensitivity, but their measurement range is quite limited.
6. Semiconductor devices:
Semiconductor devices used for temperature measurement are usually consists of
diodes or integrated circuit transistors.

6. 6
Advantages:
• Cheap
• Linear temperature relation within given range(-55°C to 150°C)
• Better linearity than RTD and thermocouples
•
Disadvantages:
• Small scale of temperature
• Inaccuracy ±3%
• Requires external power supply
However, they are widely used to monitor pipes and cables, where their low cost means
that it is feasible to mount multiple sensors along the length of the pipe/cable to detect
hot spots. Semiconductor devices have higher linearity and accuracy than
thermocouples and resistance thermometers. As a result, in many situations, they are a
feasible alternative to these. Although their precision is somewhat low and their
measuring range is fairly limited (50 to 150°C), integrated circuit transistor sensors are
particularly affordable. Although diode sensors are more precise and have a larger
temperature range (270 to 200°C), they are also more costly.
7. Radiation thermometer:
Radiation thermometers measure the radiation emitted from an object to measure
temperature differences.
Advantages:
• No contact with the hot body while measuring temperature
• Wide range of temperature(-100°C to 10000°C)
• Low measurement inaccuracy like ±0.05%
• Capable of measuring moving bodies
• Portable ,battery-powered and hand-held versions also available
• No possibility of contamination
Disadvantages:
• All radiation thermometers have to be calibrated carefully for each particular
body
• Only measure the surface temperature and cannot measure the temperature of
its interior.
• The surface finish of an object can affect the accuracy of a radiation thermometer
• The accuracy of the radiation thermometer can be affected by the emissivity of
the object

7. 7
• Expensive
Radiation thermometers are notable for their noncontact, noninvasive manner of
measuring. Although calibrating for the emissivity of the measured item might be
challenging, several equipment now offer automated calibration. Radiation
pyrometers of various types are employed spanning the temperature range of 20 to
1800°C and can provide measurement inaccuracy as low as 0.05%. Narrow-band
radiation pyrometers have the capacity to record quick temperature transients with
durations as short as 10 ms. No other device can measure transients as quickly as this
one.
In summary, the choice of temperature measurement sensor depends on the specific
application, accuracy requirements, cost constraints, usability, and resolution/sensitivity
requirements.
Reference Book:
Measurement and Instrumentation, Theory and Application. Reza Langari ,Alan S. Morri