A report about Temperature Sensors

1. Slemani Polytechnic University
Technical College of Engineering
Department of Petroleum and Energy
Third Stage
Temperature Sensors
Prepared By:
Dana Mohammed Ibrahim
Rawand Tariq Ahmed
Abdulamen Sarbast Mohammed
Aland Hemin Kamal
Supervised By:
Mrs. Arazu Sabah
2022-2023

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Contents
Introduction…………………………………………………………………….3
Lecture Review…………………………………………………………………4
Types of Temperature Sensors……………………………………………...5-9
Applications………………………………………………………………..10-12
Advantages and Disadvantages……………………………………….…..13-14
Conclusion………………………………………………………………….….15
References……………………………………………………………………..16

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Introduction
Have you ever left your smartphone in your car on a hot day? If so, your screen might have
displayed an image of a thermometer and a warning that your phone has overheated. That is
because there is a tiny embedded temperature sensor that measures the interior temperature of
your phone. Once the inside of the phone reaches a certain temperature (iPhones shut down
at approximately 50°C, and Android phones approximately 60°C, for example), the
temperature sensor sends an electronic signal to an embedded computer. This, in turn, restricts
users from accessing any applications or features until the phone has cooled back down, as
running programs would only further damage the phone’s interior components.
A temperature sensor is an electronic device that measures the temperature of its environment
and converts the input data into electronic data to record, monitor, or signal temperature
changes. There are many different types of temperature sensors. Some temperature sensors
require direct contact with the physical object that is being monitored (contact temperature
sensors), while others indirectly measure the temperature of an object (non-contact
temperature sensors).

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Lecture Review
In 1821 Thomas Seebeck, while making a pot of tea, discovered that when two dissimilar
metals are joined together, a current flows, as long as the temperature at one of the junctions
is at a higher temperature than the other junction. Little did he know, as he finished his tea,
that he would be famous for discovering the current that flowed in this circuit and the EMF
(Electro Motive Force) that produced this current would be forever called the Seebeck Effect.
Seebeck was responsible for developing the most rugged and simplistic yet cost effective way
of measuring temperature over a broad range. Copper Constantan, Chromel Alumel, Iron
Constantan and Chromel Constantan, the standard thermocouple calibrations that are in use
today, were derived from this research. They work the same way the scientist’s theory said
they would work. When you apply heat to T1 and T2 is at a different temperature the two
dissimilar metals will produce an EMF. The EMF is different for different metals and
unfortunately it is not linear, but it is accurate enough to handle most process applications.
Accuracy improvements have been made primarily by closer control of the chemical
composition; today thermocouples have accuracy as low as 1/2-degree Fahrenheit. There have
been other calibrations introduced since then and many improvements to the way
thermocouples are used; but the credit for developing thermocouples as we use them today
goes to Thomas Seebeck.

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Types of Temperature Sensors
The sensors come in different types, which are categorized based on their connection. There
are two main categories when it comes to temperature sensors, depending on the type of
application being used:
1. Contact Temperature Sensors
2. Non-contact Temperature Sensors
1. Contact Temperature Sensors
Contact temperature sensors measure the degree of hotness or coldness of an object or
substance via direct contact. They are generally used to detect a wide range of temperatures in
different solids, liquids, or gases.
2. Non-Contact Temperature Sensors
These temperature meters are never in direct contact with an object or substance; therefore,
they are widely used in hazardous environments such as power plant industries. They measure
how hot or cold something is via radiation emitted by a heat source.
Different Types of Temperature Sensors
To understand how temperature sensors work, contact and non-contact temperature sensors
are further split up into the following types:
1. Thermometer
2. Thermostat
3. Thermistors
4. Thermocouples
5. Negative Temperature Coefficient (NTC) Thermistor
6. Semiconductor-based Temperature Sensor
7. Resistive Temperature Detectors (RTDs)
1. Thermometer
When we think of temperature, we all know how to measure temperature with a thermometer,
especially the mercury-filled glass thermometer you probably used back in high school.
However, there are many types of thermometers now available.
Bi-metal thermometers are a type of contact temperature sensor that consists of a connected
gauge and stem. The sensor tip contains a spring that sits inside the stem sensing end, which
attaches to a rod, leading up to the gauge needle. It is the movement in the sensing coil when
heat is applied that causes the needle in the gauge to move, displaying the temperature reading.

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Gas-filled and liquid thermometers are also a type of contact temperature sensor that
works similar to bi-metal thermometers; however, they have a bulb that is either filled with a
gas or liquid. The bulb is located inside the sensing end of the probe, which when heated
expands the gas, or heats the liquid, signaling the attached rod to move the needle, displaying
the temperature reading.
2. Thermostat
Thermostats are a type of contact temperature sensor that includes a bi-metallic strip
containing two dissimilar metals (aluminum, nickel, copper, or tungsten).
It is the difference in the coefficient of linear expansion of the two metals that creates a
mechanical bending movement when exposed to heat.

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3. Thermistors
Thermistors or thermally sensitive resistors change their physical appearance when a
temperature change occurs. They consist of ceramic materials (oxides of nickel or
manganese/cobalt coated in glass) that allow them to be easily disfigured.
Most thermistors have a negative temperature coefficient (NTC). This means when an increase
in temperature happens, their resistance decreases. However, some thermistors have a positive
temperature coefficient (PTC); when the temperature rises, the resistance increases.
4. Thermocouples
Thermocouples are one of the most common temperature sensors due to their reliability,
accuracy, sensitivity, simplicity, and wide temperature operating range.
They have two wires that contain two dissimilar metals (e.g., copper and constantan) that
connect at two different points to form a junction. One point is known as the “cold junction”,
kept at a specific temperature, and the other is known as the “hot junction”. It is the voltage
between the two wires that records the temperature change.
Thermocouples may not be as accurate as resistive temperature detectors (RTDs); however,
they are much more cost-effective and have an extensive temperature range (-200 °C – 1750
°C).

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5. Negative Temperature Coefficient (NTC) Thermistor
An NTC thermistor is a sensitive temperature sensor that reacts to very small temperature
changes, providing high accuracy and huge resistance, even at low temperatures. NTC
thermistors have a range of -50 °C to 250 °C. As soon as the temperature starts to increase,
resistance rapidly drops. It is important to note, that because of the large resistance and fast
reflection, NTC thermistors require linearization.
6. Semiconductor-based Temperature Sensor
Semiconductor-based temperature sensors (also known as IC sensors) have a dual integrated
circuit (IC) containing two similar diodes. The diodes and temperature-sensitive voltage
measure the temperature. These sensors give a reasonably linear output; however, they are less
accurate between 1 and 5 °C.
Semiconductor-based sensors are ideal for embedded applications, but unlike other
temperature sensors, their electrical and mechanical performance are not as robust as
thermocouples and RTDs.

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7. Resistive Temperature Detectors (RTDs)
Resistive temperature detectors (RTDs), also known as resistance thermometers, are a type of
temperature sensor that gives very precise measurements. They are made from high-purity
conducting metals (platinum, copper, or nickel) that are wound into a coil. Their electrical
resistance is similar to a thermistor temperature sensor.
Platinum RTDs are the most accurate, therefore, they are more expensive. At Atlas Scientific,
we believe in providing customers with the highest quality and most accurate measuring tools,
which is why all of our temperature sensors are made from Class-A platinum.

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Applications
Temperature sensors are extremely useful for a variety of industries to cater to both
commercial and consumer needs. Below are the most common applications that use
temperature sensors.
1. Medical Applications
Temperature sensors are used for quick and accurate measurements of patient temperatures.
They are also used in MRI imaging machines and portable ultrasound scanners.
2. Electrical Appliances in Our Homes
Temperature sensors are used in many electrical appliances that you probably didn’t know
about. They are found in refrigerators to keep food and drinks cold, in ovens for cooking food
to specific heats, and in air conditioners/wall heaters. They are also found in battery chargers
to prevent under charging and overcharging electrical appliances.

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3. Oil Mining
Temperature sensors are fundamental for safe and effective practices in the oil mining
industry. Oil drills are equipped with inbuilt temperature sensors that notify workers when
they need to stop drilling.
4. Vehicles
Temperature sensors are found in radiators inside different vehicles. These warn you if the
temperature of the engine becomes too hot, which prevents the engine from exceeding its
temperature limit. They are also used in climate control settings, allowing you to cool or warm
the inside of the vehicle.
5. HVAC Systems
HVAC systems require temperature sensors to provide optimal temperatures for a particular
room or building. They are also useful for detecting leaks, such as air conditioning units.

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6. Renewable Energy
Renewable energy sources require an effective production of energy to function; therefore,
they depend on temperature sensors to regulate and measure temperature. Temperature sensors
are required for wind turbines, biomass combustion applications, solar heating pumps, and
geothermal monitoring.
7. Chemical Industries
Chemical industries use high-quality and effective temperature sensors to measure extremely
high temperatures in chemical reactions.
8. Integrated Circuits
Integrated circuits are found in desktop computers, laptops, mobile phones, and other
electronic devices we use daily. They are dependent on integrated silicon temperature sensors
to avoid overheating.

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Advantages and Disadvantages
Common advantages of Temperature Sensors:
 Temperature sensors are low-cost, precise, and extremely reliable in repeated
experiments.
 They are desirable for both embedded and surface mount applications.
 They have a faster response time because of the lower thermal mass.
 The vibrating wire type is normally full-interchangeable. It means that one indicator
can be used for all sensors. It also has a particular technology for verifying long-
term stability, simple and fast output.
 They generally have an IP-68 rate by their weather-proof body.
 They have some indicators that are suitable for direct temperature presentation. So,
they can be used for remote detecting and data logging.
 Their temperature probes have precise linearity and low hysteresis.
 Finally, it should be said that temperature sensors are completely airtight. They are
fully sealed by electron beam welding with a pure vacuum inside them.
Common disadvantages of Temperature Sensor:
 The drawbacks of thermocouples are; least stability, nonlinearity, low voltage,
required reference, sensitivity, etc.
 The drawbacks of RTD are; expensive, absolute resistance is loess, required current
source not strong as compared to the thermocouple.
 The drawbacks of the thermistor are; required current source, self-heating, fragile,
non-linearity, support is limited, etc.
 The drawbacks of IC sensor are; operation is slow, required power supply, self-
heating, configurations are limited, the temperature is upto150oC, etc.

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Also, there are Compare of advantages and disadvantages of three most popular temperature
sensors:
Sensor Advantages Disadvantages
Thermocouple
 No resistance lead wire
problems
 Fastest response
 Simple, rugged
 Inexpensive
 High temperature
operation
 Point temperature sensing
 Non-linear
 Low voltage
 Least stable, repeatable
 Least sensitive
RTD
 Most stable, accurate
 Contamination resistant
 More linear than
thermocouple
 Area temperature sensing
 Most repeatable
temperature
measurement
 Current source required
 Self-heating
 Slow response time
 Low sensitivity to small
temperature changes
Thermistor
 High output, fast
 Two-wire ohms
measurement
 Economical
 Point temperature sensing
 Non-linear
 Limited range
 Fragile
 Current source required
 Self-heating

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Conclusion
In conclusion, temperature sensor placement is crucial for a good process control result. It is
important to determine your critical temperatures of the process and use the proper sensors to
monitor those temperatures. In Practical in a heating application like heat trace is to place the
sensor in the most extreme location; the lowest expected location for minimum temperature
control and the highest expected location for maximum temperature control. The temperature
sensor can only process the information supplied to it and placement is everything. Also, there
are some problems with Temperature Sensors which is self-heating, in the most part limited
temperature range, based on which scenario the temperature sensors effects on it.

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References
1. What is a temperature sensor? | Fierce Electronics
2. What is an embedded computer? | Fierce Electronics
3. Comparing Contact and Non-Contact Temperature Sensors (azosensors.com)
4. How Do Temperature Sensors Work? | Atlas Scientific (atlas-scientific.com)
5. Temperature Sensor Comparison Guide | Watlow
6. Temperature Sensor: Types, Working Principles, Advantages | Linquip
7. Advantages and disadvantages of temperature sensor | thermocouple, RTD, thermistor