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Types of Thermometers: All You Need to Know

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Types of Thermometers A thermometer is a device that detects temperature or a temperature difference (the degree of hotness or coldness of an object). A thermometer has two important components: (1) a temperature sensor (e.g., the pyrometric sensor in an infrared thermometer or the bulb of a mercury-in-glass thermometer) that fluctuates when the temperature changes, and (2) a mechanism of converting this change into a numerical value (such as the noticeable scale that is printed on a mercury-in-glass thermometer or the digital readout on an infrared model). Thermometers are frequently used to monitor processes in technology and industry, as well as in meteorology, medicine, and scientific study.

Two thousand years ago, Greek philosophers were aware of some of the thermometer’s concepts. The thermometer’s “development from a crude toy to an instrument of precision occupied more than a century,” according to Henry Carrington Bolton (1900), and its early history is “encumbered with erroneous statements that have been repeated with such dogmatism that they have received the false stamp of authority.”

Santorio Santorio (Sanctorius, 1561-1636), an Italian physician, is widely credited with inventing the first thermometer, but its standardization took place in the 17th and 18th centuries. Daniel Gabriel Fahrenheit achieved two important advancements in the history of thermometry during the first decades of the 18th century. He created the Fahrenheit scale (the first standardized temperature scale to be widely used) and the mercury-in-glass thermometer (the first widely utilized, accurate, and practical thermometer).

Types of Thermometers
An early thermometer (Reference: www.sciencelearn.org)

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Working Principle of Thermometers

Empirical or absolute thermometers are two types of thermometers. The thermodynamic absolute temperature scale is used to calibrate absolute thermometers quantitatively. Empirical thermometers do not always agree with absolute thermometers on their numerical scale readings. Still, to qualify as thermometers at all, they must agree with absolute thermometers and with each other in the following way. Given any two objects isolated in their respective thermodynamic equilibrium states, all thermometers agree on which of the two should be used. This does not necessitate that the relationship between the numerical scale readings of any two empirical thermometers is linear, but it must be strictly monotonic. Temperature and thermometers have this fundamental property.

The so-called “zeroth law of thermodynamics,” as expressed in textbooks, fails to convey this information on its own, but James Serrin’s 1977 statement of the zeroth law of thermodynamics, while technically abstract, is more informative for thermometry: “The Zeroth Law states that there is a topological line M that functions as a material behavior coordinate manifold. The ‘hotness levels’ are the points L of the manifold M, and M is known as the ‘universal hotness manifold.'”

The temperature of a thermal radiation bath by a universal constant is proportional to the frequency of the peak of its frequency spectrum; this frequency can be obtained independently of calorimetry, thermodynamics, and the properties of particular materials, from Wien’s displacement law of thermal radiation.

Planck’s principle states that when isochoric adiabatic work is the sole means of changing the internal energy of a closed system, the ultimate state is never colder than the beginning state, except for phase transitions with latent heat, it is always hotter than the original state.

Empirical thermometers are founded on numerous principles. Several of these ideas are founded on the fundamental relationship between the state of a suitable material and its temperature. Only a few materials, referred to as “thermometric materials,” are suited for this function. Radiometric thermometry, on the other hand, is only a little affected by material constitutive connections. In that way, radiometric thermometry can be considered “universal.” This is due to the fact that it is based primarily on the universality of thermodynamic equilibrium and has the universal attribute of emitting blackbody radiation.

Types of Thermometers
A typical liquid In Glass thermometer principle (Reference: instrumentationtools.com)

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Types of Thermometers

Thermometers come in a range of shapes and sizes, depending on the user’s needs. As previously stated, they are mostly used to measure the temperature of objects (living and non-living). As a result, only one type of thermometer is utilized to take body temperature readings. In studies or laboratory testing, however, a different set of thermometers is employed to determine boiling point temperatures and freezing points.

Thermometers are divided into two categories based on their functions:

  • Clinical Thermometers
  • Laboratory Thermometers


Clinical Thermometers

Clinical thermometers, often known as medical thermometers, are built specifically for clinical use. These thermometers are used to determine the body’s temperature. A simple clinical thermometer consists of a long, narrow glass tube with a mercury-filled bulb at the end. The mercury level shows the human body’s temperature. Mercury, on the other hand, is a poisonous element. As a result, analog thermometers have been replaced by sophisticated digital thermometers that can monitor the temperature without ever touching the body. Before using these thermometers, it is always a good idea to sanitize them.

The average body temperature is 37 degrees Celsius. This can range from 35 to 42 degrees Celsius. As a result, clinical thermometers have a temperature range of 35 to 42 degrees Celsius.

Different types of clinical thermometers that we use to assess body temperature on a daily basis are as follows:

Digital Thermometer

Heat sensors are used in most digital thermometers to determine the temperature of the human body. They also have an electronic circuit and a display screen for showing temperature measurements. They can be used to take readings from the rectum, under the tongue, or under the armpit.

Digital thermometers are a form of thermometer that is more advanced than traditional thermometers. When used correctly, these types of thermometers are considered to be the most accurate. They are also simple to use, affordable, and readily available.

Types of Thermometers
A clinical digital thermometer (Reference: instrumentationtools.com)

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Electronic Ear Thermometer

Electronic ear thermometers use infrared technology to determine body temperature from inside the ear canal. They’re called tympanic thermometers because they use the tympanic membrane within the ear to measure temperature. This type of thermometer is great for children. They are, however, costly, and if the thermometer is not properly put in the ear or if there is too much wax inside the ear, they may not accurately measure the body temperature.

Electronic ear thermometers use infrared energy emitted by the heat source to determine the body temperature. As a result, these thermometers capture body temperatures quickly.

Types of Thermometers
An Electronic Ear Thermometer (Reference: schoolnursesupplyinc.com)


Forehead Thermometer

The forehead thermometers, like the electronic ear thermometers, use infrared technology to read heat. They use infrared sensors to measure the temperature of the superficial temporal artery, a sub-branch of the carotid artery. These thermometers are modern and have become highly common in airports, stations, malls, and stadiums for gauging people’s temperatures. Their non-contact habit is the main reason for their popularity. This means that when getting temperature readings using a forehead thermometer, no physical contact is required.

Forehead thermometers are not as accurate as regular digital thermometers, and their temperature readings are typically 1°F (0.6°C) lower than those of digital thermometers.

Types of Thermometers
A Forehead Thermometer (Reference: acsmaterial.com)


Pacifier Thermometer

Pacifier thermometers are intended for newborns that are at least three months old. If a baby feels at ease with a pacifier, this may be the simplest approach to figure out his or her body temperature. Although pacifier thermometers are simple to use, they are inaccurate and only record approximate body temperatures. When monitoring the body temperature, they need the baby to be calm for a few minutes, which might be difficult. This can lead to inaccuracies in temperature readings.

Types of Thermometers
A Pacifier Thermometer (Reference: cascadehealth.com)


Plastic Strip Thermometer

Because they do not produce precise temperature readings, plastic strip thermometers are ineffective for detecting body temperatures. They serve as a guide to determining whether or not a person has a fever. To use plastic strip thermometers, we must place the strip on our forehead, and the colors on the strip will change in response to our body temperature. If the color changes to dangerous, there’s a good probability you’ve got a fever. These thermometers are unreliable. They’re also single-phase thermometers that can be thrown away.

Types of Thermometers
A Plastic Strip Thermometer (Reference: alibaba.com)


Mercury Thermometer

The most basic thermometers are mercury thermometers, which were once the sole way to monitor body temperature. They are the most precise thermometers and are used in the same way that digital thermometers are. These thermometers, on the other hand, do not utilize batteries and do not have any electrical circuits or displays. Mercury thermometers are comprised of a glass tube with a range of temperature readings. One end of the glass is filled with mercury in liquid form.

When we place this thermometer under our tongue, it begins to rise in accordance with our body temperature. When the mercury reaches the end of its journey, the appropriate reading is body temperature. Mercury thermometers, on the other hand, are no longer frequently used due to safety concerns (mercury poisoning) and are banned in several countries.

Types of Thermometers
A Mercury Thermometer (Reference: indiamart.com)


Laboratory Thermometers

Because clinical thermometers cannot be used to measure temperatures other than those of the human body, various specific thermometers are available to measure temperatures for other uses. Laboratory thermometers, in particular, are thermometers that are used to monitor temperatures other than body temperatures. Lab thermometers are another name for these thermometers. They aid in the measurement of boiling points, freezing points, and the temperatures of a variety of other objects in labs and testing.

Laboratory temperatures are intended for use in laboratories only and should never be used in clinical or medical settings. Furthermore, maximum-minimum thermometers assist weather forecasters in determining the maximum and minimum temperatures at any given place. Laboratory thermometers typically have a temperature range of -10 to 110 degrees Celsius.

Laboratory thermometers come in a variety of sizes and shapes to accommodate a wide range of temperature measurements. Some of the most frequent types are as follows:

Liquid-in-Glass Thermometer

Liquid-in-glass thermometers, as the name implies, are made with a sealed glass containing a liquid such as mercury or red alcohol. The volume of liquids in thermometers fluctuates as the temperature rises or falls. As the temperature rises, the liquid expands in response. The rinsing level of a liquid in the glass tube also aids in indicating the temperature. These thermometers are fragile since they have a glass tube. As a result, they’re housed in protective housings that have temperature readings written on them. Furthermore, because they do not need a power supply, liquid-in-glass thermometers are convenient, inexpensive, and ideally suited for places where there is an electrical problem.

Types of Thermometers
A Liquid-in-Glass Thermometer (Reference: slideplayer.com)


Bimetallic Strip Thermometer

Two distinct metals are used to make bimetallic strip thermometers. When the temperature rises, the metals are bound together so that they expand at various rates. These thermometers’ two metals expand to various lengths as well. As a result, the bimetallic strip bends or curls towards the side of the bimetallic strip that has a lower thermal expansion coefficient. When the bimetallic strip moves, it deflects a pointer across a calibrated scale, which aids in determining the temperature. Furthermore, bimetallic thermometers are sturdy, low-cost, and simple to install and operate.

Types of Thermometers
A Bimetallic Strip Thermometer (Reference: reotemp.com)


Thermocouple Thermometer

Bimetallic strip thermometers are made from two different metals. When the temperature rises, the metals become entangled and expand at different rates. The two metals in these thermometers also expand to different lengths. As a result, the bimetallic strip bends or coils towards the side with a lower thermal expansion coefficient. When the bimetallic strip vibrates, it deflects a pointer across a calibrated scale, allowing the temperature to be determined. Bimetallic thermometers are also durable, low-cost, and easy to install and use. The instrument shows the temperature that was measured. Temperatures up to 2800 K are commonly measured using these thermometers. The thermal junction thermoelectric thermometer is another name for thermocouple thermometers. For more information about thermocouple thermometers, visit this link.

Types of Thermometers
A Bimetallic Strip Thermometer (Reference: amazon.com)


Pyrometer Thermometer

Pyrometer thermometers, sometimes known as pyrometers, are remote-sensing devices that aid in the measurement of temperatures at a distance. The temperature of the object is usually determined by the thermal radiation emitted by these thermometers. One of the biggest advantages of these thermometers is that they don’t require you to touch anything. Pyrometers are therefore ideal for monitoring the temperatures of moving objects or surfaces. They’re also useful for gauging the temperatures of items that can’t be touched due to their intricate structure or greater temperatures. Pyrometers are used to measure temperatures above 2000 degrees Celsius.

Types of Thermometers
A Pyrometer Thermometer (Reference: indiamart.com)


Platinum Resistance Thermometer

A platinum wire is used to monitor the temperature in platinum resistance thermometers. The wire is connected to an electrical resistance that varies in response to the surrounding temperature. This means that as the temperature increases, the resistance of the material utilized in these thermometers rises as well. The purpose of platinum resistance temperatures is to detect the outside temperature. These thermometers are a little slow, despite their high temperature precision. These thermometers are typically used to measure temperatures between 500 and 2300 degrees Celsius.

Types of Thermometers
A Platinum Resistance Thermometer (Reference: indiamart.com)


Probe Thermometer

One of the most common and commonly used types of thermometers is the probe thermometer. They’re primarily utilized to take temperature readings of meals and liquid samples in real-time. The quick temperature readings of these thermometers make them perfect for hygiene testing at retail outlets and laboratories in the food industry. Probe thermometers are usually equipped with a pointed tip that aids penetration and immersion. Fixed probes and wired probes thermometers are the two types of probes available.

Types of Thermometers
A Platinum Resistance Thermometer (Reference: temperature.co)

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