What Are Thermometers and How Do They Work? A Comprehensive Guide

by Joost Nusselder | Last Updated:  May 30, 2022

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A thermometer is a device that measures temperature or a temperature gradient. A thermometer has two important elements: the temperature sensor (e.g. the bulb on a mercury-in-glass thermometer) in which some physical change occurs with temperature, plus some means of converting this physical change into a numerical value (e.g. the visible scale that is marked on a mercury-in-glass thermometer).

What is a bbq thermometer

What’s the Deal with Thermometers?

Thermometers (best ones for BBQ smokers reviewed here) are tools used to measure temperature, which is the level of heat or coldness of an object or substance. They come in different types, but the primary function of all thermometers is to give a numerical value that represents the temperature of the object or substance being measured.

How Thermometers Work

Thermometers work by measuring the changes in energy that occur when temperature changes. The most common method is to use a temperature sensor, which is a device that changes in some way when it is exposed to heat or cold. This change is then converted into a numerical value that is displayed on the thermometer.

The Importance of Accuracy

Accuracy is a crucial feature of any thermometer. If a thermometer is not accurate, it can cause a lot of problems, especially in sectors where temperature is critical, such as in the medical field. To ensure accuracy, thermometers are standardized and calibrated to give correct readings.

The Different Scales Used in Thermometers

Thermometers can use different scales to measure temperature, but the most common ones are Celsius and Fahrenheit. Celsius is the scale used in most countries, while Fahrenheit is commonly used in the United States. Another scale that is less common but still used is Kelvin.

The Evolution of Thermometers: From Simple Instruments to Modern Devices

During the sixteenth and seventeenth centuries, the earliest thermal instruments were developed. These simple instruments were designed to measure changes in temperature and were constructed by trapping air in glass tubes with the open end of the tube submerged in a reservoir of water. These open thermometers were termed thermoscopes and were the first kind of thermometers invented.

The Invention of the Thermometer

The inventor of the thermometer is a topic of debate among scientists. Galileo Galilei, Santorio Santorio, and Cornelius Drebbel are all credited with the invention of the thermometer. However, it was Galileo who experimented with designs and produced the first sealed thermometer. His unique design used a single bulb filled with air and a partially filled container of water. As the temperature changed, the air in the bulb expanded or contracted, causing the water level to rise or fall. Galileo’s thermometer was not standardized and individual readings could vary.

The Surviving Illustration of the First Thermometer

The earliest surviving illustration of a thermometer was produced by Hero of Alexandria in the first century AD. His design used a glass tube filled with water and inverted in a container of water. As the temperature changed, the water level in the tube would rise or fall, indicating the temperature.

The Grand Duke of Tuscany’s Contribution

The Grand Duke of Tuscany, Ferdinand II, was instrumental in the development of closed thermometers. His use of alcohol instead of water allowed for more sensitive temperature measurement and the ability to measure lower points.

The Role of Glass in Thermometers

Glass has played a crucial role in the development of thermometers. Its ability to trap air and allow for the expansion and contraction of the bulb has made it an ideal material for thermometer construction. Glass tubes are still used in modern thermometers, although electronic and digital devices have largely replaced the need for glass bulbs.

The Importance of Temperature Measurement

Temperature measurement is crucial in a range of industries, including medicine, food production, and manufacturing. Accurate temperature measurement can help ensure the safety and quality of products and processes. The evolution of thermometers has allowed for greater precision in temperature measurement and has played a vital role in the advancement of science and technology.

Thermometer Applications: Beyond Measuring Temperature

Thermometers are not limited to measuring temperature in cooking and baking. They have a wide range of uses, including:

  • Determining body temperature
  • Measuring the temperature of liquids, solids, and gases
  • Recording temperature changes in scientific research
  • Monitoring the internal temperature of meat during processing
  • Measuring the sugar content of foods
  • Stating the relative humidity of the air

Utilizing Different Methods and Materials

Thermometers come in a variety of types, classified according to the techniques and materials used in their construction. Some of the most popular types include:

  • Traditional liquid thermometers
  • Electronic thermometers with sensors that convert temperature changes into electrical signals
  • Fiber optic thermometers that use light to measure temperature changes
  • Smaller, fixed-scale thermometers that are calibrated to a specific temperature range

Important in Scientific Research

Thermometers are critical instruments in scientific research, where accuracy and precision are essential. They are used to measure temperature changes in a variety of materials, including liquids, solids, and gases. Thermometers are also used to determine the boiling and freezing points of substances and to monitor the temperature changes during chemical reactions.

Popular in Cooking and Food Processing

Thermometers are commonly used in cooking and food processing to ensure that food is served at the proper temperature and to prevent foodborne illnesses. Some of the most popular uses of thermometers in cooking and food processing include:

  • Measuring the internal temperature of meat to ensure that it is cooked to a safe temperature
  • Recording the temperature of hot foods to ensure that they are held at a safe temperature
  • Measuring the sugar content of foods to determine the proper amount of sugar to add to a recipe
  • Monitoring the temperature of food during processing to ensure that it is cooked evenly and thoroughly

New and Modern Uses

Thermometers are finding new and modern uses in a variety of industries, including healthcare, energy, and manufacturing. Some of the most innovative uses of thermometers include:

  • Using thermometers to monitor the temperature of power plants and other energy facilities
  • Using thermometers to monitor the temperature of materials during manufacturing processes
  • Using thermometers to monitor the temperature of the body during medical procedures

Liquid Thermometers: Measuring Temperature with a Classic Device

Liquid thermometers are devices that measure temperature changes by using a liquid compound, such as mercury or alcohol, that expands or contracts when exposed to heat or cold. The device is made up of a glass tube containing the liquid and a bulb at the bottom that is filled with the same liquid. As the liquid in the bulb expands or contracts, it moves up or down the tube, which is marked with a standard scale for temperature readings.

Uses and Applications of Liquid Thermometers

Liquid thermometers have been used for generations in a variety of settings, including:

  • Household: Used for measuring body temperature, fever, and basal body temperature tracking.
  • Medical: Used in hospitals and clinics for patient care and diagnosis.
  • Industrial: Used in laboratory, educational, and sales settings for measuring temperature in piping, tanks, and vats.
  • Meat: Used in cooking to determine the internal temperature of meat for food safety.
  • Educational: Used in science classes to teach about thermal expansion and temperature measurement.

Restrictions and Disposal of Liquid Thermometers

While liquid thermometers are a common and useful device for measuring temperature changes, there are certain restrictions and regulations that apply to their use and disposal. Some key points to keep in mind include:

  • Mercury thermometers are no longer suitable for disposal in many states due to the potential for mercury release during cleanup or disposal.
  • The ASTM has established standards for the production and use of liquid thermometers to ensure accuracy and safety.
  • Liquid thermometers containing acid or blood are considered devicerelated waste and must be disposed of according to specific regulations.
  • Breaking a liquid thermometer can be dangerous due to the potential for chemical release and should be handled with care.

The Versatile Dial Thermometer: A Broad Selection of Options for Any Application

Dial thermometers come in a variety of sizes, dials, and connection types, making them a versatile tool for many different fields. They are designed to be easy to read and use, with a clear view of the temperature scale. Some additional features include:

  • Dual ranges for added versatility
  • Adjustable stems for tilt or angle
  • Hermetically sealed heads for added accuracy
  • Bimetal construction for added durability
  • Stainless steel construction for added strength
  • NPT connections for easy installation
  • Broad temperature ranges for use in hot or cold applications
  • Remote location options using capillary tubing
  • Pocket-sized options for easy storage and transport

Recommended Uses

Dial thermometers are ideal for measuring the temperature of water, food, tanks, compost, and many other applications. They are mainly used in building and machine construction, as well as in the food industry. Some recommended uses include:

  • Measuring the temperature of hot water tanks
  • Monitoring the temperature of food during cooking or storage
  • Measuring the temperature of compost piles
  • Monitoring the temperature of machinery and equipment

Installation and Connection

Dial thermometers come in a variety of sizes and connection types, making them easy to install in any application. Some common connection types include:

  • Surface mount
  • Sanitary mount
  • Threaded connection

When choosing a dial thermometer, it is important to consider the installation and connection options that are available. Some items to consider include:

  • The diameter of the stem
  • The length of the stem
  • The type of connection
  • The accuracy rating

Electronic Thermometers: The Electrically Accurate Way to Measure Temperature

There are several models of electronic thermometers available, each designed for specific purposes. Some of the most common types include:

  • Oral thermometers: used to measure the temperature inside the mouth
  • Axillary thermometers: used to measure the temperature under the arm
  • Rectal thermometers: used to measure the temperature inside the rectum
  • Ear thermometers: used to measure the temperature inside the ear canal
  • Forehead thermometers: used to measure the temperature on the forehead

Recording Temperature with Electronic Thermometers

Electronic thermometers are great for recording accurate temperature readings. They are designed to measure the temperature of hot or cool objects and can be used to measure the temperature of water, air, and other substances. To use an electronic thermometer, follow these steps:
1. Turn on the thermometer and wait for it to beep or signal that it is ready.
2. Place the probe in the substance you want to measure the temperature of.
3. Wait for the temperature reading to stabilize.
4. Read the temperature on the digital screen.

How Meat Thermometers Work: The Science Behind Temperature Measurement

When it comes to measuring the temperature of meat, the probe is the star of the show. This thin, metal rod is inserted into the meat and measures its internal temperature. But how does it work? Here’s a breakdown:

  • The probe contains a resistor, a small component that measures resistance to electrical flow.
  • The resistor is made of a semiconductor material, which means its resistance changes as the temperature changes.
  • When the probe is inserted into the meat, the heat causes the metal to expand, which in turn changes the resistance of the resistor.
  • The thermometer measures the resistance of the resistor and uses that information to calculate the temperature of the meat.

The Display: How Meat Thermometers Show Temperature Readings

Once the thermometer has calculated the temperature of the meat, it needs to display that information in a way that’s easy to read. Here’s how it works:

  • The thermometer has a small computer chip that processes the information from the probe.
  • The chip converts the resistance measurement into a temperature reading, usually in degrees Fahrenheit or Celsius.
  • The thermometer then displays that reading on a small screen or dial.

Why Meat Thermometers are Important for Safe Cooking

Meat thermometers are an essential tool for anyone who wants to cook meat safely and avoid foodborne illness. Here’s why:

  • Different meats require different cooking temperatures to be safe to eat. For example, chicken needs to be cooked to an internal temperature of 165°F to kill harmful bacteria.
  • Without a meat thermometer, it’s difficult to know if meat has been cooked to the correct temperature.
  • By using a meat thermometer, you can be sure that your meat is safe to eat without overcooking it and making it dry and tough.

So there you have it – the science behind how meat thermometers work. Whether you’re a professional chef or a home cook, a good meat thermometer is an essential tool for ensuring that your food is cooked safely and deliciously.

How to Use a BBQ Smoker Thermometer Like a Pro

A BBQ smoker thermometer is a tool that measures the internal temperature of food while it is being cooked. It uses a metal strip that is sensitive to heat and expands when exposed to it. This expansion triggers motion, which moves the temperature dial to show how hot it is inside the BBQ smoker.

The Benefits of Using a BBQ Smoker Thermometer

Using a BBQ smoker thermometer has several benefits, including:

  • Preventing overcooking or undercooking the food.
  • Allowing you to control the temperature of the BBQ smoker more accurately.
  • Knowing when the food is done without having to cut into it.
  • Providing a standard for recording and measuring the temperature of the food.
  • Familiarizing yourself with the internal temperature of different types of food, such as pork, beef, and poultry.
  • Ensuring the food is safe to eat by measuring the internal temperature to prevent foodborne illnesses.


So, that’s how thermometers work and what they’re used for. They’re a useful tool for measuring temperature, especially in the medical field. You should now know how to choose the right one for your needs. So, go ahead and get one for yourself!

Joost Nusselder, the founder of Lakeside Smokers is a content marketer, dad and loves trying out new food with BBQ Smoking (& Japanese food!) at the heart of his passion, and together with his team he's been creating in-depth blog articles since 2016 to help loyal readers with recipes and cooking tips.