Many, if not all, of us have used thermometers in one way or another, be it to determine the weather outside or to measure the temperature of the body. But what do you know about them? Do you know where or how these devices are used? Today, we will tell you all about the different types of thermometers and their uses.
Here are all the details about the different types of thermometers, their functions, and how to properly use these devices.
What is a thermometer?
First of all, let’s define the word ‘thermometer’. The name comes from merging two Latin terms together: ‘thermo’, which means heat, and ‘meter’, which means a measuring device.
When you combine them, you get ‘thermometer’, which is a device used to measure heat. In other words, it is a tool that allows you to measure the temperature of anything.
To express temperature in numeric format, most thermometers use degrees Celsius (°C) or Fahrenheit (°F). In science, you can also find thermometers with the Kelvin (K) scale, which is tied to the temperature of the absolute zero.
There are various types of thermometers, depending on the sphere of use and the mechanism involved in determining the temperature.
In this post, we will tell you about the most common types of thermometers.
Types of thermometers
There are 6 kinds based on how they work.
This type is also known as a pressure-filled or vapour-pressure thermometer. It determines the temperature based on the change of pressure in a gas or liquid.
Manometric thermometers can be filled with gas (nitrogen), condensation (alcohol, chloromethane, diethyl), liquid (metals with low melting points, silicon liquids, metaxylene) or mercury.
This type is the oldest and most common kind of thermometer. It is used almost everywhere, and its principle of operation is very simple.
It consists of a glass bulb and stem filled with a working liquid (alcohol or mercury) and an inert gas. When the temperature changes, the liquid expands or shrinks.
When paired with a temperature scale, it is possible to use this occurrence to determine the temperature.
Advantages of liquid-in-gas thermometers include:
- Simple displays that are very easy to read
- Typically measure in both °C and °F
- Most are wall mountable
- Can be immersed in liquids
- They require very little maintenance
- Variable measurement range, resolution and accuracy
This type determines the temperature based on the difference in pressure or volume of the gas it is filled with. There are constant pressure and constant volume gas thermometers. The latter is more commonly used.
A gas thermometer can be filled with any gas, but the most popular option is hydrogen. This type works best with very low temperatures.
4. Bimetal (bimetallic)
This is a mechanic type that works with a bimetal strip. Bimetal means that it is made of two metals.
The strip is sensitive to change in temperature, and it causes mechanical displacement, which is used to determine the temperature.
Bimetallic thermometers are perfect for higher temperatures as they become less sensitive and accurate at lower temperatures. They can be found in many household appliances like stoves.
Digital or electronic thermometers are the newest in the field. Instead of using liquids or gases paired with a temperature scale, they have a digital screen which can show you the readings in mere seconds.
A digital thermometer has a thermistor that reacts to the change in temperature and projects the result on the device's screen.
All of the ones we have mentioned above require contact to determine temperature. An infrared thermometer uses thermal radiation that objects emit to measure temperature.
This means that they can tell temperature from a distance. Some people call them ‘temperature guns’ as most are handheld and look like miniature guns.
Some benefits of infrared thermometers are:
- Non-contact allows extreme temperatures to be safely taken
- Measurements are available at the pull of a trigger
- Laser-targeting systems allow accurate placement of the sensor
- Variable measurement range, resolution and accuracy
All of the types we mentioned in this section can be used for different purposes: industry, science, cooking, or medical purposes.
However, we want to talk a little bit more about clinical thermometers, as they are probably the most common ones that everyone has to deal with.
There are six most common clinical thermometers used in hospitals and homes:
One of the oldest types, mercury-filled thermometers are slowly disappearing from most countries. In addition to not being the most accurate, they might be very dangerous if broken. The mercury inside is toxic to people and the environment.
A safer alternative to the mercury ones, these thermometers use coloured alcohol that expands when exposed to increased temperature. However, both of these liquid-filled thermometers require some time to show the temperature.
3. Temperature strips
Although temperature strips are not thermometers per se, they are often used in hospitals as a way of quickly determining a patient’s temperature.
These strips contain liquid crystals that react to heat by changing colour. Each colour corresponds with a certain body temperature. Temperature strips are fast, but they are not the most reliable.
This type is mostly used to determine a person’s temperature through their ear. However, some determine the temperature near a person's forehead. It works almost instantly; in a few seconds, you can get a precise temperature reading on a small screen.
Digital thermometers are quickly replacing all of the old liquid-in-glass types. They are fast, accurate and convenient. With the help of oral, rectal and armpit digital thermometers, you can get your results in seconds.
Even though they are only a form of digital thermometers, they are still different. They are meant for women trying to get pregnant. It allows women to track their ovulation, as it is accurate to 1/100 fraction of a degree.
Some versions also have a function that lets you see previous readings, which makes it easier to take note of the changes.
Uses of thermometers
As we have established, the main use of a thermometer is to measure temperature. You can measure the temperature of many things to get useful information about your surroundings and yourself.
For example, if you measure the temperature of the air outside, you will know how to dress appropriately. If you measure your body temperature, you will find out whether you have a fever or not.
But wait, there are more thermometer functions. These devices are also used in science and production to measure the temperatures of different metals, liquids, gases and other materials. You can also use the device to figure out the temperature of your food while cooking.
How does a thermometer work?
The following is the mechanism of operation for liquid-in-glass thermometers:
As the temperature around the bulb heats up, the liquid rises in the glass tube. The glass tube is mounted on a backboard that is marked in units called degrees.
When it is hot, the liquid inside the thermometer will expand and rise in the tube. When it is cold, the liquid will contract and fall in the tube. The temperature is read by finding the level of the liquid in the tube and the number on the temperature scale across from it.
What is the proper way to use a thermometer?
It all depends on the type of thermometer. Here is how to use thermometers:
- Oral: Place the thermometer under the tongue and keep your mouth closed in order to get an accurate reading. Wait until the device beeps or approximately 5 minutes for a manual thermometer.
- Rectal: Gently insert the tip of the device into the rectum and wait for the beep or for about 5 minutes as above.
- Axillary: Place the axillary thermometer under the arm with the tip in the deepest crease.
- Tympanic: Pull the top of the earlobe up and back, place the tip (covered with the probe cover) in the ear canal opening. Press the button until it beeps.
- Temporal artery (forehead): Press the button down and sweep probe across the forehead.
Where are thermometers used?
These devices are used wherever there is a need to measure temperature, for example:
- In the kitchen when you need to measure the temperature of hot food in a steam tray or chafing dish, as well as cold items in a salad bar, and to measure how quickly a soup or sauce is cooling (to ensure that it does not spend excessive time in the temperature danger zone)
- At home when you need need to measure someone's body temperature to determine if they are sick
- In Chemistry laboratories in schools to measure the temperature of different solutions when they react
- In hospitals, when doctors measure their patients' body temperature.
- In meteorological stations.
These are not the only places where these devices come in handy. They can be used literally anywhere as their uses are quite diverse.
How many types of thermometers are there?
Based on how they work, there are 6 types:
Other sources classify thermometers as:
- Forehead strips
- Non-contrast infrared
- Electronic ear thermometers
That is it for our classification of the different types of thermometers. We hope that you have learned something new about these devices.