In simple words, a Thermometer is a device to use for measuring temperature. This device now comes in varies forms and types to use for different applications. The probe Thermometer is the earliest type that came to our world in the 18th century. Since then, this useful device has changed a lot. Digital meters and infrared meters are examples of how the new technology did change this versatile temperature measuring meter. As mentioned, the probe thermometer is the earliest type, which uses an expanding liquid to show the temperature rise or fall. Liquids behave differently under temperature changes; some change colors, some expand.

Expected properties of a Thermometer

Well, we will discuss the basic probe-type meter here.


1) It should be visible

And, this is the reason why thermometers are made of glass or other transparent material. Glass is the top material choice though. Glass doesn’t react with chemicals such as mercury and alcohol. The user should detect even the slightest change of liquid movement inside the meter. And, that is why colored mercury or alcohol is filled (yellow and red are common colors.)

2) Thermal expansion

Why we can’t use water here? Well, water doesn’t expand much when exposed to temperature changes. Also, the liquid inside the Thermometer should have a uniform thermal expansion. This expansion should be dependable.

3) High boiling point

Most liquid-filled meters cannot be used for measuring very high temperatures. For example, alcohol-filled meters can’t exceed the 200 degrees Celsius limit. Mercury has a higher boiling point when compared to alcohol.

4) A good conductor of heat

Another reason why we can’t use water as the liquid for a Thermometer. You know water has the highest specific heat capacity. So, using water as the liquid will prevent you from detecting minor temperature changes.

Why mercury and alcohol

These two liquids are the best options for a Thermometer. And, that is why these liquids are filled in almost every Thermometer today. OK, let’s get to know about a mercury a bit better now. Mercury is a metal in liquid form at room temperature. Mercury is very visible, hence used in the meter. Its low freezing point of -39 °C and very high boiling point of 357 °C fulfill all expected temperature properties. The liquid is known for linear expansion, hence the meter gives accurate readings. The fact that it is a good heat conductor leads to a faster response time.

Anyway, mercury thermometers lost its grounds in the late 90s. Experts in the medical world discovered the downsides of using mercury meters when taking body temperatures. Mercury can cause serious, life-threatening conditions including death. And, this is where the use of alcohol began to rise. Even though alcohol doesn’t come with reliable and unique properties as mercury, it is safer than mercury. So, you can use alcohol for a Thermometer that is designed for taking body temperature. Alcohol has a low boiling point of -112 °C, which is significant and a boiling point of 78 °C. You can measure high temperatures with it. The brighter color makes it easy to detect even a slight temperature rise or drop. Also, it expands readily than mercury, making it more practical for today’s world’s applications.


Top uses of a Thermometer

Temperature is a parameter that affects almost everything around us including us. We can consider it as the most measured and monitored parameter. Industrial, food, pharmaceuticals, manufacturing, metalwork, and beverage are some of the examples we can highlight here.

Medical Thermometer

The probe thermometer was the one that we did use for this purpose in the 90s. But, the new technology and modern manufacturers did invest new types and forms for more accurate, safe, and easy readings. A digital Thermometer is convenient to use and more accurate than old-days probe-type meters. No mercury or alcohol to leak. Also, digital meters are more accurate when compared to old-days manual meters.

Modern probe Thermometer

These meters are widely used in many industries such as beverage and food. Come with either fixed probes or wire probes. Measuring temperature is a critical task in the food and beverage industry as a slight drop or rise in the temperature can cause texture changes and bacterial growth. Long-probe meters are used for measuring temperatures of beverages and other liquids. In the food industry, frying oil temperature also should be measured before frying any food in it to ensure proper cooking of meat and other foods. Anyway, you should use a Thermometer that can measure high temperatures in these industries. For example, in the metalwork industry, a meter should be able to measure high temperatures up to 1500 degrees Celsius. Mercury-filled or alcohol-filled meters are not suitable for such industrial applications.

Thermocouple Thermometer

These are the meter to use for high-temperature and low-temperature applications. These meters can measure temperatures ranging from minus value to high values up to 2000 degrees Celsius. Also, these meters come as fixed probes and cable/wire probes for easy use. Many thermocouple types are there to measure temperature ranges.

Temperature data loggers

An advanced version of the Thermometer. In other words, a data logger that is optimized to detect temperature changes. A data logger comes with its internal memory to save the measured data. Later, you can retrieve the data on an external device such as a laptop or a mobile device. Measuring the temperature and saving the data at the same time is the top advantage of investing money in a temperature logger. So, the monitoring process is automated with a compact device.

General Thermometer

These are the meters that homeowners use for measuring room temperature. Comes as analog or digital types. Very cheap to buy; you can buy a meter for home use for just $5 today. These meters will serve you for years. You can buy a classic mercury meter for this purpose as you don’t need to worry about mercury and body contact. Anyway, make sure you keep the meter reach out of children.


Some final words

The thermometer is a widely-used device for measuring temperature in many industries today. Comes in many forms and types to fulfill all your specific applications. The days of analog meters are coming to an end now as digital meters are more accurate and easy-to-use, also; less complicated. A thermocouple is a robust meter type to use for measuring temperatures within a greater range. A quick tip: never use a mercury-filled meter for taking body temperatures. Also, don’t keep it where your kids can take it. Mercury contact can kill someone in the worst scenario.

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1 Comment

Delmer October 1, 2018 at 9:46 pm

I never read before such a depth and details.

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