How Do Thermometers Work?
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Thermometers have advanced quite a bit since the first iterations were introduced in 1600 by Galileo. Hundreds of years ago, he created a device called a thermoscope that responded to temperature by means of water, gravity, and buoyancy.
In 1724 when Gabriel D. Fahrenheit proposed the scale now named after him, he had already created both alcohol- and mercury-based thermometers. After using them to measure the temperature of water, he designated the freezing point of water as 32 degrees and the boiling point as 212 degrees.
Less than twenty years later, Fahrenheit’s scale received competition from Anders Celsius when he proposed that the designations between the freezing and boiling points of water should instead be on a scale from 0 to 100 degrees. This scale was originally called Centigrade (from the Latin word for one hundred), but it is now generally referred to as Celsius.
And yet another scale, Kelvin, made an appearance in the 1800s. Named after Sir William Thomson, Baron Kelvin of Largs, it measures the point when there is no more atomic motion (the coldest possible temperature) as zero and is usually reserved for scientific research and manufacturing standards.
Though the question remains: how do today’s modern thermometers work? Keep reading to discover the basics of thermometer functionality and learn some safety tips when using one.
Thermometers rely on heat expansion.
The health monitoring devices we use today apply the same scientific methods that were discovered centuries ago. The thermometers invented by Fahrenheit that contained alcohol and mercury both rely on the fact that atoms expand as they get warmer. The expansion of mercury’s atoms and those of carbon, hydrogen and oxygen (the elements form a covalent bond to create alcohol) causes each organic chemical to rise within the thermometer tube. A scale (Fahrenheit or Celsius, or both) is marked along the side of the thermometer to assist in reading the temperature, guided by the reference points of freezing and boiling.
Another more recent thermometer that uses a heat expansion design involves a mechanical process activated by metal’s response to heat. This model is called a spring or bi-metal thermometer and it looks like a clock face but shows temperature markings instead of clock time. This design houses a metal spring that expands in response to heat, which causes the hand of the thermometer to move.
Digital thermometers use signal technologies.
All digital thermometers include an electrical sensor, such as a thermocouple, a resistance temperature detector (RTD), or a thermistor, all of which respond to temperature in predictable ways. RTDs and thermistors (a portmanteau of thermal and resistor) each change their resistance value as their temperature changes. A thermocouple has two temperature-dependent electrical conductors on each end that connect to each other via a wire. Based on the level of voltage that is produced, the temperature is determined.
Each sensor’s electrical signal is then converted to a digital interface. This is made possible by a series of pulses (digital signals) being calculated, then interpreted, and results in the findings displayed on an LED screen.
Another thermometer model that features a digital display is an infrared thermometer. This device reads the level of infrared light (electromagnetic radiation produced by heat) coming from an object or person and infers the corresponding temperature. Most digital thermometers need household batteries to operate, whether they are designed for non-contact or internal use.
Thermometers can produce varying “normal” temperatures.
According to medical professionals, the “normal” human temperature of 98.6˚F is based on an oral temperature reading, which means other methods produce temperature readings that are interpreted in relation to that standard.See Disclosure 1
For instance, a temperature recorded using the ear or rectum (frequently used with small children) is generally 0.5˚ F to 1˚ F higher than 98.6 ˚ F. Likewise, armpit and forehead readings are usually 0.5˚ F to 1˚ F lower. Keep these deviations from the norm in mind when taking your temperature to determine your overall health and wellness.
The method of temperature taking is especially important to note when you are communicating with a health care professional during a virtual visit or phone call.
Safety tips to follow when using a thermometer.
When using a thermometer, it is important to follow all the safety guidelines and device-specific instructions included in the product manual in order to ensure accurate readings and avoid injury. Additionally, you should always sanitize internally placed thermometers before and after each use.
An effective cleaning method is washing the part of the instrument that’s inserted in the body with water and soap, rinsing it, then drying it off. Unless the thermometer is waterproof, avoid getting the area that contains the batteries wet. Another option is to sanitize it with rubbing alcohol or an alcohol wipe. For cleaning that’s specific to your device, consult the user’s manual.
Which thermometer is best for you?
With so many options to choose from, trying to pick the best thermometer for your needs might feel overwhelming. Depending on your budget, there are models at every price point. Whether you want a device that simply takes body temperature or a connectable smart thermometer that can track your data over time in a paired app and features a color-changing light that turns red when a fever is indicated, both options are available.
There are also thermometers that are designed specifically for monitoring the health of a baby. And while knowing exactly how a thermometer works isn’t crucial to supervising your family health care, having a new understanding of why the results can be trusted as accurate might provide some peace of mind.
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These statements and any information contained herein are intended for educational purposes only and are not meant to substitute for medical care or to prescribe treatment for any specific health condition. Carefully review product labels for instructions and important safety information and consider consulting with a health care professional regarding your use of health and wellness products.