Temperature Measurement Overview

What Is Temperature?

The temperature is a numerical measurement of how cold or hot something might be. It is possible to measure the temperature of many different things, including the air, body temperature, water, and more. When it is warmer, it means that the kinetic energy of the molecules in the space being measured is higher. When the temperature is lower, the molecules are moving more slowly. The lowest possible temperature is absolute zero. At absolute zero, it means that all molecular motion ceases. This is a hypothetical temperature. Even in deep space, the temperature only gets to three degrees above absolute zero.


How Is Temperature Measured?

A wide range of different types of equipment is in use for measuring temperature today. Thermocouples are voltage devices that can show the temperature by measuring the amount of voltage change in a device. When the output voltage of a thermocouple rises, the temperature also goes up. Thermocouples are generally inside of metal and ceramic shields that protect them from the outside environment. Another type of electrical device for measuring temperature is a resistive temperature device. They are linear, unlike thermocouples. Some devices may also have change of state sensors in them that will measure the change in temperature. These simply indicate a change in state, such as water to steam. They do not actually provide an accurate measure of the temperature.


What Are the Various Units That Temperature Can Be Measured In?

The following are all of the ways to measure temperature. Depending on what one is measuring and why, it may be appropriate to record it in different ways. Some of these methods are still in use, while others are antiquated and only useful from a historical perspective.

  • Celsius – Celsius, or centigrade, is a scale of temperature measurement named after Ander Celsius, an astronomer from Sweden. He developed the first version of this temperature scale in the 1700s. Up until 1954, 0 degrees Celsius referred to the freezing point of water, and 100 degrees Celsius was the boiling point of water. With the introduction of the Kelvin scaled, things changed.
  • Fahrenheit – The Fahrenheit scaled is a temperature measurement scale based on a proposal from Daniel Gabriel Fahrenheit in 1724. According to this scale, water becomes ice and freezes at 32 degrees F, and water will boil at 212 degrees F. Most countries today use the Celsius scale for measuring temperatures, but some countries around the world still use Fahrenheit. Those countries that use this scale include:
    • The Bahamas
    • The Cayman Islands
    • Palau
    • The United States
  • Kelvin – The Kelvin scale features absolute zero as 0K. In the Kelvin scale, water will frees at 273.16K, and water will boil at 373.16K. This temperature scale has not been around for quite as long as Celsius and Fahrenheit, but it still started well over a hundred and fifty years ago. Lord Kelvin wrote a paper called On an Absolute Thermometric Scale that spoke of the need for an absolute zero temperature, which at that time would have been -273 degrees Celsius.
  • Rankine – This temperature measurement scale is named after William John Macquorn Rankine, who proposed the scale in 1848. In the United States, some fields of engineering make use of this temperature scale. 0 degrees R is the same as 0 degrees K – it is the temperature for absolute zero. However, the scale varies from there, with the freezing point of water being 491.67 R.
  • Newton – Sir Isaac Newton created the Newton scale for temperature around 1700. His was actually the first real attempt at creating some type of temperature scale. The scale was not entirely accurate, and it included reference points that included “glowing coals” and “cold air in winter”. He determined that zero degrees would be the temperature at which water would freeze and 33 degrees would be the temperature at which water would boil. This was similar to the Celsius scale, and it is easy to see that it is a direct precursor to it.
  • Réaumur – Another term for this scale is octogesimal division. This temperature scale sets the freezing point of water at 0 degrees and the boiling point of water at 80 degrees. Rene Antoine Ferchault de Réaumur proposed a similar scale to this in 1730, which is why this scale bears his name. This was a popular form of temperature measurement in Europe until the 1790s, although some countries were still using the system all the way through to about the middle of the 19th century.
  • Rømer – The Rømer scale, named after a Danish astronomer named Ole Christenson Rømer, started out by using zero as the freezing point of brine. The boiling point of water was set at 60 degrees according to the scale. However, this scale changed when Rømer realized that the freezing point of pure water was actually different from the freezing point of brine, which many temperature scales use to determine the freezing point. While no one still uses this scale, it does have some historical significance since it was the first calibrated scale.
  • Delisle – The scale was invented by Joseph-Nicolas Delisle in 1732 and used the temperature of boiling water as the zero point. He added 150 degrees to get to the freezing temperature of water.

Because of all of the vast differences in these scales, converting from one to another can be problematic. Finding conversion charts, as well as conversion calculators online is the fastest and simplest way to make the conversions.


Why Is It Necessary to Measure Temperature in Electronics

Electronics are sensitive devices for the most part, and if the temperature in electrical devices goes too high or too low, then it could result in damage to the equipment. Heat damage can occur in electronics in two different ways. One example would be an electronic device such as a videogame console.

The temperature of the unit will increase while it is in use. If it gets too hot, it can actually damage the electronics that are in the device, rendering them useless. In many types of electronics, there are fail-safes to shut the equipment down when the temperature rises. The new PlayStation 4 console will do this if the temperature gets too high.

A different example might be taking a phone out with you on a hot day and leaving it in the car. The temperature will increase and has the potential to damage the device, as there is no way to turn off the heat. Cold can have the same effect on some types of electronics, including computers, but heat is generally the biggest problem. This is why some types of electronics, such as the aforementioned computers, have fans in them to keep things cool.


What Types of Measurement Devices Are Available?

  • Dial Thermometers – A dial thermometer, sometimes called a differential absorption lidar thermometer, makes use of a metal pointer on a circular dial, which features the temperature scale. They feature one of several types of temperature sensors including bi-metal, vapor-tension, liquid, or gas-filled.
  • Digital Thermometers – A digital thermometer features sensors and probes for measuring temperatures, and they tend to be far more accurate than traditional mercury thermometers. They are generally portable and have a digital readout that makes it easy to see the temperature. Some will offer both Fahrenheit and Celsius readings.
  • IR Thermometers – This is a type of noncontact thermometer. They determine the temperature by recording the thermal radiation. They are accurate and easy to use. Some of the most common uses for IR thermometers include checking for hot and cold spots in a home that may determine leakage of air into and out of the home. Firefighters use them to look for hotspots. They can even detect hotspots on electrical circuit boards.
  • Liquid in Glass Thermometers – This is the most common type of thermometer. They feature a glass tube that contains a bulb filled with mercury at one end. The liquid could be silver or red. As the temperature heats up, the mercury rises through the tube. This is a simple method of measuring temperature, but is it not the most accurate.


What Other Ways Exist to Measure Temperature?

The above are the most common types of measuring temperature. However, they are not the only methods of temperature measurement. Some of the other options include thermocouples, mentioned in the first part of the article. Silicone diodes, resistive temperature detectors, and thermistors are some of the other ways to measure temperature for different applications.


What Are Temperature Probes?

A temperature probe is an element that attaches to a measurement device, such as a digital thermometer or a thermostat. The probe picks up the temperature of any area that it is in, which provides an accurate and fast measurement of the temperature. When part of a thermostat, the probe can pick up the temperature and relay it, which will let the thermostat know whether the temperature is too high, too low, or just right.


What Are Thermal Imaging Cameras

Thermal imaging cameras are cameras used for taking the temperature of a location by showing infrared radiation as visible light on the screen. This lets users see where there is high heat or cold spots. One of the most common uses for the thermal imagers is with firefighters. They use them to look for hot spots first, as well as to see through smoke and darkness. The imagers can pick up body heat as well, which can help with rescue efforts. Most of the time, the cameras are handheld, but some of the newer versions are helmet mounted for firefighters.


What Are Thermometer Kits?

A thermometer kit is generally the simplest and most cost effective way for someone to buy a high quality thermometer, as well as the other accessories they need to use it, such as the probes and the case. Some of the kits come with other items, such as voltage detectors. When choosing a kit, it is important to look at all of the items that come with it to make sure they are necessary for you. Some may only need to have the thermometer and do not need the clamps or multimeters that some of the kits offer. However, those who are in the electronics field, whether they do it as a profession or they are a hobbyist, will find that buying a kit that contains a multimeter and thermometer saves money and provides them with tools they really need.


What Are Calibrators?

Devices used to measure temperature, through bi-metals, which create a small amount of voltage when they are combined, or through one of the other temperature detection methods, need to be accurate. In order to be accurate though, they first need to undergo calibration. Good calibrators ensure the highest level of accuracy in the temperature measurements you get from your device.


What Types of Calibrators Are Available?

  • Drywell Calibrators – This type of calibrator is capable of offering accuracy and portability at good prices. They can provide high levels of accuracy and stability. To calibrate, users put the thermometer probes into the calibrator. With the larger, block calibrators, it is possible to calibrate several thermometers at the same time.
  • RTD Calibrators – RTD stands for resistance temperature detector. These types of calibrators will help to ensure these devices and detectors are always accurate. They are actually quite common in laboratories, as well as electronics manufacturing and engineering facilities.
  • Thermocouple Calibrators – These calibrators will ensure accuracy in thermocouples, which are not always as easy to calibrate as other temperate devices. Proper calibrators help to make the process as simple as possible though. They can simulate the thermocouple, and many of the calibrators will work with a variety of different types of thermocouples.


Whenever purchasing any type of calibrator, or temperature measuring device for that matter, it is important to buy only the correct device for your specific needs. Make sure the calibrator you choose will work with the thermocouple or thermometer you happen to own as well.