Understanding Temperature and Transmitters

 

Because temperature is one of the basic metrics used in the measurement of flow, density, and other factors, the temperature transmitter is one of the most widely used field devices in industry today. Understanding one helps in selecting the other.

César Cassiolato

 

AT A GLANCE

·           Temperature history

·           Accep

ted scales

·           Transmitter types

 

Temperature has a long history, grounded in personal understanding, like sticking a toe into the water before jumping in. Understanding a bit of history can help before you dive into selecting your next temperature transmitter.

Temperature is defined as the measure of the average kinetic energy of the molecules of a substance, represented in a numerical scale with larger values indicating a greater average kinetic energy. However, this has not always been the case. The road to standardized temperature measurement has been a long one.

Historians date the first attempt to establish a temperature scale back to 130-200 B.C. by the Greek doctor Galeano, who suggested the sensations of hot and cold be measured in a scale with four divisions, thus giving birth to the first temperature scale. It would still be centuries until well-defined temperature standards emerged. With the invention of the first thermometer by Galileo Galilei in 1592, advancements in temperature measurement began picking up pace.

In the following decades, many temperature scales were conceived. All were based on one or more arbitrarily fixed points, but none were universally accepted. In 1714 Gabriel Fahrenheit, a Dutch manufacturer of precision instruments, created the first accurate and repeatable mercury thermometer. His scale, degrees Fahrenheit, became the first universally accepted temperature scale in h