Of course, there are many follow-up questions regarding where or when such as: on just the surface, in the center, on average, instantaneously, or steady state, to name a few.
The standard temperature measurement technique that many people first encountered was the mercury (Hg) thermometer to determine if they had a 98.6° or higher temperature. Its first location will not be discussed. These days, since mercury is a potent neurotoxin and potential environmental threat, its replacement is rapidly occurring in consumer, professional, and industrial applications.
Alcohol is commonly used in place of mercury in liquid in glass or bulb thermometers. In bulb thermometer measurements, the sensor provides both the measurement and an easy to read visual interface for the user. However, there is no electrical signal for communication and/or use in a control system. Perhaps, the second temperature measurement that most people encountered was the home thermostat that, in the 20th Century, was commonly a bimetallic coil. It also provides an easy to read gauge as part of the measurement but does not provide an electrical output.
Temperature sensing is an essential aspect of industrial applications from food and beverage, oil and gas and other industrial processing to healthcare, automotive and other end products that typically requires an electrical signal. For digital thermometry, the U.S. National Institute for Science and Technology (NIST) suggests that this could be one of three sensor types: platinum resistance thermometer (PRT), thermistor, and thermocouple. However, other sensing techniques such as resistive temperature detectors (RTDs) and temperature sensor ICs should also be considered for these applications
For challenging applications, such as very high temperatures, more sophisticated sensing techniques include infrared temperature sensors and fiber optic temperature sensors.
A recent market study predicts that the temperature sensors market is expected to grow from USD 5.13 Billion in 2016 to USD 6.79 Billion by 2022, at a CAGR of 4.8% between 2016 and 2022.