The history of temperature stretches back for thousands of years. Temperature has always been an important and essential part of daily life and society, ever since bakers and blacksmiths relied on temperature to control chemical reactions.
Nowadays, temperature is better understood than ever, and a wide range of temperature-measuring equipment – thermoscopes, thermocouples and many types of thermometer – is necessary to measure and to help control it.
This blog series hopes to open your eyes about the history of temperature measurement, from the ancient through to the modern day. Enjoy!
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| Some of TME's thermocouple probes |
Two metals are used, one contained within the thermocouple, and one forming a probe which acts as a sensor to test the temperature of a substance or atmosphere. The word 'thermocouple' comes from the idea of the 'coupling' of two different metals.
The difference between their temperatures is expressed electrically through their difference in voltage. As the temperature of the metal inside the thermocouple is already known, the difference between the two temperatures can let us easily deduce the temperature of the metal attached to the probe.
This deduction is usually carried out electronically by a tiny microchip inside the instrument, so that the scale or display on a thermocouple thermometer simply shows the temperature which the probe has sensed.
Thermocouples are used extensively in electrical engineering and industry. For instance, they are essential in fields such as heating appliance safety, radiation testing and in many areas of manufacture.
Thermocouples can be found in many different types (such as K, T, J, E, N and B), named after the metals from which their wires are made. Two popular thermocouple types are K and T.
K type thermocouples are known for offering a wide temperature range (-200 to +1372 degrees C) at low cost, and are popular across a wide range of uses.
T type thermocouples do not have such a wide temperature range (-200 to +400 degrees C), however they are known to be highly accurate, with an accuracy of 0.25 of a degree C. This makes them ideal for use in food manufacturing, processing or catering, as temperature regulations in the food industry tend to be very strict, and very small fluctuations of temperature can make a huge difference.
Thermocouple probes can be adapted to cater for a wide variety of specific usages. Penetration, or needle probes are perfect for identifying the core temperature of semi-solid products, such as a pack of meat. Air probes register the temperature of still or moving air around the probe. General purpose, or immersion probes can be immersed in liquid, or held under a flowing tap, which is very useful for testing the temperature of a tank of liquid, and surface probes are used primarily to measure the surface temperature of items such as pipes or radiators.
These days, most industries have requirements for measuring or monitoring temperature, from food manufacture to legionella prevention, building, transport and even space travel, as well as medical thermometers. We've come a long way since Philo of Byzantium noticed bubbles appearing in a jug left in the sun!
