Capillary thermometers are instruments used for measuring temperature, often using the zeroth law of the thermodynamics.
History of the thermometer
The first known thermometer was actually made to demonstrate the principle of thermal expansion of the air, by the scientist Philo of Byzantium (280 – 220 BC), active in the Library of Alexandria.
The Galilean thermoscope or thermometer is instead attributed to Galileo Galilei. Built in 1607 (and perfected by Fahrenheit in 1709), it consists of a glass cylinder filled with alcohol, with ampoules indicating the temperature inside. These are filled with a liquid too. When the thermal equilibrium with the surrounding environment is reached, two groups of bottles created, one lower than the other. The temperature marked on the lower ampoule among those of the upper group marks the current atmospheric temperature.
From a physical point of view, Galileo’s thermometer uses the Archimedes principle, that is, if we have two fluids of different densities, the one with lower density will tend to rise upwards while the one with higher density will tend to fall.
When the atmospheric temperature increases, therefore, the liquid in the ampoules decreases in density.
Liquid and gas thermometers
Although apparently very different from the mercury or gallium thermometers that we all know, the principle that governs the operation of all liquid thermometers is the same, i.e. thermal expansion, given that when temperature changes, not only does the density vary fluid, but also its volume.
Gases also behave in the same way as fluids, with the only difference that gas thermometers are much more precise and are used for the calibration of other thermometers.
Bimetallic foil thermometer
The bimetallic foil thermometers, on the other hand, are formed by a U or spiral foil, consisting of two metals with different expansion coefficients, such as iron and copper, coupled and welded together. One end of this foil is connected to an index or pointer which moves along a graduated scale. As the temperature increases, the foil curves from the less expandable part of the metal and the deformation moves the pointer, allowing to observe the temperature variation.
Capillary thermometers
The capillary thermometer also exploits the principle of dilation of the fluids which, stressed by the heat, allow the expansion of an internal spiral always connected to a pointer. The key elements in this type of thermometer are:
- Bulb: element in direct contact with the heat source, it can be made of copper or brass, depending on the temperatures to be detected.
- Capillary: the ”cable” in perforated copper that connects bulb and spiral (sensitive element). Inside, synthetic liquid flows which allows the expansion of the parts: based on the temperature range to be detected, the length of the capillary is calculated according to the principles of viscosity of the fluid.
- Spiral (sensitive element): this component is made of copper, and connected to one of the ends of the capillary. Allows movement based on the heat transmitted by the bulb to the spiral, and consequently to the reading index (pointer).
Thanks to the expansion principle described above, we are able to obtain a very precise reading of the temperature.
IMIT capillary thermometers
IMIT produces a wide range of capillary thermometers, mainly dedicated to the assembly on boilers, catering appliances and electrical appliances in general, capable of operating on a temperature range from 0°C to 350°C.
Based on the desired detection temperature, the material of the bulb can vary from copper (up to 120°C) to brass (for higher temperatures).
Aesthetically, the monitor that houses the graduated index and pointer can be square, round or rectangular, according to the dedicated housing, and the internal reading quadrants can be customized with colors and characters, making them completely customizable.
Certifications and production
IMIT thermometers are built according to European CE regulations, also respecting the EAC requirements for the Russian market. All the materials used refer to ROHS FREE regulations in respect of the environment and health. Furthermore, the production is followed by numerous tests and controls in order to guarantee the highest quality and reliability of detection of the final product.
To find out more, browse our website and download our catalog. For further inquiries or commercial information for the industry sector, send an email to info@imit.it. Our staff will reply as soon as possible.
To find out more, browse our website and download our catalog. For further requests or commercial information about our products for industry, send an email to info@imit.it. Our staff will reply as soon as possible.