Vakiotilavuuslämpömittari

Vakiotilavuuslämpömittari, known in English as a constant volume gas thermometer, is a scientific instrument used for measuring temperature. It operates on the principle that the pressure of a gas at constant volume is directly proportional to its absolute temperature, as described by Gay-Lussac's Law.

The thermometer consists of a bulb filled with a gas, typically hydrogen or helium, connected to a manometer. The gas in the bulb is kept at a fixed volume. As the temperature changes, the pressure of the gas also changes. The manometer measures this pressure difference, which is then used to determine the temperature. A separate reservoir of mercury can be raised or lowered to maintain the volume of the gas constant.

Vakiotilavuuslämpömittari is considered a primary thermometer because it relies on fundamental physical laws and does not require calibration against another temperature standard. It is highly accurate and is often used to establish temperature scales or calibrate other thermometers. However, it is less practical for everyday use due to its size, complexity, and the need to maintain a constant volume. It is primarily found in research laboratories and metrology institutes. The gas used and the pressure range also influence its accuracy and the temperature range it can measure.