Hot wire resistance transducers

The basic process involved in any temperature measurement is heat transfer by conduction. A resistive element in physical contact with the system is employed for the temperature measurement of a system. Changes in the resistance of the resistive element are a measure of temperature and this change can be measured by a suitable electrical circuitry. Care should be taken to avoid any self-heating error due to the current flowing through the resistive element. The material used for the resistive element is platinum or tungsten. A fine wire of either of these materials is mounted inside a metallic or glass enclosure. In a hot-wire level transducer, the level of a liquid in a container is measured by means of a fine wire or thin ribbon of platinum kept vertically inside the liquid column. In a hot-wire pressure transducer (also known as pirani vacuum gauge), s gas is allowed to flow in a chamber which contains a hot-wire filament. Here heat transfer takes place between the molecules of the gas and the hot wire. For the measurement of flow rate of fluids, hot-wire anemometer can be used.