Gas in metal expansion thermometers

Gas-in-metal expansion thermometers (or gas-actuated thermometers) use the principle of ideal gas pressure, where temperature changes cause pressure variations in an inert gas (e.g., Helium, Nitrogen) inside a metal bulb, rather than volumetric expansion. These rugged, high-accuracy instruments, often used for ranges from -200°C to +700°C, provide rapid response times and can feature capillary tubes for remote, long-distance monitoring up to 60 meters