McLeodgaugemålere

McLeod gauges are instruments used to measure low pressures, typically in the vacuum range. Developed by Herbert William McLeod in 1874, they are a type of absolute pressure gauge, meaning they measure pressure relative to a perfect vacuum. The operation of a McLeod gauge relies on the principle of gas compression.

In a McLeod gauge, a known volume of gas at the pressure to be measured is isolated. This gas is then compressed by a column of mercury. By measuring the volume of the isolated gas and the final height of the mercury column, the original pressure can be calculated using Boyle's Law. Because the mercury column creates its own vacuum reference, the gauge is independent of atmospheric pressure.

McLeod gauges are known for their accuracy and reliability in the low vacuum range, generally from 10⁻³ to 10⁻⁶ Torr. However, they are manual instruments and require careful operation. They are not suitable for measuring fluctuating pressures or very high vacuum levels. Their design also means they are not practical for continuous monitoring or for use in automated systems. Despite these limitations, McLeod gauges remain a valuable tool for calibration and in laboratory settings where precise low-pressure measurements are required.