Gas Purity Monitor – Thermal Conductivity Route

Author

S Vignesh

Abstract

This paper presents a method to check the purity of gases by measuring the thermal conductivity. Gas purity is of great importance to industry in general. Power of Industrial lasers have increased dramatically over the past few years, therefore maintaining a highly pure atmosphere in laser resonator is important. Similarly, there are many other industries which look for gas purity. Technique for checking the purity of a gas depends on the type of gas. There are a number of sensors to measure the purity of gases but they are costly. The purity of gas can be checked by comparing it with the thermal conductivity of a reference gas (pure). If constant electrical power if applied to a sensor through which gas stream flows then, Thermal conductivity of a gas stream will affect the temperature of the sensor system. The temperature can be accurately measured by measuring electrical resistance. We use a wheatstone's bridge and pass the pure and impure gases through two arms. When both the gases are pure the bridge will be balanced. If there is an imbalance in the bridge, a small voltage will be developed which is then amplified and fed to a NI- DAQ and checked if there is any impurity. We use a NIDAQ because we can look for the minimum purity.