This technique generally consists of an infrared source, a sample cell, reference cell, optical filters, a mechanical chopper to modulate the infrared source, and an infrared detector. The IR detector can be one of several designs, but the basic function is to detect the amount of energy absorbed by the component of interest in the sample. While many gases are measurable using UV spectroscopy, SO2 and NO are gases most frequently measured via this technology. Therefore, low-level SO2 measurements can be made in the presence of water in the process sample. Its application has been widely accepted in the majority of industries, including refining, petrochemical, and chemical.
Paramagnetic analysis is particularly effective for measuring oxygen as a dilutent gas in systems.
All paramagnetic oxygen analysers require a dry, non-condensing sample. Should a liquid of any type get into the measurement cell area, it ceases to function and, in some instances, the cell cannot be recovered. Analysers use techniques such as a torsion bar that is caused to swing by the passage of oxygen in the sample gas as it is attracted through the magnetic cell. A null balance principal can be used to correct the tendency for the bar to move by applying a current through a coil attached to the bar. The current required is proportional to the oxygen concentration in the sample gas.