The Pentol SO3 monitor is based on a wet-chemical process.
The gas sample is measured by means of a heated probe. In the probe head, the sample is cooled down and diluted in a mixture of isopropanol and water. The SO3 condenses and reacts with the sulfuric acid in the liquid phase, eliminating all problems related due to insufficient heating is known from manual measurements.
The sample is then transported to the instrument by the peristaltic pump and reacts with bariumchloranilate, colouring the sample according to the SO3 concentration. The concentration is then measured with a photometer that can be calibrated automatically.
This procedure allows measuring repeatedly and very accurate directly in the plant or in laboratories.