The Sonimix 2130 NOx converter tester has been designed to generate a stable NO₂ concentration with a small reaction time. It is based on the sonic nozzles technology (ISO 6145-6 technology) and high stability pressure regulators. The NOx converter tester is often used together with a multi-steps gas divider also based on sonic nozzles and high precision pressure regulators. In order to validate NOx measurements, the efficiency of the NO₂ converter must be higher than 90 %, it is therefore very important to check easily and precisely the efficiency of the NO₂ converter. The SONIMIX 2130 converter tester is based on the process known under the name of Gaseous Phase Titration.