At what point pressure compensation must be used for exhaust gas measurements?

The manufacturer of the exhaust gas measurement system ECM recommends pressure compensation if the pressure in the exhaust tract deviates by more than 35kPa from the environment. Starting from a pressure difference, the measurement errors for the lambda and NOx values become larger.

Pressure compensation is mainly used for lambda and NOx measurements, since the measured values are recorded at points in the exhaust system where there is a high back pressure. For this reason, compensation is not necessary for NH3 measurements, since the acquisition takes place after exhaust gas recirculation (low backpressure).