QUESTION: On what materials would I use the SITRANS LR 400 with purging unit?

ANSWER: The purging system is really dependant on the environmental or process conditions, rather than the specific material. Regions with very high humidity will need more purging systems than climatically dry regions. Essentially any powder that has high moisture content has the potential to stick and build up over time. A slight build-up of dry powder (like in the cement industry) is transparent to the microwave signal and purging isn't necessary. For example, a flour vessel that is traditionally prone to product build-up inside and rat-holing because of the humid climate might need the purging system.