The thermometer systems which provide for self-testing even when installed in an industrial process are based on either the resistance thermometer or the thermocouple principle.

These “in-process-verifiable” thermometers offer the user the opportunity to make extremely accurate additional measurements in the course of a process to monitor measurement accuracy. The sensors are equipped with a tiny opening into which a “monitoring” sensor can be inserted.

This is a great benefit especially for the monitoring of processes in the food and beverage industries as well as in pharmaceutical and chemical industries.