Method for monitoring a process system having a field bus in the process automation technology

A system for monitoring a process in a process plant, comprising:

• a process control unit;
• a plurality of field devices;
• a fieldbus of process automation technology via which said plurality of field devices exchange with said process control unit telegrams in regular data traffic for process control;
• and
• a monitoring unit, which is connected to the fieldbus and separate from said process control unit, wherein:
• a monitoring application is provided which is stored in said monitoring unit;
• said monitoring application is configured to tap said telegrams of regular data traffic,
• said monitoring application further is configured to test said regular data telegrams for data relevant for the monitoring application, in order to obtain the data relevant for monitoring the process plant by the monitoring application;
• said monitoring application is configured to process the data relevant for the monitoring application as actual-values in a process modeling application;
• and
• said process modeling application is configured to generate an error signal when a process in the process plant is not running properly by determining a deviation between desired-values and actual-values by comparing the desired-values and the actual-values.