Dear all,
Unfortunately we have not been able successfully gain level control under dynamic circumstances.
Yesterday, the team and I concluded that we could not operate the SCM pasteurizer under vacuum conditions as we could not measure the volume in the deaerator. The root cause is an obstruction in the capillary tube of the “dry” side in the dearator (vacuum). Due to this, the vacuum correction did not take place for the measurement.
The team and I tried to overcome this problem, by measuring the pressure at the wet side (in the discharge line) and the dry side (vacuum line), and correcting the wet measurement with the dry measurement. The principle of this idea is the same as the that of the differential pressure transmitter, but instead of having a single readout, we had two and correct them in the PLC to provide the level feedback. Initial result where positive, we could realize a stable state in both vacuum environment as well as atmospheric. Unfortunately, the frequency with which this happened was way too slow, most likely as a result of the output frequency of the PT’s (1hz). This caused the system to get unstable under dynamic circumstances, of which temperature is our biggest issue.