Thanks for the reply. I am happy to hear that other people also have observed this. Therefore, I usually allow a 5 minutes “stabilization time” after the sterilization holding starts. The remaining holding time I call the qualification/validation holding time (i.e. holding time minus first 5 minutes). If I do not do this, I risk to not pass the following tests according to EN 285 (because of this overshoot):
- all temperatures recorded in the chamber are within a 2.5 °C band around the sterilization temperature set point.
- all temperatures recorded in the chamber by one thermocouple do not fluctuate more than 1.0 °C.
- all temperatures recorded in the chamber do not differ from each other by more than 2.0 °C at the same moment in time.
All other tests are then evaluated in the remaining time (F0 value, saturated steam conditions, minimal temperature etc…), except for the equilibration time (otherwise that would be cheating and easy to achieve :)) and the bioindicator challenge test of course, because we cannot avoid these to be exposed these first 5 minutes.
The equilibration time for the load probes is usually 0-5 seconds (my chamber is 715 liters), so they comply with 15 seconds or less.
As far as I know, the equilibration time is only applicable to test the load probes (compared to the coldspot/slowest to heat point in the chamber: usually drain). Anyways, if I were to include the chamber probes, they would all comply (since they are “hotter” spots/faster to heat compared to the equilibration time reference (drain)).
I am still trying to find out the following:
The emptier the chamber, the larger this overshoot is (a fully loaded chamber does not show an overshoot at all). I would expect that if the PID control was not well regulated, the pressure in the chamber would show a similar overshoot, which it doesn’t… (it is “straight” over the whole holding time). This means that the steam at the top of the chamber is briefly superheated for some reason?