How does your autoclave control different phases of the process? e.g. heating phase to exposure/sterilization phase?
Most autoclaves have a sterilization temperature range or band, where the control system (CS) of the autoclave controls the temperature of the load during the sterilization phase. For example: an autoclave that sterilizes at 121°C, might have a sterilization temperature range of 120.0 to 123.0. This way, once the autoclave reaches 120.0, hardly ever will go down in the next few minutes, because the CS will increase the temperature until it reaches 121.0, varying between 120 to 123; in this example, the equilibration time is calculated using 120.0 as the end point temperature, or start of the sterilization phase.
Is this scenario similar to yours? Does your autoclave use saturated steam or superheated water?
On a side note: the equilibration time is the time it takes the load to reach the sterilization temperature, once the autolave had reached it; since the chamber gets heated faster than the load.