Autoclave - PQ - Sensors Jump in Temp in Immediate Next Run

Hello All,

I would appreciate any input from knowledgeable people out there on this forum for the following behavior noticed in the Thermocouples (TCs).

This is a liquids cycle - minimum load run in the autoclave PQ. In the 3rd and final run, the distribution and penetration TCs jumped about 2C in their temps after 6 minutes into the sterilization phase. The penetration TCs were within the setpoint + over temp limit temp band for the unit. The distribution TCs were above that max limit by 2C on average.For the rest of the sterilization phase they all remained at this elevated temp.

This was not seen in the first 2 runs. The TCs were all cooled down to room temp in between the runs - by replacing the liquid with fresh room temp water.

What could factors/reasons could have caused this jump in the TCs temp?

Thanks in advance.

Did you notice if the chamber pressure increased also?

The first thing that I think of is a superheated steam condition. Do the TC’s remain in place?

I verified the pressure readings for these 3 runs. There was no increase in the pressure for the 3rd run.
The TCs remained in place. We had a temperature and pressure wireless data logger in the geometric center of the autoclave. The SST (Saturated Steam Tables) temp reading for the pressures recorded by this wireless logger were very close to the temperatures recorded for the same logger. In other words, super heating was not seen.

Any new thoughts!

Now I’m confused. You say there was no increase in pressure for the 3rd run. You also say that the pressure/temp relationship is consistent with saturated steam.
If you could post the actual temps and pressures during the exposure phase it may help to figure this one out.


Just a few ideas:

  1. probe placement - did the probes move/touch a cart/chamber
  2. probe calibration - post cal would confirm (you didn’t drop any by chance?)
  3. a stuck steam valve/trim valve - check your maintenance records for historical issues
  4. check the solenoid valve going to your steam valve/trim valve/jacket - did you have something going on there
  5. radio interference? I’m doubtful but I’ve heard this happens sometimes

Basically, if all of your probes showed elevated temperatures then the problem must be your autoclave; it’s either too much steam in the chamber or the jacket is getting too hot. I’d confirm with the load and drain probes.

Oh, and you might want to simply go through your cycle parameters again to make sure they didn’t get changed or something. (Probably not, just saying.)

You should post data tables and load patterns - we nerds love that stuff. :slight_smile:

Good luck, I hope you find the problem.

You describe the temperature change as a jump. I assume this means that the temperatures changed abruptly within a very short period of time (1 second/few seconds). Also you state that the jump happened to both distribution and penetration TCs. Based on this, it would be possible that the irregularity is caused by the measurement equipment, rather than the autoclave. The reason is distribution TCs would respond differently to an actual temperature change than penetration TCs.

When using thermocouples I assume that a pre calibration and adjustment has been performed. Was this calibration performed using software? If yes, does the software allow extrapolation of the adjustment when the temperatures exceed the limits of the calibration range? My point is a jump in temperature can be seen when the TCs reach the limit of the calibration range. The reason is the adjustment may apply within the calibration range only. So if the TCs are outside the calibration range and the software does not allow extrapolation, the adjustment will not be in effect.

I hope this is useful.


I think balance is a problem of pressure and temperature. Assuming the absence of air within the autoclave chamber that would unbalance the pressure and temperature. Without air, yet properly calibrated and balancing using a PID control with good management of leaks in terms of heat losses by dissipation of all this camera can be solved.


Dear Kindly check the same for drain line this might be happened due to problem in drain line on exhaust valve which operates during sterilization phase in order to remove non consensable gases

Tell me please should i re-do test if some of my (1 or 2) TC jumped for 2C.
For example i have 12 sensors, 11 goes in difference with 1 degrees(121,2-122,5), but 1 goes with temp. 123,7
In criteria wrote that all of them should be put in 2C

sorry for bad english