Autoclave Drain issue during Temperature Mapping

Hi All,

We are doing a loaded chamber temperature mapping of both a dry and liquid cycle. As part of the validation, we need to put a T/C near the controlling probe, which is located in the chamber drain. It was a requirement that the temperature difference between the T/C (let’s call this the drain T/C) and the controlling probe to be within 1 degC . Inspection of the probe showed that it is located at about 60 cm down the chamber drain.

Several runs were performed with the drain T/C in the opening of the drain inside the chamber. Most of the runs failed as the drain T/C was reading temperatures higher than the controlling probe. After some discussions, it was decided to insert the drain T/C into the chamber. This presented a problem as we don’t know how far the T/C was inserted into the drainpipe (as visual confirmation is definitely impossible), nor do we know if the T/C is touching the pipe (which most probably is), or if it’s anywhere near the controlling probe. Runs had varying results on the drain temperature, maybe due to the reasons given above. With some runs, the drain T/C is still reading higher temperatures (>1.6 deg difference) than the controlling probe. Sometimes, if we pushed too far, the T/C will read temperatures lower (>1 degC) than the controlling probe. As a CAPA, validation suggested that the piping on the mechanical side be retrofitted with a port especially made for the drain T/C with its location adjacent to the controlling probe.

May you please give me some thoughts on our approach to this requirement (taking out the requirement from our quality standards is not an option unfortunately)? Is it really possible that the drain T/C is reading higher temperatures than the controlling probe even if it is inserted into the drainpipe?

Your help is very much appreciated. Thank you.

Best regards,


If the control probe is 60cm from the chamber then it will likely read lower than the chamber temp unless the drain line is perfectly insulated. I agree with the installation of a port near the drain probe.
I assume that the control probe is calibrated, right?
What brand of autoclave is it?

There are many causes of this problem - like if you use TC and the drain control probe is pt100 there are differences in measurement. Second, maybe if you put TC probe too deep the condenser will fall on the TC and TC will measure lower temperature. Third, mayhe vacuum cycle absorb your TC if it is too deep…and maybe your TC touch the side of the drain line…but first, you must be sure that the TC and control probe have the same values in referent bath.

I have seen a similiar problem in our autoclave requalification. Was no able to pinpoint RC but did do the folowing CA resulting in passing results:

clear drain of any debris
place drain TC just above the drain preventing metal to metal contact
did a recalibration of autoclave probes.

hope this helps