Hi ALL, there is opinion that moisture can penetrate through the tip of type T thermocouple, but to me, the tip looks well sealed with plastic, how possible moisture can penetrate into it? I’m using this type thermocouple in the validation of refrigerator and incubator, and I put the tip into the water in various containers for temperature mapping, and found that the water temperature never reach the chamber air temperature, is this the possible reason?
thanks for explanations!
I have not sen this to be a problem with Type T. i have performed numerous thermal maps with Type T in liquid.
Haveyou looked into the integrity of the equipment? Is the equipment calibrated? I would check the equipment settings before blaming the TCs
The phenomenon of the water ingressing through the Type T thermocouples and ultimately out to the monitoring device does occur. I have seen it occur when validating steam sterilisers, the combination of heat and pressure forces a small amount of water out through the thermocouple sheaths and results in water getting into expensive monitoring devices (not good). This is unlikely to happen when mapping refrigerators or incubators as the pressure and temperature combination are not sufficent to force the water through. For safety of the device we put slits in the thermocouple outer sheath just short of the monitoring device so any water that does ingress out through the thermocouple is drained away.
Hope this helps.
thanks a lot for opinions from you guys, I’ll start the steam sterilization validation soon, the tips of the thermocouple look seamless covered with plastic (PTFE?), is it possible for the steam penetrate into it?
we have other choice to use ValProbe, my question is, if I want to measure the inner temperature of a piece of long tubing, I’ll cut a small hole and insert the flexible wire of the ValProbe into it, sealed with silicone, the main body of the ValProbe stay outside of the tubing, how can I know the main body of the ValProbe will not conduct the outside temperature into the monitor wire inside the tubing?
Typically, we use the Type T thermocouples in autoclaves, we leave a loop in the thermocouples prior to them reaching the mapping equipment. You can also carefully, cut with a razor blade into the exterior sheath to allow the moisture to leak out so to speak. We stopped using the Type Ts with the plastic sheath as they did not always provide the readings that we needed. Now we use Type T SLE premium grade wire and weld our own tips.
[quote=Hanks]Hi ALL, there is opinion that moisture can penetrate through the tip of type T thermocouple, but to me, the tip looks well sealed with plastic, how possible moisture can penetrate into it? I’m using this type thermocouple in the validation of refrigerator and incubator, and I put the tip into the water in various containers for temperature mapping, and found that the water temperature never reach the chamber air temperature, is this the possible reason?
thanks for explanations![/quote]
Does anyone else see the simple answer to this question??? You are expecting the fast response of the TC’s in air to equate to the TC in a thermal mass? The reality is what you are seeing is natural and not a problem. The water is going to be much slower to react to ambient conditions because you are measuring the thermal mass. The open air TC’s have no thermal mass to change and are more succeptable to the rapid changes in air temperature. This has nothing to do with the exposure to water impacting the TC. This is the reason people do their PQ in a solution to simulate what the product will actually see during operation.
Reason that water temperature never reach set air temperature is in ammount of heat your chamber deliver to load. Air is not good heat exchanger and amount of heat chamber trough the air deliver to water container is not enough to heat them. You have two solutions:
Put the control probe of the incubator in the water container same as you want to mapping (it is worse solution). Water can damage maybe probe.
Use water bath and put water container in the water bath (better solution). In this case water is the medium which transfer the heat and you have set temperature in the water bath and in the containers.
P.S In some cases of sterilization under higher pressure as preparation vessels, steam can really penetrate in the thermocouples and make bad results. Same situation can happen in water autoclaves and if you dont cut the thermocouples water can make contact with SIMs.
The below statement was taken directly from the Kaye Validator User’s Manual (
Use of Thermocouples in Moist Heat Environments
When validating moist heat processes, a sealed PTFE tip thermocouple should be used with a drip cut on the outer insulation close to the SIM module to reduce the possibility of drawing moisture into the SIM. To add a drip cut, remove 4 inches (10 cm) of the outer insulation from each thermocouple at a point where natural drainage can take place without water reaching the terminal screws.
Also, GE recommends shaving open about 1/4 inch from each of the red and blue inner wire jackets at opposite ends of the outer insulation drip cut to allow condensate drainage from within the individual wires.
If moisture does collect in the SIM, remove the SIM from the instrument, open, and allow to air dry before storage.
But please note this will only happen when validating a moist heat process (steam sterilisation, etc), if you are validating a refrigerator or incubator you will not see water be drawn through the thermocouples.