Qualification of vacuum oven

Hello All,

For temperature mapping a vacuum oven for drying can anyone advise on the best practice for placing thermocouples:

The vacuum oven will be used to dry reference standards and raw materials/powders at a given temperature to determine the loss on drying.

The oven will first contain glass stoppered weighing bottles (=drying vessels) under the test conditions for about 30 minutes, to dry them.

The second step for the vacuum oven contains the weighing bottles filled with the reference standard or raw material, to start the drying process of the sample.

For temperature mapping the oven would you attach thermocouples conductively to the shelves of aluminium (good conductor), knowing that the sample is located in a drying vessel of glass (bad conductor) or would you attach the thermocouples conductively to the bottom of the drying vessels instead to the shelves.

If anyone has experience or suggestions, I would appreciate your feedback