CPU Working temperature success ! (updated)

UPDATE

The original subject line for this post was CPU Working temperature test fails too early and I just changed it to reflect last findings. What we have found is that the board was not receiving enough power when it was heated. Tested in room temperature, all went well, but once heating it up to around 50 °C, the current demand exceeded the power supply capabilities. Once replaced with stronger power supply , the CPU is reaching 80 °C without any problems.

ORIGINAL

As part of preparations to use a new product in the outdoors we have been running several tests to verify the max working temperature of the MKR 1400 GSM and found that it dies sooner than expected. I would like to share the test method and get your feedback on what may be causing the problem.

There are two Arduino boards participating in the test, one inside an heating oven (the tested MKR 1400) and the other one (MKR 1010 WIFI with ETH shield) near the oven, with a DHT 22 temperature sensor attached to it.

The temperature sensor sits on top of ABS box containing the tested MKR 1400. The test runs at 1 minute intervals. The oven is started and set for maximum 60 °C, the outside board measures ambient temperature and the tested MKR 1400 measures its own CPU temperature using TemperatureZero library.

As can be seen in the graph, once the ambient temperature reaches 47 °C the CPU reaches 54 °C and dies. The MKR 1400 will return to life only after power recycle.

Any comments are welcome, we want to find out if there is a problem with the test, or is it a protection mechanism shutting down the processor, or is it the limitation of the product.

Thanks for your help.