Reported temperature of Zwave+ D/W sensor fluctuates with pattern

[theoverriet 4]

Hi,

I've got a Fibaro D/W sensor (new Zwave+ version) to which I attached an external temperature sensor (the DS18B20: 

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It does measure the temperature rather well, but what's strange is that it fluctuates with a pattern. Attached images show what I mean. I heated the environment of which I measure the temperature. The temperature is gradually rising, but as you clearly see almost every 30 minutes or so (sometimes longer, sometimes shorter) the sensor gives me a temperature that's lower than expected. And what's strange about it is that this reported lower temperature is exactly the same for some hours and than suddenly rises to a new level that keeps constant for some hours.

 

Does anyone has any idea how to solve this?

 

regards,

Theo

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