Hi Bob,
thank you very much for the fast response.
I already have downloaded this document . It looks like that you are right and there is difference between the case, pcb and ambient temperature.
When I measure the PCB temperature close around the ADS1118 it is always lower then the temp on the case.
PCB temp: 33.0-33.4
ADS1118 Case temp: 34.3C
Internal temp sensor : 36.3125 C
I any case the ADS1118 is the most warmed up place on this part of the pcb ?!?
I am using the MSOP 10 Package.
In past projects I have used the LTC2480 from Linear , but the sampling rate is to low so I decided to use the ADS1118 which is very easy to implement. But with the temp sensor of the LTC2480 very accurate internal measurements are possible with minimal deviations compared to the "outside" temperature.
It looks like we will have to redesign our pcb with more GND copper around.
Will sent you pcb pictures soon.
Best regards
Kresimir