No concrete calculations are performed for RUTX09 under your described conditions. However, as a reference, you could check data for TRB142 device here.
In general, if the temperature/load increases, then the MTBF will be shorter/worse.
Calculating MTBF is already time-consuming task. Adding different conditions introduces much more calculations. The added modes usually introduce mistakes in the calculations that are already sometimes "calculated" guesses (in regards to some components). Thus, if you have a requirement for specific values, you would need to contact your local Teltonika sales representative for further discussion.
As for calculating MTBF, Metrology laboratory refers to IEC 61709 standard and has provided the following workflow:
- Checking every passive component's datasheet, to find out temperature ratings.
- Use temperature rating to calculate other variables, which can be used to check the IEC 61709 standards table values, which are then used to calculate the failure rate of the component.
- Evaluating every IC'S technology, and selecting the correct category from the tables provided in the IEC 61709 standard.