1. There is a thermometer in the instrument screen.
2. There is a thermometer in the instrument shelter.
3. There is a thermometer in the shelter.
-------------------------
Which expression is gramamtical?
I've never heard the terminology "instrument shelter" or "instrument screen." It might be better to say one of the following:
There is a thermometer in the instrument case.
There is a thermometer among the instruments.
The grammatically correct expression is:
1. There is a thermometer in the instrument screen.