Can someone tell me how am I supposed to determine the polarity of the sensors? + and - are printed on the board but the sensors have no markings except T and CTD on them.
‘T’ is the transmitter.
The ‘+’ has w small plastic circle around its pin.
Great it works!
But tell me why wasn’t the polarity of the sensors explained in the manual in the first place? 
Polarity wasn’t indicated in the manual I got nor is it indicated in the online manual.
You are right, maybe we should indicate it in the manual, for people with less experience.