P&ID Symbols for Level Measurement

Please provide details regarding the standard P&ID symbols followed for float type level indicator, magnetic level indicator, level switches as the same are not covered in ISA 5.1
I think there's enough guidance in ISA 5.1 to cover all these situations. Firstly, P&IDs don't have to include details of the particular technology used to perform the task - general LI, LIT, LSL, LSH etc. symbols can be used.

However, if you wish to be more specific, the examples in Section 6 should give you enough to go on. Possible examples include 6.6 #1 float-actuated LCV and 6.8 Level examples, in particular combinations of # 4, 9, and 12. Use your imagination and/or annotate your diagram. As long as the intent is clear to the reader.