LMN_PER = Manipulated Value Peripheral.
LMN_PER is calculated by the formula: LMN_PER= LMN* 27648/100 and is written to the PQW table in the memory location pointed to by the output tag.
The value of LMN_PER (PQW value) is not affected by any changes to the scaling of the input (PIW).
If your output is either 0% or 100% (27648), it is likely your gain or Ti parameter is too high, especially if it is oscillating between the two values. Set your SP to within 1% of the PV, set your gain, Ti and Td to zero, and set your PID to automatic mode. Slowly raise your gain (0.2 or so) and see what output you get.