SCM5B33, True RMS Input Analog Modular Signal Conditioner

This module provides a conversion of Alternating Current (AC) signals into a Direct Current (DC) Voltages that represent the True Root Mean Square (RMS) value of the signal.

This is used on various Sensor outputs, including Linear Variable Differential Transformers (LVDT) or Rotary Variable Differential Transformers (RVDT) . The Va and Vb outputs from the LVDT or RVDT can be measured and used to compute the position, to a high degree of precision.

The LVDT or RVDT needs to have a stable AC excitation, that is typically 3 to 7 Vac, at a frequency of 2500 Hz to 5000Hz.

The LVDT / RVDT position can be calculated real time using the following formula;

Position = m (Va - Vb) / (Va + Vb) + b

Whereby
"m" is the Engineering Units scale or conversion factor
"Va" is the output voltage of one of the secondary coils and "V"b is the output voltage of other secondary coil.
"b" is the offset of the resultant measured when the LVDT or RVDT is in middle position of it's stroke, also referred to the null or zero position. 

An illustration of "How an LVDT / RVDT works". https://www.rdpe.com/ex/hiw-lvdt.htm