The oil moisture calculation model in HMP378F probes is based on average water solubility behavior of transformer oils. The ppmw output is calculated as follows:
ppmw = aw × 10 (A/(T+273.15)+B)
- water activity
- A, B
- coefficients (average or oil specific)
- temperature (°C)
Typically, moisture in transformer oil measurement with HMP378F has a ppm accuracy of ±10 % of the reading. If additional accuracy is needed, see HMP378F calculation model with oil-specific coefficients.