As companies transition from calendar-based battery maintenance to real time battery monitoring or to a new portable monitor vendor, the challenge is to reconcile the historical data with the new solution, this is particularly true for the cell/unit ohmic data.
The measurement of the ohmic value can be made using either AC or DC signal as the perturbation method and depending on the method used the value. will be reported as a Impedance, Resistance, or Conductance If the new monitoring equipment uses a different perturbation method from the old, that can be a challenge as the values reported for the same cell or unit will be different between the new and historic data. Even when the methodology used is the same, if the level and frequency of the perturbation signal is not identical the value reported will be different.
Because the differing values make it difficult to evaluate the batteries condition on an ongoing basis, a typical request from the user is to ask the new equipment vendor to provide a correction factor to bring the new readings closer to the values that had been collected in the past. This may seem to be a logical solution, but there are too many variables including the operating environment to ensure an accurate conversion for every reading. There is however a better way.