Fluid Properties · DWG LS-025

Oil analysis normalizer & wear rate calculator

Correct lab ppm for makeup oil (top-offs) and unequal sample intervals. Output is a true generation rate (ppm per 100 / 1,000 hours), an undiluted equivalent, and a next-sample interval from criticality and last severity.

LubeSuite methodLast reviewed

Source: Falk manual 138-050 · Machinery Lubrication: Setting time-dependent limits

The makeup-oil correction is a mass balance that assumes constant wear between samples. Sample-interval multipliers are rules of thumb; the gearbox oil-change interval is from the Falk manual.

Machine & samples
Use the running volume, not the drum size. Needed for top-off dilution.
Top-offs between samples

Each makeup event dilutes wear metals (and most contaminants). Hours are meter hours at the top-off, same scale as the samples. Makeup ppm is 0 for new/clean oil. If makeup is used oil, enter its last known ppm per element (same value applied to all wear metals unless you edit per-row later — default 0).

Model: constant sump volume. Oil is consumed/leaked then replaced — remaining oil mixes with makeup. Wear is assumed constant between the two samples.
Lab results (ppm unless noted)
Property Kind Previous Current Makeup ppm
Leave a cell blank to skip that property. Makeup ppm defaults to 0 (clean oil). Additives usually fall; wear usually rises.
Next sample interval
How the numbers are built

Wear (and most contaminants) are treated as a constant generation rate G in concentration units per operating hour. Top-offs are discrete mixing events at constant sump volume V.

  • Between events: C ← C + G · Δh
  • At a top-off of volume v with makeup concentration Cm:
    f = min(1, v / V)
    C ← C · (1 − f) + Cm · f
  • Solve the affine relation Cmeasured = a + b · G for G.
  • Undiluted equivalent (what you would have seen with no makeup): Cprev + G · ΔH.
  • Reported rate = G × N hours (100 / 250 / 500 / 1,000).

If miles are entered on both samples, a second rate in units per 1,000 miles (or km — same unit you typed) is shown. It is independent of the hour-based top-off clock; top-offs still use hours.

Sample frequency starts from typical industrial OA programs (engine ~250–500 h, gearbox ~500–2,000 h, hydraulic ~500–3,000 h, turbine monthly–quarterly) then multiplies for criticality, environment, last severity, oil type, and makeup rate. High makeup is not a reason to stretch an abnormal machine.

This is a plant-floor mass balance, not a lab LIMS. It does not replace OEM condemning limits, spectrographic detection limits, or a used-oil analyst. Always match units to the report (ppm vs mg/kg are equivalent for this purpose).