About ROC and Least Squares Fit

Qualitrol ROC total dissolved combustible gas measurement whitepaper


ROC (Rate of Change) is a measurement of gas generation rate; the rate at which gas-in-oil (ppm) levels change over a specific period of time. At minimum, the last three days of ppm measurements are used to make this calculation. ROC is calculated by fitting a minimum number of ppm measurements to a straight line using a standard least squares fit method. The slope of the calculated straight line is reported as the ROC, in ppm/day.

The calculated ROC can be used to generate a caution or alarm event for each gas and the total dissolved combustible gas (TDCG). TDCG is defined as: H2 + CH4 + C2H6 + C2H4 + C2H2 + CO. Along with ROC a “goodness of fit” indicator is calculated, which represents the scatter associated with the data points relative to their resulting least squares fit line.

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