Windchill Risk and Reliability Desktop Help > Windchill Weibull > Degradation Analysis > Weibull Panes for Degradation Analysis > Weibull Parameters Pane for a Degradation Data Set > Degradation Models
Degradation Models
When performing degradation analysis, in the Weibull Parameters pane or ALT Parameters pane, Model determines the degradation model to use in the analysis. The following table provides equations and result fields for all supported models. In these equations, y represents performance, x represents time, and a, b and c are the model parameters for which to solve.
Model
Equation
Result Field(s)
Exponential
y = beax
a, b
Gompertz
y = abc^x
a, b, c
Linear
y = a + bx
a, b
Logarithmic
y = a ln x + b
a, b
Loyd-Lipow
y = a − (b / x)
a, b
Power
y = bxa
a, b
To solve for parameters, the equation for the model is transformed into its linear format and then uses the least sum of squares method to solve for a and b. The one exception is the Gompertz model. Because it has three parameters, linear regression methods cannot be used. Instead, To solve for its parameters, an iterative process holds c constant while solving for a and b. Using numerical analysis methods, values of c are systematically tested until the parameters converge on the values of the three parameters that yield the least error.