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Onset/Endset Model

The onset/endset point is defined as the intersection of an initial tangent line with a final tangent line. The tangent lines are fitted as follows:

with k=0 to n

Select Onset when determining the intersection of two lines when the inflection occurs after the initial tangent (baseline).

Select Endset when determining the intersection of two lines then the inflection occurs before the final tangent (baseline).

Using This Model

Use the Onset/Endset Point analysis option to determine the point at which a change in the slope of the curve occurs (i.e., the onset point of a transition). See Using the Analysis Settings Options to select associated analysis options before beginning.

When to use Onset vs. Endset

In TRIOS versions up to 2.5.2, the Onset model should be used when the flat asymptote is to the left of the transition region when plotted on temperature:

The Endset model should be used when the flat asymptote is the right of the transition region when plotted on temperature:

The difference between the two becomes important when the transition region is characterized using the inflection option in the analysis settings since the inflection point is determined by identifying the point where the slope attains its maximum value either to the left or right of the region:

If, on the other hand, the tangent or manual tangent setting is used for the transition region, the two models become completely equivalent since you set the inflection point manually and the models are no more than a simple intersection of two given straight lines:

Procedure

Click on the desired Curve to analyze.
Select Onset point from the Analysis > Functions menu based on the transition as described above.
To define the analysis region, select from one of the following options:

Using the mouse, select the analysis region by dragging the mouse along the curve, then proceed to step 4.

Select Set Limits . Markers display on the graph. The number of markers displayed vary based on the analysis options selected.

Using the mouse, position the markers in the desired location as described below, OR

Manually enter the limits through the Limits window within the Analysis > Function > Settings option.

To position the markers:

Tangent options (2 markers): Place first marker where you want the data for the tangent line to begin. Position the second marker where you want the second tangent line to end.
If you are using manual mode to define the tangents, position two markers where you want the start and stop limits for each individual tangent line.
When the transition type is inflection, the analysis routine will locate the inflection between the analysis range so be sure to bracket this region between the two analysis (tangent) markers.

Once the markers are positioned in the desired location, click Start to execute the analysis. Alternatively, you can manually enter the limits through the Analysis window. Select Cancel to cancel from the analysis functions.

Onset/Endset Analysis Options

Onset/Endset Type: Select between the following options:

Tangent: Uses the selected point to calculate a tangent line
Manual tangent: Allows you to define the start and stop limits for the onset tangent line

Transition Type: Select between the following options:

Tangent: Uses the selected point to calculate a tangent line
Manual tangent: Allows you to define the start and stop limits for the inflection tangent line
Inflection: Determines the inflection point between the onset and end limits

To delete the analysis, select the desired analysis then select from the Analysis menu. Use to delete all analyses.

See Also

Adjusting an Analysis Result

Basic Steps to Analyzing Data