Combine plots - the toolbar button

Sometimes there is a need to calculate transient curves as linear combination of two measured ones. E.g. in case of cold-plate measurements when the temperature swing of the cold-plate is measured back with a thermocouple, the real junction temperature is obtained by subtracting the cold-plate temperature from the measured junction temperature curve.

The aim of this option is to support such manipulations. It is available through the toolbar button or via the Combine Plots item of the Manipulate menu. The option is available for projects having exactly the same time scale, for the smoothed views (.rec files). Linear combinations of the following type can be created:

C_A x Op _A ± C_B x Op

where C's are constant coefficients and Op's are operand expressions. The following items can be used as operands:

• thermal transients of two (virtual) measuring channels,
• thermal transient of a (virtual) measuring channel and a constant,
• any of the above items and a previously created linear combination.

The Combine channels window (that pops up when the Combine Plots function is invoked) can be used to define such a linear combination. Operands and the plus or minus operator can be chosen from pull-down menus - see Figure 4-41. Figure 4-42 shows the result of linear combination of two channels of a two channel measurement. The legend key of the resulting plot is the expression of the linear combination itself.

Figure 4-41: Linear combination of measurement results from different T3Ster measurements

Figure 4-42: The resulting combined transient (pasted through the Windows clipboard)

Figure 4‑42 actually compares the measurement of the same device in two slightly different fixtures. The constant coefficients can be used to fit curves without one by one calibration.

Note that in the present version of T3Ster-Master the linear combination of plots cannot be fed into the evaluation engine for further processing.

Shifting the curves is an ideal tool for displaying curves scaled in absolute temperature.

The Smoothed response curves show temperature differences, so they normally end at 0 ^oC at their cool end. Adding a constant corresponding to the temperature of the environment at measurement time we automatically get absolute temperature curves (Figure 4‑43, Figure 4‑44).

Figure 4-43: Shifting a curve by a constant

Figure 4-44:  Cooling curve, relative and shifted by the ambient temperature