Duty Cycle for a Surface Heat Source

I am trying to plot the Duty Cycle for a Goal Dependent Surface Heat Source. I would like to know when it is on and when it is off. In this way, I could eventually calculate the total amount of work for that Heat Source. I cannot figure out the best way to do this. The surface that I am using as my goal criteria is on the top of a heatsink, while the heat source is on the other side of the heatsink.

I have tried setting a MIN Temp goal on the heat source surface, then plotting that. Whenever that temperature is decreasing, I assume that the source is toggled to OFF. Whenever that temperature is increasing, I assume that the source is toggled to ON. But it seems like there should be an easier way to do this.

The ideal solution would be an output that simply told me the amount of work for each heat source (Power * time), but I don't see this anywhere.

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