I discovered the following was posted by me on the wrong section of the Forum.
I have two 750 hot water elements to heat the settled WVO before it drops into the SimpleCentrifuge bowl. The hot water thermostat is set at 150F. I like to know when the elements are keeping up with the VO flow rate of 1/2 gal/ min. I installed a blue light bulb that is wired to the thermostat. When the temp drops below the 150F, the elements are energized and the light is turned ON. When the 150F temp is reached, the light goes OFF.