The output of the Watlow Firerods is being controlled by a common AC rheostat. The stock rheostat and its axle have been replaced with a multi-turn precision rheostat for accuracy, driven by a DC motor with a modified speed control circuit which is controlled by our CompuLAB interface and custom software. In layman terms, we only have to enter our desired input power in our software and it automatically adjusts the power of the Firerods to match it throughout our testing.
We installed our single phase Lutron DW-6091 power analyzer between our AC power source and our thermal load. The power analyzer allows us to take readings of the input apparent power, real power, input voltage and frequency and of the power factor of the power supply, all of which are transferred directly to our software via its RS232 interface. The Lutron DW-6091 is a Class G 1.5 measuring instrument, meaning that all results are 1.5% accurate or better. During our thermal tests only the input real power is of concern to us, which is exactly the same amount of electric power transformed to heat inside our copper core.
Lutron DW-6091 Power Analyzer