An apparatus includes a first analog-to-digital converter configured to measure a first reference voltage and a third reference voltage. The apparatus also includes a second analog-to-digital converter configured to measure a second reference voltage and a fourth reference voltage. The apparatus also includes a controller configured to calculate a first resistance ratio, and determine a positive high voltage associated with the positive high voltage direct current input signal based, at least in part, on the first resistance ratio. The controller is further configured to calculate a second resistance ratio, and determine a negative high voltage associated with the negative high voltage direct current input signal based, at least in part, on the second resistance ratio.