Abstract: Apparatus for electrostatic spray painting having a painting chamber to which is connected a spray gun fed by a paint powder delivery system. A powder supply provides a high potential across the painting chamber and the spray gun to develop an electrostatic field to pull the paint powder ejected by the spray gun toward a workpiece positioned within the paint chamber. A humidity sensor is located in proximity with the paint powder delivery system for detection of an amount of moisture. A humidity signal is produced in response to the sensed humidity. A remote computer may be connected to receive a plurality of process condition signals including the humidity signal and to provide a display indicative thereof.