| 摘要 |
A system for electrostatic deposition of a coating on an article from a charging device includes a direct current high voltage supply having first and second terminals across which the high voltage is impressed The article to De coated is held at a potential substantially equal to the potential on one of the high volt go terminals. The article is suspended for relatively free movement toward and away from the device The system includes a high-speed switch coupled between the high voltage terminals and a control circuit for controlling the switch A sensing resistor in the high voltage output circuit monitors the current between the high voltage terminals The control circuit includes a slope-detecting or fixed difference circuit responsive to the sensed current to detect toorapid changes therein, such changes being indicative of close proximity of the article to the charging device and the possibility of high voltage arcing therebetween The fixed difference circuit compares a sampled signal, related to the sensed current by a fixed difference, with a signal related to the instantaneous value of the sensed current to predict a condition conducive to high voltage arcing The control circuit additionally includes an automatic ranging circuit for comparing a sampled signal related to the actual current through the sensing resistor with a signal related to a predetermined multiple of the instantaneous current through the sensing resistor. |
