Abstract: In a system for treating articles automatically while the articles are in a stopped treating position, an improved triggering circuit activates the treating device. In one embodiment, multiple cans are simultaneously spray coated by a corresponding number of spray coating guns. An indexing type conveyor with pockets for holding cans moves cans along the same path until a group of pockets holds cans in spraying positions proximate a group of coating guns. When the conveyor has moved a sufficient distance to bring the group of cans to the proper spraying positions, the conveyor is stopped for a predetermined period of dwell time sufficient to complete the spraying operation before the conveyor is again moved. A separate proximity sensor for each spraying position determines the presence or absence of a can in each spraying position independently. Any given spray gun is activated only if the sensor associated with that spraying position has sensed the presence of a can for some predetermined interval of time.