Abstract: An infrared dryer is provided for a printing press which uses a series of carriers, each comprising one or more gripper bars, on a conveyor to respectively carry printed sheets past the dryer. The sensor produces different binary signals in response to the presence or absence of material, viz, a gripper bar structure or carried sheets in the path, each carrier producing a predetermined number of transitions between the presence and absence signals, the only change between an empty carrier and one carrying a sheet being the duration of the presence and absence signals. A microprocessor is programmed to cyclically count from zero to the predetermined number of transitions, with each count cycle representing the passage of a carrier. The microprocessor also measures and compares the total durations of the presence and absence signals during each count cycle. If the presence signal duration exceeds the absence signal duration, then the heater is actuated to a preselected operating intensity.