1. A method of controlling a sensor system that includes, along a line, a plurality of sensors to acquire a physical quantity in detection ranges according to existence of a workpiece moving on the line, that determines whether there is the workpiece in the detection ranges based on a sensor-specific sensing level that is the physical quantity multiplied by a sensor-specific gain parameter, and in which the sensors are provided such that, when the workpiece is present in any of the detection ranges, there is no workpiece on the line excluding all the detection ranges, the method comprising: for each sensor from among the plurality of sensors, monitoring the sensing level and selectively adjusting the corresponding sensor-specific gain parameter in such a manner that the sensor-specific sensing level is equalized among the plurality of sensors in a case where it is determined that there is no workpiece in any of the detection ranges, and in such a manner that when the workpiece is in any of the detection ranges, the corresponding sensor-specific gain parameter is not adjusted.