System for coating a surface of an object with a spray coating tool spraying atomised coating particles, for example paint, comprising a coating material supply in communication with the coating tool, comprising a coating material pump setting a coating material flow rate, a conditioning hood defining a spray chamber and having - a coating tool mounting end, - an output end opposite the coating tool mounting end, which output end is adapted to be positioned in proximity of the surface of the object to be coated, wherein in operation: - the spray coating tool is mounted at the coating tool mounting end, and - the output end is positioned in proximity of the surface of the object to be coated, and - the spray coating tool is operated to spray atomised coating particles which travel from the coating tool, through the spray chamber and the output end to the surface of the object, a carrier gas installation in communication with the coating tool mounting end of the conditioning hood or with the coating tool, adapted to provide a carrier gas that in operation carries the atomised coating particles, characterized in that the system further comprises: a particle sensor (23; 36) provided in the conditioning hood, e.g. in the spray chamber, detecting the particle size distribution and/ or the particle density, a central control system communicatively connected to the particle sensor (23, 36) and to the coating material supply and/ or the carrier gas installation, for controlling the coating process based on input data from the particle sensor, such as the coating material flow rate. a conditioning hood defining a spray chamber and having - a coating tool mounting end, - an output end opposite the coating tool mounting end, which output end is adapted to be positioned in proximity of the surface of the object to be coated, - a coating tool mounting end, - an output end opposite the coating tool mounting end, which output end is adapted to be positioned in proximity of the surface of the object to be coated, wherein in operation: - the spray coating tool is mounted at the coating tool mounting end, and - the output end is positioned in proximity of the surface of the object to be coated, and - the spray coating tool is operated to spray atomised coating particles which travel from the coating tool, through the spray chamber and the output end to the surface of the object, - the spray coating tool is mounted at the coating tool mounting end, and - the output end is positioned in proximity of the surface of the object to be coated, and - the spray coating tool is operated to spray atomised coating particles which travel from the coating tool, through the spray chamber and the output end to the surface of the object, a carrier gas installation in communication with the coating tool mounting end of the conditioning hood or with the coating tool, adapted to provide a carrier gas that in operation carries the atomised coating particles, characterized in that the system further comprises: a particle sensor (23; 36) provided in the conditioning hood, e.g. in the spray chamber, detecting the particle size distribution and/ or the particle density, a central control system communicatively connected to the particle sensor (23, 36) and to the coating material supply and/ or the carrier gas installation, for controlling the coating process based on input data from the particle sensor, such as the coating material flow rate. a particle sensor (23; 36) provided in the conditioning hood, e.g. in the spray chamber, detecting the particle size distribution and/ or the particle density, a central control system communicatively connected to the particle sensor (23, 36) and to the coating material supply and/ or the carrier gas installation, for controlling the coating process based on input data from the particle sensor, such as the coating material flow rate.