METHOD FOR DETECTING PRESENCE OR ABSENCE OF TRANSPARENT FILM

PURPOSE:To enable presence or absence of a transparent film to be detected accurately by measuring radiation energy of a container at a position for coating a film at a first position and then measuring an addition energy at a second position. CONSTITUTION:A thermo pile 3 is provided at a first position A within a transportation region of a conveyer 1. Further, a thermo pile 4 is provided at a second position B which is adjacent to the position A at a downstream side of the conveyer 1 and at the same time an incandescent bulb 5 for radiation is provided, thus enabling infrared rays to be emitted to a glass bottle 2B. For detecting whether a transparent film is present at a specified part or not, a radiation energy T1 and an addition energy T2 are measured, a reflection energy T3 is calculated from an expression T3=T2-T1, and then it is compared with a reference value of a predetermined reflection energy. A reference value T0 of radiation energy on a threshold straight line 30 of the measured addition energy T2 is calculated and then it is judged that a film is not present in the case of T0-T1>0 according to the previously measured radiation energy T1 and it is judged that a film is present in the case of T0-T1