Thus, if water leakage is occurred at a place indicated by a reference code P in a buried water piping having main pipes 3 and branch pipes 4, sensors H35, V42, V52 in proximity, which indicate dense hatching, firstly detect the signal and then adjacent sensors H25, H34, V43, V53, which are a little bit thinner hatching, detect the signal. したがって、主管3と分岐管4とを有する埋設水道配管において、参照符号Pで示す箇所で漏水が発生した場合、濃いハッチングを施して示す近接のセンサH35,V42,V52が先ず検知し、次に少し薄いハッチングの隣接のセンサH25,H34,V43,V53が検知する・・・。 - 特許庁