| 摘要 |
PURPOSE:To detect an opposite phase and phase absence stably at low cost by a small-sized constitution while improving the precision of the detection, by turning off an output relay once the opposite phase or open phase state occurs. CONSTITUTION:A voltage detecting circuit 1 for opposite phase and open phase in R-phase is connected in respective phases R, S, and T and detects a voltage dropping below a normal voltage in case of the occurrence of an opposite phase or open phase state; and it is connected to the 1st voltage level deciding circuit 3 while insulated by a photocoupler 2. An S and T open phase voltage detecting circuit 4 is connected to the phases S and T respectively and detects a voltage dropping below the normal voltage in case of open of the phases S and T; and it is connected to the 2nd voltage level detecting circuit 5. A relay driving circuit 6 turns off the output relay 7 when an opposite phase or open phase occurs. Consequently, the precision of the opposite phase and open phase detection is improved, the detection is carried out stably, and a small-sized, inexpensive constitution is realized. |
