| 摘要 |
PURPOSE:To reduce the consumption of a current by providing plural sensors which judges normalcy and abnormality from the flow of the current, a sensor loop current scanning circuit, and plural sensor loop current detecting circuits, and judging abnormality of plural loops by successive switching. CONSTITUTION:Output signal states on output signal lines 22a-22n of the sensor loop current scanning circuit 22 are varied according to a specific timing chart. Then only when logical levels on the output signal lines 22a-22n are 1, the 1st-the 4th sensor loop current detecting circuits 23-26 flow currents to corresponding loops. The currents flows to the respective sensors 31-34 successively for a specific time so that a current flow through only one selected sensor loop momentarily, and thus the currents flow while switched successively, so all the loops are monitored cyclically. Consequently, a long power failure guarantee time is secured even with a small-capacity battery. |
