SEISMIC SENSOR

PROBLEM TO BE SOLVED: To obtain a unit for detecting vibration or impact due to earthquake or the like by making a decision whether the vibration level is higher than a set seismic level or not based on the detection output from a vibration sensor and producing a corresponding output or interrupting power supply to a load. SOLUTION: A microcomputer 26 converts variation in the frequency of a vibration sensor 25 into the variation of vibration and analyzes the vibration pattern. When the vibration has the vibration pattern of earthquake, the vibration level is determined and a corresponding seismic level is calculated. A decision is then made whether the seismic level thus calculated is higher than a seismic level set by a set switch 15 and when the former is higher, a corresponding relay output is fed to an output relay 27. The relay 27 has output terminals 7-9 connected with machines for which power supply must be interrupted on the occurrence of earthquake or a generator or alarm to be actuated on the occurrence of earthquake. On the occurrence of earthquake having seismic level higher than a set level, these machines are interrupted or actuated surely.