MAT SENSOR

摘要

A mat sensor having high reliability, the failure of which is detectable even if it is temporary. In the first invention, two sensor portions (21, 22) are disposed as shown in the figure, and the states (ON/OFF) of the outputs of both sensor portions (21, 22) are detected. A signal indicative of normal condition is generated when the output states of the sensor portions (21, 22) are coincident. Under this condition a mechanical movement is permitted to operate if both sensor portions (21, 22) are OFF. In the second invention, an object is detected from a change in the capacitance value of a sensor portion. Even though only one sensor portion is used, a mechanical movement can be stopped by detecting even a temporary contact failure resulting from degradation of the sensor portion.