| 摘要 |
PURPOSE:To prevent a trouble of alarm malfunction from occurring, by checking a shift of a displacement signal from a zero point when an approaching motion is initiated, so that a warning is issued when the shift is excessive but the zero point is compensated when it is not the case. CONSTITUTION:At the timing of initiation of approaching motion with which a displacement signal S3 from a tracer head is started to be actually used, a shift of the displacement signal from a zero point is detected in such a condition that the signal is aerially free. Further, in dependence upon whether or not the sum of the shift amount (d) and an upper limit (l) of detection by a displacement alarm exceeds a maximum value of direct displacement signals which are generated, when it is smaller, the zero point is automatically compensated, but when it is not the case, an alarm signal S2 is delivered to a control panel 6 with no above-mentioned shift amount (d) being stored in a memory. With this arrangement, it is possible to prevent a trouble of displacement alarm malfunction which possibly occurs when the shift amount (d) is taken unconditionally.
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