SYSTEM FOR MEASURING LENGTH OF LOCK BOLT

摘要

PROBLEM TO BE SOLVED: To provide a system capable of accurately measuring the length of a lock bolt even if the lock bolt is fixed in the ground by mortar or tension or compression force is applied to the lock bolt. SOLUTION: The system for measuring the length of the lock bolt consists of an exciting coil having a steel rod 10 as a magnetic core, first and second detection coils 12A and 12B respectively arranged on both sides of the exciting coil, an AC power supply 13 for exciting the exciting coil, a differential circuit 14 receiving the outputs of the first and second detection coils to perform subtraction and a detection circuit 15 receiving the output of the differential circuit to perform detection. Since the induced voltage of the detection coil near to the lock bolt increases when one end of the steel rod is connected to the lock bolt 20 to excite the exciting coil, the length of the lock bolt is measured on the basis of increase quantity.