B-Clock System for the KEK Main Ring

For the monitor of magnetic field of the dipole magnets of the KEK main ring, the "B-clock" system was constructed. This system is useful to control the R.F. acceleration system. As the sensors of magnetic field, we use a Hall probe and a stationary search coil. The measurement is done in the power house for the main magnets, and data are transmitted to the central control room and the auxiliary equipment houses. At present the accuracy of this system is about 10-3. We plan more accurate system of 10-4 accuracy with the aid of N.M.R. magnetometer.