| 摘要 |
<p>PROBLEM TO BE SOLVED: To detect a terrestrial magnetism level always precisely by a method wherein a magnetic-sensor output from a magnetic sensor arranged near the running road of a vehicle is observed at a prescribed sampling cycle and a terrestrial magnetism level corresponding to a histogram creation section in which the number of appearances of its observed value is most is used as a recent terrestrial magnetism level. SOLUTION: A magnetic-sensor output from a magnetic sensor 1 to the noninverting input of a comparator 2 is given to a CPU 5 via an A/D converter 4. In addition, a threshold value which is output by the CPU 5 is given to the - output of a CPU 2 as a reference V3 via a D/A converter 6. The CPU observes the magnetic-sensor output at a prescribed sampling cycle, an observed value is stored in a RAM during the predetermined histogram creation time, and a histogram is created. Then, a terrestrial magnetism level corresponding to a histogram creation section in which the number of appearances of the observed value is most is found, a margin is added, and a threshold value is created.</p> |
