| 摘要 |
PURPOSE:To eliminate the need to vary the frequency of a checking signal by comparing the output of a filter circuit when a rectangular wave signal of constant frequency is applied as a checking signal to the filter circuit with a predetermined reference value. CONSTITUTION:The rectangular wave signal of specific frequency is applied to the filter circuit 1. While the amplitude of this rectangular wave signal is considered to be 1 and the period is denoted as T=1/F0, the signal is developed into an equation in a figure. When the filter circuit 1 is checked, changeover switches 5 and 10 are so set that the output of a rectangular wave oscillation circuit 21 reaches a comparing circuit 13 through the filter circuit 1 and is compared with the reference value. Consequently, if the filter circuit 1 is normal, the output of a converting circuit 8 becomes 2/pi. If, however, the basic frequency of the filter circuit 1 deviates or if the fundamental frequency decreases in gain, the output becomes >=2/pi because of harmonic components. For the purpose, the output of the converting circuit 8 is compared with the reference value to decide the abnormality of the filter circuit 11 and the need to vary the frequency of the checking signal is eliminated.
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