| 摘要 |
A height sensor comprises a pair of light-emitting elements disposed at positions spaced at different distances from a surface desired to be measured, the elements alternately emitting light rays, and a light-receiving element for receiving a light ray generated from each light-emitting element and reflected by the measured surface, the element producing a signal corresponding to the quantity of light received. The signal outputted from the light-receiving element is logarithmically converted by a logarithmic converter circuit. The output thereof thus has its direct current components removed by a filter. The value, covering from one peak to another peak, of the remaining alternating current components is equal to the value obtained by subtracting a logarithmically converted value of the signal outputted from the light-receiving element when causing one light-emitting element to give forth a light ray, from a logarithmically converted value of the signal outputted from the light-receiving element when causing the other light-emitting element to give forth a light ray. By rectifying this filter output, it is possible to detect the height up to the measured surface without being influenced by dirt on the measured surface upon the output of the light-receiving element.
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