| 摘要 |
The composition of etchant solution withdrawn from an etcher is monitored to diagnose a component deficiency. A light sensor is responsive to the color density of light rays passing through the etchant. A meter relay is responsive to the light sensor and if the color density of the etchant falls outside preset levels a pump is energized causing addition of a constituent component into the etchant. A second light sensor senses the color density of the light rays passing through the etchant after the addition of the constituent component. A second meter relay is responsive to the second light sensor. If no improvement of the etchant color is detected, the second meter relay causes the discontinuance of the constituent component addition and switches to the addition of another constituent component.
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