How to keep a camera in calibration after a blanket wash
After a blanket wash or a roller wash, gloss and ink film change, and camera brightness follows. The old threshold suddenly alarms on everything or on nothing. Match a signed sample again, confirm brightness is back in the allowed window, then resume inspection. Do not reject on the old template in the first moments af
After a blanket wash or a roller wash, gloss and ink film change, and the brightness in the camera follows. The old threshold suddenly alarms on everything or on nothing. After the wash, match a signed sample again, confirm the brightness is back inside the allowed window, and only then resume inspection. Do not keep rejecting with the old template in the first moments after the wash.
A brightness change is not a defect change
When the ink built up on the blanket is washed off, a solid can jump one step darker or one step lighter, and the camera treats the whole plate as a defect. If the threshold is loosened then, real defects stop alarming once the ink film returns to normal. The order after a wash is: print until a person confirms the colour is back inside the signed range, then see whether the grey of the same solid in the camera is back inside the original window, and only then resume comparison.
If the template must be learned again, use this newly confirmed sample. Do not use the first sheet after the wash, while it is still not stable.
After the wash
| Step | Do | Do not |
|---|---|---|
| Just washed | Match the colour first | Judge the whole roll at once on the old threshold |
| Colour back inside the signed range | See whether the solid grey is back in the window | Loosen the threshold straight away |
| Grey outside the window | Relearn a confirmed sample, or adjust the light | Learn the template from the sheet that is not yet stable |
Check at a job change
- Write down the grey of one solid on the signed sample.
- After the wash and the colour match, read that same solid again.
- Open inspection only when it is back in the window, and write this wash into the record.
