Corona Wire
Definition
A high-voltage wire in the ESDA instrument that deposits electrostatic charge uniformly over the Mylar surface; charge density is higher at points where the Mylar is depressed into indented furrows, producing the latent charge image.
- Instrument
- ESDA (Electrostatic Detection Apparatus)
- Function
- Deposits high-voltage charge on the Mylar film
- Effect at indentations
- Higher charge density over depressed furrows
- Result
- Produces the latent charge image of indented writing
Common questions
Why does the charge concentrate over indented strokes rather than spreading evenly?+
The Mylar sits closer to the document surface at a depression, which changes the local electric field so more charge accumulates there than on the flat surrounding paper, and that difference is what the toner cascade later reveals.
Does the corona wire itself touch the document?+
No. It charges the Mylar film that has been placed over the document, so the process is non-contact and does not add any marks to the original paper.
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