On-line Thickness Measurement
Choices
We all want the same thing with on-line thickness measurements:
- High accuracy
- Low cost
- Instant feedback
- Cross-web
- Compact
- Integrated into data-logging system
- etc. etc.
Sadly we have to make compromises and in many cases our specific coating can be measured only be methods we might dislike for other reasons.
The table indicates the applicability of the key commercially-available methods to different types of coating. See the individual tabs for explanations of each method along with their strengths and limitations. Finally, see the Cross-web tab to help think through how best to monitor the cross-web uniformity of the coating.
| Factor | Interf. | OD | Near-IR | Beta | Gamma |
| Optically clear | Yes | Yes | Yes | Yes | Yes |
| Optically rough | No | No | Yes | Yes | Yes |
| Opaque | No | No | No | Yes | Yes |
| Chemically similar | OK | OK | No | Yes | Yes |
| Single device | Yes | Yes | Yes | No | No |
| Two devices | No | No | No | Yes | Yes |
| Particulates (Large) | No | No | No | Yes | Yes |
| Particulates (Nano) | Yes | Yes | Yes | Yes | Yes |
| Atom insensitivity | Good | Good | Good | Good | Poor |
