Moving vs
Fixed heads
|
Scienta scanning heads installation |
Fixed heads (1-3 heads) installation |
| Start-up |
After the web has stabilized it will take about 30..45 s before a full profile is produced. |
Immediate single spot measurement values available. |
| Accuracy |
The profile is always consistent. Hourly cleaning and standardization improve the measurement accuracy. Calibration is checked hourly with integrated sample. |
Problematic because of dust build-up will affect measurement accuracy. Furthermore, 3 heads may be differently calibrated, which also influences measurement accuracy. |
| Measurement reliability |
Measures points across the web continuously therefore producing a reliable overall coverage of the web.
Systematic problem areas (e.g. faults in production line) will not go unnoticed. |
Measures continuously only three points on the web. Any problem elsewhere on the web will go unnoticed. This is particularly risky if there is a systematic problem outside the measured points. |
| Source half life compensation |
Every hour automatically. |
Must be done between the runs and the paper web must be broken. Cannot be automated. |
| Service |
Easy. Heads go all the way off web. Changing of parts such as protective foils is easy. |
Must be done while the line is down. Continuous dust build-up may increase frequency of service. |
| Safety |
Heads are off-web while threading. |
Heads must be cleared somehow for the threading bar. |
| Splicing |
Heads are off-web while splicing. |
Heads may get dirty when web tension varies. |
| Cost |
1 head and a scanner is cheaper than 3 heads. |
