Measuring Coated Glass Using the SpectraProbe S/8
The color of coated glass is closely monitored on glass coating lines. There are two main types of glass lines: continuous glass and piece glass. This measurement method is for piece glass only. Any on-line instrument used for measurement of glass must be capable of differentiating between acceptable and unacceptable product and alerting when an "out-of-tolerance" condition is obtained so that outliers can be segregated and necessary corrections made to the process in real time.
The HunterLab SpectraProbe S/8 can accurately detect differences between acceptable coated glass and product that is off-color and can show side-center-side color differences.
The SpectraProbe S/8 (Top Mount)
The Application
The SpectraProbe S/8 is mounted for measurement over the coated glass (top mount) or below the coated glass (bottom mount) or both. A traversing rail allows the sensor to move over the entire surface of the product. The sensor is typically installed near the operator inspection station, downstream of the vacuum coating process.
| Recommended Color Scale | CIELAB as a full color descriptor |
| Recommended Single-Number Indices | dE* for indication of total color difference from a standard |
| Recommended Illuminant/Observer | D65/10°. |
Measurement Method
1. Configure a product setup for each type or color of coating with the following parameters:
| ... | Page 1, Color Information | |
| Color Scale | L*a*b* | |
| Optional Index | dE* | |
| Data Collection Units | Samples | |
| Data Collection Frequency | Every Sample | |
| Secondary Calibration | Every 60 minutes | |
| Illuminant | D65 | |
| Observer | 10 Degrees | |
| Page 2, Product Standard, Tolerances, and Corrections | ||
| Product Standard | Numeric for existing products, Adhoc for new products | |
| Offset Correction | Enter values only if hitching the SpectraProbe S/8 to a benchtop system (such as the UltraScan XE) on which the product standards have been measured. | |
| Tolerances | Typically 0.5 for each component of the color scale | |
| Page 3 | ||
| CMC Parameters | Not used | |
| Optional Parameters | Not used | |
| Tolerance Alarm Deadband | 5% | |
| Optional Digital Display | Delta Values | |
| Shade Sorting | Off | |
| Cross Test | Check Auto Edge Detect | |
| Page 4 | ||
| Page Titles and Descriptors | As desired |
2. Set the Glass System Configuration as follows:
| ... | Dimensions | |
| Start Offset | Enter the distance from the home position to the point where both edge detectors are 1 cm from the edge of the glass. | |
| Stop Offset | Enter the distance from the home position to the far side of the glass where both edge detectors are 1 cm off the glass. | |
| Det Spacing | 5 cm (typically) | |
| Normal Run | ||
| Read Duration | 750 ms (line speed dependent: maximum 32,765) | |
| Delay | 0 ms for front edge read. Delay can be increased to being read after leading edge (line speed dependent: maximum 32,765) | |
| Read Position | Enter position for reading. Maximum number is displayed next to the box in brackets. | |
| Cross Run | ||
| Read Duration | 750 ms maximum | |
| Edge Read | 750 ms maximum | |
| Speed | 20 cm/s (glass width dependent: 50 cm/s maximum) | |
| Edge Speed | 10 ms | |
| Auto Det Speed | 5 cm/s | |
| Backup Distance | 0 cm for edge reading; increase to move inside the edge | |
| Length Run | ||
| Read Duration | 750 ms | |
| Number of Readings | 20 (typically). Increase for longer glass and more zones (maximum 72) |
3. Begin the run.
4. Length and cross tests may be performed at any time during the run by selecting the appropriate menu button. The run is paused during the test and resumes once the test has been completed. Data from the tests can be displayed and stored just like data from the run can.