Quality
At Optical filters Ltd we embrace quality as a keystone of our business and it is our policy to continually challenge and to improve upon our quality goals. Optical filters is an ISO 9001 registered company.
OIS/3 - Optical Inspection standard for display filters and emi windows
We operate our own inspection standard which has been generated by matching our manufacturing capability to a broad cross-section of customer's requirements and raw material limitations. This standard covers the handling and inspection procedures for filters, our returns policy and the manufacturing tolerances.
Handling Techniques
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Handle the filters by holding them between thumb and finger at the edge. Avoid touching the front or back surfaces
-
Do not remove the protective foil until final installation of the filter. To inspect pull back the foil on both sides to expose half of the filter. Inspect it for defects. Replace the foil and repeat for the other half of the filter. If handling a product with a surface treatment or coating, protective plastic gloves must be worn.
-
Inspection should be carried out in a dust free zone under specified lighting conditions. Clean lint free wipes or dry compressed air should be used to remove surface dust.
-
If necessary to remove the protective foil, place the filter onto a clean tissue.
Returns policy
All filters are fully inspected prior to despatch and packaged so as to prevent damage during transit or storage. Incorrect handling of filters can cause significant damage. We will only accept returns for defects under the following conditions
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The filter is returned within 14 days of despatch
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The filter is returned with the protective foil or tissue in place
-
The handling procedures detailed above have been followed during your inspection of the product.
Inspection Procedure
The underlying principle of inspecting optical filters is to simulate the viewing conditions that will occur when the filter is in use. The equipment and inspection procedure are both controlled to establish a consistent assessment of the filters
All of our laminated filters are assessed for the following:
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Scratches
-
Inclusions
-
Dimensions within tolerance
-
Mesh angle and structure (for emi shielded windows)
-
General appearance of the filter.
-
Build and termination according to the agreed production release note.
Scratches and Inclusions
All filters are inspected in our inspection bay against both black and white backgrounds. A light box with a white diffuser is mounted in the bottom of the enclosure, whilst fluorescent tubes without a diffuser are mounted to the inside top of the inspection bay. The filter is inspected for 10-30 seconds with transmitted light and then for a further 10 seconds under reflected light.
-
Inspection under transmission will examine the filter for optical clarity and inclusions
-
Inspection under reflection will assess the front surface for scratches and coating defects. If an inclusion, scratch or defect is found, it is accessed according to the specifications laid out hereafter.
Note:
-
Any defect that causes an immediate distraction is a cause for rejection.
-
Do not inspect the filter from the rear surface, as this does not simulate real viewing conditions.
-
Please refer to the product details for information on the correct handling and cleaning techniques for the substrate.
All plastic and glass elements contain defects. The following table 3.4.1 classifies substrates into groups of materials with similar surface properties. Table 3.4.2 details the accept and reject criteria for each group.
e.g HC Polyester-AT = II/III
There are certain inherent material and process effects that are excluded from this assessment procedure. These include extrusion marks, the slight rippled surface effects on hard coat finishes, and laminate ripple where materials under 0.5mm thick are used.
Table 3.4.1 : Scratch classification of substrates
|
Group |
Substrate |
|
I |
Optical Polished glass |
|
II |
Optical or conductive coated
glass
Plain/plain glass
VRD/plain glass
PSC- N/G coated acrylic
H/C or N/G - Polyester -AT |
|
III |
Plain/plain
acrylic
H/C or N/G - Polycarbonate -AT |
|
IV |
Spray coated H/C and N/G plastic surfaces |
| V |
Any glass window or filter over 500mm in length or widthPlain / plain polycarbonate |
|
VI |
Conductive coated plastics |
|
VII |
Any plastic window or filter over 500mm in length or width |
Inclusion classification of substrates
|
Group |
Substrate |
| I |
Optical Polished glass |
|
II |
Optical coated glass
|
Plain/plain
acrylic |
| Plain / plain polycarbonate |
Conductive coated
glass |
| Plain / plain glass |
VRD / plain
glass |
| PSC - N/G coated acrylic |
|
|
|
III |
H/C or N/G polyester -
AT
H/C or N/g polycarbonate - AT |
|
IV |
Conductive coated
plastic
Cast N/G acrylic
Polarising materials - Linear and circular |
|
V |
Spray coated HC or N/G plastic surfaces |
|
VI |
Any window or filter over 500mm in length or width |
Table 3.4.2 Assessment criteria for visual defects
|
Scratches |
Classification = mean width of scratch (mm)
Unit = accumulated length of scratch (mm) per 100mm diameter inspected |
Group
scratch
Width
(mm) |
I |
II |
III |
IV |
V |
VI |
VII |
|
>0.40 |
0 |
0 |
0 |
0 |
0 |
0 |
25 |
0.31 to
0.40 |
0 |
0 |
0 |
0 |
0 |
0 |
25 |
0.21 to
0.30 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0.11 to
0.20 |
0 |
0 |
0 |
0 |
25 |
50 |
50 |
0.05 to
0.10 |
0 |
0 |
25 |
50 |
50 |
50 |
N/A |
|
<0.05 |
0 |
50 |
50 |
50 |
N/A |
N/A |
N/A |
|
<0.03 |
25 |
N/A |
N/A |
N/A |
N/A |
N/A |
N/A |
Total
defects
allowed |
25 |
50 |
50 |
50 |
50 |
75 |
75 |
|
Inclusions and Pinholes |
Classification = mean diameter (width + length)/2
Unit = mean number of defects per 100mm diameter |
Group
Defect |
I |
II |
III |
IV |
V |
VI |
|
>0.1 |
0 |
0 |
0 |
0 |
0 |
1 |
|
0.7 to 1.0 |
0 |
0 |
0 |
0 |
1 |
1 |
|
0.50 to 0.75 |
0 |
0 |
0 |
1 |
2 |
3 |
|
0.30 to 0.50 |
0 |
0 |
1 |
2 |
4 |
5 |
|
0.20 to 0.30 |
0 |
3 |
3 |
3 |
6 |
8 |
|
0.10 to 0.20 |
0 |
N/A |
N/A |
N/A |
N/A |
N/A |
|
<0.10 |
N/A |
N/A |
N/A |
N/A |
N/A |
N/A |
|
Total Defects allowed |
0 |
3 |
3 |
4 |
6 |
10 |
Tolerances
|
Material |
Laminate Thickness |
Machined Parts |
Assembled parts |
Acrylic
Polycarbonate
Polyester |
+/-0.2: <1.5mm
+/-0.3: 1.6 to 5.0mm
+/- 0.5: >5.0mm |
+/-0.2: <300mm
+/-0.3: 301 to 500mm
+0/-1.0: 501 to 1000mm
+0/-2.0: >1000mm |
+/-0.3 : <200mm
+/-0.5 : 201 to 500mm
+/-1.0 : >501mm
+0/-3.0 : >1000mm |
|
Glass |
1.0 to 1.2mm
1.4 to 1.7mm
1.8 to 2.3mm
2.8 to 3.2mm
>4.0: +/- 0.5mm |
+/- 0.2:
<200mm
+/-0.3: 201 to 300mm
+/-0.5: >300mm |
Mesh Angle and Structure
The following points detail the inspection criteria applied to blackened mesh during inspection:
- Colour: Uniform shade without
streaks or noticeable variations in the shade
- Blackening: uniform shade without any unblackened spots or handling marks
- Mesh Structure: No broken wires, snags, tears or physical damage. The mesh shall extend to all edges of the window. Any folds, discoloration or small adhesive outflow onto a mesh extension is acceptable.
- Straightness: The mesh should be aligned with a ruler within +/-5°. Small deviations (waves) with a peak to peak length of less than 12.5mm will be disregarded.
- Mesh geometry: Shall be uniform and regular with regard to aperture size and straightness. Wire diameter and mesh count (opi) shall be verified against the work instructions.
General Appearance
Windows are cleaned and packed before despatch (following the handling and cleaning procedures outlined in the product information)
Build and Termination
All of our filters are made to a production release note (PRN). This document outlines the materials, dimensions, termination and inspection classification for a filter. It may also include a drawing of the window. The customer must approve this document prior to production. All finished parts should meet the criteria set out in this document.
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