 |
| Distinctness of Image Meter (DOI) |
 |
|
| Glow Box™ Model GB11-8GM. An instrument method for evaluating the Distinctness of Image (D.O.I.) of automotive finishes and selective coatings. |
| Meets General motors' engineering standard: "test for evaluating distinctness of image: GM 9101P." |
|
 |
Evaluation of appearance by this D.O.I. meter involves the projection of image forming photographic patterns (Landolt Rings) onto a painted surface. The various sizes of image forming patterns are shown in Figure 1. These rings are projected from a fluorescent lighted box at a distance of 10 cm over the sample to be measured. The smallest set of rings are assigned a value of 100. The next uniformly increasing larger rings have a value of 90. The other eight sets of rings of increasing sizes are designated 80, 70, 60, 50, 40, 30, 20 and 10; thus a rating scale is obtained which can be used to quantitatively evaluate the Distinction of Image of the painted surface.
Due to differences which exist in visual acuity between different operators it is recommended that a control standard be made by the operator with an assigned D.O.I. value of about 80 and used to standardize the readings.
Figure 1 Landolt Ring Film transparency that is attached to acrylic cover plate before the instrument is turned over. |
A special adaptation of Glow Box™ Model GB11-8GM has been used for more than a decade in the coating industry for the evaluation of smoothness of a painted surface. The technique, called Distinctness of Image (D.O.I.) Test, is described herein. Since the test is assuming increasing importance in the coatings industry, the Glow Box™ has been redesigned to make it easier to use. The product is known as Glow Box™ GB11-8GM.
In the original model, legs were rigidly attached to a Glow Box™ to support the illuminated surface at the specified 10cm distance from the painted surface. The Distinctness of Image Test Film (D.O.I.) was held against the lighted acrylic surface of the box by a glass plate.
In the redesigned model of this test equipment, the Glow Box™ is held in place over the coated surface by placing it (in inverted position) on a new special frame that supports the D.O.I. film at the 10cm distance. The equipment is shipped with the glass plate in place under the aluminum retaining band. A layer of foam is between the glass plate and the acrylic plate for shipment. The D.O.I. film is in a transparent envelope. The foam, as well as the transparent envelope, can be discarded.
Remove the screws which hold the retaining band in place, and lift the band off, along with the glass plate. Next lay the D.O.I. film (which has been removed from its transparent envelope) on the white translucent cover plate of the Glow Box™, and put the glass plate on top. Replace the retaining band, pressing it firmly against the glass as the screws are tightened in their slots.
The only other assembly required to prepare the equipment for use is to screw the legs into place on the bottom of the frame. Then plug the light box cord into a 115V AC wall outlet, push the switch (through the hole in the red acrylic cover) to turn on the light, and place the box in inverted position on the aluminum frame. Follow the directions in the D.O.I. application sheet for the paint evaluation procedure. |
| Checking the Smoothness of Painted Surfaces |
One of the most ingenious uses of a Glow Box™ came, we are told, from a Du Pont laboratory interested in evaluating the smoothness of paint films.
Various other paint manufacturers as well as automobile manufacturers are using this procedure now to obtain a quantitative measure of the smoothness (or the roughness) of paint finishes. They accomplish this with a special 8-1/2" by 11" photographic transparency attached to the acrylic cover plate of a modified Model GB11-8GM Glow Box™. The transparency has ten blocks of C’s in different sizes. The Glow Box™ with the C film attached is turned over and used upside down, 10cm above the surface to be checked (see note 2 below). When the Glow Box™ is in this position and the light turned ON, an observer looking at the painted surface sees the reflections of the illuminated patterns as either open C’s or closed O’s, depending on the smoothness of the painted surface and on the size of the C’s. |
| |
- Since the film has blocks of ten different size C’s, the smallest “C’s” that appear as C’s rather than O’s give a quantitative measure of the smoothness of the paint finish. The range, quantitatively, is from 10 to 100 in increments of 10. The smoother the paint finish, the higher the value.
- For this application, we supply the Model GB11-8GM Glow Box™. It has four supports that enable the user to place the Glow Box™ “upside down” 10 cm above the painted surface.
- This method is officially known as General Motors' Engineering Standard; Test for Evaluating Distinctness of Image: GM 9101P. (This was dated January 1977 and carried a reference of page W-65.201.)
- The “C” film transparency can be obtained from "GARDCO".
|
| The D.O.I. Meter has dimensions of 12"W x 12"L x 8" H. Four legs are attached to the corners to provide a distance of 10cm from the lighted surface to the specimen. The lighted surface area is 8-1/2" x 11". |
 |
Test surface should be clean and free of oil or dirt. Make measurements in an area where the lighting does not exceed 75 foot candles (See Light Meters). Too much light overpowers light source from instrument. This will result in lower readings.
Place meter so that smallest Image Forming Patterns will be towards observer. From either side of instrument observe the Distinctness of Image of the panel at approximately 15 to 30 degrees from normal with eyes at a distance of 25-30 cm (10 - 12 in.) from the panel. For first readings, place your control standard and sample under the meter. Glance over both the control standard and sample and determine if sample is better or worse than the control. This provides a qualitative “go” or “no go” reading. |
| Quantitative Evaluation of D.O.I. |
Next to each of the image forming patterns is a value that indicates a rating of 100, 90, 80, 70, 60, 50, 40, 30, 20 and 10. These numerical values may be used to quantitatively evaluate Distinctness of Image. Readings should be made for the left half of the sample from the left side of the D.O.I. meter and for the right half of sample from right side.
Note the 80 D.O.I. control standard and determine the pattern in which all circles and openings are seen distinctly. Observe next smaller pattern and circle openings. If all openings are visible, but only a few are visible in the next smaller pattern then the rating should be that of the entirely visible pattern. But, if at least 50% or more of the smaller patterns are visible a rating midway between the two patterns should be recorded. i.e. If a distinct pattern with an 80 rating is entirely visible and the circles and openings in the 90 pattern circles and openings are over 50% visible then a rating of 85 should be recorded. However, if only a few of the 90 patterns are visible, then the value would still be 80. |
- 6' Cord and Plug For 110 VAC with 4CM Legs
|
- Landolt Ring Film
- Glass Plate
|
|
|
|
|
Prices subject to change  Prices listed in US dollars for domestic shipments within US, Canada, & Mexico only Export orders require quotations - click here for a quote For more info call us 1-800-762-2478 or 954-946-9454. |
|
| Item Number |
Item |
Prices |
| GL-GB11-8GM |
D.O.I. Meter |
$945.00 |
| ™ - Trade Mark of Instruments For Research & Industry |
|
|
|
