How to Select a Film Viewers 

The success of Radiography in Non-Destructive Testing (NDT) not only lies in the inspection, but also on the interpretation of radiographs. The correct interpretation can only be done if the operator uses the Film Viewer which is manufactured and operated as per International standards and keeping the industrial requirement in mind. Here, we shall discuss some of the major points a user shall look into while selecting a Radiography Film Viewer:

Light Source

• LED’s are recommended as preferred light source as they produce a bright and uniform luminance.
• Life Expectance of LED’s is around 40,000 hours which eliminate the need of stocking the expensive and harder to find spare incandescent bulbs which are also becoming obsolete with time.
• Usage of LED’s make the Viewer more compact due to non-requirement of huge fans and also lesser distance between LED and the screen as compared to other sources.

Intensity

• The light source shall have sufficient intensity to enable viewing of film density of 4.0
• The Luminance of the transmitted light through the radiograph shall not be less than 30 cd/m² for Film density less than or equal to 2.5 and 10 cd/m² for film densities greater than 2.5.
• To achieve the maximum illuminance value, the brightness shall be at least 105 cd/m².
• The user shall also see that the screen is uniformly illuminated for a better interpretation. The uniformity factor ‘g‘ as per ASTM E1390 should be > 0.5.

Design & Construction:

• The screen size shall be compatible to interpret the film properly without excessive glare affecting the eyes of the operator.
• User should verify that the viewing screen is made of scratch free material.
• The viewer shall contain a variable intensity control to allow the selection of optimum intensities for film with varying densities.
• The viewer with suitable markings for voltage and frequency range, power consumption and maximum brightness in cd/m2 shall be considered at the time of selection.
• The user shall also select the viewer keeping his/her requirement in mind in terms of portability and hence the weight plays an important role

Heating:

• The viewer shall be equipped with a suitable fan, blower, or other means to provide stable temperature at the viewing port to avoid damaging the radiographic film while viewing.
• As per IS/ISO 5580:1985, the housing temperature should not exceed 60° C at the intermittent operation of 1 hour, hence the housing material plays a key in selecting a film viewer. Aluminum Housing should be preferred as it acts as a heat sink.

International Standards and References:

• ASTM E-1390: Standard Guide for Illuminators used for viewing Industrial Radiographs
• BS EN 25580:1992: Specification for minimum requirements for industrial radiographic illuminators for non-destructive testing
• E 1742-06: Standard practice for Radiographic Examination
• IS/ISO 5580:1985: Non-destructive testing – industrial radiographic illuminators – minimum requirements