Direct or indirect Visual Inspection - What is the difference?
Visual testing, often abbreviated as VT, is an optical or visual non-destructive material testing. It is used for quality assurance or in maintenance and repair. Visual inspections are carried out during series production or as final inspection. Visual inspection distinguishes between direct and indirect visual inspection. It is defined in the standard DIN EN 13018 (General principles of visual inspection).
Direct visual inspection
In the case of direct visual inspection, the component to be inspected is tested by an inspector. Testing, analysis and assessment are carried out by one person. The direct visual inspection can be carried out with tools such as borescopes.
Advantages of direct visual inspection with borescopes
- Non-destructive testing with simple technical equipment
- Mobile use
- Ideal for sampling
- No comparable test results, since no documentation
- Depends on the experience / the ability of an individual to judge
Indirect visual inspection
In indirect visual inspection, the area to be inspected is captured by a camera and displayed on a monitor. The test image can be subjected to further work steps. For example, the image can be enlarged, details can be visually highlighted for analysis reasons or the image can be saved for documentation purposes. By displaying on a screen, several people can judge.
The trend is towards indirect visual inspection, as the use of camera technology offers more possibilities and leads to more efficient interruption of the production process. The indirect visual inspection is carried out e.g. by means of videoscopes or stationary inspection solutions. In industries with high quality requirements, inspections solutions are used, that provides high resolution images.
Advantages of indirect visual inspection
- Digitalization enables image optimization for better defect evaluation
- Secure 100 % controls
- Defects can be documented
- Better analysis possible
- Tracking of documented defects for process optimization
- Acquisition costs higher than with direct visual inspection
- More space required than with direct visual inspection