Remote Visual Inspection 101
September 16, 2011
Remote visual inspection (RVI) is one of the most dependable NDT techniques of checking parts of machinery that are inaccessible through unaided means. A videoscope allows the user to look at what is inside the engines, pipes, tubes, and a wide range of parts to find out if anything is amiss with the internal pieces having to disassemble the product being inspected. This particular video inspection method is not necessarily restricted for manufacturing purposes but is also useful for preventative maintenance, aviation, law enforcement, medical, power generation and countless other purposes.
Before the advent of the videoscope with chip in tip technology, remote visual inspections of materials, equipment and product were limited to either rigid borescopes or flexible fiberscope. Good quality borescopes will always give the best possible image since they typically use high quality optical rod lens systems, which give unsurpassable image quality and true color transmission.
However, applications are limited, since these are rigid and not flexible, especially when an inspector is attempting to insert the probe into an area that warrants bending around corners. If an application required a flexible probe, the user was once limited to a flexible fiberscope, which would offer a flexible probe typically with two-way or even four-way articulation to help steer the tip through tight areas. These worked well, however the image quality was typically rather poor because these instruments required the use of a pixilated image bundle, which gives an image similar to looking through a thick screen window. Image quality depends on the type of image bundle used, and pixel count typically ranging from 10,000 to 17,000 pixels.
If video was required, the user would then have to couple a camera to the borescope or fiberscope with a special video camera mount. This system worked well, however, it limited the image size and, depending on the magnification of the coupler, it would increase the pixel size. This would, in turn, decrease image quality when using a fiberscope with a small pixel count.
In the 1980s, when the first videoscopes were introduced, the user was somewhat limited to applications because of the large diameter of these units. A typical videoscope back in the ’80s would be upwards of 16 millimeters in diameter. This was primarily due to the size of the charged couple device (CCD) sensors available at the time.
The first systems were also cumbersome and difficult to work with. Many manufactures offered systems to be pieced together, making portability very difficult. The wheel barrel approach was to supply a videoscope with a separate camera control unit, light source, monitor and recording device, if images were required. As you can imagine, this type of system would work well in a test cell or lab, however it was not the system of choice for those who required mobility, such as those working on a flight line; in a confined area; or where power was not readily available.
With advances in technology, the RVI industry is now moving toward the videoscope and away from the older fiberscope technology. With CCD and complementary metal-oxide-semiconductor (CMOS) becoming smaller and less expensive, which allows manufacturers to build much smaller diameter probes at a more affordable price, many users have replaced older fiberscopes with new videoscopes.
In a CCD image sensor, pixels capture light and move it toward the edge of the chip, where it is converted into a digital signal. In a CMOS sensor, the light is converted at the pixel itself, no electrical conveyor belt required. Depending on the sensor size used, one can expect to see much better resolution when using a CCD sensor because of the higher pixel count ranging from 290,000 to 440,000, where the cheaper CMOS systems typically have between a 160,000 and 300,000 pixel count.
Understanding the applications and capabilities of this equipment is very important when packaging a system for maximum portability and flexibility. With newer light sources available, one must determine if LED has enough illumination in large areas and if a high output white light source is required. With most systems turning to CCD with LED or CMOS with LED, this is very important. Also, one must keep in mind what type of storage media is required, still images, video, or a combination of both. Most smaller diameter videoscopes offer two-way articulation, while the larger diameters offer four-way articulation. Many systems also offer interchangeable optical tip adapters, which allow the user to change direction of view and field of view of the videoscope.
Articulation-or steering of the typical videoscope-is usually controlled either by an electric motor via a joy stick, or by the use of knobs or levers. Both systems have proven to work well with more systems using the motorized joystick system, which allows the user to simply move the joystick in a direction and the tip will articulate.
With all systems there are pros and cons. With the motor driven articulation, one does not feel articulation and if the unit is not centered before removing it from an inspection, the user risks damaging the articulation cables or motors (which are very expensive to repair). The cons are that, with a four-way knob system, the user typically needs a scope holder or must hold the scope in one hand while articulating with the other. With the lever type, one has the best of both, since the user can hold the scope and operate the articulation easily with one finger, still have a feel for the movement and reduce the risk of damaging the articulation cable or motor. This is because the unit can be centered once one removes his or her finger from the lever.
Richard Wolf Industrial Borescopes has developed a new videoscope system, chip in tip, with a direct USB output. Any laptop or PC with a USB 2.0 input running Windows-based software can be used. The live image from the VIPAQ can be seen on the monitor or display of the laptop or PC in real time. With the push of a button on the body of the videscope it is possible to store digital pictures directly on the computers hard disk.
A driver and software is provided with each VIPAQ videoscope. With standard software such as MS Movie Maker, it is possible to record video sequences on the computers hard disk as well. With remote buttons on the handle of the videoscope, the users can quickly and easily control:
Power for the camera electronics and control unit built in the videscope handle is delivered from the computer via the USB port. There is no external power required to operate the videoscope. A power supply unit is also included in the event the user would like to simply plug the VIPAQ into a monitor for S-video operation.
The flexible tip of the videoscope is steerable by a remote control thumb lever on the 4.7 millimeters and by steering knobs on the 6.3 millimeter and 8.3 millimeter versions. Both systems offer friction brake to allow the user to lock the tip as desired. The 4.7 millimeter has a dedicated forward viewing tip with a wide 115 degree field of view, which is perfect for looking into large dark areas. The larger, 6.3 millimeter versions have interchangeable tip adapters with various forward and side viewing optics.