Depending on the version, a laser is found either inside the PaintChecker measuring head or inside the light source unit, which generates the pulsed laser radiation for the photo-thermal coating thickness measurement. The emitted laser radiation cannot be seen by the human eye because the wavelength is in the near infra-read spectral range. The laser radiation is emitted through the emission lens which is integrated in the centre above the glass plate on the measuring head, and it is  focused by this lens in such a way that at the measuring distance the smallest illumination spot is formed. For non-moving measured objects, the measuring spot can be set to a diameter of approx. 3 mm. For measurements in motion, the measuring spot is rectangular and has a size of approx. 15 x 5 mm. The irradiated area along the path of the rays is not constant, and in different locations it has a different size. When moving from the emission lens towards the measured object, one will find that the irradiated area will shrink between the emission lens and the measuring distance of approx. 200 mm. At measuring distance itself, the irradiated area is smallest, and it grows with increasing distance from the measuring distance.

The laser power is in the range of  16 to 20 W, and it is reduced by the optical components within the measuring head by approx. 30%, so that at the emission lens a power of 11 to 14 W is found. The laser power is not emitted continuously, but in the form of pulses with pulse lengths between  1 ms and 100 ms. Exactly one laser pulse is emitted per measurement.

For determining the laser class for the PaintChecker, all the optical characteristic data for the laser as well as the operating modes and utilisation modes are considered, and the laser power  occurring in the most critical case is calculated and assessed. The basis for this is the German accident prevention regulations for laser radiation  DIN EN 60825-1(VDE 0837 part 1): 2001-11. It is different if the PaintChecker Standard version is used or if it is integrated into a measuring chamber. This results in different laser classes, because of the different utilisation types and because certain protective measures may already be integrated in the measuring chamber.


Standard version

In its basic version, the PaintChecker measuring device is delivered without additional protective measures and therefore it belongs into  laser class 4. This means that the invisible laser radiation emitted by the measuring head is dangerous to the eye when directly irradiating it. When working near to the PaintChecker measuring head during its operation, suitable laser protection goggles must be worn. In addition, one member of staff must be nominated and trained as the laser protection officer who will monitor its operation and carry our regular staff training.


Measuring chamber

If the PaintChecker measuring device is delivered inside a measuring chamber, it belongs to laser class 1, this means that the invisible laser radiation emitted from the measuring chamber is not dangerous to the eye or skin.  A number of protective measures prevent dangerous laser radiation from escaping and protect the user. These protection measures include the laser protection film on the front door, the light-proof housing, a door safety switch, the fixed installation of the measuring head and the directed emission of the laser pulses. A laser protection officer is not necessary as long as nobody is working within the protected laser area.

If work within the unprotected laser area is necessary, laser class 4 of the Standard version again applies, including the corresponding requirements.


Integration into existing installations

In some cases, the operator wants to integrate the PaintChecker Standard version coating thickness measuring tool into an existing installation. Laser class 4 always applies in such a case. Only through adequate protection measures can the  laser class be reduced. Often a suitable protection concept must be drawn up, taking the technical features of the installation into account. In the simplest case, the measuring device will be installed inside a light-proof housing. If the possibility of feeding-in components and monitoring is desired, component locks and brush-covered openings or inspection windows with laser protection film can be installed. Additional electrical safety installations on doors and openings prevent laser radiation from being emitted when these are open. Signal lamps indicate the status of the measuring device to the operator. On account of the path of rays described above, the danger from the laser can be effectively reduced by maintaining an adequate safety distance, because the power per unit area falls as the distance from the measuring head increases.

For granting a lower laser protection class, the integrated measuring device must be approved in the form of an expert assessment taking the specific environmental conditions and the safety measures already taken into account. Based on this expert assessment the entire measuring system can be classified in a lower laser class (e.g. laser class 1). These can be provided by the Physikalisch Technische Bundesamt (PTB) in Braunschweig and the Deutsche Montan Technik (DMT) in Dortmund.