Micro Foreign Object Debris  ( FOD ) the microscopic threat

Wear and tear  is hard to describe in terms of time, amount  and effect.  The result is debris.  It’s effect  can be enormous even at low incident rate and low amounts of particles.  A benefit of  passive witness plates is that  they are patient evidence collectors not requiring power nor attendance.  The witness plates of a PDM system can be placed besides  or under guidance rails near support wheels etc. to investigate the generation of particles large enough for disposition.   The passive evidence collection  does not only gather the particles for sizing and counting.  Of each particle the position on the witness plate is as well logged in the raw output of the  Particle Deposition Monitor.  By means of  certified SEM pin stubs with double coated adhesive carbon tabs the particles can be transferred and investigated down to their nature.  In this way  rate, amount and further required information can be captured in a cost effective way.   Particle Deposition measurement equipment does not need to be at site to do measurements, only witness plates are required.   The collection of information is done in a passive manner. Some plants use up to 100 witness plates and a single instrument to carry out all their monitoring. Normal microscopic evaluation of the particles as addition to the counting and sizing can be carried out as well because the witness plates are made of transparent glass. Storage of the particles as evidence over a long period of time can be done on the witness plates in the witnessplate boxes.  A last word to the use of witness plates automated paint shops.  The witness plates are made of  a laboratory type of glass capable of withstanding high temperatures. The marking on the discs  is not affected by high temperatures up to 300 deg centigrade and therefore suitable to follow cars in the process previous to the actual paint job.