INSPECTION , TESTING & MEASUREMENT
However , in case a measurement is taken too close to a sample ’ s edge , then readings get affected due to the magnetic field reaching beyond a specimen ( Figure 3 ).
Figure 3 . Graphical representation of an “ edging ” effect
In case a sample is small and a probe inevitably always lands near an edge , you can obtain more accurate results by using an appropriate “ thin tip ” probe . It is also suitable for measurements in intricate locations . Further below you can find two types of “ thin tip ” probes offered by Helmut Fischer GmbH for measurements on ferrous and non-ferrous substrates :
FGA06H-MC probe . Measures non-ferrous and non-metallic coatings on steel or iron substrates . Mechanical design is especially suited for precise probe positioning ( e . g ., near edges )
FTA2.4-MC probe . Measures electrically non-conducting coatings on nonferromagnetic metal substrates . Mechanical design is especially suited for precise probe positioning ( e . g ., near edges )
Table 2 : Thin tip probes
The FGA06H-MC probe works with FMP10 deltascope , FMP20 dualscope , FMP30 deltascope , FMP40 dualscope , and FMP100 dualscope . Meanwhile , FTA2.4-MC operates with FMP10 isoscope , FMP20 dualscope , FMP30 isoscope , FMP40 dualscope , and FMP100 dualscope . Follow the link below for more details about the FMP range of instruments and how to access probes ’ technical information .
https :// fischerinstrumentation . co . uk / privacy-policy / product-portfolio / dry-film-thickness-gauge-fmp /
Finally , it ’ s essential to consider that coating thickness measurements can also take place inside bores and holes . In this case , it ’ s often impossible to obtain a reading without a specialist probe .
Table 3 demonstrates suitable probes for measurements in hard to read locations .
FAW3.3 probe . Measures electrically non-conducting coatings on nonferromagnetic metal substrate materials . It is suited for measurements on plane specimens or in pipes boreholes and recesses . It can also be used when surfaces exhibit a damp condition ( acidic contamination of test surface ).
FAI3.3-150 probe . Measures electrically non-conducting coatings on nonferromagnetic metal substrate materials . Suited for measurements in pipes , boreholes , grooves , etc . Smallest permissible inside diameter : 9 mm . Maximum insertion depth : 150 mm .
FGABI1.3-150 probe . Measures non-ferrous and non-metallic coatings on steel or iron substrates . Suited for measurements in bore holes , pipes , or grooves . Smallest permissible inside diameter : 9mm . Maximum insertion depth : 150mm
FGABI1.3-260 probe . Measures non-ferrous and non-metallic coatings on steel or iron substrates . Suited for measurements in boreholes , pipes , or grooves . Smallest permissible inside diameter : 9mm . Maximum insertion depth : 260mm
Table 3 : Probes for coating thickness measurements in hard to reach locations
The list of probes in table 3 works with the FMP family of instruments .
Sample Geometry Most of the time , the final sample geometry may be more complicated with round and concave surfaces , and as a result , the measuring can be problematic . As an example , in the automotive industry , most of the measurements acquired on car bodies are either on a convex or a concave surface .
Sample geometry has one of the most significant impacts on the coating thickness measurement readings , often producing a deviation from the real value ( Figure 4 ). In this case , operators are forced to conduct a re-calibration for every shape . It adds complications to the measurement procedure with increased testing times and a substantially higher room for errors .
56 SEPTEMBER 2020 read online : www . surfaceworld . com