BS EN 4875:2020 pdf free.Aerospace series Surface treatments Test method for measurement of electrical contact resistance.
BS EN 4875 This document describes the electrical contact resistance testing method applicable to conductive and non-conductive coatings applied on test specimens made of conductive materials (unless otherwise specified) for aerospace applications. An objective of this practice is to define and control many of the known variables in such a way that valid comparisons of the contact properties of materials can be made.
This test may be locally destructive depending on the process tested.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and deilnitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
• ISO Online browsing platform: available at http://www.iso.org/obp
• LEC Electropedia: available at http://www.electropedia.org/
3.1 contact resistance
resistance to current flow between two touching bodies, consisting of constriction resistance and film resistance
The contact electrodes shall be in copper or pure silver plated copper (use of pure silver plated copper electrode is recommended).
For copper electrode, the polishing shall be done as a minimum with a P1200 metallographic abrasive paper.
For pure silver plated copper electrode, the polishing shall be done cautiously.
In both cases, the electrodes shall exhibit a polish mirror surface.
The measurement of the roughness is mandatory when specified by the OEM/manufacturer.
Due to the risk of loss of the flatness of the surface/parallelism of plots due to the wear of the electrode during preparations/measurements, it is recommended to check the flatness of the surface/parallelism of plots using a calibrated thin film (50  max.) which allows to identify a deviation of measurement.
The electrodes shall be cleaned with materials that remove soil without damaging the plating (e.g with isopropyl alcohol). The electrodes shall be handled during all cleaning and subsequent operations so that mechanical damage or contamination is avoided.
The deviation shall be checked at the beginning of each day of test and after 50 measurements.
When using an ohmmeter, a measured value of shall be indicated on the measuring apparatus. If necessary, the measuring apparatus is adjusted to 0, otherwise the indicated value should be deducted.BS EN 4875 pdf download.