Changes

The procedures and standards for testing electrical contacts described below are mostly concentrated on contact applications in electromechanical devices. Since the range of applications for electrical contacts is very broad, a complete description of all relevant test procedures would extend the scope of this chapter of the Data Book. Therefore we limited the content here to contact coatings and switching contacts for information and power engineering. Because of the ongoing miniaturization of electromechanical devices the testing for effects of corrosive influences by the environment play an important role. Special testing procedures, such as these for brazed, soldered, and welded contact joints are covered already in chapter 3 [[Manufacturing Technologies for Contact Parts|Manufacturing Technologies for Contact Parts ]]

Since the criteria which determine the electrical life of switching contacts depend depends on the type of switching devices they are used in, they are described in more detail under the testing procedures in information and power engineering.

For applications at low switching loads contact layers with thicknesses in the range of just a few micrometers are widely used. For testing such thin layers , the actual coating properties must be distinguished from the functional properties. Coating properties include, besides others, porosity, hardness, and ductility.Depending on the application, the most important function properties are for example frictional wear, contact resistance, material transfer, or contact welding behavior. Besides these other technological properties such as adhesion strength, and solderability, maybe of importance for special applications like those for electronic components.

Testing of the contact behavior in the communications technology is usually performed on the actual devices such as ,for example , in relays. Experience has shown , that the interaction between all design and functional parameters such as contact forces, relative movement, and electrical loads, are determining the failure mode. Therefore only statistical performance tests on a larger number of switching devices lead to meaningful results.

The testing of electrical contacts for power engineering applications , serves on the one hand the continuous quality assurance, on the other one the new and improvement development efforts for contact materials. To optimize the contact and switching performance , contact materials and device designs have to complement each other. The success of such optimizing is proven through by switching tests.

The assessment of contact materials is performed using metallurgical test methods as well as switching tests in model test set-ups and in commercial switching devices. While physical properties , such as melting and boiling point, electrical conductivity, etc. are fundamental for the selection of the base metals and the additional components of the materials, they cannot provide a clear indication of the contact and switching behavior. Metallurgical evaluations and tests are used primarily for determining material and working defects. The actual contact and switching behavior can however only be determined through switching tests in a model switch or preferably in the final electromechanical device.

Model testing devices offer the possibility of quick ratings of the make and break behavior and give a preliminary classification of potential contact materials. Since such tests are performed under ideal conditions , they cannot replace switching tests in actual devices.

The electrical testing of commercially produced switching devices should follow DIN EN or IEC standards and rules. Special test standards exist for each type of switching device , which are differentiated by:

The following chapters are limited to metallurgical analysis and the testing of the most important properties of switching devices such as electrical life, temperature rise, and switching capacity.