What is normal? Anyone with teenagers has probably been asked to be normal. Perhaps that is due to your “normal” protein intake being when you “snap into a Slim Jim,” or how you consider unpackaged circus peanuts a “normal” handout for Halloween. In either case, one might get your house pranked, and neither are applicable to the topic at hand, normal force.
What is normal force?
Normal force is a perpendicular force to the surface of contact. To help you visualize this, the free body diagram shows normal force (Fn) perpendicular from the interaction of the block and surface.
In the case of connector, we are measuring the amount of force that is required to displace a connector pin. The permanent set is also evaluated to understand the loss of normal force due to mechanical deformation of the contact after being mated.
Permanent set occurs when a material has been stressed beyond its yield point, and will have permanent deformation or set. The easiest way to visualize this effect is the think about how a piece of colored plastic will turn white in an area that has bent. It does not return to its original shape, and will have irreversible effects.
Why is it important and what are we measuring?
Normal force testing is to establish the force vs deflection characteristics of the contact system through the normal deflection range. It is important to the performance of a product, and without enough normal force, oxide layers on the surface of a contact will not be removed during mating. Also, normal force is important to maintain a gas tight interface. A typical end of life target for normal force would be around 40 grams for a contact with gold plating, and 100 grams for tin plating.
In a previous blog, thermal aging was discussed as it is used as part of many other tests. Normal force also utilizes thermal aging as part of the test sequence. The Samtec normal force test is per EIA-364-04 “Normal Force Test Procedure for Electrical Connectors.” The test is completed on two groups of parts, one of which includes thermal aging.
Group 1
- Measure Contact Gaps
- Test normal force
Group 2
- Measure Contact Gaps
- Expose parts to thermal aging
- Measure Contact Gaps
- Test normal force
Samtec publishes all of its reports on www.samtec.com and can be found according to the series pages. To see the qualification test report that includes LLCR test results for the SEAM/SEAF series please click here, or type in the series name of the part you are interested in on samtec.com.
[…] here to see what the normal force looks […]