Fritting tension
As a fritting voltage ( English wetting voltage ) refers to a voltage that a contamination resistance by beating. The current flowing in the process is called the fritting current , the name is derived from the fritter . Foreign layers can represent electrically non-conductive oxides, corrosion , contamination, etc. on electrical contacts or cable connection points.
The figure shows a resistance-voltage characteristic of an electrical contact covered with foreign layers: If you apply a small voltage to this contact, you first measure a high-ohmic contact resistance R 0 (a few M ohms ). If you increase the voltage, the resistance drops only slightly at first. Upon reaching the fritting voltage U F , the resistance breaks up the residual value of R S together. The contact voltage U S that is now established is called the fritting voltage.
High fritting voltages are particularly disturbing when switching and contacting signals with low voltages, such as those used in bus systems or in measurement technology. After a certain runtime of the system, they can lead to errors that are sometimes difficult to find. This disruptive effect can be reduced by a suitable selection of the contact material, for example gold . A frictional movement of the switching contacts and / or a high contact pressure can also avoid this disruptive effect.
The fritting voltage is taken into account in the telecommunications sector for subscriber lines , which are also used as digital subscriber lines (DSL). In order to avoid contact problems at the terminal points of the connection line, a direct current (fritting current) in the range of a few mA is provided in the ITU-T Standard G.992.3 in order to safely exceed the necessary fritting voltage at all cable clamping points.
Individual evidence
- ↑ http://www.nhp.com.au/files/editor_upload/File/TNL/TNL-42.pdf
- ↑ http://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=13C3236_AppNote&DocType=CS&DocLang=EN
- ↑ Recommendation G.992.3: Asymmetric digital subscriber line transceivers 2 (ADSL2). ITU-T, accessed September 1, 2013 .