Latching relay

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Polarized relay with identification of the switch position depending on the polarity

A latching relay , also remanence called a self-holding is relay , which only required to switch a current pulse. It belongs to the so-called bistable relays . In common parlance, the term “latching relay” is often used synonymously with impulse relays or pulse relays , although these have a different functionality and different areas of application.


The residual magnetism ( remanence ) of an electromagnet is used in the latching relay . After a switch-on pulse, the armature (which actuates the contacts) remains attached to the coil core . This state continues until an opposing pulse (usually via a second winding on the relay) builds up an opposing magnetic field in the relay, which extinguishes the existing magnetic field so that the armature falls off.

Some latching relays have an integrated permanent magnet to support the low remanence .

Hold-open relays have magnetically conductive materials at the contact points between the armature and the relay core. This ensures that the remanent magnetism (which remains after the pull-in current has been switched off) is sufficient to hold the armature on the coil core. Hold-open relays are used in particular where electrical energy is not always available for operation.

Application in telecommunications technology

In telecommunications technology, the flat relay 48 was also used as a latching relay. In order to reliably prevent a normal flat relay from sticking, a separating sheet (also called adhesive sheet, which should actually be called anti-adhesive sheet) made of diamagnetic material is inserted at the point of contact between armature and relay core , e.g. B. brass or copper. After switching off the excitation current, the remanent magnetism is too low to generate a sufficient force between the armature and the coil core at this gap, which means that the armature falls off safely.

Flat relays without a separating plate and with a pierced armature and a remanent rivet inserted into the hole can be used as latching relays. They were used with the communal changeover switch and selector star switch .

Other areas of application

Latch relays are also available as signal relays for safety-related controls, e.g. B. in railway safety technology. Double coil relays are used, for example, in model railways to control signals .

See also


  • Kurt Pribich, Harald Gessinger, Helmut Haslinger: Components of communications technology: a textbook and reference book for all communications technology . 10., corrected u. erg. ed., Kohl and Noltemeyer Verlag, Dossenheim (Heidelberg) 1980, ISBN 3-88173-001-X .
  • Paul Volk: Drive technology in metal processing. Springer Verlag, Berlin 1966.
  • Karl Schüler, Kurt Brinkmann: Permanent magnets. Materials and Applications, Springer Verlag, Berlin / Heidelberg 1970.
  • Ernst Kauffmann, Erich Herion, Harri Locher: Electropneumatic and electrohydraulic controls. Friedrich Vieweg & Sohn Verlag, Braunschweig / Wiesbaden 1992, ISBN 978-3-528-04360-5 .

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