Small loads have to be processed mainly in applications where signals must be forwarded to control inputs. As such, this can also relate to proximity or fill-level sensors, which are used as signal generators in automated processes.
Definition of problem
When acquiring sensor signals for transmission to the controller, weak loads are switched. As such, the switching current in the output circuit is only a few milliamps.
Oxide or sulfide layers build up on the contacts due to the surrounding atmosphere. These layers cause increased contact resistance. In the event of higher switching currents, these layers are destroyed by the resulting electric arcs, so that reliable switching is always possible. However, for weak loads, the switching current is not sufficient to generate an electric arc. For this reason, after some time, reliable switching is no longer ensured.
For these areas of application, relays with gold-plated contacts are used. Gold is an inert element. For example, there is no connection to sulfur particles from the surrounding air, and as such, no sulfide layer builds up. For this reason, a constant low contact resistance is achieved with gold-plated contacts. Due to these properties, weak loads can be reliably switched.
Phoenix Contact provide relay modules with gold-plated contacts. These are indicated by the extension AU in the order designation.