Brochure/Catalogue

for EMR for SSR
Contact resistance Electrical resistance between the closed relay contacts.
In most applications, the contact resistance does not play a signicant role in
the reliability of a relay. However, a low contact resistance can only be reliably
achieved above a certain load (see item entitled ”Contact material” or ”Minimum
switching capacity”).
With very small loads, signicantly higher contact resistances can occur,
especially with switching voltages below 30 V and switching currents below
10mA. In such cases, it is recommended to use hard gold-plated contacts.
After the relay has been operated in a permanently off or on state for several days
(e.g. due to adverse environmental conditions such as harmful gas atmospheres)
or after it has been stored, it is recommended that a certain number of cycles be
performed before measuring the contact resistance. This is achieved by means of
electrical cleaning, which can be performed by switching a sufcient load and by
self-cleaning caused by contact friction during the switching process.
x
Contact welding,
Adhesive bonding (contacts)
Capacitive loads
Often occurs due to excessive inrush currents, e.g. when switching capacitive
loads. See also the item entitled “Inrush currents“.
However, this can also occur when switching loads without high inrush currents,
although this will often be at the end of the contact‘s service life.
This happens due to material peaks on the contour surfaces which are caused by
material migration and/or combustion.
These material peaks then merge during the switch-on process, since the current
of the load is conducted via this small contact point, which then leads to a brief
but strong temperature increase that can weld the contacts.
x
Continuous current Current that can be carried continuously without exceeding the limit values for
contact heating under certain conditions. Consider the derating curve.
This current can also be switched on and off in the case of AC voltages.
With DC voltages, this is only possible to a limited extent. See diagram: DC load
limit curve.
x x
Continuous operation Operating mode in which a relay remains energised until it reaches thermal
equilibrium. Unless otherwise specied, all Weidmüller relays are suitable for
continuous operation.
x x
D
DC load switching capacity,
DC load limit curve,
DC breaking capacity
Values below the DC load switching capacity curve (for max. permitted switching
voltage/current at resistive load) can be switched on and off reliably; e.g. an arc is
extinguished (max. arc duration is 10 ms at resistive load).
The position and shape of the load-limit curve is inuenced by the contact
material and relay construction (contact gap, opening speed of the contacts, etc.)
The DC breaking capacity can be increased by connecting relay contacts in
series. This is shown with dashed lines in the DC Load Limit Curves diagrams,
if specied. For further information, please refer to the item entitled “Series
connection of relay contacts“.
Information about the electrical lifespan should not be derived from these curves!
x
DC switching capacity
(resistive), max.
Calculated product for resistive loads from continuous current and switching
voltage in W.
When switching inductive loads, it is recommended to reduce the switching
capacity in order to achieve the longest possible service life.
The reduction results from the arc, which is signicantly stronger when
switching inductive loads than when switching resistive loads.
The specied switching capacity refers to 24 V DC switching voltage. For other
DC switching voltages, refer to the DC load limit curve provided in the data sheet.
x
EMR = Electromechanical relay
SSR = Solid-state relay
Glossary: Relay modules and Solid-state relays
W
Technical appendix/Glossary
W.20 2737920000