Brochure/Catalogue

for EMR for SSR
Mounting distance Distance between two adjacent components when using parallel, same
orientated positioning; or the distance to other electrical components, e.g. on a
terminal rail. Because of the insulation requirements or the self-heating (derating)
it may be necessary to increase the minimum gap between the components or
select a different positioning. Self-heating can be improved by increasing the
mounting distance. This can help to reduce the derating of the switching current.
In addition to this denition, the following applies:
• Densely packed installation: Designed with minimum mounting distance to
products from the same Weidmüller product series. Unless otherwise stated,
from the point of view of self-heating, Weidmüller relay modules and solid-state
relays are suitable for densely packed installation with other products from
the same Weidmüller product series. It is recommended that there should
be a mounting distance between these and other components from other
Weidmüller product series or components from other manufacturers, as this
can lead to a reduction in the insulation properties or to an unacceptable
increase in self-heating.
• Individual installation: components are mounted with gaps so that there are no
thermal inuences from adjacent components.
x x
Mounting position Electromechanical relay modules and solid-state relays (SSR) from Weidmüller
can be installed in almost any position unless otherwise specied in the data
sheet. The mounting positions used in the industrial environment are: mounted
on a terminal rail in a horizontal or vertical installation position in an upright
control cabinet. These positions are also checked when determining the derating
curves. However, the most common method of installation is on a horizontally
aligned terminal rail. It is not recommended to install the relays upside down
(relay pointing downwards) as this is not taken into account when determining
the derating curves. This would also lead to heat accumulation and the risk of a
pluggable relay slipping out of the socket due to vibrations.To ensure the proper
current ow and heat dissipation, the connections must have adequate cross-
sections. Several factors must be taken into consideration when positioning:
including the insulation requirements, heat dissipation and the possible mutual
magnetic and thermal inuence.
x x
MTTF MTTF is the abbreviation for Mean Time To Failure and is also designated as the
mean operating service life. For relay modules and solid-state relays, the MTTF
value is equal to the MTBF because no repair is performed on the products. They
are replaced after a defect, which means that there is no repair time.
The MTTF value of relay modules is calculated on the basis of the B10 value (see
item entitled “”B10 value””) and the switching cycles occurring in the application.
It can be calculated using the following formula for electromechanical relays:
MTTF = B10 ÷ (0.1 × n)
The value ”n” is the number of annual switching cycles in the application. The
user must enter this value together with the appropriate B10 value in the formula
in order to calculate the possibility of failure of the relays used in the application.
The MTTF value of solid-state relays is calculated using the parts counting
method, based on the basic failure rates from SN29500. This is possible because
a solid-state relay is not subject to mechanical wear, meaning that the statistical
failure values of the individual components within the solid-state relay can be
added together. Electrical connections and plug-in connections were not taken
into account when calculating the values specied in the data sheet.
The failure rates of electronic components increase considerably after approx. 8
to 12 years, causing the MTTF values to decrease (see EN 61508-2: 2011-02,
7.4.9.5, Note 3).
x x
EMR = Electromechanical relay
SSR = Solid-state relay
Glossary: Relay modules and Solid-state relays
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Technical appendix/Glossary
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