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Technical Information – Relays
Voltage between Conductors vs.
Conductor Pitch
Rated voltage conductors (VDC)
Conductor pitch (mm)
A = w/o coating at altitude of 3,000 m max.
B = w/o coating at altitude of 3,000 m
or higher but lower than 15,000 m
C = w/coating at altitude of 3,000 m max.
D = w/coating at altitude of 3,000 m or higher
C
A
D
B
Temperature and Humidity
PCBs expand or contract with changes in temperature. Should
expansion occur with a relay mounted on the PCB, the internal
components of the relay may be shifted out of operational
tolerance. As a result, the relay may not be able to operate with
its normal characteristics.
PCB materials have “directionality,” which means that a PCB
generally has expansion and contraction coefficients 1/10 to 1/2
higher in the vertical direction than in the horizontal direction.
Conversely, its warp in the vertical direction is 1/10 to 1/2 less
than in the horizontal direction. Therefore, take adequate counter-
measures against humidity by coating the PCB. Should heat or
humidity be entirely too high, the relay’s physical characteristics
will likewise be affected. For example, as the heat rises the PCB’s
insulation resistance degrades. Mechanically, PCB parts will
continue to expand as heat is applied, eventually passing the
elastic limit, which will permanently warp components.
Moreover, if the relay is used in an extremely humid environment,
silver migration may take place.
Gas
Exposure to gases containing substances such as sulphuric acid,
nitric acid, or ammonia can cause malfunctions such as faulty
contacting in relays. They can also cause the copper film of a PCB
to corrode, or prevent positive contacts between the PCB’s
connectors. Of the gases mentioned, nitric acid is particularly
damaging as it tends to accelerate the silver migration. As a
counter-measure against gas exposure damage, the following
processes on the relay and PCB have proved useful.
Item Process
Outer Casing, Sealed construction by using
housing packing, etc
Relay Use of simplified hermetically sealed
type relay, DIP relay, reed relay
PCB, Copper Firm Coating
Connector Gold-plating, rhodium-plating process
Vibration and Shock
Although the PCB itself is not usually a source of vibration or
shock, it may simplify or prolong the vibration by resonate with
external vibrations or shocks. Securely fix the PCB, paying
attention to the following points.
Mounting Position
Depending on where the relay is mounted, the function of the
relay (and the performance of the circuit which includes the relay)
may be adversely affected.
The relay may malfunction if it is mounted near a transformer or
other device that generates a large magnetic field, or much heat.
Provide an adequate distance between the relay and such
devices.
Also, keep the relay away from semiconductor devices, if they are
to be mounted on the same PCB.
Mounting Direction
To allow a relay to operate to its full capability, adequate
consideration must be given to the mounting direction of the relay.
Relay characteristics that are considerably influenced by
mounting direction are shock resistance, life, and contact
reliability.
Shock Resistance
Ideally, the relay must be mounted so that any shock or vibration
is applied to the relay at right angles to the operating direction of
the armature of the relay. Especially when a relay’s coil is not
energized, the shock resistance and noise immunity are
significantly affected by the mounting direction of the relay.
Life
When switching a heavy load that generates arc (generally, having
a greater impedance than that of the relay coil), substances
spattered from the contact may accumulate in the vicinity,
resulting in degradation of the insulation resistance of the circuit.
Mounting the relay in the correct direction is also important in
preventing this kind of degradation of the insulation resistance.
Contact Reliability
Switching both a heavy and a minute load with a single relay
contact is not recommended. The reason for this is that the
substances scattered from the contact when the heavy load is
switched degrade the contact when switching the minute load.
For example, when using a multi-pole contact relay, avoid the
mounting direction or terminal connections in which the minute
load switching contact is located below the heavy load switching
contact.
Correct
Incorrect
Mounting Method Process
Rack Mounting No gap between rack’s guide & PCB
Screw Mounting Securely tighten screw.
Place heavy components such as
relays on part of PCB near where
screws are to be used.
Attach rubber washers to screws
when mounting components that are
affected by shock (such as audio
devices.)
PCB Relays
Omron A5 Catalogue 2007 1-282 11/9/06 10:16 am Page 25