NIM2-MAN-19V01 (1104)
Copyright © 2019 Define Instruments
9
4.4 - EMC Installation Guidelines
The Nimbus IoT has been designed to cope
with large EMC disturbances.
This has been
achieved by continual testing and improve-
ment of filtering and layout techniques.
The Nimbus IoT meets CE noise requirements,
and even surpasses them in many tests. (For
full details and test results, see Appendix
A.) However in some applications with
less than optimum installations and large
power switching, the EMC performance
of the unit can be further improved by:
A
Installing the unit in an earthed
Metal
Enclosure
(as in Fig 2). This is particular-
ly useful if the control box is mounted
close to large power switching devices
like contactors. Every switching cycle
there is a possibility of generating a
large amount of near field radiated
noise. The
Metal Enclosure
, acting as
a faraday cage, will shunt this radiation
to ground and away from the unit.
B
Increasing the physical distance from
the power devices. For example, in-
creasing the control box distance from
6" to 12" from the noise source will re-
duce the noise seen by the control box
by a factor of 4. (Probably the cheapest
and best results in this situation could
be obtained by adding RC snubbers to
the contactors or power switches.)
C
Using shielded cable on sensitive input
and control signal lines. Good results
can be obtained by grounding the
shields to the metal enclosure close to
the entry point. All cables act as aeri-
als and pick up unwanted R.F. radiated
signals and noise; the earthed shield
acts as a faraday cage around the ca-
bles, shunting the unwanted energy to
ground.
Shields can also help with capacitively
coupled noise typically found in circum-
stances when signal cable is laid on top
of noisy switching power cables. Of
course in this case you are better off to
keep separate signal and power lines.
D
Laying cable on earthed cable trays
can also help reduce noise seen by the
Nimbus IoT. This is particularly useful if
there are long cable runs, or the unit is
close to radiating sources such as two
way radios.
E
Relay A's outputs have built in MOV's to
help reduce EMI when switching induc-
tive loads. EMI can further be reduced
at the load by adding snubbers for AC
signals or a flyback diode for DC coils.
E - Removal from DIN Rail
(Fig 4)
To unclip the unit from the DIN rail, power
the unit down and remove the power
connector.
Then insert a small screwdriver into the slot
on the red hook (just visible when the power
connector is removed), and lever it down.
This will release the hook, allowing the unit
to be detached from the
DIN rail
.
Fig 4
