EMC INSTALLATION GUIDELINES
Although Red Lion Controls products are designed with a high degree of
immunity to Electromagnetic Interference (EMI), proper installation and
wiring methods must be followed to ensure compatibility in each application.
The type of the electrical noise, source or coupling method into a unit may be
different for various installations. Cable length, routing, and shield
termination are very important and can mean the difference between a
successful or troublesome installation. Listed are some EMI guidelines for a
successful installation in an industrial environment.
1. A unit should be mounted in a metal enclosure, which is properly connected
to protective earth.
2. Use shielded cables for all Signal and Control inputs. The shield connection
should be made as short as possible. The connection point for the shield
depends somewhat upon the application. Listed below are the
recommended methods of connecting the shield, in order of their
effectiveness.
a. Connect the shield to earth ground (protective earth) at one end where
the unit is mounted.
b. Connect the shield to earth ground at both ends of the cable, usually
when the noise source frequency is over 1 MHz.
3. Never run Signal or Control cables in the same conduit or raceway with AC
power lines, conductors, feeding motors, solenoids, SCR controls, and
heaters, etc. The cables should be run through metal conduit that is properly
grounded. This is especially useful in applications where cable runs are
long and portable two-way radios are used in close proximity or if the
installation is near a commercial radio transmitter. Also, Signal or Control
cables within an enclosure should be routed as far away as possible from
contactors, control relays, transformers, and other noisy components.
4. Long cable runs are more susceptible to EMI pickup than short cable runs.
5. In extremely high EMI environments, the use of external EMI suppression
devices such as Ferrite Suppression Cores for signal and control cables is
effective. The following EMI suppression devices (or equivalent) are
recommended:
Fair-Rite part number 0443167251 (Red Lion Controls #
FCOR0000)
Line Filters for input power cables:
Schaffner # FN2010-1/07 (Red Lion Controls # LFIL0000)
6. To protect relay contacts that control inductive loads and to minimize
radiated and conducted noise (EMI), some type of contact protection
network is normally installed across the load, the contacts or both. The most
effective location is across the load.
a. Using a snubber, which is a resistor-capacitor (RC) network or metal
oxide varistor (MOV) across an AC inductive load is very effective at
reducing EMI and increasing relay contact life.
b. If a DC inductive load (such as a DC relay coil) is controlled by a
transistor switch, care must be taken not to exceed the breakdown
voltage of the transistor when the load is switched. One of the most
effective ways is to place a diode across the inductive load. Most Red
Lion products with solid state outputs have internal zener diode
protection. However external diode protection at the load is always a
good design practice to limit EMI. Although the use of a snubber or
varistor could be used.
Red Lion part numbers: Snubber: SNUB0000
Varistor: ILS11500 or ILS23000
7. Care should be taken when connecting input and output devices to the
instrument. When a separate input and output common is provided, they
should not be mixed. Therefore a sensor common should NOT be
connected to an output common. This would cause EMI on the sensitive
input common, which could affect the instrument’s operation.
Visit www.redlion.net/emi for more information on EMI guidelines, Safety
and CE issues as they relate to Red Lion products.
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