Red Lion LEGEND - Manual (Page 42)

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 (RLC part number 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 RLC 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.
RLC 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 RLC’s web site for more information on EMI guidelines, Safety and CE
issues as they relate to Red Lion Controls products.
WIRING CONNECTIONS
The bottom board has a removable terminal block on the left where the power
connections are made. The plug-in relay board also has a removable terminal
block and is located at the bottom right of the unit. The top board has a removable
terminal block where the signal inputs, user inputs, solid state outputs, and serial
communications connections are made. When wiring the unit, remove the
terminal block and use the numbers on the top label to identify the position
number with the proper function. All conductors should meet voltage and current
ratings for each terminal. Also cabling should conform to appropriate standards
of good installation, local codes and regulations. It is recommended that power
supplied to the unit (AC or DC) be protected by a fuse or circuit breaker. Strip the
wire, leaving approximately ¼" bare wire exposed (stranded wires should be
tinned with solder). Insert the wire into the terminal and tighten down the screw
until the wire is clamped in tightly. Each terminal can accept up to two 18-gage
wires. After the terminal block is wired, install it in the proper location at the rear
of the unit. Wire each terminal block in this manner.
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