Red Lion PXU - Manual (Page 5)

55
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 at http://www.redlion.net/Support/InstallationConsiderations.
html for more information on EMI guidelines, Safety and CE issues as they
relate to Red Lion Controls products.
1.0 s
eTTing The
C
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i
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J
umper
When Input Type is selected as one of the two current input types (0-20 or
4-20), the current input jumper must be installed. The current input jumper is
factory set for Temperature and Voltage input types. To change the jumper to
configure the input for a current input type, the inside of the unit must be
accessed and the jumper position changed.
To access the jumper, locate the two latches located on top and bottom of the
front of the unit. Starting with the top latch, insert a small flat-blade screwdriver
between the case latch and bezel while using your thumb to push out on the
bezel until the latch is disengaged. Repeat this process with the bottom latch.
After the latches are disengaged, using the flat-blade screwdriver, gently pry out
on the bezel in several areas until the unit releases from the case.
Look for the Current Input Jumper which will be located close to the pc board
area that connects to the input terminals. If a current input type is desired,
position the jumper across both pins. If input type is anything other than a
current input, position the jumper on only one pin.
JUMPER
PIN HEADER
JP8
FACTORY SETTING
Thermocouple, RTD
or Voltage Input
JUMPER
PIN HEADER
JP8
Current Input
(4-20 mA or 0-20 mA)