Emc Installation Guidelines; Hardware Installation - Siemens SITRANS RD500 Operating Instructions Manual

EMC INSTALLATION GUIDELINES

Although Siemens 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.
a. The mounting clip that connects to the DIN rail should have the DIN rail
connected to protective earth.
2. Use shielded (screened) cables for all Signal and Control inputs. The shield
(screen) pigtail 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.
c. Connect the shield to common of the module and leave the other end of the
shield unconnected and insulated from earth ground.
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.
Therefore, keep cable runs as short as possible.
HARDWARE
INPUT SWITCHES
Each input is independently configurable for sinking or sourcing signals. A
filter capacitor is also selectable for avoiding contact bounce.
FILTER
SRC/SNK:
8
SRC/SNK
ON-SRC - Connects an internal 10K pull-down
FILTER
7
resistor to common.
SRC/SNK
FILTER OFF-SNK - Connects an internal 20K pull-up
6
SRC/SNK
resistor to +5V.
FILTER
5
SRC/SNK
FILTER
FILTER:
4
SRC/SNK
ON - Connects a capacitor to the input, thereby
FILTER
3
SRC/SNK
reducing the input response to 50 Hz.
FILTER
OFF - Provides maximum input response of 300 Hz.
2
SRC/SNK
FILTER
1
SRC/SNK
ON

HARDWARE INSTALLATION

SEPARATE BASE
FROM MODULE
1
2
MODULE BASE
7ML19985MD01
ATTACH THE MODULE BASE
TO THE DIN RAIL
3
4
SITRANS RD500
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
TDK part number ZCAT3035-1330A
Steward part number 28B2029-0A0
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. 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.
Note: Reference manufacturer's instructions when installing
any EMI suppression device.
7. Also, 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 effect the instrument's operation.
ATTACH MODULE TO BASE
5
MODULE BASE
Page 3