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Siemens SITRANS RD500 Panduan Petunjuk Pengoperasian

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:

SRC/SNK

ON-SRC - Connects an internal 10K pull-down

FILTER

resistor to common.

SRC/SNK

FILTER

OFF-SNK - Connects an internal 20K pull-up

SRC/SNK

resistor to +5V.

FILTER

SRC/SNK

FILTER

FILTER:

SRC/SNK

ON - Connects a capacitor to the input, thereby

FILTER

SRC/SNK

reducing the input response to 50 Hz.

FILTER

OFF - Provides maximum input response of 300 Hz.

SRC/SNK

FILTER

SRC/SNK

HARDWARE INSTALLATION

SEPARATE BASE

FROM MODULE

MODULE

BASE

7ML19985MD01

ATTACH THE MODULE BASE

TO THE DIN RAIL

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

MODULE

BASE

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