Specifications

Devices Emitting high EMF Minimizing EMI: System Design Guidelines
8 VisiLogic: Getting Started
Minimizing EMI: System Design Guidelines
Before you design your control system, please read the following guidelines:
U
nitronics products are designed to operate in a typical industrial environment.
These guidelines show you how to design your system for optimal performance
in noisy environments.
After installation, check your system periodically, in particular after installing
new machinery close to the system.
Devices Emitting high EMF
High voltage, high current, and high frequency circuits such as high voltage /
high current power supplies, high power converters and amplifiers, contactors
and solenoids, motors and motor-drives may cause severe electro-magnetic
disturbances that may affect the operation of other nearby computerized
devices such as PLCs or I/O modules.
Such high voltage, high current, and high frequency circuits should not
share the same cabinet with PLCs or I/O modules.
If this is unavoidable, within the cabinet, either:
1. Physically separate these sources from PLCs and I/O modules with large
metal earthed plates. Such a plate should be large enough to partition the
cabinet into two cubicles.
2. Separate these sources and their cabling from PLCs and I/O modules as
described in the section Wiring Separation.
Wiring Separation
Use separate wiring ducts for each of the following groups:
1. Digital inputs, digital outputs, 24VDC (power supply for the PLC and I/O
Expansion Modules), communications, analog inputs, and analog outputs.
2. Lines that are connected to the power grid, 230/115, 24VAC, all AC lines
such as motor driver outputs, noisy DC lines such as DC servo drives and
motors.
Separate these groups by at least 10cm (4"). If this is not possible, cross
the ducts at a 90J angle.
Enclosing and Earthing
1. It is recommended to install the PLC and I/O modules in a closed metallic
cabinet. This will significantly improve interference immunity.
2. Make sure that the cabinet and cabinet door are properly earthed. Please
refer to the cabinet manufacturer instructions for proper installation and
earthing.
3. When you earth devices, minimize wire impedance by using a wire that is
as short and thick as possible, 3.3mm
2
(12 AWG), up to 10cm long
recommended. Connect the line to nearest possible grounding point in the
cabinet, preferably a grounding plate or the cabinet body. Be sure to
remove any paint or other non-conductive coating between the wire
terminal and metal as this may cause poor conduction.