Before you design your control system, please read the following guidelines:
Unitronics 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.
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:
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.
Separate these sources and their cabling from PLCs and I/O modules as described in the section Wiring Separation.
Use separate wiring ducts for each of the following groups:
Digital inputs, digital outputs, 24VDC (power supply for the PLC and I/O Expansion Modules), communlications, analog inputs, and analog outputs.
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 90˚angle.
It is recommended to install the PLC and I/O modules in a closed metallic cabinet. This will significantly improve interference immunity.
Make sure that the cabinet and cabinet door are properly earthed. Please refer to the cabinet manufacturer instructions for proper installation and earthing.
When you earth devices, minimize wire impedance by using a wire that is as short and thick as possible, 3.3mm2 (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.
Route each I/O signal / signal-group along
with a dedicated common wire (e.g. 0V). This serves as a signal return
path and increases interference immunity.
Connect common wires at the respective common pins of the module where
the specified I/O port is located. Please refer to the module installation
guide for details.
For all types of analog and high-speed I/Os:
Use shielded twisted pair cable
Do not use the shield as a signal or as a return conductor
Ground the shield at the closest grounding
point to the I/O port, preferably a grounding plate or the cabinet
body.
This connection method usually gives the best interference immunity.
However, in some cases, grounding the shield at both ends of the cable
is preferable. In this case, be sure that both points have the same
potential in order to eliminate ground currents through the shield.
Route those signals separately from high voltage / high current and AC wiring, as explained in the section Wiring Separation.
Some environments may induce greater EMI than the typical industrial environment. Extra power and/or signal line filtering may improve the system’s immunity to EMI.
If signal-line filtering is required, please use the following guidelines in addition to the guidelines provided by the filter manufacturer:
Place the filter as close as possible to the target device(s); maximum wire length is 10 cm.
Signal lines can be filtered using rounded ferrite cores. To maximize their effect, wind the wire through the ferrite core multiple times to attentuate high frequencies as shown below.
Always pass both the signal and signal return
wires thru the ferrite core.
If multiple I/O lines share the same common return wire, pass all of
these I/O lines and their return wire through the same ferrite core.
The examples below are based on the EX-A1.
If
the power-supply is closer to the PLC than it is to the module’s power
supply (EX-A1):
- Create 0V and 24V junctions
at the PLC respective terminals (see the following figure) and directly
connect the PLC main supply lines to the EX-A1.
- Continue daisy-chaining the supply lines to the expansion I/O units.
Please ensure that the wire segment which carries the 0V between
the EX-A1 and the PLC does not branch.
When the power-supply
is near the PLC, connect the PLC first as shown in the next figure.
If
the power-supply is closer to the EX-A1 than it is to the PLC:
- Create 0V and 24V junctions
at the EX-A1 respective terminals (see the following figure) and directly
connect the EX-A1 main supply lines to the PLC.
- Split the supply lines at the EX-A1 terminals and continue daisy-chaining
them to the expansion I/O units.
Please ensure that the wire segment which carries the 0V between
the EX-A1 and the PLC does not branch.
When the power-supply
is near the EX-A1, connect the EX-A1 first as shown in the next figure.
Some environments
may induce greater EMI than the typical industrial
environment. Extra power and/or signal line filtering may improve the
system’s immunity to EMI.
If power-line filtering is required, please
use the following guidelines in addition to the guidelines provided
by the filter manufacturer:
Use of power-line filters that comprise an earthing terminal is recommended. Ground the filter earth terminal as explained in the section Enclosing and Earthing.
Place the filter as close as possible to the target device(s). The maximum wire length is 10 cm.
When using the EX-A1 expansion adapter:
Place one filter
for both the PLC and the EX-A1 as instructed below.
Please note that you must use a single line filter for both
the PLC and EX-A1.
If the power-supply is closer to
the PLC than it is to the EX-A1:
- Install and connect the power-line filter as close as possible to
the PLC. The maximum wire length is 10 cm. Please refer to the
filter manufacturer documentation for installation information.
- Create 0V and 24V junctions
at the PLC respective terminals (see the following figure) and directly
connect the PLC main supply lines to the EX-A1.
- Continue daisy-chaining the supply lines to the expansion I/O units.
Please ensure that the wire segment which carries the 0V between
the EX-A1 and the PLC does not branch.
When the power-supply
is near the PLC, connect the PLC first as shown in the next figure.
If
the power-supply is closer to the EX-A1 than it is to the PLC:
- Install and connect the power-line filter as close as possible to
the EX-A1. The maximum wire length is 10 cm. Please refer to
the filter manufacturer documentation for installation information.
- Create 0V and 24V junctions
at the EX-A1 respective terminals (see the following figure) and directly
connect the EX-A1 main supply lines to the PLC.
- Split the supply lines at the EX-A1 terminals and continue daisy-chaining
them to the expansion I/O units.
Please ensure that the wire segment which carries the 0V between
the EX-A1 and the PLC does not branch.
When the power-supply is
near the EX-A1, connect the EX-A1 first as shown in the next figure.
Note that the communication cable is ended by RJ45 plugs. The plug comprising a yellow-green grounding wire must be connected to the PLC as shown in the following figure.
This yellow-green wire must be grounded to
the metal door panel or cabinet body (which must be also well grounded)
using a screw. There cannot be any paint or other non-conductive coating
between the wire terminal and metal as this may cause poor conduction.
DO NOT extend the wire.
