23
Maximum Cable Lengths
USER GUIDE
SMART-NET NETWORK TOPOLOGY
SMART-SENSOR
™
2004 – 2014 Reliable Controls
®
Corporation. All rights reserved.
MAXIMUM CABLE LENGTHS
The total combined cable length of a SMART-Net
™
from the controller, including any daisy-
chained SSs, to the final SS should not exceed 80 meters (250 ft). The actual maximum
functional network length can vary based on the type of cable used. For longer networks
and total cable length, use appropriate data cable with a lower resistance and capacitance
per meter (foot). Installing one or more SSX modules will also increase the number of SSs
and total cable distance that can be installed (further details on the SSX are supplied later
in this section).
The following formulas can be used to calculate the maximum length of selected cable.
R
max
=
V
max
D=
R
max
I
max
R
c
Where: D = distance in meters
R
max
= maximum total cable resistance
R
c
= resistance per meter of cable
V
max
= maximum voltage drop (= 0.5 VDC)
I
max
= maximum current
0.03 A per SMART-Sensor
™
LED
0.005 A per SMART-Sensor
™
LCD
0.015 A per SS with backlight
0.002 A per SS with CO
2
Poor modular connector installation, high-resistance connections or excessive cable length
may cause the SMART-Net
™
voltage to drop below the minimum necessary for SS
communication. If this occurs, a Power Lo message may appear on the screen of the
affected SS-L. On an SS model with no LCD screen, the Test LED will remain solid off when
connected if it does not have sufficient voltage.
The recommended wire type is Category 3 or 5, 24AWG solid core. This allows the flexibility
of connecting RJ11 crimp connectors, but still works well for the terminal blocks.
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