Hitachi HIDIC EH-150 Applications Manual page 20

3.2.2 Restrictions on Connection Configuration
1] Restrictions on maximum network length
The maximum network length refers to the distance between the devices that are farthest apart or the
longest of the trunk line distances (between termination resistors).
Termination
resistor
Drop line
The communication cables in the network can be either of the two types: thick cable (trunk cable) or thin
cable (drop cable).
There is only a slight signal damping in a thick cable, thus it can be used for communication over
relatively long distances.
On the other hand, the signals tend to be attenuated in a thin cable; this type of cable is thus not suited
for communication over long distances.
The following tables list each cable specification and the restriction values corresponding to the
communication speeds.
Refer to the page 3-4 and 3-5 for definition of drop line length , total drop line length.
Thick cable
Recommended
manufacturer
Type
Configuration
Specifi
Size (AWG)
cation
Standard outer
diameter (mm)
Baud Rates
125 kbps
250 kbps
500 kbps
2] Restrictions when the trunk line is composed of both thick and thin cable
It is possible to combine both thick and thin cables to construct the trunk line.
However, the length of each cable type must satisfy the following relations.
In addition, if both types of cables are used, note that the value should not exceed the maximum current
capacity of each cable (Refer to the chapter 12).
Baud Rates
125 kbps
250 kbps
500 kbps
L (thick): Length of thick cable
L (thin): Length of thin cable
Device Tap
Communication
power supply
Device
Table 3.2 Cable specification
Showa Electric Wire &
Cable Co., Ltd.
TDN18
Power supply
Signal pair
18
Approx. 11.6
Table 3.3 Restriction values by the baud rates
Maximum network length
Thick cable
500 m max.
250 m max.
125 m max.
Table 3.4 Maximum network length
Maximum network length
L (thick) + 5 × L (thin) < 500 m
L (thick) + 2.5 × L (thin)
L (thick) + L (thin)
Trunk line
The longer of the two becomes
the maximum network length.
Thin cable
Recommended
manufacturer
Configuration
pair
Specifi
14 Size (AWG)
cation
Standard outer
diameter (mm)
Drop line length
Thin cable
100 m max. 6 m max.
100 m max. 6 m max.
100 m max. 6 m max.
< 250 m
< 100 m
3-4
Chapter 3 System Configuration
Device
Showa Electric Wire &
Cable Co., Ltd.
Type TDN24
Signal pair
24
Approx. 7.0
Total drop line
length
156 m max.
78 m max.
39 m max.
Termination
resistor
Power
supply pair
22