How To Connect Termination Resistors; Grounding System For Communication Cable - IDTECK LX505 User Manual

completely absorbed by the receiver and a portion of signal is reflected back into the transmi
ssion line. The decision whether or not to use termination resistors should be based on the c
able length and data rate used by the communication system.
For example, if you use 9,600 baud rate and 1,200m length of cable, the propagation veloci
ty of cable is 0.66 x speed of light (This value is specified by the cable manufacturer), if we a
ssume the reflections will damp out in three round trip up and down the cable length, the tr
ansmitted signal will stabilize 18.6us after the leading edge of a bit. Since the data bit is cap
tured in the middle of the bit which is approximately 52us after the leading edge of a bit. Th
e reflection stabilizing time 18.6us is much before the center of the bit therefore the termin
ation resistors are not required.
However, if you install the cable to maximum length, the impedance of cable and network is
mismatched and the transmitted signal is overlapped by the reflected signal. In this case, it is
recommended to add termination resistors to the end of the receiver lines. A 120Ω resistor c
an be used for termination resistor in parallel between the receiver lines "A" and "B" for 2 wir
es RS485 system. A termination resistor of less than 90Ω should not be used and no more th
an 2 terminations should be used in one network system.
2.2

How to Connect Termination Resistors

2.3

Grounding System for Communication Cable

통신 케이블을 올바른 접지 시스템의 사용을 권장 합니다.
We recommend you to use a proper grounding system for the communication cables. The b
est grounding method is to put the shield wire of the communication cable to the 1st class e
arth grounding; however bringing the earth ground to the communication cable isn't easy a
nd the installation cost increases. There are three grounding points you can find during insta
llation;
1. Earth Ground
2. Chassis Ground
3. Power Ground
The most important point about grounding system is not to connect both ends of shield wir
p.16 Installation Tips & Check Points