Earth Ground - IDTECK ITDC ITDCSR EIO88 User Manual

IDTeck – iTDC 2~4 DOOR ACCESS CONTROLLER
after the leading edge of a bit. Since the data bit is captured in the middle of the bit, which is
approximately 52us after the leading edge of a bit. The reflection stabilizing time 18.6us is much before
the centre of the bit therefore the termination 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 can be used for termination resistor
in parallel between the receiver lines "A" and "B" for 2 wires RS485 system or "RX+" and "RX-" for 4
wires RS422 system. A termination resistor of less than 90Ω should not be used and no more than 2
terminations should be used in one networking system.
4.2.2 HOW TO CONNECT TERMINATION RESISTORS
Figure: Termination resistors for 2 wire RS485 communication system
Figure: Termination resistors for 4 wire RS422 communication system
4.2.3 GROUNDING SYSTEM FOR COMMUNICATION CABLE
We recommend to using proper grounding system on the communication cable. The best method for
grounding system is to put the shield wire of the communication cable to the 1
however it is not so easy to bring the earth ground to the communication cable and also the installation
cost is raised.
There will be three grounding point where you can find during installation;

1) Earth Ground

2) Chassis Ground
3) Power Ground
The most important point for grounding system is not to connect both ends of shield wires to the
grounding system; in this case there will be a current flow through the shield wire when the voltage level
of both ends of shield wire is not equal and this current flow will create noise and interfere to
communications.
101-001 (iTDC), 101-002 (EIO88), 101-145 (iTDCSR) -16-
st
class earth grounding;
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