IDTECK GE313, Operating Manual

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4.1.2 CABLE SELECTION TABLE
Reference Description Cable Specification Maximum Distance
①
GE313 Power (DC12V)
DC Power -> GE313
Belden #9409, 18 AWG
2 conductor, unshielded
Belden #9512, 22 AWG
4 conductor, shielded
②
Reader (Power and Data)
Exit Reader -> GE616 Belden #9514, 22 AWG
8 conductor, shielded
Belden #9512, 22 AWG
4 conductor, shielded
③
Door Contact
Exit Button
Sensor Input
Input -> GE313
Belden #9514, 22 AWG
8 conductor, shielded
④
Door Lock, Alarm Device
Lock (Alarm) -> GE313
Belden #9409, 18AWG
2 conductor, unshielded
⑤
RS232 Cable
Converter -> Host P.C.
Belden #9829, 24 AWG
2-twisted pair, shielded
⑥
RS485 Cable
GE313 -> GE313
GE313 -> Converter
Belden #9829, 24 AWG
2-twisted pair, shielded
P
+
P
: Need thicker wire if you connect the reader with high current consumption.
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4.2 CHECK POINT DURING THE INSTALLATION
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4.2.1 TERMINATION RESISTOR
Termination resistors are used to match impedance of the network to the impedance of the transmission line
being used. When impedance is mismatched, the transmitted signal is not completely absorbed by the receiver
and a portion of signal is reflected back into the transmission line. The decision whether or not to use termination
resistors should be based on the cable 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 velocity of cable is 0.66 x speed of light
(This value is specified by the cable manufacturer), if we assume the reflections will damp out in three round trip
up and down the cable length, the transmitted signal will stabilize 18.6us 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 center 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 120
Ω resistor can be used for termination resistor in
parallel between the receiver lines “A” and “B” for 2 wires RS485 system. A termination resistor of less than
90
Ω should not be used and no more than 2 terminations should be used in one networking system.