Yokogawa DR240 - Manual (Page 24)

3-5 IM DR231-11E
Overview and Specifications of RS-422-A/RS-485 Interface
3
In the case of two-wire system
Connect send and receive terminals with the same signal polarity on the terminal arrangement of the
RS-422-A/RS-485 module. Only two wires are used in connecting to other units.
Terminator (externally applied) 120 ohm, more than 1/2 W
#1
No terminators are inserted between #1 through #n-1 (internal OFF)
RS-422-A/RS-485
module
of the DA100/DR
#2 #n
(#n
≤
31)
Terminator (Internal ON)
Host
Computer
SG
RDB( + )
RDA( - )
SDB( + )
SDA( - )
FG
SG
RD B
RD A
SD B
SD A
(SG)
(B)
(A)
(B)
(A)
FG
SG
RD B
RD A
SD B
SD A
(SG)
FG
SG
RD B
RD A
SD B
SD A
(SG)
(B)
(A)
(Diagram below shows the case when the port of the host computer is RS-232-C)
Terminator (externally applied) 120 ohm, more than 1/2 W
#1
No terminators are inserted between #1 through #n-1 (internal OFF)
RS-422-A/RS-485
module
of the DA100/DR
#2 #n
(#n
≤
31)
Terminator (Internal ON)
FG
SG
RD B
RD A
SD B
SD A
(SG)
(B)
(A)
(B)
(A)
FG
SG
RD B
RD A
SD B
SD A
(SG)
FG
SG
RD B
RD A
SD B
SD A
(SG)
(B)
(A)
SHIELD
RD( + )
RD( - )
TD( + )
TD( - )
Host
Computer
Converter
Z - 101HE
(SHARP)
RS-232-C
Note
• The method in eliminating noise depends on the condition in which it is used. In the example, shielded cable is grounded
only at the DR (one-sided grounding). This method is effective in eliminating noise in long distance communication in
which there is potential difference between the ground of the PC and the ground of the DR. When there is no potential
difference between the ground of the PC and the ground of the DR, grounding both sides (two-sided grounding) is some-
times effective. In addition, there are cases when grounding both sides with one side having a capacitor connected in series
is effective.
Consider all the above cases in eliminating the noise.
3.3 RS-422-A/RS-485 Interface Connection