Thermcraft XST-3-0-36-3V - Manual (Page 42)

Installation Installation and Operation Handbook
1-12 2408 and 2404 Controller
Wiring of 2-wire EIA-485 serial communications link
Com
Note:
All resistors are 220 ohm 1/4W carbon composition.
Local grounds are at equipotential. Where equipotential is not available wire into
separate zones using a galvanic isolator.
Use a repeater (KD845) for more than 32 units.
A
B
PC
Eurotherm Universal
Communications Interface
KD485
RX TX Com
Com TX RX
Up to 32 S2000 controllers or
Interface Units may
be included on the network
232
Com B A
Com
A
B
Com
A
B
Com
A
B
Local Earth
Local
Ground
Zone 1 Local
Ground
Zone 2
Area 1 Com
A
B
E
F
D
Local
Earth
HE
HF
HD
Series 2000
Controller
HE
HF
HD
Series 2000
Controller
For reasons of safety
do not connect to
local earth here.
Local
Earth
Local
Earth
Local
Earth
Local
Earth
Local
Earth
HE
HF
HD
Series 2000
Controller
Galvanic
Isolation
Barrier
Local
Ground
Zone 1
Local
Ground
Zone 1
Local
Ground
Zone 1
Figure 1-9 EIA-485 wiring
2-wire EIA-485 is a connection which allows up to 32
controllers to be multi-dropped from a single communications
link over a distance of up to 1.2Km. To ensure reliable
operation of the communications link, (without data
corruption due to noise or line reflections) the connections
between the controller should be made using a twisted pair of
wires inside a screened cable with the connections
terminated with resistors in the manner shown in this
diagram. This diagram also shows the use of a KD485
converter to connect the EIA-485 link into a standard EIA-232
computer port.