Contrel EMA90, User Manual, Page: 27 / 64

EMA90 - USER MANUAL
-27-
8.4.2) RS485 CONNECTION NOT SHIELDED
Once a RS485 network has been configured; to communicate between the Host (computer) and the
instrument(s) (EMA) a serial interface converter must be wired between PC and instrument(s) as
mentioned on the above picture.
In serial line over 500 mt, connect a line termination resistor (Rt=100
Ω
- 120
Ω
) between the two
twisted pair cables leading from the converter at the end of the network (last connected instrument).
It’s recommended to use always twisted pair cable with minimum cross-section of 0.36mm
2
(22AWG)
and capacity less than 60 pF/m.
8.4.3) RS485 CONNECTION SHIELDED
Although the signal is given by the difference between A and B voltage, a ground connection is
needed to eliminate or to reduce the common mode noise induced (into the bus).
To reduce the EMI interferences need to connect the shield directly to a ground at one end and with a
series RC network at the other end.
R = 100
Ω
C = 33µF.
The max length of the stubs is 20cm.
RS232/RS485
converter
Max 32 EMA; max 1200
N
L N
S1 S2 S1 S2 S1 S2
I1 I2 I3
L1V
L2V
L3V
Vaux
Do2-
Do2+
D
i1
+
D
i1
-
D
i2
+
D
i2
-
CE
N
L N
S1 S2 S1 S2 S1 S2
I1 I2 I3
L1V
L2V
L3V
Vaux
Do2-
Do2+
D
i1
+
D
i1
-
D
i2
+
D
i2
-
CE
D
i1
+
D
i1
-
D
i2
+
D
i2
-
D
i1
+
D
i1
-
D
i2
+
D
i2
-
A
B
D
o
1
-
D
o
1
+
A B D
o
1
-
D
o
1
+
A
B
D
o
1
-
D
o
1
+
A
B
D
o
1
-
D
o
1
+
T
x
R
x
g
n
d
T
x
R
x
g
n
d
T
x
R
x
g
nd
T
x
R
x
g
nd
Rt
Max 32 EMA; max 1200 mt
RS232
A
B
D
i1
+
D
i1
-
D
i2
+
D
i2
-
A B D
i1
+
D
i1
-
D
i2
+
D
i2
-
A B
N
L N S1 S2 S1 S2 S1 S2
I1 I2 I3
L1V
L2V
L3V
Vaux
Do2-
Do2+
D
i1
+
D
i1
-
D
i2
+
D
i2
-
A
B
CE
N
L N S1 S2 S1 S2 S1 S2
I1 I2 I3
L1V
L2V
L3V
Vaux
Do2-
Do2+
D
i1
+
D
i1
-
D
i2
+
D
i2
-
A
B
CE
D
o
1
-
D
o
1
-
D
o
1
+
D
o
1
+
D
o
1-
D
o
1+
D
o
1-
D
o
1+
RS232/RS485
converter
T
x
T
x
R
x
R
x
g
n
d
g
n
d
Tx R
x
gn
d
Tx R
x
gn
d