3590EKR, 3590EXP, 3590EXT, 3590 EBOX, CPWE, CPWET series indicator E-AF03_05.01_14.07_EN_T.doc
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This implies that
the maximum distance can not be covered with the maximum possible speed
. For an
approximate value, one can consult the following table:
Baud rate
Total capacity of
the cable (pF)
1200
400000
2400
200000
4800
100000
9600
50000
19200
25000
38400
12000
57600
8000
115200
4000
As a general rule, if one has any doubts, it is always preferable to
choose the cable with a greater section.
Verify that the grounding satisfies the requirements of section 1.2. Especially, all the digital masses, as well as the
analogue masses, and the power circuits, must be connected to the grounding bar and this last one must be
connected to the grounding pole.
The shielding can be connected into a single point of the entire network (as shown in Figure 1) or both its ends,
however it’s important that
all the masses have the same potential
, in order to avoid the forming of current rings.
On the RS485 network normally one connects 2
termination resistances
equal to the characteristic impedance of the
cable (tipically 120 Ω, see Figure 1),
ONLY
on the 2 devices
which are at the 2 ends of the ring connection
(for
example indicator and last device). The terminal resistance is not supplied with the ports of the indicator.
The difference of potential between the A(+) and B(-) terminals in rest conditions (for example with instrument in set-up
phase),
must be of at least 0,2 V
.
To create a resistive divider which maintains this difference of potential also when all the transmitters are disabled,
inert in the RS485 port of the indicator where there are the termination resistances, the
polarisation
or
fail-safe
resistences
(R
FS
in Figure 1). The value of these resistances is between 390 Ω and 2,2 kΩ.
NOTE: in particular, the value of each of these resistances must be greater than the value calculable through the
formula:
1
2
,
0
2
dc
eq
FS
V
R
R
in which:
V
dc
is the power supply voltage of the line
R
eq
is the overall resistance to the A(+) a B(-) heads, supplied by the parallel of the 2 termination
resistances and all the input resistances of the devices connected to the bus.
EXAMPLES:
-
Presuming that a connection has 120 Ω as termination resistance and 32 connected devices, each having
an input impedance of 12 kΩ. The V
dc
power supply is 6 V.
One calculates R
eq
, equal to about 52 Ω, and R
FS
which must be at least equal to 754 Ω.
-
Presuming that a connection has 120 Ω as termination resistance and 32 connected devices, each having
an input impedance of 12 kΩ. The V
dc
power supply is 12 V.
One calculates R
eq
, equal to about 52 Ω, and R
FS
which must be at least equal to 1534 Ω.
The connection between the indicator and the digital load cells is made with RS485 protocol in the COM3
configured as CoMAuX.
The indicator can be connected with up to 16 digital load cells.
It’s possible to connect the indicator to digital load cells with 485 4-wire protocol through 422/232 converter. In this
case one is required to connect the double TX of RS422 cable to TX+ and TX- converter’s pins and the double RX of
RS422 cable to RX+ and RX- converter’s pins
