Series PC Manual V 1.0 - Rev. 3
– 03/01/01
DS Europe
22
10.7. SERIAL PORT CONNECTION
To set up RS485 serial output connection to a remote unit, such as a computer or PLC, it
is necessary to know specific connection layout of the chosen serial card interface (RS-
485) because there is no standard connection.
figure 10
: Connection of the transducer to a remote unit (Computer)
In
figure 10
there is an example of connection to an RS485 serial port of a computer.
Connect the DATA + and DATA – wires to the terminal board.
Check carefully, referring to the RS485 card manuals (for the computer or for PLC), that
DATA + of the transducer is connected to the DATA + of the remote unit, and likewise the
DATA – of the transducer is connected to DATA – of the remote unit.
The best immunity to interference, for an RS485 serial connection, is obtained by using
100% shielded connection cables made by twisted pairs.
In addition, if necessary, use cables with double shielding.
In case of cables with double shielding, it is preferable to connect the shields to ground so
that the internal shield is connected to ground at on end (towards the transducer, for
example) and the external shield is connected to ground at the opposite end (towards the
computer, for example). This procedure must also be done when the interconnection cable
is passing through metal conducts in order to obtain more efficient shielding.
Whenever necessary it is also wise to consider the use of opto-insulators for serial lines.
The overmentioned considerations, however, are always to be assessed with respect to
the specific application used and are only indicative.
Should you not succeed in stabilising the connection between the computer and
transducer:
1. Try inverting the DATA + signals with the DATA – signals and vice versa;
2. Check all connections to the other units on the data line, if present;
3. Make sure the maximum interconnection length has not been exceeded;
4. Check that the parameters of the serial communications port (computer) correspond to
those indicated in chapter 9.7;
5. Check computer serial port performance using another computer (also fitted with
RS,485 MULTI-DROP interface)
