IDENT-I • IVI-KHA6-4HRX, IVI-KHD2-4HRX
Serial interface/DIP switches
Subject to reasonable modifications due to technical advances. Copyright Pepperl+Fuchs, Printed in Germany
epperl+Fuchs Group • Tel.: Germany (06 21) 7 76-0 • USA (330) 4 25 35 55 • Singapore 7 79 90 91 • Internet http://www.pepperl-fuchs.com
Date of issue 27.08.2001
13
5.2 RS 422 and RS 485 interfaces
With these two standards, the data signal is defined as the voltage differential be-
tween two conductors. Since possible interferences have the same effect on both
conductors, provided a tightly twisted pair is used, a more secure data transmission
is obtained than with the RS 232 interface, particularly at high transmission rates.
The RS 422 standard provides a symmetrical four-wire connection that is insensitive
to interference. The transmit and receive lines are separate, so that full duplex oper-
ation is possible.
With the RS 485 standard, the transmit and receive lines are coupled, permitting half-
duplex operation only. The transmitter is disabled to allow the receipt of data. The abil-
ity of multi-point connections is not implemented in the control interface unit.
Connection details are shown in the diagram on page 3. Terminals 15 to 18 should be
used for the RS 422. For the RS 485, Terminals 17 and 18 should be connected.
5.3 20 mA current loop or TTY interface
The TTY interface was originally designed for teletype control. Two pairs of conduc-
tors are used, one to send, and one to receive data.The data can be transferred in full
duplex mode, which is not supported by the control interface unit. Current loop trans-
mission is very resistant to interference and therefore offers secure data transmission,
even where long lengths of cable are used.
The current loop connections of the control interface unit are galvanically isolated by
opto-couplers. The control interface unit represents the passive side of the transmis-
sion, i.e. the current and voltage required for transmission must be provided at the
other end.
5.4 Connection cables
The maximum cable length between the control interface unit and the host computer
will vary according to the data transmission speed, the interface standard and the lev-
el of interference. For this reason it is only possible to give approximate values:
A screened twisted twin-core cable with a minimum wire cross-section of 0.14 mm
2
should be used for the connection.
The screen of the read head lead is connected on both sides to earth (PE) with low
resistence and low induction. For that the attached terminal block can be used (see
figure 5.3). Please make sure that the screen is kept as small as possible.
Standard Max. cable length
RS 232 15 m
RS 422 1000 m
RS 485 1000 m
20 mA current loop 1000 m
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