Rs-232C Interface Configuration; Current Loop Configuration - Hach EC1000 Instruction Manual

7.2 RS-232C Interface Configuration

Note: Shield ground is
normally tied at one end
of cable only (prevents
ground looping).
Note: If the lines can be
disabled through hardware
or software, then this
jumper is
not needed.

7.3 Current Loop Configuration

The RS-232C interface configuration is suitable in cases where the distance between the
analyzer and an external device is relatively short (50 feet or less). Longer distances make
the interface connection vulnerable to electrical interference and data transmission errors.
For distances longer than 50 feet use the current loop configuration. To select the RS-232C
format, jumper No. 2 must be set to the closed position and jumper No. 1 must be open
(Figure 22, and Table 8).
Jumper No.
Position
Connections are made at TB1 on the serial interface board (Figure 18 on page 64 and
Figure 22). For typical RS-232C connections from the instrument to an IBM personal
computer, and the two most common cable configurations, see Figure 22.
If some other system is used to communicate with the instrument, see Table 6 on page 47
and Table 9 for generic cable configuration and definition of terms. Because there is no
handshaking with the pH meter, the RTS and CTS lines must be jumpered at the host
computer. The DSR and DTR lines also must be jumpered at the host computer. If these
lines can be disabled through hardware or software at the host computer, the jumpers are
not required.
Jumper No. Function
1 Selects current loop interface
2 Selects RS-232C interface
3 Selects analyzer as the output voltage source in current loop mode
4 Selects analyzer as the input source in current loop mode
A current loop interface configuration is used to transmit data over longer distances via a
twisted-pair cable with each pair individually shielded.
The current loop interface mode is selected by placing jumper No. 1 in the closed position
and jumper No. 2 in the open position (Figure 23 and Table 10). X's are based on current
loop sourcing; see Table 11. Connection in the current loop configuration is made using
posts 4 through 7 of TB1 on the circuit board. There is no standard format for connector
pin use in a current loop configuration; the user must wire connectors and cables as
required for the individual installation.
Table 10 Jumper Settings for Current Loop
Jumper No.
Position
In the recommended connection configuration, the voltage source for both the input and
output loops is provided by the external computer or printer interface. This configuration
provides an optical isolation between the analyzer and the current loop. In the second
connection configuration, the analyzer is set up to provide both of the voltage sources.
Table 8 Jumper Settings for RS-232C
1 2
open closed
Table 9 Dip Switch Descriptions
1 2
closed open
77
3 4
open open
3 4
X X