Hanna Instruments HI 504, Инструкция по эксплуатации

Страница: 58 / 116

58
CONNECTIONS
The connections for the 6-pin RS485 terminal provided
are as follows:
There is an internal short between the two A pins and be-
tween the two B pins .
The instrument has no internal line termination . To terminate
the line, an external resistor equal to the characteristic line
impedance (typically 120
Ω)
must be added at both ends
of the line .
The RS485 can connect up to 31 HI504 on the same
physical network . All the units are slave devices and are
monitored and controlled by a single master station (typi-
cally an industrial PLC or PC) .
Each
HI504 unit is identified by its Process ID number,
included in the 00 to 99 interval, which corresponds to the
Process ID configured through the setup item G .11 .
(If the instrument does not recognize the address within the
command string, then it discards all the following bytes) .
As additional feature, the controller is also provided with
two pins (5V and GND) in order to apply the Fail Safe
Open Line protection method . To avoid erroneous readings
in Open-Line conditions, pull-up and pull-down resistors
should be connected as shown .