User Guide

59
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 120Ω) must be added at both ends of
the line.
The RS485 can connect up to 31 HI 504 on the same physi-
cal network. All the units are slave devices and are monitored
and controlled by a single master station (typically an indus-
trial PLC or PC).
Each HI 504 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-