Delta OHM HD45 17A, Manual

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In measurement continuous printing, values are the average computed on a number
of measurements equal to the number set for parameter P#002.
In models supplied also with a RS485 output, both serial outputs can be connected at
the same time, but the transmitters support only one communication channel at a
time. If mini-USB and RS485 outputs are both connected, the mini-USB
output prevails and the instrument replies only to commands sent via USB
connection and not to any commands sent on the RS485 line.
8. RS485 COMMUNICATION
HD45…S… and HD46…S… models are supplied with a RS485 serial output with
MODBUS-RTU protocol. RS485 connection is located in the instrument internal
terminal block (see section “CONNECTION AND INSTALLATION”) and is suitable for
fixed installations.
Thanks to RS485 output, several instruments can be connected to form a network,
consisting of a minimum of 1 instrument to a maximum of 247, connected in a
sequence through a shielded cable with twisted pair for signals and a third wire for
the common.
Fig. 8.A: Connection to RS485 network for HD45 and HD46 models
As shown in figure 8.A, resistors for impedance matching (line terminations) must be
set at the two network ends. To polarize the line during non-transmission periods,
resistors are connected between signal and power supply lines. Polarization resistors
are located in a single point of the line, generally near the “Master” unit.
The cable shield must be connected to both line ends.
The cable should have the following features:
RS232C / RS485
or
USB / RS485
converter
Line
termination
Line
termination