Rs 485 Communication - Hanna Instruments HI 23 Series Instruction Manual

RS 485 COMMUNICATION

SPECIFICATIONS
CONNECTIONS
46
HI 23xy2 and HI 24xy2 are provided with an RS485 port.
RS485 standard is a digital transmission method that allows
long lines connections. Its differential transmission system
makes this standard suitable for data transmission in noisy
environments.
The RS485 standard is implemented in EC process meter
controllers with the following characteristics:
Data rate: Data rate:
Data rate: Data rate: Data rate: 1200, 2400, 4800 and 9600 bps
Communication: Communication:
Communication: Communication: Communication: Bidirectional Half-Duplex
Line length: Line length: Line length: Line length: Line length: up to 1.2 Km typical with 24AWG cable
Loads: Loads: Loads: up to 32 typical.
Loads: Loads:
Internal termination: Internal termination: Internal termination: Internal termination: Internal termination: none
The connections for the 4-pin RS485 terminal
provided (#1 on page 8) are as follows:
The instrument has no internal line termination. To terminate
the line, an external resistor equal to the characteristic line
impedance (typically 120 ohm must be added at both ends
of the line.