ABB Endura AZ40 Gebruiksaanwijzing - Pagina 9

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4.2 Two-wire and four-wire connection

MODBUS serial communications can be configured as either

2-wire or 4-wire serial links – see Fig. 4.1. The transmitter must

be added to the link configuration on the host system – refer to

information supplied with the host system.

1 2 3 4 5

2-wire connection

4-wire connection

Fig. 4.1: 2-wire and 4-wire MODBUS serial links

SK1

SK2

Endura AZ40 | Oxygen and carbon monoxide equivalent (COe) analyzer | COM/AZ40/MOD–EN Rev. A

4.3 Pull-up and pull-down resistors

To prevent false triggering of slaves when the master (host

computer) is inactive, fit pull-up and pull-down resistors to the

RS422/485 interface in the host computer.

Resistors are normally connected to the interface by

hard-wired links or switches – refer to the manufacturer's

instructions

4.4 Termination resistor

For long transmission lines, fit 120 termination resistors to

the last slave in the chain and the master receiver – see

Fig. 4.2.

Last slave

COM

Rx–

Rx+

Tx–

Tx+

120  termination

resistor

Fig. 4.2: Connecting multiple slaves

4.5 Serial connections

Make connections to the MODBUS serial board as shown in

Fig. 4.1. On systems with multiple slaves, make connections to

two- or four-wire link configurations in parallel as shown in

Fig. 4.2. When connecting cable screens, ensure that ground

loops are not introduced.

The maximum serial data transmission line length for both

RS422 and RS485 systems is 1200 m (3937 ft.).

The types of cable that can be used are determined by the total

line length:

— Up to 6 m (19.7 ft.) – standard screened or twisted pair

cable.

— Up to 300 m (984 ft.) – twin twisted pair with overall foil

screen and an integral drain wire.

— Up to 1200 m (3937 ft.) – twin twisted pair with separate

foil screens and integral drain wires.

120  termination

First slave

resistor

COM

Rx–

Rx+

Tx–

Tx+

computer

Master

Host