The principle of the RS422-interface and RS485 bus:

If data transmission is realized by means of RS422-interfaces or RS485-bus, common-mode interferences along the transmission line will be reduced to a large extent. If transceiver and receiver signal are routed on two separated cable pairs (full duplex operation), a RS232-signal can be easily converted into a RS422- or RS485-signal.

Using the RS485-interface the transceivers can be switched off making the interface bus-capable. That means: In contrast to a RS422-interface up to 32 instruments can be cabled parallely via 4-wire-bus. All receivers register the commands but only the device with the correct address activates the output and answers. Instruments that fail, switch off automatically and do not interrupt the network.

On the other hand, no further devices or module can be connected to instruments which are networked via a RS485-bus, because the output is only activated for one address. Therefore a RS422 network distributor has to be used for data acquistion system with several active modules (ALMEMOŽ 5590-1/-3).

Arrangement:

By means of two outputs the RS422-distributors can be installed in a distance of up to 1000 m and can be arranged in-line or star-shaped. The RS485-bus can be cabled in any way enabling branches at any point but the total length is limited to 1000 m.

Power supply:

Network distributor and branch box can be supplied locally by means of the ALMEMOŽ-instrument (4-wired cabling) or centrally by means of an external power supply (6-wired cabling, cable length up to 50 m). In case of a power failure the complete network is interrupted when RS422-distributors are used, however it is still working with RS485-branch-boxes.

Devices:

Within the ALMEMOŽ-system there are two drivers for the RS422-distributor or RS485-bus. For connecting a computer the RS232/422-converter ZA 5099-AS is available. For networking with the data acquisition system ALMEMOŽ 5590-3 the ALMEMOŽ output module ZA 5099-AS has to be used. ALMEMOŽ-instruments can be connected by means of the RS422 network distributor ZA 5099-NVB or RS485 branch box ZA 5085-NV. Using transmitters the RS485-interface is optionally integrated, avoiding additional hardware.

Example of application:                 

ZA 5085 NV: RS485-network-branch-box:
                      1 output RS485, 1 connection for ALMEMOŽ-instruments
                      incl. cable (length 1.5m), all connections for clamping or plugging,
                      power supply from measuring instrument or bus (selectable by jumper),
                      galv. sep.

ZB 5099 AS: RS422/485-network-driver:
                      RS232-RS422/485-converter not galv. sep.
                      full duplex, TX+, TX-, RX+, RX-

ZA 5099 FS: RS422/485-network-driver:
                     ALMEMOŽ-RS422/485-converter for
                     ALMEMOŽ 5590-3 not galv. sep., full duplex,
                     TX+, TX-, RX+, RX-

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