network at device level


Thread Starter

Ed Crofts

i am looking into connecting numerous analog (4-20ma) devices onto a network communicating to a plc or other, ive reviewed signal conditioners etc. any views on the most efficient way to do this would be appreciated thanks in advance

Hakan ozevin

By most "efficient" way if you mean:
1. To be cheap then try where they have a cheap multiplexer for analog signals. You can command this card with a simple PLC/RTU of any trade.
2. To be accurate and/or rapid then there are lots of distributed I/O's (Phoenix, Weidmüller, Wago, Siemens,...) using several standards (Profibus, Modbus, Instabus, even Ethernet).
Think about the cabling costs in comparing the above two alternatives.
Of course it is important also where you are trying to connect these signals (PLC, DCS, PC, which model?).
I think you are asking a general question in a general way, where everyone may have a general answer.

Hakan Ozevin

Lim Chin Siong

you may like to contact "Pepperl + Fuchs", i know they have some multiplexer for this application.
There's another more efficient way of doing this, without ANY cable and without requiring an RTU/PLC . Check out for their integrated Analog I/O + Controller + Radio Transceiver module slaves and RS232/485 +Controller +Radio Transceiver master . The typical configuration works something like this:
-slave units placed wherever you want them , each with modular distributed I/O (for example slave #1 can have 4 analog inputs, slave #2 might have 4
analog inputs plus 8 analog outputs, slave #3 might have 12 analog inputs and 4 analog outputs , etc up to 255 max slaves). Each slave consists of the distributed i/o modules (each having from 4 to 255 analog i/o channels) plus
a controller and a radio transceiver .
-one master unit that consists of a rs232/485 interface, plus a controller and a radio transceiver. The master gets wired into your PLC, PC or whatever rs485 network, or serial rs232 link, and you talk MODBUS to the master to
access the slave registers mapped into the master memory . Their embedded firmware takes care of the rest and handles the radio network transparent to the user .

-each network can have only one master and up to 255 slaves , however you can colocate up to 32 different networks in the same reception area .

Matt Tudor, MSEE
Elmar Technologies