Do 4-20ma Can Be Superimposed On RS-485 Cable

Instead of waiting, you could pick up the phone and talk it through with the equipment supplier, Mildred. It seems people are frightened to do that these days.

Here is a description of the HART protocol

http://en.wikipedia.org/wiki/Highway_Addressable_Remote_Transducer_Protocol

No, 4-20mA is not superimposed on the RS-485 line or vice versa.

There are multiple, separate, individual connections on this device.

One connection is 4-20mA HART (yes, HART is an FSK signal superimposed on the DC 4-20mA). Its connections will have a (+) and a (-).

A second connection is RS-232, which supports Modbus RTU. It will like have a Rx, Tx and a signal ground.

A third connection is RS-485, which supports Modbus RTU. It will likely have a connector with A, B and signal ground.

The 4-20mA does not mix with either the RS-232 or RS-485.

(4-20 )mA it is not superimposed on any RS(232/485)it is superimposed on (FSK) frequency shift keying to make up (HART communication protocol) if you want to communicate between (4-20mA.HART) device and your PLC(control) or p.c use on of these adapters converters FXA191 FXA193 FXA1195 via RS232/usb ports .to make a control orders regarding with

RS232 or RS485 in your flow rate they are for operation software program that comes on a disc and installed in your P.C it is just to monitor not to handle (4-20mA.HART).for read or write data.

good luck .

Tnks for your feedback frnds...