Hart Network wiring

Steve_D

Member
Join Date
Jul 2002
Location
Albury/Wodonga
Posts
92
Hi guys, I am about to purchase a Hart to modbus converter to interrogate a few flow meters on hart and get the info via modbus. All looks good except the wiring diagram for the HART PART is very simplistic, i.e the converter at the start and a single line across the line of flow meters with a single line down to each meter. This is clearly 2 wires (+ and -) but I assume they are daisy chained, i.e. the 2 wires out of one become the two wires into the next. Am I right or can I bring two wire into a terminal strip and parallel the signal wires off these?
Thanks in advance
 
It depends on what you're doing with the HART 4-20mA output from each of the flow meters.

1) If you need a process variable data value (like flow rate) from each of the flow meters, then you need a separate HART-Modbus converter for each flow meter.

The 4-20mA runs in series through the HART-Modbus converter, AI, power supply and back to the flow meter (order does not matter).

The AI gets a modulating 4-20mA, the converter gets the total value.

2) If you need only the total from the flow meter, then the device uses Multi-drop mode - one HART-Modbus converter is needed which can poll and get data from multiple field devices.

The 4-20mA is wired in parallel to HART-Modbus converter.

HART_Multidrop_network_en.jpg
 
Last edited:
Thanks DANW..its the second one, I thought as much but its comforting to get a second opinion (and by way of no one correcting you a third,fourth and onwards opinion)
 

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