HART Multidrop to 4-20mA

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Thread Starter

NorthSeaMonkey

Hi,

I'm new to Control.com and hoping someone on here may be able to assist.

I have in the past worked with Rosemount 3095 multi variable transmitters, a tri loop barrier was installed at the marshaling cabinet and 3PVs modulated onto a HART signal were converted to 3 4-20mA outputs.

Also in the past I have worked with Rosemount 3051 transmitters in a multi drop configuration using a HART single pair current loop.

I now have an application where single 3051 differential pressure transmitter is installed, a second instrument is required. Typically there are no spare cores available. Pulling a new cable would be costly.

Can anyone advise of a product which would work similarly to the 3095/tri loop barrier and convert two measured DPs modulated onto a single HART loop back to two 4-20mA loops for hand off to an aging DCS?

Any help gratefully received.

Kind regards
Chris
 
You're asking for a dual instrument Tri-Loop, aka Hex-Looper(?), that would have to integrate

- HART master functionality

- Multidrop functionality (single pair of wires to multidrop both field transmitters)

- break-out analog box functionality to get data into analog form on the host side, like the Tri-Loop or Moore Industries HCS.

I suspect the market demand for such a commercial box just isn't there or Moore Industries would have one.

Most HART multiplexors will not solve the problem because typically each instrument is connected with its own 2 wire cable to a Mux and you only have one 2 wire cable.

HART multidrop will run with both transmitters on a single pair in parallel, with both devices running at 4mA and a HART master in control of the HART 'bus'.

If you can live with a module that's a Modbus RTU slave on the output side, ICP-DAS's HART-710 Hart-to-Modbus converter supports HART Multidrop on the field side.
http://tinyurl.com/mwptcl9

Getting to analog will probably be too costly, requiring a Modbus master and slave Modbus-to-AO. Maybe an Automation Direct PLC with Modbus master and an AO card? But all at less cost than a 2nd twisted pair cable?
 
Moore Industries does have a device that could achieve this. their HART Interface Module [HIM], but you would need two of them to communicate with two transmitters.

The HIMs can operate as Primary or Secondary HART masters. one could take each role to talk to one of the multi-dropped transmitters. or "Listen" mode could be used if the transmitters can be configured to send their PVs via burst mode.
 
Pepperl+Fuchs has HART Loop Converter products [KFD2-HLC] that are functionally similar to Moore Industries' HIM. "Each HLC is able to power and communicate with one HART-field device. It sets the field device into burst mode and converts up to 4 HART-variables into analog output signals."
 
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