HART Transmitter to a Non-HART PLC AI Card

Hello Guys n Gals!

In Our plant, we have mostly Honeywell DCS, Which reads HART enabled transmitters without any fuss.
However, in few areas we have Honeywell PLC as well, and somehow these are connected to all HART enabled transmitters.

The Problem I have is with Flow transmitters. eventually the requirement is to read -Flow rate as well Totalized flow value.

Now, Since the The Flow Meter is a smart trasmitter it does produce totalized flow value but it transmit it only via HART. however, the PLC card is able to read only 4-20mA signal(Flow Rate) and unable to read this totalized flow value.

So, the Question is, Do we have some intermediate device, which i can connect to the Flow Meter, and get two 4-20mA signals one for Flow Value & another for Totalized value. So, as to connect this two values to normal PLC AI Card?

any suggestions in this regards based on your experiences is vastly appreciated.

Cheers!

Rajesh.

Use a Hart Triloop Signal Converter:

http://www.emerson.com/catalog/en-us/rosemount-333-hart-tri-loop

rajeshkothari said:

Since the The Flow Meter is a smart trasmitter it does produce totalized flow value but it transmit it only via HART.

Click to expand...

That is odd. If I am not mistaken, HART is a protocol that is overlaid on a standard 4-20mA signal. So if a transmitter has HART, it also has a 4-20mA output.
Ah, I get it now. You need both flowrate and totalized flow at the same time. Forget what I wrote.

1. When you use a break-out box, the digital HART value is converted to an analog 4-20mA or 1-5Vdc.

It is very unlikely that your total value is small enough to be represented by 4-20mA to be a useable value.

Most total are fairly large values, for example, 4,292,888 liters/gallons. That number has over 4 million parts of resolution.

A number that large has more resolution than than is practical with a 4-20mA signal.

An analog 4-20mA is good for something between 2,000 to 16,000 parts of resolution.

You might be able to scale the total in the flow meter so that
4,292,888 is 4.3 (million) or 4,292 (*thousand) and gain some magnitude of the total by sacrificing the low order resolution.

If the total value needs its full resolution, then the alternative is to convert HART to Modbus and pull the Modbus value which should be maintain the same resolution as the original HART value.

There are commercial HART-to-Modbus converter modules, like Moore Industries HCS module.

2) I've been told that the Emerson/Rosemount TriLoop requires the HART transmitter to work in 'burst' mode. I have researched whether the Triloop's burst mode requirement is true or not, but if it is true, you should be aware that many HART transmitters do not support burst mode and would not be not compatible with the Triloop.

Moore Industries HIM is a competitive model to the Triloop, a HART breakout box that converts HART values to analog. The HIM works in either burst mode or normal (non-burst) mode.

However, working without burst mode will not increase the inherent resolution of the analog output. Converting a total is likely to be a disappointing exercise.

Instead of attempting to get total from 4-20MA, you would probably be better off doing the totalizing in the PLC based on a set interval.

At 1sec interval with a flowrate in units/min (example gal/min):
FlowTotal_gal = (FlowRate_galmin/60) + FlowTotal_gal

At 1sec interval with a flowrate in units/hr (example gal/hr):
FlowTotal_gal = (FlowRate_galhr/3600) + FlowTotal_gal

maybe this,

www2 emersonprocess com/siteadmincenter/PM%20Rosemount%20Documents/00809-0100-4841.pdf