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4-20mA to HART Conversion

Thread Starter: Preetbrar   Started: 5/12/2012 10:18 AM   Replies: 4

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  5/12/2012, 10:18 AM
Preetbrar
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Dear Sir,

We have Siemens MICRO2000 Clorine Analyser, which has 4-20mA output. Client is insisting on HART Communication with device to Yokogawa DCS. If I listen to Siemens guy he said that it is possible using different HART Comminicators. Now if I suggest my client to use HART Communicator then following I want to know:

1. Suggest me some make and model.
2. Will there be continuous output from it? as I have seen it as Handheld device only.
3. If you have some system architecture or design to use 4-20mA as HART. Please give me, it would be helpful to convince my client.

Thanks in advance.

Regards,

Davinder Singh
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  5/12/2012, 4:51 PM
danw
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To work with HART, you need to have a HART signal.   What makes you think the Micro 2000 has HART?

The Siemens Micro 2000 color brochure from the link on the web site
http://www.water.siemens.com/en/products/chemical_feed_disinfection/analyzers_process_controllers/Pages/micro2000_residual_analyzer.aspx
shows 2 different 'electronic' modules that use the measurment module, an SFC or an MFC.

The electronic interfacing spec for both is the same (except the number of analog outputs):
- Analog outputs: 1 available 0/4 to 20 mA, configurable.
Load <500 Ohm, accuracy < 0.5% FS. Galvanically isolated
up to 50V relative to earth
- Interfaces: RS 232; RS 485 to connect with the Wallace &
Tiernan® ChemWeb-Server, OPC-server or CMS software, and
can interface for sensor-actuator bus

I don't see the word HART.  Where do you find evidence that the device has HART?

All the chit chat about communicators or other HART topics is superfluous if the device doesn't have HART to start with.

Hart is used extensively for configuration purposes.

Some people use HART to get additional variables.

Other use HART to get diagnostic data.

What is the intended purpose of the HART request?

I ask because I suspect that if the request is serious, you'll have to develop an alternative approach.




=== Edited by danw @ 5/12/2012 4:59 PM [GMT ] ===
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  5/12/2012, 5:13 PM
Preetbrar
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Dear Danw,

"Using HART devices can communicate their data over the transmission lines of the 4-20mA system"

Above was the feedback from Siemens guy. I had the same feeling as you have that is why I put it here to get the feel if somebody has done similar installations. As per my knowledge, we need to do configuration, control and Diagnostics from DCS over the certain communication protocol, which should be builtin or Add-on feature of Transmitter itself. I think using 3rd party device also we can't achieve this. Any suggestions?

Thanks and Regards,

Davinder Singh

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  5/12/2012, 9:18 PM
danw
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HART is a dead end.  HART must be implenmented in the field instrument and as far as I can see, it isn't.  There's no feasible path to faking HART (who's going to write the DD (device descriptor) file needed by any HART master?)   If the manufacturer doesn't see that as profitable, how can you afford to do it?

You should investigate what kind of data and abilities the optional OPC server offers.

A modern DCS is always an OPC client which can communicate with an OPC server, which needs a low level driver to talk to the field device.   This analyzer offers an OPC server of some sort.

OPC always provides process variables.
OPC sometimes provides diagnostic data.
OPC rarely provides configuration access.  Nothing prevents it from doing so, but it just isn't common.

What is available depends on what the instrument provider makes available via its digital protocol, which gets read by OPC.

So you need to research what's available via OPC vs whatever it is that your customer is asking for.
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  5/13/2012, 11:39 AM
SonicRanger
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Hi Preetbrar,

I do not know this device, but on the site of the SFC/MFC a communications module is mentioned, which can be connected / built in to this device.
Check this link:

http://www.water.siemens.com/SiteCollectionDocuments/Product_Lines/Wallace_and_Tiernan_Products/Brochures/WT.040.565.000.IE.PS.0509.pdf

No HART available here, but ProfinetIO, Profibus DP or Modbus TCP. I am almost sure that your DCS is capable to use read one of these protocols.

Try to be one step ahead of your customer in knowledge, and convince him that it is not always possible to have all instruments talking the same protocol.

Best Regards,

SonicRanger.
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