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Join Date: May 2009
Posts: 4

HART Multi-drop Connections

12/15/2009 8:24 AM

can anybody expline....how the HART multi drop connections r done.....using 1 pair of instrumentation cable(power & signal) between 2 transmitters? is it possible in 2 wire transmitters

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Commentator

Join Date: Nov 2008
Location: Houston, Texas
Posts: 70
#1

Re: Expline HART multidrop connections

12/15/2009 8:48 AM

Check out this document http://www.samson.de/pdf_en/l452en.pdf this might help explain HART multi drop applications. HART is a diagnostic communication protocol application that rides on the 4-20 mA signal. You can also do a quick google search for HART multi drop applications and you will find a lot of helpful information. You can also check out this site for more information. http://www.hartcomm.org/.

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Guru
Engineering Fields - Instrumentation Engineering - New Member

Join Date: Dec 2009
Location: San Antonio, TX USA
Posts: 845
Good Answers: 28
#2

Re: HART Multi-drop Connections

12/15/2009 10:44 AM

Check out the HART foundation's web site. Go to training. There are some great tutorials. You can even print yourself a certificate if you can pass the quiz at the end of the course! Skip from lesson to lesson until you find your answer if you don't want to take the time to do the whole thing.

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Anonymous Poster
#3

Re: HART Multi-drop Connections

12/17/2009 6:01 PM

Not a big deal. However,

1) Using Ohm law, check for voltage drop at the very last transmitter on your HART segment. Make sure the very last transmitter (15 transmitters max) receives enough power to communicate (say, 18 or 16 volts as minimum voltage). Depends on supplied voltage, device wattage (consumption), distance from PS to device(s) and wire resistance (i.e. cross section).

2) In your lab, hook up power supply and 375 HART Communicator (or whatever model or software package via HART-modem) to each transmitter individually. Follow menu tree, get to Multidrop section and set transmitter address in each device other than 0 (from 1 to 15). Each device must have unique HART address from 1 to 15.

3) In HART communicator menu, choose the way transmitters are gonna talk to HART Master - be polled by the Master or work in Burst mode (send messages out to the line constantly). This should be driven by your automation strategy and HART Master capabilities.

4) Connect wires in parallel (i.e. Power Supply "+" to "+" terminal on each device, and Power Supply "-" to "-" terminal on each device.

It's worth of having a look to HART wiring scheme in a transmitter manual or using HART foundation materials, as you may need to add line terminator (a combination of resistor and capacitor) at the last transmitter - to prevent standing wave in the line.

Normally, length of HART multidrop segment is limited by approx. 1000 meters (depending on number of transmitters tied up to a segment etc. - see item 1 ).

Cheers.

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