Can somebody give me information about a Hart resistor, what it is, where it use and how work.

thanks very much.

Martin Medina

 

In short, HART requires a loop impedance of at least 230ohm for communications be possible. Typically, a 250ohm resistor is used in series in the loop.

Check out this application guide for more info.

http://www.hartcomm.org/download/appguide.pdf

 

The resistor has two functions:

1. Shunt/terminator: for HART transmission is done by modulating the loop current at 1200/2200 Hz about 1 mA, but reception is done by picking up a voltage drop. The resistor acts as a shunt so that the transmitted current creates the voltage drop sensed by the receivers.

2. Short protection: the DC power supply if connected directly to the HART devices will short the superimposed AC communication signal. The resistor ensures that the DC supply does not short the AC signal.

This is explained in chapter 3 and 11 of the book "Fieldbuses for Process
Control: Engineering, Operation, and Maintenance" (buy online in hardcopy or
download immediately in softcopy). If your email does not support this hyperlink feature correctly, please copy the URL and paste it into your Internet browser. Mind the line wrap, make sure to get the complete path all the way to the 3036: http://www.isa.org/Template.cfm?Section=Shop_ISA&Template=/Ecommerce/Product Display.cfm&ProductID=3036

Jonas Berge
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