What is the maximum distance a 4-20mA Hart signal can cover using ordinary Cu conductors? Is there any way we may use Hart signal over 1.5Km for PITs?

 

Check out the Hart Foundation web site at

http://www.hartcomm2.org/hart_protocol/tech_info/wire_length.html

Here Mr Hart blogs on about his favorite industrial comm protocol.

"In general, the installation practice for HART communicating devices is the same as that for conventional 4-20mA instrumentation. Individually shielded twisted pair cable, either in single pair or multi-pair varieties, is the recommended wiring practice. Unshielded cables may be used for short distances, if ambient noise and cross-talk will not effect communication. The minimum conductor size is 0.51mm diameter (#24 AWG) for cable runs less than 1,524 meters (5,000 ft.) and 0.81mm diameter (#20 AWG) for longer distances"

Given that these are words right from Mr. Hart's mouth, one could conclude that as in most 4-20mA apps, sufficient power supply voltage, truly twisted pair, and shielding are the biggies. (Yes, I know there's no Mr. Hart, but humor me)

For a discussion on the distance capabilities of 4-20mA current signals, check out Mr. Tsakir's essay, "A 4-20mA Signal Goes the Distance" at http://www.kele.com/tech/Electric/TRefCLoop2.html

Carl

 

It is highly unlikely that you can run a 4-20 mADC loop 1.5 km and have a readable signal at either end.

You would do yourself a favor to pull the digital signal off the transmitter and send it via Ethernet.

Soon you will be able to do it by WirelessHART and a WirelessHART-to-Ethernet gateway.

Walt Boyes
Editor in Chief
Control magazine
www.controlglobal.com
blog:Sound OFF!! http://www.controlglobal.com/soundoff
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